AbstractThe improvement of toughness and heat resistance of phenolic resin was examined by blend of novolac and copolymers prepared fromp‐hydroxyphenylmaleimide (HPMI) and acrylic ester. Copolymers of HPMI and acrylic esters, such as methyl acrylate, ethylacrylate,n‐butylacrylate, or 2‐ethylhexyl acrylate, were synthesized. Average molecular weights, glass transition temperatures (Tg) and thermal decomposition temperatures were measured. The miscibility of the copolymers with novolac was evaluated. It was found that these copolymers had higher average molecular weight and higher thermal decomposition temperature than those of novolac; they also had good miscibility with novolac. Molding compounds were prepared by hot roll‐kneading of mixtures, which involved novolac, the copolymer, hexamethylenetetramine (hexamine), and glass fiber. Test pieces of the modified phenolic resins were prepared by transfer molding from the molding compounds. It was found that phenolic resin, modified with HPMI/ethylacrylate copolymer or HPMI/n‐butylacrylate copolymer, which consisted of numerous units of acrylic ester, showed both good toughness and good heat r
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