Thermal decomposition of copolymers from ethylene with some vinyl derivatives

The thermal degradation of ethylene-vinyl acetate (EVA), ethylene-vinyl-3,5-dinitrobenzoate (EVDNB) and ethylene-vinyl alcohol (EVAL) copolymers have been studied using differential thermal analysis (DTA) and thermogravimetry (TG) under isothermal and dynamic conditions in nitrogen. Thermal analysis indicates that EVA copolymers are thermally more stable than EVDNB samples. The degradation of the copolymers considered occurs as an additive degradation of each component polyethylene (PE) and poly(vinyl acetate) (PVA), poly(vinyl-3,5-dinitrobenzoate) (PVDNB) or poly(vinyl alcohol) (PVAL). The apparent activation energy of the decomposition was determined by the Kissinger and Flynn-Wall methods which agree well.     

Grafting reactions of vinyl acetate onto poly[(vinyl alcohol)-co-(vinyl acetate)]

The grafting preference of vinyl acetate onto the methine carbon of poly(vinyl alcohol) (PVOH) versus the acetate group of poly(vinyl acetate) (PVAc) was determined as part of an attempt to prepare novel branched PVOH from partially hydrolyzed PVAc. The results showed long chain grafting on the acetate groups of the PVAc units rather than the methine carbons of the PVOH or PVAc units. Decreasing the monomer or initiator concentration decreased the molecular weight of the graft copolymer formed. Of the initiators studied, ammonium persulfate gave the largest increase in copolymer molecular weight. Both hydrolysis and reacetylation combined with gel permeation chromatography (GPC) and ¹³C-NMR of the fully hydrolyzed material were used to estimate the number and location of grafts. © 1996 John Wiley & Sons, Inc.     

Radiation effects on the thermal degradation of poly(vinyl chloride) and poly(vinyl alcohol)

Radiation effects on the formation of conjugated double bonds in the thermal degradation of poly(vinyl chloride) (PVC) and poly(vinyl alcohol) (PVA) were investigated. Thin films of PVC and PVA were either irradiated with γ-rays at ambient temperature (pre-irradiation) and then subjected to thermal treatment, or irradiated at elevated temperatures (in situ irradiation). An extensive enhancement of the thermal degradation was observed for the pre-irradiation of the PVC films, which was more effective than the effect of the in situ irradiation at the same absorption dose. For the PVA degradation, however, the effect of the in situ irradiation was larger than that of the pre-irradiation. The results were explained and related mechanisms were discussed based on radiation-induced chemical reactions and their individual contributions to the thermal degradation behaviors of the two polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3089–3095, 1998     

Thermal degradation of ethylene (vinyl acetate)

Ethylene (vinyl acetate), EVA, is a copolymer which is thermally degraded at high temperatures, with acetic acid release at approximately 620 K. This release can be studied by using thermal methods, and in particular thermogravimetric analysis.The present work was focused on establishing the polymer weight loss with temperature in order to calculate the activation energy of the overall deacetylation process. To obtain the final results, a Mettler TC50 instrument coupled with a Mettler TC11 microprocessor was used.The activation energies of four different industrial EVA formulations were calculated. The results obtained by applying different kinetic methods reported in the literature agreed reasonably well; they were compared in order to select the best method of reporting EVA deacetylation results.The authors wish to express their appreciation to DGICYT (Spain), Project AMB 94-107, for financial support of this study.     

Characterization of poly(vinyl alcohol) during the emulsion polymerization of vinyl acetate using poly(vinyl alcohol) as emulsifier

During the emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) (PVA) as stabilizer and potassium persulfate as initiator, the VAc reacts with PVA forming PVA-graft-PVAc. When the grafted polymer reaches a critical size it becomes water-insoluble and precipitates from the aqueous phase contributing to the formation of polymer particles. Since particle formation and therefore the properties of the final latex will depend on the degree of grafting, it is important to quantify and to characterize the grafted PVA. In this work, the quantitative separation and characterization of the grafted water-insoluble PVA was carried out by a two-step selective solubilization of the PVAc latex, first with acetonitrile to separate PVAc homopolymer, followed by water to separate the water-soluble PVA from the remaining acetonitrile-insoluble material. After the separation, the water-soluble and water-insoluble PVA were characterized by Fourier Transform Infrared (FTIR) spectroscopy and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses, from which the details of the PVA-graft-PVAc structure were obtained. © 1996 John Wiley & Sons, Inc.     

