Showing papers in "Journal of Polymer Science Part A in 1981"
156 citations
TL;DR: In this paper, two closely related series of polyesters that contain mesogenic units interconnected by flexible spacers along the main chain were prepared and characterized for their liquid crystal properties, which were examined by DSC, hot-stage microscopy on a polarizing microscope, smallangle light and wide-angle x-ray scattering methods, and visual observation of stir-opalescence of the polymer melts.
Abstract: Two closely related series of polyesters that contain mesogenic units interconnected by flexible spacers along the main chain were prepared and characterized for their liquid crystal properties. All of these polymers showed theotropic behavior, which was examined by DSC, hot-stage microscopy on a polarizing microscope, small-angle light and wide-angle x-ray scattering methods, and visual observation of stir-opalescence of the polymer melts. The effect of the length of the flexible spacer and the nature of the substituent, which is on the central aromatic ring of the mesogenic unit, on the stability and molecular order of the mesophase for each of the polymers was investigated and the results are discussed on the basis of the thermodynamic data obtained.
153 citations
TL;DR: In this article, the effects of various substitutional groups on the thermal properties and the solubilities of PPTA were discussed and liquid crystal formation was noticed for PPTA substituted with bulky groups such as 9-anthrylmethyl group.
Abstract: N-substituted poly(p-phenylene terephthalamide)s (PPTA), such as N-alkylated, N-aralkylated, and N-carboxymethylated poly(p-phenylene terephthalamide), were synthesized from PPTA and the corresponding halides by the polymer reaction via the metalation reaction in a solution of sodium methylsulfinylcarbanion in dimethyl sulfoxide at low temperature. The introduction of various substitutional groups into the amide groups of PPTA increased their solubilities, but decreased their thermal stabilities compared with PPTA. The effects of various substitutional groups on the thermal properties and the solubilities are discussed. Liquid crystal formation was noticed for PPTA substituted with bulky groups such as 9-anthrylmethyl group.
139 citations
TL;DR: In this paper, a study of ionizing radiation-induced changes in the chemical composition, crystalline content and structure, and flow properties in polytetrafluoroethylene (PTFE) was described.
Abstract: This article describes a study of ionizing radiation-induced changes in the chemical composition, crystalline content and structure, and flow properties in polytetrafluoroethylene (PTFE). Irradiations conducted in the presence of oxygen cause acid fluoride end groups to be formed, which on exposure to water vapor hydrolyze to form carboxylic acid end groups. Analyses by infrared (IR) spectroscopy indicate that when irradiated in a vacuum PTFE exhibits defect absorption bands which have been attributed to branch and crosslink formation. The crystalline content of PTFE which increases after exposure to radiation was monitored by IR spectroscopy, density, x-ray diffraction on unoriented samples, and differential scanning calorimetry (DSC) as the measurement probes. The melt viscosity of PTFE exposed to various radiation doses in air decreases dramatically after irradiation. Between 2.5 and 5 Mrd an increase in viscosity is attributed to the formation of branches and crosslinks. The effects of preirradiation crystallinity and postirradiation heat treatment were studied. A model is presented to explain the mechanism of the observed radiation effects.
116 citations
TL;DR: In this paper, the synthetic route to polyetherimides by displacement of nitro-groups from disubstituted bis-imides and bisphenols is described.
Abstract: The synthetic route to polyetherimides by displacement of nitro-groups from disubstituted bis-imides by the dianion of bisphenols are described. The prepration of bis-imides and bisphenol dianions, their polymerization, and some of the properties of the polymers are presented in detail. The 13C-NMR spectra of intermediates and products were used to establish compositions and determine molecular weights.
113 citations
TL;DR: Fourier transform infrared spectra, including absorbance difference spectra are presented which indicate that the accepted mechanism of tertiary amine-catalyzed copolymerization of cyclic anhydrides and epoxy resins requires modification.
Abstract: Fourier transform infrared spectra, including absorbance difference spectra, are presented which indicate that the accepted mechanism of tertiary amine-catalyzed copolymerization of cyclic anhydrides and epoxy resins requires modification. Results also show that the kinetic model is complicated by the lack of steady-state concentrations of the active species. The effect of silica filler and silane coupling agents on the reaction are also examined.
86 citations
TL;DR: In this paper, the atactic 100% 1,2-polybutadiene was prepared with n-butyllithium modified with bis piperidino ethane.
Abstract: 1,3-Butadiene was polymerized anionically to polybutadiene which contained up to 100% 1,2-addition product. The atactic 100% 1,2-polybutadiene was prepared with n-butyllithium modified with bis piperidino ethane. The polymerization was done in hexane solvent at −5 to +20°C polymerization temperature.
76 citations
76 citations
TL;DR: In this paper, non-empirical LCAO MO SCF computations were performed on the ground and core-hole states of a range of nitrogen-containing model systems which encompass most of the common functionalities of interest in the study of polymers.
