摘要:

Based on the effects of solvent and temperature on the 282-MHz19F-NMR spectrum of poly(vinylidene fluoride), PVF2, in perdeuterated dimethylacetamide (DMA-d9) solution at -20°C, nine minor CF2resonances that are due to structures in the vicinity of reversed monomer enchainments have been identified.19F-19F spin-spin decoupling and two-dimensional19F-correlation spectroscopy (19F-2D COSY) have been used to assign these resonances. In several cases these assignments differ from those made previously.

ISSN:0022-233X    

DOI:10.1080/00222338908053841

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Infrared spectroscopic characterization of composites is possible by many sampling techniques, including transmission, specular reflection, diffuse reflection, internal reflection, photoacoustic, and emission. The choice of technique depends on the physical form of the specimen and, in particular, on the scattering characteristics of the reinforcement. Examination of the interphase between the reinforcement and the matrix, in isolation from the rest of the composite, requires some sort of a model system involving either (a) an increased interfacial volume (e.g., use of a high-surface-area analog of the reinforcement), (b) spectroscopic labeling of the interphase, or (c) the use of a model for the reinforcement surface (e.g., a coated internal-reflection spectroscopy element). Several examples of category (a) and (c) are described here. It is demonstrated that the surfaces of commonly used reinforcements (e.g., metal oxides, aramids, carbon) modify the local crosslinking chemistry of epoxy matrices. In particular, the desorption of water from the reinforcement surface and preferential adsorption of polar components of the matrix precursor reduce the local crosslink density and modify the chemical properties of the polymer in the interphase.

ISSN:0022-233X    

DOI:10.1080/00222338908053842

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Although not yet widely used in analytical laboratories, the tremendous development of low-cost FTIR spectrometers should allow photoacoustic spectroscopy to become a commonly used technique for polymer analysis. The ability to determine depth profiles in a broader range than ATR makes FTIR-PAS a particularly attractive method to follow the effect of chemical treatments or the penetration of coatings in polymeric materials. The possibility to obtain a spectrum from as-received samples is also of great interest to the analytical chemist. The only limitation of this technique is the need to use a great number of scans to enhance the signal-to-noise ration. However, continued improvements in PA cell design should increase the overall sensitivity, leading to shorter data-collection times.

ISSN:0022-233X    

DOI:10.1080/00222338908053843

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Copolymers of vinyl chloride with isobutylene, propylene, and ethylene, ranging in composition from 1 to 10 mol% alkene, have been prepared by free-radical polymerization at 50°C. The polymers have been characterized by elemental analysis, gel permeation chromatography (GPC),13C NMR, and differential scanning calorimetry (DSC). Models for various sequence distributions are used to calculate the chemical shifts in the13C-NMR spectra by the Lindeman-Adams additivity rule. The spectra of the copolymers with 0.8 to 3.2 mol% ethylene are best fit when a random sequence distribution is used. The copolymer with 7.7 mol% ethylene is found to have 10% of comonomer in block-of-two arrangements. The calculations for the propylene and isobutylene copolymers indicate a random comonomer distribution although other arrangements cannot be ruled out unequivocally. For all copolymers, a singleTgis obtained at all compositions, which is consistent with the13C-NMR data.

ISSN:0022-233X    

DOI:10.1080/00222338908053844

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

In 1978, Jarry and Monnerie showed that the stationary fluorescence polarization technique can be used to measure orientation in mobile uniaxially symmetric systems. Determination of segmental orientation in stretched rubbery networks may then serve to validate and improve elaborated models of rubberlike elasticity in conjunction with stress-strain measurements. As a preliminary, the basic principles of the fluorescence polarization technique and its application to investigation of molecular behavior of mobile anisotropic networks are described. Then, the theory of segmental orientation of real networks with constraints on junctions, proposed by Erman and Monnerie in 1985, is reviewed. Illustrative data on elasticity and orientation behavior ofcis- 1,4-polyisoprene networks are consistent with theoretical predictions. The effect of temperature on segmental orientation is attributed to changes in the configurational factor expressed in the theory. In fluorescence polarization experiments, only the orientation behavior of the labeled species is observed. Thus, comparison of the behavior of anthracene end-labeled and center-labeled chains has revealed that dangling chains are very strongly orientationally coupled to network chains. It is, however, a local effect which does not imply an overall anisotropy of dangling chains at equilibrium. Orientational coupling between flexible probes of different lengths and polymer matrix was also investigated and compared with that of rigid probles.

