Low viscosity unsaturated polyester resins

Low viscosity unsaturated polyester resins for making buttons, in all their marketable forms which can be made from polyester resins, by conventional processing techniques such as centrifugation and casting, essentially comprising:

• (A) an alkyd prepared by esterification of
• (a) a compound selected from the group consisting of maleic anhydride, maleic acid, fumaric acid and mixtures thereof alone or in association with a compound selected from the group consisting of phthalic anhydride phthalic acid adipic acid, sebacic acid, dodecanediois acid, and mixture thereof with
• (b) one or more glycols, essentially comprising dipropylene glycol, and at least
• (B) one ethylenically unsaturated monomer copolymerizable with (A), selected from the group consisting of styrene, vinyl toluene and a mixture thereof, in an amount of 20-30% by weight of the total (A)+(B), said unsaturated polyester resins being characterized in that said alkyd (A) has a molecular weight/double bond factor between 300 and 390 and an amount of free functional groups constituted by hydroxyl groups+carboxyl groups, from 80 to 100, inclusive expressed as mg of KOH per g of alkyd.