Miscibility of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) blends by transesterification

The effects of transesterification on the miscibility of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) were studied. Blends were obtained by solution precipitation at room temperature to avoid transesterification during blend preparation. The physical blends and transesterified products were analyzed by wide-angle x-ray scattering, differential scanning calorimetry, and nuclear magnetic resonance spectroscopy. It was found that the physical blends are immiscible and when the extent of transesterification reaches 50% of the completely randomized state, independent of blend composition, the blends are not crystallizable and show a single glass transition temperature between those of starting polymers. The interchange reactions were significantly influenced by annealing temperature and time but negligibly by blend composition. © 1996 John Wiley & Sons, Inc.     

Interval kinetic gravimetric sorption of acetone in random copolymers of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate)

Interval sorption kinetics of acetone in solvent cast films of random poly(ethylene terephthalate)-co-(ethylene 2,6-naphthalate) (PET-co-PEN) are reported at 35°C and at acetone pressures ranging from 0 to 7.3 cm Hg. Polymer composition is varied systematically from 0% to 50% poly(ethylene 2,6-naphthalate). Equilibrium sorption is well described by the dual-mode sorption model. Interval sorption kinetics are described using a two-stage model that incorporates both Fickian diffusion and protracted polymer structural relaxation. The incorporation of low levels of PEN into PET significantly reduces the excess free volume associated with the glassy state and, for these interval acetone sorption experiments in ∼ 5 μm-thick films, decreases the fraction of acetone uptake controlled by penetrant-induced polymer structural relaxation. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2973–2984, 1999     

Reactive blending of poly(ethylene 2,6-naphthalate) and Vectra A

In situ composites based on poly(ethylene 2,6-naphthalate) (PEN) and a thermotropic liquid crystal polymer (Vectra A950) were prepared by melt blending under different processing conditions. Thermal behaviour, mechanical and physical properties and morphology of the blends were investigated. The DSC analysis indicates that, as expected, Vectra enhances the crystallization process of PEN. Moreover, mechanical and thermal tests evidence the significant role of 20 wt% Vectra on increasing the material performances; tensile properties, coupled with SEM, show that strength and modulus of PEN are significantly improved when Vectra domains are long and continuous fibrils. The overall results can be attributed to the compatibilisation of the system induced by the mixing conditions that affect the extent of transreactions occurring in the melt. To deepen this aspect, the soluble and insoluble fractions in a PEN solvent were isolated and thoroughly characterized: both the fractions contain PEN/Vectra copolymers. The results underline the potentiality of the PEN/Vectra system for different high-performance applications requiring superior strength and modulus, heat stability or barrier properties.     

Synthesis,physical characterization,and acetone sorption kinetics in random copolymers of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate)

Random copolymers of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) were synthesized by melt condensation. In a series of thin, solvent cast films of varying PEN content, acetone diffusivity and solubility were determined at 35°C and an acetone pressure of 5.4 cm Hg. The kinetics of acetone sorption in the copolymer films are well described by a Fickian model. Both solubility and diffusivity decrease with increasing PEN content. The acetone diffusion coefficient decreases 93% from PET to PET/85PEN, a copolymer in which 85 weight percent of the dimethyl terephthalate in PET has been replace by dimethyl naphthalate 2,6-dicarboxylate. The acetone solubility coefficient in the amorphous regions of the polymer decreases by approximately a factor of two over the same composition range. The glass/rubber transition temperatures of these materials rise monotonically with increasing PEN content. Copolymers containing 20 to 80 wt % PEN are amorphous. Samples with <20% or >80% PEN contain measurable levels of crystallinity. Estimated fractional free volume in the amorphous regions of these samples is lower in the copolymers than in either of the homopolymers. Relative free volume as probed by positron annihilation lifetime spectroscopy (PALS) decreases systematically with increasing PEN content. Acetone diffusion coefficients correlate well with PALS results. Infrared spectroscopy suggests an increase in the fraction of ethylene glycol units in the trans conformation in the amorphous phase as the concentration of PEN in the copolymer increases. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2981–3000, 1998     

Non-isothermal crystallization kinetics of poly(trimethylene terephthalate)/poly(ethylene 2,6-naphthalate) blends

