Thermal degradation of copolymers of 36Cl-vinyl chloride and methyl methacrylate

The degradation of copolymers of vinyl ³⁶Cl-chloride and methyl methacrylate has been studied using film samples, slow heating rate and high vacuum conditions. Volatilization has been followed using thermal volatilization analysis and radioactive assay of methyl chloride and hydrogen chloride. By carrying out duplicate experiments with and without an ice trap at ? 100°, it is possible to measure methyl chloride alone and both products, respectively, so that each product can be estimated. Yields have been found to agree well with those predicted from sequence distribution calculations. Some differences in behaviour compared with earlier work using powder samples and nitrogen flow conditions are discussed.     

Thermal degradation of poly(vinyl bromide), vinyl bromide-methyl methacrylate copolymers,and poly(vinyl bromide)-poly(methyl methacrylate) blends

Degradation behavior has been compared for PVB, five VB-MMA copolymers which span the composition range, PMMA, and PVC by using thermogravimetry in dynamic nitrogen and thermal volatilization analysis (TVA) under vacuum for programmed heating at 10°C/min. Volatile products have been separated by subambient TVA and identified. PVB is substantially less stable than PVC but shows inmost respects analogous degradation behavior. The introduction of VB into the PMMA chain leads to intramolecular lactonization with release of methyl bromide at temperatures a little above 100°C; after this reaction is complete, however, the polymer is more stable toward volatilization than PMMA. Copolymers with moderate and high VB contents also lose hydrogen bromide. Carbon dioxide is a significant product at intermediate compositions. The variation of product distribution with copolymer composition is discussed in relation to the several reactions involved and comparisons are made with VC-MMA copolymers. PVB-PMMA blends snow some features of degradation behavior in common with the PVC-PMMA system but also very important differences. The effect of PVB is only to stabilize the PMMA; the mechanism is discussed. The role of PVB as an additive and VB as a comonomer for fire-retardant PMMA compositions is briefly considered in relation to earlier studies.     

Thermal degradation of vinyl chloride homo- and copolymers in solution

The results of investigations on the thermal degradation of vinyl chloride (VC) homo- and copolymers in dilute and concentrated solutions are presented. Depending upon the nature of the solvent, the thermal degradation of VC polymers in solvents which do not react with the macromolecules may be accelerated or retarded compared with degradation in the solid phase. The effects are explained from the standpoint of the influence of solvation effects, i.e. specific (donor-acceptor) and non-specific (Van der Walls) interactions between macrochains and solvent molecules. Specific interactions between the solvent and the abnormal structures present in the macrochains of VC polymers bring about either a reduced or an increased rate of polymer dehydrochlorination, depending upon the basicity of the solvent, whilst non-specific solvation always tends to intensify the degradation of polymeric molecules due to the increased small-scale dynamics of macromolecules.     

The thermal degradation of copolymers of vinyl acetate with methyl methacrylate and other monomers

The thermal degradation of copolymers of vinyl acetate with methyl methacrylate, styrene and ethylene has been investigated using thermal volatilization analysis and thermogravimetry, together with analysis of volatile and involatile degradation products. All three copolymer systems show some of the features characteristic of the homopolymers of the monomers concerned. There is evidence, however, for an intramolecular lactonization process in VA—MMA copolymers, involving reaction of adjacent VA and MMA units with elimination of methyl acetate. This reaction occurs less readily than the analogous process in vinyl chloride—MMA copolymers. Mechanisms of the various degradation reactions are discussed.     

Thermal degradation studies in poly(vinyl chloride)/poly(methyl methacrylate) blends

The miscibility, morphology, and thermal properties of poly(vinyl chloride) (PVC) blends with different concentrations of poly(methyl methacylate) (PMMA) have been studied. The interaction between the phases was studied by FTIR and by measuring the glass transition temperature (T_g) of the blends using differential scanning calorimetry. Distribution of the phases at different compositions was studied through scanning electron microscopy. The FTIR and SEM results show little interaction and gross phase separation. The thermogravimetric studies on these blends were carried out under inert atmosphere from ambient to 800 °C at different heating rates varying from 2.5 to 20 °C/min. The thermal decomposition temperatures of the first and second stage of degradation in PVC in the presence of PMMA were higher than the pure. The stabilization effect on PVC was found most significant with 10 wt% PMMA content in the PVC matrix. These results agree with the isothermal degradation studies using dehydrochlorination and UV-vis spectroscopic results carried out on these blends. Using multiple heating rate kinetics the activation energies of the degradation process in PVC and its blends have been reported.     

