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Synthesis of 16-alkene functional hyperbranched polymer

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Title:
Synthesis of 16-alkene functional hyperbranched polymer
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Azarnoush, Setareh
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English
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xv, 98 leaves : illustrations ; 28 cm

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Subjects / Keywords:
Alkenes -- Synthesis ( lcsh )
Esterification ( lcsh )
Polymers ( lcsh )
Alkenes -- Synthesis ( fast )
Esterification ( fast )
Polymers ( fast )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

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Bibliography:
Includes bibliographical references (leaves 93-98).
Thesis:
Department of Chemistry
Statement of Responsibility:
by Setareh Azarnoush.

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|University of Colorado Denver
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Auraria Library
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ocn785939193
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Full Text
A
SYNTHESIS of 16-ALKENE FUNCTIONAL
HYPERBRANCHED POLYMER
by
Setareh Azamoush
B.Sc, Shahid Beheshti University, 2006
A Thesis Submitted to the University of Colorado Denver
in partial fulfillmen of the requirments for the
degree Master of Science Chemistry
2011


This thesis for Master of Science
degree by
Setareh Azamoush
has been approved"^
2-C'/ ^
Date


Azarnoush. Setareh( M.Sc Chemistry)
Synthesis of 16-Alkene Functional Hyperbranched Polymer
Thesis directed by Professor Bowman Christopher
ABSTRACT
Application of the thiol-acrylate Michael addition reaction, the thiol-yne click reaction and an
esterification process was used in this work to synthesize a new 16- functional alkene
hyperbranched polymer. The hyperbranched polymer was prepared by a divergent method
starting with pentaerythritol tetra(3-mercaptopropionate) as a core which then underwent thiol-
acrylate Michael addition followed by thiol-yne and thiol-ene click reaction.
The 16- functional alkene terminated hyperbranched polymer was characterized by NMR
spectroscopy. MALDI-TOF mass spectroscopy and gel permeation chromatography.
This abstract accurately represents the content of the candidate's thesis. I recommend its
A
/
publication.
Professqj Bowman Christopher


DEDICATION
I dedicate this thesis to my Grand mother, my parents my husband, and my
daughter for their encouragement and support throughout this work.


ACKNOWLEDGMENT
My thanks to my advisor Professor Christophere Bowman and Professor Jeff Knight
for his contribution, support and motivation to my research.
Also I wish to thank Professor Jeff Stansbury for his support and advice.
I also wish to thank all the people in Bowman research group and Stansbury research
group and acknowledge the National science foundation and National institute of
Health for the fundings.


TABLE OF CONTENTS
List of figures ..............................................................ix
List of table ............................................................. xvii
Chapter
1.Background and Introduction..................................................1
1.1 Introduction..............................................................1
1.2.1. Synthesis of dendritic structures......................................10
1.2.1.1. Divergent synthesis approach.........................................10
1.2.1.2. Convergent synthesis approach........................................13
1.2.2. Synthesis of hyper branched polymers.................................16
1.2.2.1 .Step-growth polycondensations.....................................16
1.2.2.2. Polyesters...........................................................17
1.2.2.3. Second method of synthesis of hyper branched polymer:
Self-condensing vinyl polymerization of AB monomers................19
1.2.2.4. Third method of synthesisng hyperbranched polymer: Multi-branching
ring-opening polymerization of latent ABX monomers..................19
1.3. Click reactions........................................................21
1.3.1. CuAAC click reaction...................................................22
1.3.2. Diels -Alder click reaction (DA).......................................25
vi


1.3.3. Thiol-ene click reaction(TEC)........................................27
1.4. History................................................................35
1.4.1 History of Hyper branched polymer....................................35
1.4.2 History of Dendrimers.................................................37
1.5. Applications of hyper branched polymers................................42
2.Synthesis of 16-Functional Alkene Hyperbranched polymer...................45
2.1 Introduction............................................................45
2.2 Materials and Methods..................................................50
2.2.1 Materials.............................................................50
2.2.2 Method...............................................................51
2.2.2.1 Procedure for Synthesis of Tetra-Alkyne Molecule( Tetra-yne)........51
2.2.2.2 Procedure for Synthesis of 16- functional hydroxyl
hyper branched polymer...............................................52
2.2.2.3 Procedure for Synthesis of 16-Alkene functinal terminated
hyperbranched polyme...............................................54
2.2.3. Instruments used for Characterization................................56
vii


2.3 Results and Discussion
57
2.3.1. Result of synthesis of Tetra-yne via Thiol-acrylate
Michael addition (First step) Reaction................................57
2.3.2. Result of synthesis of 16-Functional Hydroxyl Terminated
Hyperbranched Polymer via Thiol-Yne Reaction..........................61
2.3.3. Result of Synthesis of 16-Alkene functional Hyperbranched
polymer via Esterification............................................67
2.4 Conclusion..............................................................75
Appendix
A Synthesis of 12-Alkene hyper branched polymer............................76
References.............................................................93
viii


LIST OF FIGURES
Figure
1.1 . Characteristic features of hyperbranched polymer structures. Several different
branch features are illustrated for a hyperbranched polymer and the fact that this
hyperbranched polymer can be synthesized from a typical AB2 monomer. This
figure was taken and reproduced from reference 1.........................2
1.2 This figure shows different dendritic molecules and the differences between
those molecular types. This image was taken from and reproduced from
reference1 ...4
1.3 This figure shows an ideal dendrimeric molecules structure. 4 This figure was
taken and reproduced from reference4.....................................6
1.4 This figure shows the difference in the structure of hyperbranched polymers and
dendrimers5. This image was taken and reproduced from reference
1.5 This figure shows the divergent growth of dendrimer.This image was taken and
reproduced from reference
ix


1.6 This figure shows the convergent growth of dendrimer. 5This image was taken
from and reproduced from reference5......................................14
1.7 . Hyperbranched polymer synthesis by polycondensation through the reaction of
Bis(MPA) andTMPto synthesize a hyperbranched aliphatic polyester11. This
image was taken and reproduced from reference 11.
.........................18
1.8 This figure shows the ring opening polymerization of enantiomerically pure
glycidol to synthesize a chiral hyperbranched polyglycerol dendron.11 This
image was taken and reproduced from reference n.
...................................20
17
1.9 This figure shows an example of the CuAAC reaction This image was taken
and reproduced from reference17..........................................22
1.10 This figure shows CuAAC was used in the synthesis of highly dense
glycodendrimers. This image was taken and reproduced from reference .23
1.11 This figure shows convergent synthesis via "ClickCuAAC.17 This image was
taken and reproduced from reference17.................................24
1.12 This figure shows an example of Diels Alder Reaction.17
This image was taken and reproduced from reference17.....................25
1.13 This figure shows an example of a Diels Alder reaction as a click reaction.17
This image was taken and reproduced from reference17.....................26
1.14 The thiol-ene click reaction mechanism17. This image was taken and
x


reproduced from reference17.
28
1.15 The step growth mechanism of alternating propagation (addition) and chain
transfer in thiol-ene reactions. This image was taken from reference ................29
1.16 The various reaction steps in the thiol-yne polymerization reaction. This image
was taken and reproduced from reference ...................................31
1.17 Poly thioether dendrimer synthesis via TEC and esterification reactions17. This
image was taken and reproduced from reference.17...........................33
1.18 Synthesis of carbosilane-thioether dendrimers using TEC click reactions24.
This
image was taken from
reference.24..........................................34
1.19 An example of a double click reaction17. This image was taken from
Reference
17...............................................................35
1.20 The structure of the original cascade molecule14. This figure was taken from
and reproduced from reference14............................................38
1.21 This figure shows octopus dendrimer and its use to complex metal ions. This
figure was taken and reproduced from
reference4......................39
XI


