Study of dynamic mechanical properties of poly(vinyl chloride)–ethylene vinyl acetate copolymer and poly(vinyl chloride)–chlorinated ethylene vinyl acetate copolymer mixtures

The compatibility of the mixtures poly(vinyl chloride)—ethylene vinyl acetate copolymer and poly(vinyl chloride)—chlorinated ethylene vinyl acetate copolymer was studied by the method of dynamic mechanical testing. The character of G′ and G″ was confronted with the Takayanagi model. In all cases a limited compatibility of the components was observed.     

Comparison of polystyrene,poly(styrene/acrylonitrile), high-impact polystryrene,and poly(acrylonitrile/butadiene/styrene) with respect to tensile and impact properties

The tensile behaviors of polystyrene (PS), poly(styrene/acrylonitrile) (SAN), high-impact polystyrene (HIPS), and poly(acrylonitrile/butadiene/styrene) (ABS) were examined systematically in the wide range of strain rate, 1.7 × 10^?4–13.1 m/s. When glassy and brittle PS was a criterion, the incorporation of a polar group (SAN) only strengthened the hardness, and the fracture mode was the same as for PS. The introduction of dispersed rubber particles (HIPS) weakened the hardness a little but offered a new deformation mechanism, i.e., microcrazing (whitening), and contributed to the improvement of impact strength. In the heterogeneous system, the enhancement of matrix strength [e.g., preorientation or blending with poly(phenylene oxide) for HIPS] makes possible another deformation mechanism, i.e., shear band formation (cold drawing), which is superior to microcrazing for achieving higher impact strength. ABS, which incorporates concurrently two factors (polar group to matrix phase and dispersed rubber particles), can be regarded as an enhancement of the matrix strength of HIPS. In spite of the remarkable magnitude of its impact strength compared with that of the other three polymers, the deformation mechanism of ABS was limited to microcrazing. This indicated that only the introduction of a polar group (as nitrile group) could not strengthen the matrix as much as preorientation or blending with poly(phenylene oxide).     

Non equilibrium annealing behavior of poly(vinyl acetate)

The water absorbed by poly(vinyl acetate), PVAc, at 23°C was found in two states. The first, which can account for up to 4 weight percent, was bound to the polymer. The second was in a freezable or clustered form. The latter type of water had no effect on PVAc's glass temperature, whereas, the former kind plasticized T_g. In annealing studies, the enthalpic and dielectric response of PVAc when held at a fixed temperature increment, ΔT, below T_g, was observed to be independent of the amount of bound water. The time dependence of the shift in the dielectric relaxation spectrum and the recovery of the enthalpy towards its equilibrium value as PVAc approached its equilibrium glassy state from a lower temperature as compared to a higher temperature was initially slower. This delayed response to expansion was of the order of the polymer's average relaxation time at the lower temperature. A model was proposed to explain this asymmetric behavior based upon changes in the polymer's free volume as well as its occupied volume.     

Conducting polymer composites: Polypyrrole and poly(vinyl chloride-vinyl acetate) copolymer

Composites of a polypyrrole (PPy) and poly(vinyl chloride-vinyl acetate) copolymer (PVC-PVA) were prepared both chemically and electrochemically. An insulating polymer was retained in the blend and the thermal stability of the polymer was enhanced by polymerizing pyrrole into the host matrix in both cases. The composites prepared electrochemically gave the best results in terms of conductivity and air stability. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 667–671, 1997     

Effect of poly(vinyl acetate/vinyl alcohol) copolymer with a thiol end group as a steric stabilizer on dispersion polymerization of styrene

In dispersion polymerization of styrene in ethanol, effects of a reactive steric stabilizer, poly(vinyl acetate/vinyl alcohol) copolymer with a thiol end group (P(VAc/VA)-SH), were investigated. In the absence of the thiol end group, the dispersion coagulated at the middle stage of the polymerization, while in the presence of the thiol end group, the polymerization proceeded successfully to result in close to monodisperse particles. The reactive thiol group acts as a site of formation of the block copolymer, that is, polystyrene-b-P(VAc/VA), which is utilized as an effective dispersant. From the measurement on molecular weights during the course of polymerization, two polymerization loci were realized. Addition of butyl methacrylate to styrene affected markedly not only rate of polymerization but also particle size. © 1996 John Wiley & Sons, Inc.     

