Modelling of size‐exclusion chromatograms from molecular weight distribution calculations. Application to the grafting of polymers onto functionalized silica

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Abstract
The objective of this paper is the modelling of the molecular weight distribution (MWD) and the polydispersity index (P. I.) of polystyrene grafted on porous silica beads prefunctionalized by a thiosilane molecule. Grafting occurs by a transfer reaction to the fixed mercapto groups. We have analysed the MWD of both grafted and ungrafted polymers by size‐exclusion chromatography (SEC). A good agreement between the experimental SEC diagrams and those calculated from the reaction rate constants is obtained with the following hypotheses: (1) the medium is a two‐phase system constituted of an interparticle phase and a porous intraparticle phase with a high local mercapto group concentration in the pores; (2) a higher transfer efficiency of the transfer agent in the pores (what could be attributed to a higher mobility of the very short chains inside the pores); (3) a lower termination rate in the pores, which results in a higher rate of polymerization than in the interparticle phase (probably due to an increase of the medium viscosity).