Polar association in polyethylacrylate observed at small shear and large elongation: Effect of concentration of polar solvent

2000 
Polyethylacrylate is a polar rubber that exhibits strain-induced association in elongation, a behavior quite similar to strain-induced crystallization of crystallizable rubbers. Two questions are considered: whether or not strain-induced association is suppressed when the polymer is diluted with polar solvents and whether or not some extent of polar association is present even in the quiescent state and can be detected under small shear deformation. Dynamic mechanical measurements were performed in shear in the linear region of viscoelastic properties for a gel-free rubber plasticized with dibutyl-phthalate (DBP). The elongational data were linearized according to a previously developed linearization scheme. The linearized elongation modulus-time curve was in good agreement with the shear modulus-time curve, with a factor of 3, for 15% and 20% DBP. This is similar to the case for nonpolar elastomers. Therefore, at these concentrations, there is no polar association. For 0% and 10% DBP, the elongational curve was significantly higher than three times the shear curve, indicating that strain-induced polar association did occur. The rubbery plateau modulus observed in the shear measurements hardly changed from 0% to 10% DBP. On further dilution, it decreased as expected. At 10% DBP, the polar association appears to be enhanced. When the polymer is diluted beyond 10% DBP, there is no indication of the association under both strained and unstrained condition.
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