Poly(ethylene terephthalate‐co‐isophthalate) copolyesters obtained from ethylene terephthalate and isophthalate oligomers

A series of poly(ethylene terephthalate‐co‐isophthalate) copolyesters containing upto 50%‐mole of isophthalic units were prepared by polycondensation from ethylene terephthalate and ethylene isophthalate fractions of linear oligomers containing from 5 to 6 repeating units in average. The polyesters were obtained in good yields and with high‐molecular‐weights. The microstructure of the copolyesters was studied as a function of reaction time by ¹³C‐NMR showing that a random distribution of the comonomers was achieved since the earlier stages of polycondensation. The melting temperature and enthalpy of the copolyesters decreased with the content of isophthalic units so that copolyesters containing more than 25% of these units were amorphous. Isothermal crystallization studies made on crystalline copolyesters revealed that the crystallization rate of copolyesters decreased with the content in isophthalic units. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Toughening of bismaleimide resin by modification with poly(ethylene phthalate) and poly(ethylene phthalate-co-ethylene isophthalate)

Aromatic polyesters were prepared and used to improve the brittleness of the bismaleimide resin composed of 4,4′-bismaleimidediphenyl methane and o,o′-diallyl bisphenol A. The aromatic polyesters contain poly(ethylene phthalate) (PEP) and poly(ethylene phthalate-co-ethylene isophthalate) (10 mol % isophthalate unit) (PEPI). PEP and PEPI were effective modifiers for improving the brittleness of the bismaleimide resin. The most suitable composition for the modification of the bismaleimide was inclusion of 20 wt % PEP (MW 18,200), which led to an 80% increase in the fracture toughness with retention of flexural properties and a slight decrease in the glass transition temperature, compared with the mechanical and thermal properties of the unmodified cured bismaleimide resin (Matrimid resin). Microstructures of the modified resins were examined by scanning electron microscopy and dynamic viscoelastic analysis. The thermal stability of the modified resin was slightly lower than that of the unmodified resin by thermogravimetric analysis. The toughening mechanism is discussed in terms of the morphological and dynamic viscoelastic behavior of the modified bismaleimide resin system. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1349–1357, 1997     

Microstructure and crystallization of melt‐mixed poly(ethylene terephthalate)/poly(ethylene isophthalate) blends

Physical blends of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI), abbreviated PET/PEI (80/20) blends, and of PET and a random poly(ethylene terephthalate‐co‐isophthalate) copolymer containing 40% ethylene isophthalate (PET₆₀I₄₀), abbreviated PET/PET₆₀I₄₀ (50/50) blends, were melt‐mixed at 270°C for different reactive blending times to give a series of copolymers containing 20 mol % of ethylene isophthalic units with different degrees of randomness. ¹³C‐NMR spectroscopy precisely determined the microstructure of the blends. The thermal and mechanical properties of the blends were evaluated by DSC and tensile assays, and the obtained results were compared with those obtained for PET and a statistically random PETI copolymer with the same composition. The microstructure of the blends gradually changed from a physical blend into a block copolymer, and finally into a random copolymer with the advance of transreaction time. The melting temperature and enthalpy of the blends decreased with the progress of melt‐mixing. Isothermal crystallization studies carried out on molten samples revealed the same trend for the crystallization rate. The effect of reaction time on crystallizability was more pronounced in the case of the PET/PET₆₀I₄₀ (50/50) blends. The Young's modulus of the melt‐mixed blends was comparable to that of PET, whereas the maximum tensile stress decreased with respect to that of PET. All blend samples showed a noticeable brittleness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3076–3086, 2003     

Relationship between physical properties and chemical structures of poly(ethylene terephthalate-co-ethylene isophthalate)

A series of copolyesters based on different ratios of polyethylene terephthalate (PET) to polyethylene isophthalate (PEI) have been synthesized. With the involvement of PEI, the copolyesters become less crystallizable and even amorphous when PEI content is above 20%. The WAXD profiles of the crystallizable copolyesters infer that the crystals come from PET homopolymer. DSC cooling runs indicated that the copolyesters with PEI no more than 15% are easily crystallizable, while the copolyester with 20% PEI is not easily crystallized at a cooling rate above 5°C/min. Heating runs indicated that the copolyesters with PEI below 20% show melting processes. Nonuniform results were provided by WAXD and DSC, however, the effect of PEI on the ability of crystallization was deduced similarly from WAXD and DSC. Glass transition temperatures have been measured by DSC. Due to the flexibility of PEI chain, glass transition temperatures of the copolyesters decrease linearly with increasing composition of PEI as predicted by the principle of additive contribution. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1191–1195, 1999     

