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

✍ Scribed by Tianxi Liu; Shanger Wang; Zhishen Mo; Hongfang Zhang

Publisher
John Wiley and Sons
Year
1999
Tongue
English
Weight
181 KB
Volume
73
Category
Article
ISSN
0021-8995

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✦ Synopsis

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.

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