Synthesis and Chemical Degradation of Branched Vinyl Polymers Prepared via ATRP:  Use of a Cleavable Disulfide-Based Branching Agent

Abstract

Highly branched poly(2-hydroxypropyl methacrylate) has been prepared by atom transfer radical polymerization (ATRP) in methanol at 20 °C using a disulfide-based dimethacrylate (DSDMA) branching agent. The mean degree of polymerization of the primary chains was fixed at 50; since ATRP has reasonably good living character, the molecular weight distribution of these primary chains is relatively narrow, which allows significantly better control than conventional radical polymerization. Varying the proportion of the DSDMA produced a series of soluble branched polymers, provided that there was on average less than one branching agent per primary chain. However, higher levels of DSDMA lead to macrogelation, as expected. The soluble branched polymers were characterized using triple detector gel permeation chromatography (GPC). The most highly branched copolymers had weight-average molecular weights of up to 540 000, with polydispersities of around 8.0 and Mark−Houwink α parameters as low as 0.21 being obtained. 1H NMR spectroscopy confirmed that very high monomer conversions were obtained (>99%), and the final branched copolymers contained little or no unreacted pendent vinyl groups. The disulfide bond in the DSDMA branching agent was readily cleaved using either dithiothreitol or benzoyl peroxide. GPC studies confirmed the progressive decrease in molecular weight and polydispersity during the chemical degradation of one of the branched copolymers with reaction time. Eventually, the final polydispersity of this degraded branched copolymer was comparable to that of linear poly(2-hydroxypropyl methacrylate) prepared in the absence of any disulfide-based dimethacrylate branching agent. Thus, all the disulfide bonds had been cleaved, reducing the branched copolymer to its near-monodisperse primary chains.

Controlled multi-vinyl monomer homopolymerization through vinyl oligomer combination as a universal approach to hyperbranched architectures

“…To further prove that our proposed strategy leads to such a highly branched structure, a cleavable polymer was designed and prepared via in situ DE-ATRP from a degradable disulphide divinyl monomer (DSDA) 35 . Within the DSDA monomer is a disulphide bond that can be cleaved quickly under reducing conditions, thus allowing us to observe the degradation profile and hence determine if a hyperbranced structure (will be degraded into small units) or a cyclized structure (will 'untie' into a linear chain) is formed.…”

Versatile synthetic approach to reversible crosslinked polystyrene networks via RAFT polymerization

“…[1][2][3][4][5][6][7] There has been great interest in the synthesis of polymers with disulfide linkages using a variety of polymerization methods. 4,[8][9][10][11][12] We have shown with the use of a difunctional reversible addition-fragmentation transfer (RAFT) agent that a,x-telechelic poly(styrene) (PSTY) (with thiol end-groups) 13,14 was synthesized with chains of near uniform length. 15 These chains upon oxidation formed monocyclic structures with one disulfide linkage under dilute conditions or linear multiblocks with many disulfide linkages under concentrated conditions.…”

Synthetic Approaches to Flexible Fluorescent Conjugated Polymers

“…37 Further studies on polymer PPB 3 have revealed the unique ability of the material to undergo self-assembly reorganization into core-shell nanoparticles upon polyanion complexation.…”

“…The disulfide functionality can be cleaved under reducing conditions using tributyl phosphine, [32][33][34] dithiotreitol (DTT), [35][36] or glutathione (GSH). 37 spectra were recorded on a 400 MHz Avance Bruker NMR spectrometer. Chemical shifts were reported in parts per million (ppm) for 1 H NMR on the δ scale based on the middle peak (δ = 2.50 ppm) of the dimethylsulfoxide (DMSO)-d6 solvent as an internal standard.…”

“…Functional, application-specific side-chain modifications include folate-substituted PPEs for the detection of cancer cells, 36 or sugar-substituted PPEs for the sensing of metals, toxins, and sugar-binding proteins. 37 A 2009 review by Bunz provides a more detailed overview of the use of side-chain modifications of PPEs for sensing applications. 38 An unsubstituted or an alkyl-substituted PPE backbone exhibits blue-green fluorescence with a maximum around 430 nm.…”