Preparation of polymer single chain nanoparticles using intramolecular photodimerization of coumarin

We present a new and easy method for preparing polymer single chain nanoparticles (SCNPs). It uses the photodimerization of coumarin groups located on the same chain to obtain the intrachain cross-linking required for chain collapse in solution. To demonstrate the approach, samples of a random copolymer composed of N, N-dimethylaminoethyl methacrylate (DMAEMA) and 4-methyl-[7-(methacryloyl) oxy-ethyl-oxy]coumarin (CMA), with 7 or 13 mol% of CMA, were synthesized via the reversible addition-fragmentation chain transfer (RAFT) polymerization. We show that well-defined SCNPs could be obtained by the intrachain photodimerization of coumarin groups upon lambda > 310 nm UV irradiation in a dilute copolymer solution. The coil-to-globule transition induced by intrachain photo-cross-linking was investigated by means of H-1 NMR spinspin relaxation time (T-2). The result indicates that the photoinduced chain collapse is accompanied by a sharp increase of the fraction of chain segments having reduced mobility. SCNPs were further used as a nanoreactor to synthesize gold nanoparticles (AuNPs) in situ. In tetrahydrofuran, the rate of AuNP formation was found to be dependent on the polymer chain conformation and mobility determined by the dimerization degree of coumarin. This provides a means to optically control the kinetics of AuNP formation.