Size exclusion chromatography polymerization mechanism

We report here the results of our recent studies of poly(alkyl/arylphosphazenes) with particular emphasis on the following areas (1) the overall scope of, and recent improvements in, the condensation polymerization method (2) the characterization of a representative series of these polymers by dilute solution techniques (viscosity, membrane osmometry, light scattering, and size exclusion chromatography), thermal analysis (TGA and DSC), NMR spectroscopy, and X-ray diffraction (3) the preparation and preliminary thermolysis reactions of new, functionalized phosphoranimine monomers and (4) the mechanism of the polymerization reaction. 

MALDI (matrix assisted laser desorption and ionization) combined with size-exclusion chromatography is increasingly being used to study the microstructure of polymers [542-544], MALDI allows the desorption and ionization of macromolecules with molecular mass up to hundreds of kilodaltons with little or no fragmentation. The MALDI mass spectra provides structural information for identification of the polymer repeat units or copolymer sequence, end group mass and mechanism of polymerization for polymers with a narrow polydispersity (< 1.25). For samples of high polydispersity MALDI fails to provide reliable information. The separation of polydisperse samples by size-exclusion chromatography provides fractions suitable for characterization by MALDI. MALDI can also be used for mass calibration of size-exclusion columns. 

The authors reported the generation of polymers in the presence of a large excess of oxidant (monomer oxidant 1.6 1.0 vol/vol) without any information on the mechanism of polymerization, polymer molecular weight, or role and influence of oxidant on the enzyme or reaction kinetics. Subsequently, the laccase-catalyzed polymerization of acrylamide in water without any initiator (b-diketone) at temperatures ranging from 50 to 80 °C was reported however, the reactions were efficiently carried out at room temperature with the use of laccase/b-diketone (2,4-pentanedione) initiator to produce polyacrylamide in 97% yield (Mn = 2.3 x 10 ) [24,25]. The molecular weight of the polymer in these studies was determined by size exclusion chromatography. At 50, 65, and 80 °C when the polymerization was carried out for 4h, polyacrylamides with M = 9.4,9.2, and 10 x 10, respectively, were produced with the highest yield of 70% at 65 °C. 

Feldermann, Ah Toy A, Davis TP, Stenzel MH, Bamer-Kowollik C. An in-depth analytical approach to the mechanism of the RAFT process in acrylate free radical polymerizations via coupled size exclusion chromatography-electrospray ionization mass spectrometry (SEC-ESI-MS). Polymer 2005 46 8448-8457. 

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