摘要:

AbstractThe influence of crystallinity and crosslinking on the depression of the glass transition temperature in nylon 6 by water has been investigated by dynamic mechanical methods. Radiation crosslinking by high‐energy electrons was effective in preventing morphological changes during the measurement of the incremental change in heat capacity (ΔCp) atTg, which was performed by differential scanning calorimetry. The experimentally determined value of ΔCp, when normalized to account for the crystalline phase, was found to deviate from a linear two‐phase relation and was reduced further than would be expected based on this model. It is proposed that nylon 6 is best described by a three‐phase model which consists of a crystalline domain, a wholly amorphous domain, and an “intercrystalline” region. The importance of this in explaining the relatively large depression ofTgby small quantities of water is illustrated by applying equations derived to account for the compositional dependence ofTgin polymerdiluent mixtures, based on a classical thermodynamic interpretation of the glass transition

ISSN:0098-1273    

DOI:10.1002/pol.1984.180221001

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe degree to which a polymer film develops plastic flow depends largely on the total strain ϵ and the elongation timeth. The magnitude and the time dependence of the elastic component ϵeof the total deformation are controlling factors, respectively, in the solubility and diffusion processes. The plastic deformation ϵplseems not to contribute to the transport properties. The nonlinearity in solubility due to ϵ may be conveniently handled. In this study, the solubility of ethyl acetate vapor in poly(vinylidene fluoride) was determined as a function of pressure and total elongation at 30°C. These results suggest that the strain magnitude and time de pendence of the component deformations play important roles in transport beha

ISSN:0098-1273    

DOI:10.1002/pol.1984.180221002

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe thermodynamic and structural properties of a series of hydrogenated polybutadienes, crystalized in the bulk and from dilute solution, have been investigated. These polymers are ethyl‐branched ethylene copolymers with narrow molecular weight and composition distributions. Despite the fact that for both modes of crystallization these random‐sequence copolymers display a lamellar crystalline habit, all of the independent physical chemical measurements are quantitatively consistent in indicating a relatively thin crystallite with a large amorphous disordered overlayer. This is seen to be a very general phenomenon for copolymer crystallization. The core thicknesses, determined from Raman LAM and from small‐angle x‐ray scattering, are in good agreement. Quantitatively consistent values of the degree of crystallinity are obtained from the density, enthalpy of fusion, Raman internal modes, Raman LAM, and small‐angle x‐ray scattering. It is significant that independent thermodynamic and structural methods give the

ISSN:0098-1273    

DOI:10.1002/pol.1984.180221003

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe glass transition temperature and characteristic ratio of poly(dl‐isobornyl methacrylate) have been determined. The results indicate that in the case of certain polymethacrylates the chain flexibility depends mostly on the bulkiness of the side group, while the glass transition temperatures depend mostly on side‐group rigid

ISSN:0098-1273    

DOI:10.1002/pol.1984.180221004

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractAnalytical expressions describing the kinetics of photoinitiated free‐radical polymerization are derived for a variety of conditions. The effect of the exponential attenuation of intensity of light in the direction of incidence in the system is carefully accounted for in each case. An attempt is made to include the depletion of initiator due to its photolysis in the kinetic scheme. The marked difference between the polymerization kinetics in well‐stirred and unstirred systems is shown by comparing them under limiting conditions. The variation of this difference with the optical density of the system is illustrated graphically. The influence of light absorption by components other than the photoinitiator (e.g., solvent, monomer) is examined. The order of the polymerization reaction with respect to initiator as determined by conventional kinetic experiments depends on the amount of light absorbed by components of the system other than the photoinitia

ISSN:0098-1273    

DOI:10.1002/pol.1984.180221005

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractFourier transform infrared (FTIR) studies of polystyrene (PS)/poly(vinyl methyl ether) (PVME) miscible blends as a function of temperature are presented. Below the lower critical solution temperature (LCST) little change is observed in the interaction spectrum obtained via digital subtraction techniques. Once above the LCST, the magnitude of the interaction spectrum decreases as a result of the phase separation process. Comparison of the behavior of the ether CO stretching band in the reference PVME and in the blends has yielded a lower limit estimate for the interaction energy of about 0.15 kcal/mo

