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.     

Dynamic study of the noncrystalline phase of 13C-labeled polyethylene by variable-temperature 13C CP/MAS NMR spectroscopy

The ¹³C spin-lattice relaxation times T₁ of ¹³C-labeled polyethylene crystallized under different conditions were measured at temperatures from ?120 to 44°C by variable-temperature solid-state high-resolution ¹³C nuclear magnetic resonance (NMR) spectroscopy, in order to determine accurately the dynamics of the noncrystalline region of the polymer. From these results, it was found that the T₁ minimum for the CH₂ carbons in the noncrystalline region of solution-crystallized polyethylene with high crystallinity appears at higher temperature by about 20°C than that of melt-quenched polyethylene with low crystallinity. This means that the molecular motion of the CH₂ carbons in the noncrystalline regions is more constrained at a given temperature in the material of higher crystallinity. Furthermore, dynamics of the noncrystalline region is discussed in terms of the ¹³C dipolar dephasing times.     

Component analysis of proton NMR spectra of linear polyethylene in the α-transition temperature range and phase distribution

Broad-line ¹H NMR spectra of linear polyethylene at temperatures in the α-transition range can be analyzed in terms of contributions from the crystalline and noncrystalline components provided molecular motion in the crystalline region is adequately considered. The spectrum of solid n-C₃₂H₆₆ or n-C₄₄H₉₀ prior to melting is used to take account of the contribution of the crystalline region of the polymer to molecular motions. The temperature dependence of the component distribution in the polymer is briefly discussed for a wide range of temperatures, together with previously reported results at low temperatures. The noncrystalline component is in a rigid glassy state at very low temperatures but with rising temperature it transforms to a mobile glassy state with restricted molecular motion, and transforms partially to the rubbery state at high temperature. The crystalline component remains rigid at low temperature, but some molecular motion is associated with it at higher temperatures in the α-transition range.     

Environmental effects in free-radical polymerizations. Part III. Vinyl chloride and n-butyraldehyde

The properties of poly(vinyl chloride) samples prepared by a free-radical process in the presence of n-butyraldehyde have been studied from the point of view of polymer tacticity, branching, molecular weight, and relative crystallinity. The postulate of a polymer radical–aldehyde complex, invoked to explain the increased crystallinity, was tested. The polymers had a lower degree of polymerization and branching than normal, and these parameters rather than increased syndiotacticity were responsible for the high degree of crystallinity. Both molecular weight and branching affect the crystallinity, since polymer samples prepared in the presence of various transfer agents with similar molecular weights were less crystalline than those prepared in aldehyde, but yet more crystalline than high molecular weight bulk polymer. Polymers prepared in aldehyde had a lower degree of branching than those formed in other transfer agents. It was concluded that aldehyde was effective in increasing the crystallinity of poly(vinyl chloride) in these two ways, and so appeared to be unique among the transfer agents. There was no evidence for assuming any complexing between polymer radicals and aldehyde.     

Small-angle x-ray and light scattering studies of the morphology of blends of poly(ϵ-caprolactone) with poly(vinyl chloride)

Solvent-cast films of blends of poly(?-caprolactone) (PCL) with poly(vinyl chloride) (PVC) were examined by low-angle x-ray scattering and by small-angle light scattering. X-ray scattering from crystalline compositions were analyzed using the Tsvankin–Buchanan technique and led to values of the repeat period of the lamellar structure and the thickness of the crystalline and amorphous layers. With increasing content of PVC, the amorphous layer thickness increased sufficiently to accommodate the PVC, leading to values of the linear crystallinity consistent with macroscopic measurements by density and DSC techniques up to about 50% PVC by weight. Above this concentration, the lamellar structure no longer appeared to be volume filling. At high concentration of PCL, the polymer consisted of volume-filling spherulites containing the lamellar substructure. Spherulite sizes were measured by light scattering and absolute light scattering intensities were consistent with calculations based upon the degree of crystallinity and anisotropy of the spherulites. Compositions containing more than 60% PVC were amorphous. Low-angle x-ray scattering was interpreted in terms of the Debye–Bueche theory which leads to values for a correlation distance l_c and the mean-square electron density fluctuation 〈η²〉 (which was also obtained from the invariant). By the method of Porod, the correlation distances were resolved into persistence lengths within the two phases, which were determined as a function of composition. The fluctuation 〈η²〉 was analyzed in terms of a two-phase model to show that its value was somewhat larger than would be obtained if the phases were composed of the pure components. It was not possible to uniquely determine their compositions. The data were consistent with the existence of a transition zone of the order of 30 Å thick between phases.     

