A novel method for predicting molecular weight properties in emulsion polymerization processes

A novel method for predicting the molecular weight (MW) properties of chain transfer agent (CTA) modified polymers was developed by investigating zero-one and pseudobulk, seeded emulsion polymerizations of styrene, employing n-dodecanethiol as a CTA. Polymerizations were conducted at 50;The developed method used kinetic models developed by Clay and Gilbert (1995), which described the instantaneous number MWDs of polymers produced in zero-one and pseudobulk emulsion polymerization systems, and the use of gas chromatography (GC) to monitor the total mass of CTA in the polymer latex. In general, it was found that this method was able to predict the weight average MWs of the n-dodecanethiol modified polymers to within 20%. However, errors in excess of 100% were commonly found in the estimated number average MWs. In addition to this, the method was able to make accurate predictions of the polymers' MWDs at monomer conversions greater 50%. However, at conversions less than 50%, the method failed to predict the experimentally observed bi-modal MWD of the n-dodecanethiol modified polymers.;These discrepancies in the predicted number average MWs and low conversion MWDs are attributed to the formation of large quantities of low MW polymer immediately after initiation. Additionally, there is also some uncertainty in the kinetic rate coefficients and models used to predict these quantities. With further development, it is believed that this method could be used as an alternative to exiting methods for predicting the MW properties of CTA modified emulsion polymers via on-line analyses of the polymer latex (e.g. on-line GPC).