Molecular weight determination of star polymers and star block copolymers using GPC equipped with low-angle laser light-scattering

Gel permeation chromatography equipped with a low-angle laser light-scattering detector (GPC-LALLS) was employed to determine the Mn and Mw of any polymer system such as flexible polymers (polystyrene, PSt), rod-like polymers (poly(n-hexylisocyanate), PIC), star polymers ((PSt)n and [poly(α-methylstyrene)]4, (PαMSt)4), linear block copolymers (polystyrene-block-polyisoprene, PSt-block-PIs) and star block copolymers ((PSt)4-star-(PIs)7). For the homopolymers (PSt, PIC, (PSt)n and (PαMSt)4), the determined MnGPC-LS and MwGPC-LS values are in good agreement with the MnOSM and MwLS values determined by osmometry and light scattering, respectively. For the block copolymers (PSt-block-PIs and (PSt)4-star-(PIs)7), two composition distributions (CDs) have to be considered: one is a CD among the different molecular weights and the other is a CD among the same molecular weights. Block copolymers are classified into four groups from the viewpoint of a combination of the two CDs. In any group, new analytical equations for determining Mn and Mw were derived by the assumption that the block copolymers, which appear at the same elution volume of the GPC chromatogram, have the same molecular weights. The resultant Mn BCGPC-LS values were in good agreement with the MnOSM values. GPC-LALLS was found available for determining Mn and Mw of the block copolymers.