Improved Mechanistic Insights into Radical Sulfinyl Precursor MDMO-PPV Synthesis by Combining Microflow Technology and Computer Simulations

Abstract

A kinetic model using Predici is developed and applied to obtain an improved mechanistic understanding of the radical sulfinyl precursor polymerization route for poly(2-methoxy-5-(3'-7'-dimethyloctyloxy-4-((octylsulfinyl)methyl))-1,4-phenylenevinylene) (MDMO-PPV) synthesis. In this route, the premonomer-1-(chloromethyl)-5-((3,7-dimethyloctyl)-oxy)-2-methoxy-4-((octylsulfinyl)methyl)benzene (MDMO) is subjected to a base-induced elimination reaction using NatBuO as base and s-BuOH as solvent. Microreactors are used to ensure rapid mixing of reaction components and sharp quenching at precisely determined time points. Systematic kinetic data that follows the very fast precursor polymerizations with reaction time have in this way become available for the first time. Via the applied kinetic model, the presence of a chain transfer reaction is unambiguously confirmed and kinetic rate coefficients have been deduced, which fall within the typical expectations of radical chain reactions. Two models were further compared, one including chain reinitiation (noninhibition model) and one excluding reinitiation (inhibition model) of the by chain transfer-generated radical species. Investigation of trend lines suggest a preference of the reinitiation model, thereby implying that MDMO-PPV synthesis follows mostly a conventional free radical polymerization mechanism that only differs with respect to its initiation mode and the biradical nature of the propagation step.