ISSN:0022-233X    

DOI:10.1080/00222338908053845

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A method for determining the compositional heterogeneity of copolymers is described. A low-angle laser light-scattering (LALLS) photometer is added on-line to a dual-concentration-detector gel-permeation chromatograph (GPC) in order to measure heterogeneity at each elution volume interval. Experimental results for polystyrene-poly(di-methylsiloxane) diblock copolymers and blends are discussed, and these give overall heterogeneity parameters which are in good agreement with theory. The technique shows, however, that some of the samples originally thought to be copolymers were actually blends or contained homopolymer. Both random errors and errors inherent in the analysis are examined. The largest inherent error arises from the assumption that there is no distribution of molecular weights within a single GPC fraction. An alternative to this assumption is described, and its use considerably reduces the inherent errors. All types of error are reduced by selecting a solvent such that the refractive index increment of the copolymer under investigation is small, and the refractive index of the solvent should ideally fall between those of the two copolymer components. The accuracy of the technique increases linearly with copolymer molecular weight and the square of the difference in component refractive index increments.

ISSN:0022-233X    

DOI:10.1080/00222338908053846

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

It is well known that most pairs of high molecular weight polymers are immiscible. This is so because the combinatorial entropy of mixing of two polymers is dramatically less than that of two low molecular weight compounds [1–3]. The enthalpy of mixing, on the other hand, is often a positive quantity. Therefore, dissimilar polymers are only miscible if there are favorable specific interactions between them leading to a negative contribution to the Gibbs free energy of mixing. Miscible polymers tend to phase separate at elevated temperatures. This lower critical solution temperature (LCST) behavior is interpreted in terms of the equation of state or the freevolume contribution [1–3]. About 30 pairs of dissimilar polymers have been found to exhibit the LCST behavior.

ISSN:0022-233X    

DOI:10.1080/00222338908053847

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The gas chromatographic method of characterization of polymer blends with regard to the state of binary polymer mixtures, origin of miscibility in miscible blends, evaluation of the noncombinatorial free energy parameters χ23′ and χ23*′ for miscible blends, and structural information of microphase-separated copolymer systems, etc. are reviewed with discussions of some selected polymer-polymer systems. A brief discussion of the principle and practice of GC with a polymer stationary phase, of the evaluation of χ and χ*, of sources of error and accuracy of the method, and of column support materials and support loading is also presented. Preliminary results of an inverse gas chromatography study of the newly reported miscible polymer pair poly(vinyl propionate) and poly(ethyl acrylate) are presented.

ISSN:0022-233X    

DOI:10.1080/00222338908053848

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Thermal behavior of chlorinated atactic polypropylene (CAPP) obtained by thermal chlorination of atactic polypropylene was evaluated by thermogravimetric analysis and differential thermal analysis (DTA). It was found that the initial decomposition temperature, integral procedural decomposition temperature, activation energy, and char yield increase with an increase in chlorine content. The thermal stability of CAPP was found to be lower in air than in nitrogen. This has been ascribed to thermooxidative degradation in air. DTA study shows that onset decomposition temperature, glass transition temperature, and polymer melting temperature increase with increasing degree of chlorination. The possible reasons for the phenomena are discussed.

ISSN:0022-233X    

DOI:10.1080/00222338908053849

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A quantitative description for the dynamic mechanical properties of a reacting system as a function of both the viscoelastic and kinetic intrinsic behavior of the polymeric system was developed in this work. The model was tested experimentally by subjecting plaques of tetraglycidyl-4,4′-diaminodiphenylmethane partially cured with diaminodiphenyl sulfone to dynamic mechanical measurements at four isothermal temperatures. The kinetic viscoelasticity model was used to analyze the resulting data and to obtain both the characteristic intrinsic kinetic and viscoelastic parameters. The effects of temperature on the model parameters were investigated. Activation energies provided by the model for the curing reaction were found to agree with those obtained experimentally by other techniques. Experimental frequency was found to be an important factor in the kinetic analysis of dynamic mechanical data of curing systems. Finally, the analogy between dielectric relaxation and dynamic mechanical relaxation was found to be exploitable in developing modeling methodologies and analysis techniques applicable to both.

ISSN:0022-233X    

DOI:10.1080/00222338908053850

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor