Ganga Radhakrishnan

Modification of the dynamic swelling behaviour of poly(2-hydroxyethyl methacrylate) hydrogels in water through interpenetrating polymer networks (IPNs)

Abstract Interpenetrating hydrogel networks based on poly(vinyl alcohol) (PVA) and 2-hydroxyethyl methacrylate have been synthesized. Water absorption and desorption properties of these hydrogels were analysed extensively. The influence of solutes (urea, potassium iodide, d -glucose, sodium chloride) on equilibrium water content (EWC) of these gels was also studied. Incorporation of PVA into poly(2-hydroxyethyl methacrylate) in the form of an interpenetrating polymer network (IPN) increases the EWC. The existence of different classes of water in this IPN system is shown by water melting curves using differential scanning calorimetry. The morphological features of these films were studied by scanning electron microscopy.

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.

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.

Tetraphenylethane iniferters: Polyurethane‐polystyrene multiblock copolymers through “living” radical polymerization

Toluene diisocyanate-based polyurethane iniferters containing tetraphenyl-ethane groups in between polyurethane blocks were prepared by the reaction of isocyanate-terminated prepolymers and 1,1,2,2-tetraphenyl-1,2-ethanediol. When these iniferters were decomposed in the presence of styrene, polyurethane-polystyrene multiblock copolymers were obtained through a “living” radical mechanism. The effect of changing polyol on the Tg, thermal stability, and molecular weight of polyurethane iniferters as well as block copolymers was studied. The molecular weight of the block copolymers increased with increasing both polymerization time and conversion.

Determination of hexavalent chromium by on-line dialysis ion chromatography in a matrix of strong colourants and trivalent chromium.

Hexavalent chromium detection in the presence of a high load of colourants without any false positive and in-procedure oxidation of Cr(III) is an important area of study. Colourants are a class of interfering substances in many spectroscopic analyses and chromatographic separations and detection. A purification method using an on-line dialysis technique for ion chromatography (IC) has been developed to remove water-soluble anionic dyes and particulate colourants and other substances to facilitate Cr(VI) quantification and the method is discussed. The dialysis was optimized with Cr(VI) standard solutions for quantification. The efficacy of the procedure for the removal of anionic dyes and detection of Cr(VI) was checked with a Cr(VI) spiked synthetic preparation containing a water-soluble dye and trivalent chromium. Soluble Cr(VI) extracted with organic dyes from environmental samples was analyzed. The method has a detection limit of 5 microg/l, recovery rate of 100% and analysis time less than 20 min.

Mechanical and Thermal Properties of Networks Prepared from Reactive Poly(urethane‐imide)s and Blocked Polyurethane Prepolymer

Reactive poly(urethane-imide)s with varying functionality were prepared using 4,8-diphenyl-1,5-diazabicyclo(3.3.0)octane-2,3,6,7-tetracarboxylic dianhydride, 4,8-(di-p-phenylol)-1,5-diazabicyclo(3.3.0)octane-2,3,6,7- tetracarboxylic dianhydride and N-methylaniline blocked polyurethane prepolymer (1). The resulting polymers with reactive phenylol groups, pendent in the dianhydride, were treated with 1 to give poly(urethane-imide) networks. The cast films were characterized by FT-IR, TG, static and dynamic mechanical analyses. Thermal stability of the polymers was found to be higher than that of the conventional polyurethane. Higher cross-linking leads to lower damping and improved strength.

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

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.