The CO2 permeability of uniaxially drawn high-density polyethylene (HDPE) was investigated and drastic changes were observed as a function of draw ratio. An estimation of variations in both density and fractional free...
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The CO2 permeability of uniaxially drawn high-density polyethylene (HDPE) was investigated and drastic changes were observed as a function of draw ratio. An estimation of variations in both density and fractional free volume of the amorphous component in the drawn polymers was made on the basis of experimental data. The dramatic variations in permeability resulting from drawing were shown to be the consequence of changes of fractional free volume in the amorphous phase of the drawn polymer. Good correlation exists between measured solubility and diffusion coefficients of drawn samples and the estimated fractional free volume;this correlation agrees with the existing free volume theory for diffusion in polymers.
We propose a new technique, which is a combination of the test and real particle methods proposed originally by Widom, for the calculation of the chemical potentials of molecular systems from computer simulation. The ...
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We propose a new technique, which is a combination of the test and real particle methods proposed originally by Widom, for the calculation of the chemical potentials of molecular systems from computer simulation. The technique involves the creation of a hole in the fluid by removing a particle from the simulated system, and subsequently reinserting it as a test bead. The equations for the calculation of chemical potentials are derived, and it is shown that the results obtained by this method for Lennard-Jones fluids are accurate over larger ranges in temperature and density than other traditional methods. In spite of these advantages for simple systems, the proposed technique is expected to be of greatest value when dealing with complex systems containing ionic or polymeric molecules.
In this paper we explore the crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and miscible blends of PBT with a polyarylate based on Bisphenol A and a 75/25 mole rati...
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In this paper we explore the crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and miscible blends of PBT with a polyarylate based on Bisphenol A and a 75/25 mole ratio of isophthalic and terephthalic acids. For PBT, a regime II --> III transition is indicated near 210-degrees-C (DELTA-T approximately 30-degrees-C) and the fold surface free energy (sigma(e)) was found to be in the range of 57-75 erg/cm2. This leads to a work of chain folding (q) of approximately 3-5 kcal/mol folds. Analysis of the crystallization data of van Antwerpen and van Krevelen for PET shows that crystallization occurs in regime II across a wide range of T(c). Sigma(e) was estimated to be approximately 140 erg/cm2 and q approximately 10 kcal/mol from their data. These values are roughly twice that of PBT, consistent with the longer flexible segments in the PBT repeat unit. Crystallization data for three PBT/PAr blends was analyzed using a modified Lauritzen-Hoffman method and compared to that of pure PBT.
In a previous paper we illustrated a Monte Carlo method to calculate the incremental chemical potential between polymer chains of length nu and nu + 1 at all densities. In this document we present a statistical mechan...
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In a previous paper we illustrated a Monte Carlo method to calculate the incremental chemical potential between polymer chains of length nu and nu + 1 at all densities. In this document we present a statistical mechanics model that allows for its quantitative evaluation as a function of chain length and temperature for macromolecular systems at zero density. Through this approach the incremental chemical potential at zero density is shown to be a strong function of chain length at low temperatures, but becomes chain length independent even for short chains (nu greater-than-or-equal-to 3) at higher temperatures. The temperature where the chemical potential becomes essentially chain length independent is a definition of the Boyle transition for finite chain length polymers, and we show that this transition temperature has a well defined chain length dependence. Chain dimensions and incremental entropies associated with chain segments are also found to decrease significantly when the temperature is reduced below this theta-temperature thus providing that chain segments are localized in the vicinity of other segments in the collapsed state. The consequences of these results on the modeling of the phase equilibria of polymer solutions are also examined.
Poly(enamino nitrile) (PEAN) forms miscible blends with several commercial polymers including poly(ethylene oxide) (PEO), poly(4-vinylpyridine) (P4VP), and tertiary amide polymers such as poly(ethyloxazoline) (PEOX), ...
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Poly(enamino nitrile) (PEAN) forms miscible blends with several commercial polymers including poly(ethylene oxide) (PEO), poly(4-vinylpyridine) (P4VP), and tertiary amide polymers such as poly(ethyloxazoline) (PEOX), poly(N-vinylpyrrolidine) (PNVP), and poly(N,N-dimethylacrylamide) (PDMA) as determined by the transparency of blend films and the observation of a single glass transition temperature which changes smoothly with composition. Binary blends containing more than 50 wt % of PEO showed PEO melting endotherms indicating the development of PEO crystallites in the homogeneous amorphous mixture. At higher temperatures PEO/PEAN blends undergo phase separation which signals the existence of a lower critical solution temperature. An endothermic transition associated with phase separation was clearly discernible by calorimetry, as was an exothermic transition associated with redissolution. These reversible phase separation and redissolution processes were observed by hot-stage optical microscopy. Strong hydrogen-bonding interaction between enamine hydrogen atoms and electronegative oxygen or nitrogen atoms on the other component polymers was evidenced by FT-IR and is suggested as a specific interaction which favors miscibilities in these blends.
