Compounds containing at least one alicyclic epoxy group are highly capable of cationic polymerization as compared with olefinic epoxy groups and glycidyl type epoxy groups and, therefore, they are materials suited for use in cationically polymerizable resin compositions or cationically polymerizable ultraviolet-curable resin compositions. They are reactive with acid anhydride type curing agents or amine type curing agents and therefore are in wide use as diluents for epoxy resins. They are also used as stabilizers for polyvinyl chloride resins.
Hithertofore various compounds have been designed as such alicyclic epoxy-containing compounds, the starting materials being butadiene, cyclohexenecarbinol, cyclohexenedicarbinol, cyclohexenylaldehyde, cyclohexenecarboxylic acid, tetrahydrophthalic anhydride, dicyclopentadiene, cyclopentadiene and the like. However, most of the compounds contain at most two alicyclic epoxy groups per molecule and have molecular weights less than 1,000.
Our research has revealed the following facts. Such alicyclic epoxy compounds as mentioned above are low in molecular weight and have a low viscosity. Therefore, when used as diluents for epoxy resins, they disadvantageously give brittle cured products although they function as good diluents. Similarly, when used as constituents of cationically polymerizable resins or cationically polymerizable ultraviolet-curable resins, they give only brittle cured products, lacking in flexibility, presumably because they have a low molecular weight and contain an insufficient number of alicyclic epoxy groups per molecule. Furthermore, the cured products have insufficient water resistance. When used as stabilizers for polyvinyl chloride resins, they are disadvantageous in that they have high solvent extraction and migration potentials because of low molecular weights. Furthermore, articles produced by using such compounds for the purposes mentioned above are used outdoors in many instances and, in such instances, it is a prerequisite that the alicyclic epoxy compounds as raw materials should also have weather resistance. However, none of the alicyclic epoxy compounds so far known can solve these problems. The advent of a compound that can solve the problems is therefore earnestly awaited.
The present inventors made intensive investigations in an attempt to propose alicyclic epoxy compounds with which the problems mentioned above could be solved and, as a result, found that epoxidized polyesters having a certan specific structure can achieve the intended object. Based on this finding, they have now completed the present invention.
On the other hand, the present inventors made investigations in an attempt to develop an advantageous method of producing such epoxidized polyesters.
Hydrogen peroxide is a so-far known epoxidizing agent. However, any technology is not known for commercial epoxidization of high-molecular-weight polyesters with hydrogen peroxide. According to the results of a study made by the present inventors, this is presumably because (1) the reaction involving hydrogen peroxide is a non-homogeneous reaction and the rate-determining step is the contact between the aqueous hydrogen peroxide solution layer and the oily starting material layer, so that the rate of reaction is slow with high-molecular-weight polyesters which are highly viscous, (2) for handling and safety reasons, hydrogen peroxide is generally used in the form of an aqueous solution having a concentration of at most 60% and, when the rate of epoxidization is slow, this allows increased secondary reactions, such as addition of water, catalyst and/or cocatalyst to the epoxy groups formed, whereby the selectivity decreases and/or the reaction system acquires an increased viscosity or even turns into a gel, and (3) the aqueous phase thus becomes less separable and problems arise, for example postreaction treatment procedures, such as washing with water, become difficult. This tendency is more remarkable with hydroxyl group-containing polyesters, hence the epoxidization of hydroxyl group-containing polyesters has been considered more difficult.
As a result of their intensive investigations made to solve these problems, the present inventors found that the desired epoxidized polyesters can be produced in a commercially advantageous manner (1) when the epoxidization is performed in the presence of a specific weakly basic compound using a specific solvent or (2) when the epoxidization is conducted in a nonaqueous system using peracetic acid.
Accordingly it is an object of the invention to provide novel and useful epoxidized polyesters and a commercially advantageous method of producing said epoxidized polyesters.