Photocatalytic degradation of methyl methacrylate copolymers

The photolytic and photocatalytic degradation of the copolymers poly(methyl methacrylate-co-butyl methacrylate) (MMA-BMA), poly(methyl methacrylate-co-ethyl acrylate) (MMA-EA) and poly(methyl methacrylate-co-methacrylic acid) (MMA-MAA) have been carried out in solution in the presence of solution combustion synthesized TiO₂ (CS TiO₂) and commercial Degussa P-25 TiO₂ (DP 25). The degradation rates of the copolymers were compared with the respective homopolymers. The copolymers and the homopolymers degraded randomly along the chain. The degradation rate was determined using continuous distribution kinetics. For all the polymers, CS TiO₂ exhibited superior photo-activity compared to the uncatalysed and DP 25 systems, owing to its high surface hydroxyl content and high specific surface area. The time evolution of the hydroxyl and hydroperoxide stretching vibration in the Fourier transform-infrared (FT-IR) spectra of the copolymers indicated that the degradation rate follows the order MMA-MAA > MMA-EA > MMA-BMA. The same order is observed for the rate coefficients of photocatalytic degradation. The photodegradation rate coefficients were compared with the activation energy of pyrolytic degradation. In degradation by pyrolysis, it was observed that MMA-BMA was the least stable followed by MMA-EA and MMA-MAA. The observed contrast in the order of thermal stability compared to the photo-stability of these copolymers was attributed to the two different mechanisms governing the scission of the polymer and the evolution of the products.     

Thermal degradation of copolymers of methyl methacrylate and 2,6-dimethoxycarbonyl-1,6-heptadiene

The thermal degradation under vacuum of copolymers of methyl methacrylate and 2,6-dimethoxycarbonyl-1,6-heptadiene of different compositions has been investigated. It has been found that the presence in the polymer chains of small amounts of cyclic structural units from the diene monomer considerably reduces the amount of degradation which occurs in poly(methyl methacrylate) at temperatures lower than 300°C. On the basis of the results of the analysis of the degradation products, a mechanism is suggested which accounts for this effect.     

Thermal stability of poly(acryloyl chloride) homopolymer and copolymers of acryloyl chloride with methyl methacrylate

The thermal stabilities of poly(acryloyl chloride) homopolymer and copolymers of acryloyl chloride with methyl methacrylate covering the entire composition range were studied by thermogravimetric analysis. At each extreme of the composition range incorporation of comonomer units results in a copolymer which is less stable than the PMMA homopolymer. The activation energies of the decomposition of the copolymers were calculated using the Arrhenius equation and found to decrease from 32.2 to 12.5 kJ mol^?1 as acryloyl chloride concentration of the copolymer increases, indicating that the copolymers of higher acryloyl chloride concentration should easier decompose than other copolymers. The reactivity ratios of the copolymer were calculated and found to ber ₁(AC)=0.2±0.02 andr ₂(MMA)=0.9±0.1.     

Friedel-Crafts acylation reactions in copolymers of methyl methacrylate and styrene and in mixtures of the homopolymers

In the presence of SnCl₄ in 1,2-dichloroethane solution, copolymers of styrene and methyl methacrylate undergo a Friedel-Crafts acylation reaction between the ester groups and the ortho position of adjacent styrene units to form a partial ladder polymer. This has been confirmed by infrared and ultraviolet spectral analysis and by observing the influence of substituted styrenes on the rate of the reaction. A similar reaction can be induced to occur between polystyrene and poly(methyl methacrylate). Thermal analysis measurements demonstrate that the degradation properties of copolymers of styrene and methyl methacrylate are profoundly changed by this treatment.     

Thermal degradation of mixtures of poly(methyl methacrylate) and silver acetate

The degradation behavior of silver acetate—PMMA blends at salt/polymer ratios of 1:1, 1:5, and 1:10 has been studied by using thermal volatilization analysis (TVA) as the principal technique. Degradation of the salt has also been examined; it gives a variety of products best explained by a series of reactions resulting from an initial cleavage of CH₃COO. radicals and silver atoms. Silver acetate, when present with PMMA during degradation, results in a severe destabilization of the polymer, which breaks down to monomer at a high rate at temperatures as low as 200°C. This effect is explained by diffusion of radicals from silver acetate decomposition into the polymer phase, in which they initiate chain scission and depolymerization.     

