Ch. Wohlfarth

Influence of hydrogen bonds on the properties of low molecular weight polyoxypropylene, as studied by nuclear magnetic resonance and thermodynamic measurements: further indication for a transient entanglement

Nuclear magnetic resonance (n.m.r.), differential scanning calorimetry (d.s.c.) and thermodynamic measurements were performed in polypropylene glycol (PPG) melts with molecular weights ranging from 520 to 3200 g mol−1. They are compared with recent ultrasonic experiments showing local modes, normal modes, and a characteristic low frequency relaxation in samples with Mw > 1300 g mol−1. This additional relaxation process for higher molecular mass material was also detected by n.m.r. measurements. As an explanation for this process, a special entanglement between transient intermolecular structures formed by hydrogen bonds and having effective molecular weights above the critical values is discussed.

Anwendung der kontinuierlichen Thermodynamik auf die Berechnung des Phasengleichgewichtes in athermischen Lösungen polydisperser steifkettiger Polymere

Die kontinuierliche Thermodynamik wird auf die Berechung des isotrop-nematischen Phasengleichgewichtes in Systemen aus einem Losungsmittel und einem polydispersen Polymer angewandt. Die Makromolekule werden als starre Stabchen betrachtet und sind durch eine Schulz-Flory-Verteilung bezuglich ihrer Segmentzahl (Molmasse) charakterisiert. Am Beispiel des Flory-Modells fur die chemischen Potentiale starrer Stabchen wird der Einflus der Verteilungsfunktion und ihrer Momente auf das Phasenverhalten im athermischen Grenzfall diskutiert. Continuous thermodynamics is applied to the calculation of the isotropic-nematic phase equilibrium in systems composed of one solvent and a polydisperse polymer. The macromolecules are considered to be rigid rods and will be characterized by a Schulz-Flory distribution with respect to their segment number (molar mass). The influence of the distribution function and its moments on the phase equilibrium is demonstrated by using the example of the Flory model for the chemical potential of rigid rods in the athermal case.