Poly(ethylene isophthalate)s: effect of the tert-butyl substituent on structure and properties

A comparative study of the two isophthalic acid deriving homopolyesters poly(ethylene isophthalate) (PEI) and poly(ethylene 5-tert-butyl isophthalate) (PE^tBI), including synthesis, crystal structure, and thermal and permeability properties, was carried out. The two polyesters were prepared by condensation polymerization in the melt. In both cases, minor amounts of cyclic dimers were observed to form, which were characterized by nuclear magnetic resonance and mass spectroscopy. PEI and PE^tBI were thermally stable up to 400 °C and they appeared to be semicrystalline polyesters, having their melting temperatures between 130 and 135 °C. Their glass-transition temperatures were 62 and 94 °C, respectively. The crystal structure adopted by the two polyesters seemed to consist of a regularly folded conformation, clearly different from the almost extended conformation characteristic of poly(ethylene terephthalate). Gas permeability measurements for N₂, O₂, and CO₂ revealed that PE^tBI is more permeable to these gases than PEI, in spite of having a higher T_g. Furthermore, water vapor diffusion was found to be increased by the insertion of the tert-butyl group, whereas water absorption diminished. The differences in gas and water vapor transport properties observed for these two polyesters were discussed on the basis of their respective molecular structures.     

Interpretation of intrinsic viscosity/temperature data for solutions of poly(phenyl acrylate) and poly(ethylene oxide)

Measured intrinsic viscosities ([η]) at several temperatures (T) within the interval 280–350 K have been found to increase with T for solutions of poly(phenyl acrylate) (PPA) in ethyl lactate. A decrease of [η] with T was observed for aqueous solutions of poly(ethylene oxide) (PEO) at several temperatures within the range 276–358 K. The results have been treated on the basis of eight excluded volume theories, among which the best consistency was afforded by those of Kurata-Stockmayer-Roig, Fixman, and Stockmayer (Padé). These yielded values of ?3.4 × 10^?3 to ?4.7 × 10^?3 deg^?1 and ?0.9 × 10^?3 to ?2.4 × 10^?3 deg^?1 for the temperatur coefficient of the unperturbed dimensions of PPA and PEO, respectively. The derived θ-temperatures were 287 K as the upper critical solution temperature for PPA in ethyl lactate and 365–382 K as the lower critical solution temperature for aqueous PEO.     

Molecular mechanism of photolysis and photooxidation of poly(neopentyl isophthalate)

The mechanism of photodegradation of poly(neopentyl isophthalate), an aromatic polyester as model for industrial polyester coatings, was studied on the molecular level. Changes in the chemical structure of molecules caused by UV irradiation (mercury lamp) were investigated using several analytical techniques. Photodegradation leads both to chain scission and to crosslinking, taking place simultaneously as measured by SEC. Extensive exposure results in appreciable amount of insoluble material (gel). Generation of carbonyl CO and hydroxyl OH/OOH groups in the polymer structure was monitored with ATR-FTIR. MALDI-ToF MS provided detailed structural information on the degradation products of the polyester. In the initial stage of degradation Norrish photocleavage (type I) takes place. Radicals generated in this reaction (photolysis) can directly abstract hydrogen or can react with oxygen creating primarily acid and hydroxyl end groups (photooxidation). Moreover hydrogen abstraction taking place along the polymer backbone followed by oxidation reactions leads to further fragmentation of the polymer chain. The highly informative data provided by MALDI-ToF MS allowed establishing the pathways of photolysis and photooxidation.     

Miscibility of polystyrene with poly(ethylene oxide) and poly(ethylene glycol)

The intrinsic viscosity of polystyrene–poly(ethylene oxide) (PS–PEO) and PS–poly(ethylene glycol) (PEG) blends have been measured in benzene as a function of blend composition for various molecular weights of PEO and PEG at 303.15 K. The compatibility of polymer pairs in solution were determined on the basis of the interaction parameter term, Δb, and the difference between the experimental and theoretical weight-average intrinsic viscosities of the two polymers, Δ[η]. The theoretical weight-average intrinsic viscosities were calculated by interpolation of the individual intrinsic viscosities of the blend components. The compatibility data based on [η] determined by a single specific viscosity measurement, as a quick method for the determination of the intrinsic viscosity, were compared with that obtained from [η] determined via the Huggins equation. The effect of molecular weights of the blend components and the polymer structure on the extent of compatibility was studied. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1471–1482, 1998     

Crystallization and properties of poly(ethylene terephthalate) copolymers containing 5-tert-butyl isophthalic units

