摘要:

AbstractElectron beam‐induced polymerization of trimethylolpropane triacrylate (TMPTA) and its methacrylate analog (TMPTMA) was studied using nuclear magnetic resonance (NMR) relaxation time measurements. Free induction decays (FID) of partially polymerized samples consist of a short Gaussian component and a longer component comprised of a distribution of simple exponentials. The relative intensity of the Gaussian component increases with radiation dose.T1andT1ρvalues were measured as a function of temperature and radiation dose. The relaxation is due primarily to methyl group reorientation at low temperatures, ethyl group reorientation at intermediate temperatures, and whole‐molecule reorientation at high temperatures. In both compounds, theT1andT1ρvalues at the high temperature minima increase with increasing dose, and the minima values can be used to estimate the degree of polymerization. The temperature at which theT1ρminimum occurs increases with dose, suggesting an increase in the glass transition temperature,Tg, with polymerization. The polymerization appears to have very little effect on the low temperature CH3reorientation in TMPTA. In TMPTMA the polymerization appears to reduce the mobility of the methacrylate methyl

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290901

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractWhile consideration of the crystalline domains have long dominated research in understanding the properties of semicrystalline polymers, a satisfactory understanding of crack growth in these materials can only be realized by developing corresponding analytical tools to characterize the amorphous region. Since slow stable cracks in these materials preferentially form between crystalline lamellae, the role of tie molecules—the amorphous chains that bridge crystalline lamellae—are particularly important in this regard. Unfortunately, there is no method readily available for quantitative assessment of tie molecules. Through deformation and subsequent chlorination of polyethylene films, it is demonstrated that infrared dichroism can be used to determine relative tie‐molecule concentration. Using this technique, one can a priori predict which resin in a series having comparable densities but widely varying molecular weights or comonomer distributions exhibits better crack resis

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290902

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe explicit form of the Mueller scattering matrix, which characterizes the small‐angle light scattering from an anisotropic sphere when the requirements of the Rayleigh‐Gans‐Debye (RGD) approximation are fulfilled, contains all information obtainable about the RGD scattering from an anisotropic sphere taken as a model for a spherulite. A comparison of angular dependences of single matrix elements for the Lorenz‐Mie sphere, the Rayleigh particle, and the simplified form of the presented matrix (taking a sphere without inherent anisotropy, i.e., Δn= 0) shows very good agreement within the limits of RGD approximations. The polarized small‐angle light scattering intensitiesHυ andVυ are combinations of the single matrix elements. Their explicit form is in accord with the expressions forHυ andVυ intensities recently rederived from a 2 × 2 amplitude scattering matrix. It has been shown that the angular dependence of matrix elements is determined by the (n̄— 1)/Δnparameter, wheren— is the mean refractive index andδnis the anisotropy, both measured relative to the surrounding medium. The expressions forHυ andVυ intensities derived by Stein and Rhodes fail for a sphere without inherenet anisotropy ( δn= 0); and the commonly used procedure of size determination from a maximum ofHυ intensity has limited validity (it holds only approximately under the condition of a small phase shift and small (n̄‐1)/ δn). Further theoretical work must be done to understand and construct scattering models for situations where the RGD

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290903

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractSorption and diffusion of methane and 1‐butene in poly(vinyl chloride) (PVC) powder have been investigated by the step‐response method using gas chromatography. The sorption equilibrium constant of 1‐butene was lower than that of chlorine, despite the higher critical temperature of 1‐butene, while the sorption of methane was negligibly small at temperatures much higher than critical. The diffusivity of 1‐butene in PVC showed a discontinuous dependence on temperature at the glass transition point, suggesting that the micro‐Brownian motion of the polymer chain enhances the diffusivity at the higher temperature. Below the glass transition temperature, the diffusivity of 1‐butene in PVC showed a lower value than has been measured for other smaller molecules such as chlorine and hydr

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290904

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe separation of styrene‐methacrylate copolymers by chemical composition was studied using high‐performance liquid chromatography (HPLC). With the combination of acrylonitrile (polar) gel and nonpolar eluent or of styrene (nonpolar) gel and polar eluent, poly(styrene‐co‐methylmethacrylate) was separated by the adsorption mechanism. The former is designated as normal and the latter as reversed phase. With other combinations, the copolymer was separated mainly by fractional dissolution mechanism. The sample eluted slightly earlier as molecular weight decreased. The molecular weight effect on the reversed‐phase HPLC was smaller than that on the normal phase. A gel with an exclusion limit of 3 × 103exhibited greater molecular weight dependence and worse resolution than a gel with an exclusion limit of 50 × 104.Poly(styrene‐co‐n‐butyl methacrylate) also was separated on the basis of chemical composition by normal and reverse‐phase HPLC. However, poly(styrene‐co‐t‐butyl methacrylate) was separated only by reverse‐phase HPLC. When octadecyl methacrylate gel was used instead of styrene gel in reverse‐phase HPLC, a good separation was not obtained. This indicates a specific interaction between the phenyl group of t

