Relationship of deformation behavior to thermal transitions of ethylene/styrene and ethylene/octene copolymers

Abstract

The stress-strain response of low-crystallinity ethylene-octene (EO) and ethylene-styrene (ES) copolymers with 7-20 mol % comonomer was compared over a temperature range that spanned the glass-transition and crystal melting regions. Above the onset temperature of the glass transition, the copolymers exhibited elastomeric behavior with low initial modulus, uniform deformation to high strains, and high recovery after the stress was released. In the glass-transition range, an initial lowstress elastomeric response was followed by a distinct "bump" in the stress-strain curve. On the basis of the temperature and rate dependence of the stress-strain curve, local strain-rate measurements, local temperature changes, and recovery characteristics, the "bump" was identified as high strain yielding. Hence, the stress-strain curve sequentially exhibited the features of elastomeric and plastic deformation. Following high strain yielding, strain hardening dramatically increased the fracture strength. This behavior was defined as elastomeric-plastic. Elastomeric-plastic behavior in the broad glass-transition range constituted a gradual transition from elastomeric behavior at higher temperatures to low-temperature plastic behavior with high modulus and macroscopic necking. Because of the lower glass-transition temperature of EO, Ϫ40°C as compared with Ϫ10°C for ES, the onset of elastomeric-plastic behavior occurred at a significantly lower temperature. The concept of a network of flexible chains with fringed micellar crystals serving as the multifunctional junctions that provides the structural basis for elastomeric behavior of low-crystallinity ethylene copolymers was extended to elastomeric-plastic behavior by considering a network with a fraction of rigid, glassy chains.

Isolated Ethylene Units in Isotactic Polystyrene Chain: Stereocontrol of an Isospecific Post‐Metallocene Titanium Catalyst

“…[10,11] On the other hand in copolymer c the ethylene units within the polystyrene chain could form sequences long enough to be incorporated into the crystals. [12] Moreover, for all the copolymers no endothermic transitions are detected after the first DSC scan following the behavior of the isotactic polystyrene.…”

The effect of temperature on the viscoelastic response of semicrystalline polymers

“…(38). After finding the best fit value ␥ (i) , this procedure is repeated twice for the new intervals [␥ (iϪ1) , ␥ (iϩ1) ], to provide an acceptable accuracy of fitting.…”

“…36 According to this approach, a sophisticated microstructure of a semicrystalline polymer is replaced by a single phase, whose response captures essential features of the time-dependent behavior of the polymer. Following [20,22,37,38], we treat the equivalent phase as a network of macromolecules connected by temporary junctions (entanglements, physical crosslinks on the surfaces of crystallites, and fringed micellar crystals serving as the multifunctional junctions 37 ). To simplify the derivation of stress-strain relations, we assume the network to be incompressible.…”

Nanostructure Evolution of Homogeneous Poly(ethylene‐co‐1‐octene) as a Function of Strain

“…Under mechanical load the materials exhibit homogeneous straining behavior, and features of both elastomeric and plastic deformation. [5] Following the notions of Peterlin, [6,7] tensile failure modes related to the load-elongation behavior of the materials are both discussed on a molecular level and on the colloidal or nanodomain scale. On the molecular level, three processes are addressed as: fine chain slip (going along with crystallite thinning), coarse chain slip (going along with crystallite disruption), and chain scission.…”