摘要:

Two devices were evaluated in the pyrolysis-gas chromatographic analysis of a linear polyethylene standard. The Chemical Data Systems Coil Probe, a pulse-type pyrolyzer, and the Du Pont 950 Thermogravimetric Analyzer, a continuous heat-type unit, were studied. The latter was connected to the gas chromatograph using an interface designed to allow on-column collection of pyrolyzates.

ISSN:0022-233X    

DOI:10.1080/00222337408065818

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Techniques utilizing mass spectrometry, thermogravimetry, and gas chromatography in combination to study polymer degradation kinetics and mechanisms are described. The ability to observe volatile species generated under controlled thermal and environmental conditions and the simultaneous accumulation of weight loss data enables acquisition of both kinetic and mechanistic parameters in single run experiments. Polymer degradation mechanisms are best understood when initial oxidative sites can be established. Consequently, data points obtained with these techniques in conjunction with bulk phase analyses provide powerful tools for determining the primary reactions occurring during polymer oxidations.

ISSN:0022-233X    

DOI:10.1080/00222337408065819

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

During the cross-linking under themal conditions of two pre-polymers, a variety of compounds may be formed in addition to the desired cross-linked network, i.e., branched chain, large ring, and linear chain of twice pre-polymer molecular weight. In order to evaluate these processes with as little chemical complication as possible, a series of two component methyl silicone pre-polymers (Sylgard 184, 186, and 188) have been cross-linked with vinyl silicone pre-polymer at various rations of reactive groups and concentrations in silicone oil. These rubbers were evaluated by thermomechanical analysis (TMA) and then swollen with n-hexane. The cross-link density was evaluated from TMA and hexane swelling. The extracts were studied by gel permeation chromatography. As the “catalyst” concentration (active hydrogen containing prepolymer) was increased from 5 to 60%, the percent and average molecular weight of the hexane-soluble fraction was found to decrease for the 186 and 188 samples. No higher molecular weight fraction was extractable from the 184 sample. For all samples the modulus and cross-link density increased until 10 to 30% catalyst was present. Above this concentration these parameters dropped off gradually. Evidence is offered to support the view that polymerization in dilute soulution promotes cross-linking. The molecular weight changes noted for the extractables from the 186 and 188 sample suggests that branched chain formation predominates as a side reaction product. Little original pre-polymer is extractable in an unreacted state. Differential scanning calorimetry was employed to follow the thermodynamics of the reaction.

ISSN:0022-233X    

DOI:10.1080/00222337408065820

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The kinetics of thermal shrinkage of the stretched polypyromellitimide (PI) films, Du Pont Kapton H, were investigated by thermomechanical analysis (TMA) at a constant rate of heating. The two-stage model of extended polymers has been applied to analyze the TMA data. The activation energy of the contraction reaction could be obtained from TMA curves at various heating rates. The one-step shrinkage of the 12.5% stretched PI film gives an activation energy of 10 kcal/mole for the first shrinking. From the 30% stretched sample, the second activation of contraction is 25 kcal/mole, and from 40% sample the third one is 33 kcal/mole. These three contraction reactions are observed successively for the TMA curves for highly stretched samples, and correspond to the various kinds of molecular motion of this special rigid polymer structure, which are also observed in the dynamic mechanical and dielectric properties of the same polymer.

ISSN:0022-233X    

DOI:10.1080/00222337408065821

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

When poly(ethylene terephthalate) was quenched from above Tgand then heated, it exhibited a step increase in thickness in the glass transition region at every rate tested. When the polymer was cooled more slowly than it was heated, a higher Tgand a slightly larger step increase in thickness were observed as the cooling rate was reduced. These experimental results appear to be adequately interpreted on the basis of the normal structural changes that occur in a glass as its thermal history is varied. Two observations, however, were not easily included in this view. First, the polymer, on cooling from above Tg, exhibited an abnormally high expansion coefficient over much of the range of temperature in which it exists as a fluid. Second, the polymer exhibited a step increase in thickness when it was heated at the same rate at which it had previously been cooled.

ISSN:0022-233X    

DOI:10.1080/00222337408065822

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Mobility transitions closely related to the glass transitions of three binary polymer-polymer blend systems have been determined by thermo-optical analysis (TOA). TOA in this instance consists of the automated observation of birefringence relaxation in scratched transparent polymer and polymer blend films during their programmed heating. The blend systems studied were: I. polystyrene (PS) + poly (2,6-dimethyl-1,4-phenylene oxide) (PMMPO); II. poly (2-methyl-6-phenyl-1,4-phenylene oxide) (PMPPO) + PMMPO; and III. PS + PMPPO. Blend Systems I and II display a single TOA transition temperature at each blend composition indicating homogeneity and true thermodynamic compatibility of the polymer pairs. Blend System III displays two TOA transition temperatures at each blend composition indicating incompatibility and resultant liquid-liquid phase equilibration in molten mixtures of PS and PMPPO.

ISSN:0022-233X    

DOI:10.1080/00222337408065823

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Dynamic thermoacoustical analysis has been described for the characterization of certain physicochemical properties of fibers. The method consists of a continuous measurement of the propagation time of constant frequency sonic pulses transmitted through the sample which is being held under light tension and heated under programmed temperature. The sonic pulses are generated by subjecting a piezoelectric crystal with electrical pulses of 7 kHz frequency. Dynamic thermoacoustical curves were obtained with a variety of synthetic fibers and cellulose fiber. The fibers were heated from room temperature to their respective melting points or decomposition temperature. Theoretical principles are discussed with respect to the relationship between sonic responses and the fundamental properties of polymers. The dynamic viscoelastic equation, based on Maxwell-Wiechart model for polymers, has been combined with sonic pulse propagation equation in order to relate the sonic response with the viscoelastic parameters of unoriented and oriented polymers. It is shown that the sonic response under dynamic heating condition is influenced by two factors: 1) orientation of polymer molecules and 2) sonic viscoelastic function of the polymer. It has been further demonstrated that the orientation of fibers practically remained unchanged on heating under the experimental conditions examined. The dynamic thermoacoustical curves for fibers revealed only the characteristic viscoelastic properties of polymers as a function of temperature.

ISSN:0022-233X    

DOI:10.1080/00222337408065824

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A pyrolyzer with programming capability has been coupled in series with a thermal conductivity cell and a mass chromatograph. The thermal conductivity cell gives the flexibility for selective trapping of decomposition products, and also provides data that are complementary to thermogravimetric and differential thermal analyses. The mass chromatograph is composed of two gas chromatographs that are run parallel from a common injection port. Each chromatograph uses a different carrier gas and is equipped with a gas density balance detector. The instrument simplifies identification of mixtures of unknowns in directly providing molecular weights, absolute quantities, and gas chromatographic retention times of the constituents. In this respect, the present system is analogous to pyrolysisgas chromatography-mass spectrometry.

ISSN:0022-233X    

DOI:10.1080/00222337408065825

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0022-233X    

DOI:10.1080/00222337408065807

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor