Application Of Glaser Coupling Reaction In The Preparation Of Cyclic Polymers

The relations between structures and properties of polymers have attracted many researchers'attention. Cyclic polymers with "endless" polymer main chains show distinctively unique properties due to their closed ring topology compared to linear and branched ones. As new functional polymers, they could be applied in some important fields, such as material modification, nanotechnology and biological medicine, etc. However, their practical applications are greatly bound by the complicated and tedious synthetic procedure.Highly-efficient ring-closure technique is one of the synthetic strategies for preparation of cyclic polymers, which involves intra-molecular cyclization of linear precursors with hetero-difunctional or homo-difunctional end groups under high dilute conditions. Functional linear precursors can be easily obtained by different polymerization techniques and end-group modification. Therefore, selecting appropriate cyclization conditions is very important for cyclic polymer preparation.In this thesis, Glaser coupling reaction is used as cyclization technique to synthesize cyclic polymers. The Cu(I) catalyzed Glaser coupling of terminal alkynes can be conducted at room temperature in air, resulting in the formation of 1,3-diyne. Using this method, we have prepared cyclic poly(ethylene oxide) (c-PEO), cyclic polystyrene (c-PS), and cyclic poly(ethylene oxide)-block-polystyrene (c-PEO-b-PS) indicating that this is an universal method for the synthesis of cyclic polymers. The main results obtained are showed as follows:1. Two cyclic homo-polymers have been synthesized:c-PEO and c-PS. Firstly, a,co-dihydroxyl PEO were obtained by ring-opening polymerization (ROP) of ethylene oxide (EO) initiated by co-initiator of 2,2-dimethyl-1,3-propanediol and diphenylmethylpotassium (DPMK), terminated by anhydrous methanol. After the reaction between hydroxyl end-groups and propargyl bromide in the presence of NaH,α,ω-dipropargyl PEO were obtained. Then, the linear precursors solution was added dropwise to catalyst solution [Cu(I)Br/N,N,N',N''-pentamethyldiethylenetriamine (PMDETA) dissolved in pyridine] at a rate of 2μmol/h to avoid intermolecular reactions and ensure the purity of cyclic products. c-PS was synthesized using the same manner, except that linear PS was obtained by anionic polymerization initiated by lithium naphthalenide and end-capped with EO. All the intermediates and target products were characterized by GPC,1HNMR,FT-IR and MALDI-TOF MS in detail.2. Cyclic block copolymer, c-PEO-b-PS, have been designed and synthesized. Firstly,α,ω-dihydroxyl PS were used as macro-initiator in the presence of DPMK to initiate ROP of EO to give the triblock copolymer, poly(ethylene oxide)-block-polystyrene-block-poly(ethylene oxide) (PEO-b-PS-b-PEO). Then, the end hydroxyls were modified to propargyls. In the cyclization process, since pyridine can be acted as ligand, we tried to improve the cyclization condition without adding of PMDETA. It confirmed that the intra-molecular cyclization was also carried out with the efficiency as high as 100%, and no inter-molecular reactions were detected. All the intermediates and target products were characterized by GPC,1H NMR and FT-IR in detail.