New crosslinkable polymers, in particular polymerization products of 5-maleimidyl-isophthalic acid derivatives and 5-(nadic acid)-isophthalic acid derivatives and vinyl monomers and polycondensation products of the said isophthalic acid derivatives and diamines, diols or aminoalcohols and optionally a di-, tri- or tetra-carboxylic acid derivative are described. These polymers are distinguished by good processability and good solubility in customary organic solvents and are suitable for the manufacture of various industrial products, such as thin films, thick films and compression mouldings. spThis is a Divisional of application Ser. No. 696,349, filed on June 15, 1976, now U.S. Pat. No. 4,115,368, issued on Sept. 19, 1978.