Dynamics of the "Strong" Polymer of n-Lauryl Methacrylate below and above the Glass Transition

Abstract

Dielectric spectroscopy (DS) and dynamic light scattering (DLS) are employed to study the dynamics of poly(n-lauryl methacrylate) (PnLMA) (M w = 1.1 x 10 5 ) at temperatures below and above the glass transition temperature T g (T g 225 K). The DS and DLS data show no evidence for the splitting between the primary (α-) and secondary (β-) relaxations within the experimental frequency range. The main process affecting DS and DLS is the mixed αβ-relaxation which bears similarities to a single α-process with regard to the T-dependence of the relaxation times. Excellent agreement between the two sets of experimental relaxation times was found. The distribution of relaxation times exhibits a pronounced temperature dependence : from a Kohlrausch-Williams-Watts (KWW) exponent of β KWW 0.25 at T T g to β KWW 1 at T T g + 100 K and at a frequency of about 1 MHz. PnLMA is therefore, to our knowledge, the only polymer with a Debye (β = 1) distribution of relaxation times at megahertz frequencies so far. The extremely broad distribution near T g and the weak normalized temperature dependence of the relaxation time apparently contradict the phenomenologically established correlation between the two in many glass formers. This contradiction might arise from concentration fluctuations of the long alkyl chain which can broaden the relaxation spectrum near T g . In addition to the main β-process, a fast β-relaxation can be resolved in both experiments and originates from the polyethylene-like alkyl chain.