The fusion of highly crystalline poly(vinyl chloride)

Low molecular weight PVC polymers of known degree of crystallinity (44% by x-ray diffraction), prepared in the presence of the chain-transfer agents n-butyraldehyde and n-butyl mercaptan, are examined by differential scanning calorimetry in order to ascertain temperatures and heats of fusion. Initial thermal scans are accompanied by large endotherms and appreciable weight losses due to the lability of the terminal groups originating from the chain-transfer agents. However, further successive scans result in approximately invariant endotherms attributable to crystalline fusion. The maximum melting point, about 265°C, exceeds the value for commercial PVC, about 210°C, but is lower than a value deduced for a hypothetical completely syndiotactic polymer, about 400°C. The average heat of fusion ΔH_u is 1180 ± 90 cal/mole, and the resultant entropy of fusion is 1.1 cal/deg/bond. The present ΔH_u value differs significantly from previously reported values of 660–785 and 2700 cal/mole, based on melting point depression theory, but appears to be concordant with known heats for a series of vinyl polymers.     

X-ray diffraction and infrared studies on annealed highly syndiotactic poly(vinyl chloride)

X-ray diffraction scans and infrared absorption spectra for the C-CI stretching region were obtained for a highly syndiotactic poly(vinyl chloride) (PVC) sample made by the urea clathrate method. When the polymer was annealed at a series of increasing temperatures up to 180°C, x-ray diffraction measurements showed that the crystallinity increases steadily with annealing temperature. Even at 50°C an increase above the original value of 63% was detectable and by 180°C it had reached 70% with a further increase to 78% after cooling to ambient temperature. There is a concurrent significant increase in the lateral crystallite dimensions. However, the infrared spectrum did not change, in agreement with the recent prediction of Moore and Krimm that there is no observable band splitting from interchain interaction in crystalline regions, thus indicating that these C-CI bands cannot be used as a measure of crystallinity. The results from computer curve fitting of the spectra suggest that at least 85% of the polymer consists of long planar syndiotactic sequences and there is therefore substantial order along the chain direction. A mechanism for the increase in crystallinity on annealing, involving the lateral ordering of these regular chains, is discussed. Furthermore, as the temperature is raised some amorphous material is converted to a nematic phase, and this may crystallize during the subsequent cooling.     

Characterization of highly irradiated poly(vinyl chloride)

Irradiated poly(vinyl chloride) has been characterized by various techniques. The very high doses (up to 20 Mgy) produce dramatic changes in the material. Chemical changes were studied by TGA analysis. Surface morphology and microstructure were determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). PVC irradiated at the highest dose, 20 MGy, shows a structure consisting mainly of carbon which, in some cases, is crystalline. This carbon-rich material also shows a particular affinity for the adsorption and desorption (after electron bombardment) of ambient gases, as is clearly shown in electron stimulated desorption (EDS) experiments performed in this study.     

Comparison of x-ray diffraction and thermal analysis methods for assessing order in poly(vinyl chloride)

Thermal analysis and wide-angle x-ray diffraction were used to assess the crystallinity for a series of poly(vinyl chloride) (PVC) samples, and the use of two complementary techniques was found beneficial. Two polymers were studied; a commercial suspension grade PVC, and an experimental grade of higher syndiotacticity. Both were examined as powders, and after processing. All samples were also examined after heat treatment at various temperatures between 100 and 175°C. Annealing the suspension grade of PVC appeared to cause a small change in total crystallinity, but little change in crystallite size. When the low temperature powder was annealed, some increase in crystallinity was detected. However, when this polymer was milled, there was a significant increase in crystallite size, and crystallinity seemed to increase further. Particularly noticeable was the increase in the amount of high melting crystallites.     

X-ray diffraction studies on liquid crystalline order in vinyl polymers with mesogenic side-groups

X-ray studies on some vinyl polymers with azobenzene sidegroups were performed. A model of layered structure rearrangement resulting from the substitution of the methacrylate main chain for the acrylate is proposed. It has been shown that the perfection of a layered structure is reduced with shortening of the flexible tail of the mesogenic group. Improvement of LC order with increase of temperature was revealed.     

Miscibility of semirigid thermotropic liquid crystalline polycarbonate with poly(vinyl chloride)

Miscibility and morphology of polymer blends of semirigid thermotropic liquid crystalline (LC) polycarbonate (LCPC) with three commercial amorphous poly(vinyl chloride)s (PVC) having various molecular weights were investigated by means of differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). No phase separation was observed in the LCPC/PVC polymer blends. LCPC forms miscible polymer blends with the PVCs independent of molecular weight. The dynamic storage modulus of the LCPC/PVC polymer blends changes systematically with blend composition.     

Pyrolysis of poly(vinyl chloride)

A pyrolysis–gas chromatography–mass spectrometric technique has been developed to study the thermal degradation of poly(vinyl chlorides) polymerized at different temperatures. Hydrogen chloride and benzene evolution during successive stages of pyrolysis have been quantitatively determined and correlated to the tacticity and molecular weight of the polymer. It was found that lowering the temperature of polymerization and molecular weight depresses benzene evolution and increases char weight but does not affect the HCl yield. It is suggested that the syndiotactic trans microstructure favored at low temperature of polymerization yields polyenes which cannot cyclize to form benzene. As the molecular weight decreases, the increase in number of vinyl chain ends facilitates pyrolytic crosslinking and char formation.     

