CROSS-LINKED POLY(L-LACTIDE) AND POLY(EPSILON-CAPROLACTONE)

Several methods of introducing crosslinks into poly(L-lactide) (PLLA) were studied. Electron beam irradiation was not effective in crosslink ing PLLA, and, moreover, caused severe polymer degradation and embritt lement of the material. Peroxide crosslinking of PLLA with dicumyl per oxide (DCP), however, resulted in gelation. At high peroxide concentra tions (13-25 wt%) and high curing temperatures (192 degrees C), a gel fraction equal to 1 could be determined gravimetrically. Peroxide cros slinking with DCP caused chemical modification of the PLLA polymer cha in, with the decomposition products having a plasticizing effect on th e resulting network. For the in situ crosslinking, a tetrafunctional m onomer, 5,5'-bis(oxepane-2-one) (5,5'-BO), was synthesized and used in the copolymerization with epsilon-caprolactone and L-lactide. Differe ntial scanning calorimetry (d.s.c.) and swelling experiments showed th at network formation did take place. A pronounced difference in reacti vity between the L-lactide and the 5,5'-BO crosslinker was observed, w ith this difference in reactivity being found to be comparable to the difference between L-lactide and epsilon-caprolactone. Swelling experi ments carried out with crosslinked PLLA showed that incorporation of t his crosslinker into the polymer network increased at higher polymeriz ation temperatures and longer polymerization times. When 1 mol% of cro sslinker was used in the copolymerization with L-lactide, a significan t increase in the impact and tensile strength was obtained when compar ed to uncrosslinked PLLA. Copyright (C) 1996 Elsevier Science Ltd.