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.     

Adhesive properties of ethylene and vinyl acetate copolymers

Surface properties of ethylene and vinyl acetate copolymers (EVAs) are considered depending on their composition and history of surface formation. The kinetics of structural transformations in the near-surface layers of copolymers is investigated. Relaxation times and the equilibrium state of the EVA surface are determined. The orrelation dependence between the surface energy of copolymers and their adhesive properties for substrates of different natures is constructed.     

Thermoxidative degradation of vinyl alcohol/vinyl acetate copolymers. IV. Statistical copolymers

The thermoxidative degradation of vinyl acetate/vinyl alcohol statistical copolymers was studied under dynamic thermal conditions and compared with that of block copolymers. The dependence of thermal characteristics or kinetic parameters on the content of ? OH groups of copolymers was established.     

Thermal stability of copolymers of vinyl acetate and methyl acrylate

The thermal degradation of a series of copolymers of vinyl acetate and methyl acrylate and the two homopolymers poly(vinyl acetate) and poly(methyl acrylate) obtained using Ce(IV) as initiator has been investigated using differential thermal analysis (DTA) and thermogravimetry (TGA) in dynamic nitrogen. The kinetic parameters E, n, and A have been obtained following several methods of thermogravimetric analyses. The stability increases as the methyl acrylate content in the copolymer composition increases. The incorporation of 5 mol % of vinyl acetate in the copolymer produces a marked decrease in stability compared to the homopolymer poly(methyl acrylate). There is evidence for an intramolecular lactonization process in vinyl acetate—methyl acrylate copolymers.     

Birefringence control for binary blends of cellulose acetate propionate and poly(vinyl acetate)

Structure and optical properties for binary blends composed of biomass-based cellulose acetate propionate (CAP) and poly(vinyl acetate) (PVAc) have been studied. It is found that the blends exhibit high level of transparency, although the dynamic mechanical analysis in the solid state suggests that phase separation occurs in the blend. Furthermore, the birefringence resulting from molecular orientation decreases with increasing the content of PVAc. In particular, the blend with approximately 50 wt% of PVAc exhibits no birefringence even after stretching.     

Thermal degradation of some cross-linked copolymers of vinyl acetate

Pyrolysis in combination with gas chromatography and thermogravimetry were used to study the thermal degradation of some cross-linked copolymers of vinyl acetate with divinylbenzene and ethylstyrene. The temperature was varied in the range 200° and 800°. The thermal decomposition products of the analyzed copolymers vary greatly, both with the temperature and with the composition of the samples. The experimental data obtained led to the assumption of a complex degradation mechanism, evidenced by the overlapping processes and the unexpected contents of certain evolved compounds as a function of composition.

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Zusammenfassung Pyrolyse in Kombination mit Gaschromatographie und Thermogravimetrie wurde zu Untersuchung des thermischen Abbaus einiger vernetzter Kopolymere von Vinylacetat mit Divinylbenzol und Äthylstyrol herangezogen. Die Temperatur wurde im Bereich von 200–800° variiert. Die thermischen Zersetzungsprodukte sind sehr unterschiedlich, abhängig von der Temperatur und der Zusammensetzung der Probe. Aus den experimentellen Daten wird auf einen komplexen Zersetzungsmechanismus geschlossen, der durch die Überlappung der Prozesse und durch das auftreten bestimmter unerwarteter Verbindungen in Abhängigkeit von der Zusammensetzung bestätigt wird.

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. 200–800°. , . , .

     

Reactivity differences between isolated and vicinal vinyl acetate functions in high pressure ethylene/vinyl acetate copolymers

Three ethylene/vinyl acetate copolymers (3.5, 12.0 and 18.8 mol% VA; average melt index 8.5 g/10 min) were transformed into ethylene/vinyl alcohol copolymers and ethylene/vinyl alcohol/vinyl acetate terpolymers by homogeneous saponification. The reaction rate increased with mol% VA. This feature originated in the reactivity differences beteen vicinal and isolated VA functions. Simultaneous steric and polarity effects caused the reaction rate differences. ¹H-NMR, i.r., dielectric measurements and additional saponification reactions confirmed the difference of reactivity.     

