1. Enzyme Catalyzed Esterification of
Telechelic Polymers
Clive T. Chirume, Junyoung Seo, Dr. Kevin Cavicchi
University Department of Polymer Engineering
Of Akron
250S. Forge Street
Akron, OH 4435
Introduction
There are a number of hydroxyl functional
polymers that can be modified to produce
functionalized polymers for the preparation of well-
defined block copolymers. For example it possible to
attach a carboxylic acid function reversible addition
fragmentation chain transfer (RAFT) agent to a
hydroxyl end-functional polymer to generate a
macromolecular RAFT agent through the formation of
an ester. While different methods have been developed
for carboxylic acid/alcohol esterification reactions a
recent route is using an enzymatic catalyst, which
requires mild reaction conditions compared to other
approaches. The objective of this project is to
investigate the esterification of poly (butadiene) and
poly (ethyleneoxide) using Novozym 435 a
commercial enzymatic catalyst for esterification. If
this is successful, the synthesis of block copolymers
will be investigated.
Telechelic polymers.
Figure 1.
Figure one shows the three types of telechelic
polymers. These polymers can be used as an important
back bone for building polymers with complex
structures.
To be able to produce block copolymers,
polymerization has to be carried out and there are
different types of polymerization technics such as
atom transfer radical polymerization (ATRP) and
nitroxide-mediated polymerization (NMP), etc. in this
project, the Reversible Addition-Fragmentation chain
Transfer (RAFT) polymerization (Figure 2) will be
used for the preparation of the block copolymers.
RAFT polymerization consists of a macromolecular
RAFT agent, Initiator, monomer and a solvent (not
strictly required if the monomer is in liquid form).
Figure 2- RAFT mechanism.
Thiocarbonylthio compounds such as dithioesters,
trithiocarbonates, dithiocarbamates, and xanthates are
normally used as the RAFT agents. Figure 3 illustrates
a generic structure of a RAFT agent.
Figure 3- RAFT agent (CTA) form.
Through the esterification of a telechelic polymer and
a S,S-Bis(R,R-dimethyl-R-acetic acid)-
trithiocarbonate RAFT agent, a thioester
macromolecular RAFT agent (or CTA i.e. chain
transfer agent) can be produced in the presence of an
enzyme catalyst. The catalyst used is Novzym 435
because it reacts at different rates as a function of
substrate chain length, and this results in products that
are relatively more uniform in length.
Experimental
Materials. Novozym 435 used as the enzyme catalyst.
Polybutadiene hydroxyl functionalized 1200 wt. is
used as the telechelic polymer. N-Methyl-2-
pyrrolidone (NMP) and xylenes are the solvent that
dissolve both the RAFT agent and polybutadiene. 1-
Dodecanethio, acetone, sodium hydroxide, carbon
disulfide, chloroform, hydrochloric acid and toluene.
All of these chemical were procured from Sigma-
Aldrich.
Instrumentation. A GPC instrument including: A.
Autosampler, B. Column, C. Pump, D. RI detector, E.
UV-vis detector is used to calculate the molecular
weight. Varian NMR spectrometer system used to
verify the structures of synthesized throughout the
project i.e. RAFT agent and macromolecular RAFT
agent.

2. Synthesis of RAFT agent.
Synthesis of S, S-Bis(R,R-dimethyl-R-acetic acid)-
trithiocarbonate, 1. Carbon disulfide (27.4 g, 0.36
mol), chloroform (107.5 g, 0.9 mol), acetone (52.3 g,
0.9 mole), and tetrabutylammonium hydrogen sulfate
(2.41 g, 7.1mmol) were mixed with 120 mL of mineral
spirits in a
1 L jacketed reactor cooled with tap water under
nitrogen. Sodium hydroxide (50%) (201.6 g, 2.52 mol)
Was added dropwise over 90 min in order to keep the
temperature below 25 °C. The reaction was stirred
overnight. 900 mL of water was then added to dissolve
the solid, followed by 120 mL of concentrated HCl
(caution! gas, mercaptan odor) to acidify the aqueous
layer. Stir for 30 min with nitrogen purge. Filter and
rinse the solid thoroughly with water. Dry to constant
weight to collect 41.3 g of earth-colored product. It can
be further purified by stirring in toluene/acetone (4/1)
or by recrystallizations from 60% 2-propanol or
acetone to afford a yellow crystalline.1
Synthesis of Macromolecular RAFT agent
(Esterification process).
1g of raft agent (HOOC-RAFT-COOH), 3.9372g of
polybutadiene (HO-PB-OH) i.e. a ratio of 1/1.1 with
polybutadiene in excess are reacted in the presence of
Novozym 435. The reaction was done in different
environments i.e. dean-stark under nitrogen and
vacuum. The reactions were conducted in bulk both
environments and using a solvents (NMP and
Xylenes) in the vacuum environment. All reactions
were carried out at 80o
C for 24 hrs. The bi-products of
the reaction are water and the macromolecular RAFT
agent.