Physical and mechanical properties of ultra-oriented high-density polyethylene fibers

Ultra-oriented high-density polyethylene fibers (HDPE) have been prepared by solid-state extrusion over 60–140°C range using capillary draw ratios up to 52 and extrusion pressures of 0.12 to 0.49 GPa. The properties of the fibers have been assessed by birefringence, thermal expansivity, differential scanning calorimetry, x-ray analysis, and mechanical testing. A maximum birefringence of 0.0637 ± 0.0015 was obtained, greater than the calculated value of 0.059 for the intrinsic birefringence of the orthorhombic crystal phase. The maximum modulus obtained was 70 GPa. The melting point, density, crystallinity, and negative thermal expansion coefficient parallel to the fiber axis all increase rapidly with draw ratio and at draw ratios of 20–30 attain limiting values comparable with those of a polyethylene single crystal. The properties of the fibers have been analyzed using the simple rule of mixtures, assuming a two-phase model of crystalline and noncrystalline microstructure. The orientation of the noncrystalline phase with draw ratio was determined by birefringence and x-ray measurements. Solid-state extrusion of HDPE near the ambient melting point produced a c-axis orientation of 0.996 and a noncrystalline orientation function of 0.36. Extrusion 50°C below the ambient melting point produced a decrease in crystallinity, c-axis orientation, melting point, and birefringence, but the noncrystalline orientation increased at low draw ratios and was responsible for the increased thermal shrinkage of the fibers.     

Effect of temperature and solvents on stereospecific polymerization of vinyl alkyl ethers catalyzed by aluminum sulfate–sulfuric acid complex

The effect of polymerization temperature and solvents was determined on the crystallinity of polymers of vinyl isobutyl ether and of vinyl n-butyl ether prepared with aluminum sulfate–sulfuric acid complex catalyst. Principally, the methyl ethyl ketone (MEK)-insoluble fractions of these polymers were used for characterization. Density, per cent crystallinity by x-ray diffraction, infrared ratio, and dilatometric volume contraction of these polymer fractions were used as criteria of crystallinity. The MEK-insoluble fractions of poly(vinyl n-butyl ethers) prepared in carbon disulfide in the temperature range of ?30 to +25°C did not show any significant difference in the values of the above crystallinity parameters. The polymer obtained at 50°C. was less crystalline than the rest of the polymers. The MEK-insoluble fractions of poly(vinyl isobutyl ethers) prepared at 0–50°C. in carbon disulfide and n-heptane solvents also did not significantly differ in their degree of crystallinity. They were, however, decidedly less crystalline than the MEK-insoluble fractions of the corresponding polymers obtained at ?20°C. These data a indicate that on increasing the temperature of polymerization the crystallinity of the polymers was either unchanged or decreased slightly. The polymerizations of vinyl n-butyl ether and vinyl isobutyl ethers were also carried out in binary mixtures of carbon disulfide with n-heptane, chlorobenzene, and MEK. Generally, increasing the concentration of carbon disulfide increased the inherent viscosities of polymers as well as the weight percentage of their MEK-insoluble fractions. The MEK-insoluble fraction of poly(vinyl isobutyl ether) prepared in carbon disulfide-MEK mixture (volume ratio 2:1) was isotactic and highly crystalline. Likewise, the MEK-insoluble fractions of two polymers of vinyl n-butyl ether prepared in MEK itself were also isotactic and highly crystalline. Compared to poly(tetramethylene oxide), these latter fractions exhibited less dependence of rate of crystallization upon temperature. Consequently, at low degrees of supercooling they crystallize much more rapidly than does poly(tetramethylene oxide).     

