Synthesis and photoresponsive behaviors of well-defined azobenzene-containing polymers via RAFT polymerization

The well-defined photoresponsive polymethacrylate containing azo chromophore, poly{1'-octyloxy-4'-(6-methacryloxy)hexyloxy-5'-phenylmethaneone-(2-phenyl)azobenzene (AHMA)} (PAHMA), was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization in anisole solution using 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) as the RAFT agent and 2,2'-azobis(isobutyronitrile) (AIBN) as an initiator. The kinetic plots of polymerization were first-order and the molecular weights (M(n(GPC))s) of the homopolymer (PAHMA) with relatively low polydispersity index values (PDIs <= 1.37) increased with monomer conversions throughout the polymerization processes. Furthermore, the kinetic plots of chain extension with both methyl methacrylate (MMA) and styrene (St) using the obtained PAHMA as a macro-RAFT agent were also first-order. The M(n(GPC))s of the diblock copolymers, PAHMA-b-PMMA and PAHMA-b-PS, increased with the respective monomer conversions. These results indicated that most of the PAHMA chains were still "living". The structure and properties of the polymers were characterized by H-1 NMR, GPC, and UV-vis spectra. The photoisomerization of the polymer was examined. On irradiation with a linearly polarized Kr+ laser beam, the birefringence was induced in the polymer films to the level of 0.075. With illumination of linearly polarized Kr+ laser beam at modest intensities (120 mW/cm(2)), significant surface relief gratings (SRGs) formed on the polymer films were observed.