STATISTICAL N-BUTYL ACRYLATE (SULFOPROPYL)AMMONIUM BETAINE COPOLYMERS.4. DYNAMIC-MECHANICAL PROPERTIES

The dynamic mechanical behavior of butyl acrylate-based zwitterionomer s from the glassy to the terminal zones is described. Two T(g)'s had b een detected previously by differential scanning calorimetry (DSC) for zwitterion contents, F(B), above 4.5 mol %. The biphasic morphology o f these materials and the increasing importance of the ''hard' phase r elative to the ''soft'' phase are confirmed. The glass transition of t he soft phase (T(g)S) increases by only 1.5-degrees-C/mol % zwitterion content. A well-defined rubbery zone is evident, whose pseudoequilibr ium modulus increases as G(N)-degrees is-proportional-to F(B)2.2. The terminal zone is increasingly retarded to higher temperatures or lower frequencies (thus extending the rubbery plateau range) with zwitterio n content. An unusual feature of the moduli-frequency curves is the ap pearance of a zone of constant slope intermediate to the rubber and te rminal zones. The addition of a stoichiometric amount of LiClO4 furthe r extends the length of the rubbery plateau zone but has little effect either on the T(g)S or on the rubbery modulus. This indicates that th e salt enhances the strength of the zwitterionic interactions but does not enhance phase separation. All samples appear to be thermorheologi cally simple; however, the shift factors fit a simple WLF equation onl y at low zwitterion contents.