Polymer molecular-weight distribution, determination

The comparison among these techniques is tabulated in Table 22.1. In summary, HdC is a separation technique with low selectivity however, the efficiency can be very high. Especially in PCHdC, high analysis speed can be achieved over a wide MW range. ThFFF performs best for the separation of high MW samples. SEC has an intermediate selectivity between FldC and ThFFF. Practicality makes SEC the most suitable method for the common MW range of synthetic polymers. SEC is by far the most commonly used technique for molecular weight distribution determinations. However, HdC is better for the fast analysis purpose. 

OS 61] ]R 20] ]P 44] The polymer molecular-weight distribution of a static mixer-based processing, which was determined both by UV and refractive index analysis. 

Faraone, A., Magazu, S., Maisano, G., Villari, V., and Maschio, G., Possibilities and Limits of Photon Correlation Spectroscopy in Determining Polymer Molecular Weight Distributions, Macromol. Chem. Phys., 200, 1134 (1999). 

Details of the PLP experiments on aqueous solutions of non-ionized MAA are reported in ref. The polymerizations were carried out in a in a QS 110 cell (Hellma-Worldwide) of 10 mm path length. The reaction solutions were purged with nitrogen for 4 min and thermostated for 20 min prior to PLP. For each mixture, at least two PLP experiments were performed. To reach monomer conversions up to 5%, between 25 and 300 pulses were applied. Monomer conversion was determined by weighing the polymer after freeze-drying. The polymer molecular weight distribution was determined via aqueous-phase using two injections for each sample. 

Stacy in 1985 was able to determine molecular weights of PPS by light scattering of solutions above 200 C and used the values to calibrate molecular weight distributions determined by gel permeation chromatography above 200°C. Heterogeneity index (M /M ) for PPS is near 1.7, less than the value of 2.0 expected of condensation polymers. The difference is the absence of a low molecular weight tail in PPS. 

Mass Spectrometry. Advances in soft ionization techniques and developments in high resolution mass spectrometers has led to the possibility of determining intact molecular ions up to 1 x 10 Da and the measurement of the entire MWD (235,236). The application of mass spectrometry techniques to characterize polymer molecular weight distribution has evaluated (237-243). The MWD of polystyrene SRM 1487 and a narrow MND polymethylmethacrylate (MW 6300) determined by MALDITOF mass spectrometry have been compared with results from the ultracentrifuge and GPC (244). 

Polymer Melt Index Apparatus (Provides relative polymer molecular weight 12.16 (Melt Index) and relative data on polymer molecular weight distribution by determining the Melt Flow Ratio (MFR), which is the ratio of I,. (Flow Index) value divided by the Melt Index.)... 

TFFF can be used for the separation and molecular-weight distribution determination of polymers in the molecular weight range lO -lO. As a tech-... 

Tatro SR, Baker GR, Fleming R, Harmon JP. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry determining Mark-Houwink-Sakurada parameters and analyzing the breadth of polymer molecular weight distributions. Polymer 2002 43 2329-2335. 

Once the polymer is separated into various molecular weight species, they are detected by two basic types of detectors. A universal detector, called a differential refractometer, is used to monitor polymer molecular weight distribution. The UV detector, which provides higher sensitivity than the refractometer, is used for determining low-molecular-weight additives and impurities. 

Macromolecular Chemistry Physics 200, No.5, May 1999, p.1134-42 POSSIBILITIES AND LIMITS OF PHOTON CORRELATION SPECTROSCOPY EV DETERMINING POLYMER MOLECULAR WEIGHT DISTRIBUTIONS Faraone A Magazu S Maisano G Villari V Maschio G Messina,University... 

Polymer molecular weights influence material properties and molecular weight distributions determine melt flow characteristics. 

The phenomena we discuss, phase separation and osmotic pressure, are developed with particular attention to their applications in polymer characterization. Phase separation can be used to fractionate poly disperse polymer specimens into samples in which the molecular weight distribution is more narrow. Osmostic pressure experiments can be used to provide absolute values for the number average molecular weight of a polymer. Alternative methods for both fractionation and molecular weight determination exist, but the methods discussed in this chapter occupy a place of prominence among the alternatives, both historically and in contemporary practice. 

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