Very long-time crystallization kinetics for ethylene-methacrylic acid ionomers neutralized with zinc, sodium, lithium and magnesium

Papers by our group [1] (Grady et al., 2013) and another group [2] (Paul et al. 2012) examined crystallization of random copolymers of ethylene and methacrylic acid after room temperature annealing. Similar conclusions were reached concerning the crystallization process; primary crystals were either unchanged or changed very little after annealing while secondary crystallization occurred over long time scales after annealing. The current work confirms these general conclusions for four different cations (Zn²⁺, Na⁺, Li⁺ and Mg²⁺), with the latter two not studied in either of the previous studies. Even after 6 years of annealing at room temperature, the crystallization rate is constant with logarithmic time, i.e. the material continues to crystallize. The acid copolymer does not crystallize with room temperature annealing, although secondary crystals of the acid copolymer thicken with annealing.