Gel permeation chromatography: calibration procedures for chains containing p-phenylene units

Experimental gel permeation chromatography calibrations have been obtained for polystyrene standards, polysulphone fractions, and polycarbonate fractions in chloroform at 30°. Chloroform is a good solvent for all three polymers which have similar polymer solvent interactions. The fractions have narrow molecular weight distributions, so that viscosity average molecular weight can be taken as the peak molecular weight of a chromatogram. The experimental polysulphone and polycarbonate calibrations are compared with curves calculated from the polystyrene calibration using equations which assume that the unperturbed mean-square end-to-end distance and hydrodynamic volume are universal calibration parameters. For molecular weights between 20,000 and 100,000 both universal calibration procedures were found to be acceptable. For polycarbonate extended chain length was also found to be satisfactory for universal calibration. For polycarbonate molecular weights below 20,000, the predicted molecular weight calibration deviated from the experimental data. Possible reasons for this difference are discussed.     

Facile synthesis of high molecular weight aromatic polyformals containing phthalazinone moiety

High molecular weight aromatic polyformals containing phthalazinone moiety were simply synthesized with a high‐intensity mixing methodology without the presence of phase‐transfer catalyst. Aromatic polyformals can readily be afforded in a very short time and at temperatures ranging from 50 to 140 °C. These polyformals showed high glass‐transition temperatures together with superior thermal properties when compared with a 4,4′‐isopropylidenediphenol (BPA)‐type polyformal and polycarbonate. The glass‐transition temperatures of these aromatic polyformals ranged from 94 to 229 °C. The molecular weights of the polyformals were examined by gel permeation chromatographic technology, and the result showed that the cyclic formation during the condensation could be dramatically reduced at elevated temperature. The molecular weights and solubility increased with an increasing content of bisphenol A in the polyformals. The result demonstrated that the aromatic polyformal with 50% phthalazinone moiety showed the comparable thermal properties with commercial BPA polycarbonate. This method promisingly opened an effective approach to synthesize aromatic polyformals with high molecular weight and without cyclic formations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1441–1448, 2002     

Study on the determination of the molecular weight of polyethylene with ultrahigh temperature GPC

Ultrahigh or high molecular weights of polyethylenes (PE) and their distributions are for the first time determined at 160° or 170°C by gel permeation chromatography (GPC). The thermostability of PE at high temperatures is discussed. In order to calculate the real molecular weight of PE, a new calibration curve is established. For PE with high molecular weight more reliable and accurate results can be obtained by GPC measurements at these temperatures. The application of ultrahigh temperature GPC for polymer characterization is demonstrated in this paper.     

Thermal analysis kinetics applied to flame retardant polycarbonate

The degradation kinetics of polycarbonate with flame retardant additive was investigated by means of thermogravimetric analysis. The samples were heated from 30 to 900°C in nitrogen atmosphere, with three different heating rates: 5, 10 and 20°C min^–1. The Vyazovkin model-free kinetics method was applied to calculate the activation energy (E _a) of the degradation process as a function of conversion and temperature. The results indicated that the polycarbonate without flame retardant additive starts to loose mass slightly over 380°C and the polycarbonate with flame retardant additive, slightly over 390°C (with heating rate of 5°C min^–1). The activation energy for flame retardant polycarbonate and normal polycarbonate were 190 and 165 kJ mol^–1, respectively.     

Thermal decomposition of methylxanthines

The thermal decomposition of theophylline, theobromine, caffeine, diprophylline and aminophylline were evaluated by calorimetrical, thermoanalytical and computational methods. Calorimetrical studies have been performed with aid of a heat flux Mettler Toledo DSC system. 10 mg samples were encapsulated in a 40 μL flat-bottomed aluminium pans. Measurements in the temperature range form 20 to 400°C were carried out at a heating rate of 10 and 20°C min⁻¹ under an air stream. It has been established that the values of melting points, heat of transitions and enthalpy for methylxanthines under study varied with the increasing of heating rate. Thermoanalytical studies have been followed by using of a derivatograph. 50, 100 and 200 mg samples of the studied compounds were heated in a static air atmosphere at a heating rate of 3, 5, 10 and 15°C min⁻¹ up to the final temperature of 800°C. By DTA, TG and DTG methods the influence of heating rate and sample size on thermal destruction of the studied methylxanthines has been determined. For chemometric evaluation of thermoanalytical results the principal component analysis (PCA) was applied. This method revealed that first of all the heating rate influences on the results of thermal decomposition. The most advantageous results can be obtained taking into account sample masses and heating rates located in the central part of the two-dimensional PCA graph. As a result, similar data could be obtained for 100 mg samples heated at 10°C·min⁻¹ and for 200 mg samples heated at 5°C min⁻¹.     

