Semi-interpenetration of Poly(ethylene glycol) into Poly(L-lactic acid) network

Abstract

Radical crosslinking of methacrylate-endcapped PLLA (PLLA-Meth) with PEG dispersed in the crosslinked PLLA network was carried out in order to prepare hydrophilic PLLA/PEG semi-interpenetrating network (semi-IPN). PLLA was first prepared by direct condensation polymerization from L-lactic acid. The number average molecular weight of PLLA was around 3,000-5,000 Da. PLLA with one or two methacrylate end groups were prepared by reacting PLLA or PLLA-diol chain with methacrylic anhydride. The degree of substitution of methacrylate on PLLA as determined by 1H NMR was over 90% when 40 equivalents (relative to PLLA chains) of methacrylate was added in the reaction. The gel content of thermal cure using benzoyl peroxide as an initiator was 62% while no crosslinking occurred by 2-hydroxy-2-methylpropiophenone initiator induced by UV. The PLLA/PEG semi-IPN was carried out by heating the PLLA-Meth mixed with PEG (Mw = 20,000 Da) at 150 °C in the presence of 10% of benzoyl peroxide. Water uptake of the prepared PLLA/PEG semi-IPN was as high as 9% for the composite having 40% (by weight) of PEG.