Abstract: Nonempirical LCAO MO SCF computations (in the ΔSCF formalism) were performed on the ground and core-hole states of a range of nitrogen-containing model systems which encompass most of the common functionalities of interest in the study of polymers. The data complement those previously presented on oxygen functionalities and show that for specific functionalities (e.g. nitrate esters and nitriles) substituent effects can be substantially different than normally anticipated on the basis of a simple additivity model. A comparison was drawn in appropriate cases with experimental data on simple model systems and polymers.
68 citations
TL;DR: The kinetic behavior of CrO3 in its reaction with wood has been elucidated in this article, where various reactions take place between crO3 and the lignin and cellulose in wood.
Abstract: The kinetic behavior of CrO3 in its reaction with wood has been elucidated. Various reactions take place between CrO3 and the lignin and cellulose in wood. CrO3 reacts with cellulose in a two-step reaction: the first step is an adsorption of CrVI onto the cellulose to form CrVI/cellulose activated complexes. The second step is a CrVI → CrIII reduction taking place on the cellulose surface. The CrIII formed is only physically adsorbed to the cellulose or very weakly bound as small amounts of CrIII can be released into the reaction medium. The CrVI adsorbed by cellulose appears mainly to be reduced to CrIII. The reaction of CrVI with lignin has been shown to be the composition of the three successive reaction of Cr2O72−, HCrO4−, and CrO42− with the guaiacyl units of lignin. Insoluble and stable CrVI/lignin complexes in which chromium maintains its hexavalent oxidation state are formed. Rate constants and energies of activation for all the reactions have been determined. The fixation of CrO3-derived compounds on wood has been explained as the combination of the various reactions investigated. The results indicate that 60% of Cr is fixed irreversibly to the lignin of wood as CrVI and 40% is weakly bound, probably just precipitated, on the cellulose surface as CrIII of which small amounts can be released in a water medium. The complex CrVI and CrIII species forming complexes with the guaiacyl units have been identified.
65 citations
TL;DR: The reactivity ratios of 180 published oxonium copolymerization systems have been reviewed in terms of the extended Kelen-Tudos method as mentioned in this paper, and a quantity suitable for classification of the systems has been introduced.
Abstract: The reactivity ratios of 180 published oxonium copolymerization systems have been reviewed in terms of the extended Kelen–Tudos method. Only 32 (17.8%) systems were described in sufficient detail for reevaluation and classification. r Values, together with their 95% confidence limits have been calculated. A quantity δ□, suitable for classification of the systems, has been introduced. Of the 32 reevaluated systems, five were found to belong to class I and 14 to class I(!), i.e., 19 systems for which the conventional copolymerization equation was found to be adequate. Class II systems were not found. Finally, 13 systems were judged to belong in class III, i.e., systems for which the experimental data are inconsistent and the published r values meaningless.
TL;DR: In this article, a simple method of encapsulating water-insoluble pesticides in a starch matrix is described, which consists of mixing the pesticide with alkali starch followed by precipitation with a calcium chloride solution.
Abstract: A simple method of encapsulating water-insoluble pesticides in a starch matrix is described. The method consists of mixing the pesticide with alkali starch followed by precipitation with a calcium chloride solution. A starch–calcium adduct that entraps the pesticide in small cells within granular particles is formed. Liquid and solid pesticides were successfully encapsulated by the new method. By use of the herbicide trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl) benzenamine] as core material more than 90% recovery and encapsulation was achieved. Use of acid-modified starches and flours resulted in a lower percentage of encapsulation. Effective encapsulation was also achieved by replacing calcium chloride with strontium chloride or barium chloride.
ARCO1
TL;DR: In this article, the course of intermolecular reactions induced by peroxide decomposition in linear polyethylene has been determined and compared with similar reaction systems in which the substrate is a lowmolescular-weight alkane.
Abstract: The course of intermolecular reactions induced by peroxide decomposition in linear polyethylene has been determined and compared with similar reaction systems in which the substrate is a lowmolecular-weight alkane. Efficiency of intermolecular coupling is 40% for an alkane and 25–30% for the polymer system. Competing reactions, which reduce coupling efficiency, are mainly disproportionation of the initially formed radicals and to a minor extent further reactions involving the products from the peroxide decomposition. The low efficiencies found are similar to those well studied when initial radicals are produced by radiolysis in polymer and alkane systems.
TL;DR: In this paper, a case of polymer aging in which powerful synergisms are found between radiation and temperature was investigated and it was shown that these aging effects are mediated by a thermally induced breakdown of peroxides initially formed by the radiation.