Poly(3-hydroxyoxetane)—an analog of poly(vinyl alcohol): Synthesis,characterization, and properties

The spontaneous polymer formed from 3-hydroxyoxetane (HO), as first reported by Wojtowicz and Polak, is linear, low molecular weight, water-soluble, atactic, poly(3-hydroxyoxetane) (PHO) of high crystallinity with ? OCH₂CH(OH)CH₂OH end units. The highly crystalline nature of this atactic polymer may be related to the crystalline nature of atactic poly(vinyl alcohol) since PHO can be considered a copolymer of vinyl alcohol and formaldehyde. Spontaneous PHO apparently is formed in a cationic polymerization by the carboxylic acids produced by the air oxidation of HO on standing at room temperature for several months. The polymerization can be duplicated by the addition of 2% hydroxyacetic acid to HO. The rate of this unusual cationic polymerization increases greatly with acid strength, e.g., trifluoromethanesulfonic acid reacts explosively with pure HO. A mechanism is proposed for this cationic polymerization. High molecular weight, water-soluble, linear atactic, and highly crystalline PHO (mp = 155°C) was made by polymerizing the trimethylsilyl ether of HO with the i-Bu₃Al–0.7 H₂O cationic catalyst followed by hydrolysis. Two ¹H-NMR methods for measuring the tacticity of PHO were developed based on finding two different types of methylene units at 400 MHz with the methine protons decoupled. Also, an ¹H-NMR method was developed for measuring branching in HO polymers. High molecular weight, linear PHO with enhanced isotacticity (80%) has been obtained in low yield as a water-insoluble fraction with T_m = 223°C. The low molecular weight PHO prepared previously by the base-catalyzed, rearrangement polymerization of glycidol is highly branched.     

Stereospecific polymerization of methacrylonitrile. I. Characterization of crystalline polymethacrylonitrile

Methacrylonitrile (MAN) was polymerized with diethylmagnesium. Acetone-insoluble portions of the polymers are found to be crystalline. Highly crystalline portions can be isolated by further extraction of the acetone-insoluble parts with dimethylformamide (DMF). A film of DMF-insoluble fraction can be oriented uniaxially by hot-press rolling. The crystalline PMAN is insoluble in the usual solvents for amorphous PMAN because of their crystallinity and is easily soluble in CF₃COOH or Cl₂CHCOOH. The viscosity–molecular weight relationship was determined in Cl₂CHCOOH at 30°C. as [η] = 3.24 × 10^?3M^0.520. We found several crystalline bands in the infrared spectra, for example, at 1192 and 885 cm.^?1. Formation of the carbonyl group in the polymer is discussed, and it is concluded that it may be formed by the hydrolysis of conjugated cyclic imine or hydrolysis of the nitrile group in the polymer to acid amide.     

Polymerization of β-carbomethoxypropionaldehyde

High molecular weight crystalline poly(carbomethoxyethyl)oxymethylene was prepared from β-carbomethoxypropionaldehyde with the use of organometallic compounds. The characterization, fractionation, x-ray analysis, and viscosity measurement were carried out. Degradation by hydrochloric acid gave a highly crystalline but soluble polymer of a lower molecular weight. It was interesting to note the high solubility character of the polymer in organic solvents in contrast to the poor solubility of the isomeric poly(acetoxyethyl)oxymethylene. From the relationship among the intrinsic viscosity, Huggins' constant, and the solubility parameter of solvent, the solubility parameter of the polymer was determined to be 9.3 (cal/ml)^1/2.     

