Long Chain Branched\nPhenolphthalein Poly(ether sulfone)\nfor Effective Toughness Improvement in Epoxy Networks

The incorporation of linear thermoplastic resin is commonly\nutilized\nto improve the toughness of the epoxy system. However, practical application\noften encounters issues, such as poor compatibility, noticeable phase\nseparation, and limited toughening effect. Branched-chain polymer,\ncharacterized by a branched structure, numerous voids, and a higher\nnumber of active end groups compared with its linear counterpart,\nhas more advantages as a toughening agent. In this study, trifunctional\nmonomer 1,1,1-tri (4-hydroxyphenyl) ethane (THPE) was introduced into\nthe molecular chain of linear phenolphthalein polyaryl ether sulfone\n(PESC) to form a branched structure in the resulting polymer. By adjustment\nof the proportion of THPE, long-chain branched PESCs (LCBPESCs) with\nvarying degrees of branching were successfully synthesized and characterized\nfor their molecular structure, molecular weight, and thermal properties.\nTo evaluate the toughening effect, properties of the epoxy resin/methyl\ntetrahydrophthalic anhydride system mixed with LCBPESCs of different\nmasses after curing were investigated. Results demonstrated that after\ncuring, significant improvement in phase separation and toughness\nof LCBPESC-toughened epoxy resin occurred, and the corresponding toughening\nmechanism. Specifically, when LCBPESC-30 with 5 phr was added, the\nimpact strength of the epoxy system increased by 68%, leading to a\nsubstantial enhancement.