Long-subchain Janus-dendritic copolymers from locally confined click reaction and generation-dependent micro-phase separation

Abstract

In this study, we put forward a divergent synthetic strategy to prepare long-chain Janus-dendritic copolymers with polystyrene (PSt) and poly(tert-butyl acrylate) (PtBA) as each half-dendron. To achieve the exact Janus arrangement, the chemical confinement of half-dendron end-groups and the local confinement of the click reaction were combined. Herein, chemical confinement was satisfied by maintaining one reactant in excess, whereas local confinement was fulfilled through “burying” one reactant. Seesaw macromonomers of PSt and PtBA with one alkynyl group at the chain centre and two bromo groups at the chain ends were used as the constituent units to divergently click onto the related half-dendron. Briefly, the first generation of Janus-dendritic copolymer, J-(PSt)¹/(PtBA)¹, was synthesized under chemical confinement through click chemistry onto a core molecule with two azido groups. Afterwards, the next two generations of Janus-dendritic copolymers, J-(PSt)²/(PtBA)² and J-(PSt)³/(PtBA)³, were obtained by click reactions under alternating local and chemical confinement. Fractional precipitation and thin layer chromatography were used to purify the desired products. The variations in chemical composition, end groups, branching units and molecular weight throughout the whole synthesis were monitored with nuclear magnetic resonance spectroscopy, Fourier transfer infrared resonance spectroscopy and gel permeation chromatography. Differential scanning calorimetry, small angle X-ray scattering, atom force microscopy as well as laser light scattering were used to investigate the microphase separation behavior in bulk and the selective solvent. The research results will pave the pathway to polymer synthesis under physical principles and the study of the self-assembly of copolymers with complicated architecture.