The influence of incorporating 5-tert-butyl isophthalic units (^tBI) in the polymer chain of poly(ethylene terephthalate) (PET) on the crystallization behavior, crystal structure, and tensile and gas transport properties of this polyester was evaluated. Random poly(ethylene terephthalate-co-5-tert-butyl isophthalate) copolyesters (PET^tBI) containing between 5 and 40 mol% of ^tBI units were examined. Isothermal crystallization studies were performed on amorphous glassy films at 120 °C and on molten samples at 200 °C by means of differential scanning calorimetry. Furthermore, the non-isothermal crystallization behavior of the copolyesters was investigated. It was observed that both crystallinity and crystallization rate of the PET^tBI copolyesters tend to decrease largely with the comonomeric content, except for the copolymer containing 5 mol% of ^tBI units, which crystallized faster than PET. Fiber X-ray diffraction patterns of the semicrystalline PET^tBI copolyesters proved that they adopt the same triclinic crystal structure as PET with the comonomeric units being excluded from the crystalline phase. Although PET^tBI copolyesters became brittle for higher contents in ^tBI, the tensile modulus and strength of PET were barely affected by copolymerization. The incorporation of ^tBI units slightly increased the permeability of PET, but copolymers containing up to 20 mol% of the comonomeric units were still able to present barrier properties.     

Change in the molecular weight distribution of poly(ethylene oxide) caused by the complexation with poly(acrylic acid)

The complexation between poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) was made by using double the molar quantity of either polymer component at pH 2 where the resulting complex completely precipitates. After the removal of the precipitate, PEO or PAA remaining in the supernatant was subjected to gel permeation chromatography to investigate the change in the molecular weight distribution (MWD) caused by the complexation. No remarkable difference is observed in the MWD curves for PEO[1] (M_w=1.37 × 10⁴) before and after the complexation with PAA[1] (M_w=1.10 × 10³) and PAA[2] (M_w=4.16 × 10⁵). However, the MWD curves of PEO[2] (M_w=1.26 × 10⁵) and PAA[2] become shortened and shift to the low molecular weight side after the complexation with PAA[1] or [2] and PEO[2], respectively. This tendency is enhanced by increasing the complexation temperature. From these results, it is indicated that the complexation between PEO and PAA deals with an equilibrium reaction, and the equilibrium constant is dependent on the chain length of both polymer components and also on the complexation temperature.     

The unperturbed molecular dimensions of poly(ethylene oxide) in aqueous solutions from intrinsic viscosity measurements and the evaluation of the theta temperature

Intrinsic viscosity measurements were carried out on five well characterized fractions of poly(ethylene oxide) in aqueous solutions at 24.9°, 34.9°, and 45.5°C. The Stockmayer-Fixman extrapolation was applied to the data: it yields the unperturbed dimensions K₀ of the chain. The unperturbed root-mean-square end-to-end distance $\text{〈}\text{R}\text{?}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}_0$ calculated for the polymer fractions in water indicate that the polymer molecules are expanded in this solvent as the temperature is raised. The temperature coefficient of unperturbed dimension, $\text{d In}\text{〈}\text{R}\text{?}{}^2\text{〉}{}_0\text{d}\text{t}\text{= 0.024}\text{K}{}^{\mathrm{?1}}$, calculated for poly(ethylene oxide) in water using the present data is about 100 times higher than the literature values of 0.23 (±0.02) × 10^?3 K^?1 and 0.2 (±0.2) × 10^?3 K^?1, respectively, obtained from force-temperature (‘thermoelastic’) measurements on elongated networks of the polymer in the amorphouse state and form viscosity measurements on this polymer in benzene. A value of θ=108.3°C was obtained from the temperature dependence of the interaction parameter B in the Stockmayer-Fixman equation.     

Influence of poly(ethylene glycol)‐containing additives on extrusion of ultrahigh molecular weight polyethylene/polypropylene blend

The influence of poly(ethylene glycol) (PEG)‐containing additives on the extrusion behavior of ultrahigh molecular weight polyethylene/polypropylene (UHMWPE/PP) blend was studied. It was found that the addition of small amounts of PEG to UHMWPE/PP blend resulted in significant reduction of die pressure and melt viscosity, and obvious increase of the flow rate at a given die pressure, while PEG/diatomite binary additives enhanced the improvement in the processability of UHMWPE/PP blend. When pure HDPE was extruded with the die through which UHMWPE/PP/PEG blend was previously extruded, the extrusion pressure of HDPE increased with the extrusion time gradually. This meant that PEG might migrate to the die wall surface and coat it in the extrusion of UHMWPE/PP/PEG blend. FTIR spectra and SEM micrographs of the UHMWPE/PP/PEG extrudates indicated that PEG located not only at the surface but also in the interior of the extrudates. So, the external lubrication at the die wall, combined with the internal lubrication to induce interphase slippage of the blend, was proposed to be responsible for the reduction of die pressure and viscosity. In addition, an ultrahigh molecular weight polysiloxane and a fluoropolymer processing aid were used as processing aids in the extrusion of UHMWPE/PP as control, and the results showed that only minor reduction effects in die pressure and melt viscosity were achieved at their suggested loading level. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1282–1288, 2006     