Kinetics of the complex process of thermo-oxidative degradation of poly(vinyl alcohol)

The thermo-oxidative degradation of poly(vinyl alcohol) (PVA) has been investigated by TG+DTG+DTA simultaneous analysis performed in static air atmosphere, at four heating rates, namely 3, 5, 10 and 15 K min⁻¹. TG, DTG and DTA curves showed that, in the temperature range 25–700°C, four successive processes occur. The first process consisting in the loss of physical adsorbed water is followed by three processes of thermal and/or thermo-oxidative degradations. The processing of the non-isothermal data corresponding to the second process (the first process of thermo-oxidation) was performed by using Netzsch Thermokinetics — A Software Module for Kinetic Analysis. The dependence of the activation energy evaluated by Friedman’s isoconversional method on the conversion degree shows that the investigated process is complex one. The mechanism of this process and the corresponding kinetic parameters were determined by Multivariate Non-linear Regression Program and checked for quasi-isothermal experimental data. It was pointed out that the first process of thermo-oxidation of PVA consists in three consecutive steps having Avrami-Erofeev kinetic model. The obtained results can be used for prediction of the thermal lifetime of PVA corresponding to a certain temperature of use and an endpoint criterion.     

FTIR Study of the Thermal Degradation of Poly(vinyl Alcohol)

The degradation of poly(vinyl alcohol) was investigated using TG analysis and Fourier transform infrared spectroscopy to determine the effect of atmosphere on the process of degradation. In the spectra, four vibrational modes were identified that characterised the major steps of the degradation process. These were the O-H, C-H, C=O and C=C stretching modes. The mechanism observed for degradation in an inert atmosphere was in accordance with the accepted mechanism of elimination followed by pyrolisation. Evidence of conjugated polyenes, however, was not observed. For the air atmosphere, oxidation in both steps of the degradation process was observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ultrasonic degradation of solutions of poly(vinyl acetate) in dioxan: The effects of the temperature and polymer concentration

The ultrasonic degradation of poly(vinyl acetate) (PVAc) solutions was carried out in dioxan at 25, 30, 35, 40, and 45 °C to investigate the effects of the temperature and solution concentration on the rate of degradation. The kinetics of degradation were studied by viscometry. The calculated rate constants indicated that the degradation rate of the PVAc solutions decreased as the temperature and solution concentration increased. The calculated rate constants were correlated in terms of the concentration, temperature, vapor pressure of dioxan, and relative viscosity of the PVAc solutions. This degradation behavior was interpreted in terms of the vapor pressure of dioxan, the viscosity, and the concentration of the polymer solutions. With increasing temperature, the vapor pressure of the solvent increased, and so the vapor entered the cavitation bubbles during their growth. This caused a reduction in collapsing shock because of a cushioning effect; therefore, the rate of degradation decreased. As the solution concentration increased, the viscosity increased and caused a reduction in the cavitation efficiency, and so the rate of degradation decreased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 445–451, 2004     

Block copolymers of poly(ethylene oxide) and poly(vinyl alcohol) synthesized by the RAFT methodology