Preparation of block copolymers from occluded vinyl acetate macroradicals

Stable vinyl acetate macroradicals were produced by polymerization in a nonviscous poor solvent, a viscous good solvent and a viscous poor solvent. These macroradicals were then allowed to react with a second vinyl monomer to produce block copolymers. The formation of block copolymers was monitored for rate and yield data. The block copolymers produced were poly(vinyl acetate-b-methyl methacrylate), poly(vinyl acetate-b-acrylic acid), poly(vinyl acetate-b-vinylpyrrolidone), poly(vinyl acetate-b-acrylonitrile), poly(vinyl acetate-b-styrene), and poly(vinyl acetate-b-methyl acrylate). The block copolymers were characterized by yield, precipitation in selected solvents, pyrolysis gas chromatography, and differential scanning calorimetry.     

Factors influencing the aqueous solution behaviour of vinyl alcohol with vinyl acetate copolymers

Variations, as a function of temperature, are reported in the magnitude of values for the partial molal volume, partial molal expansibility, flowing volume and surface pressure for dilute solutions of a series of poly(vinyl alcohol-co-vinyl acetate) copolymers of various vinyl acetate contents and acetate sequence length. The temperature range investigated, from 5° to 30°, showed that, for all the examples examined, a general behaviour pattern was observed, indicating the predominance of hydrophilic interactions at temperatures below approximately 10°, with hydrophobic interactions predominating between 10° and 20°. The variations can be related to the detailed microstructure of the polymer backbone.     

Molecular architecture and physicochemical properties of some vinyl alcohol-vinyl acetate copolymers

Two series of vinyl alcohol-vinyl acetate copolymers were prepared by homogeneous and heterogeneous acetylation of the same precursor poly(vinyl alcohol). Their intramolecular monomer distributions were analyzed by IR spectrometry, calorimetry, and differential thermal analysis. The results show a more blocky distribution for the heterogeneously prepared copolymers. The properties of these (co)polymers in dilute aqueous solution were determined by means of viscometry. Whereas the copolymer-solvent interaction parameter of the homogeneously acetylated, random copolymers hardly varied with acetate content, a definite minimum was found for the blocky copolymers at about 7 mole% vinyl acetate. These findings were attributed to the incompatibility of dissimilar sequences, which sharply decreases with decreasing vinyl acetate sequence length. Up to about 17 mole% vinyl acetate content, the solvent quality for the copolymers is at least as good as for poly(vinyl alcohol). In addition, the dilute solution properties of the samples were established in water saturated with 1-butanol. For copolymers with up to about 17 mole% vinyl acetate, at 25°C this mixture is a better solvent than water. The highest increase in solvent quality was found for the homopolymer, whereas the increase diminished with acetate content, irrespective of the intramolecular vinyl acetate distribution. These findings are explained in terms of preferential adsorption of 1-butanol onto the (co)polymer backbone due to hydrophobic interactions and prevention of this process by the bulky acetate groups.     

Thermal degradation of vinyl alcohol/vinyl acetate copolymers V. Study of the reaction products of statistical copolymers

By coupling the evolved gas detection method with various analysis methods, the thermal decomposition products of the statistical vinyl alcohol/vinyl acetate copolymers were analysed. The data are presented comparatively with those obtained for the corresponding block copolymers of the same composition. The differences in the nature and amounts of the reaction products are explained by the structural characteristics of the copolymers.     

Structure and property relationships in ethylene–vinyl acetate copolymers

The effects of vinyl acetate content on crystallinity of ethylene–vinyl acetate (E/VA) copolymers were investigated by x-ray diffraction and differential thermal analysis (DTA). The values of these parameters obtained from DTA were found to agree quantitatively with data calculated from x-ray, probability equations, and copolymer theory. The melting points of the crystalline copolymers, and the molar amounts of vinyl acetate to produce a completely amorphous rubber corresponds exactly to that predicted by the Flory theory. The random character expected in E/VA copolymers is thereby confirmed. The physical properties of E/VA copolymers of all ranges of compositions and crystallinity were determined. Depending directly upon vinyl acetate content, the copolymers changed progressively from highly crystalline polyethylene to semicrystalline polyethylene, a completely amorphous rubber, a soft plastic with a glass transition near room temperature. Properties which were correlated with copolymer composition include: crystallinity, melting point, density, modulus, tensile strength, glass transition, and solubility. Finally, the effect on crystallinity and physical properties of replacing the acetoxy group in E/VA with the smaller, highly polar hydroxyl group (ethylene—vinyl alcohol copolymer) was also investigated.     

Electrochemical dehydrochlorination initiation for vinylidene chloride-vinyl chloride copolymers

Direct electrochemical initiation of dehydrochlorination is possible for polyvinylidine chloride VDC and copolymers of VDC with vinyl chloride VC. The ratio of the VDC and VC links in the initial polymer affects the rate of the dehydrochlorination and the structure of the products. Institute for Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine, 50 Kharkovskoe Shosse, 252660 Kiev-94, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 3, pp. 180–183, May–June, 1997.     

