1. Field of the Invention
This invention relates to a new process for the production of organic polyhydroxyl compounds by the polymerization of olefinically unsaturated monomers, containing a portion of hydroxy-functional monomers, in the presence of cyclic compounds capable of polymerization reactions and low molecular weight polyhydric alcohols, to the polyhydroxyl compounds obtained by this process and to their use as a binder component in one- or two-component coating compositions, more particularly one- or two-component polyurethane coating compositions.
2. Description of the Prior Art
For ecological reasons, solvent emissions should be kept to a minimum during the application of coating compositions. For this reason, many high solids systems have recently been developed although, ideally, they should be free from solvents.
Ester-modified polyhydroxyl polyacrylates are valuable binder components in regard to their lacquer properties and may be processed as binders in combination with organic polyisocyanates to form coatings characterized by high resistance to chemicals, hardness and also flexibility (U.S. Pat. No. 3,892,714). The production of ester-modified polyhydroxy polyacrylates from the reaction of cyclic esters, particularly lactones, is described for example in EP-A-0,339,472 and in EP-A-0,339,477. According to U.S. Pat. No. 4,082,816, the ester-modified copolymers are prepared in a one-pot reaction in solvents, but must not contain any hydroxyl groups. According to PCT application WO 90/03991, this reaction is carried out in the absence of solvents and results in polyhydroxyl compounds which may be used as the binder component in powder coating compositions or solvent-containing coating compositions.
All of these known processes are attended by the disadvantage that the ester-modified polyhydroxyl compounds obtained as end products generally have too high a viscosity for the production of solventless or low-solvent coating compositions. Accordingly, it is an object of the present invention to provide a process for the production of modified, more particularly ester-modified, polyhydroxy polyacrylates which are comparable to known products in regard to their lacquer properties, but which differ advantageously from those products by having a considerably lower viscosity.
This object may be achieved by the process according to the invention described in detail hereinafter, in which low molecular weight polyhydric alcohols are used as component c). Both in unmodified form (no reaction with component b)) and after modification by reaction with component b), component c) acts as a reactive thinner resulting in a significant reduction in the viscosity of the system as a whole. The possibility of significantly reducing the viscosity of the end products through the use of the starting component c) in accordance with the invention was not foreseeable because the relevant prior art advises against using solvents containing hydroxyl groups by restricting the alcoholic components to the hydroxy-functional monomers.