Cyclic acetal polymerization active sites

Plasma polymerized N-vinyl-2-pyrrolidone films were deposited onto a poly(etherurethaneurea). Active sites for the immobilization were obtained via reduction with sodium borohydride followed by activation with l-cyano-4-dimethyl-aminopyridinium tetrafluoroborate. A colorometric activity determination indicated that 2.4 cm2 of modified poly(etherurethaneurea) film had an activity approximately equal to that of 13.4 nM glucose oxidase in 50 mM sodium acetate with a specific activity of 32.0 U/mg at pH 5.1 and room temperature. Using cyclic voltammetry of gold in thin-layer electrochemical cells, the specific activity of 13.4 nM glucose oxidase in 0.2 M aqueous sodium phosphate, pH 5.2, was calculated to be 4.34 U/mg at room temperature. Under the same experimental conditions, qualitative detection of the activity of a modified film was demonstrated by placing it inside the thin-layer cell. 

Cyclic acetals are known to produce long lived species provided proper Initiators are used ( 7)- Nevertheless, their polymerization Is more complex than that of THF backbiting causes the formation of small cycles and transacetallzatlon Is Important ( ) their active sites are tertiary cyclic oxonlum groups like THF - but In addition are also In equilibrium with alkoxycarbenlum species. The enhanced reactivity of the latter could lead to Interesting synthetic applications. We have Intestlgated the polymerization of... 

Other stereoregular polymers with asymmetric carbon atoms in the main chain as stereoisomerism sites have been obtained by ring-opening polymerization of optically active cyclic monomers. These monomers include epoxides (100-104), episulfides (105,106), aziridines (107-109), lactides(110), lactones (111-116), thiolactones (117), lactcunes (118-120), cyclic acetals (121), and N-carboxy cuihydrides (122). Some stereoregular polymers containing atropoisomeric units as stereoisomerism sites (VIII (123) and IX (124)) have also been synthesized. 

In cationic polymerizations, electron-deficient initiators (mostly Bronsted or Lewis acids) react with electron-rich monomers. The active chain end (ACE) bears a positive charge with the active sites being either carbenium or 0x0-nium ions. Molecular weights are often limited by the inherent sensitivity to impurities, chain transfer, and rearrangement reactions. Suitable monomers for cationic polymerizations are vinyl monomers with electron-donating moieties or cyclic structures containing heteroatoms, while the latter case is termed cationic ROP. Eligible monomers include cyclic ethers, acetals, and amines as well as lactones and lactams (Scheme 3). 

When living poly(methyl methacrylate) (PMMA) prepared by group transfer polymerization (GTP) is used as a macroinitiator for the ROP of cyclic carbonates, a site transformation from the silyl ketene acetal (GTP-mechanism) to an alcoholate (anionic ROP-mechanism) with a metal-free counterion occurs (Scheme 12.5). The GTP of PMMA was initiated with l-methoxy-l-trimethylsilyloxy-2-methyl-l-propene (MTS) in combination with catalytic amounts of tetrabutyl ammonium cyanide in THF as solvent. Towards the end of the reaction, DTC is dissolved in the reaction mixture and lequiv. of fluoride anions (e.g. tris(dimethylamino) sulfonium difluorotrimethylsilicate TASF), with respect to the active species, is added. In this way, good yields of the respective block copolymers were obtained. A model experiment for this site transformation is the polymerization of DTC with MTS as the initiator and TASF as the desilylating agent. The fluoride anion promotes desilylation of the silyl ketene acetal with formation of an enolate, which reacts as a carbon-centered nucleophile with the carbonyl carbon of DTC, thereby... 

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