Synthesis of End-functionalized Polyesters byRing-Opening Polymerization of ε-Caprolactone

Sammanfattning: 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.