Poly(propylene)/poly(ethylene terephthalate‐co‐isophthalate) blends and glass bead filled composites: Microstructure and thermomechanical properties

Blends of poly(propylene) (PP) and poly(ethylene terephthalate‐co‐isophthalate) (co‐PET) (95/5) with and without compatibilizing agent (maleic anhydride PP), as well as composites of these blends with glass beads (50 wt%) with and without silane coupling agent surface‐treatment, were prepared and studied on a basis of the material microstructure and thermomechanical properties. Infrared and Raman spectroscopy, as well as transmission electron microscopy, displayed evidence of MAPP compatibilizing action for the blend. Differential scanning calorimetry showed a remarkable effect of nucleation rate increase exerted by co‐PET on the PP crystallization. Moreover, glass beads were found to increase the PP nucleation rate slightly. PP crystallinity hardly varied with the composition. Wide angle X‐ray diffraction allowed determination of differences in the orientation of the poly(propylene) b‐axis, with more homogeneous orientations in the presence of both co‐PET and glass beads. MAPP promoted the PP b‐axis orientation. Differences in PP α′ relaxation could be analyzed through dynamic‐mechanical thermal analysis (DMTA). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1841–1852, 2004     

Miscibility of C60-end-capped poly(ethylene oxide) with poly(vinyl chloride)

The miscibility of blends of single [60]fullerene (C₆₀)-end-capped poly(ethylene oxide) (FPEO) or double C₆₀-end-capped poly(ethylene oxide) (FPEOF) with poly(vinyl chloride) (PVC) has been studied. Similar to poly(ethylene oxide) (PEO), both FPEO and FPEOF are also miscible with PVC over the entire composition range. X-ray photoelectron spectroscopy showed the development of a new low-binding-energy Cl2p doublet and a new high-binding-energy O1s peak in FPEO/PVC blends. The results show that the miscibility between FPEO and PVC arises from hydrogen bonding interaction between the α-hydrogen of PVC and the ether oxygen of FPEO. From the melting point depression of PEO, FPEO or FPEOF in the blends, the Flory-Huggins interaction parameters were found to be −0.169, −0.142, −0.093 for PVC/PEO, PVC/FPEO and PVC/FPEOF, respectively, demonstrating that all the three blend systems are miscible in the melt. However, the incorporation of C₆₀ slightly impairs the interaction between PEO and PVC.     

DSC and TMDSC study of melting behaviour of poly(butylene succinate) and poly(ethylene succinate)

The subsequent melting behaviour of poly(butylene succinate) (PBSU) and poly(ethylene succinate) (PES) was investigated using DSC and temperature modulated DSC (TMDSC) after they finished nonisothermal crystallization from the melt. PBSU exhibited two melting endotherms in the DSC traces upon heating to the melt, which was ascribed to the melting and recrystallization mechanism. However, one melting endotherm with one shoulder and one crystallization exotherm just prior to the melting endotherm were found for PES. The crystallization exotherm was ascribed to the recrystallization of the melt of the crystallites with low thermal stability, and the shoulder was considered to be the melting endotherm of the crystallites with high thermal stability. The final melting endotherm was ascribed to the melting of the crystallites formed through the reorganization of the crystallites with high thermal stability during the DSC heating process. TMDSC experiments gave the direct evidences to support the proposed models to explain the melting behaviour of PBSU and PES crystallized nonisothermally from the melt.     