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290905

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractDynamic thermoacoustic measurements were used to observe the curing of epoxy resin. Measurements were made at the modulation frequency (20 Hz) as a function of time. A two‐step increase of the thermoacoustic signal output was notable and could be explained in terms of the transitions liquid → rubber →

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290906

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThermal diffusivityDof filler‐polyimide composites was investigated using flash radiometry. The fillers used were: diamond, alumina, boron nitride, aluminium nitride, silicon carbide, and silicon carbide whiskers, Composite films were prepared by casting a polyamic acid solution with dispersed filler on a glass plate and then annealing. The effects of filler type, size, content, and shape onDwere studied.Dincreased with increasing average filler particle diameter and filler content. For the composite filled with fine Al2O3whose average particle diameter is about 0.2 μm, aggregates of filler were observed with dimensions up to a few microns. The formation of thermal paths through this aggregate enhances thermal diffusion. For the composites filled with high thermal conductivity filler such as BN and AIN, there was a strong increase inDabove a filler content of 20 vol %.Dwas ten times larger than that of unfilled polyimide when the BN content was 54 vol %.Dof the SiC‐whisker composite increased strongly up to a filler content of 18 vol %. Above this contentDsignificantly decreased, probably because of interconnected voids formed by mold shrin

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290907

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractA potential ceramic precursor, a phenylpropylsilsesquioxane co‐oligomer from Petrarch Systems (Petpps), was studied under conditions where fiber spinning is performed. The reaction kinetics of residual silanols of Petpps are studied using Fourier transform infrared spectroscopy in the temperature range 100–150°C. The activation energy and the reaction order of the silanol condensation reaction in the molten Petpps are determined. A combination of gel permeation chromatography, liquid chromatography, and nuclear magnetic resonance spectroscopy is used to study the possibility of copolymerization between the phenyl and propyl silane moie

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290908

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractNew measurements of the heat capacity in the melt of poly(trimethylene succinate) (PTMS), poly(trimethylene adipate) (PTMA), and poly(hexamethylene sebacate) (PHMS) from 310 to 400 K are presented. Based on these data and literature data on eight other molten polylactones and poly(ethylene sebacate) (PES), an addition scheme is developed for linear, aliphatic polyesters that leads to the equation:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} C_p \hbox{ (linear aliphatic polyesters)}\\ \qquad \qquad \qquad \qquad \qquad \qquad {\rm = N}_{{\rm CH}_{2}}\ {(13.7711 + 0.04871}\ {\rm T)} + {{\rm N}_{\rm COO}}\ {(57.7678 + 0.04810}\ {\rm T)} \\ \end{array}$$\end{document}which represents the ATHAS‐recommended melt heat capacities for all linear polyesters. Combining previously discussed solid heat capacities, derived from an approximate frequency spectrum, with the new liquid heat capacities, the various thermodynamic functions (enthalpy, entropy, and Gibbs function) could be derived using the ATHAS computation scheme. The average value of residual entropy at zero kelvin of 5.3 ± 1.8 J/(K mol) per mobile bead for glassy linear polysters was found to be somewhat higher than for many other polymers in the data bank, but closer to that observed for linear, aliphatic polyamides. The phase transitions of PTMS, PTMA, and PHMS are also analyzed using the quantitative baselines available from the heat capacity stu

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290909

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe results obtained during the isothermal curing of diglycidyl ether of bisphenol‐A‐based thermosets cross‐linked with pure diaminodiphenyl methane and pure diaminodiphenyl sulfone and with their mixtures have been analyzed to determine how the dc conductivity changes with time during the conversion of its liquid to a gel. The complex permittivity data are first analyzed to show that ac measurements can be used to obtain the ionic conductivity over a considerable period of the curing process. The procedure allows one to obtain the dc conductivity without having data as a function of frequency. The shape of the complex plane plots of the electrical modulus are semicircles, but with small deviations that appear at long times during the curing process. The dielectric consequences of the chemical changes with time during the cross‐linking of the thermoset are analogous to the frequency dependence of the complex permittivity of a liquid. The analysis shows that the dc conductivity σoof a thermoset during its cure follows a power law, σo∝ (tg—t)x, wheretis the curing time (t

ISSN:0887-6266    

DOI:10.1002/polb.1991.090290910

出版商:John Wiley&Sons, Inc.    

年代:1991

数据来源: WILEY