A methodology for the synthesis of well‐defined poly(ethylene oxide)‐block‐poly(vinyl alcohol) (PEO‐b‐PVA) and PVA‐b‐PEO‐b‐PVA polymers was reported. Novel xanthate end‐functionalized PEOs were synthesized by a series of end‐group transformations. They were then used to mediate the reversible addition–fragmentation chain transfer polymerization of vinyl acetate to obtain well‐defined poly(ethylene oxide)‐b‐poly(vinyl acetate) (PEO‐b‐PVAc) and PVAc‐b‐PEO‐b‐PVAc. When these block copolymers were directly hydrolyzed in methanol solution of sodium hydroxide, polymers with brown color were obtained, which was due to the formation of conjugated unsaturated aldehyde structures. To circumvent these side reactions, the xanthate groups were removed by adding a primary amine before hydrolysis and the products thus obtained were white powders. The polymers were characterized by gel permeation chromatography, ¹H NMR spectroscopy and FT‐IR. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1901–1910, 2009     

Synthesis of Poly(vinyl acetate)-block-poly(dimethylsiloxane)-block-poly(vinyl acetate) Copolymers by Iodine Transfer Photopolymerization in Miniemulsion

Summary: Iodine transfer polymerization of vinyl acetate in aqueous miniemulsion, initiated by UV radiation in the presence of an α,ω-diiodo-poly(dimethylsiloxane) macrophotoiniferter has been performed. The formation of a triblock copolymer latex PVAc-b-PDMS-b-PVAc has been evidenced by ¹H-NMR and size exclusion chromatography. The size of the PDMS and PVAc blocks were modulated thus opening the way to a wide range of copolymers with different properties. A detailed study of the reaction mechanism showed the importance of the aqueous dispersed medium to achieve a controlled polymerization.     

Study of the Drying Behavior of Poly(vinyl alcohol) Aqueous Solution

This paper deals with the drying behavior of poly(vinyl alcohol) aqueous solution containing an active substance and placed into a Petri box. The objective is to reduce the drying time while respecting some constraints. To succeed, it is important to understand complex mechanisms governing heat and mass transfers. During the drying, the product thickness shrinks and its properties evolve. Drying kinetics in convective and infrared radiation are presented.     

Synthesis of poly(vinyl acetate)‐b‐polystyrene and poly(vinyl alcohol)‐b‐polystyrene copolymers by cobalt‐mediated radical polymerization

Well‐defined poly(vinyl acetate) macroinitiators, with the chains thus end‐capped by a cobalt complex, were synthesized by cobalt‐mediated radical polymerization and used to initiate styrene polymerization at 30 °C. Although the polymerization of the second block was not controlled, poly(vinyl acetate)‐b‐polystyrene copolymers were successfully prepared and converted into amphiphilic poly(vinyl alcohol)‐b‐polystyrene copolymers by the methanolysis of the ester functions of the poly(vinyl acetate) block. These poly(vinyl alcohol)‐b‐polystyrene copolymers self‐associated in water with the formation of nanocups, at least when the poly(vinyl alcohol) content was low enough. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 81–89, 2007     

A comparative study of thermal ageing characteristics of poly(ethylene‐co‐vinyl acetate) and poly(ethylene‐co‐vinyl acetate)/carbon black mixture

In this comparative study, the effect of carbon black (CB) on the thermal ageing characteristics of poly(ethylene‐co‐vinyl acetate) (EVA) was investigated. EVA, containing 13% vinyl acetate (VA), and poly(ethylene‐co‐vinyl acetate)/carbon black mixture (EVA/CB) containing 13% VA and 1% CB were aged at 85°C in air up to 30 weeks. Sol‐gel analysis experiments were made to determine the percentage gelation of both virgin and aged samples. FT‐IR measurements were performed to follow the chemical changes which took place in the samples during ageing. Dynamic and isothermal thermogravimetric studies were performed for determination of the thermal stabilities of virgin and aged samples. Sol‐gel analysis results showed that EVA itself has a tendency to form a gel under thermal treatment, whereas EVA/CB never becomes a gel when being thermally aged under the same conditions. As a result of FT‐IR measurements, some oxidation products such as ketone, lactone and vinyl species were observed through thermal ageing of EVA. It is also clear that these kind of oxidation products did not appear to a considerable extent in EVA/CB. Thermal analysis experiments exhibit that thermal stability of EVA decreased through thermal ageing; whereas that of EVA/CB remained almost unchanged. Copyright © 2004 John Wiley & Sons, Ltd.     