ISSN:0098-1273    

DOI:10.1002/pol.1984.180221006

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe radius of gyrationRg, the hydrodynamic radiusRh, and the intrinsic viscosity [η] have been measured for polystyrene in cyclohexane (at the θ temperature and 44.5°C), 2‐butanone (at 30°C), and toluene (at 30°C) in the molecular weight range 2.38 × 105≤Mw≤ 5.47 × 106to elucidate the excluded‐volume effects on dynamical behavior in dilute polymer solutions in the crossover region from θ to good‐solvent conditions. The results are compared with theoretical predictions of current thermal blob theories and the Pade approximant theory of Tanaka. It is found that the ratio ofRh/Rgdecreases with an increase in the excluded‐volume effect, following the prediction of the simple blob theory, but that its magnitude is about 15% higher than the theoretical value. Experimental variation of [η] withRhand/orRglies in between predictions of the scaling law and the Pade approximant. The concentration dependence of the diffusion coefficient is also compared with predictions

ISSN:0098-1273    

DOI:10.1002/pol.1984.180221007

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractRegression rates as functions of air flow rates and oxygen content of the oxidant gas as well as the distance of the polymer surface from the top of the reaction vessel have been investigated for poly(methyl methacrylate), poly(α‐methyl‐styrene), a polymide, and isotactic polypropylene. The results are discussed from the standpoint of reaction kinetics, considering regression rates and energies of activation for diffusion and degrada

ISSN:0098-1273    

DOI:10.1002/pol.1984.180221008

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe annealing behavior of low‐density melt‐crystallized polyethylene is discussed in terms of an unprecedented lamellar diffusion mechanism. For this purpose a combined small‐angle x‐ray diffraction (SAXS) and differential scanning calorimetry (DSC) study has been carried out. The presence of an initial double‐lamellar population is directly evidenced by electron microscopy of freeze‐cut and stained sections. The intercalation of thinner lamellae within the dominant wide‐lamella population gives rise to an x‐ray periodicity of 220 Å (structure I). The independent stacking of thinner lamellae within the material contributes to a second periodicity at 110 Å (structure II). During annealing at successively higher temperaturesTA, the low‐molecular‐weight components from the thin lamellae progressively diffuse out of the double population, reinforcing the stacks of thinner lamellae. At the melting temperature of the thinner crystals a complete segregation of these lamellae takes place, and a new periodicity (structure III) corresponding to stacks of collapsed thick lamellae emerges. The periodicity of structure III increases further withTA. The thin lamellae of structure II can be extracted by a solvent, removing the corresponding SAXS peak and DSC maxima. The partial removal of thin lamellae from structure I by means of solvent extraction concurrently yields a decrease of the SAXS period. The present results suggest that molecular segregation of a low‐molecular‐weight fraction, contributing to the population of thinner lamellae

ISSN:0098-1273    

DOI:10.1002/pol.1984.180221009

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractPiezoelectric, elastic, and dielectric properties of films of poly(β‐hydroxybutyrate) (PHB), an optically active natural polymer, were measured as functions of frequency and temperature. In mechanical properties, three relaxation processes were observed at 10 Hz: the α dispersion at 130°C, the β dispersion at room temperature, and the γ dispersion at −120°C. It was concluded from x‐ray diffraction and the thermal expansion coefficient that the α dispersion can be ascribed to thermal molecular motions in the crystalline phase, that the β dispersion is the primary dispersion due to the glass transition, and that the γ dispersion is related to local molecular motion of the main chains in the amorphous phase. Piezoelectric relaxations were also observed in these relaxation regions. It is proposed that the high‐temperature process is due to ionic dc conduction. The piezoelectric relaxation at room temperature is ascribed to the increase of piezoelectric activity in the oriented noncrystalline phase, in which the sign of the piezoelectric modulus is opposite to that in the oriented c

ISSN:0098-1273    

DOI:10.1002/pol.1984.180221010

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY