Mid Sweden University

The main objective of this work was to investigate the ring-opening polymerizations

of cyclic esters by enzyme catalysis and cationic activated monomer polymerization

in the search for new polymer materials and fiber-based composites. Candida

antarcica lipase B was used for end-functionalization of poly(ε-caprolactone) and in

the copolymerization of D,L-lactide and ε-caprolactone. The reactions were

characterized with regard to polymer structure and molecular weight distributions by

NMR, MALDI-TOF MS and GPC.

The copolymerization of D,L-lactide and ε-caprolactone initially leads to a

nonrandom incorporation of lactide. D,L-Lactide is incorporated as the dimer in the

initial stage, when ε-caprolactone is practically excluded from the reaction. During

this stage, the polymerization is slowed by the presence of D,L-lactide as compared to

a neat ε-caprolactone polymerization. After the initial stage, ε-caprolactone and

lactide are polymerized at approximately equal rates.

In cationic activated monomer polymerizations of ε-caprolactone, lactic acid can act

as initiator, catalyst and terminator. Molecular weights distributions and reaction

times are comparable with the corresponding lipase-catalyzed reactions. If more

nucleophilic initiators, e.g. methyl β-D-glucopyranoside, sucrose or raffinose, are

present in the reaction mixture, lactic acid catalyzes the reaction without participating

in the initiation. The regioselectivity of the acylation is well agreement with the

corresponding lipase catalyzed reaction.

Both methods have several advantages: the catalysts can be handled without need

for extraordinary precautions with regard to atmosphere, humidity or equipment. The

polymerizations are performed under mild reaction conditions, with non-toxic

catalysts that can be recycled, and show the possibility of controlling end-group

functionalization with high precision.