Molecular architectures of four‐arm star‐shaped styrene‐butadiene copolymer

To understand the molecular architectures of styrene‐butadiene four‐arm star (SBS) copolymers, a size exclusion chromatography combined with laser light scattering (SEC‐LLS) has been used to determine their weight‐average molecular weight ( M w ) and radius of gyration (〈 S 2 〉 1/2 ), and a new method for the establishment of the Mark‐Houwink equation from one sample has been developed. Based on the Flory viscosity theory, we successfully have reduced the 〈 S 2 〉 1/2 values of numberless fractions estimated from many experimental points in the SEC chromatogram to intrinsic viscosities ([η]). For the first time, the dependences of 〈 S 2 〉 1/2 and [η] on M w for the four‐arm star SBS in tetrahydrofuran at 25°C were found, respectively, to be 〈 S 2 〉 1/2 = 2.62 × 10 −2 M   w 0.54(nm) and [η] = 3.68 × 10 −2 M   w 0.64(mL/g) in the M w range from 1.4 × 10 5 to 3.0 × 10 5 . From data of [η] and 〈 S 2 〉 1/2 for linear and star SBS, we have obtained the information about the branching, namely, the ratios ( g and g ′) of 〈 S 2 〉 and [η] for star SBS to that of the linear SBS of the same molecular weight, which agree with theoretical predictions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 961–965, 2005