Macromolecular dioxolenium salts

Preparation of Macromolecular Dioxolenium Salts. Living polystyrene prepared by the polymerization of styrene in THF with a-methylstyrene tetramer dianion reacted with a 2.1-molar amount of ethylene oxide for three hours at room temperature a 6.6-molar amount of adipoyl chloride was added, and the mixture was stirred for 20 horns a 20-molar amount of ethylenebromohydrin was added. This mixture was stirred for 44 hours. The bromoethylated polystyrene was precipitated in excess methanol and freeze-dried from benzene in a vacuum system. A 1-nitropropane solution of polystyrene dioxolenium salt was prepared by reaction of bromoethylated polystyrene with silver perchlorate in 1-nitropropane. Silver bromide was removed from the reaction mixture by filtration. Molecular weight of the product was measured by a vapor-pressure osmometer it was 1910 for living polystyrene and 5190 for the bromoethylated polystyrene. Bromine analysis of the bromoethylated polystyrene showed 67.9% of the calculated value. 

The polymerization of THF with poly-THF dioxolenium salt was carried out in nitromethane at 0°C. The results are shown in Table III. The agreement of the observed Mn with the calculated value from conversion, assuming the formation of living polymer was fairly good. The number of ester groups per polymer chain analyzed from IR spectra (7) remains four, as shown in Table III the values are similar to those in Table II. These results substantiate the formation of macromolecular dioxolenium salt at both ends of PTHF. 

Polymerization of cyclic ethers by macromolecular dioxolenium salt yielded block copolymers. No termination or chain transfer was observed with THF, but some termination with BCMO and considerable chain transfer with OBH occurred. Cyclic formals such as TEX or DOL do not form block copolymers, showing that the initiation mechanism is not via bonding. 

Grafting from is based on the use of a macromolecular initiator, that is, a polymer backbone containing dioxolenium salts as precursors of carbenium and oxocarbeniura ions (i.e., labile halides or acylhalides). The last two functional groups can be transformed into a carbenium ion by reaction with a silver salt containing a stable anion. When the monomer used is a strong nucleophile (such a cyclic imino ethers) the labile halide itself can initiate graft copolymerization. 

Block or graft copolymem can be obtained by cationic polymerization of THF with macromolecular initiators. The recommended groups for the initiation are the dioxolenium cation, the acyl cation and the super acid ester, each of which can be introduced into the backbone polymer by reaction with silver salts of strong acids. Introduction of the dioxolenium group into polystyrene was carried out by the following route32 ... 

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See also in sourсe #XX -- [ ]

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