New high-yield,one-step synthesis of polyglycolide from haloacetic acids

In a new, one-step synthesis, polyglycolide was prepared by the reaction of bromo- or chloroacetic acid with triethylamine in a nitromethane solution. It was discolored, by iodoacetic acid possibly as a result of iodine formed by the decomposition of triethylammonium iodide. The structure of polyglycolide was characterized by hydrolysis, ¹H-NMR and IR spectra, and x-ray powder diffraction, which indicated partial crystallinity. A mechanism is proposed for the formation of polyglycolide. A lower limiting value of the number-average molecular weight of 10⁴ was determined by cryoscopy in 1,3-dinitrobenzene for polyglycolide prepared from bromoacetic acid; the measurement was inaccurate because of the low solubility of the polymer. No significant effect of solvent (acetone, ether, or chloroform) on yield or melting point was observed; a higher yield was obtained in nitromethane. The polymer obtained with tri-n-propylamine and bromoacetic acid had properties similar to that obtained with triethylamine. No polymer was obtained with N,N-dimethylaniline and bromoacetic acid or with triethylamine and bromoacetic acid in aqueous solution.     

Infrared dichroism of polyethylene crystallized by orientation and pressure in a capillary viscometer

Polarized infrared absorption spectra have been obtained by Fourier-transform spectroscopy for several crystalline and noncrystalline absorption bands of polyethylene crystallized by orientation and pressure in capillary viscometer. An analysis of data obtained at room temperature yielded degrees of crystallinity which are in good accord with values obtained from calorimetry and density measurements. The dichroism of the infrared absorption bands for the crystalline region revealed an extreme degree of orientation consistent with previous x-ray studies and also demonstrated that the degree of orientation is a good or better than that obtained from drawn polyethylene films with extension ratios of 20. Dichroism of bands from the amorphous phases revealed that the noncrystalline chain segments are in a comparatively relaxed state compared with results for drawn films having extension ratios of about 2 to 7. This is 1/10 to 1/3 the extension ratio of drawn polyethylene which shows maximum crystalline orientation. The results also indicated that the ratio of the GTG′ to GG segment conformations in the amorphous regions is larger than that of amorphous portions in unoriented polyethylene. The vinyl endgroups were shown to be highly oriented, while the main bulk of the amorphous polymer was fairly relaxed, i.e., of low orientation. It is concluded that the amorphous polyethylene state is strongly dependent on the nature of the crystalline–amorphous interface.     

The drawing behavior of linear polyethylene. I. Rate of drawing as a function of polymer molecular weight and initial thermal treatment

The drawing behavior of a series of linear polyethylene homopolymers with weight-average molecular weight (M?_w) ranging from 67,800 to ～3,500,000 and variable distribution (M?_w/M?_n = 5.1?20.9) has been studied. Sheets were prepared by two distinct routes: either by quenching the molten polymer into cold water or by slow cooling below the crystallization temperature (～120°C) followed by quenching into cold water. When the samples (2 cm long) were drawn in air at 75°C using a crosshead speed of 10 cm/min it was found that for low M?_w polymers the initial thermal treatment has a dramatic effect on the rate at which the local deformation proceeds in the necked region. At high M?_w such effects are negligible. An important result was that comparatively high draw ratios (λ > 17) and correspondingly high Young's moduli could be obtained for a polymer with M?_w as high as 312,000. It is shown how some of the structural features of the initial materials (mainly studied by optical microscopy, small-angle x-ray scattering and low-frequency laser Raman spectroscopy) can be interpreted in terms of the molecular weight and molecular weight distribution of the polymers. Although crystallization and morphology can be important at low M?_w, it suggested that the concept of a molecular network which embraces both crystalline and noncrystalline material is more helpful in understanding the drawing behavior over the whole range of molecular weights.     

Morphology and modulus–temperature behavior of semicrystalline poly(ethylene terephthalate) (PET)

The influence of the thermal history on the morphology and mechanical behavior of PET was studied. The degree of crystallinity (density measurements) and the morphological structure (electron microscopy and small-angle x-ray diffraction) depend on the crystallization temperature. The viscoelastic parameters obtained from the modulus–temperature curves are mainly determined by the morphology of the samples. The glass-transition temperature, T_i, is a function of the crystallinity and the crystallization temperature. It is maximum for a crystallinity between 0.34 and 0.39 for a sample crystallized isothermally between 120 and 150°C. This dependence on crystallization conditions is ascribed to the conformation of the amorphous chain segments between the crystalline lamellae as well as the concentration and the molecular weight of the polymer material rejected during isothermal crystallization. Both factors are supposed to be temperature-dependent. The value of the rubbery modulus is a function of both the volume concentration of the crystalline lamellae and the structure of the interlamellar amorphous regions (chain folds, tie molecules, chain ends, and segregated low molecular weight material). Annealing above the crystallization temperature of isothermally crystallized samples has a marked influence on their morphology and mechanical behavior. The morphological structure and the viscoelastic properties of annealed PET samples are completely different from those obtained with samples isothermally crystallized at the same temperature.     