Investigation of the epoxide–carboxylic acid reaction in model compound and polymerization reactions

The reaction of epoxide and acid has been studied in the model reaction of bisphenol-A diglycidyl ether and acetic acid with several base catalysts at 60, 95, and 115°C. The results suggest that no greater than 5% side reactions occur. A series of polyhydroxylester polymers were prepared from bisphenol-A diglycidyl ether and adipic acid. The polymers gel rapidly upon heating at 200°C. Terpolymers of bisphenol-A diglycidyl ether, bisphenol-A, and azelaic acid were prepared. These also gel at 200°C when 50 mole-% of the active hydrogen reactant is azelaic acid.     

Influence of polydispersity and long chain branching on the melt viscosity of polycarbonate

The Newtonian and non-Newtonian melt viscosities of bisphenol A polycarbonate (PC) at 280°C were treated according to the generalized multivariable power function, where the average molecular weights, polydispersity degree and branching degree are considered as variables. The shear rate was also considered as a variable for non-Newtonian conditions. In the same way, the melt fluidity was treated as a multivariable power function. It has been found that the same melt flow properties of polymer can be obtained by an appropriate combination of Newtonian melt viscosity (being a function of molecular weight) and long chain branching. The experimental data on PC agree with the theoretical approach of Bucche and Graessley.     

Structural stabilization of phase separating PC/polyester blends through interfacial modification by transesterification reaction

Competition between phase separation and transesterification in immiscible polymer blends of polycarbonate (PC) and a copolyester (PET) is studied as a function of time and temperature by differential scanning calorimetry (DSC) and small-angle neutron scattering (SANS). We found that (1) Global structure coarsens at T ≤ 200°C due to the dominance of phase separation over transesterification and melts at T ≤ 220°C due to the dominance of transesterification at the domain interface. However, transesterification is slow but still significant even at T ≤ 200°C. (2) An intricate balance of transesterification and phase separation rates controls global and interfacial structures. (3) Interfacial structures become measurable under certain conditions, and the interfacial thickness between PC or PET and the copolymers generated by transesterification increases with time. (4) DSC results are consistent with results obtained by SANS, but the latter is more sensitive than the former and differentiates the structural change at different length scales caused by phase separation and transesterification. © 1994 John Wiley & Sons, Inc.     

Chain-backbone motion in glassy polycarbonate studied by polarized infrared spectroscopy

Chain-backbone motion in glassy polycarbonate has been investigated both under isothermal stress, and also under zero stress during isothermal annealing of freely contracting film specimens. In both types of experiment, backbone motion was detected by measuring the change in infrared dichroism. The dichroism of absorption bands at 1364 and 2971 cm^?1, which have transition moment vectors directly related to the chain-backbone orientation, was studied. Under tensile stress in the homogeneous region of deformation, changes of up to 2.2° in the mean chain-backbone orientation angle were measured at 23°C. With the onset of cold drawing a total orientation change of some 8° was observed. For the isothermal annealing experiments, a film specimen holder employing conductive heating with radiative losses was employed. It enables infrared measurements to be made while the temperature of the contracting specimen is maintained constant to ± 0.5°C. Oriented specimens were prepared by isothermal stretching of polycarbonate films to strains of the order of 100%. Changes in the mean chain-backbone orientation angle were observed during annealing of these oriented films at temperatures between 80°C and the glass transition (149°C). Chain motion proceeded during annealing, and chain segments were observed to move cooperatively. The temperature at which the polymer is prestretched has a pronounced effect on its subsequent relaxation during annealing: when the sample was stretched at 23°C. motions were detected during annealing at temperatures as low as 81°C, while, if it was stretched at 154°C, no motion was detected at annealing temperatures below 127°C. The data are discussed in comparison with theories of the glassy state that predict the absence of chain-backbone motion at temperatures significantly below the glass transition. A shift in frequency of the ν_a (CH₃) absorption peak in stretched polycarbonate was measured by using polarized radiation. The effect was interpreted in terms of changes in the intermolecular bonding structure of the oriented polymer.     