1.22 This figure shows the first cascade molecule synthesized and its synthetic
route4.
This image was taken from and reproduced from reference4.
.................40
1.23This figure shows applications of hyperbranched polymers.11
This image was taken from reference11....................................44
2.1 The synthetic strategy of synthesizing the 16-functional alkene terminated
hyperbranched polymer. Here the numbers in the scheme refer to the material that
was used and synthesized and these numbers are further used in the procedure
method............................................................48
2.2 shows the first, second and third step reaction
mechanism..................49
2.3 . *H NMR Spectra of the tetrayne. 'H NMR, CDCI3: 2.48 ppm (4H), 2.57-2.65
ppm(16H),2.73-2.80 ppm (16H), 4.12 ppm (8H), 4.67 ppm (8H).The structure
drawn is one arm of four arm since they are chemically equivalent......58
XII


2.4 *H NMR of reactant in comparisons with product of reactant A) PETMP and B)
propargyl acrylate and C)Tetra-yne.....................................60
2.5 'H NMR (DMSO-J6) of 16-hydroxyl terminated hyper branched polymer. *H
NMR spectra analysis; 3.13-3.21 ppm (4H), 3.51-3.60 ppm(8H),4.05-4.31
ppm(16 H)4.54-4.60 ppm(8H),4.75-4.84(8H),................................62
2.6 A) *H NMR spectra of thioglycerol (reactant) B) *H NMR of second step product
16-hydroxyl terminated hyperbranched
polymer...........................64
2.7 a) FTIR spectra from before () and after (...) the reaction are shown. This
result shows that the thiol peak at 2675 cm'1 and the alkyne peak at 2130 cm'1
disappear as the reaction reaches high conversions, b) Conversion of alkyne(...).
and thiol() as a function of time that shows the thiol-yne click reaction
reached high conversions.......................................................66
xiii


2.8 *H NMR spectra of 16-functional alkene terminated hyper-branched Polymer. *H
NMR spectra analysis CDCI3, 2.28-2.49 ppm(67.6 H), 2.49-2.95 ppm(55.39 H),
3.03-3.19 ppm(3.7 H), 4.05-4.46 ppm (32 H), 4.95-5.20 ppm(41.8 H),5.72-5.90
ppm(16.5 H)..............................................................68
2.9 A) *H NMR spectra of 4-pentenoic acid, B) *H NMR spectra of 16-Alkene
Functionalized Hyper Branched Polymer. The peaks of protons on the double
bond
of 4-pentenoic acid anhydrid at 5-6 ppm appeared in the product *H NMR spectra
and this indicates that this reaction
completed.... ,...70
2.10 MALDI-TOF Mass Spectroscopy of 16- alkene functionalized hyper branched
polymer which has m/z=3130 which is ionized by Na+, [M+ Na+].....................72
xiv


2.11 Gel permision chromatography of 16-alkene functionalized hyper-branched
polymer with Mn of 3200 Indicated by b. a has Mn of 6600and c has
Mn of
.............................................................73
2.12 HPLC/MS result of 16-alkene functionalized hyper- branched polymer, This is
the MALDI of fraction collected from The sample at 6-7 minutes that contain
the
product. The product peak is shown with m/z of 1571 which Is a doubly
charged
ion [M+ (NH4+)2]...........................................................74
A.1MALDI-TOF spectroscopy of 12-Hydroxyl macromolecule, higher molecular
weight are indication of coupling of product in high temperatures.........80
A.2 MALDI-TOF spectroscopy of 12-Hydroxyl macromolecule. 0.5 wt% (.25mol
%)
Irgcure 651 was Used. Tri-propargyl amine was mixed with 50% excess
thioglycerol and initiator and was high vacuumed and nitrogen purged and the
mixture was irradiated using acrticure, EFOS UV lamp with filter pass of 365
xv


and light intensity of 10 mw/cm for 24 hour time duration. It shows very small
amount of product peak at m/z=802 indicating this amount of initiator is not
sufficient..............................................................................82
A.3 MALDI-TOF spectroscopy of 12-Hydroxyl macromolecule. 2 wt% (lmol %) of
Irgcure 651 was used. Tri-propargyl amine was Mixed with 50% excess
thioglycerol and initiator and was high vacuumed and nitrogen purged and the
mixture was irradiated using acrticure, EFOS UV lamp with filter pass of 365
and
light intensity of 10 mw/cm for 24 hour time duration. It shows larger peak of
product peak at m/z=802 and 803 indicating this amount of initiator
sufficient....................................................................83
FigA.4 MALDI-TOF spectroscopy of 12-hydroxyl macromolecule. 2 wt% (lmol %)
of irgcure 651 was used. Tri-propargyl amine was mixed with 50% excess
thioglycerol and initiator and was high vacuumed and nitrogen purged and the
mixture was irradiated using acrticure, EFOS UV Lamp With Filter Pass of 320-
500 nm and light intensity of 30 mw/cm for 4 hour time duration. It shows
XVI


larger peak of product peak at m/z=802 and 803
85
A.5.MALDI-TOF spectroscopy of 12-Hydroxyl macromolecule. 2 wt% (lmol %) of
irgcure 651 was used. Tri-propargyl amine was mixed with 50% excess
thioglycerol and initiator and was high vacuumed and nitrogen purged and the
mixture was irradiated using Acrticure, EFOS UV lamp with filter pass of
365nm and light intensity of 10 mw/cmA2 For 4 hour time duration. It shows
peak of product peak at m/z=802 ........................................87
A.6 MALDI-TOF spectroscopy of 12-Hydroxyl macromolecule. 2 wt% (lmol %) of
Irgcure 651 was used. Tri-propargyl amine was mixed with 50% excess
thioglycerol and initiator and was high vacuumed and nitrogen purged and the
mixture was irradiated using Acrticure, EFOS UV lamp with filter pass of 365
nm and light Intensity of 10 mw/cm2 for 8 hour time duration.lt shows the
product peak at m/z=802
................................................88
A.7 MALDI-TOF spectroscopy of 12-hydroxyl macromolecule. 2 wt% (lmol %) of
xvii


Irgcure 651 Was Used. Tri-propargyl Amine was mixed with 50% Excess
Thioglycerol and Initiator and was high vacuumed and Nitrogen pinged and the
mixture was irradiated using Acrticure, EFOS UV lamp with filter pass of 365
nm and light intensity of 10 mw/cmA2 for 48 hour time duration. It shows the
product peak at m/z=802 ...................................................89
A.8 Shows the MALDI-TOF spect of 12 hydroxyl. 0.25 mol% Initiator was added
four times to the mixture and radiated with 30
mw/cmA2..................91
A.9 Maldi-Tof spect of 12 hydroxy functionalized hyper- branched polymer
.......92
XVIII


LIST OF TABLES
Table
1.1 Click reaction characteristics. This table was taken and reproduced from
reference.17.........................................................32
1.2 A brief history of hyperbranched polymers. This image was taken and
reproduced from 1........................................................37
A.IThe calculated molecular masses for all the possible products from reaction of
Thioglycerol and tri-yne reaction.....................................79
xv


1. Background and Introduction
1.1. Introduction
Dendritic molecules branch repeatedly and possess structural symmetry and low
polydispersity. Polymers can be divided into four types based on their overall
architecture, consisting of linear, crosslinked, branched and dendritic structures1.
Dendritic molecules can be further divided into two groups depending on their
degree of branching and the corresponding symmetry of their structure.1 The
degree of branching is generally defined as the ratio of branched, terminal and
linear branches in a polymer structure.1,2 Figure 1.1 shows the differences
between the branches in a hyperbranched polymer, including branched, terminal
-j
and linear units Overall, the degree of branching provides a criterion that can be
useful in classifying dendritic molecules based on their structural perfection as
compared to an ideal, perfect dendrimer.4
1