Molecular weight distribution in a poly(vinyl chloride–vinyl acetate) copolymer

The molecular weight distribution of a vinyl chloride–vinyl acetate copolymer has been studied by three methods: (a) solution fractionation; (b) osmometry and light scattering; (c) gel permeation chromatography. In (a), the fractions were precipitated from a tetrahydrofuran solution by water, then characterized. The data yielded models for the intrinsic viscosity and the molecular weight distribution, in terms of the copolymer molecular weight. In (b), the unfractionated copolymer was characterized by osmometry and light scattering, using in the latter case the two currently accepted theories for the determination of the true weight-average molecular weight. Conflicting data suggest caution in the use of these theories. In (c), the original fractions served to establish a calibration curve which yielded exceptionally low results when applied to the analysis of the unfractionated VC–VAc copolymer. Further investigations using proposed universal calibration theories bring to light serious discrepancies.     

Dielectric and dynamic mechanical behavior of poly(vinyl acetate) containing small concentrations of cholesteryl additives

Dielectric loss measurements at four temperatures and as a function of frequency are presented for the poly(vinyl acetate) (PVAc) systems containing small concentrations of cholesterol, cholesteryl acetate, cholesteryl oleate, cholesteryl nonanoate, cholesteryl benzoate, cholesteryl oleyl carbonate, p-methoxy benzilidine-p-n-butyl aniline, diphenyl ether, and cetyl acetate. For the first five systems, the α-relaxation temperature for sure PVAc was found to be increased in the presence of the said additives. The results of the dielectric depolarization spectroscopy at 1 kHz and the dynamic mechanical analysis also conform with these observations. It is inferred that the segmental motion in PVAc is hindered by these first five additive molecules through a specific dipolar interaction. These additives are therefore described as antiplasticizers to PVAc as they extend the glassy region over a wider temperature interval. The analysis of the dielectric data to give the dielectric decay function and the β parameter reveals that the two types of the additives, viz., plasticizers and antiplasticizers, can be distinguished by the opposite signs obtained for the ratio Δβ/ΔC, where C is the concentration. The analysis based on the WLF theory shows that the WLF reference temperature T⁰ is higher than that for pure polymer if the additive is an antiplasticizer while the same is lower for the plasticizing additives. The apparent enthalpy of activation for the dielectric relaxation process is found to be higher in the case of additives which show antiplasticization of PVAc.     

Blends of poly(vinyl acetate) and poly(ethyl methacrylate): Some mechanical properties

Poly(vinyl acetate) (PVAc) and poly(ethyl methacrylate) (PEMA) were solution blended in chloroform and cast into films on mercury surface. Some mechanical properties of the films were studied with the Instron Testing Machine. Tensile strength (TS), initial modulus (IM) and elongation at break of the films were found to depend highly on blend composition, and increased above the values for the pure polymers, each showing a peak at about 20% PEMA. The peak values of TS, IM, and elongation at break depended on an important factor, (M _v)_rc the ratio of the molecular weights of (PEMA) to (PVAc). Improvements to the mechanical properties of the polymers due to blending were considered to be as a result of the presence of favorable and strong (PVAc-PEMA) intermolecular interactions which reveal miscibility and compatibility of the polymers. A lower critical value (M _v)_rc of 4.9 was found, above which no phase separation would be expected on blending these two polymers to the extent of 20% by weight of PEMA.     

