Abstract: A method for producing a high molecular weight saturated polyester comprising adding to a saturated polyester with the terminal group being substantially hydroxyl group, having a number average molecular weight of 5,000 or more and being in the molten state, diisocyanate containing isocyanate group the amount of which corresponds to 1/10 to 2 equivalents of the amount of the hydroxyl group.

Abstract: An unsaturated alkyd having a number-average molecular weight of at least 5000 obtained by esterification and then deglycolization reaction of (a) at least 10 mol % of an .alpha., .beta.-unsaturated polybasic acid or an anhydride thereof relative to 100 mol % of the total polybasic acid including any saturated or non-.alpha., .beta.-unsaturated polybasic acid (or anhydride thereof) and (b) at least 50 mol % of a polyhydroxy alcohol having a boiling point of 300.degree. C. or less at 760 mmHg relative to 100 mol % of the total polyhydroxy alcohol summed up with another polyhydroxy alcohol not defined above. The polyester resin can be widely used in a various applications by employing the excellent physical properties thereof.

Abstract: A high molecular weight unsaturated polyester having a number-average molecular weight of 5,000 or greater, the polyester being represented by a general formula: ##STR1## wherein G denotes a glycol residue, m denotes 1 to 10, n denotes 1, and M denotes a number corresponding to a number-average molecular weight greater than 5,000. The high molecular unsaturated polyester of the present invention is an unsaturated polyester having a large molecular weight unattainable by conventional methods, and can find wide application by utilizing its improved physical properties.