Combining Atom Transfer Radical Polymerization and Disulfide/Thiol Redox Chemistry:  A Route to Well-Defined (Bio)degradable Polymeric Materials

Abstract

Linear well-defined degradable polymethacrylates with internal disulfide link were prepared by atom transfer radical polymerization (ATRP) of methyl, tert-butyl, and benzyl methacrylate using bis [2-(2-bromoisobutyryloxy)ethyl] disulfide as the initiator and CuBr/2,2′-bipyridine as the catalyst at 50 °C. The disulfide bond was cleaved to thiol by reduction with tributylphosphine, yielding polymers of half the molecular weight of the starting materials. Degradable gels were prepared by the copolymerization of methyl methacrylate and a disulfide-containing difunctional methacrylate, bis(2-methacryloyloxyethyl) disulfide, using similar reaction conditions. The produced gels were reduced with tributylphosphine to form soluble, low molecular weight linear poly(methyl methacrylate) fragments containing thiol groups at the chain end and along the backbone, originating from the disulfide difunctional initiator and monomer, respectively. The disulfide-cross-linked gels were further used as "supermacroinitiators" for the bulk ATRP of styrene at 90 °C, employing CuBr/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine as the catalyst. The length of the polystyrene pendant chains could be controlled by varying the reaction time. The prepared gels with segmented structure swelled more than the starting polymethacrylate gels in both THF and toluene. Degradation experiments confirmed the high degree of chain-end bromine functionalization of the "supermacroinitiators".

Synthesis of Photocleavable Linear Macromonomers by ATRP and Star Macromonomers by a Tandem ATRP−Click Reaction: Precursors to Photodegradable Model Networks

“…[21][22][23][24][25][26] In addition, ATRP has been used for the preparation of a number of photoactive polymers and degradable materials. 8,[27][28][29][30] We recently reported the synthesis of ozonizable MNs comprised of an ozonizable azido-poly(tert-butyl acrylate) (ptBA) MAC cross-linked with tri-and tetrafunctional small molecule alkynes. 25 This study showed that degradation of the MNs occurred primarily at the olefin moieties located at the center of the MACs and that the major degradation products were three-and four-arm star polymers depending on which cross-linker was used (tri-or tetrafunctional alkyne, respectively).…”

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.…”

“…10,23,24 Therefore, crosslinking is dependent upon the radical addition across the double bonds of the bifunctional monomer attached to the polymer backbone. This produced networks that are stochastic and, but more importantly, can be reduced back to soluble linear polymer chains.…”

Synthetic Approaches to Flexible Fluorescent Conjugated Polymers

“…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.…”

“…Water-soluble CPs bearing multiple ionic functional groups are described as conjugated polymer electrolytes (CPEs). 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.…”