A wide variety of epoxidized triglyceride oils was examined as renewable monomers in photoinitiated cationic polymerization. Unsaturated triglyceride oils were obtained from commercial sources and exhaustively epoxidi...
A wide variety of epoxidized triglyceride oils was examined as renewable monomers in photoinitiated cationic polymerization. Unsaturated triglyceride oils were obtained from commercial sources and exhaustively epoxidized and characterized by chemical and spectroscopic methods. The oils were photopolymerized as thin films using diaryliodonium and triarylsulfonium salt photoinitiators bearing long-chain alkoxy substituents. The course of the photopolymerizations was monitored using differential scanning photocalorimetry. The effects of the structures of both the cation and the anion of the photoinitiator on the polymerization rates were investigated. The photopolymerization rates were also found to be dependent on the structure and epoxy content of the monomers. The photopolymerized polymer networks were characterized by thermal analysis as well as by mechanical techniques.
Modified Williams-Landel-Ferry (WLF) equations were developed to calculate the chemoviscosity of an epoxy resin system exhibiting a complex curing reaction. The complex curing reaction of this resin was first resolved...
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The synthesis of high‐molecular‐weight polyethers and copolyethers based on 4‐hydroxyacetophenone azine and α,ω‐dibromoalkanes was carried out in N ‐methyl‐2‐pyrrolidone via Williamson etherification using th...
The synthesis of high‐molecular‐weight polyethers and copolyethers based on 4‐hydroxyacetophenone azine and α,ω‐dibromoalkanes was carried out in N ‐methyl‐2‐pyrrolidone via Williamson etherification using the caesium salt of the diol. Polyethers were composed of a homologous series of flexible methylene spacers with m = 5−12, while the copolyethers contained a 1:1 mole ratio of two different spacers with m = 5/7, 6/8, 7/9, 8/10, 9/11 and 10/12. polymers with relatively short spacers ( m = 5−8 methylene groups) exhibit enantiotropic mesomorphism, whereas those having m = 8−11 are tentatively identified to be monotropic. The polyether with m = 12 is crystalline. Copolyethers are enantiotropic and their mesophase ranges are considerably wider than those of the homopolyethers. The mesophases were identified to be nematic by polarised light microscopy. The transition temperatures of both the homopolymers and copolymers show classical even‐odd variations as a function of the spacer length.
The equibiaxial elongational viscosity of polystyrene was determined using a lubricated squeezing technique. Constant strain rates up to Hencky strains of 4.5 could be maintained by a newly constructed instrument. Tes...
The equibiaxial elongational viscosity of polystyrene was determined using a lubricated squeezing technique. Constant strain rates up to Hencky strains of 4.5 could be maintained by a newly constructed instrument. Test results from controlled stress and controlled strain rate measurement were consistent and yielded well-defined steady-state viscosities. Measurements appeared to be unaffected by sample geometry, although proper lubrication is important in achieving steady state. The measured biaxial viscosity appeared to be strain rate thinning above a biaxial strain rate of almost-equal-to 0.01 s-1 at 160-degrees-C. As anticipated in the Newtonian region, biaxial elongational viscosity was approximately six times the shear viscosity. Thinning indices of both shear and biaxial elongational viscosities were 0.75. Data obtained at various temperatures were shifted following the time-temperature superposition principle. The resulting master curve could be fitted by a Carreau model with n almost-equal-to 0.3 and a time constant of 110 s.
An examination is made of several melt miscible polymer blends with the aid of dielectric spectroscopy and differential scanning calorimetry (DSC). These included PEO/PMMA, poly(caprolactone) (PCL)/poly(vinyl chloride...
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An examination is made of several melt miscible polymer blends with the aid of dielectric spectroscopy and differential scanning calorimetry (DSC). These included PEO/PMMA, poly(caprolactone) (PCL)/poly(vinyl chloride) (PVC), and poly(butylene terephthalate (PBT)/polyarylate (PAr). It is the goal of this research to understand if the characteristics of the interphase in all cases examined were similar tho those found fpr the PVDF/PMMA system. It is found that that the unusual spectra obtained for the PCl/PVC blend do not constitute an isolated example and suggest strongly that the fundamental physics underlaying the crystal-amorphous interphase in miscible blends is more complicated that thought before.
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