Bernhard Wunderlich

Theory and Measurements of the Glass‐Transformation Interval of Polystyrene

Equations for the apparent heat capacity in the glass‐transition interval as functions of temperature, heating rate, and thermal history have been developed and programmed for computation. The hole theory of liquids was used as basis for the analysis of the glass transition. Experimental information was derived from dynamic differential thermal analysis, DDTA, on polystyrene.The maximum of the apparent heat capacities found experimentally agrees with the theory. The peak temperatures Tm can be expressed over four decades of heating rates by logq = A′ − B/Tm, where q is the heating rate, A′ is an approximate constant, and B is the activation energy for hole formation. Higher cooling rates lead to higher activation energies on subsequent heating, indicating the need to recognize a hole size distribution.The minimum in the heat capacity that precedes the maximum on heating through the glass‐transition interval could be detected on quenched samples. Mathematical expressions for the minimum temperature and mag...

Motion in Polyethylene. I. Temperature and Crystallinity Dependence of the Specific Heat

Data for the specific heat of polyethylene as a function of crystallinity are collected from 1° to 420°K. Specific heats, entropies, and enthalpies of the completely amorphous and crystalline polyethylene are extrapolated. The glass transition is located for the amorphous at 237°K with a ΔCp of 2.1 cal deg—1 (mole CH2)—1. Specific‐heat values at constant volume are calculated for the crystalline polyethylene.

Motion in Polyethylene. II. Vibrations in Crystalline Polyethylene

Using the specific heats of completely crystalline polyethylene as a basis, the vibrational spectrum is discussed. The vibrational spectrum is found to consist of three completely separate parts. (A) The high‐frequency CH2‐stretching vibrations between 2850 and 2930 cm—1 which contribute little to the specific heat below 350°K. (B) The low‐frequency optical vibrations between 720 and 1480 cm—1 which contribute above 150°K increasingly to the specific heat

Motion in Polyethylene. III. The Amorphous Polymer

The heat capacity of completely amorphous polyethylene is separated above 250°K into contributions from the optical vibrations, the acoustical vibrations and hindered rotations, the trans—gauche equilibrium, and the hole equilibrium. The glass transition interval which stretches from 250° to 120°K can be explained by a separate freezing in of the hole equilibrium at 237°K and a slower freezing in of the trans—gauche equilibrium, which is completely arrested at 120°K with 0.165 of the bonds left in the gauche position.

A thermodynamic description of the defect solid state of linear high polymers

Abstract It is attempted to describe the solid state of linear crystalline polymers using the defect concept. This metastable solid state which is normally found in polymers is described thermodynamically. Changes in state are traced as a function of heating rate. The limiting experimental maximum melting point on fast heating, Tm, is described by the equation InXA=HuR(T−3m—Tm−1) which contains as parameters the activity of crystallizable units in the melt, XA, the heat of fusion at Tm, ΔHu, and the experimental maximum melting point on fast heating of large defect free lamellae into a melt XA = 1:Tfm. For linear polyethylene experimental evidence is cited which supports the theoretical description.