Glass transition of partially ordered macromolecules

Abstract

An operational definition of the glass transition as the transition between the solid and liquid states of amorphous or partially ordered matter is given, particularly as it applies to flexible macromolecules. This is followed by a description of the basic observations of glass transitions via thermal analysis using calorimetry. Partial order is treated as it is found in semicrystalline, mesomorphic, and semimesomorphic samples. Examples of these three types of partial order are discussed as developed in our laboratory. Semicrystalline polymers may possess a rigid amorphous fraction in their amorphous areas. The glass transition of the remaining mobile amorphous fraction is usually shifted to higher temperature relative to the fully amorphous samples, and is frequently broadened with a temperature range that may reach more than 100 K. The time dependence of the glass transition causes hysteresis phenomena and physical aging, both of which are strongly affected by partial order. The glass transitions of liquid crystals are similar to the transitions of the isotropic state in magnitude, but may be shifted in temperature. A gradual, more local glass transition has been observed within condis crystals (conformationally disordered crystals) of small and large molecules. The glass transition of a partially condis crystalline polymer shows a rigid amorphous fraction, in addition to a gradual glass transition within the mesophase and is illustrated by the example of a thermotropic polyether based on the semiflexible mesogen 1-(4-hydroxyphenyl)-2-(2-methyl-4-hydroxyphenyl)ethane.

Invited Lecture G8 at the 28th Europhysics Conference on Macromolecular Physics in Ulm, Germany, Sept. 27–Oct. 1, 1993 “The submitted manuscript has been authored by a contractor of the U.S. Government under the contract No. DE-AC05-84OR21400. Accordingly, the U.S. Government retains a nonexclusive, royalty-fee license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.”