Synthesis and Properties of Multicleavable Amphiphilic Dendritic Comblike and Toothbrushlike Copolymers Comprising Alternating PEG and PCL Grafts

Abstract

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 m B 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 m B n C 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 1 H 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 m B n comblike copolymer. In vitro drug release results revealed that the drug release kinetics of the disulfide-linked A m B 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.

Synthesis of multifunctional ABC stars with a reduction-labile arm by consecutive ROP, RAFT and ATRP processes

“…Star copolymers and their precursors were characterized by 1 H nuclear magnetic resonance ( 1 H NMR) and gel permeation chromatography (GPC), and the reduction-triggered topological transformation was preliminarily investigated. The success of this study further paves a versatile way to generate reduction-labile ABC stars with rich chemical compositions and adjustable macromolecular parameters, and the resultant stars may have a great potential in multi-stimuli responsive smart materials towards biomedical applications [40][41][42][43][44][45][46].…”

“…As well-documented, the disulfide linkage can be efficiently cleaved in the presence of reducing agents such as Bu 3 P and glutathione, which has been widely used to enhance the functions and multipurpose applications [40][41][42][43][44][45][46]. In this study, PCL-PNIPAM-PtBA star was chosen as a model sample to understand the degree of cleavage since the cleaved PNIPAM (hydrophilic) and PCL-b-PtBA (hydrophobic) had quite different solubility.…”

Recent developments in the synthesis of sequence controlled polymers

“…There is no universal mechanism for synthesis of alternating copolymers by chain growth polymerization, but most successful routes usually rely on large difference in monomer reactivity ratios. For example, monomer pairs such as styrene and maleic anhydride [41], styrene and maleimide [42][43][44][45], styrene and pentafluorostyrene [46], styrene and methacrylates [47], epoxide/aziridine and CO [48], epoxides and CO 2 [49], as well as epoxides and anhydrides [50], were copolymerized through various reaction mechanisms to make alternating copolymers.…”

Fluorescence Studies on Self-association of Biodegradable Pyrene-labeled Poly(L-lysine) Grafted with Poly(caprolactone)

“…Among the variety of known biodegradable polymers, aliphatic polyesters such as poly(ε-caprolactone) (PCL) have been widely used as the hydrophobic segment of the amphiphilic copolymers because of controlled degradability, excellent biocompatibility, and flexible mechanical properties [17,18]. One procedure for the production of well-controlled PCL is the ring-opening polymerization (ROP) of cyclic ε-caprolactone (ε-CL) monomer in the presence of catalysts such as stannous octanoate [19].…”