Pergamon Prog. Polym. Sci., Vol. 20, 703-760, 1995 Copyright 0 1995 Elsevier Science Ltd Printed in Great Britain. All tights reserved. 0079%6700/95 $29.00 00079-6700(94)00001-1 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO PHYSICAL AGING OF POLYMERS JOHN M. HUTCHINSON Department of Engineering, Aberdeen University, King’s College, Aberdeen, AB9 2UE, U.K. Abstract - The general area of physical aging of polymers is reviewed. Various phenomenological aspects are introduced and discussed in terms of bulk structural changes evidenced by dilatometric and calorimetric studies, and are compared with the wide variety of information available from microstructural investigations involving spectroscopic and scattering techniques. Current models for describing the relaxation kinetics of the non-equilibrium glassy state are compared. Finally, the effects of physical aging on mechanical properties are reviewed, highlighting especially those areas which remain controversial. Keywords - Physical aging, polymers, glasses, glass transition, enthalpy relaxation, volume relaxation, creep. CONTENTS Notation 1. Introduction 2. The thermodynamic state of the glass 2.1. Background 2.2. Dilatometry and volume relaxation 2.3. Calorimetry and enthalpy relaxation 2.4. Comparison of dilatometric and calorimetric studies 3. Microstructural aspects 3.1. Introduction 3.2. Positron annihilation lifetime spectroscopy 3.3. Electron spin resonance spectroscopy 3.4. Fluorescence spectroscopy 3.5. Photochromic probes and labels 3.6. Small angle X ray scattering 3.7. Summary of microstructural aspects 4. Theoretical treatments 4.1. Introduction 4.2. Free volume 4.3. Configurational entropy 4.4. Model of Moynihan, Hodge and others 4.5. KAHR model 4.6. Robertson-Simha-Curro theory 4.7. Coupling model 4.8. Summary of theoretical aspects 5. The effects of physical aging on mechanical properties 5.1. Introduction 5.2. Phenomenological aspects 5.3. Time-aging time superposition 704 706 708 708 709 712 716 717 717 718 720 720 722 723 725 725 725 726 727 727 729 731 732 734 734 734 735 741 703