Synthesis And Properties Of Macrocyclic Graft Copolymers Based On The Cyclic PEO-Supported Multifunctional Initiation System

The cyclic molecules with some special properties could be found some actual applications in many fields,such as the formation of organic nanotubes,ion complex and ion transport across membranes and so on.The synthesis and properties of cyclic polymers have attracted important interest due to their special properties caused by the lack of chain ends and their circular architecture in recent years.Previous studies about cyclic polymers were only focused on the preparation of single polymer ring. However,there are relatively limited reports on preparation of macrocyclic graft copolymers due to the difficulty of synthesis.Herein,by means of cyclic PEO-supported multifunctional initiation system,a series of macrocyclic graft copolymers composed of a hydrophilic PEO as ring were synthesized and their properties were explored.The main results have been obtained as follows:1.A novel method for synthesis of amphiphilic macrocyclic graft copolymers was suggested by a combination of anionic ring-opening polymerization(AROP) and atom transfer radical polymerization(ATRP).The anionic ring-opening copolymerization of ethylene oxide(EO) and ethoxyethyl glycidyl ether(EEGE) was carried out first using triethylene glycol and diphenylmethylpotassium(DPMK) as co-initiators,and the linear well-definedα,ω-dihydroxyl poly(ethylene oxide) with pendant protected hydroxylmethyls(l-poly(EO-co-EEGE)) was obtained.The monomer reactivity ratios of them are r_1(EO)=1.20±0.01 and r_2(EEGE)=0.76±0.02 respectively.Because of r_1(EO)＞1,r_2(EEGE)＜1,and r₁×r₂≈1,the anionic copolymerization of EO and EEGE is apt to the ideal nonazeotropic copolymerization.2.The obtained linear copolymer l-poly(EO-co-EEGE)) was cyclized by reaction with tosyl chloride(TsCl) at pseudo-high-dilution in the presence of solid KOH.The crude cyclized product containing the extended linear chain polymer was hydrolyzed and then purified by trapping withα-CD.The pure cyclic copolymer with multipendant hydroxymethyls[c-poly(EO-co-Gly)]was esterified by the reaction with 2-bromoisobutyryl bromide,and then used as macroinitiators to initiate polymerization of styrene(St),and a series of amphiphilic macrocyclic graft copolymers composed of a hydrophilic PEO as ring and hydrophobic polystyrene as side chains(c-PEO-g-PS) were obtained.The interaction of the dyes molecules with c-PEO-g-PS was studied.The experimental results confirmed that the c-PEO-g-PS has the stronger conjugation ability with the dyes than that of the corresponding comb-PEO-g-PS under the same conditions.3.The cyclic macroinitiators for ATRP were used to initiate polymerization of 2-(dimethylamino) ethyl methacrylate(DMAEMA) and tert-butyl acrylate(tBA) respectively,and two series of macrocyclic graft copolymers were obtained.The macrocyclic graft copolymers composed of a PEO as ring and PDMAEMA as side chains(c-PEO-g-PDMAEMA) had the pH-sensitive and temperature-sensitive properties.The macrocyclic graft copolymers could self-assemble and form micellar or "reverse" micellar structures in water if external conditions such as pH, temperature and so on were finely tuned.The experimental results confirmed that cyclic graft copolymer with longer side chain(PDMAEMA) showed the lower critical micellization pH value,and cyclic graft copolymer,compared with its' corresponding ring-opening graft copolymer,showed the lower critical micellization pH value.In addition,the double hydrophilic macrocyclic graft copolymers c-PEO-g-PAA were acquired by the hydrolysis of the cyclic graft copolymer c-PEO-g-PtBA.4.The same cyclic copolymer of EO and glycidol(Gly) with multipendant hydroxymethyls[c-poly(EO-co-Gly)]as the macroinitiator was used further to initiate the ring-opening polymerization ofε-caprolactone(CL),and a series of amphiphilic macrocyclic graft copolymers composed of a hydrophilic poly(ethylene oxide) as ring and hydrophobic poly(ε-caprolactone) as lateral chains.The grafting length and density of side chains were well controlled.