Core-Cross-Linked Micelles Made by RAFT Polymerization with a Polycationic Outer Shell Based on Poly(1-methyl-4-vinylpyridinium)

Abstract

A convergent synthesis of amphiphilic polymers with a polystyrene (PS) core and a polyelectrolytic poly(1-methyl-4-vinylpyridinium iodide) (P4VPMe+I–) shell is reported. The polymers were obtained by reversible addition–fragmentation chain transfer (RAFT) polymerization in water using a trithiocarbonate chain transfer agent [R0-SC(S)SPr, R0 = −C(Me)(CN)CH2CH2COOH]. Two types of particle structure, both having a spherical morphology and diameters in the 85–150 nm range, have been obtained as stable latexes with polymer content up to 10% in weight. The first structure consists of core-cross-linked micelles (CCMs), where amphiphilic P4VPMe+I–-b-PS arms are cross-linked at the hydrophobic end by the use of diethylene glycol dimethacrylate. The Coulombic repulsion between the outer shells of the precursor micelles ensures the absence of macrogelation during the cross-linking step. The second structure consists of nanogels (NGs), where the entire hydrophobic core is cross-linked during the last step of simultaneous chain extension and cross-linking of a P4VPMe+I–-b-PS intermediate with a short PS block. The lack of radical polymerization for the 4VPMe+I– monomer and the lack of chain extension with styrene for a R0-P4VPMe+I–-SC(S)SPr intermediate were circumvented by the synthesis of R0-P4VP-b-PS-SC(S)SPr containing a short PS block by sequential RAFT polymerization of 4-vinylpyridine (4VP) and styrene, followed by quantitative cationization of the P4VP block by MeI and subsequent sequential (for the CCMs) or simultaneous (for the NGs) chain extension and cross-linking.