ISSN:0032-3888    

DOI:10.1002/pen.760190402

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractInfinite network formation is discussed using the theory of molecular size distribution functions. The necessary and sufficient conditions of infinite network formation in simultaneous crosslinking and main chain scissions are reviewed. Also, the condition of endlinking associated with main chain scissions is outlined; the condition of endlinking of special terminal groups is given. Infinite network. formation in condensation as well as addition polymerizations is studied. It is shown that the existence of branch units in condensation polymerization is only the necessary condition of infinite network formations, whereas the sufficient condition is related to the form of branch units; the necessary condition in addition polymerizations is the simultaneous occurrence of chain transfer to polymer and chain termination by recombination.

ISSN:0032-3888    

DOI:10.1002/pen.760190403

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractProblems of the characterization of network structure by investigating the network formation and its response to mechanical stress have been analyzed. Attention has been devoted to the effect of reactivity of functional groups and cyclization on the formation of network structure and to problems of obtaining the equilibrium modulus and its relation to the concentration of elastically active network chains (EANCs). It has been demonstrated that a theoretical description of network formation must be based on reliable information on the rules of joining of functional groups and on their relative reactivity; the tree‐like approximation offers a number of structural parameters of the sol and gel including, e.g, chemical clustering of units of a certain type. The main obstacles to reaching the equilibrium modulus are long relaxation, times of lightly crosslinked networks and the occurrence of secondary relaxations. In correlating the equilibrium modulus and the concentration of EANCs, it is necessary to find conditions under which the Mooney‐Rivlin constantC2can be neglected and to carry out the required corrections of the modulus, if experimental conditions differ from those of network format

ISSN:0032-3888    

DOI:10.1002/pen.760190404

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractSome polymer networks show an anomalous increase in the modulus or reduced stress at very high elongations. This behavior has now been investigated definitively by determining stress‐strain isotherms for both crystallizable and noncrystallizable networks, prepared using several curing techniques (carried out so as to yield a wide range in degree of cross‐linking). The networks were studied unfilled at a number of temperatures, and at several degrees of swelling. The results clearly implicate strain‐induced crystallization as the origin of the upturn in the modulus, and thus demonstrate that the wide spread interpretation of this upturn in terms of limited chain extensibility is inco

ISSN:0032-3888    

DOI:10.1002/pen.760190405

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractIn the simplest model of rubber‐like materials only two kinds of forces are assumed: network forces with identical temperature dependence, and liquid forces which. are isotropic. For this simple model the relation between the temperature dependence of the network forces and that of the observed elastic force is calculated. When the elastic equation of the network is of the classical one term type, the well‐known equation of Flory, Ciferri and Hoeve is found without using assumptions about the physical meaning of the front factor in the elastic equation. When the elastic equation of the network is of the Mooney‐Rivlin type with two terms, the difference between the temperature dependence of the observed forces and of the network forces is found to depend on the ratio of the coefficients in the Mooney‐Rivlin equation and on the elongation. The effect of the internal pressure is to add a factor to this term. The conclusion is that detailed knowledge about the network forces is needed in order to establish the value of the correction term for thermal expansion in the equation for the temperature dependence of the elastic force in the m

ISSN:0032-3888    

DOI:10.1002/pen.760190406

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe role of interchain excluded volume and entanglement in the elastic behavior of polymeric networks is theoretically examined. A three‐chain network model is used, with each chain confined within an infinite, rectangular cylinder. The cylinders and the network crosslinks, are assumed to deform affinely. When the cross sections of the cylinders are small, the network elastic free energy equation has the form\documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta F_e = A[\lambda _x^2 + \lambda _y^2 + \lambda _z^2 - 3] + B[\lambda _x^{ - 2} + \lambda _y^{ - 2} + \lambda _z^{ - 2} - 3] + C{\rm }\ln [\lambda _x \lambda _y \lambda _z] $$\end{document}The λs represent the macroscopic deformation ratios. The constantsA,BandCare functions of the number of each type of network chain (i.e.,Acontains the number of tie chains;Ccontains the number of loops and tie chains;Bcontains the number of dangling chain ends, unattached chains, loops and tie chains), their unperturbed dimensions and the sizes of the cylinders which confine th

ISSN:0032-3888    

DOI:10.1002/pen.760190407

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractLinear 1,2‐polybutadiene is cross‐linked near its glass transition temperature by γ‐irradiation while strained in simple extension with a stretch ratio λo. After release, the sample retracts to a state of ease (λs). From λo, λs, and stress‐strain measurements in extension from the state of ease, the concentrations of network strands terminated by trapped entanglements (vN) and by cross‐links (vx) can be calculated. Forvx/vN≡R′o>1, retraction to the state of ease is rapid. ForR 0o≃ 0.3 or less, retraction is slow and extends over many logarithmic decades of time scale. When an eased sample is stretched to λowhere the cross‐links do not contribute to stress, the subsequent stress relaxation of the entanglement network toward equilibrium is also very slow ifR′ois small. The slow timedependent processes are attributed to a high proportion of untrapped entanglements on dangling branched structures. The concentration of trapped entanglement strands,vN, can also be calculated from the equilibrium stress at λo. The fraction of trapped entanglements agrees rather well with the predicti

ISSN:0032-3888    

DOI:10.1002/pen.760190408

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractOur recursive method is extended to calculate several new parameters for stepwise polyfunctional polymerization. In the pregel region we calculate weight average molecular weight,Mw, for polydisperse reactants and effective average functionality,fe, of a reacting mixture. These quantities are useful for systems employing reactive oligomers. We also calculate weight average number of branches per molecule,Bw, and the weight average of a longest chain. These should be useful for viscosity relations. In the postgel region we give relations for the extent of reaction in the soluble fraction. This result can be used to calculate sol properties directly from existing pregel relations. We also calculate the weight fraction of pendant chains on the gel,wp, and the average molecular weight of the elastically effective network chains,Mc,w.

ISSN:0032-3888    

DOI:10.1002/pen.760190409

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractSingle phase interpenetrating polystyrene networks were synthesized using a room temperature photopolymerization method. Divinylbenzene was used for crosslinking both networks in most cases; a few IPNs were prepared using acrylic acid anhydride to provide labile crosslinkages in the primary network. The IPNs were characterized by means of equilibrium swelling in toluene. The results of these experiments closely approached the predictions of a swelling equation derived under the assumption that the two networks were elastically independent. Deviations from the swelling equation predictions could be explained in terms of contributions from internetwork entanglements. Small amplitude dynamic mechanical measurements indicated that the presence of the small amount (∼10 percent) of tight primary network chains had no perceptible effect on the linear viscoelastic propertie

ISSN:0032-3888    

DOI:10.1002/pen.760190410

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractWe have measured the advancing contact angles of drops of methanol‐ethylene glycol mixtures on films of previously studied polyurethane‐epoxy interpenetrating polymer networks. The extrapolated critical surface tensions were in excellent agreement with those obtained from advancing contact angles of drops of water‐methanol mixtures. A sharp minimum is observed in the critical surface tension at network compositions where we have previously found maxima in ultimate mechanical properties. We advance a physical explanation based on unrelieved surface strains. We have also measured the toluene vapor transmission (permeability, diffusion and sorption coefficients) in these films. These results, together with the previously obtained water vapor permeabilities, are in complete accord with the expected morphologies of these net

ISSN:0032-3888    

DOI:10.1002/pen.760190411

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY