Determination of molecular weight of PDPS modified copolymers

Molecular weight (MW) determinations of polydiphenylsiloxane-co-polydimethy lsiloxane (PDPS/PDMS), polydiphenylsiloxane-co-polymethylphenylsiloxane (PD PS/PMPS) and polydiphenylsiloxane-co-polymethyl(3,3,3-trifluoropropyl)silox ane (PDPS/PMFPS) statistical copolymers by gel permeation chromatography (G PC), GPC coupled differential viscometer (GPC-DV) and light scattering (LS) techniques have been compared and discussed. The MW obtained by GPC-DV in the PDPS/PDMS and the PDPS/PMPS series agreed with that obtained by LS very well. In PDPS/PDMS copolymers, it was found that the MW obtained by GPC wa s much lower than that obtained by GPC-DV and LS, as Ph2SiO content is high er than 50 mol%. In PDPS/PMFPS copolymers, the MW obtained by GPC was far d ifferent from that obtained by GPC-DV and the deviation decreased with incr easing Ph2SiO mol%. The cc values of the copolymers can be explained by the structure of the polymer in tetrahydrofuran (THF). Based on the relatively soluble copolymers, not only the differential refractive index increments (dn/dc) of PMPS, PDMS and PMFPS homopolymers but also that of the PDPS homo polymer in THF could be calculated by their corresponding copolymers.