Effects of arm number on the properties of transparent elastomers prepared from styrene–butadiene block copolymer

Abstract

A series of the SBS transparent elastomers were prepared from star-shaped SBS having different arm number by solution-casting. Their structure and physical properties were characterized by scanning electron microscope, ultraviolet spectrometer, wide-angle X-ray diffractometer, differential scanning calorimetry, dynamic mechanical thermal analysis, tensile testing, and contact angle measurements. The results revealed that the miscibility, optical transparence (Tr), tensile strength (σb), elongation at break (eb), and elasticity at low temperature of the star SBS increased with an increase of arm number. The six-arm SBS having relatively high molecular weight exhibited a simultaneous enhancement of Tr (90% at 800 nm), σb (6.0 Mpa), and eb (1260%). This indicated that the SBS materials having six arms had higher transparence and elasticity than others. Moreover, the water contact angle on surface of the star-shaped SBS film increased with an increase of arm number that is enhancement of hydrophobicity. Therefore, the relatively high arm number and molecular weight played an important role in the improvement of the miscibility and properties of the SBS sheets as a result of the compacted architecture of the hyperbranched molecules. This work provides a convenient way to obtain materials with both high transparence and elasticity by increasing the arm number. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 729–736, 2006