Free volume and oxygen transport in cold‐drawn polyesters

Poly(ethylene terephthalate) (PET), poly(ethylene terephthalate‐co‐4,4′‐bibenzoate) (PETBB55), and poly(ethylene 2,6‐naphthalate) (PEN) were cold‐drawn to achieve uniform extension without crystallization or stress whitening, and oxygen transport properties were studied at temperatures from 10 to 40 °C. Correlation of oxygen solubility and polymer specific volume made it possible to consider the oriented polyester as a one‐phase densified glass. Orientation was viewed as decreasing the amount of excess‐hole free volume and bringing the nonequilibrium polymer glass closer to the equilibrium condition. Between 10 and 40 °C, the amount of excess‐hole free volume in PET decreased as the polymer approached the glass transition temperature. In contrast, temperature changes in this range had little effect on the excess‐hole free volume in PETBB55 and PEN, which were well below their glass transition temperature. Gas diffusion was viewed as discrete jumps of the oxygen molecule between holes of excess‐free volume. The jump length was extracted from the activation energy for diffusion according to a channel‐formation model. The result agreed well with the hole spacing estimated from a simple lattice model using the hole density reported in the literature. Extending the lattice model to estimate the mean excess‐free volume hole radius from the fractional free volume resulted in good correlation with the hole radius obtained from positron annihilation lifetime spectroscopy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 493–504, 2004     

Oxygen‐barrier properties of cold‐crystallized and melt‐crystallized poly(ethylene terephthalate‐co‐4,4′‐bibenzoate)

This study examined the oxygen‐transport properties of poly(ethylene terephthalate‐co‐bibenzoate) (PETBB55) crystallized from the melt (melt crystallization) or quenched to glass and subsequently isothermally crystallized by heating above the glass‐transition temperature (cold crystallization). The gauche–trans conformation of the glycol linkage was determined by infrared analysis, and the crystalline morphology was examined by atomic force microscopy. Oxygen solubility decreased linearly with volume fraction crystallinity. For melt‐crystallized PETBB55, extrapolation to zero solubility corresponded to an impermeable crystal with 100% trans glycol conformations, a density of 1.396 g cm^?3, and a heat of melting of 83 J g^?1. From the melt, PETBB55 crystallized as space‐filling spherulites with loosely organized lamellae and pronounced secondary crystallization. The morphological observations provided a structural model for permeability consisting of impermeable platelets randomly dispersed in a permeable matrix. In contrast, cold‐crystallized PETBB55 retained the granular texture of the quenched polymer despite the high level of crystallinity, as measured by the density and heat of melting. Oxygen solubility decreased linearly with volume fraction crystallinity, but zero solubility corresponded to an impermeable defective crystal with a trans fraction of 0.83 and a density of 1.381 g cm^?3. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2489–2503, 2002     

Oxygen‐barrier properties of cold‐drawn polyesters

The improvement of oxygen‐barrier properties of glassy polyesters by orientation was examined. Poly(ethylene terephthalate) (PET), poly(ethylene naphthalate), and a copolymer based on PET in which 55 mol % of the terephthalate was replaced with bibenzoate (PET‐BB55) were oriented by constrained uniaxial stretching. In a fairly narrow window of stretching conditions near the glass‐transition temperature, it was possible to achieve uniform extension of the polyesters without crystallization or stress whitening. The processes of orientation and densification correlated with the conformational transformation of glycol linkages from gauche to trans. Oxygen permeability, diffusivity, and solubility decreased with the amount of orientation. A linear relationship between the oxygen solubility and polymer specific volume suggested that the cold‐drawn polyester could be regarded as a one‐phase densified glass. This allowed an analysis of oxygen solubility in accordance with free‐volume concepts of gas permeability in glassy polymers. Orientation was seen as the process of decreasing the amount of excess‐hole free volume and bringing the nonequilibrium polymer glass closer to the equilibrium (zero‐solubility) condition. Cold drawing most effectively reduced the free volume of PET‐BB55. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 862–877, 2002     

