Strain birefringence in ethylene‐propylene copolymers

Abstract

A series of polymeric networks were prepared by the γ‐radiation crosslinking of two ethylene‐propylene copolymers containing 62 and 69 mol % ethylene units. The elastomeric materials thus obtained were studied in elongation, both swollen and unswollen, over the temperature range −30 to 95°C. The experiments involved measurements of both the elastic force and birefringence, using primarily changes in temperature at constant length (rather than changes in length at constant temperature). There is evidence for crystallization in these networks, as manifested by marked decreases in force and increases in birefringence at relatively low elongations and at temperatures as high as 70°C. As expected, the birefringence and related quantities were found to be more sensitive to crystallization than the force, with the stress‐optical coefficient showing the greatest sensitivity. The results obtained in the elongation‐temperature regions presumably free from effects of network crystallization were used to calculate values of the temperature coefficient of the unperturbed dimensions of the chains, and values of the optical‐configuration parameter. Both are widely used to characterize (spatial) configurations of chain molecules. Values of the former quantity are in very good agreement with those predicted some years ago using a rotational isomeric state model for ethylene‐propylene chains of various chemical and stereochemical compositions. The extension of these theoretical calculations to include the stress‐optical coefficient should provide further information on crystallization in ethylene‐propylene elastomers and the configurational characteristics of these copolymeric chains.

The Current State of Silicone-Based Dielectric Elastomer Transducers

“…[ 217 ] Therefore, bimodal networks exhibit both signifi cant ultimate stress and major ultimate strain. [ 214 ] Bimodal networks can be created with a random distribution of short polymer chains within the long chains (homogeneous bimodal networks) [ 214,[220][221][222] or as heavily cross-linked short chain clusters joined to the long chain network (heterogeneous bimodal networks). [223][224][225] Bejenariu et al [ 225,226 ] prepared both homogenous and heterogeneous bimodal networks and evaluated them as candidates for dielectric elastomers.…”

Photoelastic Studies of Some Polybutadiene Networks

“…(Such crystallization was readily detected by such measurements on several ethylene-propylene chemical copolymers. 23 It should be considerably less pronounced in the present case judging from the differences in the melting points of the two systems, and differences in the discrepancy (probably from network crystallization) 23 between theoretical 24 , 25 and observed 13 • 26 values of the elongation modulus.) The data obtained under conditions where there is no evidence of cyrstallization are used to calculate values of the temperature coefficient of the unperturbed dimensions of the network chains, and values of the opticalconfiguration parameter.…”

Silicone rubber films modified by ethylenoxy moieties: Characterization and drug delivery properties

“…In this case, it is expected that more dangling chains are produced which in turn reduce the extensibility of the samples 45 and since longer chains between crosslinks are present, the Young's modulus of the films is reduced. 46,47 The E values of Table IV have been plotted in Figure 4 vs. the corresponding swelling degree q in chloroform (Table III). The theoretical correlation of E and q for a particular crosslinked polymer, can be derived by combining the expressions of the functional dependence of E and q on the mean molecular weight by number between two consecutive crosslinks, M c .…”