MELT BLOCK COPOLYMERIZATION OF EPSILON-CAPROLACTONE AND L-LACTIDE

AB block copolymers of epsilon-caprolactone and (L)-lactide could be p repared by ring-opening polymerization in the melt at 110 degrees C us ing stannous octoate as a catalyst and ethanol as an initiator provide d epsilon-caprolactone was polymerized first. Ethanol initiated the po lymerization of epsilon-caprolactone producing a polymer with epsilon- caprolactone derived hydroxyl end groups which after addition of L-lac tide in the second step of the polymerization initiated the ring-openi ng copolymerization of L-lactide. The number-average molecular weights of the poly(epsilon-caprolactone) blocks varied from 1.5 to 5.2 X 10( 3), while those of the poly(L-lactide) blocks ranged from 17.4 to 49.7 X 10(3). The polydispersities of the block copolymers varied from 1.1 6 to 1.27. The number-average molecular weights of the polymers were c ontrolled by the monomer/hydroxyl group ratio, and were independent on the monomer/stannous octoate ratio within the range of experimental c onditions studied. When L-lactide was polymerized first, followed by c opolymerization of epsilon-caprolactone, random copolymers were obtain ed. The formation of random copolymers was attributed to the occurrenc e of transesterification reactions. These side reactions were caused b y the epsilon-caprolactone derived hydroxyl end groups generated durin g the copolymerization of epsilon-caprolactone with prepolymers of L-l actide. The polymerization proceeds through an eater alcoholysis react ion mechanism, in which the stannous octoate activated eater groups of the monomers react with hydroxyl groups. (C) 1997 John Wiley & Sons, Inc.