PURPOSE: To obtain the titled composition having improved head resistance in the solventless liquid state at ordinary temperature, by preliminarily reacting a polyfunctional maleimide with a thermosetting resin, adding a trialkenyl isocyanurate and a polyfunctional acrylate, etc. thereto, and cooling the reaction product.

CONSTITUTION: (A) 2W90wt% polyfunctional malemimide having two or more N-maleimide groups in the molecule is preliminarily mixed and reacted with (B) 4-90wt% thermosetting resin preferably a cyanate resin, at 70W200°C. (C) A trialkenyl isocyanurate, preferably a compound of formula I (R1 is 2W4C alkenyl), and (D) a polyfunctional (meth)acrylate having two or more acryloyl groups, e.g. an organic compound of formula II (R2 is 1W40C aliphatic, alicyclic, aromatic organic group, etc.; X is H or methyl; m is an integer 2W6) in the total amount of 4W60wt% are added and mixed with the resultant reaction product at 30W130°C and cooled to give the aimed composition. The amounts of the components (C) and (D) are 2W58 wt% and 2W58wt% respectively.