Poly(ethylene terephthalate) reinforced by N,N′‐diphenyl biphenyl‐3,3′,4,4′‐tetracarboxydiimide moieties

Starting with 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and methyl aminobenzoate, we synthesized a novel rodlike imide‐containing monomer, N,N′‐bis[p‐(methoxy carbonyl) phenyl]‐biphenyl‐3,3′,4,4′‐tetracarboxydiimide (BMBI). The polycondensation of BMBI with dimethyl terephthalate and ethylene glycol yielded a series of copoly(ester imide)s based on the BMBI‐modified poly(ethylene terephthalate) (PET) backbone. Compared with PET, these BMBI‐modified polyesters had higher glass‐transition temperatures and higher stiffness and strength. In particular, the poly(ethylene terephthalate imide) PETI‐5, which contained 5 mol % of the imide moieties, had a glass‐transition temperature of 89.9 °C (11 °C higher than the glass‐transition temperature of PET), a tensile modulus of 869.4 MPa (20.2 % higher than that of PET), and a tensile strength of 80.8 MPa (38.8 % higher than that of PET). Therefore, a significant reinforcing effect was observed in these imide‐modified polyesters, and a new approach to higher property polyesters was suggested. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 852–863, 2002; DOI 10.1002/pola.10169     

End‐group modification of poly(2,6‐dimethyl‐1,4‐phenylene ether) and in situ synthesis of poly(2,6‐dimethyl‐1,4‐phenylene ether)‐b‐poly(ethylene terephthalate) block copolymer

The preparation of poly(2,6‐dimethyl‐1,4‐phenylene ether)‐b‐poly(ethylene terephthalate) block copolymer was performed by the reaction of the 2‐hydroxyethyl modified poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE‐EtOH) with poly(ethylene terephthalate) (PET) by an in situ process, during the synthesis of the polyester. The yield of the reaction of the 2‐hydroxyethyl functionalized PPE‐EtOH with PET was close to 100%. A significant proportion of the PET‐b‐PPE‐EtOH block copolymer was found to have short PET block. Nevertheless, the copolymer structured in the shape of micelles (20 nm diameter) and very small domains with 50–200 nm diameter, whereas unmodified PPE formed much larger domains (1.5 μm) containing copolymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3985–3991, 2008     

Poly(ethylene terephthalate) copolyesters derived from (2S,3S)‐2,3‐dimethoxy‐1,4‐butanediol

Novel poly(ethylene terephthalate) (PET) copolyesters, abbreviated PEDMBT, containing optically active (2S,3S)‐2,3‐dimethoxy‐1,4‐butanediol (DMBD) as the second comonomer were investigated. Copolymers with ethylene glycol to DMBD ratios between 95/5 and 50/50 as well as the two parent homopolymers, PET and PDMBT, were prepared by a two‐step melt polycondensation. The resulting copolymers were found to approximately have the composition of the polymerization reaction feed and a random microstructure. Polymer intrinsic viscosities varied from 0.4 to 0.6 dL g^?1 with weight‐average molecular weights ranging from 16,000 to 44,000. PEDMBT copolyesters were distinguished in being much more soluble than PET and showing an increasing affinity for water with the content in dimethoxy groups. According to the asymmetric constitution of DMBD, they displayed optical activity in solution. Both melting and glass‐transition temperatures of the copolyesters were observed to steadily decrease with the content in DMBD. PEDMBTs were found to be crystalline for contents in DMBD up to 30 mol %. Both powder and fiber X‐ray diffraction revealed that the same crystalline structure is shared by PET and the crystalline copolyesters. The homopolyester PDMBT resulted in becoming a polymer with a crystallinity comparable to PET but with a significantly different crystalline structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3250–3262, 2001     

Segmented block copolymers of poly(ethylene glycol) and poly(ethylene terephthalate)

