摘要:

AbstractThe mechanical and optical behavior in the dry and swollen states of loosely crosslinked epoxy networks prepared from the diglycidyl ether of bisphenol A, phenylglycidyl ether, and 4,4′‐diaminodiphenylmethane was investigated, and the weight fraction of sol in the networks was determined. The crosslinking density was controlled by an excess of diamine and by the fraction of monoepoxide. The reaction proceeded to almost full conversion of epoxy groups. With increasing content of monoepoxide or with increasing excess of diamine, the main transition region is shifted to lower temperatures. The dependence of the viscoelastic modulus on temperature and the optical behavior indicate that the networks are homogeneous. In all cases, the sol fraction is adequately described by the theory of branching processes (cf. Part I). The equilibrium modulus related to the dry state is the same irrespective of whether it is obtained by measurements in the dry or swollen state. The mechanical behavior in the rubbery state can be described by the theory of phantom networks with fully suppressed fluctuations of crosslinking (front factorA= 1) or by the theory of phantom networks with fully released fluctuations of crosslinks (front factor)A=fe−2/fe] and contribution of trapped entanglements of the Langley‐Graessley type (cf. Part I). In the analysis of the equilibrium behavior, it is advantegeous to use the plot of superimposed dependences ofGeon the gel fraction, which considerably reduces the effect of experimental inaccuracy in determination of composition and degree of con

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220211

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe probabilityW(t) that a given numbertof segments of an infinite chain lie within a given sphere can be expressed in terms of the single‐pass length probability and the probability of reentrance into the sphere. The problem of calculating these two probabilities is equivalent to that of a diffusing particle exiting or entering the sphere after a given time, when the surface of the sphere is an absorbing wall. It is shown that the boundary condition,c= 0, usually applied to an absorbing surface cannot be used for the present purpose. The boundary condition used instead is the so‐called radiation condition ∂c/∂z=kc; it is shown that whenkapproaches infinity the final answer forW(t), which is given in the form of an infinite series, approaches the correct limit. In this same limit the ratio 〈t〉2/〈t〉2h

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220212

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe ion etching technique has been applied to a morphological study of mechanically blended polypropylene (PP) with high‐density polyethylene (HDPE). Samples blended to PP/HDPE compositions of 65/35 and 85/15 by weight were highly drawn and then heat treated for 30 min at selected temperatures up to 163°C. When these samples are carefully ion‐etched several features are observed in electron micrographs, namely (i) crosshatched, and (ii) twisted or layered textured inclusions of HDPE crystals within arrays of lamellalike PP crystals situated perpendicular to the direction of drawing. X‐ray diffraction measurements of the drawn samples heat treated in the range 145–163°C for 30 min shows that oriented HDPE crystallizes withb‐axis orientation along the drawing direction. Supporting evidence is obtained from electron diffraction measurements. The molecular weight of the HDPE component is a major factor in theb‐axis‐oriented growth of HDPE crystals in

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220213

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA numerical method has been employed to calculate crystallization temperature as a function of position in slabs or films of polyethylene quenched to various temperatures. The method is iterative, and combines a recent theoretical fit to empirical data for rate of crystal growth as a function of temperature with a solution to the thermal diffusion equation which takes latent heat into account. Results apply strictly only to transcrystalline regions near external surfaces but also provide lower limits to crystallization temperatures throughout the interiors of samples where spherulites nucleate ahead of the general crystallization front. Emphasis is given to assessing the relative importance of various physical parameters in determining crystallization temperatures.

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220214

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220215

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY

ISSN:0098-1273    

DOI:10.1002/pol.1984.180220216

出版商:John Wiley&Sons, Inc.    

年代:1984

数据来源: WILEY