Polyamide synthesis by ester aminolysis. I. A new route for nylon-6,6 synthesis

A new route for nylon-6,6 synthesis has been studied. The process is grounded on the synthesis of an α-amino ω-ester monoamide precursor (AME-6,6) easily available in reacting in the bulk hexamethylene diamine and dimethyl adipate at a low temperature (T ≅ 50°C) preferably in the presence of a phenol derivative. In such conditions AME-6,6 precipitates with a very good yield (90–95%). One of the greatest advantages of AME-6,6 is to keep the stoichiometric balance for further polyamidation; that is not the case in other processes. Moreover AME-6,6 is very stable, e.g., even stored at room temperature under air during 50 days. Polyamides-6,6 have been obtained from AME-6,6 (used freshly prepared or after storage) in glass laboratory reactors by direct heating under vacuum (T = 270°C) with number-average molecular weights of roughly 20,000. © 1996 John Wiley & Sons, Inc.     

Mechanism of thermal degradation of poly(vinyl chloride)

The mechanism of thermal degradation of poly(vinyl chloride) has been studied by pyrolysis up to 400°C in a thermobalance under four kinds of dynamic atmospheres: helium, oxygen, air, and hydrogen chloride. The gaseous product from the thermobalance was analyzed for hydrogen chloride by the argentometric determination of chloride ions by using Mohr's method. An attempt was made to analyze for other gases in the product stream by chromatography with the use of a glass column, but failed due to the accumulation irreversibly of hydrogen chloride on the column. The molecular weights of the samples were determined by measurements of viscosities at 25°C in cyclohexanone; their molecular weight distributions were studied by fractionation and gelpermeation chromatography (GPC). From the thermograms, the mechanism of degradation in different heating atmospheres, the rate, the heat effect, the energy of activation, and the order of decomposition were deduced.     

Kinetics of polyesterification: Effect of diol chain length

Kinetics of polyesterification of maleic anhydride with polyethylene glycol (PEG) of varying molecular weights have been evaluated. The investigations have been carried out by employing heating cycles comparable to those employed in industrial processes and under nonisothermal conditions. The rate of reaction was found to decrease with increase in the chain length of the polyether. The energy of activation was estimated as 26.91, 40.25, and 47.30 Kcal/mol for PEG of molecular weights 200, 300, and 400, respectively. © 1994 John Wiley & Sons, Inc.     

Thermoplastic and thermosetting properties of polyphenylsilsesquioxane particles prepared by two-step acid-base catalyzed sol-gel process

Polyphenylsilsesquioxane (PhSiO_3/2) particles were synthesized by a two-step acid-base catalyzed sol-gel process, in which phenyltriethoxysilane used as a starting alkoxide was hydrolyzed and condensed in the first step under two different acid-catalyzed conditions. The PhSiO_3/2 particles prepared under an acid-catalyzed process without using a solvent were thermally hardened after the first heating up to 200°C. In contrast, the PhSiO_3/2 particles prepared under an acid-catalyzed process with ethanol as a solvent were thermally softened with the repeated heating processes up to 200°C. From the gel permeation chromatography measurements, it was found that the average molecular weight of the particles prepared with the use of ethanol was decreased in comparison with that of the particles prepared without using ethanol. The addition of ethanol in the sols during hydrolysis and condensation reaction under the acid-catalyzed process caused the decrease in the average molecular weight, which should result in the changes of thermal property of PhSiO_3/2 particles from thermosetting to thermoplastic.     

Template polymerization of multiacrylate

By reacting poly (2-hydroxyethyl methacrylate) with acryloyl chloride, multiacrylate connected through a covalent bond with polymethacrylate chain (template) has been obtained. The free-radical polymerization of multiacrylate in dilute dioxane solutions at 75°C and 85°C was examined by IR spectrophotometry and the distribution of molecular weights of the resultant products was evaluated by gel permeation chromatography. The findings show that under selected conditions the polymerization proceeds along ordered acrylic double bonds on the template and results in a ladder-type polymer. At a temperature of 85°C, in addition to the intramolecular cyclopolymerization, intermolecular reactions proceed to a minor extent. © 1994 John Wiley & Sons, Inc.     

