Connection Between Kinetics And Particle Formation Process Of SET-DT Suspension Polymerization Of Vinyl Chloride And Synthesis Of Its Block Copolymers

The living radical polymerization of vinyl chloride(VC)can be realized at low temperature by single electron transfer-degenerative chain transfer living radical polymerization(SET-DT LRP),and poly(vinyl chloride)(PVC)with few structural defects,good heat-resistance and living iodine ends can be prepared and VC-based block copolymers can be further obtained by chain-extending of the "living" PVC with other monomer(s).In aqueous suspension SET-DT polymerization of VC using iodoform as an initiator and sodium dithionite/sodium bicarbonate(Na2S2O4/NaHCO3)as a catalyst system,anionic radicals formed in the water phase would diffuse to the oil phase to promote VC polymerization,so the polymerization kinetics and particle formation process affect mutually.In this thesis,the connection between VC SET-DT suspension polymerization kinetics and the particle formation process was studied,and two kind of new VC-based block copolymers were synthesized and characterized,aiming to improve the polymerization rate and control ability of VC SET-DTLRP and extend the modification method of PVC by block copolymerization.Firstly,SET-DT suspension polymerizations of VC were carried out using Na2S2O4/NaHCO3 as the catalyst system and iodoform(CHI3)as the initiator to study the influence of concentration,type of dispersants and stirring speed on polymerization rate and PVC particle features.It was found that polymerization temperature would be rapidly increased when the concentration of cellulose dispersants was greater.The polymerization rates of VC SET-DT polymerizations using different dispersant systems showed the following order;all modified celluloses(A4M/65SH50)>modified cellulose/polyvinyl alcohol(65SH50/KH20)composite dispersants>all PVA dispersants(KH20/B72).At the initial stage of polymerization,the droplet/particle breakerage rate was greater than the coalescence rate,the droplet/particle size distribution moved toward the smaller particle size and Sauter mean size decreased.Then,the droplet/particle coalescence rate was increased and exceeded the breakerage rate,the droplet/particle size distribution moved toward the greater particle size and Sauter mean diameter increased.When the polymerization conversion reached about 30%,the droplets/particles were no longer aggregated or broke up,until the polymerization was finished.The morphology of PVC particles observed by scanning electron microscope(SEM)showed that PVC resin prepared by using cellulose dispersants didn't contain surface membrane structure and the primary particles structure could be seen clearly.So,the anion radical SO2-·formed in water phase would diffuse into the droplets/particles with lowest resistance and the polymerization rate was the greatest Conversely,the continuous surface membrane would be formed when PVAs were used as dispersants,which hindered the diffusion of SO2-·and the polymerization rate was relatively lower.The macroscopic particle formation mechanism of VC SET-DT suspension polymerization was proposed.I-PVC-I with different molecular weights were prepared by varying the monomer/initiator molar ratios.Secondly,the SET-DT solution polymerizations of N-acrylmorpholine(NAM)using CHI3 or I-PVC-I as initiators and Na2S2O4/NaHCO3 as the catalyst system were conducted.Due to the existence of reversible equilibrium reaction between the anion S2O42-and the anion radical SO2-·,the equilibrium constant was greatest and the polymerization rate of NAM was greatest in the DMF.The order of reaction rate of NAM in DMF was 500(monomer/initiator)>200>1000 because CHI3 also acted as a chain transfer agent.PNAM-b-PVC-b-PNAM copolymers were synthesized by block copolymerization of NAM using I-PVC-I with different molecular weights as macro-initiators.The copolymerization rate was greater when I-PVC-I with greater the molecular weight was used,which might be caused by the viscosity of the copolymerization system.Nuclear magnetic resonance spectrum(1H NMR),infrared spectrum(IR)and gel permeation chromatography(GPC)analysis proved that PNAM-b-PVC-b-PNAM copolymers were successfully synthesized.PNAM-b-PVC-b-PNAM copolymers exhibited two glass transition regimes.Solubility parameters calculation of PVC and PNAM indicated that PVC and PNAM were not compatible.AFM observation of the spin-coated copolymer films showed that PNAM-b-PVC-b-PNAM copolymers would self-assembled into "sea-island" structure.With the increase of PVC content,the PVC "islands" would gradually increased until they were aggregated.Finally,glycidyl methacrylate(GMA)SET-DT solution polymerization using I-PVC-I as macro-initiators and Na2S2O4/NaHCO3 as the catalyst system were carried out to prepare PGMA-b-PVC-b-PGMA copolymers.The polymerization rate of GMA was slow in the studied conditions.It was proved by NMR analysis that not all I-PVC-I participated in the block copolymerization.Solubility parameters calculation indicated PVC and PGMA were not compatible.AFM results showed that the "island" PGMA phase would gradually aggregated as the PVC content increased.PGMA-b-PVC-b-PGMA copolymers were used as a compatibilizer for blends of PVC and Nylon with a low melting-temperature,and showed a certain compatibilizing effect on the PVC/Nylon alloy.