A. Sultan Nasar

Preparation and properties of poly(urethane-imide)s derived from amine-blocked-polyurethane prepolymer and pyromellitic dianhydride

Abstract Poly(urethane-imide)s were prepared using amine-blocked-polyurethane (PU) prepolymer and pyromellitic dianhydride. The PU prepolymers were prepared by the reaction of different diols (polypropyleneoxy glycol, polytetramethyleneoxy glycol, polycaprolactonediol and hydroxyl terminated polybutadiene) and different diisocyanates (2,4-tolylene diisocyanate, 1,4-phenelene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate and 4,4′-methylenebis(cyclohexyl)isocyanate) and end capped with N-methylaniline. The polymerization was faster with aromatic isocyanates than with aliphatic isocyanates. The effect of imide content on the thermal and mechanical properties was studied. The poly(urethane-imide)s were characterized by FTIR, GPC, TGA and for dynamic and static mechanical properties. Weight average molecular weight (Mw) of the polymers did not vary significantly with change in –NCO/–OH ratio where as number average molecular weight (Mn) increased with increasing –NCO/–OH ratio, correspondingly, the dispersity (PD) decreased. Polymers with higher hard segment content exhibited higher glass transition temperature. The thermal stability of the PU was found to increase significantly by the introduction of imide component.

The thermal dissociation of phenol-blocked toluene diisocyanate crosslinkers

Abstract Several toluene diisocyanates blocked with various substituted phenols were prepared. They were characterized by elemental analysis, infra-red and 1 H nuclear magnetic resonance spectroscopy. The deblocking temperatures were determined by use of infra-red spectroscopy and by carbon dioxide evolution methods. The thermal stability of the blocked isocyanate was less for the ortho -substituted phenols than for the para isomers. Dissociation temperatures were also reduced by electron-withdrawing groups. The dissolution temperatures of the adducts were determined in propylene glycol, poly(ethylene glycol) 400 and hydroxyl-terminated poly(butadiene).

Synthesis of poly(urethane-imide) using aromatic secondary amine-blocked polyurethane prepolymer

A set of poly(urethane-imide)s were prepared using blocked Polyurethane (PU) prepolymer and pyromellitic dianhydride (PMDA). The PU prepolymer was prepared by the reaction of polyether glycol and 2,4-tolylene diisocyanate, and end capped with N-methyl aniline. The PU prepolymer was reacted with PMDA until the evolution of carbon dioxide ceased. The effect of tertiary amine catalysts, organo tin catalysts, solvents, and reaction temperature were studied and compared with the poly(urethane-imide) prepared using phenol-blocked PU prepolymer. N-methyl aniline blocked PU prepolymer gave a higher molecular weight poly(urethane-imide) at a lower reaction temperature in a shorter time. Amine catalysts were found to be more efficient than organo tin catalysts. The reaction was favorable in particular with N-ethylmorpholine and diazabicyclo(2.2.2)octane (DABCO) as catalysts, and dimethylpropylene urea as a reaction medium. The poly(urethane-imide)s were characterized by FTIR, GPC, TGA, and DSC analyses. The molecular weight decreased with an increase in reaction temperature. The thermal stability of the PU was found to increase by the introduction of imide component.

Synthesis and properties of imidazole-blocked diisocyanates

Imidazole-, 2-methylimidazole- and benzimidazole-blocked hexamethylene diisocyanate and isophorone diisocyanate have been prepared and characterized by elemental analyses, IR and NMR spectroscopy. The structure–property relationship of these adducts has been established by reacting with hydroxyl-terminated polybutadiene (HTPB). The cure rate of the adduct increases from the imidazole to 2-methylimidazole and to the benzimidazole-blocked adduct. Also, the cure rate of the adducts based on hexamethylene diisocyanate is higher than those based on isophorone diisocyanate. Simultaneous TGA/DTA results also confirm this trend. The gas chromatogram of the imidazole-blocked isocyanate confirms that the thermolysis products are blocking agent and isocyanate. The solubilities of the adducts have been measured in polyether and hydrocarbon polyols: the 2-methylimidazole and benzimidazole-blocked hexamethylene diisocyanate adducts show higher solubility than the rest. © 1999 Society of Chemical Industry

Synthesis and properties of aromatic secondary amine‐blocked isocyanates

N-Methylaniline-, diphenylamine-, and N-phenylnaphthylamine-blocked toluene diisocyanates (TDI) were prepared and characterized by IR, NMR spectroscopy, and nitrogen content analyses. The structure–property relationship of these adducts was established by reacting with hydroxyl-terminated polybutadiene (HTPB). The cure rate of the adduct increases from the N-phenylnaphthylamine- to diphenylamine- and to N-methylaniline-blocked TDI adduct. Simultaneous TGA/DTA results also confirm this trend, and the thermal stability of the adduct decreases in the following order: N-phenylnaphthylamine–TDI > diphenylamine–TDI > N-methylaniline–TDI. The gas chromatogram of the amine-blocked isocyanate confirms that the thermolysis products are the blocking agent and isocyanate. The solubilities of the adducts were carried out in polyether, polyester, and hydrocarbon polyols, and it was found that the N-methylaniline–TDI adduct shows higher solubility than the rest and also found that the polyester polyol shows higher solvating power against the adducts than the polyether and hydrocarbon polyols.

