Crystal structure and drawing-induced polymorphism in poly(aryl ether ether ketone). IV

• Published in: Journal of applied polymer science Vol. 73; no. 2; pp. 237 - 243
• Main Authors: Liu, Tianxi, Wang, Shanger, Mo, Zhishen, Zhang, Hongfang
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 11.07.1999; Wiley
• Subjects: Applied sciences; crystal structure; drawing-induced polymorphism; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; poly(ether ether ketone); Properties and characterization; Structure, morphology and analysis; Solid state; Hot drawing; Oriented polymer; Aromatic polymer; Polyetheretherketone; Experimental study; Lattice parameters; Polymorphic transformation; Conformation; Crystalline structure
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/(SICI)1097-4628(19990711)73:2<237::AID-APP10>3.0.CO;2-L

A new crystal modification induced by strain and denoted as form II exists alongside the dominant form I structure in the uniaxially oriented poly(ether ether ketone) (PEEK) and the related polymers. The crystal structure of form II for PEEK is also found to possess a two‐chain orthorhombic packing with unit cell parameters of a equal to 0.475 nm, b equal to 1.060 nm, and c equal to 1.086 nm. More extended and flattened chain conformation of form II relative to that of form I is expected to account for an 8% increase in c‐axis dimension, which is attributed to the extensional deformation fixed in situ through strain‐induced crystallization during uniaxial drawing. Annealing experiments suggest that form II is thermodynamically metastable and can be transformed into more stable form I by chain relaxation and reorganization at elevated temperature without external tension. This strain‐induced polymorphism exists universally in the poly(aryl ether ketone) family. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 237–243, 1999