Amphiphilic block copolymers on a dendrimer core

Abstract

Scope and Method of Study: The purpose of this research was to synthesize amphiphilic block copolymers on a dendrimer core and to use the polymers as templates for styrene latexes at the nanoscale. Materials in this research included amphiphilic dendrimers with both polystyrene/poly(t-butyl acrylate) and polystyrene/poly(acrylic acid) at end branches, and dendritic polystyrene latexes. The dendrimers with amphiphilic end branches were for dispersion of nanomaterials and were for use as molecular weight and size standards and hosts for the transport of biologically important guests. Dendritic polystyrene latexes were for applications in nanotechnology.

Findings and Conclusions: The 64-branch poly(propylene imine) (PPI) dendrimer was converted to the dendrimer initiator with 2-bromoisobutyramide end groups. Polystyrene (PS) was grown by atom transfer radical polymerization (ATRP), and poly(tert-butyl acrylate) (PtBA) was then grown by ATRP. The tert-butyl protecting groups of the PS-PtBA block copolymers were removed to give poly(styrene-bacrylic acid) (PS-PAA). The measured molecular weights were much less than the calculated molecular weights of star polymers with 64 branches and also larger than the molecular weights calculated for linear PS or PtBA. The molecular weights increased as the calculated degree of polymerization of the PtBA segment increased, which supported the growth of PtBA blocks. The branched amphiphilic PS-PAA block copolymers were stars with small numbers of branches resulting from growth at a small number of initiator sites per dendrimer. Styrene was polymerized in emulsions containing the dendritic PS-PAA. The resulting polystyrene latexes were broader in particle size distribution and 40-60 nm in diameter in the presence of the surfactant sodium dodecyl sulfate (SDS), however, narrower in particle size distribution and over 100 nm in diameter in the absence of SDS. Branched dendritic aggregates of the PS-PAA showed aggregation characteristics of amphiphilic PSPAA block copolymers.