Preparation Of Integral SIB Thermoplastic Elastomer

Styrene-isoprene-styrene(SIS) and styrene-butadiene-styrene(SBS) triblock copolymer have been widely used in many fields, such as medical care, package and auto. SIS and SBS have different application due to their different flexible midblocks. SIS was mostly used in adhesive, pressure sensitive adhesive and bonding agent, while SBS was mostly used in asphalt modifier and sole material. In this ariticle, in situ epoxidation and anionic graft-onto method were utilized to synthesis SIS-g-PB graft copolymers that combine the advantages of SIS and SBS at molecular level. The work was carried out as follow:Firstly, peroxyformic acid generated by formic acid and hydrogen peroxide was utilized to epoxidize the SIS and SBS at0℃. Their characterization results show that their epoxidation both occurred at the1,4-structure of diolefine. No side reaction was detected at such low temperature. The relationship between reaction time and epoxidation degree shows that the epoxidation activity of SIS is2.3times of SBS.Secondly, polybutadienyllithium macroanions, synthesized by anionic polymerization, were grafted onto the epoxidized SIS copolymers at the ratio of polybutadienyllithium macroanions and epoxidation group of1.25:1. The obtained SIS-g-PB graft copolymer was purified by a precipitation separation process, in which PB homopolymer was totally removed by using ethanol and tetrahydrofuran. The GPC and1H-NMR results showed that the graft efficiency decreased with the increase of branch length, but increased with the increase of epoxidation degree. The inherent viscosity also increased with the increase of branch length.Finally, the Tg of PB branches, ESIS with different epoxidation degree and SIS-g-PB copolymer was characterized by DSC. The result showed that the Tg of PB bracnehes increased with the increase of molecular weight. The introduction of epoxidation group also increased the Tg of ESIS. With the increase of branch length and branch number, the Tg of SIS-g-PB copolymer decreased and tended to the Tg of pure PB branch. The influence of branch length to Tg was larger than that of branch number. The theoretical Tg predicted by Fox equation was basically in accordance with the measurement value.