Modified lsocyanurate Foams-Part III

Abstract

of combustibility was introduced in Part II. It was shown that combustibility was predominantly controlled by the polymer hydrogen content. The level of halogen or phosphorus had little or no effect on the relative combustibility.Reduction of hydrogen content in the polymer by use of less than 10% of low equivalent weight, high hydrogen content diols eliminated the requirement for more costly, flame retardant polyols. The reduced level of urethane component leaves a more highly aromatic structure, with a subsequent < improvement in char formation and lower smoke generation.In the present work, the objective was to make further improvements toward lower combustibility by replacing the low equivalent weight, high hydrogen content diol with a brominated diol of small molecular size or with thermally stable groups. The latter results from formation of oxazolidin-2-one groups via reaction of isocyanate with epoxide. In both procedures, the brominated diol or diepoxide was added in a prepolymer step to consume a portion of the -NCO groups and the remaining -NCO was trimerized to isocyanurate in the foam step.A third procedure involved conversion of a small number of -NCO groups to carbodiimide linkages with subsequent increase in molecular weight. The , -NCO-capped &dquo;prepolymer&dquo; was then trimerized to the isocyanurate in the foam step.Ashida and Frisch (3) employed the prepolymer, procedure to make low friability foams. Diepoxide was reacted with polymeric isocyanates followed by trimerization of the resultant oxazolidin-2-one prepolymer with 2,4,6-tris (dimethylaminomethyl) phenol (DMP-30, Rohm and Haas Co.) to form the modified isocyanurate foam. The prepolymer approach at about 10 NCO/1 epoxide mole ratio resulted in the preparation of low friability (<30%), low combustibility foams. Fast reactivities were also observed (2-5 sec. cream time, 20-50 sec. rise time.In the present work, a catalyst combination was employed to control the reaction profile. Prepolymers containing oxazolidin-2-one, urethane and carbodiimide linkages were converted to foam by trimerization of the unreacted -NCO groups. Foam °c ombustibility and friability were the primary physical properties measured in this study. _ . Experimental Section 1. Raw Materials -A description of raw materi-_ ' als is shown in Table 1. The preparation of _ bT,N,N-~tris s (dimethy1anlinopropyl) hexahydro-s. triazine (MAT) employed the method disclosed by Kan et al, (4) as based on the reaction of formaldehyde with dimethylaminopropyl amine. 2. ,Prepolymer Preparatiorr -The isocyanate was ' heated to 80-100°C and then diepoxide or diol was added. The reaction mixture was held at 80-100°C for 0.5-3 hours. Mole ratios, reaction times and temperatures, prepolymer viscosities and equivalent weights of representative samples are compiled in _. Tables 2 and 3. For carbodiimide formation, P-API-901 1 was . heated for 12-18 hours at 150°C-in the presence of 1% Niax 3-CF. Viscosities and -NCO contents of . these carbodiimide &dquo;prepolymers&dquo; are shown in Tabl...