Intrinsic Long-chain branches, effect

The application of refractive index and differential viscometer detection in SEC has been discussed by a number of authors [66-68]. Lew et al. presented the quantitative analysis of polyolefins by high-temperature SEC and dual refractive index-viscosity detection [69]. They applied a systematic approach for multidetector operation, assessed the effect of branching on the SEC calibration curve, and used a signal averaging procedure to better define intrinsic viscosity as a function of retention volume. The combination of SEC with refractive index, UV, and viscosity detectors was used to determine molar mass and functionality of polytetrahydrofuran simultaneously [70]. Long chain branching in EPDM copolymers by SEC-viscometry was analyzed by Chiantore et al. [71]. 

Branching reduces the hydrodynamic volume relative to the mass of the coil. The intrinsic viscosity of branched macromolecules is thus lower than that of their unbranched (linear) counterparts. The effect is particularly marked in the case of long-chain branching. If the number of branch points in a polymer homologous series increases with the molar mass, then the [rj] values also decrease relative to those of linear molecules. Thus, the slope of the log f (log 2) curve continuously decreases with increasing molar mass,... 

The intrinsic viscosity depends on the hydrodynamic volume of a molecule and is thus sensitive to the presence of long chain branching, since the presence of branches causes the molecule to occupy a smaller volume than a linear molecule of the same molecular weight. A measure of this effect is the branching parameter g, which is the ratio of intrinsic viscosities of branched and linear polymers having the same molecular weight ... 

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