**ADVANCES IN POLYESTER SYNTHESIS USING**

**LIPASE-CATALYSIS**

[Richard A Gross]{.underline}

NSF I/UCRC for Biocatalysis and Bioprocessing of Macromolecules,
Department of Chemistry and Biological Sciences and Engineering,
Polytechnic University, Six Metrotech Center, Brooklyn, 11201

This lecture will focus on recent advances by our laboratory using
*in-vitro* lipase-catalysis for lactone ring-opening and condensation
polymerizations. Studies of the kinetics and mechanism of *Candida
antartica* Lipase B (CALB) catalyzed ε-caprolactone (ε-CL)
polymerizations were performed. The kinetic plot of
Ln(\[M\]~0~/\[M\]~t~) versus time is linear (*r*^2^ = 0.998) indicating
that termination did not occur and the propagation rate is first order
with respect to monomer concentration.

Lipases can polymerize macrolactones that are otherwise difficult to
polymerize by conventional catalysts. In fact, with immobilized CALB as
catalyst, poly(PDL) with M~n~ up to 90 000 and \>97% monomer conversion
was obtained within 20 minutes. Poly(PDL) has hydrolyzable ester units
as well as a T~m~, T~g~, and %-crystallinity of 97^o^C, -27^o^C, and
60%, respectively. Poly(PDL) forms hard-tough materials that elongate
from 100 to 200%. Hence, poly(PDL) and its copolymers are a new set of
materials made available by lipase-catalysis.

The ability to substitute water with other initiators has allowed for
the preparation of polyesters with various end-groups. Regioselective
initiation of lactone-ring opening by carbohydrates was found to be a
simple way to conjugate carbohydrates at the terminus of polyesters.

Soluble polymers from reduced sugars were synthesized with absolute
molecular weights up to 117 000 (*M*~w~), without chemical activation of
the monomer acid groups or the addition of an organic solvent. Although
highly polar reactants were used, they formed a monophasic liquid medium
when gently mixed and heated without addition of a polar aprotic
solvent. The lipase-catalyst (Lipase B from *Candida antartica*
immobilized on Lewatit beads) suspended in the monophasic liquid was
selective and highly active. Polyesters rich in hydroxyl functionality,
such as poly(sorbityladipate), were prepared without the need to use
protection-deprotection chemistry. While the lipase was highly selective
for sorbitol polymerizations, it was promiscuous for glycerol
copolymerizations. This promiscuity led to
poly(1,8-octanoyladipate-co-glyceroladipate) chains that are rich in
mono-substituted glycerol terminated branches. Thermal analysis of the
sorbitol and glycerol copolymers revealed they are semi-crystalline, low
melting, soft materials. The lipase-catalyzed polyol condensation
synthetic strategy is anticipated to be broadly applicable to many
natural and synthetic polyols.

Mahapatro, A., Kumar, A., Kalra., B and Gross. R. A.;
***Biomacromolecules***, Vol 4, No. 3, 544-551, (2003); Focarete, M. L.;
Gazzano, M.; Scandola, M.; Kumar, A.; Gross, R. A.;
***Macromolecules**;* **2002**; *35*(21); 8066-8071. Y. Mei, A. Kumar,
and Richard A. Gross, ***Macromolecules***, 35, 5444-5448, 2002. R.
Kumar and R.A. Gross, **J. Am. Chem. Soc**., 124(9) (2002). R. A. Gross,
A Kumar, B Kalra, *Chemical Reviews*, 101(7), 2097-2124 (2001). A Kumar,
R.A Gross, *J. Am. Chem. Soc.* 122,11767-11770 (2000). A Kumar, B Kalra,
A Dekhterman, R. A. Gross, *Macromolecules*, 33, 6303-6309 (2000).