Several Influencing Factors Of Styrene/Butadiene Emulsifier-free Miniemulsion Polymerization Mediated By Macro-RAFT Agent PEPDTA-SMA

In this work, based on the method of reversible addition-fragmentation chain transfer radical polymerization (RAFT), the styrene/butadiene block copolymer was synthesized successfully with maleic anhydride/styrene alternating copolymer (SMA) as the starting segment in the emulsifier-and costabilizer-free miniemulsion system. Wherein, styrene miniemulsion mediated by the macro-RAFT agent (PEPDTA-SMA) was used as the seeded emulsion for the next synthesis of block copolymers. Therefore, in the process of styrene miniemulsion polymerization, the controlled character of molecular weight and emulsion stability were of great significance for the subsequent polymerizations. The influence of cosolvent, alkali and costabilizer on the product’s molecular weight, molecular weight distribution (PDI), latex particle size and its distribution were mainly studied in this paper. The blend effect of maleic anhydride-modified polystyrene-b-polybutadiene-b-polystyrene (SMA-SBS) with nylon6was investigated preliminarily.The following conlusions are reached:1. Cosolvent could affect the system nucleation loci and controlled character of molecular weight. Hydrophilic cosolvent increased the system’s homogeneous nucleation, leading to broader molecular weight distribution of product. Compared with the hydrophobic cosolvent system which could not complete the emulsifier-free polymerization, using the appropriate amount of hydrophilic cosolvent resulted stable emulsion with polydispersity index lower and could achieve the subsequent block polymer.2. After partially neutralized by alkali, PEPDTA-SMA became amphiphilic and could be used as an emulsifier to prepare miniemulsion. However, side reaction of RAFT agent’s functional group (dithioester) would occur in the alkaline condition, resulting the increase of dead polymer chain. Controlling the dosage and type of alkali which could reduce the probability of occurrence of subsidiary reaction ensured the marco-RAFT agent’s hydrophilism and well-defined polymer structure. 3. Stable styrene miniemulsion with identical controlled/living characters could be achieved whether costabilizer was added. Styrene/butadiene block copolymer could be synthesized by using the polystyrene miniemulsion as the seeded emulsion. Polystyrene-b-polybutadiene-b-polystyrene emulsion was polymerized sucessfully without traditional emulsifier and costabilizer.4. Blend effect of maleic anhydride-modified polystyrene-b-polybutadiene-b-polystyrene (SMA-SBS) with nylon6was also discussed. Due to the presence of over-crosslink of polybutadiene, SMA-SBS could not achieve an ideal dispersion of the scale in the nylon matrix and not significantly improve the impact strength of nylon.