DYNAMICS OF THE STRONG POLYMER OF N-LAURYL METHACRYLATE BELOW AND ABOVE THE GLASS-TRANSITION

Dielectric spectroscopy (DS) and dynamic light scattering (DLS) are em ployed 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 approximate to 225 K). The DS and DLS data show n o evidence for the splitting between the primary (alpha-) and secondar y (beta-) relaxations within the experimental frequency range. The mai n process affecting DS and DLS is the mixed alpha beta-relaxation whic h bears similarities to a single alpha-process with regard to the T-de pendence of the relaxation times. Excellent agreement between the two sets of experimental relaxation times was found. The distribution of r elaxation times exhibits a pronounced temperature dependence: from a K ohlrausch-Williams-Watts (KWW) exponent of beta(KWW) approximate to 0. 25 at T approximate to T-g to beta(KWW) approximate to 1 at T approxim ate to T-g + 100 K and at a frequency of about 1 MHz. PnLMA is therefo re, to our knowledge, the only polymer with a Debye (beta = 1) distrib ution of relaxation times at megahertz frequencies so far. The extreme ly broad distribution near T-g and the weak normalized temperature dep endence of the relaxation time apparently contradict the phenomenologi cally established correlation between the two in many glass formers. T his contradiction might arise from concentration fluctuations of the l ong alkyl chain which can broaden the relaxation spectrum near T-g. In addition to the main beta-process, a ''fast'' beta-relaxation can be resolved in both experiments and originates from the polyethylene-like alkyl chain.