Conducting graft copolymers of pyrrole and thiophene with random copolymers of methyl methacrylate and 3-methylthienyl methacrylate

Random copolymers of 3-methyl thienylmethacrylate and methyl methacrylate were synthesized via free radical polymerization. Electro-copolymerizations of random copolymers with thiophene and/or pyrrole were carried out in acetonitrile-tetrabutylammonium tetrafluoroborate (TBAFB), water-p-toluene sulfonic acid (PTSA) solvent-electrolyte couples. Oxidative polymerization of thiophene functionalized random copolymer was also achieved by constant current electrolysis and chemical polymerization. The characterizations were done by conductivity measurements, cyclic voltammetry (CV), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermal gravimetry analysis (TGA), scanning electron microscopy (SEM).     

Thermal degradation of vinylidene chloride/vinyl chloride copolymers in the presence of N-substituted maleimides

As a consequence of their excellent barrier properties vinyl chloride/vinylidene chloride copolymers have long been prominent in the flexible packaging market. While these polymers possess a number of superior characteristics, they tend to undergo thermally- induced degradative dehydrochlorination at process temperatures. This degradation must be controlled to permit processing of the polymers. Three series of N-substituted maleimides (N-alkyl-, N-aralkyl, and N-aryl) have been synthesized, characterized spectroscopically, and evaluated as potential stabilizers for a standard vinyl chloride/vinylidene chloride (85 mass%) copolymer. As surface blends with the polymer, these compounds are ineffective as stabilizers. However, significant stabilization may be achieved by pretreatment of the polymer with N-substituted maleimides. The most effective stabilization of the polymer is afforded by N-aralkyl- or N-arylmaleimides, most notably, N-benzylmaleimide and N-p-methoxyphenylmaleimide.     

Thermal degradation and flame retardance in copolymers of methyl methacrylate with diethyl(methacryloyloxymethyl)phosphonate

Methyl methacrylate (MMA) has been free radically copolymerized, both in bulk and in solution, with diethyl(methacryloyloxymethyl)phosphonate (DEMMP), to give polymers which are significantly flame retarded when compared with PMMA, as indicated by the results of limiting oxygen index (LOI) measurements, UL 94 tests, and the results of cone calorimetric experiments. The physical and mechanical properties of the copolymers are similar to those of PMMA, except that the bulk copolymers are slightly crosslinked, and are better than those of PMMA flame retarded to a similar extent by some phosphate and phosphonate additives. Examination of the some of the gaseous products of pyrolysis and combustion, and of chars produced on burning, show that flame retardation occurs in the copolymers by both a condensed-phase and a vapour-phase mechanism. The condensed-phase mechanism is shown to involve generation of phosphorus acid species followed by reaction of these with MMA units giving rise to methacrylic acid units. The methacrylic acid units subsequently form anhydride links, which probably impede depolymerization of the remaining MMA sequences, resulting in evolution of less MMA (the major fuel when MMA-based polymers burn). By undergoing decarboxylation, leading to interchain cyclisation and, eventually, to aromaticisation, the anhydride units are probably also the principal precursors to char.     

Thermal behaviour of copolymers of methyl methacrylate and 2-ethylhexyl methacrylate

Five copolymer samples containing different mole fractions of methyl methacrylate (MMA) and 2-ethylhexyl methacrylate (EHMA) were prepared by bulk polymerisation at 70°C using 0.2% benzoyl peroxide as an initiator. The copolymer composition was determined by¹H NMR spectroscopy. Molecular weight of copolymers was determined by gel permeation chromatography and viscosity measurements. Thermogravimetric experiments were conducted to evaluate activation energy for the degradation of copolymers. Two to four reaction stages for the weight loss were observed in the copolymers. A decrease in thermal stability was observed by an increase in EHMA content.     

Thermal degradation of phenyl methacrylate-methyl methacrylate copolymers

The degradation behaviours of poly(phenyl methacrylate), four phenyl methacrylate-methyl methacrylate copolymers which span the composition range, and poly(methyl methacrylate) have been compared by using thermogravimetry in dynamic nitrogen and thermal volatilisation analysis (TVA) under vacuum, with programmed heating at 10°C/min. Volatile products have been separated by subambient TVA and identified and the cold ring fraction and partially degraded polymer have been examined by ir spectroscopy. Poly(phenyl methacrylate) resembles poly(methyl methacrylate) in degrading completely to monomer. Copolymers of phenyl methacrylate and methyl methacrylate are more stable than the homopolymers. On degradation, the major products are the two monomers. Minor products from all the copolymers include carbon dioxide, dimethylketene, isobutene and formaldehyde. Copolymers with low and moderate phenyl methacrylate contents show the formation of anhydride ring structures in the cold ring fraction and partially degraded copolymer, together with small amounts of methanol in the volatile products. Carbon dioxide is a more significant product at lower phenyl methacrylate contents.The mechanism of degradation is discussed.     