A new series of segmented copolymers were synthesized from poly(ethylene terephthalate) (PET) oligomers and poly(ethylene glycol) (PEG) by a two‐step solution polymerization reaction. PET oligomers were obtained by glycolysis depolymerization. Structural features were defined by infrared and nuclear magnetic resonance (NMR) spectroscopy. The copolymer composition was calculated via ¹H NMR spectroscopy. The content of soft PEG segments was higher than that of hard PET segments. A single glass‐transition temperature was detected for all the synthesized segmented copolymers. This observation was found to be independent of the initial PET‐to‐PEG molar ratio. The molar masses of the copolymers were determined by gel permeation chromatography (GPC). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4448–4457, 2004     

Syntheses of random PET‐co‐PTTs and some related copolyesters by entropically‐driven ring‐opening polymerizations and by melt blending: Thermal properties and crystallinity

A library of random poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and seven PET–PTT copolymers has been prepared in a high throughput manner by entropically‐driven ring‐opening polymerizations of the corresponding macrocyclic oligomers. The products have been investigated by differential scanning calorimetry and wide angle X‐ray diffraction. They show that the 50:50 copolymer displays a crystalline phase. The same phase can be formed by in situ transesterification when a 50:50 mixture of PET and PTT is melt blended. Poly(butylene terephthalate) (PBT)–PET and PTT–PBT 50:50 copolymers also show crystal phases. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Compatibilizing effect of transesterification product between components in bisphenol-A polycarbonate/poly(ethylene terephthalate) blend

The compatibilizing effect of a random copolymer, which is the transesterification product, on its corresponding blend system of bisphenol-A polycarbonate/poly(ethylene terephthalate) (PC/PET) has been studied using a Differential Scanning Calorimeter and a Phase Contrast Microscope. It was found that after a long time of transesterification between PET and PC (50/50, wt %), the obtained product, that is, TCET random copolymer, is miscible with individual homopolymers of PC and PET. The addition of the TCET copolymer into the immiscible PC/PET blend can make the glass transitions of the PC-rich phase and PET-rich phase approach each other, and eventually merge into a single glass transition when the content of TCET in the ternary mixture reaches 60 wt %. Meanwhile, the phase structure images showed that with the increasing content of the TCET copolymer in the ternary blends, the size of the phase domains decreases and the phase domains further diminish at 60 wt % TCET. All these results proved the compatibilizing effect of TCET copolymer on the PC/PET blends in their ternary mixture. The mechanism of the compatibilizing effect is directly related to the reduction of the interfacial tension between PC-rich and PET-rich phase domains in the presence of increasing amounts of TCET copolymer in the ternary blends. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2960–2972, 1999     

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     

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     

Poly(ethylene terephthalate) copolymers containing 5‐nitroisophthalic units. I. Synthesis and characterization

Poly(ethylene terephthalate‐co‐5‐nitroisophthalate) copolymers, abbreviated as PETNI, were synthesized via a two‐step melt copolycondensation of bis(2‐hydroxyethyl) terephthalate and bis(2‐hydroxyethyl) 5‐nitroisophthalate mixtures with molar ratios of these two comonomers varying from 95/5 to 50/50. Polymerization reactions were carried out at temperatures between 200 and 270 °C in the presence of tetrabutyl titanate as a catalyst. The copolyesters were characterized by solution viscosity, GPC, FTIR, and NMR spectroscopy. They were found to be random copolymers and to have a comonomer composition in accordance with that used in the corresponding feed. The copolyesters became less crystalline and showed a steady decay in the melting temperature as the content in 5‐nitroisophthalic units increased. They all showed glass‐transition temperatures superior to that of PET with the maximum value at 85 °C being observed for the 50/50 composition. PETNI copolyesters appeared stable up to 300 °C and thermal degradation was found to occur in two well‐differentiated steps. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1934–1942, 2000     

Poly(ethylene terephthalate) terpolyesters containing isophthalic and 5‐tert‐butylisophthalic units