The glass-transition temperature and non-isothermal crystallization of poly(trimethylene terephthalate)/poly(ethylene 2,6-naphthalate) (PTT/PEN) blends were investigated by using differential scanning calorimeter (DSC). The results suggested that the binary blends showed different crystallization and melting behaviors due to their different component of PTT and PEN. All of the samples exhibited a single glass-transition temperature, indicating that the component PTT and PEN were miscible in amorphous phase. The value of T_g predicted well by Gordon-Taylor equation decreased gradually with increasing of PTT content. The commonly used Avrami equation modified by Jeziorny, Ozawa theory and the method developed by Mo were used, respectively, to fit the primary stage of non-isothermal crystallization. The kinetic parameters suggested that the PTT content improved the crystallization of PEN in the binary blend. The crystallization growth dimension, crystallization rate and the degree of crystallinity of the blends were increased with the increasing content of PTT. The effective activation energy calculated by the advanced iso-conversional method developed by Vyazovkin also concluded that the value of E_a depended not only on the system but also on temperature, that is, the binary blend with more PTT component had higher crystallization ability and the crystallization ability is increased with increasing temperature. The kinetic parameters U^* and K_g were also determined, respectively, by the Hoffman-Lauritzen theory.     

FTIR spectroscopic study on crystallization process of poly(ethylene-2,6-naphthalate)

In situ Fourier transform infrared (FTIR) measurements were carried out to elucidate conformation changes occurring during the isothermal melt crystallization of poly(ethylene-2,6-naphthalate) (PEN). Based on the band assignments for the components of the amorphous, α-crystal form, and β-crystal form of PEN in film samples, the in situ data was analyzed in terms of the amorphous- and crystal-trans conformations. It was observed at a higher isothermal crystallization temperature that the formation of amorphous-trans conformations precedes the growth of crystals. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2741–2747, 1997     

Studies on the formation and characterization of poly(trimethylene 2,6‐naphthalenedicarboxylate)

Bis‐(3‐hydroxypropyl) 2,6‐naphthalenedicarboxylate (BHPN) was polymerized to poly(trimethylene 2,6‐naphthalenedicarboxylate) (PTN) in the presence of various catalysts. The order of the catalytic reactivity was Sb(III) < Zr(IV) < Sn(IV) < Ti(IV). The influence of temperature and catalyst concentration on the properties of PTN was studied with Ti(IV)butylate as a catalyst. The catalysis with titanium resulted in a yellowish polymer only if the polycondensation temperature exceeded 260 °C. PTN and its monomer BHPN were characterized by infrared spectroscopy. ¹H NMR spectroscopy was employed to determine the quantity of bis‐(3‐hydroxypropyl)ether in PTN. The content of diolether was less than 1 mol %. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 620–629, 2001     

Lamellar‐level morphology induced by combined crystallization and liquid–liquid demixing in a poly(ethylene terephthalate)/poly(ethylene‐2,6‐naphthalate) blend

The lamellar‐level morphology of an extruded poly(ethylene terephthalate) (PET)/poly(ethylene‐2,6‐naphthalate) (PEN) blend was investigated with small‐angle X‐ray scattering (SAXS). Measurements were made as a function of the annealing time in the melt and the crystallization temperature. The characteristic morphological parameters at the lamellar level were determined by correlation function analysis of the SAXS data. At a low crystallization temperature of 120 °C, the increased amorphous layer thickness was identified in the blend, indicating that some PEN was incorporated into the interlamellar regions of PET during crystallization. The blend also showed a larger lamellar thickness than pure PET. A reason for the increase in the lamellar thickness might be that the formation of thinner lamellar stacks by secondary crystallization was significantly restricted because of the increased glass‐transition temperature. At high crystallization temperatures above 200 °C, the diffusion rates of noncrystallizable components were faster than the growth rates of crystals, with most of the noncrystallizable components escaping from the lamellar stacks. As a result, the blend showed an interfibrillar or interspherulitic morphology. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 317–324, 2002     

Influence of multiwall carbon nanotube on physical properties of poly(ethylene 2,6‐naphthalate) nanocomposites

Polymer nanocomposites consisting of multiwall carbon nanotube (MWCNT) and poly(ethylene 2,6‐naphthalate) (PEN) were prepared by a melt blending process in a twin‐screw extruder. The storage modulus (G′) and loss modulus (G″) of the PEN/MWCNT nanocomposites increased with increasing frequency, and this increment being more significant at low frequency. The terminal zone slope of G′ for the PEN/MWCNT nanocomposites decreased with increasing MWCNT content, and the nonterminal behavior of those was related to the dominant nanotube–nanotube interactions at higher MWCNT content, leading to the formation of the interconnected or network‐like structures of MWCNT in the polymer nanocomposites. The decrease in the slope of the plot of log G′ versus log G″ for the PEN/MWCNT nanocomposites with increasing MWCNT content suggested the changes in the microstructures of the polymer nanocomposites by incorporating MWCNT. The incorporation of very small quantity of MWCNT significantly improved the mechanical properties of the PEN/MWCNT nanocomposites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1062–1071, 2006     

Relaxation behavior of poly(ethylene terephthalate)/poly(ethylene naphthalene 2,6‐dicarboxylate) blends prepared by cryogenic blending

