CHARACTERIZATION OF RANDOMLY BRANCHED POL YSTYRENES BY MULTI-ANGLE LASER-LIGHT SCATTERING-SIZE EXCLUSION CHROMATOGRAPHY

Characterization of randomly branched polystyrenes (PSs) has been carr ied out in THF at 25 degrees C by means of multi-angle laser light sca ttering-size exclusion chromatography (MALLS-SEC). Various kinds of PS samples were prepared by radical (co-)polymerization in the presence and absence of initiators and divinylbenzene. The precision and the re liability of the method were first checked with PS standards with narr ow molecular weight distribution. It was found that the MALLS-SEC tech nique gives precise M-w, and [S-2](z) for PS samples with both narrow and broad molecular weight distributions. The PS prepared by thermal p olymerization without an initiator was found to be almost linear. In r emarkable contrast, the polymerization with t-butyl peroxyisopropyl ca rbonate as an initiator and copolymerization with divinylbenzene affor ded 3-armed and 4-armed randomly branched PSs, respectively, in the hi gh M-w region of the resulting polymers. The branching number per macr omolecule for randomly 3- and 4-armed branched PSs was successfully de termined from the shrinking factor, the ratio of [S-2] of the branched PS to that of linear PS with corresponding M-w. The present results s how that the MALLS-SEC technique is very powerful and convenient for t he characterization of randomly branched polymers.