Preparation and photolysis of poly-p-methoxyacrylophenone and its copolymers with styrene and methyl methacrylate

Poly-p-methoxyacrylophenone (PPMeOAP) and its copolymers with styrene (PMe-OAP–S) and with methyl methacrylate (PMeOAP–MMA) were prepared. The photolysis in solution with 313 and 366 nm radiation was followed viscometrically. In solvents such as chlorobenzene and ethyl benzoate, random main-chain scission from n–π^* excited triplet state occurs. The lowest excited triplet state in formic acid and in ethylene chlorhydrin is of the character π–π^*, from which no main-chain scission occurs. In solvents in which destruction occurs, the main-chain scission is retarded by triplet quenchers, such as naphthalene, 2,5-dimethyl-2,4-hexadiene, and biphenyl. Quenching experiments indicate that the lifetime for the excited triplet state of PPMeOAP is 25 times that for polyacrylophenone. In PMeOAP–MMA copolymers, quantum yields of main-chain scissions were lower and lifetimes of excited triplets were longer than in PPMeOAP, due to hindered intramolecular photoreaction.     

Pyrolysis—gas chromatography of methyl methacrylate—styrene and methyl methacrylate—α-methylstyrene copolymers

The pyrolysis—gas chromatographic behaviour of methyl methacrylate copolymers with styrene or α-methylstyrene was investigated with a Curie-point pyrolyzer. Monomer yield from each copolymer was very high as a result of the high probability of unzipping. Though only small quantities of dimers and or trimers are formed on the pyrolysis of two copolymers, they reflect the sequence distribution of copolymers. Under some assumption, the run number of each copolymer is calculated using the amounts of dimer and or trimer formed.     

Photodegradation in solution of copolymers of methyl vinyl ketone and methyl isopropenyl ketone with methyl methacrylate

Copolymers of methyl vinyl ketone (MVK) and methyl isopropenyl ketone (MIK) with methyl methacrylate (MMA), have been prepared covering the whole composition range. Reactivity ratios have been estimated as follows: MMA/MVK, r_MMA = 0·63 ± 0·2, r_MVK = 0·53 ± 0·2; MMA/MIK, r_MMA = 0·98 ± 0·2, r_MIK = 0·69 ± 0·2. Number average molecular weights have been measured during the course of photodegradation under 253·7 nm radiation in methyl acetate solution and rates of chain scission calculated. In each system the copolymers are less stable than the corresponding homopolymers, the rate passing through a maximum at 20–30% ketone content. These results have been discussed from a mechanistic point of view.     

Thermal degradation of copolymers from vinyl acetate and vinyl alcohol

The thermal degradation of poly(vinyl acetate) (PVA), poly(vinyl alcohol) (PVAL), vinyl acetate-vinyl alcohol (VAVAL), vinyl acetate-vinyl-3,5-dinitrobenzoate (VAVDNB) and vinyl alcohol-3,5-dinitrobenzoate (VALVDNB) copolymers have been studied using differential thermal analysis (DTA) and thermogravimetry (TG) under isothermal and dynamic conditions in nitrogen. Thermal analysis indicates that PVA and PVAL are thermally more stable than VAVAL copolymers, being PVAL the most stable polymer. The presence of small amounts of vinyl-3,5-dinitrobenzoate (VDNB) in PVA or PVAL produces a marked decrease in the thermal stability of both homopolymers, being VALVDNB copolymers the less stable materials. The apparent activation energy of the degradative process was determined by the Kissinger and Flynn-Wall methods which agree well.     

Thermal degradation of copolymers of styrene and 4-nitrostyrene

The thermal degradation of styrene-4-nitrostyrene copolymers (SNS) has been studied using differential thermal analysis (DTA) and thermogravimetry (TGA) under isothermal and dynamic conditions in dynamic nitrogen. The apparent activation energy of the degradative process was determined following several methods of thermogravimetric analysis. The stability decreases as the nitrostyrene content in the copolymer increases. Fourier-transform infra-red spectroscopy has been used to analyze the degradation products at various degrees of conversion.