Synthesis Of Cationic Poly (Styrene-b-isoprene-b-Styrene) Latex Via RAFT Emulsion Polymerization And Its Application In Modification Of Emulsified Asphalt

It has been nearly 20 years since the breakthrough of controlled/living radical polymerization(CLRP).However,the large-scale industrial application of CLRP has not been realized yet.This thesis explored the possibility to prepare poly(styrene)-b-poly(isoprene)-b-poly(styrene)(SIS)cationic latex via reversible addition fragmentation chain transfer(RAFT)emulsion polymerization,and investigated the performance of SIS modified bitumen emulsion.A series of cationic amphiphilic macroRAFT agents were synthesized by design and were used as a sufactant in RAFT ab initio emulsion polymerization of styrene and isoprene to synthesize SIS latex.The followings were the main achievements:1)N,N-Dimethylacrylamide(DMAA)and N-(4-Vinylbenzyl)-N,N-dimeth-ylamine(VMA)were used as monomers for the hydrophilic block and hydrophobic block of these macroRAFT agents.With 2-{[(dodecylsulfanyl)-carbonothioyl]sulfanyl}propanoic acid(DSCTSPA)as the RAFT agent,we successfully synthesized a series of amphiphilic macroRAFT agents with a narrow molecular weight distribution,namely 30-5.0-RAFT(i.e.PDMAA30-b-PVMA5.0-RAFT,same below),40-5.0-RAFT,40-9.4-RAFT and 40-13.7-RAFT。2)RAFT emulsion polymerization of styrene mediated by 40-5.0-RAFT was successfully realized.The number averaged molecular weights of polystyrene increased linearly with monomer conversion,and molecular weight distributions were unimodal throughout the emulsion polymerization process.PDI of the final polystyrene was 1.6.After adding HCl,the VMA units were protonated and cationic polystyrene latex with good stability was obtained.3)By adding HCl and co-emulsifier(dodecyltrimethylammonium bromide,DTAB),stable cationic SIS latex was synthesized with polystyrene latex as a seed.4)5 wt%SIS was used to modify bitumen emulsion.Better modification performance was found with the emulsion of 90#bitumen than that of 70#bitumen.The addition of SIS could increase the softening point of the emulsion of 90#bitumen from 44.0℃ to 66.0℃,and the ductility(5℃,5 cm/min)from 0.4 cm to 36.2 cm.The softening point was much higher than that modified by styrene-butadiene latex and both the softening point and the ductility could meet the national standards for SBS-modified asphalt.It is suggested that the synthesized SIS cationic latex could be an excellent modifer to dramatically improve the performance of the emulsified asphalt.