Preparation Of Internal Plasticized And Amphiphilic Poly (Vinyl Chloride) Graft Copolymers By Living Radical Polymerization

Poly(vinyl chloride) is a commodity plastics which is not only widely used in chemical building materials, but also successfully applied in the medical devices (blood bags, etc.) and separation membranes. However, soft PVC products plasticized by small molecular plasticizer possess the disadvantage of plasticizer migration. Meanwhile, PVC is hydrophobic and easy to be fouled by protein or lead the coagulation of protein, affecting the performances of PVC medical devices and separation membranes. Internal plasticization is an effective way to overcome the migration of PVC plasticizer, and hydrophilic modification of PVC is a useful way to improve the biocompatibility of PVC and endows PVC with specific functions. The graft copolymerization is an important method for PVC modification, while PVC graft copolymerization based on the traditional free radical polymerization mechanism has a drawback of low grafting efficiency. In this thesis, various living radical polymerization (LRP) approaches were employed in PVC graft copolymerization. PVC with high content of graft sites were prepared and used as macroinitiators (or macromolecular transfer agent), and graft copolymerizations of butyl acrylate (BA), N-isopropylacrylamide (NIPAM) and acrylic acid (AA) onto PVC were conducted by activator regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP), single electron transfer-living radical polymerization (SET-LRP) and macromolecular design via the interchange of xanthates (MADIX) polymerization methods, respectively. The graft copolymerization kinetics, the structure and characters of PVC graft copolymers were investigated. The results will provide instruction to the synthesis and application of internal plasticized and amphiphilic PVC.Firstly, semi-batch suspension polymerizations of vinyl chloride (VC) by continuously adding of gas-state VC, and copolymerizations of VC and allyl a-bromoisobutyrate (ABiB) were carried out to synthesize PVC macroinitiator with high content of labile chlorine (U-PVC) and C-Br bonds containing PVC (PVC-co-ABiB), respectively. It was found that the average molecular weight and the thermal stability of U-PVC were decreased, and the content of labile chlorine was increased with the decrease of pressure of added gas-state VC. The molecular weights of PVC-co-ABiB were decreased with the increase of ABiB content in the feeding monomers, and the fitted reactivity ratios of VC and ABiB copolymer were rvc=1.90 and rABiB=0.09. The graft copolymerization of BA onto PVC was conducted through the method of ARGET ATRP in water and solvent, respectively, using U-PVC and PVC-co-ABiB as initiators. For aqueous graft copolymerizations, the conversion and grafting degree of BA were increased initially and then decreased with the increase of the concentration of CuCl2 and polymerization temperature. For polymerization system consisted of 1.589 g PVC,2.70 g BA,0.0048 g CuCl2, and with ascorbic acid/tris(2-pyridylmethyl)amine(TPMA)/CuCl2 (mol)= 15/5/1, the conversion and grafting degree of BA are 56.06% and 95.14%, respectively, as polymerization proceeds for 7h at 70℃. Due to the partial swelling of PVC in BA, the grafting of BA onto PVC was not uniform, and the resulted PVC-g-BA exhibits bimodal molecular weight distribution. For the solution graft copolymerizations, the greater BA polymerization rate and PBA grafting degree were achieved when PVC-co-ABiB was used as the initiator using the same catalyst system. The PBA branches were cleaved from the ester group of PVC-co-ABiB and the molecular weight distribution index of PBA was 1.29, verifying the living nature of the graft copolymerization. The grafted PBA showed good internal plasticization effect to PVC, and the glass transition temperature of PVC-g-BA copolymer with 32.75mol% PBA was reduced 80℃ compared to pure PVC.Secondly, a series of PVC-g-NIPAM amphiphilic copolymers with different graft lengths and densities were synthesized via the SET-LRP of NIPAM using PVC-co-ABiB as macroinitiator. The chemical structure, micellization behavior and thermally-induced multistep aggregation of micelles of PVC-g-NIPAM copolymers were investigated. By the kinetic analysis and the narrow molecular weight distribution of the grafted PNIPAM chain, it is proved that the graft copolymerization process has the living characteristic. The hydrophilicity of PVC-g-NIPAM was greater than pure PVC, and the water contact angle was decreased from 87° of PVC to 57.4°. PVC-g-NIPAM copolymer could form micelles consisting of a PVC core and PNIPAM corona in water at room temperature. These micelles are thermoresponsive and show a lower critical solution temperature (LCST). The micelle size and LCST of PVC-g-NIPAM copolymer were increased with the increase of the graft density and length of PNIPAM chains. PVC-g-NIPAM copolymers exhibited a very unique aggregation behavior above their LCST and formed a three-dimensional macroscopic aggregate with well-defined and tunable shapes at an extremely low concentration (0.1 wt%). The aggregates shrunk to form more compact structures with the further increase of temperature. Higher copolymer concentration, longer graft length, and lower graft density are favour to the macroscopic micelle aggregation of PVC-g-NIPAM copolymers. A self-standing and superporous PVC-g-NIPAM material having an extremely low density of 0.01 g/cm3 and a high porosity of>99% was obtained after freeze-drying the micelle aggregates.Finally, PVC macromolecular transfer agent containing ethyl xanthate groups (PVC-X) were prepared by substitution reaction between PVC and potassium ethyl xanthate. A serious of PVC-g-AA was synthesized by MADIX using PVC-X as a chain transfer agent, and employed in the modification of PVC ultrafilitration membranes. It was found that the amount of AA monomer has greater impact on the grafting degree and the greatest grafting degree of 41.72% can be achieved when xanthate (in PVC-X)/ABVN/AA was 1:1/5:160 (mol). PVC/PVC-g-AA blend membranes with different copolymer content and grafting degree were prepared by nonsolvent induced phase separation method. The membrane structures, permeability, separation performances and the fouling resistance of blend membranes were investigated. The results indicated that the hydrophilicity and permeability of the blend membranes were obviously improved. Furthermore, the antifouling ability of blend membranes was especially better at neutral or alkaline environments.