(CO)POLYMERS OF L-LACTIDE .2. MECHANICAL-PROPERTIES

The effect of copolymerization of L-lactide with several lactones and cyclic carbonates and the processing variables in compression moulding of poly(L-lactide) homopolymers on the mechanical properties was inve stigated. Sharp maxima in the impact strength versus comonomer composi tion and heat of fusion were obtained, reflecting the important role o f the presence of a crystalline fraction in the material. Crystalline domains increase the interconnectivity of a physical polylactide netwo rk and decrease the molecular weight between these physical crosslinks . The brittle strength concomitantly increases, and as the yield stres s remains more or less constant, an increase in impact strength is obs erved. Very high crystalline as-polymerized poly(L-lactide) prepared w ith less active catalysts on the other hand has an extremely low entan glement density and therefore a low brittle tensile strength.