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CPP: Chemische Physik und Polymerphysik

CPP 15: POSTER: Polymers and Biomaterials

CPP 15.24: Poster

Dienstag, 9. März 2004, 17:00–19:00, B

Influence of molecular weight on structure and dynamics in a series of nanophase-separated poly(n-butyl methacrylates) — •K. Schröter, E. Hempel, S. Hiller, and M. Beiner — FB Physik, Martin-Luther-Universität Halle-Wittenberg, 06099 Halle, Germany

A series of monodisperse n-butyl methacrylate (nBMA) systems reaching from high molecular weight polymers with about 400 monomeric units down to oligomers with only six units per chain and including also dimer and monomer was investigated by conventional and temperature-modulated calorimetry, dielectric spectroscopy as well as X-ray scattering methods. There are two main aspects that are of interest here: (i) For high molecular weight samples indications for a nanophase separation of incompatible main and side chain parts were observed. Main arguments are the coexistence of two relaxation processes with typical features of a dynamic glass transition and a prepeak in X-ray scattering data indicating a Bragg spacing of about 1.2 nm. It will be shown here that the prepeak starts to disappear below 25 monomeric units in the main chain. This shows that a certain chain length is required before nanophase separation effects will occur. (ii) Changes in the conventional glass transition (α) with chain length are analyzed based on data for our nBMA series. Of special interest is the dependence of fragility – as obtained from dielectric data for the α relaxation and calorimetric data – on chain length in a series of samples including long polymer chains as well as small molecule liquids. Thermodynamic fragility and steepness index are compared and discussed in the light of recent discussions about this topic in the literature.