Segmental dynamics in nanophase separated comb-like polymers with long side chains

Poly(α-n-alkyl β-l-aspartate)s, PnAALAs, are comb-like polymers with rod-like helical conformations which present crystallinity for long alkyl side chains (n > 10). Dielectric spectroscopy experiments for PnAALAs (10 ⩽ n ⩽ 18) show the existence at low temperatures of two secondary modes corresponding to localized motions of the carbonyl group. At higher temperatures two cooperative mobilities coexist. The first corresponds to the segmental mobility of the amorphous side chains and has the characteristic of a polyethylene-like dynamic glass transition common to various series of nanophase segregated side chain polymers with different morphologies. A second segmental mode is attributed to the restricted rotational motion of the rigid rods which is hindered when the spacing between rods decreases. An extension to the results found for other polymer series with shorter lateral chains is presented, showing the tendency to approximate amorphous polyethylene dynamics in these confined nanodomains of increasing sizes.