Abstract: Results are presented for a case of polymer aging in which powerful synergisms are found between radiation and temperature. This effect was observed with formulations of polyvinylchloride and polyethylene and occurred in simultaneous and sequential radiation-thermal experiments. Dose rate dependencies, which appear to be mechanistically related to the synergism, were also found. The evidence indicates that these aging effects are mediated by a thermally induced breakdown of peroxides initially formed by the radiation. Similar effects could be important to material degradation in a variety of other types of combined-stress environment. A new technique, which uses PH/sub 3/ treatment of intact polymer specimens to test for the importance of peroxides in the pathway that leads to changes in macroscopic tensile properties, is described.
TL;DR: In this article, the authors investigated the thermal degradation behavior of poly(1,3-phenylene isophthalamide) and poly(chloro-2,4-phenylon isophalamide) with the aid of some appropriate model compounds.
Abstract: Thermal degradation behavior of poly(1,3-phenylene isophthalamide) and poly(chloro-2,4-phenylene isophthalamide) was investigated with the aid of some appropriate model compounds. The pyrolysis products of these materials were identified by gas chromatography (GC), gas chromatography/Fourier transform infrared spectroscopy (GC/FT-IR), and gas chromatography/mass spectrometry (GC/MS). The residual chars were characterized by IR spectroscopy. Thermogravimetric analysis (TGA) was applied to study the effect of end-group concentration on the degradation characteristics of the two polyamides. Kinetic parameters that describe the thermal degradation of the polyamides were also evaluated by TGA. The results of this investigation suggest that the thermal decomposition of these aromatic polyamides involves homolytic as well as hydrolytic cleavages of the amide units.
TL;DR: A bifunctional polymer is formed when low-molecular-weight poly(2,6-dimethyl-1,4-phenylene oxide) (I) reacts with 3,3′,5,5′-tetramethyl-4,4′-diphenoquinone (II) as mentioned in this paper.
Abstract: A bifunctional polymer is formed when low-molecular-weight poly(2,6-dimethyl-1,4-phenylene oxide) (I) reacts with 3,3′,5,5′-tetramethyl-4,4′-diphenoquinone (II). Infrared (IR), nuclear magnetic resonance (NMR), and gel permeation chromotography (GPC) measurements indicate that the quinone is bound covalently to the polymer chain as a biphenyl moiety which can be located at a terminal position (III, a = 0) or an internal position (III, a > 0):
Acetylation of III produces a diacetate ester characterized by field desorption mass spectrometry to confirm the bifunctional nature of III. The reaction of I with II proceeds at 25°C but is faster at elevated temperatures or with amine catalysis. Oxidation of III with oxygen and a copper/amine catalyst of the type used initially to prepare I regenerates II from the biphenyl moiety in III in high yield and converts the remaining oxyphenylene units to high-molecular-weight polymer.
TL;DR: In this paper, the conformation changes of poly(ethylene oxide) in the blends, the interaction between copolymer and poly(methyl methyl carbinol) as well as in the reference blend, polystyrene/poly(methylene oxide), are also investigated.
Abstract: Copolymers of styrene with vinylphenyl trifluoromethyl carbinol, p-vinylphenyl trifluoromethyl carbinol, vinylphenyl hexafluorodimethyl carbinol, and p-vinylphenol are conditionally compatible with poly(ethylene oxide), depending on their composition and blending ratios, whereas copolymers of styrene and vinylphenyl methyl carbinol are much less compatible with poly(ethylene oxide), as determined by Tg criteria and differential scanning calorimetry. The crystallinity of poly(ethylene oxide) is changed in the copolymer/poly(ethylene oxide) blends, as indicated by depressions of the poly(ethylene oxide) melting point. Hydrogen-bond formation has been studied in two selected blends by infrared (IR) spectroscopy. Hydrogen bonding dissociation and reassociation as a function of temperature are reported. The conformation changes of poly(ethylene oxide) in the blends, the interaction between copolymer and poly(ethylene oxide) as well as in the reference blend, polystyrene/poly(ethylene oxide), are also investigated.
TL;DR: The compositions and sequence distributions of vinyl acetate-butyl acrylate copolymers obtained with batch and semicontinuous emulsion polymerizations have been studied by 1H and 13C NMR as mentioned in this paper.
Abstract: The compositions and sequence distributions of vinyl acetate–butyl acrylate copolymers obtained with batch and semicontinuous emulsion polymerizations have been studied by 1H and 13C NMR. The batch process gives heterogeneous copolymers while with the semicontinuous one the sequence distribution is statistical. These differences in sequence distributions have been related to the physical properties of the copolymers.
TL;DR: In this article, the correlation between oxygen index and char yield for various polymers are obtained and discussed, and the importance of polymer composition and polymer structure in affecting the flammability of a polymer is emphasized.
