| Living radical polymerization technology is one of the important synthetic methods in polymer science,which can control the molecular weight,molecular weight distribution,topology,composition and end groups of polymers.In order to reduce the cost,people continue to develop simple and new living radical polymerization systems.Xanthene-9-thione(XT)mediate free radical polymerization system developed by our group show a good regulation effect in the polymerization of styrene mediated by XT.In order to explore the ability of XT to regulate the polymerization of various monomers,the copolymerization of AA and VAc mediated by XT was studied in this thesis.PAA-b-PVAc-XT block copolymers were prepared by changing the ratio of initiator to XT,temperature,monomer concentration,monomer ratio,theoretical molecular weight and solvent.In order to explore the reinitiation activity of the XT end group,we need to determine the optimal synthesis conditions for the macromolecular initiator.The PAA-b-PVAc-XT macromolecule was then used to initiate St emulsion polymerization to prepare a PAA-b-PVAc-b-PSt block copolymer.As follows:(1)Study on the regulation of AA/VAc copolymerization mediated by XT.The polymerization process shows that there is an induction period before the polymerization.After the end of the induction period,the monomer conversion will increase rapidly with time,and the polymer Mn will increase suddenly.In the middle and late stages of the reaction,the growth of Mn will slow down,the increase will be smaller,and the PDI will broaden.The conversion of AA monomer can reach 100%during copolymerization,and the PAA mass fraction in the product decreases with the increase of the conversion of VAc monomer.The increase of XT equivalent will lead to the prolongation of the induction period,the slowing of the polymerization rate,the decrease of the monomer conversion rate,the increase of the PAA mass fraction in the product,and the increase of the XT end group content.Increasing temperature will shorten the induction period,accelerate the rate of polymerization and decrease the controllability of the reaction.Increasing monomer concentration will lead to faster polymerization rate,higher monomer conversion and higher product Mn.The decrease of AA/VAc ratio leads to a slower rate of polymerization,a decrease in monomer conversion and PAA mass fraction in the product.When the theoretical molecular weight reduced from 20 k to 5 k,the growth of polymer Mn slowed down and the control ability of XT to the polymerization process is improved.The experimental results show that XT has a certain regulation effect on the copolymerization of AA and VAc.A larger molar amount of XT can make the regulation effect more obvious,and the copolymer Mn increases linearly with the conversion rate.(2)Study on St emulsion polymerization initiated by PAA-b-PVAc-XT macromolecule.The experimental results show that the polymers prepared with dioxane or toluene as solvents are suitable for re-initiation when the temperature is 60oC,ABVN/XT=2/1,AA/VAc=1/19,monomer concentration is 20 wt%,theoretical molecular weight is 5 k.The experimental results show that the prepared amphiphilic macromolecular initiator can successfully achieve emulsification effect after saponification,and the XT end group in the polymer chain can initiate St polymerization by a-fragmentation.The stability of the emulsion will decrease in the late stage of the polymerization,and part of the product GPC curve exhibits a double peak.Increasing the temperature is beneficial to increase the initiation efficiency of the macromolecular initiator.If the mass ratio of the PAA-b-PVAc-XT macromolecular initiator to the monomer St is too high,the system will be unstable,and too low will lead to low efficiency,and the optimum ratio is 1/10-1/5. |