Combined relaxation study of poly(vinyl chloride)-plasticizer-ethylene vinylacetate copolymer compounds

Poly(vinyl chloride)-dioctyl phthalate-ethylene vinylacetate copolymer compounds of different composition were studied by combination of various computer controlled mechanical and dielectric relaxation techniques. By the high resolution (low effective frequency) quasi-static methods multiple transitions in the glass-rubber transition range were found which were shifted by increasing additive concentration according to the additivity rule of free volume. Transition temperatures detected by mechanical and dielectric techniques were found to coincide satisfactorily taking into account shifts due to differences of effective frequencies as well as loads.     

Anomalous dynamic mechanical behavior of poly(vinyl chloride)

In this paper, we present a study of the dynamic mechanicall behavior of a quenched poly(vinyl chloride). A new relaxation between the glass transition and the β transition is reported. We have related this new relaxation to an absence of physical aging.     

Phase behavior of blends of poly(vinyl chloride) with an α-methyl styrene/acrylonitrile copolymer

Poly(vinyl chloride), PVC, is shown to be miscible with an α-methyl styrene/acrylonitrile copolymer, αMSAN, containing 30 percent AN by weight using differential scanning calorimetry for blends prepared by several methods. Melt blending gave single T_g mixtures; whereas, solution techniques gave results that depended on the solvent choice and the manner in which it was removed. These blends do not phase separate on heating prior to significant PVC decomposition (～250°C) in contrast to PVC/SAN blends which have much lower cloud points. Repulsion between α-methyl styrene and acrylonitrile units in the copolymer is the principal cause for miscibility of this system as shown by an analysis based on a binary interaction model using calorimetry data for low molecular weight liquid analog compounds.     

Dynamic mechanical properties of styrene butadiene rubber and poly (ethylene-co-vinyl acetate) blends

The dynamic mechanical behaviour of uncrosslinked and crosslinked styrene butadiene rubber/poly (ethylene-co-vinyl acetate) (SBR/EVA) blends was studied with reference to the effects of blend ratio, crosslinking systems, a compatibilizer viz. maleic-anhydride grafted poly [styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS-g-MA), frequency and temperature. The two separate tan δ peaks, obtained during DMA, indicated the immiscibility of SBR/EVA system. The damping properties increased with SBR content for uncrosslinked and crosslinked blends. In the case of crosslinked systems, depending upon the type of crosslinking agent used, the glass transition temperature (T _g) of SBR phase has been found to be shifted to higher temperatures. The damping characteristics of the blends were observed to be affected by the variations in frequency. The addition of the compatibilizer improved the storage modulus and reduced the damping properties. These results have been correlated with the morphology of the blends, attested by scanning electron micrographs. The activation energy for glass transition has been computed. The experimental data on storage modulus were compared with theoretical predictions.     

Rheological behavior of poly(vinyl chloride) mixture. II. Elastic behavior

This study was undertaken in order to understand the effect of low molecular weight additives on the visco-elastic properties of polymers and, in particular, Diamond Shamrock Corporation's PVC-40 resin. The viscous response has been reported in Part I of this series (11). This report describes the elastic properties of these mixtures. A new theoretical analysis of elastic response has been formulated. The direct calculation of stored elastic energy from capillary rheometer measurements is now possible. The conclusion drawn from both the viscous and elastic response study is that a change in viscosity is not a necessary nor sufficient condition for improved processability. Increased flow is obtained by lowering the viscous losses, but the melt fracture phenomena may be unchanged. In order to completely characterize the compound, both viscous and elastic response must be measured.     

Graft copolymerization of poly(vinyl chloride) with styrene. II. Thermal behavior

Thermal behavior of graft copolymers of polyvinyl chloride with polystyrene prepared by using a cationic initiator (AlCl₃) was evaluated by measurement of rates of dehydrochlorination in nitrogen atmosphere. With increase in the extent of grafting the rates were found to decrease. Dynamic thermogravimetric analysis revealed an overall improvement in thermal stability of copolymers. Development of polyene sequences in degraded polymer samples was evaluated by measurement of electronic absorption spectra. In comparison to PVC, graft copolymer samples had fewer conjugated double bonds.     