Synthesis and characterization of hydrophilic thermotropic block copolyetheresters

The block copolyetheresters with a hard segment of poly (hexamethylene p,p′-bibenzoate) and a soft segment of poly (ethylene oxide) were prepared by melt polycondensation of dimethyl-p,p′-bibenzoate, 1,6-hexanediol, and polyethylene glycol (PEG) with molecular weights of 400, 1000, 2000, or 4000. These block copolyetheresters were characterized by intrinsic viscosity, GPC, FT-IR, ¹H-NMR, and water absorption. The thermotropic liquid crystalline properties were investigated by DSC, polarized microscope, and x-ray diffraction. The block copolyetheresters exhibit smectic liquid crystallinity due to the polyester segment. The transitions are dependent on the molar content and the molecular weight of PEG used. The block copolyetheresters show high water absorption due to the hydrophilic nature of the poly (ethylene oxide) segment. The water absorption increases with increasing PEG content. As the molecular weight of PEG increases, the water absorption increases significantly. The results indicate that the water absorption of the poly (ethylene oxide) segment in the block copolymers is affected by the presence of polyester segments. © 1995 John Wiley & Sons, Inc.     

Raman and Wide-Angle X-Ray Diffraction Studies on Molecular Structure,Crystallinity, and Morphology of Uncompatibilized and Compatibilized Blends of High Molecular Weight Polyethylene/Nylon 12

Molecular structure, crystallinity and morphology of uncompatibilized and compatibilized blends of high molecular weight polyethylene (HMWPE) and Nylon 12 were investigated by using Fourier-transform (FT) Raman spectroscopy, wide-angle x-ray diffraction (WAXD), and scanning electron microscopy (SEM). One of the important purposes of the present study is to compare the present results for HMWPE/Nylon 12 with the previously obtained results for high-density polyethylene (HDPE/Nylon 12). Uncompatibilized and compatibilized blends of HMWPE/Nylon 12 with a Nylon 12 content ranging from 10 to 90 wt% at increments of 10 wt% were prepared. The compatibilized polymer blends were prepared by adding a small amount of maleic anhydride (MAH), and SEM images show that the addition of the small amount of MAH (0.5 wt%) yields a marked improvement of dispersion of HMWPE and Nylon 12. To evaluate the crystallinity of HMWPE from Raman spectra, the relative intensities of bands at 1418 and 1129 cm⁻¹ to the intensity of a band at 1000 cm⁻¹ (I₁₄₁₈/I₁₀₀₀ and I₁₁₂₉/I₁₀₀₀) were estimated for all the uncompatibilized and compatibilized blends of HMWPE/Nylon 12. From the comparison of the relative intensities (I₁₄₁₈/I₁₀₀₀ and I₁₁₂₉/I₁₀₀₀) between the uncompatibilized and compatibilized blends of HMWPE/Nylon 12 it was found that when the Nylon 12 content reaches 40 wt% the crystallinity of HMWPE in the compatibilized blends becomes higher than that of HMWPE in the uncompatibilized blends. The uncompatibilized and compatibilized blends of HMWPE/Nylon 12 (50/50) show quite different x-ray diffraction patterns; the compatibilized blend shows a significantly larger orientational effect in the x-ray pattern of HMWPE. It seems that the increase of interaction of MAH-HMWPE with the Nylon 12 matrix leads to the additional crystallinity.     

