Vinyl resins obtained by polymerisation are being increasingly used in the form of copolymers, usually based on vinyl acetate. Another group of copolymers which is of major importance is based on polyvinyl chloride and its deri vatives. Their relatively high molecular weight, caused by the method of manufacture can make it difficult to produce high-solids paints.
One way of overcoming this problem is to use aqueous dispersions on the one hand, and on the other to formulate PVC organosols and plastisols. Polyesters, irrespective of whether they are saturated or unsaturated, i.e. with reactive double bonds for further crosslinkage to take place, are produced by the polycondensation of dihydric or polyhydricalcohols and dibasic or tribasic acids. To make unsaturated polyesters for example, one uses , maleic acid.
Another important factor apart from molecular weight ist the reactivity, i.e. the hydroxyl or acid functionality.