Synthesis Of Vinyl Chloride Block Copolymers And Surface Characteristics Of Their Membranes

Research development of reversible deactivation radical polymerizations of vinyl chloride(VC)and other monomers provides basis for preparation of living poly(vinyl chloride)(PVC)and block copolymers containing PVC and other segment with different characteristics.Till now,synthesis of living PVC and PVC block copolymers by single electron transfer-degradation chain transfer radical polymerization using iodoform as an initiator was reported by several research groups,while synthesis of living PVC and PVC block copolymers by iodine transfer polymerization was seldom reported.In this paper,iodine transfer miniemulsion polymerization method was applied to prepare PVC-polyacrylate block copolymers.The kinetics of stearyl acrylate(SA)homopolymerizations and fluoroacrylate-stearyl acrylate(FA-SA)copolymerizations,and strucutrue of block copolymers were investigated.The morphological and surface(interface)characteristics of membranes prepared from block copolymers containing PVC and superhydrophobic or hydrophilic polymer segments by spin coating and breath figure method were studied.Firstly,poly(stearyl acrylate)(PSA)and fluoroacrylate-stearyl acrylate(FA-SA)random copolymers were prepared by iodine transfer miniemulsion polymerization,using iodoform as a chain transfer agent,2,2’-azobis(2-methylpropionamidine)dihydrochloride(AIBA)as an initiator,and hexadecyl trimethyl ammonium bromide/hexadecane as main/co-emulsifier.The kinetics of polymerization and the structure of the copolymer were characterized.The results showed that both SA homopolymerizartion and FA-SA copolymerization exhibited good controllability and showed first-order kinetics.The FA/SA mass ratio has little effect on the initial polymerization rate.The polymerization rate was increased and the final polymerization conversion was greater when the polymerization temperature was 60℃.The polymerization rate was also increased as the concentration of AIBA increased.The prepared PSA and FA-SA copolymers were further used as macro-chain transfer agents to mediate VC chain extension polymerization,and PSA-b-PVC and P(FA-SA)-b-PVC copolymers were obtained.The GPC,1H NMR and ion chromatography were used to determine the composition of block copolymers.DSC analysis showed that PSA and P(FA-SA)segments in block copolymers were cry stall izable.Secondly,the block copolymer membranes were prepared by solvent casting or spin coating methods,and the morphology and contact angle of membranes were characterized.The static water and hexadecane contact angles of FA-SA random copolymer membranes were increased with the increase of FA content in copolymer.FA-SA random copolymers with FA content of 30～70%exhibited good hydrophobic and oleophobic properties,as the water contact angles of membranes were all greater than 110°,the hexadecane contact angles greater than 60°,and the surface tension less than 15 mN·m-1.The surface(interface)properties of the fluoro-containing block copolymer membranes were related to the surface enrichment ability of the fluorocarbon chain,and were affected by the membrane forming temperature and solvent.The migration ability of fluorocarbon chain in P(FA-SA)-b-PVC copolymer was increased as the temperature(in the temperature range of 15～60 ℃)increased and the PVC content in block copolymers increased.Compared with tetrahydrofuran and toluene,the fluorocarbon chain in P(FA-SA)-b-PVC copolymers exhibited greater surface migration ability when 1,1,2-trichlorotrifluoroethane was used as a solvent,and obvious needle-like structure would be formed in the membrane surface.The morphologies of amphiphilic block copolymers,such as PAA-b-PVC-b-PAA,PACMO-b-PVC-b-PACMO and PVA-b-PVC copolymers(PAA is polymeracrylic acid,PACMO is polyacryloyl morpholine and PVA is poly(vinyl alcohol)were mainly affected by block characters and the ratio of hydrophilic/hydrophobic blocks.PAA-b-PVC-b-PAA copolymer could form a smooth membrane,and the PVA-b-PVC copolymer membrane appeared holes and then disappeared as the PVA content in block copolymers increased.The PACMO-b-PVC-b-PACMO copolymer membrane was easier to form Breath Figure(BF)porous structres by spin-coating method.Finally,the static BF method was applied to prepared honeycomb-patterned porous membranes based on VC block copolymers,and influences of solvent,copolymer composition,solution concentration and humidity on the morphologies were investagiated.The suitable solvents for PSA-b-PVC,PACMO-b-PVC-b-PACMO and PVA-b-PVC copolymers were chloroform,chloroform and tetrahydrofuran,respectively.The increased humidity was beneficial to prepare honeycomb-patterned porous membranes with big pore size.PACMO-b-PVC-b-PACMO copolymer could form a uniform porous structure at a lower solution concentration,because the hydrophilic segments can stabilize the deposition of water droplets on polymer solution interface.Increasing the molecular weight of PSA-b-PVC copolymer was beneficial to form membrane with more regular pore morphology.Due to the balance between hydrophilic and hydrophobic segments,amphiphilic copolymers with greater contents of hydrophilic blocks were difficult to form membranes with honeycomb-patterned pores.The prepared honeycomb porous membranes were used as superhydrophobic surface materials and Raman enhanced active substrate.The PSA-b-PVC copolymer showed superhydrophobic performance with water contact angle of 160° when the surface layer of BF membrane was peeled off.Porous PACMO-b-PVC-b-PACMO copolymer membrane could be used as a Raman-enhanced active substrate after depositing nano-silver.The detection signal was still obvious when the concentration of Rhodamine 6G was as low as 10-9 M,indicating that the detection limit of Raman spectroscopy could be significantly improved.In conclusion,block copolymers containing PVC and PSA or P(FA-SA)were successfully prepared by iodine transfer polymerization,and influences of the structure of VC block copolymers on morphologies and surface(interface)characteristics of casting and BF membranes were illustrated.The results would provide basis for preparing of VC block copolymers and their membranes.