V. N. Denisova

Investigation of stabilizing effectiveness of alkyl(aryl)tin maleates and thioglycolates in the thermal degradation of poly(vinyl chloride)

Abstract Investigations were made on the effects of alkyl(aryl)tin salts of maleic and thioglycolic acids and their esters upon the rate of dehydrochlorination and crosslinking, and on the absorption spectrum of PVC during degradation in vacuum at 190°. It was shown that these stabilizers cause dehydrochlorination of PVC to be eight times less than the rate of polymer degradation in vacuo with removal of HC1. The stabilizers are arranged according to their stabilizing powers. The interaction of the stabilizers with 2-chlorobutane (a model for normal units of PVC) was studied at 180°. According to the rate of this interaction, the compounds are arranged in inverse order compared with that for the stabilizing efficiency. Thermal degradations of the stabilizers themselves were investigated. Experimental data concerning the thermal degradation of PVC in the presence of organo-tin salts were considered from the point of view of simultaneous reactions of the stabilizers with HC1, chloroallylic fragments and normal units of the macromolecules.

Effect of tacticity on thermal degradation of poly(vinyl chloride)

Abstract The tacticity of different samples of PVC suspension has been measured by 13C NMR spectroscopy. The dehydrochlorination of PVC samples under vacuum with continuous removal of HCl by freezing has been studied at 200 °. The values of the effective constants of dehydrochlorination rates of unstable fragments and normal units of PVC, the values of the initial and the stationary rates of degradation and the total concentrations of unstable groups in PVC samples have been obtained. It has been shown that only the contents of isotactic nonads may be compared with the values of the concentrations of unstable fragments in the samples. There is no correlation between the initial rate of PVC degradation and the content of isotactic triads or nonads. A correlation exists between the total concentration of unstable fragments and the initial rate of degradation of PVC samples. The obtained results give evidence that the tacticity of macromolecules has no significant influence on the initial stage of the thermal degradation of PVC and that the branching groups with the chlorine atom near the tertiary carbon atom and the internal chloroallylic fragments may be the main unstable groups of PVC macromolecules.

Investigation of autocatalytic thermal degradation of poly(vinyl chloride) by ESR spectroscopy

Abstract The dehydrochlorination of PVC under vacuum with continuous removal of HCl and in the presence of HCl, has been studied at 200 °C. The dependences of the intensity of the ESR signal of degraded PVC on time of degradation and HCl loss conversion have been obtained. In PVC degradation in the presence of HCl, they have an autocatalytic character. At the same percentage of dehydrochlorination, the spin concentration is significantly more in the PVC degradation in the presence of HCl than with removal of HCl. The conclusion has been made that the formation of paramagnetic centers in degraded PVC is intensified by the presence of HCl. It has been shown that during autocatalytic PVC degradation, H 2 practically does not form. The obtained results are discussed in terms of a theory of the autocatalytic thermal degradation of PVC as a branched chain reaction with degenerate branching of the chain.

Investigation of Fullerenes as High Temperature Stabilizers of Poly(methyl methacrylate) and Polystyrene

Abstract Investigation has been made on the effects of fullerenes C60 and C70 on the degradation of PMMA and PS under helium and oxygen by a DSC method. The dependences of the temperature of the onset of the thermal and thermo-oxidative degradation of the polymers on concentration of C60 and C70 have been obtained. The temperature limits of effective inhibition of the polymers by fullerenes have been determined. The temperature limit depends on the chemical structure of polymer, namely it is considerably greater in the degradation of more stable polymer. In the thermo-oxidative degradation of the polymers with addition of fullerenes, the temperature limit of inhibition of less stable PS is much less and of more stable PMMA is considerably greater than that in the presence of well-known antioxidants. It was concluded that fullerenes are more effective high temperature inhibitors of the thermo-oxidative degradation of PMMA than well-known antioxidants. The suggestion was made that the thermo-oxidative degradation of polymers initiates the oxidation of fullerenes.