Viscosity–molecular weight relationship for aminopropyl‐terminated poly(dimethylsiloxane)

Aminopropyl‐terminated poly(dimethylsiloxane) (ATPS) with different molecular weights was prepared by base‐catalyzed equilibration of octamethylcyclotetrasiloxane and 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetramethyldisiloxane with different ratios. Their number‐average molecular weights (M_n) were determined by end–group analysis, and intrinsic viscosity ([η]) in toluene was measured with a Ubbelohde viscometer. A relationship between M_n and [η] was obtained for ATPS. For 1.0 × 10⁴ < M_n < 6.0 × 10⁴, it was in accord with [η]_{toluene,25°C} = 5.26 × 10^?2 M_n^0.587. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 975–978, 2001     

Finite strain behavior of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG)

Uniaxial and plane strain compression experiments are conducted on amorphous poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate)-glycol (PETG) over a wide range of temperatures (25-110 °C) and strain rates (.005-1.0 s⁻¹). The stress-strain behavior of each material is presented and the results for the two materials are found to be remarkably similar over the investigated range of rates, temperatures, and strain levels. Below the glass transition temperature (θ_g=80 °C), the materials exhibit a distinct yield stress, followed by strain softening then moderate strain hardening at moderate strain levels and dramatic strain hardening at large strains. Above the glass transition temperature, the stress-strain curves exhibit the classic trends of a rubbery material during loading, albeit with a strong temperature and time dependence. Instead of a distinct yield stress, the curve transitions gradually, or rolls over, to flow. As in the sub-θ_g range, this is followed by moderate strain hardening and stiffening, and subsequent dramatic hardening. The exhibition of dramatic hardening in PETG, a copolymer of PET which does not undergo strain-induced crystallization, indicates that crystallization may not be the source of the dramatic hardening and stiffening in PET and, instead molecular orientation is the primary hardening and stiffening mechanism in both PET and PETG. Indeed, it is only in cases of deformation which result in highly uniaxial network orientation that the stress-strain behavior of PET differs significantly from that of PETG, suggesting the influence of a meso-ordered structure or crystallization in these instances. During unloading, PETG exhibits extensive elastic recovery, whereas PET exhibits relatively little recovery, suggesting that crystallization occurs (or continues to develop) after active loading ceases and unloading has commenced, locking in much of the deformation in PET.     

Synthesis and characterisation of copolyesters from poly(ethylene terephthalate) and poly(hexamethylene terephthalate)

Copolyesters containing poly(ethylene terephthalate) and poly(hexamethylene terephthalate) (PHT) were prepared by a melt condensation reaction. The copolymers were characterised by infrared spectroscopy and intrinsic viscosity measurements. The density of the copolyesters decreased with increasing percentage of PHT segments in the backbone. Glass transition temperatures (T_g). melting points (T_m) and crystallisation temperatures (T_c) were determined by differential scanning calorimetry. An increase in the percentage of PHT resulted in decrease in T_g, T_m and T_c. The as-prepared copolyesters were crystalline in nature and no exotherm indicative of cold crystallisation was observed. The relative thermal stability of the polymers was evaluated by dynamic thermogravimetry in a nitrogen atmosphere. An increase in percentage of PHT resulted in a decrease in initial decomposition temperature. The rate of crystallisation of the copolymers was studied by small angle light scattering. An increase in percentage of PHT resulted in an increase in the rate of crystallisation.     

Intermolecular interaction in aqueous solution of binary blends of poly(acrylamide) and poly(ethylene glycol)

The interaction between poly(acrylamide) (PAM) and poly(ethylene glycol) (PEG) in their solid mixture was studied by Fourier transform infrared spectroscopy (FTIR); and their interaction in aqueous solution was investigated by nuclear magnetic resonance spectroscopy (NMR). For the solid PAM/PEG mixtures, an induced shift of the >C?O and >N? H in amide group was found by FTIR. These results could demonstrate the formation of intermolecular hydrogen bonding between the amide group of PAM and the ether group of PEG. In the aqueous PAM/PEG solution system, the PAM and PEG associating with each other in water, i.e., the amide group of PAM interacting with the ether group of PEG through hydrogen bonding was also found by ¹H NMR. Furthermore, the effects of different molecular weight of PAM on the strength of hydrogen bonding between PAM and PEG in water were investigated systemically. It was found that the hydrogen bonding interaction between PAM and PEG in water did not increase with the enlargement of the PAM molecular weight as expected. This finding together with the viscosity reduction of aqueous PAM/PEG solution with the PAM molecular weight increasing strongly indicated that PAM molecular chain, especially having high molecular weights preferred to form spherical clews in aqueous PEG solution. Therefore, fewer amide groups in PAM could interact with the ether groups in PEG. Based on these results, a mechanism sketch of the interaction between PAM and PEG in relatively concentrated aqueous solution was proposed. The fact that the phase separation of aqueous PAM/PEG solution occurs while raising the temperature indicates that this kind of hydrogen bonding between PAM and PEG in water is weak and could be broken by controlling the temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

高分子量聚醋酸乙烯酯的醇解研究

探讨了催化剂浓度、醇解温度和反应时间等对高分子量聚醋酸乙烯酯醇解的影响,得出高分子量聚醋酸乙烯酯醇解的适合条件。