Contribution of soft segment entanglement on the tensile properties of silicone–urea copolymers with low hard segment contents

✍ Scribed by Iskender Yilgor; Tugba Eynur; Emel Yilgor; Garth L. Wilkes

• Book ID: 104087965
• Publisher: Elsevier Science
• Year: 2009
• Tongue: English
• Weight: 374 KB
• Volume: 50
• Category: Article
• ISSN: 0032-3861
• DOI: 10.1016/j.polymer.2009.07.016

✦ Synopsis

Novel, segmented thermoplastic silicone-urea (TPSU) copolymers based on rather high molecular weight aminopropyl terminated polydimethylsiloxane (PDMS) soft segments ( 10,800 and 31,500 g/mol), a cycloaliphatic diisocyanate (HMDI) and various diamine chain extenders were synthesized. Copolymers with very low urea hard segment contents of 1.43-14.4% by weight were prepared. In spite of very low hard segment contents, solution cast films showed very good microphase separation and displayed reasonable mechanical properties. Tensile strengths of TPSU copolymers showed a linear dependence on their urea hard segment contents, regardless of the structure of the diamine chain extender used. The modulus of silicone-urea copolymers is dependent on the urea concentration, but not on the extender type or PDMS molecular weight. When silicone-urea copolymers with identical urea hard segment contents were compared, copolymers based on PDMS-31,500 showed higher elongation at break values and ultimate tensile strengths than those based on PDMS-10,800. Since the critical entanglement molecular weight (M e ) of PDMS is about 24,500 g/mol, these results suggest there is a significant contribution from soft segment chain entanglement effects in the PDMS-31,500 system regarding the tensile properties and failure mechanisms of the silicone-urea copolymers.