Effect of the temperature on the chemical healing of poly(ethylene terephthalate)

The effect of temperature on the chemical healing of poly(ethylene terephthalate) (PET) – healing as a result of chemical reactions between neighboring macromolecules located in the interface surface — was studied. The healing process was carried out in vacuum on pressed partially overlapped strips of commercial PET, previously annealed at 258°C, at temperatures between 140 and 250°C for 24 h. It is demonstrated that the fracture behavior of the welded samples depends strongly on the healing temperature T_h. At T_h > 200°C the strips break beyond the contact area, at 160 < T_h < 200°C debonding occurs, and at T_h < 160°C no bonding is observed. It is assumed that the bonding effect is mainly a result of chemical reactions (solid state postcondensation and transreactions) taking place during the healing procedure.     

Crystallization behaviour of poly(ethylene terephthalate) and poly(tetramethylene terephthalate) blends

The isothermal and non-isothermal crystallization behaviour of blends of poly(ethylene terephthalate) (PET) and poly(tetramethylene terephthalate) (PBT) is investigated at low percentage of the second component. The melting behaviour of the isothermally crystallized sample shows that the crystallization behaviour in the blend is governed by the mobility of PBT. Below 200°C the crystallization process is hindered, whereas above 200°C the PET crystals are larger in case of added PBT. The non-isothermal crystallization behaviour shows that the crystallization process is hindered when the PBT content in the blend is less or higher than 6 wt.-%.     

Studies on poly(trimethylene terephthalate) filaments containing silver

Two methods were used to incorporate silver ions into poly(trimethylene terephthalate) (PTT) fibers. The first technique involved the direct addition of silver (I) sulfadiazine into PTT polymer prior to extrusion. The second method involved the use of silver-exchanged zeolites. Although no optimization with silver-exchanged zeolites was conducted, this study clearly showed that PTT fibers containing sufficient amounts of silver ions are effective in reducing pathological-microorganisms such as Escherichia coli. Incorporation of silver-exchanged zeolites into PTT imparted a silver color to the fibers which may be attributed to the partial reduction of silver ions during spinning at 256 degrees C. Because of the decomposition of silver (I) sulfadiazine, the spinnability of PTT fiber sample was not satisfactory and, therefore, this compound cannot be used as a carrier of silver ions in PTT. The thermal, tensile and antimicrobial properties of the spun filaments are reported in this paper.     

Heparinizable materials (IV). Surface-grafting on poly(ethylene terephthalate) of heparin-complexing poly(amido-amine) chains

By a chemical process poly(amido-amine) chains have been grafted on the surface of poly(ethylene terephthalate) (Dacron) devices. After treatment, it was shown that the devices could adsorb significant amounts of heparin. Most of the adsorbed heparin can be recovered only by eluting at pH greater than 10 with NaOH solution.     

Unit cell dimensions of poly(ethylene terephthalate)

The density of crystals of poly(ethylene terephthalate), (PETP), Q_c is checked by X-ray diffraction assuming a triclinic unit cell and the indices of reflections as found by Bunn. The following unit cell dimensions are found: a = 4,48Å, b = 5,85Å, c = 10,75 Å, α = 99,5°, β = 118,4°, and γ = 111,2°. This gives the density Q_c as 1,515g/cm³ which is about 4% higher than that reported by Bunn. Negligible differences in spacings for samples annealed at different temperatures (120°C–260°C) have been found. Only for an annealing temperature of 100°C the higher d-values lead to Q_c = 1,484g/cm³. For undrawn PETP films annealed at 250°C the same value of Q_c as for drawn PETP was obtained on the basis of Guinier X-ray patterns. No systematic variation of crystal plane spacings was found for drawn PETP fibers annealed at 220°C and containing mole fractions of 1,7 to 4,2% diethylene glycol, (2,2′-oxydiethanol), as comonomer.     

Process analysis: properties of poly(ethylene terephthalate) measured by near infrared spectroscopy, 1. At-line analysis of poly(ethylene terephthalate) chips

Near infrared (NIR) reflectance spectra recorded from poly(ethylene terephthalate) (PET) chips contain a sufficient amount of information to estimate the number of carboxylic end groups and the relative viscosity. To obtain reliable results, careful attention has to be paid to the calibration procedure.     

Process analysis: properties of poly(ethylene terephthalate) measured by near infrared spectroscopy, 2. In-line analysis of poly(ethylene terephthalate) melt

Near infrared (NIR) transmission spectra recorded from poly(ethylene trerephthalate) (PET) melt contain a sufficient amount of information to estimate the number of carboxylic end groups and the relative viscosity. In-line monitoring of these quality parameters is feasible.     

