Polyisocyanurate containing molding compositions

#This invention is directed to non-sticky gels of ethylenically unsaturated monomer solutions containing isocyanurate resins and which are particularly useful as sheet molding compounds. Of particular interest are polyvinylisocyanurate resin polyol blends which can be molded into intricately shaped articles having a high loading of glass fibers and which can be copolymerized with the ethylenically unsaturated monomer at relatively moderate temperatures. In particular it is directed to gelled vinylidene monomer solutions of ethylenically unsaturated polyisocyanurate resins by employing mixed polyurethane/polyisocyanurate resins free of ethylenic unsaturation as the gelling or thickening agent. It is also directed to a process for forming gelled solutions wherein a relatively large molar excess of aromatic polyisocyanate is added to a monomer solution of polyisocyanurate resin containing certain primary and secondary polyol reactants. Furthermore, it is directed to thickened ethylenically unsaturated copolymer resin solutions which can be molded and cured at moderate temperatures and pressures to form completely cured polyvinyl isocyanurate resins of low profile or deep drawn reinforced components having a filler content as high as 80%. The fully cured gelled composition retains substantially all the physical properties that would be obtained from a cast vinylisocyanurate/vinyl monomer copolymer containing no polyurethane thickener. Such fully cured vinyl isocyanurate thermoset resin exhibit especially superior tensile and flexural strength at high temperatures.

#Molding compositions employing ethylenically unsaturated polyester resins having unreacted carboxyl groups and vinylidene monomers have been thickened by the addition of inorganic materials such as calcium or magnesium oxides. Gellation takes place rather slowly with the employment of these oxides and in some instances require as many as two or three days to obtain a handleable or non-sticky condition. If not molded within a short period of time thereafter, they must be discarded since the gellation and cross-linking continues to a point where the composition is no longer tractable.

#More recently, however, cross-linked polyurethane thickened gels of polyester resins have been developed which are an improvement over the metal oxide thickened materials in that they have increased stability and can be maturated to form moldable compositions within a few hours. Such systems after complete curing exhibit improved shrinkage characteristics over the cured metal oxide cross-linked and thickened materials. Both linear and cross-linked polyurethane copolymers have been used for ethylenically unsaturated polyester resins and are described in U.S. Pat. Nos. 3,047,530; 3,290,208; 3,464,935; 3,644,569; 3,700,752; 3,859,381; 3,868,431; 3,886,229; 3,893;956; 3,962,370; 3,994,764; 3,997,490; 4,062,826; and 4,073,828. In many ways, the systems described for the thickening of ethylenically unsaturated polyester resins/monomer solutions are similar to that of the invention. However, when isocyanurate resins are substituted for polyester resins in the ethylenically unsaturated polymer-in-monomer solutions, incompatability and incomplete maturation problems lead to the formation of cottage cheese or sticky jelly-like gels which can neither be shaped, handled or used to form uniformly filled molded objects.

#A typical polyvinylisocyanurate resin can be prepared by the following technique:

#Into a chemical reactor equipped with agitator, condenser, gas pipe connections, vents, and port holes which is first flushed with nitrogen and thereafter sparged with 2 cfm. air and 6 cfm. nitrogen is added 2,680 parts of hydroxypropyl methacrylate and agitated at 30 revolutions per minute. Thereafter, 2.5 parts copper acetate catalyst, 12 parts of a 20% solution of t-butyl catechol and 5,743 parts styrene is charged to the reactor. The contents of the reactor are adjusted to 42.degree..+-.2.degree. C. and thereafter sparged with 3-4 cfm. nitrogen. Under increased agitation, 50-60 revolutions per minute, 3,063 parts of toluene diisocyanate is added at a rate of 60-70 parts per minute in four 766 part portions. After the first 766 part portion is added, the temperature is permitted to rise to 65.degree. C. After the second portion, the temperature is permitted to rise to 78.degree. C. After the third portion, the temperature is permitted to rise to 90.degree. C. and after the fourth portion, the temperature is permitted to go no higher than 93.degree. C. The reaction mix is permitted to stir for one additional hour at 90.degree. C. at which time the unreacted isocyanate content should be less than 4.5%. The reaction mix is cooled to 55.degree. C. and then mixed with 18 parts N-benzyl trimethyl ammonium hydroxide as a 40% methanol solution.

#The exothermic trimerization reaction takes place and with additional cooling, the reaction mixture should not be permitted to go above 60.degree. C. The reaction is permitted to continue until the unreacted isocyanate content in ranges between 0.05-0.15% and the viscosity ranges between 425-475 cps. At this point, 6 parts of methanesulphonic acid is added to inhibit the activity of the trimerization catalyst. The styrene/polyisocyanurate resin solution is stored for later use under conditions which inhibit further polymerization.