Cyclic polymerization

Each of the examples (5.1)—(5.4) illustrates the linking of molecules into supramolecular species that constitute new units of liquid, gaseous, or solid phases. Other provocative examples of supramolecular aggregation include the al-lotropic phases of sulfur (composed of a variety of linear and cyclic polymeric chains)9 and the remarkable Zintl salts (with anions composed of variable metal clusters).10... 

Data for examples of polymerization of PBT cyclic oligomers are shown in Table 3.2 [14], Polymerization under mild conditions (0.2-0.3mol% titanate initiator at 190 °C) for 6min led to Mws of 95000-115 000 (entries 2, 4 and 5). These results indicate that either the PBT cyclic polymerization is far more facile than observed for PET cyclics, or that the cyclics had higher purity, since the rates were faster and the final molecular weights significantly higher. As... 

B17. — —.and W. L. Miller The formation of linear polymers from diene monomers by a cyclic polymerization mechanism. I. The structure of poly-(diallylammonium halides). J. Am. Chem. Soc. 80, 3615 (1958). 

Different mechanistic interpretations of the formation of an alternating propylene/carbon monoxide copolymer of poly(spiroketal) structure were considered [107, 478, 480, 481, 489]. Any reasonable proposal, however, needs to take into account the nature of the end groups in the copolymer chains. To date this has not been possible owing to the low solubility of the copolymer in solvents other than hexafluoroisopropanol however, this solvent, probably because of its acidic nature, causes transformation of the poly(spiroketal) structure into an isomeric poly(ketone) structure [489]. The formation of a cyclic polymeric structure could be favoured by minor entropy loss due to the intramolecularity of the process [480,481] and by the peculiar conformational situation of the poly(ketone) structure [491]. 

C. Hoogzand, and W. Hubei, Cyclic Polymerization of Acetylenes by Metal Carbonyl Compounds, in Organic Synthesis via Metal Carbonyls (Eds. I. Wender and P. Pino, Wiley Interscience, New York, 1968, Vol. I, pp. 343-371). 

Infrared Spectra. The concentration of the associated and non-H bonded species are determined from the intensities of both the monomeric and associated v, band as a function of concentration and temperature. A usual assumption in calculating K is that no polymeric species absorb at the monomeric frequency. This assumption, which implies cyclic polymeric forms, seems to be valid, as shown in Section 3.3.6. It is necessary to use a concentration range sufficiently low that only monomer and one polymer (usually taken to be dimer) are important species, a condition difficult to meet in some cases. Another assumption is that the absorption coefficient does not change with temperature. Section 3.3.1 discusses the recent criticism of this ais-sumption. Despite these necessary simplifications and the major experimental difficulty of making reliable IR intensity measurements, the IR method probably is the most useful method for measuring K in solutions. 

As early as 1948, Reppe et al. reported the discovery of the cyclic polymerization of acetylene to cyclooctatetraene (eq. (29)) using nickel catalysts [84]. This discovery represented a true landmark in transition metal catalysis. 

U.S. 6733538 05/2004 Panandiker et al.l Procter Gamble Dye maintenance polymer comprising one or more linearly polymerizing monomers, cyclically polymerizing monomers and mixtures thereof... 

Wender, I., and P. Pino, eds., Organic Syntheses via Metal Carbonyls, Wiley, Vol. 1, 1968 (cyclic polymerization of acetylenes organic synthesis via alkyl and acyl Co carbonyls reactions of nitrogen compounds). 

Siloxane polymers are made by condensation (Equation 4) or cyclic polymerization (Equation 5). Low viscosity fluids, higher molecular weight poljrmers and even very high molecular weight gums may be produced from these reactions. This range of reaction products allows for flexibility in designing the molecular architecture of the sealant. 

Examples of intra-intermolecular polymerizjations are cyclic polymerizations of nonconju> gated dienes. This resembles such polymerizations by a free-radical mechanism ... 

Assistant Dean of the College of Engineering, and Director of the Polymer Research Center, University of Cincinnati, Ohio Poly(dimethylsiloxanes), cyclic Polymeric selenium Polymeric sulfur... 

In agreement with a cyclic polymerization mechanism, only slight residual unsaturation was found in the polymer by infrared studies. Copolymers of... 

The polymerization of alloocimene [121] is reported in the patent literature I39-I41). Silica gel, synthetic silicates, and various Lewis acids were used as the catalysts. However, no details concerning the structure of the polymeric products were given. More recently, the cationic polymerization of alloocimene was investigated by Jones (71). An intra-intermolecular polymerization mechanism was postulated (11-57). The iodine number of the polymer indicated the loss of two double bonds per monomer unit during polymerization. Interestingly, the use of Ziegler-type catalysts did not yield cyclic polymeric structures (95, 96). 

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