Role of grafting in the emulsion polymerization of vinyl acetate with poly(vinyl alcohol) as an emulsifier. I. Effect of the degree of blockiness on the kinetics and mechanism of grafting

The role of grafting in particle nucleation during the emulsion polymerization of vinyl acetate with partially hydrolyzed poly(vinyl alcohol) (PVA) as an emulsifier and potassium persulfate as an initiator was investigated. The polymerizations were carried out in batch with a low solids (10%) recipe. An automated reaction calorimeter (Mettler RC1) was used for the direct monitoring of the kinetics of emulsion polymerizations with three medium molecular weight PVAs differing in their degrees of blockiness (Poval 217EE > 217E > 217). Smith–Ewart case 1 kinetics (average number of free radicals per particle < 0.5) were followed in all cases, and no constant rate in interval II was observed. Contrary to what was expected, a nonlinear relationship was observed between the rate of polymerization (R_p) and the number of particles (N_p). At R_{p max,} N_p (217E) > N_p (217EE) > N_p (217), and the final N_p was independent of the degree of blockiness of PVA. The particle size distributions were broad (particle diameter = 20–100 nm) and bimodal. On the basis of these data, we concluded that particle nucleation was continuous and was accompanied by extensive limited aggregation during the particle growth stages. The evolution of the amounts of grafted PVA and poly(vinyl acetate) (PVAc) were determined in polymerizations employing the two PVAs differing the most in blockiness (Poval 217EE and 217). The grafted PVAc followed similar profiles, increasing with conversion, particularly near the end of the two reactions. The amounts of grafted PVAc were about the same in the final latexes (37–39%). In contrast, the grafting of PVA was nearly complete by the time monomer droplets had disappeared in each reaction (25% conversion). However, the extent of grafting differed significantly, with the blockier PVA having about one‐third the grafting of the more random PVA (～10% vs ～30%). In these low solids recipes, grafting appeared to be primarily a solution event, occurring predominantly in the aqueous phase and not at the particle/water interface, as was previously speculated. The PVAc grafts grew until the molecules became water‐insoluble and precipitated, forming polymer particles. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3633–3654, 2001     

超声-tio2光催化协同降解聚乙烯醇

聚乙烯醇;超声光催化;纳米锐钛矿型tio2     

Thermal degradation of polycarbonate, poly(vinyl acetate) and their blends

We have recently developed a novel approach for intimately mixing thermodynamically incompatible polymers, which utilizes the formation of inclusion compounds (ICs) formed with host cyclodextrins (CDs), followed by removal of CD and coalescence of the common guest polymers into a blend. In this paper direct insertion probe pyrolysis mass spectrometry (DIP-MS) analyses of polycarbonate (PC), poly(vinyl acetate) (PVAc) and PC/PVAc blends, obtained by coalescence from their inclusion compounds formed with host γ-CD (coalesced blend) and by co-precipitation (physical blend), have been performed. Variations in the thermal stabilities of the coalesced polymers were recorded both by TGA and DIP-MS and compared to the corresponding as-received polymers. It has been determined that for both coalesced and physical blends of PC/PVAc, CH₃COOH formed by deacetylation of PVAc above 300 °C, reacts with PC chains decreasing their thermal stability. This process was more effective for the physical blend, most likely due to enhanced diffusion of CH₃COOH, produced by deacetylation of PVAc, into the PC domains, where it can further react producing low molecular weight PC fragments bearing methyl carbonate chain ends.     

