Libraries of Statistical Hydroxypropyl Acrylate Containing Copolymers with LCST Properties Prepared by NMP

The nitroxide-mediated copolymerization of 2-hydroxypropyl acrylate (HPA) with N -acryloylmorpholine (Amor) or N,N - dimethylacrylamide (DMA) was investigated using N - tert -butyl- N -(1′-diethylphosphono-2,2′-dimethylpropyl)- O -(2-carboxyl-prop-2-yl) (BlocBuilder) alkoxyamine initiator and additional free nitroxide (SG-1). Different reaction conditions, such as the concentration of additional SG-1, were tested to optimize the homopolymerizations using a Chemspeed ASW2000 automated parallel synthesizer. Best control for the homopolymerizations (polydispersity indices of 1.2−1.3) of all three monomers was achieved using 20% additional SG-1 (relative to the initiator) at a reaction temperature of 110 °C for 2 M solutions in N,N -dimethylformamide and a monomer/initiator ratio of 100/1. Libraries of P(Amor- stat -HPA) and P(DMA- stat -HPA) were synthesized with 0−100 mol % HPA with 10 mol % increments using the optimized conditions obtained for the homopolymerizations. The resulting polymers had narrow molecular weight distributions, and their compositions, determined using 1 H NMR spectroscopy and elemental analysis, were close to the theoretical compositions. In addition, all copolymers of both libraries had single glass transition temperatures ( T g ), and the transition temperatures decreased from the T g of P(Amor) (147 °C) and P(DMA) (111 °C) to the T g of P(HPA) (22 °C) with increasing HPA content. The cloud point of P(HPA) showed concentration dependence as well as a concentration dependent hysteresis. The cloud points of aqueous solutions of the copolymer libraries could be tuned from 21.4 to 88.0 °C and to 82.9 °C for P(Amor- stat -HPA) and P(DMA- stat -HPA), respectively, at a concentration of 1 wt %. LCST behavior was observed for copolymers with >40 wt % HPA in P(Amor- stat -HPA) and >55 wt % HPA in the P(DMA- stat -HPA) library.