Synthesis and properties of long-chain branched poly(L-lactide)s by self-polycondensation of AB2 macromonomers

Long-chain branched poly(L-lactide)s (LCB-PLLAn) were successfully synthesized by self-polycondensation of AB(2) macromonomers. The control of the lactide segment length allows to investigate the effect of branching density on the crystallization and rheological behaviors of the polymers. For the polymer LCB-PLLA200, which has a degree of polymerization of lactide segments (DP) of 176, crystallization occurs rapidly under non-isothermal and isothermal conditions favored by the slow diffusion resulting from the long-chain branching. On the other hand, LCB-PLLA50 having a DP of 51 shows a noticeably low melting point caused by its densely branched structure. LCB-PLLA200 exhibits high complex viscosity in lower frequency region and high zero shear viscosity, which reflects the strong intermolecular entanglement, whereas the viscosities of the densely branched polymers are low, similar to those of typical hyperbranched polymers. This systematical study from hyperbranched to long-chain branched structures gives a new insight into the effect of branching density on the properties of polymers.