The Effect of UV-Irradiation on Poly(vinyl alcohol) Composites with Bacterial Cellulose

The development of biodegradable packaging materials, especially from renewable resources is a constant preoccupation of nowadays, because of the environmental problems caused by synthetic polymers. The combination of cellulose with other polymeric materials could be an ecologic alternative and a way to use renewable resources for food packaging. Bacterial cellulose which is produced by microbial fermentation is also a promising material which can be used not only in biomedical application, but also as food packaging material. In this research different composite films between poly(vinyl alcohol)-bacterial cellulose (PVA-BC) were obtained by casting method. The obtained films were UV irradiated for different periods of times from 1 to 10 hours, using a mercury lamp, Philips TUV-30, emitting light mainly at 254 nm. Changes in FT-IR spectra before and after UV irradiation and the modification of transparency and of the swelling characteristics of the films were observed. As it was expected the composites materials are sensitive at UV exposure.     

Synthesis and Characterization of Poly(N-isopropylacrylamide) and Poly(vinyl acetate) Diblock Copolymers via MADIX Process

The synthesis of diblock copolymers of poly(N-isopropylacrylamide) (PNIPAM) and poly(vinyl acetate) (PVAc) was performed by macromolecular design via interchange of xanthates (MADIX) process. Following the preparation of methyl (isopropoxycarbonothioyl) sulfanyl acetate (MIPCTSA) as chain transfer agent, it was reacted with vinyl acetate to obtain PVAc macro-chain transfer agent. Then, block copolymerization was completed by successive addition of N-isopropylacrylamide (NIPAM). ¹H NMR spectroscopy confirmed the presence of both blocks in the copolymer structure, with the expected composition based on the feed ratio. Size Exclusion Chromatography (SEC) was used to investigate the relative values of molecular characteristics. Only 20% of PVAc was converted to block copolymer. The resultant block copolymer structures were further examined in terms of their morphologies as well as critical micelle concentration (CMC) by using ESEM and Fluorescence Excitation Spectroscopic techniques, respectively. Morphological characterization confirmed amphiphilic block copolymer formation with the existence of mainly ca. 100 nm well distributed micelles. The thermo responsive amphiphilic behavior of the block copolymer solutions were followed by Dynamic Light Scattering (DLS) technique.     

Thermal lensing in poly(vinyl alcohol)/polyaniline blends

Nonlinear optical properties of poly(vinyl alcohol) (PVA)/polyaniline (PAni) blends were measured with the single‐beam Z‐scan technique with Fourier analysis. The results obtained with continuous wave (cw) excitation indicated that the self‐phase modulation had a thermal origin. Besides the Z‐scan technique, we also employed the time‐resolved mode‐mismatched thermal lens (TL) technique to obtain the temperature coefficient of the optical path length, ds/dT, and the thermal diffusivity coefficient, D, for the specific concentrations used in our blends. ds/dT varied between ?0.8 and ?1.0 × 10^?4 K^?1, whereas the thermal diffusivity varied between 1.0 and 1.3 × 10^?3 cm²/s. The TL technique was further used to study the aging of the blends as they were heated to 90 °C. Unlike the electrical conductivity of PAni films, which presented a strong dependence on the doping level, the thermooptic properties presented only a slight variation with doping. This feature indicated that the PVA/glutaraldehyde network made the main contribution to the thermooptic properties (D and ds/dT) in the PAni blends. Similarly, dimethyl sulfoxide as a solvent determined the thermooptic properties of PAni solutions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1949–1956, 2002     

Biomaterials of Poly(vinyl alcohol) and Natural Polymers

Polysaccharides and proteins are abundantly found in nature and are highly recommended for developing eco-friendly materials due to their special properties (biodegradability, biocompatibility, non-toxicity, low cost, etc.). However, they sometimes fail to meet specific requirements due to poor mechanical and physical properties. Poly(vinyl alcohol) (PVA) is one of the promising synthetic polymers with superior properties that can be blended with natural polymers for obtaining novel biomaterials with improved performances. This review addresses recent advance in PVA/polysaccharides and PVA/proteins biocomposites design and fabrication, mainly for the past two decades.