Synthesis,Self-assembly And Template Effect Of Amphiphilic Poly (Vinyl Chloride) Block Copolymers

Poly?vinyl chloride??PVC?exhibits good comprehensive properties and is one of the most widely used plastics.PVC prepared by the traditional free radical polymerization is of poor light and heat stability because of the presence of allyl chloride and other structural defects.In order to improve the hydrophilicity of PVC,single electron transfer-degenerative chain transfer living radical polymerization?SET-DT LRP?was employed to synthesized iodine-terminated PVC?I-PVC-I?.Amphiphilic block copolymers based on vinyl chloride?VC?and many N element-containing hydrophilic monomers were synthesized,using I-PVC-I as a macromolecular initiator.The polymerization kinetics,self-assembly behavior and template effect in the preparation of porous TiO₂ membrane of amphiphilic block copolymers were investigated.Firstly,I-PVC-I was synthesized by the aqueous suspension process using CHI₃ as the initiator and Na₂S₂O₄/NaHCO3 as a catalyst system.By using modified cellulose as the suspending agents,the rate of diffusion of SO₂-radicals from water phase to monomer phase increased,favoring to the increase of the polymerization rate effectively.I-PVC-I with number average molecular weights of 4670 and 10670 were prepared by adjusting the ratio of VC/CHI₃.Using I-PVC-I as the macromolecular initiator,SET-DT LRPs of acrylamide?AM?,N-isopropylacrylamide?NIPAM?,N,N-dimethylacrylamide?DMAA?and N-vinyl-2-pyrrolidone?NVP?were carried out in N,N-dimethylformamide?DMF?solvent.Amphiphilic PAM-b-PVC-b-PAM,PNIPAM-b-PVC-b-PNIPAM,PDMAA-b-PVC-b-PDMAA and PNVP-b-PVC-b-PNVP block copolymers with different compositions were prepared.The presence of the block structure was confirmed by nuclear magnetic resonance?NMR?and gel permeation chromatography?GPC?.The polymerization kinetics of NIPAM and DMAA initiated by I-PVC-I with different molecular weights was studied.With the increase of the number average molecular weight of I-PVC-I from 4670 to 10670,the apparent rate constant of NIPAM polymerization was increased from 0.010 min-1 to 0.021 min-1.The polymerization has "living" characteristics of first-order kinetics and the linear increases of molecular weights with the conversion.The successful preparation of above amphiphilic block copolymers indicates that SET-DT LRP is an effective polymerization method for a wide range of monomers.Secondly,the self-assembly of PNIPAM-b-PVC-b-PNIPAM copolymers with different composition in aqueous solution was carried out by the solvent evaporation method.The critical micelle concentration?CMC?,micelles size,temperature response properties and morphology of block copolymer micelles were characterized by fluorescence spectroscopy,dynamic light scattering,UV-VIS spectrophotometer and transmission electron microscope,respectively.PNIPAM-b-PVC-b-PNIPAM copolymers were self-assembled in water to form core-shell micelles with PVC core and PNIPAM shell.Due to the strong hydrophobicity of PVC,the CMCs of PNIPAM-b-PVC-b-PNIPAM copolymers are very low?<10 mg.L-1?.The size of micelles was decreased with the increase of hydrophilic block content in the block copolymer.In the process of heating,PNIPAM was changed from hydrophilic to hydrophobic phase,and the transmittance of micelle solutions was decreases gradually.Moreover,the CMC of block copolymer was decreased with the increase of hydrophobicity of block copolymer.When the hydrophobicity of copolymer was increased to a certain extent,the micelles would be aggregated and precipitated.Finally,porous TiO₂ membranes were prepared by sol-gel process using Ti?OC3H7?4 as a precursor,and PNIPAM-b-PVC-b-PNIPAM or PDMAA-b-PVC-b-PDMAA amphiphilic block copolymers as a template.The formation of hydrogen bond between the carbonyl groups of the hydrophilic block and the hydroxyl groups of the titanate was verified by Fourier transform infrared spectrometer.The surface morphology of TiO₂ membranes was observed by using scanning electron microscopy.The morphology of TiO₂ membranes was affected by the structure and composition of polymers.TiO₂ membranes prepared without template and with PVC template exhibited many cracks,and the surface was smooth with no pores.TiO₂ membranes templated by PNIPAM-b-PVC-b-PNIPAM and PDMAA-b-PVC-b-PDMAA copolymer were crack-free and highly porous with pore size closed to 100 nm and 20 nm.The TiO₂ membranes prepared by PNIPAM-b-PVC-b-PNIPAM template with higher hydrophobicity were aggregated with low porosity.The porosity and pore size of TiO₂ membranes were decreased with the increase of the ratio between Ti salt and the block copolymer.TiO₂ films templated by PDMAA-b-PVC-b-PDMAA/PDMAA template exhibieds a unique unorganized nano-structure,with the loss of porous structure.The above results would provide instruction for the synthesis and application of amphiphilic PVC block copolymers.