Structure–property relationship of blocked diisocyanates: synthesis of polyimides using imidazole-blocked isocyanates

Imidazole, 2-methylimidazole and benzimidazole-blocked aromatic and aliphatic diisocyanates have been prepared and polymerized with pyromellitic dianhydride in the presence of a basic catalyst. The polymers are characterized with FTIR, 1H NMR and 13C NMR spectroscopy and GPC, DSC and TGA. The structure–property relationship of blocked diisocyanates are discussed in terms of molecular weight of the polyimides obtained. Considering the blocking agent, GPC results show that the benzimidazole blocked adduct yields higher molecular weight polymer than the 2-methylimidazole-blocked adduct which, in turn, yields higher molecular weight polymer than the imidazole-blocked adduct. Considering the structure of the isocyanate, the molecular weight of polymer increases from isophorone diisocyanate to hexamethylene diisocyanate and to toluene diisocyanate (TDI). DSC traces of the polymers derived from TDI show glass transitions (Tg) in the temperature range 152–180 °C and the values increase from the polymer based on imidazole-blocked TDI to 2-methylimidazole-blocked TDI and to benzimidazole-blocked TDI. © 2000 Society of Chemical Industry

The Thermal Dissociation of Phenol-Blocked Toluene Diisocyanate Crosslinkers

Abstract The thermal dissociation reaction of different phenol-blocked toluene diisocyanate crosslinkers has been studied by the use of differential scanning calorimetry. It was found that dissociation occurs after melting of the adduct. The dissociation reaction rate constants, activation energies, and the heat of reaction values are reported. Adducts with orthosubstituted phenols dissociate at a faster rate than those with para isomers. The regeneration of isocyanate functionality was identified by an infrared spectrophotometer.

Synthesis and properties of imidazole-blocked toluene diisocyanates

Imidazole-, 2-methyl imidazole-, and benzimidazole-blocked toluene diisocyanates (TDI) were prepared and characterized by elemental analysis, IR, and NMR spectroscopy. Simultaneous TGA/DTA results showed that the thermal stability of the adduct decreases in the following order: imidazole-TDI > 2-methylimidazole-TDI > benzimidazole-TDI. Gelation test involving imidazole-blocked adducts and hydroxyl-terminated polybutadiene were also carried out. The cure rate of the adduct increases from the imidazole- to the 2-methylimidazole- and to the benzimidazole-blocked adduct. It is also found that the benzimidazole-blocked adduct shows better solubility in the polyols.

Synthesis of poly(urethane-imide): Effect of solvents with and without basic nitrogen atom and other parameters on the imide formation reaction between blocked-isocyanate prepolymers and pyromellitic dianhydride

N‐Methylaniline‐ and 2‐Butanone oxime‐blocked isocyanate prepolymers were prepared and their reaction with pyromellitic dianhydride (PMDA) was studied with a view to understand the effect of different parameters like solvents, temperature, blocking agents and deblocking catalysts [diazabicyclo 2.2.2 octane, (DABCO) and dibutyltin dilaurate, (DBTDL)] on the poly(urethane‐imide) formation reaction. The reactions were followed by the carbon dioxide evolved during the imidization reaction. The effect of each individual parameter was studied with the reaction time and GPC data. It was found that the reactions proceeded at a faster rate in hexamethyl phosphoric acid triamide (HMPA), a solvent having basic nitrogens, than in mesitylene. Also, in HMPA, it was found that the molecular weights (Mw) of the polymers increased with an increase in temperature up to 125°C and then decreased, whereas in mesitylene, it was found that there was no appreciable change in molecular weight up to 150°C. Of the two blocked isocyanate prepolymers studied, 2‐butanone oxime‐blocked prepolymer undergoes completion of reaction with anhydride rapidly. Among the two distinct types of deblocking catalysts tried, in the solvent HMPA, the tertiary amine showed no catalytic activity, while the organotin compound showed catalytic activity. In mesitylene, however, the effect of the catalysts on the title reaction was just the opposite. The polydispersity of the polymers was found to be relatively narrow in all cases.

Catalysis of Blocked Isocyanate-Hydroxyl-Terminated Polybutadiene Cure Reaction

The catalytic activity of three tertiary amines and three organotin compounds in the cure reaction of blocked isocyanate with hydroxyl-terminated polybutadiene was investigated. It was found that the steric factor determines the catalytic activity of the compound. The tin compounds showed higher catalytic activities than the amine compounds. The deblocking catalytic activity of the amine and tin compounds was confirmed by the identification of isocyanate functionality using infrared spectroscopy. The synergistic effect of amine and tin mixed catalysts systems in the deblocking reaction was reported for the first time.