Synthesis And Self-assembly Of Well-defined Polymer Brushes With High Grafting Density Of Alternating Amphiphilic Side Chains

Polymer brushes have attracted considerable research attention recently in the field of polymer chemistry for their unique architecture properties and application foreground.However,synthesis of well-defined graft polymer brushes was still a challenge,but along with the discovery of controlled/living polymerization technique, the preparation of well-defined polymer brushes could be realized.There are lots of reports about the self-assembly of amphiphilic copolymer in selective solvent,but only a limited number of reports are available to prepare polymer brushes with alternating amphiphilic side chains,and its self-assembly in selective solvent has barely been reported.In this paper,we report a facile synthetic strategy for the formation of a novel polymer brushes with two different grafts high densely distributed on the same unit along the backbone via the combination of three highly controlled polymerization methods,ring opening polymerization(ROP),ring-opening metathesis polymerization(ROMP)and atom transfer radical polymerization(ATRP). The micellar characteristics of the polymer brushes in selective solvent were investigated.A novel hetero-trifunctional monomer endo,endo-2-hydroxylmethyl-3(2-bromoisobutyryloxymethyl)-5-norbornene having one polymerizable cycloolefinic group for ROMP,two different initiating sites for ROP and ATRP was synthesized for the first time.The characterization of the prepared monomer was carried out by ¹H NMR,¹³C NMR,and GC-MS.A novel amphiphilic polymer brushes consisted of alternating poly(ε-caprolactone)(PCL)and poly(2-(dimethylamino)ethylmethacrylate) (PDMAEMA)side chains was synthesized via combination of ROP,ROMP and ATRP with good control over the polymerization process.This strategy consists of three steps:first,the norbornene-terminated PCL macromonomer(PCL-NBE-Br)was prepared via the ROP ofε-CL catalyzed by tin(â…¡)2-ethylhexanoate;then ROMP of PCL-NBE-Br macromonomer was carried out to convert into macroinitiator (PCL-PNBE-Br)via "grafting through" technique;last,the ATRP of DMAEMA initiated by the macroinitiator was performed to obtain the densely grafted polymer brushes via "grafting from" technique.Thus,the alternating sequence structure of the side chains was well-defined by afore-mensioned strategy.The molecular weight of the polymer brushes and the medium products were estimated by GPC and ¹H NMR respectively. The micellar characterization was carried out by DLS and TEM.The hydrodynamic diameter of the micelles,measured by DLS,was 263 nm with a narrow distribution(PDI=0.233).The TEM image showed spherical micelles with Diameter of around 200nm.