Synthesis And Characterization Of Matched Double-Chain And Loose-Fit Single-Chain Stranded ?-CD-Based Polypseudorotaxane Containing Block Copolymers

A 2-bromoisobutyryl end-capped tetraethylene glycol azobenzene-4,4'-dicarboxylic ester(Br-EG4-AZO-EG4-Br,1)was synthesized as an initiator in a way of carefully-controlled feeding ratio and slow feeding raw materials.Under the condition of n([?-CD])/ n([Br-EG4-AZO-EG4-Br])=4:1,the resulting initiator 1 was self-assembled with ?-cyclodextrins(?-CDs)in water to create a double-chain stranded polypseudorotaxanes(iPPRs)and then used to initiate in situ atom transfer radical polymerization(ATRP)of varying amounts of N-isopropyl acrylamide(NIPAAm)to prepare polypseudorotaxanes containing block copolymers(PPRs).It was found that ?-CDs accommodate both an azobenzene and a folded tetraethylene glycol chain in these block copolymers existed as a matched double-chain stranded structure.However,in the case of self-assembling with PNIPAAm-EG4-AZO-EG4-PNIPAAm which was prepared from ATRP of NIPAAm initiated by using Br-EG4-AZO-EG4-Br,the added ?-CDs are randomly distributed along the whole copolymer chain to give rise to a series of loose-fit single-chain stranded structured polypseudorotaxanes(aPPRs).These two PPRs showed a highly different structure between each other in many characterizations.According to the split and disappeared absorption peaks of characteristic functional groups in 1H NMR and FTIR spectra,?-CDs were proved locating at different positions of the copolymer chain.Moreover,the unique pipe crystallization peak of ?-CDs in WXRD spectra illustrated a folded double chain stranded structure in PPRs.The results of GPC and NOSEY indicated the possibility of ?-CDs to slide down from the chain simultaneously.Compared with Br-EG4-AZO-EG4-Br and aPPRs,the characteristic ultraviolet(UV)absorption peak of trans azobenzenes in the PPRs is obviously red-shifted,but the unique cis isomerization of these groups appears not to lead the threaded ?-CDs sliding off the polymeric chain.All these characterizations suggested a fact that the matched double chain stranded structure constructed by an azobenzene and a folded tetraethylene glycol chain jointing to enter the cavity of ?-CDs not only shows a relatively higher stability,but also can reversibly transform into the double tetraethylene glycol chain stranded structure in the process of cis isomerization of azobenzenes.