Influence of chemical structure on glass transition temperatures of poly(propylene terephthalate) and poly(propylene isophthalate)

Poly(propylene terephthalate)

1 Systematic IUPAC name: poly(oxypropyleneoxyterephthaloyl).

(PPTP) and poly(propylene isophthalate)

2 Systematic IUPAC name: poly(oxypropyleneoxyisophthaloyl).

(PPIP) were prepared by melt polycondensation. Different fractions with number-average molar masses in the range 5 000 ? 20 000 g·mol^?1 were obtained and their respective glass transition temperatures (T_g) determined by calorimetry. The solubility parameters of the polymers were obtained by viscosity measurements in different solvents and were found to be 9,4 and 9,5 cal^1/2·cm^?3/2 (19,2·10³ and 19,4·10³ J^1/2·m^?3/2) for PPIP and PPTP, respectively. The glass transition temperatures were compared with those reported for analogous polyesters and it was shown that intramolecular interactions highly influence the T_g of these polyesters, whereas the effect of intermolecular interactions seems to be less important.     

In vivo and in vitro degradation of poly(ether ester) block copolymers based on poly(ethylene glycol) and poly(butylene terephthalate)

Two in vivo degradation studies were performed on segmented poly(ether ester)s based on polyethylene glycol (PEG) and poly(butylene terephthalate) (PBT) (PEOT/PBT). In a first series of experiments, the in vivo degradation of melt-pressed discs of different copolymer compositions were followed up for 24 weeks after subcutaneous implantation in rats. The second series of experiments aimed to simulate long-term in vivo degradation. For this, PEOT/PBT samples were pre-degraded in phosphate buffer saline (PBS) at 100 degrees C and subsequently implanted. In both series, explanted materials were characterized by intrinsic viscosity measurements, mass loss, proton nuclear magnetic resonance spectroscopy (1H-NMR) and differential scanning calorimetry (DSC). In both studies the copolymer with the higher PEO content degraded the fastest, although all materials degraded relatively slowly. To determine the nature of the degradation products formed during hydrolysis of the copolymers, 1000 PEOT71PBT29 (a copolymer based on PEG with a molecular weight of 1000 g/mol and 71 wt% of PEO-containing soft segments) was degraded in vitro at 100 degrees C in phosphate buffer saline (PBS) during 14 days. The degradation products present in PBS were analyzed by 1H-NMR and high performance liquid chromatography/mass spectroscopy (HPLC/MS). These degradation products consisted of a fraction with high contents of PEO that was soluble in PBS and a PEOT/PBT fraction that was insoluble at room temperature. From the different in vitro and in vivo degradation experiments performed, it can be concluded that PEOT/PBT degradation is a slow process and generates insoluble polymeric residues with high PBT contents.     

Novel beta-emitting poly(ethylene terephthalate) surface modification

Restenosis after percutaneous interventions in coronary and peripheral arteries leads to repeat procedures and surgery in a significant number of patients. We have previously demonstrated that irradiation of an arterial site using an endovascular source (brachytherapy) is highly effective in preventing the restenotic process. To this end, a novel beta radiation delivery system was developed, based on the adsorption of (32)P (o-phosphoric acid) by pH-sensitive chitosan hydrogel on a poly(ethylene terephthalate) (PET) balloon surface. The PET balloon surface was treated with oxygen plasma and coated with chitosan hydrogel. Covalent bonds, ionic bonds, and hydrogen bonds all contribute to the adhesion between chitosan hydrogel and PET. In the aqueous phosphoric acid (PA) solution, the -NH(2) groups of chitosan were protonated by PA and the adsorption of PA occurred at the same time. The effect of PA concentration and temperature on adsorption efficiency and kinetics were studied. More than 70% PA was adsorbed on the sample surface in 0.2 mM PA solution. The surface of samples was also investigated by attenuated total reflection-Fourier transform infrared spectroscopy and scanning electron microscopy. PET surface may be modified to carry high activity beta emitters; such materials may be useful in a therapeutic setting Copyright 2000 John Wiley & Sons, Inc.     

Encapsulation of isotope on novel beta-emitting poly(ethylene terephthalate) surfaces

Recent data indicate that intravascular betaa-irradiation from centrally located sources at the time of balloon angioplasty or stenting reduces proliferation of smooth muscle cells, neointima formation, and restenosis. In an effort to simplify radiation delivery, a novel beta-radiation source was developed based on the adsorption of 32P (phosphoric acid) by pH-sensitive chitosan hydrogel on a poly(ethylene terephthalate) balloon surface. To prevent the 32P-isotope desorption in the patient's blood, the adsorbed phosphoric acid was precipitated as CaHPO4 on the surface by a saturated Ca(OH)2/5% CaCl2 solution. Various polyurethanes were applied to seal the radioactive surface by the dip-coating method. The isotope off-rate results were determined. Optimal results were obtained by serially coating with two polyurethane solutions. This approach holds promise for simplifying and improving the safety, and minimizing the cost of intravascular brachytherapy.     

