Radical-induced cationic frontal polymerisation for prepreg technology

In this study, a new type of prepreg technology has been established using a dual curing system consisting of 1,6-hexanediol diacrylate (HDDA) and frontally polymerisable components based on the epoxide resin. The study of the polymerisation of HDDA revealed (tert-butylcyclohexyl)peroxydicarbonate (BCPC) as the most suitable radical thermal initiator. The presence of BCPC resulted in a fast radical polymerisation of HDDA and no cationic ring-opening reaction of the epoxy, which was observed by monitoring the double bond and epoxy group conversion in real time-NIR rheology measurement. The formed prepreg can subsequently be cured by radical-induced cationic frontal polymerisation of the epoxy resin. Effects of HDDA amount on the radical polymerisation, stiffness of the gel, frontal parameters and thermal mechanical properties of final polymers were investigated. With 10 wt% HDDA, the formed prepreg has very good storage stability, which was proved by monitoring the epoxy group conversion during 4 months of storage at 50 °C while still a stable front can be obtained. Furthermore, the RICFP-prepregs with different fibre contents were prepared and polymerised by RICFP. Then, a snowflake composite was successfully produced using RICFP-prepreg.

Graphic abstract

Influence of shrinkage of polymer on the stationarity of propagation of frontal polymerization heat waves

The purpose of this work was to study the causes of the formation of nonlinear and spin modes in the process of frontal polymerization (FP). The latter is an autowave process of the propagation of polymerization heat waves, and is a nontraditional method for the synthesis of various polymers and polymeric composites. Monomers of metal-complexes of acrylamide with and without additions of inert and nano-fillers were chosen as objects of study. Research data on dilatometric analysis, as well as on kinetics and macrokinetics of the polymerization processes of the monomers in frontal mode are presented. On the basis of the results obtained, a conclusion was drawn on the stability loss and transition boundary from a stationary mode to nonstationary one during FP. It was shown that, during the polymerization processes, shrinkage of the resulting polymer composites occurs, commensurate with the phase of the heat wave oscillations, which disturbs the propagating heat waves from layer to layer and violates the stationarity of the process. This, in turn, results in the formation of spin-like rings and a nonstationary mode of FP.