In situ drawing of high molecular weight poly(ethylene terephthalate) in subcritical and supercritical CO2

The effects of draw conditions were studied for initially amorphous melt‐spun poly(ethylene terephthalate) fibers in the presence of subcritical and supercritical (SC) CO₂. Both in situ and posttreatment mechanical behavior along with morphological characteristics were investigated. Fibers soaked in subcritical CO₂ could be drawn to 30% higher draw ratios (DRs) compared with fibers that were cold‐drawn. In situ force response measured with a custom apparatus showed that fibers in subcritical CO₂ had no measurable resistance to deformation until strain hardening occurred. In contrast, fibers drawn in SC CO₂ displayed a yield response, a significant decrease in ductility, and a significant difference in postyield behavior. Fibers drawn in subcritical CO₂ showed slightly lower tensile properties compared with cold‐drawn samples whereas fibers treated in SC CO₂ had much lower tensile properties because of the limited DR achieved. X‐ray diffraction studies indicated that CO₂ enhances the development of the crystalline phase compared with cold‐drawn samples. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1881–1891, 1999     

Morphology and crystal structure of the poly(ethylene oxide)–hydroquinone molecular complex

The occurrence of a molecular complex between poly(ethylene oxide) (PEO) and p‐dihydroxybenzene (hydroquinone) has been determined using different experimental techniques such as differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and Fourier transform infrared spectroscopy (FTIR). From DSC investigations, an ethylene oxide/hydroquinone molar ratio of 2/1 was deduced. During the heating, the molecular complex undergoes a peritectic reaction and spontaneously transforms into a liquid phase and crystalline hydroquinone (incongruent melting). A triclinic unit cell (a = 1.17 nm, b = 1.20 nm, c = 1.06 nm, α = 78°, β = 64°, γ = 115°), containing eight ethylene oxide (EO) monomers and four hydroquinone molecules, has been determined from the analysis of the X‐ray diffraction fiber patterns of stretched and spherulitic films. The PEO chains adopt a helical conformation with four monomers per turn, which is very similar to the 7₂ helix of the pure polymer. A crystal structure is proposed on the basis of molecular packing considerations and X‐ray diffraction intensities. It consists of a layered structure with an alternation of PEO and small molecules layers, both layers being stabilized by an array of hydrogen bonds. The morphology of PEO–HYD crystals was studied by small angle X‐ray scattering and DSC. As previously shown for the PEO–resorcinol complex, PEO–HYD samples crystallize with a lamellar thickness corresponding to fully extended or integral folded chains. The relative proportion of lamellae with different thicknesses depends on the crystallization temperature and time. Finally, the observed morphologies are discussed in terms of intermolecular interactions and chain mobility. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1197–1208, 1999     

Crystallization of tethered polyethylene in confined geometries

Ordered poly(ethylene)‐poly(vinylcyclohexane) (PE‐PVCH) block copolymers are employed to study the crystallization of tethered PE in confined geometries. The high T_g of the PVCH component of these materials forces PE chains to crystallize in well‐defined geometries dictated by the mesophase structure of the block copolymer. Effects of chain tethering on crystallization are examined through comparison of singly‐tethered PE chains in PE‐PVCH (EV) diblocks and doubly‐tethered PE in PVCH‐PE‐PVCH (VEV) triblocks. Crystallinity is independent of the block copolymer mesophase structure in both the EV and VEV systems, although crystallinity in VEV depends on the molecular weight of the PE block of the copolymer. Melting temperature data indicate that spatial confinement reduces crystallite size in EV and VEV, and that the double tethering of PE chains in VEV reduces crystallite size further through topological constraints. Crystal nucleation and growth depend strongly on the type of microstructure in both EV and VEV block copolymers. Differences in the overall rate of crystallization are correlated with the dimensional continuity of the PE microdomains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37:2053–2068, 1999     

Synthesis and characterization of linear ABC triblock copolymer of ethylene oxide,methyl methacrylate,and styrene

A well‐defined linear ABC triblock copolymer of ethylene oxide (EO), methyl methacrylate (MMA), and styrene (St) was prepared by sequential living anionic and photo‐induced charge transfer polymerization (CTP) using p‐aminophenol as parent compound. In the first step, the diblock copolymer of PEO‐b‐PMMA with a protected aniline end group at PEO end was prepared by initiating of phenoxo‐anion the polymerization of EO and MMA successively, then the diblock copolymer of PEO‐b‐PMMA via deprotection of aniline at PEO end constituted a binary initiation system with benzophenone (BP) by charge transfer complex mechanism to initiate the polymerization of St under UV‐irradiation. The GPC and NMR measurements support that in copolymerization, either in the first or second step, neither homopolymer nor side reactions, such as chain transfer or chain termination, was found. The effect of the concentration of PEO_a‐b‐PMMA and St, and the polarity of solvent on the polymerization rate (R_p) of CTP is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 825–833, 1999     

Theoretical study of the Au–ethylene interaction

The basis‐set dependence and quasirelativistic and nonrelativistic effects on the Au C₂H₄ interaction are examined at the ab initio level. The effects on the interaction energies are modulated by f‐type polarization orbitals, using 19‐VE quasirelativistic pseudopotentials. Oscillation in the equilibrium Au C distance as well as in the interaction energy are sensitive to the electron correlation potential. These effects are evaluated at several levels of theory, ranging from MP2 to CCSD(T). The nature of the Au C₂H₄ interaction is related to a simple dispersion expression involving the individual properties of each component and its long‐distance behavior. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 317–324, 1999     

Poly(N-phenyl-2-hydroxytrimethylene amine): Its blends with poly(ϵ-caprolactone) and water-soluble polyethers

A new polymer with pendant hydroxyl groups, namely, poly(N-phenyl-2-hydroxytrime-thylene amine) (PHA), was synthesized by a direct condensation polymerization of aniline and epichlorohydrin in an alkaline medium. The new polymer is amorphous with a glass transition temperature (T_g) of 70°C. Blends of PHA with poly(ϵ-caprolactone) (PCL), as well as with two water-soluble polyethers, poly(ethylene oxide) (PEO) and poly(vinyl methyl ether) (PVME), were prepared by casting from a common solvent. It was found that all the three blends were miscible and showed a single, composition dependent glass transition temperature (T_g). FTIR studies revealed that PHA can form hydrogen bonds with PCL, PEO, and PVME, which are driving forces for the miscibility of the blends. © 1997 John Wiley & Sons, Inc.     

Ion binding properties of poly(ethylene oxide)-based networks in dioxane and toluene

Binding constants of alkali picrates to poly(ethylene oxide)-based networks were measured spectrophotometrically in dioxane at 25 and 40°C. The networks were synthesized from aliphatic tri- or tetrafunctional isocyanates and α,ω-diamino-poly-(ethylene glycol)s. The slopes of the Klotz binding plots appear to decrease in the lower picrate concentration range, suggesting that binding of the salt becomes more difficult at high picrate content. It was shown that under saturation conditions six to seven ethylene oxide units are required to bind a sodium picrate ion pair. The affinity of the PEO-resins for the alkali picrate can be enhanced by immobilizing a poly(crown ether) in the network. A number of competition experiments for sodium picrate in toluene was also carried out to obtain the affinity of soluble ligands for alkali salts. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1819–1824, 1997     

Chlorine degradation of polyether-based polyurethane

The tensile properties of polyether-based polyurethane (PU) filaments decrease with increasing chlorine concentrations as well as with treatment times. Fourier transform infrared (FTIR) results show the formation of quinoid, azo, and aldehyde groups in the chlorine-treated PU, and increased hydrogen bonding between the C O C in the soft segment and the N H in the hard segments. A breakdown mechanism involving chain cleavages along the ether linkages in the soft segments as well as at the urethane linkages of the hard–soft segment interfaces is proposed. Chlorine-treated PU showed increased solubility in tetrahydrofuran (THF). The molecular weight data of the THF-soluble portion of treated PU also support the proposed locations of chain scissions. The increased soft segment T_g and T_m with increasing chlorine concentrations are results of increased phase-mixing and hydrogen bonding. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3263–3273, 1997     

Raman longitudinal acoustic mode studies of poly(ethylene oxide) and α,ω-methoxylated poly(ethylene oxide) fractions during isothermal crystallization from the melt

Raman longitudinal acoustic mode (LAM) spectra have been obtained during isothermal crystallization from the melt at various temperatures of a poly(ethylene oxide) (PEO) fraction of molecular weight about 3000 and an α,ω-methoxylated fraction (MPEO) derived from it. For both fractions, we find that noninteger fold (NIF) chains are formed in the initial stages of crystallization. With time, and more rapidly at higher crystallization temperatures, the NIF chains transform into integer-fold (IF) structures. The final morphologies of the two fractions are similar, consisting of IF mixed-crystal lamellae composed mainly of extended (E) chains with embedded once-folded (F2) chains. This solid-state transformation from the NIF state may proceed through the F2 state. The effect of hydrogen bonds in the case of PEO is not to change the transformation process but to slow it when compared to MPEO. Comparison with small-angle x-ray scattering (SAXS) data indicates that in both cases the NIF chains are tilted to the lamellar surface and that the tilt from perpendicular eventually disappears as IF chains form at the later stages of crystallization. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1117–1126, 1997     

Reversible strain-induced order in the amorphous phase of a low-density ethylene/butene copolymer

This article deals with the characterization of the structural changes induced by uniaxial extension in the amorphous phase of an ethylene/butene copolymer. Volume change measurements indicate a reversible densification relevant to a strain-induced organization in the amorphous phase. The dynamic mechanical behavior shows an improvement of the β relaxation that reveals an important immobilization of the amorphous chains. The vibrational behavior investigated by means of Raman spectroscopy suggests that the strained amorphous chains are structurally analogous to the mesomorphic interfacial component. A discussion is made about the mechanism of the transformation of the amorphous phase into a mesomorphic structure compared to the more common strain-induced crystallization phenomenon. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2151–2159, 1997