Abstract: Improved fire resistance occurs for phenolphthalein-related polycarbonates and polyesters compared to bisphenol-A polymers and emphasizes the importance of polymer composition and polymer structure in affecting the flammability of a polymer. Phenolphthalein-related polymers are able to produce a higher degree of crosslinking during pyrolysis which subsequently leads to higher char yields. The correlations between oxygen index and char yield for various polymers are obtained and discussed. Polycarbonates and polyamides usually show higher oxygen indices than the corresponding polyesters of related structures. This indicates that the nature of the pyrolysis products has a measurable effect on the flammability of a specific polymer. Among many factors, polycarbonates should release more CO2 from the breakdown of the carbonate group, and polyamides should produce relatively nonflammable nitrogen-containing products during pyrolysis, thus accounting in part for these results.
TL;DR: In this paper, a poly(1-vinylimidazole) (PVI) resin was prepared with Ni/sup 2 +/, CO/sup2 +/, or Zn/sup 1 2 +/ as a template to study the adsorption of metal ions.
Abstract: Poly(1-vinylimidazole) (PVI) resin was prepared with Ni/sup 2 +/, CO/sup 2 +/, or Zn/sup 2 +/ as a template to study the adsorption of metal ions. The metal-1-vinylimidazole complex was copolymerized and cross-linked with 1-vinyl-2-pyrrolidone by ..gamma..-ray irradiation and the template metal ion was removed by treating the polymer complex with an acid. These PVI resins adsorbed metal ions more effectively than the PVI resin prepared without the template. The number of adsorption sites (As) and the stability constant (K) of Ni/sup 2 +/ complex were larger for the PVI resin prepared with the Ni ion template caused by the smaller dissociation rate constant of Ni ion from the resin. The composition of the Ni/sup 2 +/ complex in the resin remained constant. This suggests that the complexation proceeded via a one-step mechanism.
TL;DR: In this paper, a poly(p-phenylene) was alkylated with npropyl bromide, n-propyl chloride, and isopropyl-bromide in aluminum chloride.
Abstract: Poly(p-phenylene) was alkylated with n-propyl bromide, n-propyl chloride, and isopropyl bromide in the presence of aluminum chloride. Apparently, the reactions involve dialkylation with n-propyl halides and alternating mono- and dialkylation with isopropyl bromide. Alkylation with ethyl or n-butyl bromide was unsuccessful. The dialkylated polymer was sufficiently soluble to allow molecular weight determination. Mechanistic aspects of alkylation and propagation are treated.
TL;DR: In this article, solid-state 13C-NMR spectra were obtained by cross-polarization and magic angle spinning of polymers prepared by injecting ethane, ethylene, and acetylene into a radiofrequency plasma.
Abstract: Solid-state 13C-NMR spectra were obtained by cross-polarization and magic angle spinning of polymers prepared by injecting ethane, ethylene, and acetylene into a radiofrequency plasma. By use of the delayed decoupling technique to suppress protonated carbon peaks and difference spectroscopy five resolved spectral bands can be distinguished. These bands are assigned to (I) unsaturated nonprotonated, (II) unsaturated CH and CH2, (III) quaternary, (IV) methine and methylene, and (V) methyl carbons by comparison with standard 13C shifts compiled for organic materials. The relative amounts of these structural features in the polymers were determined quantitatively and the possible sources of errors considered.
TL;DR: The formation mechanism of an asymmetric porous structure for the film cast from ethyl acrylate-methyl methacrylate copolymer emulsion prepared by emulsifire-free emulsion polymerization was investigated in this paper.
Abstract: The formation mechanism of an “asymmetric” porous structure for the film cast from ethyl acrylate-methyl methacrylate copolymer emulsion prepared by emulsifire-free emulsion polymerization was investigated. The formation of this structure was affected by the emulsion stability which was varied by the postaddition of sodium sulfate or sodium dodecyl benzene sulfonate. It is concluded that it is derived from the production of porous skin film at the emulsion-air interface and the precipitation of flocculated particles at the bottom of emulsion during drying process.
TL;DR: In this paper, the primary fragmentation mechanisms in the thermal decomposition of polyurethanes were studied in detail by direct pyrolysis into the mass spectrometer, and the remarkable difference in thermal stability of the two totally aromatic polyuresthanes I and II (Fig. 1) reflects their different decomposition pathways.
Abstract: The primary fragmentation mechanisms in the thermal decomposition of polyurethanes were studied in detail by direct pyrolysis into the mass spectrometer. The remarkable difference in the thermal stability of the two totally aromatic polyurethanes I and II (Fig. 1) reflects their different decomposition pathways. In fact, polymer I undergoes a depolycondensation process that yields diiscyanate and dialcohol as primary thermal fragments. The thermal decomposition of polymer II proceeds instead via the formation of a cyclic compound that has been isolated and characterized. In contrast, open-chain fragments are generated in the thermal decomposition of the partially aliphatic polymer III.