Delayed action heat seal adhesives. I: Dielectric relaxation studies of mixtures of dicyclohexyl phthalate with poly(vinyl acetate) and polystyrene

The design of delayed action heat seal adhesives depends on the physical properties of the polymer, plasticiser and their resultant mixtures. This paper explores the relationships between various molecular interactions and the performance of the adhesives. Dielectric relaxation measurements of mixtures of poly(vinyl acetate) or polystyrene and a plasticiser, dicyclohexyl phthalate, were performed to characterise the molecular dynamics of the system. Binary mixtures over the entire composition range were examined from 244 to 408 K and over a frequency range from 10^?1 to 6 × 10⁴ Hz, and allowed the nature of the interaction between plasticiser and polymer to be quantified. Dielectric studies are compared with measurements of the glass transition temperature obtained using thermal and mechanical analysis, and indicate that over certain composition ranges segregation of the components occurs at a molecular level. These observations are discussed in relation to the design of a delayed action heat seal formulation.     

Preparation of nanoporous films from self-assembled poly(vinyl chloride-g-methyl methacrylate) graft copolymer

We report on the preparation of nanoporous films based on an amphiphilic graft copolymer of poly(vinyl chloride-graft-methyl methacrylate), i.e., PVC-g-PMMA. The PVC-g-PMMA graft copolymer was synthesized via atom transfer radical polymerization (ATRP), as confirmed by nuclear magnetic resonance spectroscopy (¹H NMR), Fourier transform-infrared (FT-IR) spectroscopy, and gel permeation chromatography (GPC) analysis. The PVC-g-PMMA graft copolymer molecularly self-assembled into nanophase domains of PVC main chains and PMMA side chains, as revealed by wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). The graft copolymer film prepared from tetrahydrofuran (THF), a good solvent for both chains, had a random microphase-separated morphology. However, when prepared from dimethyl sulfoxide (DMSO), a solvent selectively good for PVC, the film exhibited a micellar morphology consisting of a PMMA core and a PVC corona. Nanoporous films with different pore sizes and shapes were prepared through the selective etching of PMMA chains using a combined process of UV irradiation and acetic acid treatment.     

Orientation and relaxation in uniaxially stretched poly(vinyl methyl ether)-atactic polystyrene blends

Infrared measurements of the dichroic ratio of polystyrene and poly(vinyl methyl ether) absorption bands allow us to determine chain orientation for each component in their compatible blends. Influence of strain rate and temperature of stretching on orientation of both polymer chains in blends containing up to 25% PVME has been studied. Mechanical relaxation master curves at a reference temperature T=T_g+40°C have also been determined. Results are compared to previous results obtained in PS-PPO compatible blends. Although PPO and PVME chains behave differently PS chains behaviour is similar in the two types of blends and interpreted in terms of a hindrance of relaxation of PS chains induced by a modification of friction coefficients due to the molecular interactions which are at the origin of compatibility.     

Thermal characteristics of poly(ethylene terephthalate) fiber grafted with poly(vinyl acetate) and poly(vinyl alcohol)

Poly(ethylene terephthalate) (PET) fibers were grafted with poly(vinyl acetate) (PVAc) and poly(vinyl alcohol) (PVA). The effects of graft copolymers PVAc and PVA on morphological properties of PET were evaluated by differential thermal analysis, differential scanning calorimetry, and thermogravimetric analysis. Melting temperature, heat of fusion, and mass fractional crystallinity of PET was not affected by graft PVAc and PVA. No individual glass transition and melting points corresponding to the graft PVAc and PVA were observed, indicating thereby that graft copolymer mainly exists in the form of free chains inside the PET matrix. Poly(vinyl alcohol) graft copolymer degraded at much lower temperatures than poly(vinyl alcohol) in powder form. Thermal stability of PET fiber was not affected by graft PVAc, where as PET–g–PVA showed an additional degradation point at 360°C.