Development of Epoxy Resins without Hydroxyl Groups in the Molecular Chain

固化后不含羟基的环氧树脂具有较低的吸水率和介电常数。它们是理想的高性能电气和电子材料。因此，开发了各种新型环氧树脂固化剂，并对固化树脂的力学性能、介电性能和吸水性能进行了详细的研究。以1,3,5-三羟基苯-羧酸酯为三官能团活性酯时，随着羧酸残基的体积增大，环氧树脂固化的反应活性降低。玻璃化转变温度（Tg）随着羧酸残基烷基链长度的增加而降低，但通过烷基部分分支或在酯中加入苯基而升高。活性酯作为固化剂，由于固化后不留下羟基，提高了固化树脂的耐水性和电性能。然而，用活性酯固化的环氧树脂比用常规固化剂固化的环氧树脂具有更低的Tg值。因此，利用内酯基与环氧基的插入反应，制备了具有内酯键的新型多功能活性酯，并将其用作固化剂。固化树脂的Tg得到了改善，达到了142的最大值。以苯酚和甲酚三甲基硅醚为固化剂，固化树脂的Tg低至110 C，吸水率降至常规固化剂的1/10。

Epoxy resins without hydroxyl groups after curing are expected to have low water absorption and dielectric constant. They are desirable as high-performance electric and electronic materials. Therefore, various novel curing agents were developed for epoxy curing, and properties of cured resins such as mechanical and dielectric properties and water absorption were examined in detail.When esters of 1,3,5-trihydroxybenzene with carboxylic acids were used as trifunctional active esters, the reactivity for epoxy curing was decreased with the bulkiness of carboxylic acid residues. The glass transition temperature (Tg) shifts to lower temperatures with increasing length of alkyl chain of carboxylic acid residues but is shifted to higher temperatures by branching the alkyl moiety or incorporating a phenyl group into ester.The active esters as curing agents improve the water resistance and electric properties of cured resins because no hydroxyl groups are left after curing. However, the epoxy resins cured with active esters have lower Tg values compared to that cured with conventional curing agents. Therefore, novel multifunctional active esters with internal ester bonds were prepared and used as curing agents utilizing the insertion reaction of internal ester groups into epoxy groups. The Tg of cured resins were improved and the maximum value of 142ﾟC was attained.Trimethylsilyl ethers of phenol novolak and cresol novolak were used as curing agent, the Tg of cured resins was as low as 110ﾟC but the water absorption was decreased to 1/10 of that cured with conventional curing agents.