Use of fluorescence-labelled macroinitiator to investigate nucleation mechanism in nitroxide-mediated crosslinking polymerization in aqueous miniemulsion

Controlled/living radical polymerization (CLRP; e.g. nitroxide-mediated polymerization (NMP)) enables synthesis of macromolecules with well-defined structure.(1) Current challenges in CLRP include implementation in heterogeneous systems.(2.3) Ab initio emulsion CLRP is difficult due to problems with colloidal instability and transport of control agent between monomer droplets and polymer particles, but approaches based on nucleation via macroinitiator self-assembly have been Successful.(3) Miniemulsion CLRP is more straightforward because particle nucleation and control agent diffusion across the aqueous phase is avoided.(4) Ideally, each monomer droplet is converted to a particle. Deviation from this ideality in miniemulsion CLRP may lead to compromised control/livingness. Secondary nucleation causes formation of polymerization loci without control agent, i.e. lower control/livingness and broader particle size distribution. Crosslinking CLRP results in highly homogeneous polymer networks,(5) and crosslinking CLRP in heterogeneous systems affords crosslinked polymer particles of high homogeneity and different mechanical properties compared to particles prepared by non-living crosslinking polymerizations.(6) The present contribution describes a novel approach based on macroinitiator fluorescence (FL)-labelling in nitroxide-mediated crosslinking radical polymerization in aqueous miniemulsion of styrene (S) and divinylbenzene (DVB) to confirm the absence of secondary nucleation.