Long Chain Branched Phenolphthalein Poly(ether sulfone) for Effective Toughness Improvement in Epoxy Networks

The incorporation of linear thermoplastic resin is commonly utilized to improve the toughness of the epoxy system. However, practical application often encounters issues, such as poor compatibility, noticeable phase separation, and limited toughening effect. Branched-chain polymer, characterized by a branched structure, numerous voids, and a higher number of active end groups compared with its linear counterpart, has more advantages as a toughening agent. In this study, trifunctional monomer 1,1,1-tri (4-hydroxyphenyl) ethane (THPE) was introduced into the molecular chain of linear phenolphthalein polyaryl ether sulfone (PESC) to form a branched structure in the resulting polymer. By adjustment of the proportion of THPE, long-chain branched PESCs (LCBPESCs) with varying degrees of branching were successfully synthesized and characterized for their molecular structure, molecular weight, and thermal properties. To evaluate the toughening effect, properties of the epoxy resin/methyl tetrahydrophthalic anhydride system mixed with LCBPESCs of different masses after curing were investigated. Results demonstrated that after curing, significant improvement in phase separation and toughness of LCBPESC-toughened epoxy resin occurred, and the corresponding toughening mechanism. Specifically, when LCBPESC-30 with 5 phr was added, the impact strength of the epoxy system increased by 68%, leading to a substantial enhancement.