Relationships between molar mass and fracture properties of segmented urethane and amide copolymers modified by chemical degradation

• Published in: Journal of polymer science 2020-11, Vol.58 (22), p.3170-3182
• Main Authors: Bardin, Antoine, Le Gac, Pierre‐Yves, Bindi, Hervé, Fayolle, Bruno
• Format: Article
• Language: English
• Subjects: Chain scission; Chemical Sciences; Copolymers; Degradation; Elongation; Engineering Sciences; essential work of fracture; Fracture testing; Hydrolysis; Mechanical properties; Mechanics; Mechanics of materials; Oxidation; Parameter sensitivity; poly(ether‐block‐amide); Polymers; Polyurethane resins; structure–property relationship; Tensile tests; thermoplastic elastomer; Thermoplastic elastomers; thermoplastic polyurethane elastomer; Urethane thermoplastic elastomers
• ISSN: 2642-4150; 0022-3832; 2642-4169; 1542-6238
• DOI: 10.1002/pol.20200460

This publication highlights the structure–property relationships in several thermoplastic elastomers (TPEs): one poly(ether‐block‐amide) and two thermoplastic polyurethane elastomers with ester and ether soft blocks. Structural changes are induced by chemical degradation from virgin samples through hydrolysis and oxidation. Molar mass measurements show an exclusive chain scission mechanism for all TPEs, regardless of the chemical modification condition. Mechanical behavior was nevertheless obtained from uniaxial tensile testing and fracture testing while considering the essential work of fracture (EWF) concept. During the macromolecular scission process, elongation at break shows a plateau followed by a drop, while stress at break decreases steadily. Once again, the trend is identical for all TPEs in all conditions considered. The βwp parameter determined using the EWF concept exhibits an interesting sensitivity to scissions (i.e., molar mas decrease). Plotting elongation at break as a function of molar mass reveals a strong correlation between these two parameters. This master curve is particularly remarkable considering the range of TPEs and chemical breakdown pathways considered (hydrolysis and oxidation at several temperatures). Relevant structure–property relationships are proposed, highlighting that molar mass is a predominant parameter for determining the mechanical properties of thermoplastic elastomers. Several segmented urethane and amide copolymers exposed to air and seawater were investigated at several temperatures to determine their behavior in the marine environment. The aging processes result in molar mass decrease induced by macromolecular scissions and a mechanical behavior change. A strong correlation is highlighted between molar mass and failure properties, regardless of the material and the exposure. A global ductile‐brittle transition is observed, with a critical molar mass of 35 kg·mol−1.