Investigation of the Stabilizing Action of Mixtures of Fullerene C60 with Known Antioxidants in the Thermo-oxidative Degradation of Polystyrene

Abstract Investigations have been made on the effects of double mixtures of C60 with well-known antioxidants (amines, phenols, S- and P-containing compounds, Ph3Sb) on the thermo-oxidative degradation of PS by DSC method under oxygen. The influence of mixtures on the temperature of the onset of polymer degradation, T 0, has been studied. The effects of concentration of C60 on the value of the temperature limit of inhibition of PS thermo-oxidative degradation by known antioxidants, T 0 max, have been investigated. It has been shown that mixtures of C60 with Ph3Sb and phenyl-β-naphthylamine have a synergistic effect upon T 0. At a total concentration of 1.4 × 10−2mol/kg, the maximum value of T 0 is observed at a molar C60: compound ratio of 3:4 and 1:2.5 for the mixtures of C60 with Ph3Sb and phenyl-β-naphthylamine, respectively. Addition of C60 to these compounds leads to an increase in T 0 max for Ph3Sb and phenyl-β-naphthylamine. The suggestion was made that in the case of mixtures of C60 with Ph3Sb, the synergistic effect is Associated with different mechanisms of stabilizing action of the components on PS degradation, namely C60 reacts with alkyl and oxygen-containing radicals with the formation of more stable compounds while Ph3Sb decomposes polymeric and fullerene-containing peroxides and hydroperoxides. The decomposition of Ph3Sb was investigated by DSC method under oxygen. The temperature of the onset of Ph3Sb degradation was shown to be 362.5°C. It was concluded that further investigations are necessary for understanding the synergistic action of mixture of C60 with phenyl-β-naphthylamine in the thermo-oxidative degradation of PS.

Poly(propylene glycols) as effective additives to the sol-gel process in fabrication of antireflection coatings onto silica glass

Possibility of obtaining mesoporous silicon dioxide antireflection coatings with low refractive index (1.20–1.277) by using additions of poly(propylene glycols) with various molecular masses in a sol-gel process was examined. It was demonstrated that the optimal concentration of poly(propylene glycols) in the sol, at which a sol-gel process followed by heating of a sample yields a transparent film with a maximum light transmission of 98.3–99.0%, depends on the average molecular mass of the additive.

Preparation of antireflection coatings from silicon dioxide on glass and quartz by the sol-gel method with oligoethers

Antireflection coatings with a low refractive index (1.18–1.23) have been prepared on silicate glass and optical quartz from mesoporous silicon dioxide synthesized by the sol-gel method in the presence of oligoethers. The optimum concentration of the oligoester in the sol is equal to 1.5–2.5 wt %. For the single-layer double-sided coating, the maximum transmission is equal to 99.0% for the silicate glass and 99.9% for quartz.

Mechanism of poly(vinyl chloride) stabilization by mixtures of zinc and calcium carboxylates with various complexing agents

Abstract Investigations were made on the effects of zinc and calcium carboxylates, polyols and other oxygen-containing compounds, nitrogen- and sulphur-containing compounds and of mixtures of zinc calcium carboxylates, zinc carboxylates-complexing agent, calcium carboxylate-complexing agent and of zinc carboxylate-calcium carboxylate-complexing agent upon the rate of dehydrochlorination and crosslinking and on the absorption spectrum of PVC during degradation in vacuum at 180°. The interaction of the stabilizers with 2-chlorobutane (a model for normal units of PVC) was studied at 180°. It was shown that, in the thermal degradation of PVC, zinc carboxylates give synergistic mixtures with compounds having -OH, -SH or -NH groups. In the thermal degradation of PVC in the presence of mixtures of zinc carboxylates with polyols, there are exchanges between chloro-containing groups of PVC and carboxylic groups of salt and alcohol residue. Zinc salts also catalyze the interaction of polyols with double (particularly conjugated double) bonds of degraded PVC. The investigated compounds do not form synergistic mixtures with calcium carboxylates. The triple mixtures of zinc and calcium carboxylates with complexing agents are more effective stabilizers of PVC than the binary mixtures zinc carboxylate-calcium carboxylate and zinc carboxylate-complexing agent. The mechanism of synergistic interaction in PVC stabilization by these mixtures are discussed.

Deposition of thin antireflection coatings based on mesoporous silicon dioxide by the sol-gel method in the presence of carbochain polymers and statistical copolymers

Antireflection coatings with a low refractive index (1.25–1.34) were prepared from mesoporous silicon dioxide by using carbochain polymers and statistical copolymers, instead of ionogenic and noionogenic surfactants and amphiphilic block-copolymers in a sol-gel process. The optimal concentration of the organic additive in the sol, at which a transparent film with the maximum antireflection effect is formed in the sol-gel process followed by heating of a sample, was determined.

Influence of the synthesis conditions of emulsion poly(methyl methacrylate) on the surface structure of the specimens

The surface structure of poly(methyl methacrylate) specimens prepared by emulsifier-free emulsion polymerization of methyl methacrylate was examined in relation to the synthesis conditions (pH of the medium, initiator concentration, and addition of organosilicon compounds).