Figure 4- experimental parameters
Figure 5- Vacuum Figure 6- Dean-Stark
Since the reactions are reversible and one of the bi-
products is water, it has to be expelled from the
reaction, thus introduction of the vacuum and dean-
stark to facilitate that effort.2
Results and Discussions
After running quite a number of failed experiments,
the reactions in figure 4 are carried out. Reactions 1
and 2 have are carried in the vacuum and dean stark
respectively as illustrated in figure 5 and 6.
Figure 7- HNMR of the raft agent and polybutadiene
Figure 8- HNMR of reactions 1, 2 and 3
No.1
After reaction, it is transparent syrup with light brown
color. NMR peaks of No.1 show that peak of HOOC-
RAFT-COOH (blue dot) is shifted from 1.70 ppm to
1.60 ppm. The small peak at 4.56 ppm (red dot)

3. appeared, which is attributed to hydrogen of ester
groups.
No.2 and 3
After reaction, they are yellow colored syrup. As
shown NMR data of No.2 and No.3, they have same
peaks. Compared with NMR data of reagents, it is
observed that they are mixture of HOOC-RAFT-
COOH and HO-PB-OH.
Figure 9 -Gel Permeation Chromatography (GPC)
analysis.
To verify the HNMR, a GPC analysis was conducted.
The blue curve i.e. reaction No.1 has the slowest
elusion time and the orange curve represents the
polymer and it shows that it aha a greater elusion time.
Since the lesser the elusion time indicates greater
molecular weight, leads us to believe that
esterification has taken place. However in our best
results, the molecular weight of the assumed
macromolecular RAFT agent only doubled that of the
functionalized polymer. More investigations had to be
and still have to be carried out to figure out why there
is a small change in the molecular wt.
Conclusion
It can be concluded that poly-RAFT agent is
synthesized by esterification in the presence of
Novozym under vacuum. There is still some work to
be done, to figure out the right conditions for the
reaction to successfully synthesize the
macromolecular RAFT agent and ultimately the block
copolymers.
Acknowledgements
I would like to thank the NSF and AkzoNobel for
funding the REU program, the College of Polymer
Engineering and Polymer Science for providing the
infrastructure that facilitated this program. Also, I
would like to thank my advisor, Dr. Kevin Cavicchi,
my mentor Junyoung Seo for the guidance they
provided for me and the rest of Dr. Cavicchi’s lab for
their unwavering support throughout the whole
program
References
1. John T. Lai,* Debby Filla, and Ronald Shea
Macromolecules 2002, 35, 6754-6756
2. Anil Mahapatro, Ajay Kumar, Bhanu Kalra, and
Richard A. Gross*Macromolecules 2004,37,3540
3. Xia, J.H.; Zhang, X.; Matyjaszewski, K.
Macromolecules 1999, 32, 4482-4484.
4. Bosman, A.W.; Heumann, A.; Klaerner, G.;
Benoit, D.; Frechet, J.M.J.; Hawker,C.J. J. Am.
Chem. Soc. 2001, 123, 6461-6462.
5. Hawker, C.J.; Bosman, A.W.; Harth, E. Chem
Rev 2001, 101, 3661-3688.
6. Hamley. I. W. The Physics of Block Copolymers:
Oxford University Press: NewYork, 1998;
Chapter 5.
7. Loo, Y. L.; Register, R. A.; Ryan, A. J. Phys.
Rev. Lett. 2000, 84, 4120-4134.
8. Loo, Y. L.; Register, R. A.; Ryan, A. J.
Macromolecules 2002, 35, 2365-2374.
9. Xu, J. T.; Turner, S. C.; Fairclough, J. P. A.; Mai,
S. M.; Ryan, A. J.; Chaibundit, C.et al.
Macromolecules 2002, 35, 3614-3621.
10. Xu, J. T.; Fairclough, J. P. A.; Mai, S. M.; Ryan,
A. J.; Chaibundit, Macromolecules 2002, 35,
6937-6945.
11. Ryan, A. J.; Hamley, I. W.; Bras, W.; Bates, F. S.
Macromolecules 1995, 28, 3860-3868.
12. Rangarajan, P.; Register, R. A.; Fetters, L. J.;
Bras, W.; Naylor, S.; Ryan, A. J.Macromolecules
1995, 28, 4932-4938.
13. Nojima, S.; Kato, K.; Yamamoto, S.; Ashida, T.
Macromolecules 1992, 25, 2237-2242.
14. Xu, Jun-Ting; Yuan, Jian-Jun; Cheng, Si-Yuan
European polymer journal 2003, 39, 2091-2098.