A method including cryogenic grinding, melt pressing from the molten state, and quenching was used to prepare blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene 2,6‐dicarboxylate) (PEN) in which the two phases were highly dispersed. The effect of melt‐pressing times on the thermal properties and relaxation behavior of PET/PEN films were characterized with differential scanning calorimetry and dielectric spectroscopy. For short melt‐pressing times, two glass‐transition, two crystallization, and two melting peaks were observed, indicating the presence of PET‐rich and PEN‐rich phases in these blends. Longer melt‐pressing times revealed a single glass transition and a single α‐relaxation process, showing that PET–PEN block copolymers were likely to be formed during the melt pressing. The experimental findings were examined in terms of the transesterification reactions between the blend components, as revealed by ¹H NMR measurements. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2570–2578, 2002     

Studies on the formation of PEN. I. Kinetic aspects of catalyzed reaction in transesterification of dimethylnaphthalate with ethylene glycol

The transesterification of dimethyl naphthalate (DMN) with ethylene glycol (EG) was kinetically investigated in the presence of various catalysts at 185°C. The transesterification was assumed to obey first-order kinetics with respect to DMN and EG, and a rate equation was derived. The rate constant of transesterification which was calculated from the quantity of methanol which distilled from the reaction vessel was used to evaluate the activity of each metal compound. The first-order dependence on the catalyst concentration is valid below a critical concentration which was found to be dependent on the catalyst type. The order of decreasing catalytic activity of various metal ions was found to be: Pb ≥ Zn > Co > Mg > Ni ≥ Sb, but in the case of highly basic metal salts, the rate constants were found to be extremely large at the initial stage of the reaction, and then rapidly decreased with the progress of the reaction. Effects of reaction temperature were also discussed. The activation energies for zinc acetate and lead acetate were 97.84 and 108.8 kJ/mol, respectively, which were calculated from the Arrhenius equation. © 1994 John Wiley & Sons, Inc.     

The production and properties of poly(ethylene naphthalate-2,6-dicarboxylate) monofilaments

Experimental spinning and drawing conditions are described for poly(ethylene naphthalate-2,6-dicarboxylate), PEN, which produce good quality 0.5 mm monofilaments with high strength and uniformity. Mechanical properties were measured for a range of draw temperatures and draw ratios and an initial modulus of 22 GPa and a strength of 0.6 GPa were obtained by single stage drawing to a draw ratio of 6.6. The maximum birefringence achieved by single stage drawing was 0.33 compared with a theoretical maximum of 0.332 calculated from the bond polarizabilities and bond angles of the aligned monomer unit. Network parameters relevant to undrawn PEN and to the early stages in the drawing process were derived from simple rubber elasticity theory by making birefringence and shrinkage force measurements on films drawn homogeneously to low draw ratios. These suggest that the PEN network contains relatively stiff chains between entanglements and that the PEN network is modified much more in the drawing process than is the case with poly(ethylene terephthalate). A new method of measuring the birefringence of highly drawn thick filaments is described.     

Synthesis and characterization of poly(butylene terephthalates) modified by hydroquinone bis(2-hydroxyethyl)ether

A series of thermoplastic poly(butylene-co-hydroquinone bis(2-hydroxyethyl)ether terephthalates) (PBHT), with different molar ratios of hydroquinone bis(2-hydroxyethyl)ether (HQEE)/1,4-butanediol 9/91, 18/82 and 27/73, were synthesized via melt polycondensation. The compositions, thermodynamics and crystallization properties of the obtained copolyesters were characterized in detail by ¹H NMR, differential scanning calorimeters (DSC), thermogravimetric analysis (TGA) and X-ray diffraction (XRD). These results showed that the PBHTs were successfully synthesized, and the incorporation of the HQEE group significantly improved thermal properties of the polymers. However, HQEE did not change the crystal structure of PBT. The T_m values of the copolymers decreased (from 208?°C to 174?°C) with increasing content of HQEE segments, on the contrary, T_g values increased (from 37?°C to 43?°C). The temperatures for 5% weight loss did not decrease and appeared at a range of 373–377?°C.     

