Study Of Epoxidized SBS Synthesis And Its Modified Epoxy Resin Properties

Styrene-Butadiene-Styrene Triblock Copolymer(SBS) is a kind of very important thermoplastic elastomer,which has many advantages such as high stretch strength,low surface friction coefficient,good toughness in low temperature and easily process.Thanks to its excellent properties,SBS has wide applications in adhesive,modification of plast and asphaltum,waterproof materials,shoemaking and etc.Unfortunately,SBS has low molecule polarity,bad resistance of oil and low compatibility and low dhesive force with polar materials.For overcoming its disadvantages and improving its physical performance,we decided to introduce polar groups to the molecule chain of SBS by chemical modification,which also can extend its applications.In this paper,we study two process used to epoxidize SBS:In-situ peroxyformic acid method and H₂O₂/quaternary ammonium tetrakis(diperoxotungsto)phosphates(3-) method.Although these two methods have been widely studied,the epoxidation reaction still suffers from gelation reaction,and it is very hard to control product quality.So we focus on measures that can ease gelation reaction and improve the product quality in this paper.In-situ peroxyformiac acid was the most widely used epoxidation method.The advantages of this method are low cost,high epoxy degree and easy handling.But under acid catalyzing,gelation can easily occur during SBS epoxidation reaction.We take a new measure to overcome this problem by adding quaternary ammonium salt. quaternary ammonium salt is a very good gelation retardant,0.2～0.3 phr quaternary ammonium salt is efficient enough to prevent gelation during epoxidation reaction. epoxidation reaction should be performed under these conditions:reaction temperatures 60℃,reaction time 8 h,stirring speed 90～120 rpm,H₂O₂ was added two times.The best epoxidaton formulation are 100 phr SBS/1,2-dichoroethane(10～15 vol%wt),4～5 phr formic acid(98%),10～20 phr H₂O₂(10～15 vol%),0.2～0.3 phr quaternary ammonium salt.Quaternary ammonium tetrakis(diperoxotungsto)phosphates(3-) method is a promising epoxidation method.Its advantages are mild reaction condition,high reaction speed.But the product's solubility is usually very poor.We gained low gel content epoxidized SBS by controlling the pH values and reaction time.The best reaction condition is using tetraoctylammounium and quaternary ammonium hydrogensulfate salt as phase-transfer reagent,8～12%concentration H₂O₂,1 h reaction time,aqueous phase pH=3.In this paper we tried to use epoxidized SBS to modify epoxy resin.The effect of epoxidized SBS on epoxy resin cure kinetics and fracture toughness were studied.The gel-time can be reduced when increasing the epoxidized SBS amount.When blending eSBS-3 with epoxy resin,there is no difference in gel-time between anhydrous acid curing system and DICY curing system.When blending eSBS-2 with epoxy resin, small amount of epoxidized SBS can greatly change epoxy resin gel-time cured by anhydrous acid,but it only changed step by step in the DICY cured system.Fracture toughness of epoxy resins cured by phenol novolac can be improved by adding small parts of epoxidized SBS.Its impact toughness can be improve about 2.3 times by adding 5 phr eSBS-1,fracture toughness can be impoved about 4 times by adding 1 phr eSBS-1,and critical stress intensity factor K_IC can improve about 3 time by adding 1 phr eSBS-2.But it should be mentioned that blending epoxidized SBS with epoxy resin can cause some unwanted effect.The Tg and Young's modulus of cured epoxy resin reduced slightly.