I. K. Varma

Aliphatic Polyesters: Synthesis, Properties and Applications

The synthesis of aliphatic polyesters by polycondensation and ring-opening polymerization is reviewed. This includes homopolyesters, random, block, graft, star, and hyper-branched (co)polyesters. Recent progress in the synthesis of high molecular weight aliphatic polyesters is described. Specific properties of these polymers are also given. The biomedical and ecological applications of these biodegradable polymers show their technological importance and relevance.

Thermal behaviour of coir fibres

Abstract Thermal characterisation of naturally occurring coir fibres (Cocos nucifera) and modified bristle coir fibres was carried out with dynamic thermogravimetry. Thermogravimetric curves of three varieties of coir fibres (i.e. bristle, mattress and decorticated) were similar, thus indicating no difference in the chemical constituents of these varieties. Treatment of bristle coir fibres with 10% NaOH affected the thermal stability and a higher char yield was obtained. Treatment with acid (10% HCl or acetic acid) had no influence on the thermal behaviour of bristle coir fibres. Surface modification of coir fibres, by treatment with isopropyl triisostearoyl titanate, tolylene diisocyanate and unsaturated polyester resin, resulted in a reduction in weight loss below 150°C (due to absorbed moisture), which indicates that such treatment makes the fibre surface hydrophobic. No decrease in moisture absorption was observed in fibres treated with dichloromethyl vinyl silane or sebacoyl chloride. Structural changes in coir fibres heated isothermally in an air oven at 150, 200 and 250°C for 1h each were followed by FTIR. The major changes which took place could be explained in terms of oxidation, dehydration and depolymerisation of cellulosic components in the fibre. Elemental analysis of various fibre samples showed a reduction in H/C ratio of fibres heated to 250°C.

Enzymatically-modified soy protein part 2: adhesion behaviour

Adhesive properties of soy protein isolated from soy protein concentrate (SPC) and its modification by proteolytic enzymes (such as papain, trypsin, chymotrypsin and pepsin) and urease were investigated on different types of woods (such as rubberwood, Bhutan pine, teakwood and plywood). Adhesive strength and viscosity of native and enzyme modified soy protein were compared with commercially available adhesives using the same types of woods. Papain and urease modified soy protein isolate (SPI) showed better adhesive strength compared to unmodified SPI adhesive on rubberwood, while chymotrypsin modified SPI showed zero adhesive strength. All enzymatically-modified adhesives showed lower viscosity in comparison to unmodified SPI adhesive. Hydrophobicity of the native and modified SPIs was determined by the sodium dodecyl sulfate (SDS) binding method. Chymotrypsin-modified SPI (CSPI) showed maximum value of hydrophobicity followed by papain and trypsin modified SPI. Urease modified SPI showed only slight increase in hydrophobicity with respect to unmodified SPI. Structural changes after hydrolysis of SPI by different enzymes were investigated by FT-IR spectroscopy. The ratio of the intensity of νc=o of carboxyl and amide I or ratio of νc=o of carboxyl and amide II showed maximum value in case of pepsin modified SPI followed by chymotrypsin modified SPI. Papain, trypsin and urease modified SPIs showed only slight increase in the ratio of carboxyl/amide I or amide II.

Curing of bismaleimides: 3. Effect of structure on thermal behaviour of bis(amide-maleimide)

Abstract This paper describes the synthesis and characterization of six bismaleimide resins containing amide linkages in their backbones. The effect of structure on thermal behaviour was investigated by introducing phosphine oxide, fluorene, ether, methylene, m-phenylene and sulphone groups into the backbone. Thermal characterization of these bismaleimides was achieved using differential scanning calorimetry and thermogravimetric analysis. The presence of an electron withdrawing group in the backbone of the bisimide increased the curing temperature and reduced the reactivity of the maleimide bond. Thermal stability of the cured bismaleimide resins depended on their structure and it was found that the phosphorus and fluorene containing bisimide resins gave high char yields.