Poly(ethylene terephthalate‐co‐isophthalate‐co‐5‐tert‐butylisophthalate) (PETI^tBI) terpolymers were investigated with reference to poly(ethylene terephthalate) (PET) homopolymer and poly(ethylene terephthalate‐co‐isophthalate) (PETI) copolymers. Three series of PETI^tBI terpolyesters, characterized by terephthalate contents of 90, 80, and 60 mol %, respectively, with different isophthalate/5‐tert‐butylisophthalate molar ratios, were prepared from ethylene glycol and mixtures of dimethyl terephthalate, dimethyl isophthalate, and 5‐tert‐butylisophthalic acid. The composition of the terpolymers and the composition of the feed agreed. All terpolymers had a random microstructure and number‐average molecular weights ranging from 10,000 to 20,000. The PETI^tBI terpolyesters displayed a higher glass‐transition temperature and a lower melting temperature than the PETI copolymers having the same content of terephthalic units. Thermal stability appeared essentially unchanged upon the incorporation of the 5‐tert‐butylisophthalic units. The PETI^tBIs were crystalline for terephthalate contents higher than 80 mol %, and they crystallized at lower rates than PETI. The crystal structure of the crystalline terpolymers was the same as that of PET with the 1,3‐phenylene units being excluded from the crystalline phase. Incorporation of isophthalate comonomers barely affected the tensile modulus and strength of PET, but the brittleness of the terpolymers decreased for higher contents in 5‐tert‐butylisophthalic units. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 124–134, 2003     

Poly(ethylene terephthalate) copolymers containing nitroterephthalic units. I. Synthesis and characterization

The synthesis, microstructure, and thermal behavior of a series of poly(ethylene terephthalate) (PET) copolymers containing nitroterephthalic units are described. These novel copolyesters were synthesized by transesterification followed by melt copolycondensation of dimethyl terephthalate and dimethyl nitroterephthalate mixtures with ethylene glycol. The molar ratio of the two comonomers in the feed varied from 95/5 to 25/75. Furthermore, PET and poly(ethylene nitroterephthalate) homopolymers were synthesized with the same method and comparatively studied. Copolyester compositions were practically the same as in the feed, and weight‐average molecular weights ranged from 10,000 to 60,000. The two monomeric units were randomly distributed along the polymer chain, and the experimentally determined average sequence lengths were in accordance with ideal copolycondensation statistics. Melting temperatures and enthalpies of the copolyesters decreased with increasing content in nitroterephthalic units, and they all showed a single glass‐transition temperature superior to that of PET. They appeared to be stable up to 300 °C, and thermal degradation occurred in two well‐differentiated steps. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3761–3770, 2000     

Calorimetric studies of poly(ethylene terephthalate) stretching over a wide temperature range

Heat effects and structural transformations in amorphous crystallizable poly(ethylene terephthalate) (PET) during uniaxial stretching accompanied by neck formation, have been investigated by calorimetric and x-ray methods over a wide range of temperatures and deformation rates. At small deformation (not exceeding 1–2%) and at temperatures below the glass transition temperature of the polymer, PET behaves as an elastic body. Upon stretching at a constant rate, constant heat power is absorbed, heat effects during loading and unloading coincide completely, and no hysteresis is observed. At large deformations (of the order of 50%), cold drawing develops in this temperature range. The internal energy change in cold drawing is zero within experimental error. A periodic heat release during the self-oscillation regime of drawing PET corresponds to periodic changes in stress, in the rate of the neck formation, and in the appearance of the sample. The temperature limits of the region where crystallization resulting from an uniaxial drawing of the polymer is possible, have been determined, and the heat effect of this phase transition has been measured. Orientation crystallization develops only from 70 to 94°C. These limits are insensitive to changes in deformation rate within one decimal order. The structure of PET in this temperature range has been investigated. The heat of phase transition of orientation crystallization of PET has been determined from the relationship between the measured values of the internal energy change during this process and the limiting degree of crystallinity for the stretched samples. This heat proves to be 5.5 ± 0.1 cal/g.     

