Research On Removal Of RAFT End Group In Polymer Prepared By Emulsion Mediated Macro-RAFT

Reversible addition-fragmentation chain transfer technique has been reported to be one of the most versatile C/LRP methods in preparing block copolymers or gradient copolymers with predetermined molecular weight and molecular weight distribution.And emulsion polymerization technique is widely used in industrial production nowadays due to its prominent merits.RAFT polymeization would be quite promising in C/LRP practice by combining these two method.However,the polymers synthesized utilitizing RAFT agent suffered from their color and toxicity because of the thiocarbonyl-thio end groups,which severely restricts their industrial applications.Many of the effient methods used for removal of thiocarbony-thio groups are studied,however,most of them are compilcated in processing and take much in separation mediated by solution.We proposed one method by using hydrogen peroxide(H2O2)as oxidant and hydroxyl radical donor to remove trithiocarbonyl groups of RAFT emulsion polymer directly in latex to get polymer product without color or odors,After researching on oxidizing mechanism and effect on removal ratio of trithiocarbonyl groups by process condition,we got results as follow:(1)The hydroxide radicals generated by thermal decomposition of H2O2 were highly effective at scissoring the trithiocarbonyl groups from the polymer chain in the aqueous solution.And the detached moieties were further oxidized by H2O2 and hydroxide radicals.Thus,under some conditions,the oxidation process could be accomplished without compromising the polymer chain.(2)The oxidation of H2O2 method mentioned above,however,failed to treat the latex of RAFT polymer.As an alternative,the mixed solution of hydrogen chloride(HCl)and H2O2 proved to work in the case of the latex.Several controlling factors like temperature and recipe were investigated in terms of the converting rate of the trithiocarbonyl groups and the optimized conditions were identified as follows:temperature of 50?,the volume ratio of latex(20%solid content):H2O2(aq,concentration of 30wt%):HCl(aq,concentration of 7.5wt%)was 3:1:2,reaction time was 1.5h.The final conversion of trithiocarbonyl groups of polystyrene and poly(n-butyl acrylate)was over 90%and 98%,respectively.(3)The small molecular side products produced by oxidation could degrade and darken the polymer at high temperature.The colorless and thermal-stable polymer could be obtained by using the macroRAFT with Z groups of C4H9S-since the side products could be easily evaporated.