Entanglement of poly(ethylene terephthalate): A reevaluation

The mass-average based critical molar mass M_c = 9200 g·mol^?1 and the entanglement density v_e = 17,0·10¹⁹ cm^?3 of poly(ethylene terephthalate) PETP were calculated for 280°C from literature data on PETP melts, using appropriate corrections for polymolecularities.     

Calculation of macrocyclization equilibria for poly(ethylene terephthalate)

The cyclization equilibria constant K_x is evaluated for the formation of cyclic poly(ethylene terephthalate)s (PET) in the range of degree of polymerization 2 ≤ x ≤ 10 on the basis of an elaborated form of the Jacobson-Stockmayer theory. According to this theory, K_x = W( 0 )·2Γ₀(1)/(σ_cx N_A), where W( r ) is the probability density function for the chain vector r ; Γ₀(γ) is the probability distribution, when r = 0 of γ = cos Δθ; Δθ being the deviation of the bond angle formed by cyclization from its unconstrained value; σ_cx corresponds to the symmetry number of the ring; N_A is Avogadro's number. The evaluation of W( r ) is performed in different approximations. The required configurational averages for computing the density distribution W( r ) and the angular correlation factor Γ₀(1) are obtained by Monte Carlo techniques. The density W( 0 ) of chain vectors at r = 0 is overestimated by the Gaussian approximation. Values of W( 0 ) calculated in higher approximation lower K_x for x < 10. By taking into account the oriental correlation between terminal bonds of the x-meric acyclic sequence, K_x is lowered additionally by factors of ca. 2,2, 1,3 and 1,1 for x = 4, 5 and 6, respectively. Similar to other polymer chains treated so far, K_x is lowered for medium sized chain lengths by taking into account the deviation from Gaussian distribution and angular correlations of chain ends. This result is in contradiction to experimental data, which yield even higher K_x-values than expected by the classical Jacobson-Stockmayer theory for medium sized chain lengths. The inclusion of cis-ester residues into the all trans-ester PET chain only slightly reduces this discrepancy. Structural modifications of the PET chain during cyclization experiments are discussed as a rationale for the deviations from the present theory.     

Dependence of the antiviral activity of the poly(G).poly(C) complex on the size of the continuous poly(C)segments

Modification of poly(C) by various frequency treatment with adenosine non-complementary to guanosine has produced poly(G) X poly (C.A) complexes with continuous double-stranded areas the length of which is determined by C/A ratio. Studies of the antiviral activity of poly(G).poly(C,A) complexes with C/A from 10:1 to 90:1 and poly(G).poly(C) in vesicular stomatitis virus-infected chick embryo cell cultures and in experimental tick-borne encephalitis of mice demonstrated that the maximum activity is achieved at an average lengths of double-stranded areas of 90 nucleotide pairs. At the same time, a low but statistically significant antiviral activity is observed at a length of double-stranded areas of 10-30 nucleotide pairs.     

Composition and microstructure of a copolyester formed in the melt-mixing of poly(ethylene terephthalate) and poly(ethylene truxillate)

This study shows that is possible to determine the composition and microstructure of the copolyester formed in the melt-mixing process of poly(ethylene truxillate)

1 System. name of truxillic acid: 2,4-diphenylcyclobutane-1,3-dicarboxylic acid.

(PETx) and poly(ethylene terephthalate) (PET), by applying a novel method of statistical modeling of mass spectra of copolymers. The peak intensities of molecular ions appearing in the fast atom bombardment mass spectrum of the melt-mixed equimolar mixture of PETx and PET were found to reflect the relative amounts of oligomers present in the sample and to be directly related to the microstructure of the copolymer formed. The statistical analysis of copolymers allows one to generate a number of different theoretical mass spectra that can be fitted with the experimental mass spectrum data, thus determining the most likely copolymer composition.     

Studies on planar orientation and trap depth of poly(ethylene terephthalate) film

Poly(ethylene terephthalate) films with various degrees of planar orientation of the macromolecules were prepared by uniaxial and biaxial stretching. Fourier transform infrared spectra indicate that the content of gauche conformation decreases linearly with the degree of planar orientation, while the content of trans conformation increases linearly. A linear relationship between the trap depth calculated from Thermally Stimulated Current spectra and the degree of planar orientation was observed.     

On the mechanism of the flow process of poly(ethylene terephthalate)

The mechanism of “flow process” defined as drawing by which neither crystallization nor molecular orientation takes place was clarified on the basis of its direct experimental evidences on drawing of “amorphous” poly(ethylene terephthalate) films. In a certain temperature range above T_g, the polymer molecules are deformed and oriented on drawing, “inter-molecular secondary linkage” playing an important role in the transmission of the applied force. When this intermolecular linkage breaks down above a certain critical temperature, the polymer molecules may slip past each other and flow independently, resulting in a large deformation without inducing any molecular orientation and crystallization. At higher temperatures crystallization occurs inducing the orientation as well.