Synthesis and glass transition behavior of ionomers from styrene/n‐butyl methacrylate

Abstract

Styrene/n‐butyl methacrylate/potassium methacrylate ionomers have been prepared by partial alkaline hydrolysis of the copolymers. Ion contents were determined by atomic absorption and neutron activation analyses. Glass transition temperatures (by DSC) increase with ion content but reach limiting values at 1–2 mol % ions. The limiting values are 5–20° higher than those of the starting polymers—depending on the molecular weight–and increase linearly with styrene content. These relationships are approximately described by Tg = Tgx ‐ (K/M + 4)e−x where x is the molar ion content, Tg∞ is the limiting Tg value and M the molecular weight. Data are provided to indicate that the Tg increase due to introduction of ions can be balanced by aqueous plasticization at ambient relative humidity, but the sharp shoulders in the Tg variations suggest the presence of a more fundamental mechanism in addition to this. Onset of domain formation or transition from growth of number of domains to growth of the size of these domains are possible mechanisms. Hydrolysis of polyacrylates can be accompanied by intramolecular catalysis leading to less random distribution of ions in the chains. Comparative studies were made with an alternating styrene/n‐butyl methacrylate copolymer in which this effect cannot occur. Hydrolysis rate was comparable to that of the random copolymers suggesting the absence of this effect under our conditions. Ionomers prepared from the alternating copolymer showed the characteristic Tg shoulder, indicating that this is not a consequence of block ion formation.

Some properties of styrene‐based ionomers II

“…The lower values of T g of the investigated ionomers based on S‐AA copolymers obtained in emulsion than those obtained in bulk may be a consequence of different distribution of the carboxyl groups in the initial copolymers, higher molecular weight copolymers obtained in emulsion, and different molecular weight distribution 7, 34, 35…”