Photo-oxidation of poly(vinyl chloride)

The photo-oxidation of PVC has been studied over the temperature range 30–150°C. Initiation with ultraviolet (2537A) radiation has been correlated with the presence of minute amounts of ozone. The contribution of atomic oxygen and singlet oxygen (¹Δ_g) molecules to the initiation mechanism is discussed. The β-chloroketones probably formed in the photo-oxidation of PVC, decomposed according to a Norrish type I reaction without loss of chlorine atoms. The gaseous products of the photo-oxidation of PVC at 30°C were carbon dioxide, carbon monoxide, hydrogen, and methane. Hydrogen chloride was obtained only when PVC was heated at high temperatures. When PVC was photo-oxidized and then heated at high temperature, benzene was obtained in addition to hydrogen chloride. The gaseous products from the photo-oxidations of model compounds, such as 4-chloro-2-butanone and 2,4-dichloropentane, were also compared with those from PVC. Hydrogen chloride was detected only after photo-oxidation at temperatures of 25°C or higher. Therefore, it was concluded that hydrogen chloride is mainly a product of thermal decomposition. Since unsaturation was not observed in photo-oxidized PVC films, the cause of discoloration is unclear. When PVC was modified by stabilizers or additives, the oxidative degradation was further complicated by side reactions with the additives.     

Electrical conductivity of poly(vinyl chloride) obtained by photodehydrochlorination from laminated poly(vinyl chloride)/polypyrrole films

Poly(vinyl chloride) (PVC) has been converted to an electrically conductive structure by combined electrochemical and photochemical methods. PVC was cast on a polypyrrole (PPy) film electrode which had been electrochemically prepared. The PVC layer in the laminated PVC/PPy films was first dehydrochlorinated under the illumination of UV light, and the generated polyenes were subsequently doped with I₂ and FeCl₃. The maximum electrical conductivity achieved for such PVC film was 2.51 X 10^?2 and 8.63 10^?2 S cm^?1 after I₂ and FeCl₃ doping, respectively. The temperature dependence of the electrical conductivity showed different behavior in higher and lower temperature ranges. In the former (T > 243 K), the T^?1 law held, and the activation energy and bandgap were estimated as 0.25 and 0.49 eV, respectively. In the latter (T < 243 K), the conductivity mechanism followed the variable range hopping model (T^?1/4 law) in which the radius of the localized state wave function and the density of the localized states at the Fermi level were 1.25 × 10³ Å and 1.03 X 10¹⁵ eV^?1 cm^?3, respectively. © 1995 John Wiley & Sons, Inc.     

Photo-oxidation of poly(vinyl chloride)

Hydrogen chloride is evolved at an increasing rate in the light-induced oxidation of poly(vinyl chloride) films. These accelerated kinetics were shown to result from an increased absorption of light by the polyenes formed, since the quantum yield of dehydrochlorination (Φ_HCl = 0·015) is independent of the extent of the reaction in the dose range investigated. Determination of the quantum yields of the different processes involved indicate that, for each scission of the polymer backbone, 11 molecules of hydrogen chloride are evolved while three carbonyl groups, two hydroperoxides and 0·4 intermolecular crosslinks appear on the polymer chain. A mechanism that involves β-scissions of the tertiary alkoxy radicals, resulting from non-terminating interactions of α-chloro-peroxy radicals, is suggested to explain the observed increase of the polymer degradation in the presence of oxygen.     

Radiolysis of poly(vinyl chloride)

Allyl free-radical intermediates are detected by ultraviolet absorption at 255 mu in poly(vinyl chloride) irradiated at ?196°C and stored at 25°C. In vacuum at 25°C, allyl radicals are converted into polyenyl free radicals and polyenes. From the nature of allyl radical decay in vacuum, radical chain transfer between polyenyl radicals and poly(vinyl chloride) is inferred. Allyl and polyenyl free radicals are scavenged by oxygen on post-irradiation storage in air.     

Novel preparation of electrically conducting poly (vinyl chloride) by photo-dehydrochlorination from poly (vinyl chloride)/polypyrrole composite film

Polypyrrole (PPy) was deposited electrochemically on a platinum plate from a nitric acid solution of pyrrole. The PVC/PPy composite film was finally obtained by casting poly(vinyl chloride) (PVC) onto the PPy electrode from a tetrahydrofuran solution of PVC. The prepared composite film was irradiated at 90°C with a low-pressure mercury lamp in the stream of hydrogen gas saturated with steam, and the PVC film was dehydrochlorinated, leading to the formation of conjugated polyene. The electrical conductivity (σ) of the PVC film in the irradiated composite film was reveled: σ=2.51 × 10^?5S cm^?1. By iodine doping, σ was further enhanced up to 5.04 X 10^?3 S cm^?1. The tensile strength of the irradiated composite film became larger than that of the original PVC film; i.e., the stress at break was: 461 (composite film); 401 kg cm^?2 (PVC). These results were brought about by the doping of radical species to the conjugated polyene. The anion, NO^?₃, doped during the electrodeposition of PPy was photodecomposed to generate radical NO₂ and this species was doped to the polyene, resulting in the formation of electrically conductive PVC and mechanically improved composite film. © 1994 John Wiley & Sons, Inc.     

Brillouin light scattering from poly(vinyl chloride) gels

The hypersonic velocity and attenuation in PVC gels have been measured as a function of gel network volume fraction, using the technique of Brillouin light scattering. The experimental data have been analysed using the full theory for the elastodynamics of gels proposed recently by Johnson. It has been found that for two asymptotic approximations of the dynamic damping factor the tortuosity parameter is nearly always less than unity, contrary to the theoretical expectation.