摘要:

AbstractThe mechanics of adhesion have been investigated both theoretically and experimentally, using model adhesive joints consisting of a crosslinked amorphous rubber bonded to a variety of rigid polymeric substrates.An adhesive failure energy, θ, is defined which is characteristic of the bond but independent of test‐piece geometry. Both theory and experiment show that θ has the form, θ=θ0f(R) where θ0is the “intrinsic adhesive failure energy” which depends only on the physical and chemical nature of the adhesive‐substrate interface, andfis a function ofR, the “reduced” rate of failure propagation obtained from rate and temperature data using the WLF equation.θ0is the work of bond fracture across the interface and, for clean interfacial failure, is equal to the thermodynamic work of adhesionwA. Where failure is not purely interfacial, θ0can be expressed as θ0=iI+r

ISSN:0360-8905    

DOI:10.1002/polc.5070460104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThe application of Tobolsky's time‐temperature superposition principle for the stress‐relaxation behavior of amorphous polymers is reviewed, and its extension to crystalline polymers and the employment of X‐ray and optical methods is discussed. The desirability of applying the superposition principle to time‐dependent crystal orientation functions is described. The use of those techniques for the study of the relaxation of a low‐density polyethylene sample is illustrated. Spherulite orientation theory is used for analysis of th

ISSN:0360-8905    

DOI:10.1002/polc.5070460105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThe molecular theory of viscoelasticity has been modified in a previous publication for homogeneous block copolymers; the theory predicts that the maximum relaxation time of the block copolymer can be computed with the knowledge of submolecular sizes and monomeric friction coefficients. Stress‐relaxation experiments were carried out for two samples of styrene‐(α‐methyl styrene)‐styrene triblock copolymers. Maximum relaxation times were determined from the viscoelastic master curve through the use of procedureXdeveloped by Tobolksy and Murakami. Experimental results were found to be in reasonable agreement with theoretical predictions. The theory also predicts the existence of a singularity in the distribution of relaxation times at very short relaxation times, but as is discussed, this prediction cannot be verified by existing experimental te

ISSN:0360-8905    

DOI:10.1002/polc.5070460106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractOrientation measurements using differential infrared dichroism experiments have been applied to the study of the viscoelastic properties of polyurethane block polymers. The time dependence of the orientation function reflects the influence of both the viscoelastic nature of the blocks and of the two‐phase microstructure. A study of the effect of hard block length on the orientation response suggests the presence of an interlocked hard phase structure for most compositions. Such a structure severely restricts relaxation of orientation under strain. At very short hard segment lengths, this morphology is not present and extensive relaxation does occu

ISSN:0360-8905    

DOI:10.1002/polc.5070460107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractA study of the crystallization behavior of poly(ethylene coacrylic acids) and poly‐(ethylene comethacrylic acids) and their lithium, sodium, calcium, and cesium salts has been made utilizing the techniques of X‐ray diffraction, differential scanning calorimetry, and infrared spectroscopy. The acid substituent content ranged from 2.1 to 6.3 mol %. The results indicate that the acid substituents do not incorporate into the polyethylene crystal lattice and that these substituents have large effects on the kinetics of crystallization, especially in the case of the salts. The results are interpreted on the basis of a three‐phase model consisting of a polyethylene crystal phase, a mixed amorphous phase, and a micro‐phase‐separated ionic clus

ISSN:0360-8905    

DOI:10.1002/polc.5070460108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThe equilibrium shear modulusGof network polymers increases rapidly with the chain concentration ν when ν ≳ 10−3mol/cm3. This behavior is accounted for by the equationG=ΦnνRTΓ(1/λm) where Φn(=r̄t2/r̄00) may depend on n̄, the mean number of backbone bonds per chain, and Γ(1/λm) is a function of 1/λm, the mean fractional extension of chains in the isotropic (undeformed) network. In turn, 1/λm=(ΦnC̄n/q2n̄)1/2, where C̄nis a characteristic ratio (= r̄02/n/2) which, for short chains, depends on n̄, andqis a constant determined by bond angles and lengths. An expression for Γ, suggested by a well known equation for a regular cubic network of freely jointed volumeless chains, is derived and then shown to be approximated closely by Γapp=5λ 2m/(5λ 2m‐6) for 1/λm<0.88. The moduli of some 26 ethyl acrylate‐dimethacrylate networks, for which 5