Transesterification kinetics of poly(ethylene terephthalate) and poly(ethylene 2,6‐naphthalate) blends with the addition of 2,2′‐bis(1,3‐oxazoline)

The kinetics of the transesterification reaction between poly(ethylene terephthalate) (PET) and poly(ethylene 2,6‐naphthalate) (PEN) with and without the addition of a chain extender were studied with ¹H NMR. Different kinetic approaches were considered, and a second‐order, reversible reaction was accepted for the PET/PEN reactive blend system. The addition of 2,2′‐bis(1,3‐oxazoline) (BOZ) promoted the transesterification reaction between PET and PEN in the molten state. The activation energy of the transesterification reaction for the PET/PEN reactive blend with BOZ (94.0 kJ/mol) was lower than that without BOZ (168.9KJ/mol). The rate constant k took an almost constant value for blend samples with different compositions mixed at 275 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2607–2614, 2001     

Orientation of uniaxially stretched poly(ethylene naphthalene 2,6‐dicarboxylate) films by polarized infrared spectroscopy

Poly(ethylene naphthalene‐2,6‐dicarboxylate) has been uniaxially stretched at different draw ratios and at two different temperatures below and above its glass transition (T_g ～ 120 °C) respectively, at 100 and 160 °C. Crystallinity has been evaluated from calorimetric analyses and compared to the values deduced by FTIR spectroscopic data. As expected, the obtained results are quite similar and show that films stretched at lower temperature (100 °C) are more crystalline than those stretched at 160 °C. Optical anisotropy associated with orientation has been evaluated by birefringence and show that films stretched at 100 °C are more birefringent than those stretched at 160 °C as a result of a higher chain relaxation above T_g. Polarized FTIR was also performed to evaluate the individual orientation of amorphous and crystalline phases by calculating dichroic ratios R and orientation functions 〈P₂(cos θ)〉 and also show that amorphous and crystalline phases are more oriented in the case of films stretched below T_g. Nevertheless, the orientation of the amorphous phase is always weaker than that of the crystalline phase. Films stretched at 100 °C show a rapid increase in orientation (and crystallinity) with draw ratio and 〈P₂(cos θ)〉 reaches a limit value when draw ratio becomes higher than 3.5. Films drawn at 160 °C are less oriented and their orientation is increasing progressively with draw ratio without showing a plateau. A careful measurement of the IR absorbance was necessary to evaluate the structural angles of the transition moments to the molecular chain axis. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1950–1958, 2007     

Miscibility,melting, and crystallization of poly(butylene‐2,6‐naphthalate)/poly(ether imide) blends

We prepared blends of poly(butylene‐2,6‐naphthalate) (PBN) and poly(ether imide) (PEI) by solution‐casting from dichloroacetic acid solutions. The miscibility, crystallization, and melting behavior of the blends were investigated with differential scanning calorimetry (DSC) and dynamic mechanical analysis. PBN was miscible with PEI over the entire range of compositions, as shown by the existence of single composition‐dependent glass‐transition temperatures. In addition, a negative polymer–polymer interaction parameter was calculated, with the Nishi–Wang equation, based on the melting depression of PBN. In nonisothermal crystallization investigations, the depression of the crystallization temperature of PBN depended on the composition of the blend and the cooling rate; the presence of PEI reduced the number of PBN segments migrating to the crystallite/melt interface. Melting, recrystallization, and remelting processes occurring during the DSC heating scan caused the occurrence of multiple melting endotherms for PBN. We explored the effects of various experimental conditions on the melting behavior of PBN/PEI blends. The extent of recrystallization of the PBN component during DSC heating scans decreased as the PEI content, the heating rate, the crystallization temperature, and the crystallization time increased. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1694–1704, 2004     

Studies on the formation of PEN. II. Polymerization of bis(hydroxyethyl) naphthalate by various metallic catalysts

Bis(hydroxyethyl) naphthalate (BHEN) was polymerized to polyethylenenaphthalate (PEN) in the presence of various metallic catalysts. The influence of the nature and concentration of these catalysts on the rate of polymerization has been investigated. The order of decreasing catalytic influence of various metal ions on the polymerization of BHEN was found to be: Ti > Sb > Zn > Co > Pb > Ni(Mg). The effect of the reaction temperature has also been studied. The optimal concentration of these catalyst and reaction temperature were found to be 30 × 10^?5 (mol/mol BHEN) and 285–293°C, respectively. Because of its insolubility in ordinary solvent, the molecular weight of PEN was measured using the light scattering method. © 1994 John Wiley & Sons, Inc.     

Study of the Crystallization Kinetics. Poly(ethylene oxide) and a blend of poly(ethylene oxide) and poly(bisphenol A-co-epichlorohydrin)

A kinetic study of the crystallization of poly(ethylene oxide) (PEO) and of a blend of PEO+poly(bisphenol A-co-epichlorohydrin) (PBE) was performed by using DSC in a non-isothermal program at constant cooling rates. The curves obtained were analyzed by the Kissinger, Ozawa and Friedman methods, with determination of the kinetic parameters in each case. As a consequence of the presence of PBE, the kinetic parameters were altered, leading to the conclusion that PBE has some influence on the crystallization of PEO, modifying its mechanism. This revised version was published online in July 2006 with corrections to the Cover Date.