13C-NMR study of chlorinated ethylene–vinyl acetate copolymers

¹³C-NMR has been used to analyze the microstructures of a series of experimental chlorinated ethylene–vinyl acetate copolymers (15–56% CI). Previously established line assignments for EVA copolymers and substituent effect parameters for chlorine have enabled us to tentatively assign partial structures up to five carbon atoms in length. The ¹³C-NMR analyses of a commercial vinyl chloride–vinyl acetate copolymer, a commercial vinyl chloride–vinyl acetate–ethylene terpolymer, and a commercial chlorinated polyethylene support the structural assignments. Data obtained for the experimental resins indicate that the acetate groups influence the way in which chlorine is added to the polymer chain. furthermore, the data indicate the acetate groups undergo little, if any, chlorination.     

Discrimination of ethylene/vinyl acetate copolymers with different composition and prediction of the content of vinyl acetate in the copolymers and their melting points by near-infrared spectroscopy and chemometrics

Near-infrared (NIR) diffuse reflectance spectra have been measured by use of a rotating drawer for pellets of 12 kinds of ethylene/vinyl acetate (EVA) copolymers with vinyl acetate (VA, the comonomer) varying in the 7–44 wt % range. They are unambiguously discriminated from one another by a score plot of the principal component analysis (PCA) Factor 1 and 2, based upon the NIR spectra pretreated by multiplicative scatter correction (MSC). Principal component (PC) weight loadings for Factor 1 show that the discrimination relies largely upon bands due to the overtone and combination modes arising from the VA unit. We have found one “outlier” in the score plot and elucidated its spectral characteristics based upon PC weight loadings for Factor 2. Partial least-squares (PLS) regression has been applied to propose calibration models which predict the VA content in EVA. The models have been prepared for three kinds of pretreatment, the first derivative, the second derivative, and MSC; and four kinds of wavelength regions. The NIR spectra in the 1100–2200 nm region after the MSC treatment has given the best correlation coefficient and standard error of prediction (SEP) of 0.998 and 0.70%, respectively. The calibration models, prepared by NIR diffuse reflectance spectroscopy for the pellet samples, are compared with previously reported models by NIR transmission spectroscopy for the flowing molten samples, and with those by Raman spectroscopy for the pellet samples. PLS regression has also allowed us to predict melting points of the copolymers with the correlation coefficient and SEP of 0.997 and 0.78°C, respectively. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1529–1537, 1998     

Sequence distribution of partially hydrolyzed poly(vinyl acetate)

Copolymers of vinyl acetate and vinyl alcohol were studied by differential thermal analysis. The melting points of the copolymers are not a simple function of the composition, but depend on the method of preparation of the copolymers. Partial saponification of poly(vinyl acetate) with sodium hydroxide leads to high melting, ordered copolymers, while reacetylation of poly(vinyl alcohol) leads to low melting, random copolymers. Catalytic alcoholysis of PVAc yields copolymers intermediate in melting point and order. The results are treated by assuming that equal melting points indicate similar sequence length distributions of crystallizable units.     

UV aging behaviour of ethylene-vinyl acetate copolymers (EVA) with different vinyl acetate contents

The mild UV aging of ethylene-vinyl acetate copolymer (EVA) with two vinyl acetate (VAc) contents (14, 18 wt%) was performed in a xenon arc source chamber. The degradation mechanism was analyzed via attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), gel content and high temperature gel permeation chromatography (HTGPC). Photo-chemically induced deterioration was first initiated from vulnerable VAc units. Ketone formation preceded lactone generation, especially in EVA with high VAc content. Un-stable structures induced further degradation in the main chain. Competition between radiation induced cross-linking and chain scission in EVA was observed, and the later was confirmed to be dominant. Higher VAc content resulted in remarkable drop in molecular weight and growth in polydispersity. Apparent re-arrangement in crystallisation and consequent decrease in thermal stability are discussed through differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA), which accorded well with the chain scission tendency. Interaction between photo-chemical degradation and physical annealing accounted for the first increasing then decreasing tendency in the mechanical properties of both EVAs.     

The thermogravimetric behaviour of the vinyl acetate and α-methylstyrene copolymers of acrylonitrile

Journal of Thermal Analysis and Calorimetry - The influence of the copolymer nature, its comonomer content and the supermolecular structure on the thermal behaviour of the binary vinyl acetate...