Synthesis Of Diblock Copolymer Of Styrene And Diene Via RAFT Emulsion Polymerization

The block copolymers of styrene and dienes have been commercialized via living anionic solution polymerization process with high energy and material consumption. The reversible addition fragmentation chain transfer (RAFT) emulsion polymerization has been investigated extensively and proved to be a new method to synthesize block copolymers. What’s more, the RAFT emulsion polymerization process is environment friendly and the products are the latex of submicron particles. The RAFT living radical polymerization of dienes usually is accompanied by cross-linking reactions leading to gels which have great effects on the physical properties of the products. We investigated the effect of initiators concentration and polymerization temperature on chain structure and gel points of polybutadiene in RAFT emulsion polymerization aiming to synthesize the polystyrene-b-polybutadiene copolymer with long polybutadiene chain. RAFT ab initio emulsion polymerization of isoprene was investigated and polyisoprene-b-polystyrene copolymer was synthesized via RAFT seeded emulsion polymerization indicating that the process was’living’. The followings were our achievements:1) RAFT ab initio emulsion polymerization of styrene was investigated by using the amphiphilic poly(acrylic acidn-b-styrene5) trithiocarbonate as both surfactant and mediator. The length of hydrophilic segment of the macro-RAFT agent had significant impact on the nucleation process of RAFT ab initio polymerization of styrene. The molecular weights of polystyrene were in better agreement with theoretical predictions mediated by PAA20-PS5-RAFT than by PAA27-PS5-RAFT.2) The potassium persulfate (KPS) and sodium sulfite redox initiator couple can initiate RAFT seeded emulsion polymerization of styrene with the molecular weights in good agreement with theoretical predictions. The reductant sodium sulfite was continuously added to the reaction system during the polymerization process while higher pH value decreased the efficiency of the initiator couple.3) Reducing the reaction temperature can delay the gel point during RAFT seeded emulsion polymerization of butadiene. Increasing the initial concentration of initiators can delay the gel point, which indicated that short radicals could decrease the cross-linking reaction. Polystyrene-b-polybutadiene diblock copolymers were synthesized via RAFT seeded emulsion polymerization using15K polystyrene seed emulsion with high concentrations of the VA044initiators at40℃and the molecular weight of PB block at gel point was46K which was closed to50K-70K molecular weight of PB block of commercial SBS products synthesized by living anionic polymerization.4) RAFT ab initio emulsion polymerization of isoprene was investigated using amphiphilic poly(AAn-b-Sts) trithiocarbonate as both surfactant and mediator. When the n value in trithiocarbonate was lower than20, the coalescence would occur. The polyisoprene latex was synthesized successfully via ab initio RAFT emulsion polymerization using PAA27-PS5-RAFT as both surfactant and mediator. Polyisoprene-b-polystyrene (Mn:23K-30K) diblock copolymer was synthesized and the morphology of diblock copolymer particle was observed to be core/shell microstructure.