Synthesis And Responsive Behavior Of Amphiphilic Azobenzene Functionalized Block Copolymers

Amphiphilic block copolymers were applied in a wide range of fields, such as, formation of micelles in selective solvents, used as emulsifier, suspension polymerization stabilizer, crystallization modifer, etc. Block copolymers could be prepared by means of"living"/controlled polymerization and adding monomers to reaction system in order. Branched polymers have unique structure. There was less entanglement between molecular chains. Thus branched polymers showed novel performances: good solubility, low melting point and solution viscosity, and lower mechanical properties. In addition, they have many chain end functional groups. Therefore, it was considered to have high end-group reactivity. If the end groups of branched polymers were modified by functional groups, it would greatly enrich the types and applications of functional polymer materials. In this paper, we synthesized two kinds of amphiphilic block copolymers by two methods: one is the combination of electron transfer atom transfer radical polymerization (AGET ATRP) and self-condensing vinyl polymerization (SCVP) techniques with 2-(2-bromoisobutyryloxy) ethyl methacrylate (BIEM) as the inimer (initiator-monomer), another is the reversible addition-fragmentation chain transfer (RAFT) polymerization with 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) as the RAFT agent. Their properties were studied and discussed at the same time. Specific work was summarized as follows:(1) We reported the synthesis of branched poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) via a combination of AGET ATRP and SCVP techniques. The typical linear kinetics of the AGET ATRP of DMAEMA with the initiation of 2-(2-bromoisobutyryloxy) ethyl methacrylate (BIEM) was observed. The molecular weights (Mn) of the branched PDMAEMA increased with the monomer conversion. The GPC traces of these polymers were unimodal and the molecular weight distributions (Mw/Mn) were in the range of 1.30-2.10. The degree of branching (DB) determined by 1H NMR agreed well with theoretical values. The amphiphilic azobenzene functionalized star-type copolymer was then prepared via AGET ATRP chain-extnesion of branched PDMAEMA with azobenzene monomer, 6-[4-(4-methoxyphenylazo) phenoxy]hexyl(meth)acrylate (AzoMMA) as the second monomer. The GPC traces of these star-type copolymers showed the mono-peaks, which proved the successful preparation of copolymers. The properties of this star-type copolymer in controlling of drug release were also investigated. It was found that the drug release rate of chlorambucil can be controlled by various factors, such as polymer structure, light, temperature and pH values.(2) The well-defined triple stimuli sensitive block copolymer poly(2-(dimethylamino) ethyl methacrylate)-b-poly(6-[4-(4- methoxy phenylazo) phenoxy]hexyl methacrylate)-b-poly(2-hydroxyethyl methacrylate) (PDMAEMA-b-PAzoMMA-b-PHEMA) was successfully prepared via RAFT polymerization with 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) as the RAFT agent. The lower critical solution temperature (LCST) increased with the decrease of pH values. The photoisomerization behavior, surface tension and fluorescence intensities changed under different external conditions (temperature, light and pH). Their self-assembly behavior were investigated under different temperature, light and pH conditions by the combination of dynamic light scattering (DLS) and transmission electron microscope (TEM). It was found that a definite link does exist between fluorescence emission intensities and self-assemble of polymers in aqueous solution.