Formation Of Cyclic Polymers Research Articles

Selective synthesis of cyclic-polymer-free poly(ether sulfone)s with OH ends or F ends by non-stoichiometric, reversible polycondensation

Non-stoichiometric, reversible polycondensation of bisphenol disilyl ether and bis(4-fluorophenyl) sulfone is a convenient approach to synthesize telechelic PES end-capped with the excess monomer, without the formation of cyclic polymers.

Cyclic Polyester Formation with an [OSSO]-Type Iron(III) Catalyst.

The efficient formation of cyclic polyesters from the ring-opening polymerization of lactide, ϵ-caprolactone, and β-butyrolactone catalyzed by a 1,4-dithiabutanedyl-2,2'-bis(4,6-dicumylphenol) [OSSO]-FeCl complex activated with cyclohexene oxide was achieved. The catalyst was very active (initial turnover frequency up to 2718 h-1 ), robust, and worked with a monomer/Fe ratio up to 10 000. The formation of cyclic polymers was supported by using high-resolution matrix-assisted laser desorption ionization (MALDI) MS, and the average ring size (≈5 kDa for cyclic polylactide) independent of the reaction conditions. A monometallic ring-opening polymerization/cyclization mechanism was proposed from the results of a kinetic investigation.

Thermal ring-opening polymerization of an unsymmetrical silicon-bridged [1]ferrocenophane in coordination nanochannels.

Thermal ring-opening polymerization of the unsymmetrically substituted [1]ferrocenophane was performed in one-dimensional nanochannels of porous coordination polymers (PCPs). In contrast to conventional thermal polymerization in bulk, formation of cyclic polymer was inhibited in the channels. In addition, the tacticity of the resulting polymer was dependent on the pore size of PCPs.

Ring-Expansion Living Cationic Polymerization via Reversible Activation of a Hemiacetal Ester Bond.

In this paper, we provide an effective route to cyclopolymers via the Lewis acid-assisted "ring-expansion" living cationic polymerization of vinyl ethers, directly from a simple "cyclic initiator" designed with a hemiacetal ester for dynamic and reversible initiation and propagation. The built-in hemiacetal ester, or a carboxylic acid-vinyl ether adduct, is a key to control the polymerization: as the leaving group, the activated carboxylate is well-suited for designing the ring structure, differing from monovalent halogens often employed in carbocationic initiation. The choice of a Lewis acid catalyst (SnBr4) is equally crucial to retain the cyclic structure via the reversibly dissociable but relatively strong ester bond not only during propagation but also even after quenching. The formation of cyclic polymers was proved by irreversibly cleaving the hemiacetal ester linkage of the product via acidic hydrolysis into an open-chain structure, i.e., an increase in size exclusion chromatography (SEC) molecular weight (hydrodynamic radius), along with the clean transformation of the endocyclic hemiacetal ester into an α-carboxylic acid and ω-aldehyde terminals (by NMR). The polymerization was really "living" polymerization via ring-expansion, as demonstrated by successful monomer-addition experiments and a linear increase in molecular weight with conversion. This ring-expansion living polymerization would open a door to well-defined cyclic polymers free from terminus (end groups) and to hybrid macromolecules with combinations of cyclic and linear architectures.

Hydrolysis of trich loro(chlorophenyl)silanes in aqueous media

1. The hydrolysis of (mono-, di-, tri-, tetra-, and penta-chlorophenyl) trichloiosilanes in excess of water results in the formation of cyclic polymers of general formula (ClmC6H5-mSiO1.5)n with an average degree of polymerization of n=5. 2. In the hydrolysis of trichloro(pentachlorophenyl)silane individual crystalline polymers (Cl5C6SiO1.5)n of three-dimensional cyclic structure were isolated. 3. The thermoelasticity of polymers obtained by the hydrolysis of trichloro(chlorophenyl)silanes is the result of the formation of three-dimensional cyclic products of low degree of polymerization which do not readily polymerize when heated to give high polymers of cross-linked three-dimensional structure.