Low shrinking thermosetting polyester resin compositions and a process for the preparation thereof

A process for preparing a resin composition comprising the steps of:

• (a) contacting a molar excess of an alpha, beta unsaturated dicarboxylic acid or derivative thereof with an organic polyol for a time and at a temperature sufficient to form a composition comprising a carboxylic acid terminated polyester having the formula:
• ##STR15## wherein n is a number having an average value of about 2 to less than about 4, m is a number equal to the free valence of R less the average value of n, the ratio of n to m is greater than about 2.0, and R is the residuum of a polyester which contained from 2 to 4 inclusive hydroxyl groups;
• (b) contacting a Diels-Alder adduct of cyclopentadiene with an olefinic or acetylenic hydrocarbon or alkylated derivative thereof with the carboxylic acid terminated polyester of (a) in the presence of a non-oxidizing acid catalyst having a non-nucleophilic anion selected from the group consisting of fluoroboric acid, hexafluorophosphoric acid, hexafluoroantimonic acid and trifluoromethanesulfonic acid (triflic acid) for a time and at a temperature of from about 80.degree. to about 140.degree. C. sufficient to form a composition comprising an unsaturated ester having the formula:
• ##STR16## wherein n, m and R are as defined above, and R.sub.1 is the residuum of a Diels-Alder adduct of cyclopentadiene with an olefinic or acetylenic hydrocarbon or alkylated derivative thereof having from 2 to about 20 carbon atoms;
• (c) admixing a copolymerizable ethylenically unsaturated monomer with the unsaturated ester of (b);
• and
• (d) admixing a thermoplastic polymer low profile additive with the mixture of (c).