Synthesis And Micellization Of Amphiphilic Graft Copolymer With Poly(Dimethylsiloxane) Side Chains

Well-architectured poly(dimethylsiloxane)(PDMS)-containing block or graft copolymers have received widespread attention in recent years. However, most of the studies were limited to the synthesis of amphiphilic PDMS-containing block copolymers. Not much investigation has been taken on the synthesis and characterization of amphiphilic graft copolymers with a hydrophilic backbone and polysiloxane side-chains. The structures with a hydrophilic backbone and hydrophobic side-chains can form reversible hydrogels above a critical concentration and may find use as associative thickeners. Meanwhile, because the self-assembly of amphiphilic polymeric architectures with (meth)acrylic acid segments has feasibility to generate nanostructured materials and numerous potential applications in separation technology, controlled drug delivery and release, the reversible addition-fragmentation chain transfer (RAFT) radical (co)polymerizations of methacryloyl-terminated PDMS (PDMS-MA) with tert-butyl methacrylate (tBuMA) were carried out in this work. The self-assembly behavior of the resultant amphiphilic copolymers in mixed solvents was also investigated. And the main results were shown as follows:(1) Controlled homopolymerization of tBuMA with high conversion was achieved via RAFT radical polymerization in ethyl acetate.In this paper, the RAFT radical polymerizations of tBuMA were carried out in ethyl acetate (EAc) at 70 oC using AIBN as the initiator and 2-cyanoprop-2-yl dithiobenzoate (CPDB) as the RAFT reagent. Narrow molecular weight distribution (MWD) poly(tert-butyl methacrylate)(PtBuMA) was obtained. The GPC results indicated the controlled /"living"polymerization mediated by CPDB.(2) RAFT radical homopolymerization of PDMS-MA was achieved in this work.The RAFT homopolymerization of PDMS-MA in EAc with CPDB as the RAFT reagent was achieved in this work. Two independent techniques, GPC(THF) and 1H-NMR method, were employed to evaluate the conversion of homopolymerization of PDMS-MA. The results showed that the average molecular weights of homopolymers increased with the increasing of monomer conversions, and the polydispersities of polymers remained low over the RAFT process, which indicating the controlled/"living"polymerization of macromonomers.(3) Graft copolymers of PDMS-MA and tBuMA were synthesized via RAFT radical copolymerization in EAc.①Random copolymerizations of PDMS-MA and tBuMA were carried out in EAc at 70℃using AIBN as the initiator and CPDB as the RAFT reagent. The obtained copolymers were charactered by the methods of 1H-NMR and GPC. By using the Jaacks method to estimate the reactivity ratio tBuMA, a value of rtBuMA about 0.96 was obtained, which indicating the PtBuMA-g-PDMS graft copolymers with homogeneous branch spacing.②Narrow MWD PtBuMA-g-PDMS graft copolymers with gradient or blockly spacing were successfully synthesized via the RAFT block copolymers of PDMS-MA with tBuMA using AIBN as the initiator and CPDB as the RAFT reagent. The obtained PtBuMA-g-PDMS graft copolymers with different branch spacing are reported firstly.(4) The relationship between glass transition behavior and the molecular structure of PtBuMA-g-PDMS graft copolymers was discovered.In this work, the glass transition of PtBuMA-g-PDMS graft copolymers with homogeneous, gradient or blocky branch spacing were investigated by the method of DSC analysis, and the molecular sructure of the PtBuMA-g-PDMS graft copolymers were discerned. It was found that the arrangement of monomer units in copolymer chains and the length of PtBuMA moieties had important effects on the thermal behavior of PtBuMA-g-PDMS graft copolymers.(5) Amphiphilic graft copolymers with PMAA backbone and PDMS side chains (PMAA-g-PDMS) were obtained by the hydrolysis of PtBuMA-g-PDMS, and the self-assembly behavior of PMAA-g-PDMS in solution was investigated in this work.The hydrolysis of PtBuMA-g-PDMS were carried out in dry dichloromethane at room tempeture using NaI/ ((TMS)Cl) method. The molecular structures of PMAA-g-PDMS graft copolymers were also conformed by 1H-NMR, FT-IR and GPC measurements. It was found that the PMAA-g-PDMS graft copolymers could form various morphologies (sphere, large compound micelles (LCMs) and pear-necklace etc) in acetone/water by adjusting the concentration, water content and staying time. The mechanism of morphological transition with the preparation parameters was also proposed accordingly.