Читать книгу Poly(lactic acid) - Группа авторов - Страница 96

Hybrid copolymers constituted by short L‐phenylalanine (Phe) _n blocks (n ranging from 2 to 25) and LLA blocks of different length have been synthesized by ROP of LA using a Phe‐oligopeptide as macroinitiator. A variable morphology from lozenge, flower‐like, fibrillar structures, spheres, ringed spherulites, dendritic, microfibers, to braid‐like microstructures was observed due to self‐assembly of Phe‐oligopeptides in the copolymer [131].

Recently amino‐acid‐based morpholine‐2,5‐diones (MD copolymerized with lactide using DBU : thiourea (TU) catalyst : co‐catalyst system to form an interesting class of bio‐based degradable polymers with low dispersity (8.1–25.2 kDa and Đ = 1.13−1.18) in short periods (5–10 min.) [132]. Ring‐strain in monomer was found to affect the rate of homo‐ vs hetero‐propagation of monomer units and dictated the nature and richness of units in the polymer backbone. As noticed, LLA exhibited a higher ring‐strain compared with 3S,6S‐dimethylmorpholine‐2,5‐dione (DMMD) monomer and thus LLA rapidly homopropagated at a higher rate, resulted in the formation of longer LLA block. This provided a platform for the selective incorporation of α‐amino acids along a hydrolyzable polymer backbone, mimicking peptide that holds significant potential in biological applications. On the contrary, reverse behavior was observed in case of DMMD as it favored heteropropagation with LLA units [133]. In another work comparing “grafting to” versus “grafting from” strategies, the former appeared to be more successful at covalently linking the peptide to thiol functionalized PLA using thiol‐ene click chemistry mediated by AIBN initiator [134]. Core‐shell molecular bottlebrushes with a wormlike conformation related to the retention of the α‐helical conformation of poly(L‐glutamate) backbone obtained as side chains through the “grafting to” strategy on PLA‐b‐PEG copolymer was obtained using azide‐alkyne cyclo‐addition reaction [135]. Degradable poly[LA‐b‐(N‐ɛ‐carbobenzyloxy‐L‐lysine)] copolymers were obtained using LLA macroinitiators and led to controlled polymerizations with low dispersity [136]. Star‐PLA bearing triethoxysilyl propyl groups and bifunctional silylated peptides found to react via sol‐gel process to form cross‐linked networks [117].