K. Kishore

Flame retardant polyphosphate esters: 2. Condensation polymers of bisphenol A with alkyl phosphorodichloridates: synthesis, characterization and thermal studies

Polyphosphate esters were synthesized by the solution polycondensation of bisphenols with aryl phosphorodichloridates. The polymers were characterized by i.r. and 1H, 13C and 31P n.m.r. spectroscopy. The molecular weights were determined by end group analysis using 1H and 31P n.m.r. spectral data. The thermal stability of the polymers was analysed by thermogravimetry.

Synthesis and characterization of photo-crosslinkable main-chain liquid-crystalline polymers containing bis(benzylidene)cycloalkanone units

Abstract A series of new photo-crosslinkable main-chain liquid-crystalline polymers containing bis(benzylidene)cycloalkanone units have been studied. These units in the polymers function as mesogens as well as photoactive centres. Polyesters with three different bis(4-hydroxybenzylidene)cycloalkanones corresponding to three cycloalkanones, namely cyclopentanone, cyclohexanone and cycloheptanone, have been prepared. Three dicarboxylic acids with ether linkages, which were derived from oligoethylene oxides, namely triethylene glycol, tetraethylene glycol and pentaethylene glycol, have been used as spacers in these polymers. Polymerization was carried out by both solution and interfacial polycondensation; the latter method gave high-molecular-weight polymers. Structural characterizations were done by ultra-violet, infra-red and 1 H nuclear magnetic resonance spectroscopy. Liquid-crystalline properties were studied by differential scanning calorimetry and polarized-light optical microscopy. These polymers show a nematic mesophase. Liquid-crystalline transition temperatures were correlated with polymer structure. The decrease in transition temperature with increase in cycloalkanone ring size was explained in terms of the change in geometrical anisotropy of bis(benzylidene)cycloalkanone units. MNDO (modified neglect of differential overlap) calculations were performed on the model compounds, bis(4-acetyloxybenzylidene)cycloalkanones, to elucidate the geometrical variation of the mesogenic units with cycloalkanone ring size. Studies of photolysis reveal the two kinds of photoreactions that proceed in these polymer systems, namely photoisomerization and photo-crosslinking. The former reaction disrupts the parallel stacking of the chromophores and is reflected as an increase in the ultra-violet spectral intensity. The favourability of these two reactions depends on the mobility of the polymer chains. When the photolysis was done below T g , photo-crosslinking dominates over photoisomerization. Above T g , photoisomerization is followed by photo-crosslinking. The photo-sensitivity of the polymers decreases with increase in size of the cycloalkanone ring.

A novel approach to structure-flammability correlation in polyphosphate esters

The relationship between the structure and flammability of a number of polyphosphate esters has been examined. The conventional correlation of char residue with limiting oxygen index was found to be unproductive in these polymers, giving insight into the importance of gas-phase reactions in addition to condensed-phase reactions in determining their flammability. A novel approach was sought in understanding the structure-flammability relationships of these polymers relating thermal stability, phosphorus content and limiting oxygen index. An empirical relationship has been derived amongst these three parameters.

Synthesis, characterization and reactivity of polymeric peroxides

Polymeric peroxides constitute an important class of compounds. There are two main groups of these materials: (i) those formed from vinyl monomers and oxygen, and (ii) those formed from aldehydes and ketones by reaction with oxidizing agents such as hydrogen peroxide. The latter group comprises oligomeric peroxides, such as the commercial methylethyl ketone peroxide, which are used chiefly as initiators and crosslinking agents.

Novel flame retardant polyphosphoramide esters

Abstract Several new polyphosphoramide esters have been synthesized by solution polycondensation of N,N′-bis(p-chloroformylphenyl)N″-phenyl phosphoric triamide with various aromatic diols. The polymers were characterized by i.r., 1H, 13C and 31P n.m.r. spectroscopy and by their inherent viscosity. Thermo-oxidative stability and flammability of the polymers were evaluated by thermogravimetry and limiting oxygen index values respectively.

