Synthesis,Self-assembly And Membrane Modification Application Of Amphiphilic Poly(Vinyl Chloride)-Based Block Copolymers

Poly?vinyl chloride??PVC?exhibits chemical corrosion resistance and good mechanical properties,and can be used to process chemical building materials,separation membrane,medical devices and so on.However,the hydrophilicity and biocompatibility of PVC are poor,and PVC separation membranes and medical devices are easy to be contaminated by biomass and other pollutants during their operation.In order to achieve the hydrophilic modification of PVC,amphiphilic block copolymers composed of PVC and hydrophilic segments were prepared by single electron transfer-degradation chain transfer radical polymerization?SET-DTLRP?in this thesis.The kinetics of polymerization,self-assembly behavior and modification effects to PVC ultrafiltration membranes of amphiphilic block copolymers were investigated.Firstly,vinyl chloride?VC?aqueous suspension SET-DTLRPs were carried out to synthesize iodide-terminated PVC?I-PVC-I?,using CHI₃ as an initiator and Na₂S₂O₄/NaHCO₃ as catalysts.By using of two kind of modified cellulose as the suspending agents,I-PVC-I particles with no surface membranes would be formed,favoring the diffusion of SO₂^-**radicals from water phase to monomer phase and increase of polymerization rate.I-PVC-I with number average molecular weights of 13600,19200 and 34800 were prepared by changing VC/CHI₃ ratios.Subsequently,SET-DTLRPs of N,N-dimethylaminoethyl methacrylate?DMAEMA?were conducted in water-in-oil system,and SET-DTLRPs of methacrylic acid?MAA?and acrylic acid?AA?were conducted in DMF solvent,to prepare amphiphilic PDMAEMA-b-PVC-b-PDMAEMA,PAA-b-PVC-b-PAA and PMAA-b-PVC-b-PMAA copolymers,using as-prepared I-PVC-I as the macromolecular initiator,and Na₂S₂O₄/NaHCO₃ as catalysts.The structures of the block copolymers were characterized by nuclear magnetic resonance?NMR?.The kinetics of AA and MAA polymerization using different molecular weight I-PVC-I as initiators were studied.With the increase of the molecular weight of I-PVC-I,the apparent rate constant of AA polymerization was increased from 0.00718 min^-1 to 0.01065 min^-1.MAA and AA polymerizations initiated by I-PVC-I have obvious "living" characteristic with first-order kinetics and linear increase of molecular weights with conversion.The differential scanning calorimetry?DSC?results show that the compatibility between PDMAEMA and PVC segments is good and block copolymers exhibit only one glass transition temperature?Tg?.However,PAA-b-PVC-b-PAA copolymer is micro-phase separated and have two Tg at 80?and 108?,corresponding to PAA and PVC blocks.Secondly,the self-assembly of PAA-b-PVC-b-PAA and PMAA-b-PVC-b-PMAA in aqueous solution was carried out by solvent evaporation method.The critical micelle concentration?CMC?,micelles size and morphology were characterized by fluorescence spectroscopy,dynamic light scattering?DLS?and transmission electron microscopy?TEM?.CMCs of PAA-b-PVC-b-PAA and PMAA-b-PVC-b-PMAA copolymers are lower than 4 mg·L^-1.The micelles diameter is increased initially and then decreased with the increase of the mass fraction of hydrophilic segment in the block copolymer.The block copolymers contain PAA or PMAA segments can be deprotonated,so the self-assembled micelles show pH sensitivity.PMAA124-PVC307-PMAA124 was taken as a example to study the pH sensitivity of micelles.Due to the interaction of electrostatic repulsion and salt effect,the diameter of micelles was increased from 100 nm to 283 nm when pH value of the solution was greater than 8.1,the diameter of micelles was decreased to 203 nm as pH value further increased.Finally,the permeation and antifouling properties of PDMAEMA-b-PVC-b-PDMAEMA or PAA-b-PVC-b-PAA modified PVC ultrafiltration membranes were studied.The cross section of the ultrafiltration membrane was observed by scanning electron microscopy?SEM?.The blend membrane had a more complete fingerlike structure than pure PVC membrane.The PDMAEMA segments were enriched on the membrane surface and exhibited pH sensitive charges,conformations and hydrophilicity.Thus,the blend membranes exhibited maximum water fluxes near the neutral conditions,and had better antifouling properties to bovine serum albumin?BSA?as a model protein under strong acid and strong alkaline conditions.When the pH of the BSA solution is ranged from the isoelectric point of BSA and the pKa of PDMAEMA?4.8-7.78?,the blend membranes have lower flux and flux recovery ratio,and greater BSA absorption and irreversible flux decline ratio,due to the electrostatic interaction between the BSA and PDMAEMA fragments.The water flux of PVC/PAA-b-PVC-b-PAA blend ultrafiltration membrane was increased with the increase of PAA chain length,due to the enrichment of PAA-b-PVC-b-PAA copolymer on the membrane surface.The charge and conformation of the PAA segment were changed as pH value varied,resulting the reversible pH-sensitive permeation behavior of PVC/PAA-b-PVC-b-PAA blend ultrafiltration membranes.When the pH value was increased from 2.3 to 11.6,the water flux was decreased obviously.In strong acidic and basic conditions,the strong charge repulsion between PAA chains and BSA lead to a larger flux of BSA solution.The above results would provide instruction to the synthesis and application of amphiphilic PVC block copolymer.