Monitoring the progress of a branching polymethylmethacrylate reaction via online rapid gel permeation chromatography (GPC) analysis

A new methodology has been developed for the one-pot synthesis of a branched polymethyl methacrylate material. Employing a cross-linking comonomer and large amount of a chain transfer agent, a fully soluble material is produced through a conventional free radical reaction. It is thought that despite the presence of the cross-linker, a network is not formed due to the high chain transfer agent concentration instead resulting in a soluble polymer with a highly branched structure. Branched polymers are of interest for their unusual flow and viscometric properties, and this material is particularly attractive due to the relatively cheap and simple synthetic route. To better understand the mechanism of the reaction, an online monitoring system, the PL-PMC, was used to monitor the contents of the reactor at near real time during the polymerisation. A continuous stream of sample from the reactor was diluted to an appropriated level and injected into a rapid GPC analysis system comprising a differential refractive index detector, an online viscometer and a short GPC column to allow measurements in a ‘flow injection analysis’ mode. Measurements of bulk molecular weight and intrinsic viscosity parameters were made during synthesis, allowing the growth of the polymer to be closely followed. From the intrinsic viscosity measurements, the development of the branched structure was investigated as a function of reaction time. The final product was then isolated and investigated by offline analytical multi detector GPC to complete the study. Combining the data from the online monitoring investigation and the offline analysis of the final product, considerable insights into the reaction process were obtained from a single reaction.