Mechanistic studies on the action of ammonium phosphate on polymer fire retardancy

The mechanism of fire retardant action of mono- and diammonium phosphates on polystyrene has been investigated. Ignition delay and mass burning rate studies reveal that the phosphates bring down both parameters considerably though to different extents. This has been adequately explained on the basis of the existing combustion models and physicochemical behavior of the material. Similar to their action on cellulosic materials, phosphates bring about fire retardancy in polystyrene via char formation. This is suggested to occur through a series of processes consisting of initial peroxide formation, decomposition to alcohols and aldehydes, formation of alkyl-phosphate esters, dehydration and subsequent char formation. Infrared and mass spectral studies support this mechanism.

Kinetics of poly(styrene peroxide) initiated photopolymerization of methyl methacrylate

Abstract This is a first comprehensive study on the photoinitiating capability of a vinyl polyperoxide. Polymerization of methyl methacrylate photoinitiated by poly(styrene peroxide) (PSP) at 30°C has been shown to follow the usual kinetic behaviour with respect to the initiator, monomer and light intensity for a PSP concentration of 0.0021–0.034 mol-equiv l−1. At higher concentrations of PSP (0.046–0.31 mol-equiv l−1) although kinetic order with respect to the monomer and light intensity follows usual kinetics the order with respect to PSP was found to be very low (0.21), which has been attributed to the occurrence of primary radical termination which has been quantified in terms of the primary radical termination parameter (δ/Σ). The initiator efficiency was found to be very low (0.06–0.07), it has been attributed to the competing unimolecular decomposition of alkoxy radicals with primary radical initiation. The presence of PSP segments in the poly(methyl methacrylate) backbone was confirmed by 1H nuclear magnetic resonance.

SYNTHESIS AND SPECTRAL STUDIES OF POLYAMIDE-PHOSPHATE ESTERS FROM PHOSPHINE-OXIDE-CONTAINING DIOLS WITH ARYL PHOSPHORODICHLORIDATES AND THEIR THERMAL AND FLAMMABILITY BEHAVIOUR

Polyamide-phosphate esters were synthesized by interfacial polycondensation of aryl phosphorodichloridates with the diols of phenoxaphosphine and phosphine oxide in the presence of a phase-transfer catalyst. The polymers were characterized by infra-red and 1H, 13C and 31P nuclear magnetic resonance (n.m.r.) spectroscopy. The molecular weights were determined by end-group analysis using 31P n.m.r. spectral data. The phenoxaphosphine-containing polymers showed superior thermostability and flame retardancy over the phosphine-oxide-containing polymers.

Nucleation parameters for polymer crystallization from non-isothermal thermal analysis

Differential scanning calorimetry (DSC) has been used to obtain kinetic and nucleation parameters for polymer crystallization under a non-isothermal mode of operation. The available isothermal nucleation growth-rate equation has been modified for non-isothermal kinetic analysis. The values of the nucleation constant (Kg) and surface free energies (σ, σe) have been obtained for i-polybutene-1, i-polypropylene, poly(L-lactic acid), and polyoxymethylene and are compared with those obtained from isothermal kinetic analysis; a good agreement in both is seen.

APPLICATION OF POLYSTYRENE PEROXIDE AS A CURATIVE IN COATING AND MOLDING COMPOSITIONS

An attempt has been made to demonstrate the applicability of poly(styrene peroxide) (PSP) as a curative in coating and molding compositions and to compare it with a conventional curative benzoyl peroxide (Bz2O2). A typical coating formulation leads to better adhesion on aluminium and glass surfaces with PSP as curative than with Bz2O2. Similarly, a typical molding formulation, prepolymerized and cured with PSP under compression at 90 °C, resulted in a colourless, defect-free molding, having better impact and tensile strengths than when using the conventional curative Bz2O2, which afforded a brown coloured, brittle product.