MALLS measurement

Puskas, J.E. et al. Comparison of molecular weight and size measurement of polyisobutylenes by SEC-MALLS and viscometry, J. Polym. Sci. Chem., 44, 1777, 2006. 

An experimental verification of Eqs. (65)-(67) has not yet been possible because the MALLS instrument that allows measurement of has only recently become available in laboratories. Furthermore, the combination of the MALLS with the Vise detector is not a trivial problem. Several experiments are, however, in progress. This work is of great importance since a quantitative estimation of the branching density would be possible if the Zimm-Stockmayer equations for the g-factor hold true. 

The FALLS or MALLS detector measures r-related values a differential refractive index (DRI) detector is used to measure concentration, and the SEC supplies samples containing fractionated polymer solutions allowing both molecular weight and MWD to be determined. Further, polymer shape can be determined. This combination represents the most powerful one, based on ease of operation, variety of samples readily used, cost, means to determine polymer size, shape, and MWD available today. 

Experimental data [323-325] in which the MWDs are measured by SEC with on-line multiangular laser light scattering (MALLS) show the above trend [326]. Figure 24 shows some examples of the weight-average molecular weight development, which show linear increases with respect to conversion. 

Insitec now forms part of Malvern Instruments but is still based in California for process and laboratory R D. The EPCS are laser-based instruments for in-line particle measurements that provide information on particle volume concentration and size distribution. EPCS instruments are part of the larger group of electro-optical instruments (MALLS) whose principle of operation is based on light scattering from a group (or ensemble) of particles. Unlike other instruments operating on this principle, the EPCS can perform direct measurements of particle laden flow stream provided the concentration is within operating limits. 

With its multiangle capability, MALLS can be used to measure the size as well as the absolute MW of polymers. The multiangle capability seems to be particularly important for the determination of MW and RMS radius of ultrahigh MW polymers as the Debye plot deviates from the linearity. It is also important for the analysis of ultrahigh MW polymers to use accurate A2 value as well as dn/dc as the resulting MW and RMS radius tend to vary with those values. 

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