Fig. 1.1. Characteristic Features of Hyperbranched Polymer Structures. Several
different branch features are illustrated for a hyperbranched polymer and the fact
that this hyperbranched polymer can be synthesized from a typical AB2 monomer.
This figure was taken and reproduced from reference '.
2


The first group of polymers has a degree of branching of 1 (100%) and consists
of dendrimers, linear dendritic molecules and dendronized polymers. This group
incorporates polymers that have perfect, symmetrical architectures while also
being monodisperse. .
The second group of dendritic molecules consists of hyperbranched polymers,
multiarm star polymers and hypergrafted polymers'. One of the characteristics of
this group is that they have a low polydispersity yet are no longer monodisperse
or ideal in their branched structure or symmetry.1 This group is defined by having
a degree of branching of less than one (i.e., having less than 100% of the possible
branches as actual branch points). Here, they have incomplete and irregularly
branched structures .
3


Dendrimer
Hyperbranched
polymer
Dendronized polymer or
Dendrigrafted polymer
Hypergrefted polymer
Figure. 1.2.This figure shows different dendritic molecules and the differences
between those molecular types. This image was taken from and reproduced from
reference1 .
4


The name dendrimer originally came from Greek and from the word Dendron
which means tree4 due to their structural similarity to the tree. The structure of a
dendrimer starts with a core, and then the branches and end groups attach to that
core4. Figure 1.3 shows the structure of an ideal, perfect dendrimeric molecule.4
5


Otndron
Figl.3. This figure shows an ideal dendrimeric molecules structure.4 This figure
was taken and reproduced from reference4.
6


There are many similarities between dendrimers and hyperbranched polymers.
Both of these structures have higher solubility and lower solution viscosity as
compared to their linear or branched counterparts2. These structures also possess
the advantage that by alternating their terminal functional groups, they will
exhibit dramatically altered chemical and material properties. Further, it is
readily possible to modify these terminal functional groups in most dendrimer
synthesis schemes2.
One of the similarities between dendrimers and hyperbranched polymers is that
both are generally formed from either A2B or A3B monomers. The presence of
multiple A groups is the basis for the geometric growth of the molecular weight
with increasing generation and also accounts for the presence of the terminal
functional groups.
There are also several distinct differences between dendrimers and
hyperbranched polymers. Dendrimers are characteristically more monodisperse
>y
and hyperbranched polymers are more polydisperse.
Hyperbranched polymers have broader molecular weight distributions, exhibit
isomerization, and irregularity in growth with statistical distributions of
functional groups2. Overall, dendrimers show more idealized, perfectly
monodisperse, symmetric polymer structures while hyperbranched polymers
contain the general features of dendrimers and mimic many of the same
7


properties without having the perfect symmetrical structure2. Dendrimers are
much harder to synthesize whereas hyperbranched polymers are easier to
synthesize.
Figure 1.4 shows the structure of both dendrimers and hyperbranched polymer.
8


Hyperbranched polymer
Fig.l.4.This figure shows the difference in the structure of hyperbranched
polymers and dendrimers5. This image was taken and reproduced from
reference5.
9


Hyperbranched polymers have interesting physical and chemical properties that
have given them abundant and unlimited applications in different fields and areas
such as nanotechnology and chemical engineering as well as biomaterials
applications such as pharmaceuticals and drug delivery.1,2
1.2.1. Synthesis of dendritic structures
There are two possible synthetic approaches used to form dendrimers, the
divergent approach and the convergent approach.1 Both synthetic routes can
produce high regularity and controlled molecular weight products. Dendronized
polymers consist of a linear polymer with attached side groups1. These can be
achieved via two routes. The first route consists of direct polymerization of
dendritic macromonomers while the second occurs via the attachment of
dendrons to a linear polymer. In both methods, new generations are formed from
repetition of reaction steps.
1.2.1.1. Divergent Synthesis Approach
The term divergent results from the diverging growth of the branches outwards
from the core to the outside4,5. First, the synthesis starts with a reaction of
equivalent amount of functional groups on the core with reactive groups on the
monomer for synthesis of dendrimers.
10


In coupling steps of the divergent method, a new, potential branch point is
formed at each coupling site and is introduced by reaction of the peripheral
functional groups of the core with the reactive group of the newly added
monomer5. To control hyperbranched polymer formation, the peripheral
functional groups on each monomer are designed such that they are inert during
the polymer formation. After the completion of the first coupling reaction, in the
activation step the latent functional groups are activated or are activated by the
appropriate chemical environment to form a new generation of peripheral groups
that will couple to subsequent generations of monomers5. During the activation
process, conversion of the surface moieties to reactive functional groups might
occur either by coupling with a second molecule or removing a protecting group.
The coupling and activation steps are repeated until the desired generation of a
dendrimer or hyperbranched molecule is synthesized5. A schematic
representation of divergent growth is shown in Figure 1.5.4
11


Monomer
Activation
Sfep
Monomer
I
Coupling
Step
Repeat Activation
end Coupling
Fig. 1.5. This figure shows the divergent growth of a dendrimer. This image was
taken and reproduced from reference5.
12


There are several advantages in using the divergent method, including the ability
to produce high molecular weight products and also the possibility for simple
repetition of steps. This method is also very useful when the dendrimer is needed
in large scale.5
However, there are also several disadvantages, and one of them is the fact that
with increasing functional groups, it is not always possible to quantitatively react
all the functional groups and achieve full conversion. Therefore, structural defects
are possible and purification of these imperfect structures is often difficult since
they have very similar properties to the ideal dendrimer4,5.
I.2.I.2. Convergent Synthesis Approach
As mentioned above, there are some disadvantages to the divergent method,
therefore, Hawker and Frechet developed a distinct synthetic approach to
dendrimer prepration.5,6. The convergent approach is different from the divergent
in the fact that the branches are synthesized first and then connected to a reactive
core. A schematic presentation of the convergent approach is shown in Figure
1.6.
13


Fig. 1.6. This figure shows the convergent growth of dendrimer. 5This image was
taken from and reproduced from reference 5.
The main advantage of the convergent method in comparison with the divergent
method is that there are only two simultaneous reactions required for any
generation, which makes the purification of the dendrimer easier. Modification
of the focal point or the chain ends, in order to synthesize well-defined dendritic
structures becomes possible5. Although there are advantages over the convergent
methodology with the divergent approach, however, due to its difficulties in scale
up, its use is limited to one family of polyether dendrons.6
14


Depending on the dendrimer, the synthesis routes will vary. For example, the
most common synthesis route for carbosilane dendrimers is divergent and this
consists of two reactions7. The first reaction is hydrosilylation of a multivinylated
or allylated core with Pt catalyst and chlorosilane, and the second reaction is
often nucleophilic substitution using an organolithium reagent or Grignard
reagent. Hydrosilylation is an addition reaction of Si-H to unsaturated bonds7.
Hydrosilylation breaks the double bond and causes the branch juncture which
forms the next generation structure. Nucleophilic substitution brings about the
branch. By alternating these two reactions, the dendrimer generation can grow
divergently7.
Thiol-yne and thiol-ene reactions have been introduced in the synthesis route of
dendrimers and hyperbranched polymers in recent years.8,9,10 These reactions are
similar to hydrosilylation but the sulfur version causes addition of a S-H to an
unsaturated bond. Different routes such as the thiol-ene reaction change the
polarity of the interior of these macromolecules and therefore have broader
applications3 in many other areas such as stabilization and metal encapsulation.
They also have been used in polymer resin systems in order to improve the
material properties. Thiol-yne and thiol-ene click reactions are further discussed
in section 1.4.3.
15


