To provide a new diol copolymer which has diol units derived from vinylethylene carbonate and units derived from a monomer selected from among N-vinyl compounds, acrylic acid or its esters, (meth)acrylamides and vinyl ethers and/or units derived from maleic acid compounds and is useful for moldings, coating materials, hardenable pressure-sensitive adhesives, resin additives, etc.

The diol unit derived from vinylethylene carbonate is represented by formula I, and the unit derived from a maleic acid compound, by formula II. In the formulas, R1 to R5 are each H or alkyl; and M1 and M2 are each H, a metal atom, ammonium, an organic amine group or a hydrocarbon group, Here, the oxygen atom bonded to M1 may combine with a carbon atom bonded to M2 or a carbon atom bonded to M1 may combine with the oxygen atom bonded to M2, thus forming an acid anhydride group (-CO-O-CO-); in this case, M1 and OM2 are not present or OM1 and M2 are not.