Synthesis Of Ploy(Styrene-b-Butadiene-b-Sty-rene)Latex Via RAFT Emulsion Polymeriz-ation And Its APPlication In Modification Of(Emulsified)Asphalt

Ab initio RAFT emulsion polymerization of styrene targeting at low molecular weight polystyrene was investigated in term of polymerization kinetic and controlling over chain microstructures. The obtained PS latex was then used as seeds and RAFT agent to synthesize PS-b-PB. The effort was focused on the factors influencing the gelation point during the seed emulsion polymerization. Finally, series of SBS latex with different microstructures was synthesized. The possible applications of SBS latex in the modification of (emulsified) asphalt was evaluated. The obtained new understandings and achievements were highlighted as follows.(1) Employing amphiphilic macromolecular RAFT agent (PAA2o-b-PSt5-RAFT) as both mediator and emulsifier in ab initio emulsion polymerization of styrene can synthesize well-defined PS with molecular weight as low as10K and PDI about1.25.(2) In seed emulsion polymerization of butadiene, addition of emulsifier SDS, increase of the PS molecular weight, using PAA2o-b-PSt5-RAFT, addition of initiator all can delay the gelation point. In the case of PS seed theoretical molecular weight15K mediated by macromolecular PAA2o-b-PSt5-RAFT, additional SDS and initiator can delay the gelation point to the theretical number average molecular weight of PB to41K. The Experimental molecular weight of PS-b-PB block copolymer was84K. Swelling polystyrene latex particles by butadiene for8h at30℃before polymerization was found to delay the gelation point the theretical number average molecular weight of PB. Seed polymerization of butadiene showed Experimental molecular weight deviating from the theoretical vaule and the distribution of molecular weight was broad.(3) The addition of5%SBS with designed structure2K-15K-32K-15K (PS content48%) can increase softening poin of the residue of the emulsified asphalt from42.5℃to71.5℃. When5%SBS of2K-15K-38K-22K (PS content49%) containing10%gel was added, the softening point was68℃while the gel fraction of SBS2K-15K-38K-15K (PS content44%) increased to0.52, the softening point was only 52.5℃. Increasing PS content and the gel fraction would be harmful to the increase in softening point. Performance of demulsified SBS modified asphalt was not so good.