Phase transitions, relaxations, and properties of high polymers

Abstract

Starting with a nondefective bundle of macromolecules (the ideal crystal) one gets a low-defective bundle (the real crystal) by introduction of stable defects (kinks, torsional defects, jogs and folds) which are compatible with the intra-and intermolecular potential. The cooperative statistical treatment of this bundle revealsunder a certain conditiona first order transition, connected with a jump in defectconcentrations. This transition corresponds in most cases to the melting of the polymer, in some polymers (e. g. trans-polybutadiene) it splits up into a solid state transition (large kinkblocks without torsions) and the melt transition (small kinkblocks, torsional defects, jogs and folds). In the case of polyethylene the bundle model has been shown to explain quantitatively the transition data (Tm, bHm, A V~) as well as the expansion coefficient and the compressibility of the melt together with their dependence on static pressure. The calculated short-range order also is in accordance with the X-ray and electron diffraction data. By introduction of cooperatively arranged gauche-areas (for planar molecules) the meander model is established which guarantees the isotropy of the melt. Assuming the bundle diameter (calculated to about 50 A which is in the range of the observed superstructure in amorphous polymers) to be constant during crystallization a lamellae-structure results in which the meander thickness is determined by the crystallization temperature. This two phase meander model is in accordance with the experiment and implies the key to the underst.anding of molecular motions in polymers. This will be shown by a quantitative molecular interpretation of the relaxation processes (secondary, main and crystalline relaxation) in a polymer as well as of its deformation behaviour (paraelasticity, plasticity). ZUS AMMENFASSUNG :Ausgehend von einem defektfreien Bundel aus Makromolekulen (Idealkristall) erhalt man den Realkristall durch Einfuhren stabiler Defekte (Kinken, Torsionsfehler, Jogs und Falten), die mit dem intra-und intermolekularen Potential vertriiglich sind. Die kooperativ-statistische Behandlung dieses Bundels zeigt unter gewissen Voraussetzungen eine Phasenumwandlung 1. Ordnung, die sich durch eine sprung-* Presented at the Scientific Symposium "The Physics and Chemistry of Fibre Materials", Miinchen, 3rd and 4th June 1971.

Rotations of nitroxide radicals in condensed polymeric systems

“…a E As v0 is a molecular constant, ~'0eef and a--T must be functions of the molecular weight of probe molecules. From figure 1 we calculated V0efe and E values and extrapolated a value for v0 = 2"10 la s -I which is in good agreement with the extrapolated value of Pechhold (17) (v0 ---3.10 la s-i).…”

Dilatometric measurements on some polymers: The pressure dependence of thermal properties

“…Besides the intention to get more data than available in literature, we had special interest in this work. We want to check the theory of Blasenbrey and Pechhold (1,2,3) which tries to describe phase transitions and properties of the melt by a cooperative statistical treatment based on molecular calculations. These theoretical aspects will be treated elsewhere, this paper will be restricted to experimental results.…”

Versetzungstheorie des Schmelzens auf der Grundlage der Cluster-Entropie-Hypothese (CEH)

“…Eine Schmelztheorie fiir Polymere auf der Grundlage kooperativer Rotationslsomerie der Ketten hatten Blasenbrey und Pechhold [1] 1967 vorgeschlagen. In der Zwischenzeit wurde es fiJr uns immer klarer, dat~ das Schmelzen yon Molekiilkristallen und Polymeren ein zumindest 2-stufiger Proze~ ist, der sich aus einer oder mehreren Kristall-oder Konformationsumwandlungen und dem eigentlichen Schmelzen der letzten (manchmal hypothetischen) Hochtemperaturphase zusammensetzt.…”