1.2.2. Synthesis of hyperbranched polymers
Overall, there are three methods available to synthesize hyperbranched
polymers11. These three are (1) step-growth polycondensation of ABX and A2+B3
monomers11, (2) condensing vinyl polymerization of AB* monomers, and (3)
multi-branching ring-opening polymerization of latent ABX monomers.11 There
are different types of hyperbranched polymers including polyamides,
polycarbonates, polyesters and polyurethanes that have been synthesized using
these three strategies.
1.2.2.1. Step-growth polycondensations
In this method, there is a one-step polycondensation for polymerization of AB,
and there are advantages and disadvantages of this method. The advantage of it is
that this strategy obeys normal step-growth polymerization characteristics.
However, the disadvantages are that there are possibilities for gelation to occur,
and that the occurrence of gelation will make the purification process much more
difficult. Also, side reactions occur in the polymerization process, and there is the
additional disadvantage that usually ABX monomers must be synthesized or
prepared before polymerization.
The step-growth polycondensation method is still used widely in the synthesis of
a broad range of hyperbranched polymers. However, most of the polymers that
16


are synthesized via this synthetic route are macrogels. Some examples include
polyesters, polyphenylenes, polyamides, polycarbonates and polyether
polymers."
1.2.2.2. Polyesters
One method used to synthesize hyperbranched polyesters is the step-growth poly-
condensation. An example of this is the reaction of the core molecule (2-ethyl-2-
(hydroxymethyl))-1,3-propanediol and the AB2 monomer
2,2bis(hydroxymethyl)propionic acid (bis-MPA) which has been used to
synthesize hyperbranched, aliphatic polyesters Figure. 1.7 shows this synthetic
route.
17


Fig.1.7. Hyperbranched polymer synthesis by polycondensation through the
reaction of Bis(MPA) and TMP to synthesize a hyperbranched aliphatic
polyester11. This image was taken and reproduced from reference 11.
18


1.2.2.3. Second method of synthesis of hyper branched polymer: Self-
condensing vinyl polymerization of AB* monomers
This method is usually used for monomers that have one vinyl group and one
initiating moiety (i.e., an AB* monomer) to synthesize hyperbranched polymers.
The reaction can be activated using a radical, cation or anion11.
1.2.2.4. Third method of synthesizing hyperbranched polymers: Multi-
branching ring-opening polymerization of latent ABX monomers
Suzuli et al, used this technique first to synthesize a hyperbranched polyamine
polymer. This synthetic approach uses a ring opening reaction of latent ABX
monomer.
An example of this approach is Frey et al.s work, in which authors used this
technique to synthesize chiral polyglycerol by polymerizing the two enantiomeric
forms of glycidol,3. Figure 1.8 shows this reaction approach.13
19


Fig.1.8 This figure shows the ring opening polymerization of enantiomerically
pure glycidol to synthesize a chiral hyperbranched polyglycerol dendron." This
image was taken and reproduced from reference
20


1.3 Click reactions
Hyperbranched polymers and dendrimers have become very popular during
recent years due to their potential applications in a broad range of industries from
nanotechnology to dentistry and medical applications". Therefore, new methods
and approaches that can synthesize these molecules efficiently are valuable and
significant. For this reason there has been a lot of effort in research aiming to
find and identify optimal methodologies for the specific synthetic needs.
"Click" reactions have been identified as type of reaction that achieves the goals
necessary for having high yields and by product free reactions for synthesis of
hyperbranched and dendrimeric polymers. Bowman and Hoyle described the
click reactions characteristics as being reactions with high yield of product
without any byproducts, simple reaction conditions with a variety of different
starting materials, and tolerance to oxygen and water.11,14,40,41
Three of the most visible "click" reactions are the Cu'-catalyzed alkyne azide
[3+2] cycloaddition (CuAAC), the Diels-Alder (DA) cycloaddition and thiol-ene
coupling (TEC). 17,14
21


1.3.1. CuAAC click reaction
The Cu'-catalyzed alkyne azide [3+2] cycloaddition click reaction which
produces 1,4-disubstituted 1,2,3-triazole was introduced by Sharpless et al. in
2002.15,17
3EEEH
Alkyne-Azide
Cud)
Nj-R ---------
Fig.1.9 This figure shows an example of the CuAAC reaction17. This image was
taken and reproduced from reference17.
22


The CuAAC reaction is shown in figure 1.9 and it illustrates a 1,3-dipolar
Huisgen-type cycloaddition that has a high yield of products without significant
by-products being formed. Figure 1.10 illustrates an example of this reaction17.
Fig.1.10. This figure shows CuAAC was used in the synthesis of highly dense
glycodendrimers.17 This image was taken and reproduced from reference17.
Figure 1.11 demonstrates use of CuAAC in dendritic convergent synthesis that
was introduced by Lee and co-workers16,17.
23


Fig. 1.11. This figure shows convergent synthesis via "ClickCuAAC.17 This
image was taken and reproduced from reference17.
24


1.3.2. Diels-AIder click reaction (DA)
Diels-Alder (DA) cycloaddition is another kind of "click" reaction (Figure 1.12)
that in addition to the advantages mentioned above is also a metal free reaction.
Fig. 1.12. This figure shows an example of Diels Alder Reaction.17
This image was taken and reproduced from reference17.
25


Mullen et al first used this reaction in polyphenyl synthesis. They obtained
dendritic macromolecules by the reaction between tetra phenyl
cyclopentadienone and polphenylacetylene18. Figure 1.16 shows this reaction, in
which the products resemble a three-dimensional structure with nano-sized
cavities.17
Fig. 1.13. This figure shows an example of a Diels Alder reaction as a click
17 17
reaction. This image was taken and reproduced from reference .
26


1.3.3. Thiol-ene click reaction (TEC)
Thiol-ene reactions are becoming increasingly utilized, due to their specific
advantages. Some of the advantages are that they are not sensitive to oxygen or
water; therefore, there is no need to degas or keep away from moisture. They are
also tolerant to many functional groups and organic solvents. Thiol-ene reactions
use either heat or UV to generate radicals as well as the fact that they have a
high yield of relatively pure products19.
Son et al. utilized thiol-ene reactions to form carbosilane dendrimers They
used tetravinylsilane and applied the thiol-ene reaction to form a series of
multifunctional organosilicone thioethers21,29. In 2009 they reported that these
products were used as the cores to create carbosilane dendrimers. They used the
Art
thiol-ene reaction followed by Gngnard substitution .
Thiol-yne click chemistry has also been demonstrated in synthesizing
polymers40,41 and dendrimers. A sixteen functional alcohol was produced from a
tetra-yne via an AB2 molecule19. These specific examples shed light on the
varied implementations of click chemistry in the formation of hyperbranched and
dendrimeric species.
27


Hawker combined various reactions in a thorough synthetic approach for
producing multigeneration dendrimers. Thiol-ene Coupling (TEC) (Figure 1.14)
was used by Hawker for polythioether synthesis.
Fig. 1.14 The thiol-ene click reaction mechanism17. This image was taken and
reproduced from reference17. .
Since this reaction involves a type of radical addition reaction, it results in anti-
Markonikov products via sulfur-carbon bond formation.14 Thiol-ene reactions use
a step-growth radical polymerization mechanism as the reaction proceeds, which
is one type of click reaction20. The thiyl radical is formed via abstraction of
hydrogen from a thiol monomer via a primary initiating a radical. This thiyl
radical further reacts with an alkene functional group via an addition reaction, to
28


form a carbon-centered radical. The carbon-centered radical can also be formed
via reaction of the alkene functional group with the primary initiator radical.
Figure 1.15 shows this mechanism21. The thiyl radical is regenerated in this
initiation mechanism. Occurrences of these two alternative reactions will lead to
the product formation.
Fig. 1.15. The step growth mechanism of alternating propagation (addition) and
22
chain transfer in thiol-ene reactions. This image was taken from reference .
29


