Fluorescent, Thermoresponsive Oligo(ethylene glycol) Methacrylate- based Copolymers via Nitroxide Mediated Controlled Radical Polymerization

Poly[oligo(ethylene glycol) methacrylate] (OEGMAs), are known to be non-toxic, biocompatible and thermo-responsive when dissolved in water, exhibiting a lower critical solution temperature (LCST). Consequently, OEGMA based materials have found application in next-generation drug delivery and bio-sensing applications. LCST tuning of POEGMAs is readily done by changing the length of the oligo(ethylene glycol) segment in the side chain or by copolymerizing OEGMAs of varying EG lengths.1 We applied controlled radical copolymerization of OEGMAs with functional comonomers to allow not only LCST tuning but incorporation of a hole-transporting functionality, which is suitable as a fluorescent tag. Nitroxide mediated polymerization (NMP) using an alkoxyamine initiator (BlocBuilderTM) and 9-(4-vinylbenzyl)-9H-carbazole (VBK) as a comonomer, resulted in a controlled copolymerization, exhibited by a linear increase in number average molecular weight (Mn) versus conversion (X < 0.6) and resulting in final copolymers with relatively narrow molecular weight distributions (Mw/Mn = 1.3-1.6). By modifying the copolymer composition, a tunable LCST library (81 °C < LCST < 31°C) for the poly(OEGMAs-ran-VBK) was obtained. The poly(OEGMAs-ran-VBK) were then used as macroinitiators for the polymerization of a second poly(OEGMAs-ran-VBK) segment with a different composition, resulting in block copolymers exhibiting two tunable and distinct LCSTs. VBK served not only as a controlling comonomer for the synthesis of poly(DMAEMA) and poly(OEGMAs), but also as a fluorescent tag, demonstrating that NMP can be used to synthesise fluorescent, thermo-responsive “smart” materials with controlled microstructures.