Effect of structure on thermal behaviour of nadimide resins: 1

Abstract This paper describes the synthesis and characterization of high char yield forming nadimide resins. Ten nadimide end-capped oligomeric resins were prepared by reacting endo-5-norbornene-2,3-dicarboxylic acid anhydride (nadic anhydride), 1,3- bis (3- aminobenzamide ) 9,9- bis (p- aminophenyl ) florene -3,3′,4,4′- benzophenone tetracarboxylic acid dianhydride/pyromellitic dianhydride/2,2-bis(3,4-dicarboxylphenyl)-hexafluoropropane dianhydride. Structural characterization of resins was performed by elemental analysis, FT i.r. and 1 H n.m.r. Thermogravimetric studies revealed a multistep decomposition. Cured resins exhibited very high char yields in the range 63 to 77%.

Thermal characterization of methyl methacrylate-alkyl methacrylate copolymers

Abstract Several copolymers of methyl methacrylate (MMA) with lauryl methacrylate (LMA) or cetyl methacrylate (CMA) were prepared in bulk at 70°C using 1% benzoyl peroxide as initiator. The copolymer compositions were determined by 1 H nuclear magnetic resonance (NMR) spectroscopy from the peak areas at δ = 3.59 ppm (due to -OCH 3 protons of MMA) and at δ = 3.93 ppm (due to -OCH 2 - protons of LMA and CMA). The monomer reactivity ratios were found to be r 1 = 0.25 and r 2 = 0.63 for MMA (M 1 ) and LMA copolymers and r 1 = 0.65 and r 2 = 0.71 for MMA and CMA copolymers. A multistep degradation of copolymers was indicated by DSC and TG studies. Degradation in the temperature range 200–300°C was influenced by the copolymer composition. An increase in the MMA content of the copolymer resulted in a decrease in weight loss in this region. Total loss in weight was observed around 400°C. Pyrolysis gas chromatographic studies of homopolymers indicated a loss of monomer during the pyrolysis of polymer.

Thermal Behaviour of Polymers Based on Nadimides

Carbocationic polymerization of N-ortho/meta/para tolyl-exo-norbornene dicarboximide (nadimide) was carried out using Pd(II) catalyst. Under similar conditions of polymerization, poly(N-m-tolyl nadimide) showed higher molecular mass compared to poly(N-p-tolyl nadimide) and poly(N-o-tolyl nadimide). Thermal stability of these polymers was evaluated by dynamic thermogravimetry in nitrogen atmosphere. The polymers were stable up to 460°C and lost mass above this temperature in a single step. The characteristic decomposition temperature and char yield of these polymers were higher than the polymers prepared by using ring opening metathesis polymerization. The difference has been attributed to the presence of rigid bicyclic ring structure in these polymers.

The thermal behaviour of blends of trisnadimide with bismaleimide resins

Abstract The thermal behaviour of blends of tris(3-nadimidophenyl)-phosphine oxide (TNI) and bis(4-maleimidophenyl)methane (BMI) was evaluated by using differential scanning calorimetry and thermogravimetry. A decrease in the melting point of BMI resin was observed on addition of TNI. The heat of fusion depended on the blend composition and increased by increasing the BMI content. The exothermic peak temperature (due to curing reaction) in the blends was lower, thereby indicating that curing of these blends can be done at lower temperatures. The overall thermal stability of the blends was only marginally affected by the blend composition.

Thermal Behaviour of Glycidyl Methacrylate Homopolymers and Copolymers

The paper describes the effect of molecular mass and copolymer composition on thermal behaviour of homopolymers and copolymers of glycidyl methacrylate and methyl methacrylate. The polymerisation was done by using group transfer polymerization (GTP) and free radical techniques. A multistep decomposition was observed in polymers prepared by free radical technique indicating the presence of weak linkages in the backbone. Copolymers prepared by GTP had fewer weak sites and degraded in single step by a random chain scission.

Polybenzimidazoles: Thermally Stable Materials

Abstract Polybenzimidazoles were prepared in poly(phosphoric acid) from isophthalic acid (I), terephthalic acid (T), and 3,3′-di-aminobenzidine tetrahydrochloride dihydrate (DAB). Homo-polymers of I, T, and various IT copolymers have been prepared. The polymers were characterized by viscosity, IR spectra, and nitrogen estimation. The effect of copolymer composition on UV and visible spectra, solubility in various solvents, and density was also investigated. The relative thermal stability of the polymers was evaluated by TGA and DTA.