The thiol-yne reaction, which is the reaction of a thiol with an alkyne, was
determined to have a similar radical mechanism involving alternating chain
transfer and propagation reactions.23 The reaction of the thiyl radical and the
alkyne results in the formation of a carbon-centered radical. That radical will
subsequently abstract a hydrogen from the thiol which will result in the formation
of a reactive vinyl sulfide functional group. Now, it is ready to undergo the same
set of reactions as in the thiol-ene reaction, where the alkene on the vinyl sulfide
reacts with another thiyl radical to again form a carbon-centered radical that is
able to abstract hydrogen from a thiol. Thiol-yne reactions in comparison with
thiol-ene reactions will result in a higher crosslink density polymer when
multifunctional monomers are polymerized. Figure 1.16 shows this thiol-yne
reaction mechanism.
30


Fig. 1.16 The various reaction steps in the thiol-yne polymerization reaction.
This image was taken and reproduced from reference22.
The TEC methodology is sometimes preferred in combination with the other
types of click reactions (CuAAC, DA) primarily due to the ability to control the
initiation of the reaction by light and the great variety of functional groups and
monomers that are available and achieve high conversion. Table 2.2 presents
these options for three types of click reactions.14 Figure 1.17 and 1.18 show
some examples of applications of click reactions in the synthesis of dendrimers.
31


Tablel. 1. Click reaction characteristics. This table was taken and reproduced
from reference.17
Click Reaction DA CuAAC TEC
Metal-Free Yes No Yes
Solvent-Free No No Yes
Water-Compatibility Yes Yes Yes
Oxygen-Compatibility Yes Yes Yes
Controlled Initiation Yes No Yes
Reversibility Yes No No
32


Fig. 1.17. Poly thioether dendrimer synthesis via TEC and esterification
reactions17. This image was taken and reproduced from reference.17
33


SH

£

Methanol/hv | HS^^Si(0Me)3 frciick" TECi
Si-^s/S^^Si^sg^^sg^S^^^SKOMeJj) )J
THF J ^Mg-Br
Methanol/hv I HS^.U ["Click" HI
/ OH
Sj'^SN/^Si^sx^\Sj^S^\/,Si|^ss/s^OH
3 3'4
3 3 3'4
Fig.1.18 Synthesis of carbosilane-thioether dendrimers using TEC click
reactions24. This image was taken from reference.24
TEC click reactions can readily be combined with other click reactions such as
the CuAAC and DA click reactions. These strategies are often referred to as
"double click" reactions (figure 1.19).14,25
34


Fig. 1.19. An example of a double click reaction17. This image was taken from
reference ,17
1.4 History
1.4.1 History of Hyperbranched Polymers
Berzelius et al. primarily started the research on hyperbranched polymers prior
to the 20th century which started from resin formation of tartaric acid as an A2B2
monomer and glycerol as a B3 monomer26. Later, reaction of phthalic acid (both
as A2 monomer) with glycerol was reported 26.
35


Baekeland et al discovered commercial synthetic plastics and phenolic
polymers. In his research, he polymerized formaldehyde (A2 monomer) and
phenol (B3 monomer) and synthesized random hyperbranched structures28. In the
decade of the 1940s, in order to find the molecular weight distribution on three-
dimensional polymers, Flory et al used theoretical calculations and reported in
1940 that gelation occurs with respect to the degree of polymerization and
polycondensation between monomers29'32 Further, they discovered that if one A
monomer condensed with two or more B monomers, highly branched polymer
formation could be achieved without gelation.33 Kricheldorf et al synthesized
copolymers of highly branched polyesters by utilizing AB and AB2 monomers in
1982.34 The following table briefly presents the history of hyperbranched
polymers.3536
36


Tablel.2 A brief history of hyperbranched polymers. This image was taken and
reproduced from reference1.
Year Case Lead authors
Before 1900 Tartaric acid glycerol Bencelius
1901 Glycerol phthalic anhydride Smith
1909 Phenolic formaldehyde Baekeland
1929- Glycerol phthalic Kienle
1939 anhydride
1941 Molecular size distribution in theory Hory
1952 AU polymerization it theory Hory
1982 AB} AB copolymerisation Kricheldorf
1988- 1990 AU2 homopolymcrization Kim/Wcbstcr
1.4.2 History of Dendrimers
Vogtle synthesized a Cascade molecule by using different primary
monoamines and diamines and then attaching a spacer unit to the propyleneamine
structure.4. They reacted primary monoamines with acetonitrile via two Michael
addition steps to produce dinitrile4. Figure 1.20 shows this structure4. Sodium
borohydride reduced the two nitrile groups and produced the terminal di-amine. 4
37


This Michael addition step followed by reduction is repeated several times and
resulted in a cascade molecule with many branched arms4.
reaction stop
(*)
Co(ll). NjBM,
Repetitive
reaction step
(Bl

-CN
Repetitive
reaction step
(A>
NC
CoOIK Ne0H4
Repetitive
reaction step
H4N
Fig. 1.20. The structure of the original cascade molecule4. This figure was taken
from and reproduced from reference4.
38


In 1974, the same group synthesized a many-armed octopus molecule. This
compound was used to complex metal ions. Figure 1.21 shows this dendrimer,
which they used to complex metal ions.
Fig.1.21. This figure shows the octopus dendrimer and its use to complex metal
ions. This figure was taken and reproduced from reference4.
39


In 1982, Denkewalter et al used the divergent method to synthesize
polylysine dendrimers. Further, Maciejewski developed additional polymers with
cascade like structures. Later, de Gennes and Hervert demonstrated there is a
limitation in the maximum achievable generation growth due to steric hindrance.
In 1985 Tomalia synthesized PAMAM, and Figure 1.22 shows the synthesis
route they used 4. This molecule was first called a starburst dendrimer4.
40


COjM.

(A)
mo/:
^SyN.
CO
J ^ _NM,
\
(8)
COjMo
M,N
^"COjW
(A! '
o
Fig. 1.22 This figure shows the first cascade molecule synthesized and its
synthetic route4. This image was taken from and reproduced from reference4.
41


Dendrimer synthesis and research started initially from numerous studies4 but has
now been followed up on by numerous other groups. Now, more than ever in
history, this research field continues to expand and grow due to the nearly
unlimited applications for dendrimer and dendrimer-like structures in a vast
variety of industrial fields.
1.5. Applications of hyper branched polymers
The 16-alkene functionalized hyperbranched polymer synthesized in this work is
hypothesized to have specific characteristics that make it applicable in dental
composites with glass filler. It is hypothesized that the polymer has the potential
to act as an interfacial layer and would be placed in a thiol-ene resin system in
order to increase the material properties. This composite material will have
potential as a low-stress dental restorative material with high modulus.
This hyperbranched polymer possesses flexibility and contains multi-alkene
terminal functional groups that can undergo further thiol-ene reactions to couple
it both to the glass filler surface and into the polymerizing resin. This
hyperbranched molecule acts as a low compliance interfacial layer that
accommodates mobility in the system and will result in decreasing the shrinkage
stress while keeping the high modulus.
42


In other systems, improvement of mechanical properties such as hardness have
been demonstrated using hyperbranched polymers.40,42. Coupling of
hyperbranched polymers to conventional linear polymers may also lead to
significant improvements in certain properties, including solubility, mechanical
properties, viscosity, and suitability for materials processing.
Figure 1.23 shows a broad array of applications for hyperbranched and
dendrimeric polymers.11 One example is utilizing a series of hyperbranched polymers
in order to prepare high quality films and stable higher solid content composites.11 These
examples are only a few of the potential applications of these unique macromolecules.
Today more and more fields are discovering benefits from applications of these
macromolecules.
43


Delivery Devices
Liquid Crystals
Soluble Functional^
Supports
Catalysis
Sensors
> Blend Components
r Additives
Powder Coatings
High Solid Coatings
Nanofoams in Low
Dielectric Materials
Low VOC Coatings
Multifunctional Cross-linkers
Fig. 1.23 This figure illustrates selected applications of hyperbranched
polymers.11 This image was taken from reference11.
44


