Thermoresponsive Star Dendronized Polymers

Star polymers have attracted considerable attention in recent years owing to theunique architecture and physicochemical properties, such as3D sphericalmorphology, special core-shell microstructure, high density of functional groups,and low solution viscosity. Combination of the unique architecture and performancecharacteristics of star polymers with cylindrical morphology of thick dendronizedpolymers will not only afford novel star dendronized polymers, but also provide newideas for theoretical researches and may pave the way for design and applications ofnovel smart star polymer materials. Herein, a novel kind of star dendronizedpolymers, which are constituted by dynamic covalent core and OEG-baseddendronized polymer arms, were designed and synthesized by the “arm first”approach. The thermoresponsive behavior and morphology of the star dendronizedpolymers were investigated. The detailed thesis includes the following three parts:(1) Two monomers containing pyridyldisulfide group and OEG dendron weredesigned and synthesized, respectively.(2) A series of star dendronized polymers were prepared by the “arm first” approach.At first, the macro chain transfer agents bearing pyridyldisulfide (PDS) sidegroups were obtained by reversible addition-fragmentation chain transfer (RAFT)polymerization. These terminally reactive macro chain transfer agents weresubsequently used to further initiate the polymerization of OEG-based dendriticmonomers and then afforded well-defined diblock copolymers. Finally, theobjective star dendronized polymers were prepared by adding1,2-ethanedithiolas cross-linkers based on thiol-disulfide exchange reaction.(3) The structure and molecular weights of the resulting polymers werecharacterized by1H NMR and GPC measurements. UV/vis spectroscopy andAFM measurements were used to investigate the thermoresponsive behaviorsand morphologies of the polymers, respectively. The results showed that the star dendronized polymers were successfullyprepared. These star polymers showed fast and sharp phase transitions with smallhysteresis, similar to their linear dendronized counterparts. Star or sphericalmorphology of these star dendronized polymers were directly visualized by AFM,which may be ascribed to the dendronized topology of star polymers. To the best ofour knowledge, this is the first example to describe the synthesis and characterizationof thermoresponsive star dendronized polymers.