Synthesis Of Styrene/Isoprene/Butadiene Copolymers By Retarded Anionic Polymerization

In this paper, a series of linear styrene/isoprene/butadiene copolymers and star styrene/isoprene/butadiene copolymers were synthesized successfully via retarded anionic polymerization. The main contents and results are as follows.Taking cyclohexane as solvent, n-BuLi and m-Li as initiators, TIBA as retarded reagent, L-PS and S-PS had been successfully synthesized. The effect of THF on the polymerization rate and conversion rate of styrene by retarded anionic polymerization. The experimental results showed that:the polymerization reaction rate was gradually increased as n(THF)/n(Li) increased, and the conversion rate can reach100%.Taking cyclohexane as solvent,n=BuLi and m-Li as initiators, THF as structure modifier, the effects of THF on the microstructure of L-SIBR and S-SIBR had been investigated. The results showed that:the PS block content decreased,1,2-PB and3,4-PI structure content increases gradually with increasing n(THF)/n(Li).When n(TIBA)/n(n-BuLi) was0.8, linear styrene/isoprene/butadiene copolymers were prepared by retarded anionic polymerization. The influence of THF on the glass transition temperature was investigated.The effects of polymer molecular parameter on the mechanical property were investigated.The Tg of rubber phase increased with the increase of n(THF)/n(n-BuLi). With the resin molecular weight increases, the impact strength was improved, up to130.4J/m.When n(TIBA)/n(m-Li) was0.8, star styrene/isoprene/butadiene copolymers were synthesized successfully via retarded anionic polymerization. The influence of THF on the glass transition temperature was investigated. The effects of polymer molecular parameter, microstructure, and composition profiles on the mechanical property were investigated in details, and the relationship between polymer impact failure behavior and fracture surface. The experimental results showed that:the Tg of rubber phase increased with the increase of n(THF)/n(m-Li). Under the same conditions, when the Bd and Ip total mass fraction of about18%, with the resin molecular weight increases, the impact strength was improved, up to313.1J/m. In the same conditions, rubber content increased from the32.9%to45.4%, the impact strength increased gradually. When the rubber content was32%and resin molecular weight of about13X104, the impact strength was no significant change with the increase of n(THF)/n(m-Li).But when the rubber content was35%and resin molecular weight of about20×104, the impact strength increased first and then reduced with the increase of n(THF)/n(m-Li). With the increase of the polymer impact strength, flexural modulus decreased gradually, while the tensile strength slightly increased. Under the same conditions, the star styrene/isoprene/butadiene copolymers impact strength is the linear styrene/isoprene/butadiene copolymers of nearly t times. Comparing with the star styrene/isoprene/butadiene copolymers and star styrene/butadiene copolymers, the introduction of isoprene improves the impact properties of polymers, the impact properties increased nearly two times. The fracture mode of impact specimens had a shift from the semi-ductile fracture to the toughness or super-ductile fracture mode with the increase of rubber content and resin molecular weight. The fracture mechanism transoformed from cavitation, matrix peeling to shear yielding, parabolic patterns and ligament-tearing.