ISSN:0360-8905    

DOI:10.1002/polc.5070460109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractThe mechanical relaxation time in a glassy polymer depends on the magnitude of strain. The stress relaxation modulus of a styrene acrylonitrile and polybutadiene composite system (ABS) was measured at strains ranging from 0.005 to 0.10. The relaxation time was observed to shorten by up to four orders of magnitude. In addition, a decrease in the elastic contribution to the modulus was observed. These two aspects of nonlinear viscoelasticity are interpreted in terms of the excess entropy and enthalpy associated with dilatation under strain, a crucial factor for ductile behavior and the formation of crazes. Up to 0.9 cal/g of the excess enthalpy associated with the stress‐induced dilatation is obtained from the differential scanning calorimetry study. As a corollary, brittle behavior following annealing is explained by the fact that it would take a greater magnitude of strain to regain a critical amount of excess enthalpy by the stress induced dilatatio

ISSN:0360-8905    

DOI:10.1002/polc.5070460110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractA brief review of the literature concerning damped Debye lattices as models for viscoelastic relaxation in the primary transition region is presented.We have observed that polystyrene plasticized with dioctylsebacate behaves in a fashion which is inconsistent with previous predictions based on this model. We have suggested an expanded interpretation of the model which predicts that plasticizers with solubility parameters appreciably different from that of the polymer will behave differently from diluents with the same solubility parameter as the polymer. The results of further experimentation are in accord with this new prediction.Our work supports the contention that the damped Debye lattice is a viable model and clearly demonstrates that interchain interactions are important in determining physical properties in the primary transition region.

ISSN:0360-8905    

DOI:10.1002/polc.5070460111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractLittle consideration has until now been given to the effect of microphase separation in crosslinked polymers. This work deals with the correlation between the network chain length and some bulk properties of a series of seven highly crosslinked polymers prepared from dimethylsiloxane diacrylate oligomers with different lengths between their acrylic terminal groups. The occurrence of multiple transitions in the shear modulus versus temperature behavior, probably due to microphase separation, and the dependence of the transition regions and shear moduli on the siloxane network chain length were studied. The findings are compared with those of a similar work reported by us earlier, in which carboxyl‐terminated poly(dimethylsiloxanes) of similar chain lengths of the prepolymers were condensed with a trifunctional imine and yielded polymers exhibiting multiple transitions.Multiple transitions were observed in some of the crosslinked polymers, but this phenomenon disappeared with an increase in the amount of siloxane groups in the prepolymers. It seems that the reason for this suppression of microphase separation, as compared with the crosslinked carboxyl‐terminated oligosiloxanes, derives from the absence of sufficiently long organic sequences, from their limited number in the network chains, and from internal plasticization by the side chains formed as a result of inefficient crosslinking. The nature of the crosslinking site and the mechanism of crosslinking have a decisive influence on the structure and properties of the polymers including the occurrence of multiple transitions, even when the prepolymers are almost identical between their functional end gro

ISSN:0360-8905    

DOI:10.1002/polc.5070460112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY

摘要:

AbstractDielectric relaxation has been studied for poly (ϵ‐caprolactone) in dioxane solution. As expected from the head‐to‐tail structure [‐(CH2)5COO‐]x, at a given temperature there are two distinct dielectric loss peaks. Radio‐frequency bridge measurements reveal a low‐frequency peak due to a component of the repeat unit dipole parallel to the direction of the chain backbone and amounting to about 0.8 Debye per ester group. The position of this peak on the frequency scale varies with molecular weight as predicted from the longest normal‐mode relaxation time, τ1≅M[η]η0/RTThe second relaxation, which is independent of chain length, is conveniently studied over a wide range of concentrations by the technique of time‐domain reflectometry (TDR). This peak is associated with relaxation by local conformational rearrangement of a component of the dipole moment perpendicular to the chain direction, amounting to about 1.6 Debye per ester group. The extrapolated frequency of maximum loss at infinite dilution is about 3 GHz at 300K, with an apparent activation energy of about 30 kJ mol−1. The dependence of the local relaxation time on concentration can be fitted by a familiar free‐volume equation of the type τ = A exp(B/vf), in which the free volumevfis a li

ISSN:0360-8905    

DOI:10.1002/polc.5070460113

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1974

数据来源: WILEY