2. Synthesis of the 16-Functional Alkene Hyperbranched Polymer
Thiol-acrylate Michael addition, the thiol-yne click reaction and an esterification
process were all used in this work in order to synthesize a new 16-functional
alkene hyperbranched oligomer. The hyperbranched oligomer is prepared by a
divergent method starting with PETMP as a core which then undergoes a thiol-
acrylate Michael addition reaction followed by thiol-yne and esterification
reactions in subsequent generations.
The 16-functional alkene functionalized hyperbranched polymer was
characterized by NMR spectroscopy, MALD1-TOF mass spectroscopy and gel
permeation chromatography.
2.1 Introduction
In this research a 16-functional alkene hyperbranched polymer was synthesized
which has application as an interfacial layer coupled to a glass filler in composite
systems where it would be used in conjunction with a thiol-ene resin system in
order to improve the material properties.
The synthetic routes were designed to have a few efficient synthetic steps with
high yield while also being economically efficient as well as being able to use the
45


synthesis route and enlarge the scale to synthesize a large amount of these
materials since it was needed further for its application to modify the interface of
glass fillers used in composite material applications.
The synthesis route of this dendrimer was designed to first have a synthesis step
that involved the thiol-acrylate Michael addition that results in an alkyne
functional material19. The second step involves reacting the alkyne via a thiol-
yne reaction9 and finally the third reaction involves an esterification process28.
Based on these requirements, this hyperbranched polymer was synthesized using
thiol-acrylayte Michael addition which was the reaction of PETMP that contains
four thiol groups with propargyl acrylate catalyzed by triethylamine to obtain a
tetrayne molecule 19. In nucleophilic Michael addition, the double bond is
electron deficient. Triethyl amine electron lone pairs abstract hydrogens of thiols
on PETMP and causes the anionic thiols to react with the electron deficient of
propargyl acrylate when the tetra-yne is produced. This tetrayne was further
reacted with thiolglycerol using light exposure and a UV photoinitiator, Irgacure
651, to initiate the thiol-yne click reaction which is a radical reaction that helps to
obtain the 16 hydroxyl functionalized hyperbranched polymer9. The thiol-yne
reaction has many advantages as described earlier.
46


Synthesizing the tetrayne and subsequently using it in the thiol-yne reaction also
increases the change in functionality since each yne is capable of reacting twice
with each thiol functional group. Since the thioglycerol contains two hydroxyls
per thiol, each yne leads to the attachment of four hydroxyl moieties, converting a
tetrayne into a 16-functional hydroxyl in a single step. Finally, the esterification
process with 4-pentonic acid and pyridine was done and it resulted in the 16-
functional alkene hyperbranched polymer.
Figure 2.1 represents the synthetic strategy for synthesizing the 16-functional
alkene dendrimer. Figure 2.2 shows the overall synthesis route.
NMR spectroscopy, MALDI-TOF mass spectroscopy and gel permeation
chromatography were performed to verify the structure.
47


0vr?tw
} jrl A*'
16-C=C
Fig. 2.1 The synthetic strategy of synthesizing the 16-functional alkene
terminated hyperbranched polymer. Here the numbers in the scheme refer to the
material that was used and synthesized and these numbers are further used in the
procedure method.
48


4 (TEA)


Fig.2.2 shows the first, second and third step reaction mechanism.
49


2.2 Materials and Methods
2.2.1 Materials
Pentaerythritol tetra(3-mercaptopropionate) (PETMP) was donated by Evans
schematics.
2,2'dimethoxy-2-phenylacetophenone(Irgacure651) was donated by BASF
Company.
Sodium chloride, anhydrous sodium, ethyl ether, sodium bicarbonate, Sodium
sulfate, hexane, and dicholoromethane (DCM) were purchased from Fisher
Scientific company.
Commercial reagents were purchased from Sigma Aldrich. There are as follows:
propargyl acrylate, triethylamine and sodium citrate mono basic, thioglycerol,
N,N-dimethylformamide (DMF) tetrahydrofuran anhydrous, pyridine,
4(dimethylamino)pyridine (DMAP), and 3-Indoleacrylic acid (IAA).
A ultraviolet (UV) (Acticure, EFOS, Mississauga, Ontario, Canada) lampwas
used with a 320-500 nm bandpass filter.
f
50


2.2.2 Method
2.2.2.1 Procedure for Synthesis of Tetra-Alkyne Molecule( Tetra-yne)
Initial Reactant:
4.88 g (10 mmol) PETMP
4.84 g (44 mmol) Propargyl acrylate
0.28 ml (2 mmol) Triethyl amine
Initially 4.88 g of PETMP (1) was dissolved in 120 ml of DCM and 0.28 ml of
triethyl amine was added.
4.4 equivalents (to PETMP) of propargyl acrylate (2) which is 4.84 g was
separately dissolved in 60 ml of DCM. Using an addition funnel this was added
drop wise to the mixture of PETMP and triethylamine since this reaction is
exothermic and the heat that generates can degrade the material. In addition to
the fact that they were added slowly and drop wise, for the first 30 minutes, ice
was used around the reactant flask. Then, the ice was removed and it was stirred
further for 24 hours to complete the reaction. After 24 hours it was washed with
saturated sodium citrate mono basic three times, each time 200 ml of saturated
sodium citrate solution was used. Then, it was additionally washed three times,
each time 200 ml of saturated sodium bicarbonate and brine wash. 14 g (15
mmol) of clear viscous liquid was collected with 75% yield.
51


2.22.2 Procedure for Synthesis of 16-functional hydroxyl hyperbranched
polymer
Initial reactants
14 g (15mmol) Tetra-yne from above
13.7 g (127 mmol) Thioglycerol
1.35 g (5 mmol, 5 wt%) Irgacure 651
In a round bottom flask 14 g of Tetra-yne (3) was weighed and was dissolved in
40 ml of DMF.
13.7 g of Thioglycerol (5% excess) (4) was added to the flask. Thioglycerol was
used due to the presence of two hydroxyl functionalities per thiol, thus acting as
an AB2 monomer.
1.35 g of photoinitiator Irgacure 651 was added to the mixture and dissolved.
Then, it was vacuumed and nitrogen purrged. This was done due to the fact that
although the thiol-yne reaction is tolerant to oxygen; however, to a certain extent,
oxygen inhibition can occur. Therefore, to have this reaction be fully complete,
vacuuming out the oxygen and then nitrogen purging was done.
52


UV photocuring was done using UV lamp Acticure, EFOS, Mississauga, Ontario,
Canada. A bandpass filter of 320-500 nm was used in the UV light and the
intensity was fixed at 10 mW/cm2. The sample was photocured for 4 hours.
The solvent (DMF) was removed from the reaction mixture by heating under
reduced pressure (rotary evaporator). After all of DMF was removed.
ethyl ether was used as the solvent for precipitation five times in order to remove
excess thioglycerol and then high vacuumed overnight in order to dry the
product.
The product appeared as a yellow viscous oil and 17 grams (9.5 mmol) of 16-
hydroxyl functionalized hyperbranched polymer was collected with 63% yield.
53


2.2.2.3 Procedure for Synthesis of 16-functional alkene terminated
hyperbranched polymer
Initial reactant
4.73 g (2.6 mmol) 16-functional hydroxyl terminated hyperbranched polymer
from above
lOg ( 126 mmol) Pyridine Anhydrous
23g (126 mmol) 4-pentenoic Anhydride
0.77g(6 mmol) 4-(dimethylamino)pyridine(DMAP)
4.73 g of 16-functional hydroxyl terminated hyperbranched polymer (5) was
dissolved in 150 ml of anhydrous tetrahydrofuran (THF) in a round bottom flask.
This flask was purged with argon.
Molecular sieves were used to remove the excess water from the system. Pre-
treatment of molecular sieves involved placing them in an oven 24 hours before
use in the reaction to ensure that they were dried completely. The molecular
sieves were poured into the three neck flask and the solution of the
hyperbranched polymer in THF was added to it. Three equivalents (to hydroxyl
group) of anhydrous pyridine, three equivalent of 4-pentenoic anhydride (6) and
54


0.15 equivalent of 4-(dimethylamino) pyridine (DMAP) were added to the
contents. The reaction was stirred overnight. After 24 hours, water was used to
quench the reaction and was allowed 3 hours to stir. Then, DCM was used to
dilute the contents and was vacuum filtered. The contents were washed five times
with 300 ml water each time. In addition, it was washed three times each time
with 200 ml of sodium bicarbonate and three times with brine. Anhydrous
sodium sulfate was used to dry the organic layer and then it was filtered again
and concentrated using the rotary evaporator. 4.7 g (1.5 mmol) of clear viscous
liquid (7) was obtained with 57% yield.
55


2.2.3. Instruments used for Characterization
The analytical instruments that were used to characterize each step of the reaction
were 'H NMR spectra obtained from a 300 MHZ NMR spectrometer (Bruker 300
UltrShield) at ambient temperature at the University of Colorado at Boulder.
Deuterated choloroform and dimethyl sulfoxide-d6 were used as NMR solvents
for sample preparation and they are used as internal references respectively as
7.25 ppm and 2.5 ppm. NMR results are given in parts per million (ppm).
MALDI-TOF mass spectra were collected on Voyager-DE STR MALDI-TOFMS
instrument from Applied Biosystems at University of Colorado at Boulder.
Gel permeation chromatography was performed in tetrahydrofuran (THF) at the
University of Colorado at Denver.
A Fourier transform infrared spectrometer (FTIR) Magna 750, Nicolet Instrument
Corp., Madison, WI, was used at the University of Colorado at Boulder.
High performance Liquid chromatography was done on an Agilent 6220 Time-
of-Flight with an Agilent 1200 High Performance Liquid Chromatograph at
Colorado State University, Chemistry department at Fort Collins.
56


2.3 Results and Discussion
2.3.1 Result of synthesis of Tetra-yne via Thiol-acrylate Michael addition
(First step) Reaction
The first step of the synthesis route was the amine catalyzed Michael addition
reaction between PETMP and propargyl acrylate which results in the formation
of the tetrayne product. Figure 2.3 shows the'H NMR of the first step product.
57


Fig. 2.3. 'H NMR spectra of the tetrayne. *H NMR, CDCI3: 2.48 ppm (4H), 2.57-
2.65 ppm(16H),2.73-2.80 ppm (16H), 4.12 ppm (8H), 4.67 ppm (8H).The
structure drawn is one arm of four arm since they are chemically equivalent.
The reactants in this synthesis step were the PETMP and propargyl acrylate; and
therefore, the 'll NMR of these reactants are studied compared to the product and
58


Figure 2.4 demonstrates this. The proton peaks from the thiol are present in
PETMP and can be found in fig.2.4A at 1.5-1.7 ppm labeled as land this peak is
fully converted as in the *H NMR of the product, these peaks are no longer
visible.
Also, the peaks for protons of the alkene functional group in propargyl acrylate
can be found from 5.7-6.5 ppm in fig.2.4B as peaks 2 and 3. These peaks are no
longer present in the 'H NMR of the product, again indicating that the reaction
was complete.
59


A)PETMP
HS 0
<0 0 O 0 *< i * B O > O i *
6.0 15 10 1 1 1 1 ' 1 4.5 140 15 10 J |,2 r ill 1 1 1 1 r 5 10 L5 U
T nr T
o
O 0 VI BON
0 0 n 00
0 0 6 * PI
65 6.0 15 5.0 45 4.0 15 10 15
ft (PPm)
10
-------'----r
L5 L
Fig.2.4 1 H NMR of reactant in Comparisons With Product of Reactant A)
PETMP and B)Propargyl Acrylate and C)Tetra-yne.
60


After liquid-liquid extraction (as described in 3.2.2.1 section), 14g (15 mmol) of
the tetrayne was obtained with 75% yield.
2.3.2 Result of Synthesis of 16-Functional Hydroxyl Terminated
Hyperbranched Polymer via the Thiol-Yne Reaction
Thiol-yne click chemistry was used in the second step of the synthesis route. This
step was the reaction of the tetrayne molecule (first step product) with
thioglycerol under photoinitiated conditions which was accommodated by using
5wt % photoinitiator Irgacure 651 in DMF. The UV lamp with a bandpass filter
of 320-500 nm was used at 10 mW/cm2.
Figure 2.5 shows the *H NMR spectra of the 16-functional hydroxyl terminated
hyperbranched polymer.
61


Fig.2.5 'H NMR (DMS0-J6) of 16-Hydroxyl terminated hyper Branched
polymer. H NMR spectra analysis; 3.13-3.21 ppm (4H), 3.51-3.60
ppm(8H),4.05-4.31 ppm(16 H)4.54-4.60 ppm(8H),4.75-4.84(8H),
62


'H NMR of thioglycerol and the 16-functional hydroxyl terminated
hyperbranched polymer are compared in Figure 2.6.
Figure 2.6 A demonstrates the !H NMR of thioglycerol and the protons of the
hydroxyl group of thioglycerol at 4.5-4.8 ppm are labeled as 1 and 2 and the
proton of the thiol around 2 ppm is labeled as 3.
Figure 2.6 B shows the NMR spectra of the 16-functional hydroxyl
terminated macromolecule. Comparing these two NMRs shows that peak 3
decreases significantly, and peaks 1 and 2 in the product show approximately 16
hydroxyl groups on the product and therefore it is clear that the reaction achieved
63


the desired high conversion.
Fig.2.6A) 'id NMR spectra of thioglycerol (reactant) B) 'H NMR of second step
product 16-hydroxyl terminated hyperbranched polymer.
64


The fact that this reaction reached high conversions also was shown from Fourier
transform infrared spectroscopy (FTIR) studies where the thiol peak from the
thiolglycerol at 2675 cm'1 and the peak of the alkyne from the tetrayne at 2130
cm'1 were observed throughout the reaction. Both peaks disappear as the reaction
reached high conversion.
Figure 2.7 demonstrates the FTIR studies, and it indicates that thiol-yne click
reaction reached full conversion in less than half a minute.
65


Wave number (l/cm2)
Fig.2.7a) FTIR spectra from before () and after (...) the reaction are shown.
This result shows that the thiol peak at 2675 cm'1 and the alkyne peak at 2130
cm'1 disappear as the reaction reaches high conversions, b) Conversion of
alkyne(...). and thiol() as a function of time that shows the thiol-yne click
reaction reached high conversions.
66


There is a difference between the FTIR studies that was done using a very thin
layer of material on the salt plates and the scaled up synthetic reaction. This thin
layer of reactant on salt plates will not be the exact model for the real reaction
which was done with an initial amount of 14 g of the tetrayne, the synthetic
reaction mixture is not close to the thin layer on the salt plates; therefore,
although the FTIR showed that the thiol-yne reaction reached full conversion in
less than half the minute, the reaction mixture was irradiated with UV at 10
mW/cm for 4 hours to ensure high conversions.
2.3.3 Result of Synthesis of 16-Alkene functionalized Hyperbranched
polymer via Esterification.
The third step involves the formation of the 16-functional alkene by reaction of
the alcohol with 4-pentenoic acid anhydride and pyridine catalyzed with DMAP
in anhydrous THF. !H NMR of the 16-functional alkene terminated
hyperbranched polymer is presented in figure 2.8.
67


Fig.2.8 'H NMR spectra of 16-functional alkene terminated hyper-branched
Polymer. ]H NMR spectra analysis CDCI3, 2.28-2.49 ppm(67.6 H), 2.49-2.95
ppm(55.39 H) ,3.03-3.19 ppm(3.7 H), 4.05-4.46 ppm (32 H), 4.95-5.20
ppm(41.8 H),5.72-5.90 ppm(16.5 H).
68


