Novel hyperbranched resins for coating applications

Hyperbranched polycondensates derived from AB(x)-type monomers have been ge nerally recognized as the cheaper and economically more feasible counterpar ts of the well-known other members of the dendritic macromolecule family, t he perfectly branched dendrimers. Since they can be manufactured more quick ly and easily in a one-step polymerization procedure, their significantly l ower cost price puts them in a much more favourable position to be industri ally applied as coating resins. The conceptual design of a branched macromo lecule is ideally outlined for film forming applications. The viscosity in relation to their molecular weight is kept low due to their compact morphol ogy hampering chain entanglements, while on the other hand, the large numbe r of functional end groups enable efficient cross-linking. Standing apart from the standard AB(x) approaches, optionally employing a B -x starter molecule, DSM has now developed a new type of hyperbranched poly esteramides derived from cyclic carboxylic anhydrides and dialkanolamines. In a one-pot procedure, the dialkanolamine molecules react preferentially v ia the secondary amine group with the cyclic anhydride, forming in situ a b is(hydroxyalkyl)amide group (AB(2)) containing carboxylic acid. Because of the known high reactivity of 2-hydroxyalkylamide groups towards esterificat ion with carboxylic acids, a fast and efficient polycondensation at tempera tures of 140-200 degreesC without the addition of a catalyst can be perform ed. Using the dialkanolamine component in molar excess over the anhydride, gel formation is excluded and a predictable and stable melt viscosity is ob tained. The resulting hydroxyl functional resins have been applied successfully as powder coatings binder components. In addition, the presence of the reactiv e hydroxyl groups makes these hyperbranched polymers very suitable material s for further modifications. By letting them react with aliphatic and/or ar omatic monoacids, for example, polymers with different properties could be synthesized which have been found very suitable for a number of coating app lications, for example, air drying topcoats and primers and two-pack uretha ne lacquers. A combination of favourable properties, including high hardnes s and early drying, high solids content and weatherability was observed. (C ) 2000 Elsevier Science S.A. All rights reserved.