Annealing during polymerization of crystalline poly(ethylene terephthalate)

Melt-crystallized poly(ethylene terephthalate) and etched oligomer lamellae from the same polymer have been annealed under vacuum at temperatures between 200 and 260°C and times between 3 and 48 hr. The annealed samples were analyzed through determination of viscosity-average molecular weight, x-ray low-angle spacing, density, heat of fusion, and variation of melting point with heating rate. In all cases it could be shown that the crystal lamellar surfaces remained chemically reactive. Chain folds and chain ends in the surface were converted by chemical reaction to tie molecules between different crystals or different locations on the same lamella.     

Pyrolyse du polyacrylonitrile—II. Etude des effets thermiques jusqu'à 350°C

Low temperature thermal effects (below 350°C) on the pyrolysis of polyacrylonitrile have been studied by differential thermal analysis and microcalorimetry. The role of pretreating the sample in helium or air has been especially examined together with the influence of temperature and time of pretreatment. Under helium at 200–210°C, the subsequent thermal effect is reduced. Under air however no change is observed in the thermal effect although it appears to be spread over a much longer time. It therefore appears possible to minimize the heating power and its consequences by pretreating the fibre at ca. 210°C under air.     

Analysis of the Molecular Weight Distribution of Polystyrene

In this paper are reported molecular weight distributions (MWD) of polystyrenes obtained by bulk free-radical polymerization of styrene under isothermal conditions. MWD of polystyrenes were determined by gel-permeation chromatography. From analysis of the results it is apparent that samples synthesized at 80 °C and 90 °C have a bimodal MWD whereas those obtained at 100 °C and 110 °C have unimodal MWD. By two-peak deconvolution of experimental curves (at 80 °C and 90 °C) it is possible to separate the contribution of polystyrene obtained before and after onset of the gel effect.     

Synthesis and crosslinking reaction of a novel polymer containing benzoxazine and phenyleneethynylene moieties in the main chain

A novel polymer, poly( 1 ) containing benzoxazine and phenyleneethynylene moieties in the main chain with number‐average molecular weights ranging from 1400 to 9800 was obtained quantitatively by the Sonogashira–Hagihara coupling polymerization of the corresponding iodophenyl‐ and ethynylphenyl‐substituted monomer 1 . Poly( 1 ) was heated at 200 °C under N₂ for 2 h to obtain the cured polymer, poly( 1 )′ via the ring‐opening polymerization of the benzoxazine moieties. The structures of the polymer before and after curing were confirmed by ¹H‐NMR, IR, and UV–vis absorption and reflectance spectroscopies. Poly( 1 )′ was thermally more stable than monomer 1 and poly( 1 ). A specimen was prepared from a mixture of poly( 1 ) and phenol‐diaminodiphenylmethane type benzoxazine 2 by heating at 200 °C for 2 h under N₂. The poly( 1 )/ 2 resin was thermally stable than bisphenol‐A type benzoxazine resin 3 . Poly( 1 ) exhibited XRD peaks corresponding to the d‐spacings of 1.26–0.98 and 0.40 nm, assignable to the repeating monomer unit and alignment of polymer molecules, respectively. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2581–2589     

Crystallization of bisphenol-A polycarbonate. I. Influence of trimellitic acid tridecyloctyl ester on the kinetics of crystallization

The crystallization of bisphenol-A polycarbonate plasticized by trimellitic acid tridecyloctyl ester (Morflex 525) has been studied. A half-crystallization time of 100 min is observed at 170°C with 10% of plasticizer compared with a figure of 18,000 min for the unplasticized material. The kinetic study is limited to the primary crystallization process which can be described by an Avrami equation; however, the Avrami coefficients are much higher than usual. Studies on the effect of the preparation procedure of the samples and of premelting indicate that nucleation is at least partially heterogeneous.     

Microwave-assisted nitroxide-mediated miniemulsion polymerization of styrene

Nitroxide-mediated free-radical miniemulsion polymerizations (NMRPs) of styrene were successfully performed under microwave irradiation at 135 °C. The polymerizations proceeded in a controlled manner, yielding polymers that showed an incremental increase in molecular weight with conversion and had narrow molecular weight distributions. The resulting latexes were colloidally stable. The polymerization behavior, molecular weights of polymers and Z-average size of latex particles were also investigated under two different heating methods, microwave irradiation and conventional heating.