Synthesis and properties of multicleavable amphiphilic dendritic comblike and toothbrushlike copolymers comprising alternating PEG and PCL grafts

摘要

Facile construction of novel functional dendritic copolymers by combination of self-condensing vinyl polymerization, sequence-controlled copolymerization and RAFT process was presented. RAFT copolymerization of a disulfide-linked polymerizable RAFT agent and equimolar feed ratio of styrenic and maleimidic macromonomers afforded multicleavable A_mB_n dendritic comblike copolymers with alternating PEG (A) and PCL (B) grafts, and a subsequent chain extension polymerization of styrene, tert-butyl acrylate, methyl methacrylate, and N-isopropylacrylamide gave A_mB _nC_o dendritic toothbrushlike copolymers. (PEG) _m(PCL)_n copolymers obtained were of adjustable molecular weight, relatively low polydispersity (PDI = 1.10-1.32), variable CTA functionality (f_(CTA) = 4.3-7.5), and similar segment numbers of PEG and PCL grafts, evident from ~1H NMR and GPC-MALLS analyses. Their branched architecture was confirmed by (a) reduction-triggered degradation, (b) decreased intrinsic viscosities and Mark-Houwink-Sakurada exponent than their "linear" analogue, and (c) lowered glass transition and melting temperatures and broadened melting range as compared with normal A _mB_n comblike copolymer. In vitro drug release results revealed that the drug release kinetics of the disulfide-linked A _mB_n copolymer aggregates was significantly affected by macromolecular architecture, end group and reductive stimulus. These stimuli-responsive and biodegradable dendritic copolymer aggregates had a great potential as controlled delivery vehicles.