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SYNOPSISThe uncatalysed and catalysed polymerization of a hydroxyl-terminated polybutadiene with toluene diisocyanate has been studied in toluene solution at four different temperatures.The rate constants ( kl, k , ) and the activation parameters ( E a l , Ea,, AS:, AS:) for the isocyanate groups in the 4 and 2 positions were calculated. It was found that the catalysts enhance the reactivity of the 2 position isocyanate group rather than the 4 position isocyanate group. It was also found that diethylcyclohexylamine has higher selectivity than dibutyltin dilaurate to enhance the reactivity of the isocyanate group in the 2 position. The effect of solvent has also been studied. The reactivity decreased in the following order; benzene = toluene > chlorobenzene > dioxane > nitrobenzene. I NTRO DU CTlO NHydroxyl-terminated polybutadiene ( HTPB ) is a popular binder' used in solid rocket propellants. The polybutadiene chain gives higher energy value and better mechanical properties. Low viscosity of this prepolymer favours high solid loading (fuel and oxidizer). The major problem associated with HTPB is the high reactivity of primary hydroxyl groups with toluene diisocyanate (TDI, curing agent) and hence suffers from lower pot life. ' The use of hydroxylated liquid polybutadiene resin in polyurethane synthesis has been ob~e r v e d .~-~ It is an important raw material for production of polyurethane elastomers. The nonpolar hydrocarbon main chain of HTPB provides superior hydrolytic stability. The polybutadiene-urethanes are having combined properties of polyether and ester urethane systems as well as conventional rubbem6The kinetics of model urethane formation reaction between isocyanate and alcohols has been extensively However, comparatively little information has been reported on the diisocyanate-

SYNOPSISPhenol-, 2-naphthol-, and 1-nitroso-2-naphthol-blocked toluene diisocyanate (TDI) and isophorone diisocyanate ( IPDI) adducts and their polymers with PPG-1000 were prepared and characterized by nitrogen estimation, IR, and 'H-NMR spectroscopy. The absence of an IR absorption band at 2270 cm-' confirmed the completion of the reaction between the isocyanate and the blocking agents, whereas the presence o f a band at 1075-1150 cm-' confirmed the formation of poly (ether urethanes). The deblocking temperatures were determined by the use of DSC and by the carbon dioxide evolution methods. The thermal stabilities of the 2-naphthol-blocked diisocyanates were less than the phenol-blocked diisocyanates. Dissociation temperature was also reduced by the nitroso group in the blocking agent. Mass spectral data confirmed the product analysis. The solubility of the adducts were determined in the different polyols. Adducts based on IPDI showed better solubility than did those based on TDI.

ABSTRACT:Polyurethane elastomers were prepared from structurally distinct hydroxyterminated polybutadiene and polyether-ester based prepolymers with diisocyanates such as hexamethylenediisocyanate, toluenediisocyanate, and diphenylmethanediisocyanate by the one short polymerizatiQn process. The effect of crosslinking by polyfunctional alcohols such as castor oil, trimethylolpropane, and poly(vinyl alcohol) on mechanical properties is compared in case of hydroxyterminated polybutadiene based polyurethane systems. The effect of crosslinking by trimethylolpropane on the mechanical properties was quantitatively studied in all the prepolymers based polyurethane systems. Crosslinking was also induced in the polyurethanes by taking higher NCO/OH ratio (R value) and the observations on mechanical properties are compared with those prepared with trimethylolpropane crosslinking. The thermal degradation of the polymers was studied in an oxygen atmosphere and interpreted with respect to their structure.KEY WORDS Polyurethane Elastomers / Crosslinked Polyurethanes / NCO/OH Ratio Effect / HTPB Based Polyurethanes / Copolyetherester Polyols / Polyurethanes are prepared by reacting polyols with diisocyanates. The most commonly used polyols include low molecular weight hydroxyterminated polymers of saturated and unsaturated aliphatic hydrocarbon, polyethers and polyesters. The functionality of the hydroxyl containing compounds as well as isocyanates can be increased to three or more to form branched or crosslinked polymers. Other structural changes can also be made by changing the type and molecular weight of the intervening groups. Polyurethanes are unique in their crosslinking, chain flexibility and intermolecular forces which can be varied widely. The abundance of original substances used for preparing urethane elastomers in conjunction with the wide variety of reactions taking place during their synthetic cause the highly complicated chemical structure of the resulting polyurethanes. 1 -5 Crosslinking of polyurethanes is of primary importance in controlling many of their properties. 6 The degree of crosslinking was controlled by the use of polyfunctional ingredients or by taking excess diisocyanate than that of the stoichiometric requirement. Crosslinking at higher diisocyanate ratio is reported to proceed through the formation of allophanate and isocyanurate linkages. 7 A significant change in properties by crosslinking may also be expected in the case of elastomers like polyether based polyurethanes.

