Synthesis of degradable linear and bottlebrush polymer through atom transfer radical ring-opening polymerization of thionolactone

Q.U. Nisa, N.M. Bingham, P.J. Roth
University of surrey,
United Kingdom

Keywords: thionolactone, rROP, ATRP, dethionation, degradable polymers, bottle brush polymers


Vinyl polymers are common and useful materials but, because of their carbon–carbon backbones, they are not degradable. This poster will present adding degradable thioester linkages into vinyl polymers with concurrent control of the polymer architecture. This was achieved by optimising the atom transfer radical copolymerization (ATRP) of the thionolactone dibenzo[c,e]oxepin-5(7H)-thione (DOT) with acrylic comonomers. The radical copolymerization of DOT follows a mechanism termed thiocarbonyl addition–ring-opening (TARO) and leads to the incorporation of easily cleavable thioester backbone functionality. Cu(I)Br and tris[2-(dimethylamino)ethyl]amine (Me6TREN) were used as catalyst and ligand, respectively. During the initial studies, it was observed that the polymerizations were impeded by a side reaction, the Cu(I)-catalysed dethionation of DOT to give large quantities of a non-polymerizable lactone which limited the final copolymer DOT content. Through a series of optimization experiments, traditional ATRP methods were found to minimize this side reaction when performed under anhydrous conditions. These conditions led to the successful preparation of degradable acrylate-based copolymers with higher DOT content. Subsequently, the architectural control of ATRP was leveraged through the synthesis of a water-soluble bottle-brush polymer containing poly(ethylene glycol) methyl ether acrylate (PEGA) side-chains. Due to the faster copolymerization of DOT compared to PEGA, the thioester units in the arms were localized near to the bottle-brush backbone and permitted selective cleavage under oxidative conditions, presenting opportunities for smart drug delivery systems. Expanding the scope of the ATRP and TARO methods, this work presents facile access to polymer materials with tailored architectures and degradability.