Intimate blend of poly(ethylene terephthalate) and poly(ethylene 2,6‐naphthalate) via formation with and coalescence from their common inclusion compound with γ‐cyclodextrin

The experimental procedures to place poly(ethylene 2,6‐naphthalate) (PEN) guest molecules within γ‐cyclodextrin (γ‐CD) host molecules are described along with the subsequent verification of inclusion‐compound (IC) formation. In addition, the simultaneous complexing of PEN and poly(ethylene terephthalate) (PET) with γ‐CD to form their common IC is documented. Coalescence from their common γ‐CD IC generates an intimate blend of the PET and PEN polymers contained therein. Thermal analysis via differential scanning calorimetry reveals thermal behavior indicative of an intimate blend of PET and PEN. ¹H NMR analysis confirms that the intimate blending of PET and PEN achieved by coalescence from their common γ‐CD IC is not due to transesterification into a PET/PEN copolymer during thermal analysis. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 139–148, 2003     

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     

Polyterephthalates made from Ethylene glycol, 1,4‐cyclohexanedimethanol,and isosorbide

Three series of terephthalate polyesters (copolyesters and terpolyesters) containing 70, 80, and 90 mol % of ethylene glycol respectively, 1,4‐cyclohexanedimethanol (CHDM) and isosorbide in varying ratios, were synthesized by melt polycondensation. It was found that only ～75 mol % of the feeding isosorbide was incorporated in the resulting polyesters and that their content in diethylene glycol oscillated between 2 and 4 mol %. The polyesters had weight‐average molecular weights in the 25,000–33,000 g mol^?1 range and polydispersities between 2 and 2.5. The combined ¹H and ¹³C NMR analysis revealed that the microstructure of all these polyesters was at random. They showed good thermal stability with decomposition temperatures above 400 °C. Their glass‐transition temperatures were observed to increase with the content in cyclic diols, this effect being more pronounced when isosorbide was the replacing comonomer. Only the series containing 90 mol % of ethylene terephthalate units was able to crystallize upon cooling from the melt. Compared isothermal crystallizations revealed that isosorbide was more effective than CHDM in repressing the crystallizability of PET. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Isolation and identification of cyclic oligomers of the poly(ethylene terephthalate)–poly(ethylene isophthalate) copolymer

New cyclic oligomers of the copolymer of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI) were isolated and identified. A condensation polymerization was carried out at a high temperature, and the solid‐state polymerization that followed yielded the high molecular weight polymer. The oligomers were extracted from the high molecular weight PET–PEI copolymer and separated with preparative high performance liquid chromatography techniques. Their chemical structures and properties were analyzed and determined by ¹H NMR, differential scanning calorimetry, and mass spectroscopy. The oligomers observed at early retention times were a cyclic dimer and cyclic trimers and consisted of [GT]₃, [GI]₂, [GI]₃, [GT]₂[GI]₁, and [GT]₁[GI]₂. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 881–889, 2003     

Synthesis and thermal behavior of new poly(ethylene terephthalate‐imide)s

Copoly(ethylene terephthalate‐imide)s (PETIs) were synthesized by the melt copolycondensation of bis(2‐hydroxyethyl)terephthalate with a new imide monomer, N,N′‐bis[p‐(2‐hydroxyethoxycarbonyl)phenyl]‐biphenyl‐3,3′,4,4′‐tetracarboxydiimide (BHEI). The copolymers were characterized by intrinsic viscosity, Fourier transform infrared, ¹H NMR, differential scanning calorimetry, and thermogravimetric analysis techniques. Although their crystallinities decreased as the content of BHEI units increased, the glass‐transition temperatures (T_g) increased significantly. When 5 or 10 mol % BHEI units were incorporated into poly(ethylene terephthalate), T_g increased by 10 or 24 °C, respectively. The thermal stabilities of PETI copolymers were about the same as the thermal stability of PET, whereas the weight loss of PETIs decreased as the content of BHEI units increased. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 408–415, 2001