The 'H NMR spectra of the reactant and product are presented. Peaks 1 and 2 at
4.5-4.8 ppm in Figure 2.6 A which represented the hydroxyl groups of 16-
functional hydroxyl hyperbranched polymer disappeared in comparison to the 'H
NMR spectra of the product alkene in Figure 2.9 B. This outcome indicated that
the reaction was completed. 'H NMR spectra of 4-pentenoic acid is shown and
the proton peaks on the double bond of 4-pentenoic acid anhydride at 5-6 ppm
appeared in the product 'H NMR spectra (Figure 2.9B) and this result indicates
that this reaction went to completion.
69


Fig.2.9 A) 'Hi NMR spectra of 4-pentenoic acid, B) 'H NMR spectra of 16-alkene
functional Hyperbranched polymer. The peaks of protons on the double bond of
4-pentenoic acid anhydrid at 5-6 ppm appeared in the product 'H NMR spectra
and this indicates that this reaction completed.
70


Initially, the molecular weight of the 16-functional alkene hyperbranched
polymer is 3108 Da. The MALDI result showed a peak at 3131 Da which is the
sodium salt of the product, [M+ Na+], (m/z=3131) Figure 2.10 shows the
MALDI-TOF result. GPC showed the molecular weight of the product as 3052
with a PD1 of 1.08. Figure 2.11 shows the GPC results. The product was also
analyzed by HPLC/MS, a doubly charged ion.Figure 2.12 shows the HPLC-MS
result of the fraction collected at 6-7 minutes.
71


100
5*
VI
c
80
3130
60 -
40
20
O
500 1000 1500 2000 2500 3000 3500 4000
m/z
Fig.2.10 MALDI-TOF mass spectroscopy of 16- alkene functional hyper
branched polymer which has m/z=3130 which is ionized by Na+, [M+ Na+].
72


Fig. 2.11 Gel Permision Chromatography of 16-Alkene functional hyper-
branched polymer with Mn of 3200 Indicated by b. a Has Mn of 6600and c Has
Mn of 360.
73


Fig. 2.12 HPLC/MS result of 16-Alkene functionalized hyperbranched polymer.
This is the MALDI of fraction collected from the sample at 6-7 minutes that
contain the product. The product peak is shown with m/z of 1571 which is a
doubly charged ion [M+ (NH/^].
74


The GPC results indicate (peak b) a dimer of the product with Mn of 6600 that
could have happened via coupling during one of the radical initiation steps. Peak
c with Mn of 360 arises from thioglycerol from the second step, the two OH and
one SH all could have reacted with the anhydride resulting in a 3-functional
alkene molecule and theoretically calculated to be 370.5 that correlates with the
HPLC/MS result [M+H+] m/z = 372. The integration of the peak area of the GPC
results indicated that the product contains 70% 16-functional alkene terminated
hyperbranched polymer, 19% the coupling byproducts and 11% small molecular
impurities.
The results of NMR spectra of the 16-functional alkene (Figure 2.9 B) are further
elaborated when they are compared to GPC result since peaks 4 and 5 show 16.54
and 41.86 instead of 16 and 40, this slight increase is due to the presence of three
alkene terminated molecule from thioglycerol reacting with the anhydride. Also,
the presence of the dimer which is formed from coupling of the product decreases
the peak area of 4 and 5 on the 16-functional alkene NMR(Figure 2.9 B);
therefore, these two molecules effect to some aspect cancel out each other and the
NMR show the slight increase in peak area
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2.4 Conclusion
The 16-functional alkene hyperbranched polymer was synthesized via several
synthetic steps. Application of thiol-acrylate Michael addition, thiol-yne click
reaction and an esterification processes was demonstrated in this synthesis route
to yield a new 16-functional alkene hyperbranched polymer.
The 16-functional alkene terminated hyperbranched polymer was characterized
by NMR spectroscopy, MALDI-TOF mass spectroscopy and
GPC.
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Appendix A
Synthesis of 12-Alkene hyper -branched polymer
Initially, the triyne molecule was also used to synthesize a 12-functional alkene
functionalized hyperbranched polymer. Tripropargylamine was used since this
molecule is commercially available and it would optimize the reaction conditions.
However it was found due to running the reaction several times that the triple
bonds of this molecule are not very active and low yields results from the low
reactivity of triple bonds of Tripropargylamine. Later was found in literature9,
the reaction kinetics of methyl propargyl amine was almost zero.
Although the reactions with Tripropargyl amine was found to be not efficient and
gave low yields of product but different reaction conditions gave an insight of
how one can increase the conversion by alternating the different reaction
conditions.
The different elements for this step that can be alternate were: concentration of
photo initiator (0.5%, 2%), Sequence of addition of initiator (Addition of several
times initiator versus addition of the initiator one time at the beginning). Different
time of reaction, different concentration of initiator (0.5wt%, 2wt%) as well as
nitrogen purging in order to avoid oxygen inhibition, Different light intensity of
UV light, Different amount of thioglycerol used, Different filter of UV-lamp
used in order to experiment and study of different reaction conditions and get an
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understanding of how to do these reactions to get the high yield of product. It was
found that in order to synthesis 12 hydroxyl functionalized macromolecule, the
most efficient way is to use 200% excess of thioglycerol as a solvent and react
that with Tri-propargyl amine and formulated with Irg651and irradiate the
mixture with UV Acticure, EFOS, Mississauga Ontario, Canada UV lamp. With
filter pass of 320-500nm and light intensity of 30 W/cm2.These studies are
discussed in this chapter.
In this work, thermal initiator AIBN as the initiator was used. Tri-propargyl
acrylate was mixed with 50% excess of thioglycerol and AIBN. Four times of
0.25 mol% AIBN (Total of 1 mol %) AIBN was added to the solution and the
mixture was heated up to 65 deg in oil bath. Figure4.1 shows the MALDI-TOF
mass spectroscopy result. This result show an important indication of that using
AIBN thermal initiator and heating the solutions in order to activate the thermal
initiator results in coupling of the product. This indicates that thermal initiator is
not a right initiator to use for the Thiol-yne reaction of Tripropargyl amine and
thiogylerol.
Table A.l shows the calculated molecular masses for the expected products that
can result from Tripropargyl amine and thiolglycerol reaction.
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Table.A.IThe calculated molecular masses for all the possible products from
reaction of Thioglycerol and tri-yne reaction.
12-OH 779.22 780.22 786.24 802.21 818.18
10-OH 671.2 672.2 678.22 694.19 710.16
8-OH 563.17 564.17 570.19 586.16 602.13
6-OH 455.15 456.15 462.17 478.14 494.11
4-OH 347.12 348.12 354.14 370.11 386.08
2-OH 241 242 248.02 263.99 279.96
O-OH 131.17 132.17 138.19 154.16 170.13
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Fig.A.IMALDI-TOF spectroscopy of 12-Hydroxyl macromolecule, higher
molecular weight are indication of coupling of product in high temperatures.
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In this set of experiment different concentration of initiator was utilized. In one
set 0.5 wt% (.25mol %) Irgcure 651 was used in another set 2wt% Irgcure 651
(lmol% initiator) was used.
In both conditions Tri-propargyl amine was mixed with 50% excess thioglycerol
and initiator and was high vacuumed and nitrogen purged and the mixture was
irradiated using Acrticure, EFOS UV lamp with filter pass of 365 and light
intensity of 10 mw/cm2 for 24 hour time duration. Comparison of MALDI-TOF
spectroscopy results indicate that 0.5 wt% of initiator is not sufficient for this
reaction since there is a small product peak shown (Figure A.2). 2wt% initiator is
more sufficient as the product peak shows an increase (FigureA.3) compared with
the FigureA.2.
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