Random terephthalate copolyesters of ethylene glycol and propylene glycol (1 ,2-propanediol) with various contents of monomeric units of the diols were prepared by transesterification. The actual content of each monomeric unit in the copolyester was determined by 'H NMR. The thermal behaviour of the copolyesters was studied by differential thermal analysis. Kinetic order, heat and entropy of fusion, and activation energy for the thermal degradation of the copolyesters, were obtained. 0025-1 16X/83/$03 .OO

SYNOPSISGelatin was graft copolymerized with poly (glycidyl methacrylate) using potassium peroxydisulfate in aqueous medium. Effect of temperature, time, initiator, monomer, and backbone concentrations were studied. The percent grafting was found to increase initially and then decrease in all the cases except with variation of monomer concentration. The rate of grafting, grafting efficiency, and percent of grafting were calculated. The grafting results have been discussed in the light of the rate of grafting. Mechanical properties, FT IR spectra, percent swelling, and percent dye uptake were carried out on the graft copolymerization and the results discussed.

SynopsisEther-and ester-based prepolymeric diols suitable for polyurethane elastomer formation were prepared from polyoxytetramethyleneglycol and polyoxytetramethylene-oxypropyleneglycol with dicarboxylic acids like adipic acid, maleicacid, and phthalic acid. Crosslinked polyurethane elastomers were prepared from these prepolymers using various concentrations of trimethylolpropane as a crosslinker and toluenediisocyanate as the curing agent. Crosslinked polyurethanes were also prepared by a method taking excess toluenedisocyanate other than that of the stochiometric requirement and curing it at a comparatively higher temperature. The data on mechanical properties of these elastomers show that both methods of crosslinking in polyurethane imparts a similar effect on mechanical properties.

SynopsisA series of halogen-containing poly (esterurethane) s was synthesized from the prepolymers, i.e., hydroxy-terminated polyesters containing chlorine and fluorine and the diisocyanates such as toluene diisocyanate (TDI) and hexamethylene diisocyanate (HMDI) . Polyesterification of halogenated phthalic anhydride with an excess of diols such as ethylene glycol, 1,2-propanediol, and 1,4-butanediol in the presence of trifluoroacetic anhydride (TFAA) was carried out to prepare prepolymers. The prepolymers and the poly( ester urethane)^ were characterized by infrared (IR), 'H nuclear magnetic resonance (NMR) , viscosity, end-group analysis, solubility and thermal analysis namely thermogravimetric analysis (TGA) , and differential scanning calorimetry (DSC) . Kinetics of thermal degradation was also studied. Resistance of the polymers to alkaline agents and combustion was also tested. EXPERIMENTAL MaterialsHexamethylene diisocyanate (HMDI) (Fluka AG) and 2,4-toluene diisocyanate (TDI) (Fluka AG) were purified by vacuum distillation. Phthalic anhydride ( AR, Sarabhai, India), tetrachlorophthalic anhydride ( Aldrich Chem.Co., ) , trifluoroacetic anhydride (TFAA) (BDH, England), and dibutyltin di-* Present address and address for communication: