Well-Defined Poly(γ-benzyl-L-glutamate)-g-Polytetrahydrofuran: Synthesis, Characterization, and Properties

The synthesis of well-defined graft copolymers of poly(gamma-benzyl-L-glutamate)-g- polytetrahydrofuran, PBLG-g-PTHF, has been achieved via controlled termination of living PTHF branch chains with -NH- functional groups along PBLG macromolecular backbone. The PBLG backbone with different molecular weights (M-n = 2000-45000 g.mol(-1)) were prepared by anionic ring-opening polymerization of gamma-benzyl-L-glutamate N-carboxyanhydrade (BLG-NCA). Living PTHF chains with predictable chain length (M-n = 720-7000 g.mol(-1)) were prepared by living cationic ring-opening polymerization of THF with methyl triflate (MeOTf) as an initiator. The grafting efficiency (G(E)) of living PTHF chains onto PBLG backbone via controlled termination reached to near 100%. The grafting density (G(D)) along PBLG backbone and average number of PTHF branches (N-b,N-PTHF) in PBLG-g-PTHF graft copolymers could be mediated by changing the molar ratio of living PTHF chains to -NH-functional groups. Circular dichroism (CD) and FTIR spectra show that some of the graft copolymers maintain alpha-helical structure from PBLG, and the strength of CD signals for a-helical structure of the graft copolymers also decreased with increasing G(D). The crystallization degree and spherulitic growth rate of the PBLG-g-PTHF graft copolymers decreased with increasing G(D). The obvious phase separation and reticular state of aggregation morphology in PBLG-g-PTHF graft copolymers could be observed. PBLG-g-PTHF graft copolymers have no cytotoxicity and even conducive for cell survival. These graft copolymers had extremely low bibulous rate, and all the water absorption ratios were kept around 1.02 to maintain the shape and dimensional stability.