Determination of degree of crystallinity of drawn polymers by means of density measurements

The well known procedure of determining the degree of crystallinity by means of measuring the density presupposes the knowledge of both the densities ρ_c and ρ_a of the crystalline and of the noncrystalline regions. By combination of small-angle and wide-angle x-ray scattering and of density measurements it can be shown that this method is not justified in the case of drawn polyethylene if the values of ρ_c and ρ_a known from isotropic material are used. Both ρ_c and ρ_a depend considerably on annealing and drawing conditions. In addition the effective density ρ_c^* of the more densely packed phase in a two-phase structure is much lower than the value ρ_c calculated from the positions of the x-ray reflections due to a large number of lattice defects. This conclusion is based on the results of three independent sets of experiments: determination of the mean-square fluctuation of density 〈η²〉 by means of x-ray small-angle scattering; x-ray wide-angle measurements of the positions of the crystal reflections and of the halo arising from the noncrystalline regions; and comparison of densities and long periods of samples treated at various annealing temperatures.     

Effect of N-substitution on the crystallinity of polylaurolactam

Poly(N-ethyl laurolactam) and poly(N-benzyl laurolactam) were prepared from the corresponding monomers by hydrolyic polymerization. Unlike the partially crystalline poly(N-methyl laurolactam), these two homopolymers were completely amorphous by x-ray diffraction. Diffraction patterns of copolymers of N-ethyl laurolactam or N-benzyl laurolactam with laurolactam were shown to be composition-dependent. For N-ethyl laurolactam copolymers, crystallinity developed with 20% laurolactam as a comonomer and increased steadily with a subsequent change in the x-ray pattern, up to 50% laurolactam. Higher laurolactam percentages resulted in copolymers having a nylon 12 x-ray pattern. N-Benzyl laurolactam copolymers with 30% laurolactam showed only 6% crystallinity. The x-ray patterns of N-benzylated nylon 12 made with more than 50% laurolactam showed patterns similar to that of nylon 12. Differential scanning calorimetry data of all these polymers substantiate the x-ray findings. The effect of type and concentration of the N-substituent on the glass transition, melting, and crystallization temperatures of the polymers is discussed.     

Characterization of selectively degraded poly(ethylene terephthalate)

To investigate the morphology of unoriented poly(ethylene terephthalate) (PET) films and the selective character of the aminolysis of PET, 67% crystalline polymer samples were degraded with 40% aqueous methylamine at room temperature. The aminolyzed PET samples were subjected to gel permeation chromatography (GPC), viscometry, electron microscopy, and small-angle x-ray diffraction (SAXD). Weight loss and density crystallinity measurements were also made. After 24 hr of aminolysis, the amorphous regions and chain folds were completely removed. The long molecular chains in the semi-crystalline polymer were reduced to monodisperse rods having a molecular weight of 1,800. The corresponding lamellar thickness was calculated to be 101 Å, consistent with the x-ray diffraction and electron microscope (EM) measurements. The EM photographs of “stripped” crystals show the lamellar structure previously found for other selectively degraded polymeric materials. The weight of crystalline debris remaining was consistent with the initial crystallinity. After degradation the crystallinity as determined by density was 96%.     

Novel conjugated polymer containing anthracene backbone: Addition polymer of 9, 10-diethynylanthracene with 9, 10-anthracenedithiol and its properties

9,10-Diethynylanthracene was prepared by the alkaline hydrolysis of 9,10-bis (trimethylsilylethynyl) anthracene. Another new monomer of 9, 10-anthracenedithiol was prepared by the reduction of anthracene polydisulfide. A crystalline conjugated polymer of 9,10-diethynylanthracene with 9,10-anthracenedithiol was synthesized in a THF solution at 50°C by UV irradiation or by using radical initiators. The molecular weight (M?_n) of the insoluble polymer in THF is about 20000–30000 and the soluble is about 4000. From the sulfur content and IR spectrum of the insoluble polymer, it is realized that the obtained polymer has the alternating structure consisting of 9,10-diethynylanthracene and 9,10-anthracenedithiol units. X-ray pattern indicated that the polymer has a layer structure. The conductivity of the undoped polymer was about 10^?11S/cm, but enhanced up to 10^?6 S/cm by doping with iodine. The enhancement of the conductivity seems to be the existence of the CT complex among the polymer backbone and iodine or iodine anion.