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

摘要

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