Novel hyperbranched resins for coating applications

Abstract

Hyperbranched polycondensates derived from AB x -type monomers have been generally recognized as the cheaper and economically more feasible counterparts of the well-known other members of the dendritic macromolecule family, the perfectly branched dendrimers. Since they can be manufactured more quickly and easily in a one-step polymerization procedure, their significantly lower cost price puts them in a much more favourable position to be industrially applied as coating resins. The conceptual design of a branched macromolecule is ideally outlined for film forming applications. The viscosity in relation to their molecular weight is kept low due to their compact morphology hampering chain entanglements, while on the other hand, the large number 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 polyesteramides derived from cyclic carboxylic anhydrides and dialkanolamines. In a one-pot procedure, the dialkanolamine molecules react preferentially via the secondary amine group with the cyclic anhydride, forming in situ a bis(hydroxyalkyl)amide group (AB 2) containing carboxylic acid. Because of the known high reactivity of 2-hydroxyalkylamide groups towards esterification with carboxylic acids, a fast and efficient polycondensation at temperatures of 140–200°C without the addition of a catalyst can be performed. Using the dialkanolamine component in molar excess over the anhydride, gel formation is excluded and a predictable and stable melt viscosity is obtained. The resulting hydroxyl functional resins have been applied successfully as powder coatings binder components. In addition, the presence of the reactive hydroxyl groups makes these hyperbranched polymers very suitable materials for further modifications. By letting them react with aliphatic and/or aromatic monoacids, for example, polymers with different properties could be synthesized which have been found very suitable for a number of coating applications, for example, air drying topcoats and primers and two-pack urethane lacquers. A combination of favourable properties, including high hardness and early drying, high solids content and weatherability was observed.