Copolymers Long-chain branches, combined with

A useful approach to detection in polymer HPLC presents the on-line hyphenation of different measurement principles. For example, an RI detector combined with a UV photometer produces valuable additional information on the composition of some copolymers. Further progress was brought with the triple detection RI plus LALS plus VISCO [313], which is especially suitable for branched macromolecules and the tetra detection UV plus RI plus LALS plus VISCO, which enables characterization of some complex polymer systems, exhibiting a distribution not only in their molar mass and architecture, but also in their chemical composition such as long chain branched copolymers. 

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]. 

The CG catalysts produce highly processable polyolefins with a unique combination of narrow MWD and long chain branches. Ethylene-octene copolymers produced with CG catalysts have useful properties across a range of densities and melting indexes. These novel copolymer families are called polyolefin plastomers (POP) and polyolefin elastomers (POE). POPs possess plastic and elastic properties while POEs containing greater than 20 wt% octene comonomer units have higher elasticity. 

Molar mass distribution is a dominant microstracture parameter that, in copolymers, needs to be measured with additional information to account for long chain branching, comonomer incorporation, or ethylene propylene combinations (in the case of EP copolymers). The combination of GPC and IR spectroscopy has been shown to be of great value in the characterization of copolymers. The importance of automation and sample care, especially in the case of polypropylene, has been discussed as well as the significant improvement in sensitivity by the use of IR MCT detectors. There are big expectations for the analysis of ultrahigh molar mass polyolefins by the new AF4 technology. 

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