The field of enthalpy relaxation is reviewed. Current phenomenologies for dealing with the non-linear and non-exponential character of enthalpy relaxation are presented, and their successes and shortcomings are discussed. Qualitative experimental data and quantitative parameterizations are summarized, and some directions for future research are suggested.

Enthalpy relaxation and recovery in amorphous materials

https://www.umsl.edu/~chickosj/JSCPUBS/dsccal.pdf

Reference materials for calorimetry and differential thermal analysis

Reversible crystallization and the rigid-amorphous phase in semicrystalline macromolecules

Under a variety of circumstances commonly encountered in practice linear macromolecules crystallize into the form of thin platelets whose large upper and lower surfaces consist of an array of molecular folds. We refer to these as “chain-folded crystals” or “chain-folded lamellae,” the latter term usually being reserved for folded structures in polymers crystallized from the melt. The theory of the rate of formation of these platelets will be outlined, and the prediction and origin of the thin dimension given. The thin dimension of the crystal platelets is determined by kinetic factors, and the elucidation of the kinetics of growth is therefore of importance in polymer morphology on both a molecular and a macroscopic scale.

The Rate of Crystallization of Linear Polymers with Chain Folding

We present a theory for how a shear stress alone can induce structural changes in a glassy polymer to break up the rigidity of the glass and allow flow. We consider a molecular model in which the shear‐stress field is introduced as a bias on the rotational conformation of backbone bonds. It is argued that the fraction of flexed bonds is transiently increased from that in the glass and that this, additionally causing a volume increase, produces a polymer structure resembling the liquid at some temperature above the glass transition. Using these considerations along with several well‐known empirical relations, we have calculated the plastic properties of polystyrene and polymethyl methacrylate. These calculated properties correspond reasonable well with the cold‐drawing data available.

Theory for the Plasticity of Glassy Polymers

Thermal Properties of Atactic and Isotactic Polystyrene

THE thermally induced transition of solvated poly-γ-benzyl-L-glutamate (PBG) molecules from a helical to a random coil configuration has been the subject of recent investigations1–3. Similar transitions, brought about by temperature or by other changes, occur in several poly-amino-acids4, and the general phenomenon has been treated theoretically by a number of authors5.

Thermal Helix-coil Transition in Poly-γ-benzyl-L-glutamate

Thermodynamic properties of stereoregular poly(methyl methacrylate)

The reversible helix-to-random coil conformational change which occurs in solvated poly-ϵ-carbobenzosy-L-lysine, a synthetic polypeptide, has been studied. The course of this cooperative transition, which in many ways resembles a first-order phase transition, was followed both by measuring changes in optical rotation as a function of temperature, and calorimetrically by determining the heat capacity of the solution through the transition region. From the latter measurements, the enthalpy of transition was calculated. From the results it has been shown directly, for the first time, that in a statistical thermodynamical sense, the transition in this system is significantly more cooperative than that undergone by poly-γ-benzyl-L-glutamate, a closely analogous polypeptide. Thus a previously held concept that the degree of cooperation might be quantitatively similar for a wide range of such systems has been shown, for at least one important example, not to be tenable.

Helix–coil transition in poly-ε-carbobenzoxy-L-lysine

The thermodynamic properties of crystalline and amorphous poly(2,6-dimethyl-1,4-phenylene ether) (PPO11 polymer, General Electric Co.) have been studied calorimetrically between 80 and 570°K. The calculated configurational entropy of this polymer, of similar magnitude to other glass-forming liquids, is consistent with the combination of an unusually high ratio of Tg/Tm, and a low melting entropy.

H. E. Bair

Papers

Thermal Properties of Atactic and Isotactic Polystyrene

Thermal Helix-coil Transition in Poly-γ-benzyl-L-glutamate

Thermodynamic properties of stereoregular poly(methyl methacrylate)

Helix–coil transition in poly-ε-carbobenzoxy-L-lysine

Thermodynamic properties of poly(2,6‐dimethyl‐1,4‐phenylene ether)