Secondary Crystallization and Aging in Ethylene-Based Carboxylic Acid Ionomers

摘要

Ionomers are polymers with a small fraction of ionic functional groups attached to the polymer backbone. It is widely known that neutralization of these ionic groups with metal ions changes the crystallization kinetics of the ionomer. For Zn-neutralized ethylene carboxylic acid ionomers, our group* found that a classic relationship of Flory did not hold true, namely that the fractional crystallinity of a random copolymer depended on the identity of the comonomer. This result did not invalidate the theory, rather Flory did not consider the case of a second phase, namely the ionic aggregate phase, which did not disappear upon melting. Further, the rates of formation of secondary crystals relative to the crystallization amount at infinite time was independent of neutralization level for the phase-separated ionomers; in other words the Avrami constants n and K were independent of neutralization level for the secondary crystals. Very careful absolute heat capacity measurements were also used to examine the existence of immobilized amorphous phases and it was shown calorimetrically that an immobilized amorphous phase exists above the melting point of the polyethylene segments in the neutralized materials and that the amount of this phase increases with increasing neutralization level. In this presentation, results from other neutralizing cations (Li, Na and Mg) will also be shown and compared to the results of the Zn-neutralized materials.