Novel thermoplastic elastomers. II. Properties of star-block copolymers of PSt-b-PIB arms emanating from cyclosiloxane cores

✍ Scribed by Jung S. Shim; Joseph P. Kennedy

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 205 KB
• Volume: 37
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/(sici)1099-0518(19990315)37:6<815::aid-pola17>3.0.co;2-5

✦ Synopsis

Select mechanical, thermal, and rheological properties of star-blocks consisting of 5-21 polystyrene-b-polyisobutylene (PSt-b-PIB) arms radiating from cyclosiloxane cores are described. The tensile properties of products containing 23-41 wt % of PSt are substantially higher (9.6 -23.8 MPa) than those of linear triblocks of comparable arm molecular weights and compositions over the 25-85°C temperature range. The mechanical properties of star-blocks seem to be much less sensitive to diblock contamination than linear triblock thermoplastic elastomers of similar hard/soft segment composition. The tensile strength of star-blocks increases by increasing the number of arms (N w,arm ) and reaches a plateau in the N w,arm ϭ 5-10 range. Star-blocks exhibit higher strengths with lower PSt segmental M n than linear triblocks. Solvent cast triblock copolymers exhibit higher tensile strengths than compression molded products; however, star-blocks show no significant property differences between cast and molded samples. The dynamic melt viscosities of the star-blocks are substantially lower than those of linear triblocks with comparable hard/soft segment compositions, which is consistent with the star's unique microarchitecture and should lead to improved overall processibility.