Cyclic oligo

In conclusion, a variety of linear or cyclic oligo(phospholes)s and their derivatives are accessible via a set of efficient synthetic strategies. The potential of these compounds as advanced 71-conjugated systems is broadened by the presence of reactive trivalent P-centres, which allow a range of additional chemical modifications to be achieved. However, elucidation of structure-property relationships for these derivatives is still needed. 

Isosorbide and equimolar amounts of various diols were polycondensed with diphosgene in p3ridine. Different bisphenols, l,3-bis(4-hydroxybenzyloxy)pro-pane, and 1,4-cyclohexane diol were used as comonomers [59]. In some cases, large amounts of cyclic oligo- and polycarbonates were formed. 

Specifically, the co-polycondensation reaction of the dihydroxy[2]catenand 50b with the terephthalic acid derivative 47 does not proceed to high molecular-weight but affords preferentially the cyclic oligo[2]catenands 52 with n= 1,2,3 as shown by matrix-assisted time-of-flight mass spectrometry (MALDI-TOFMS) [56]. Besides the high structural flexibility of the dihydroxy[2]catenand 50b, an-... 

It is clear from comparison of the reactivity towards polycondensation of the difunctionalized [2]catenand 50b and 53 with their corresponding difunctionalized [2]catenates 50a and 54, respectively, that the mobility of the interlocked macrocycles of catenanes plays a fundamental role for the nature of the resulting polycondensates - either cyclic oligo[2]catenanes 52,54 or linear high molecular-weight poly[2]catenanes 51b,56 (Schemes 18-20). 

In 1986, Drey and co-workersp6l synthesized the first example of a cyclic oligo-p-peptide. They made use of an anhydride method based on o-phenylenephosphochloridite (OPPC) and found that cyclization of a sample of ( )-(P3-HAla)3-OH (53) led to the formation of the cyclic tripeptide 54 in 40% yield (Scheme 17). However, cyclization of the analogous enantiomerically pure peptide under identical conditions failed to produce any cyclic product. Their work showed that the conditions needed to be altered (by using an excess of diethyl phosphite) in order to ensure the starting material dissolved in the reaction mixture. More problems with solubility were encountered when dealing with the cyclic product. In this context, they noted that the enantiomerically pure c [-(5)-p3-HAla-]3 was insoluble in a variety of apolar and more polar solvents. 

Metalated halosilanes were postulated as intermediates in the reductive coupling reactions of dihalosilanes 39 to yield linear and cyclic oligo- and polysilanes (Scheme 12). 

Oxidative polymerization of aryl disulfides has been carried out under high dilution conditions for the preparation of cyclic arylene sulfides for synthesizing cyclic arylene sulfide polymers. The readily available diphenyl disulfide and dichloro disulfide with diphenyl sulfide, diphenyl ether, or p-xylene are useful monomers for the synthesis of the corresponding cyclic oligo(thio arylene)s. The reaction scheme is shown in Fig. 30 [101]. 

Poly- and cyclic oligo-(dialkyl)stannanes S(n9Sn) Poly- and cyclic oligo-(diaryl)stannanes <5(119Sn)... 

Summary A synthetic route to highly fluorescent organic semiconductors with rigid connections to curable alkoxysilanes is described. The title compounds are prepared via Heck reactions of monodisperse bromo-OPVs with allyl-alkoxysilanes. A combined extension of the Jt-system and coimection with alkoxysilanes is possible when an alkoxysilyl-styrene is used as a substrate. Hydrolysis and condensation of alkoxysilanes yields linear and cyclic oligo-OPV-siloxanes or three-dimensional networks, thus allowing the transformation of small molecules into luminescent materials with well-defined chromophores. 

The resulting products contained a significant amount of cyclic oligo(/3-hydroxybutyrate)s, which were formed by the lipase-catalyzed intramolecular cyclization of... 

Template-catalyzed syntheses of peraza-cyclophanes via the cyclic oligo Schiff bases are common (Mandal et al., 1987). The reaction of a dialdehyde and a diamine to form a cyclic oligo Schiff base is usually successful, but only a few of the di or tetra Schiff bases have been reduced to the cyclic amines. Some examples of these cyclic Schiff base-forming reactions have been reported, but this subject will not be reviewed extensively because this book covers the saturated polyaza-crowns and cyclophanes. Reducing the Schiff... 

Non-polymerizable 1,3-dioxane non-polymerizable Non-polymerizable Non-polymerizable Formation of cyclic dimer and Siloxanes 5) tetramer was reported 31 . Hexamethyltrisiloxane 1,3,5-tnoxane formation 32 331 of Considerable cyclization. Distribu- cyclic oligo- and polymers report- tion Gf cycjjc oligomers as predicted ed no quantitative data. by the J-S theory... 

It should be remembered, that cyclic acetal polymerization is always accompanied by cyclization. These aspects of polymerization are discussed in detail in Sect. 3 of this volume. Here, we wish only to stress that high-molecular-weight linear polymers are not the only products of polymerization carried out under conditions listed in Table 7-2, but some cyclic oligo- and polymers also form. 

Cyclic bisphenol-A polycarbonate oligomers have been reported by Kambour et al. [1994] to be miscible with a broad range of polymers (cohesive energy density, CED = 300 - 500 MJ/m ) (much broader than linear PC). The cyclic oligo-... 

In this chapter, we will focus on cyclic mono- and diacetylenes, as other topics, such as cyclic oligo- and polyacetylenes or dehydroannulenes [2 a], have either been reviewed in detail [1-3] or are covered by the corresponding contributions to this publication. Extremely strained systems which have been detected only by trapping reactions have been reviewed very recently [3 c] and are not included here. 

Weidmann. J.L. Kern. J.M. Sauvage. J.P. Muscat. D. Mullins. S. Kohler, W. Rosenauer. C. Rader, H.J. Martin. K. Geerts, Y. Poly[2]catenanes and cyclic oligo[2]catenanes containing alternating topological and covalent bonds Synthesis and characterization. Chem. Eur. J. 1999, 5. 1841-1851. 

Amylose, amylopectin, and glycogen are decomposed into Schardinger dextrins by bacillus macerans. These dextrins are cyclic oligo[a-(1 4)-anhydroglucoses] from six (a-dextrin), seven (j8-dextrin), or eight (y-dextrin) glucose units. In the vacancies in the centers of these rings, iodine can be incorporated to form a blue iodine inclusion complex just as in the amylose helix. The transformation of the coils into helices, which takes... 

The starting material for the production of polydimethylsiloxane (MQ) is dimethyldi-chlorosilane, which, in the presence of acid, is hydrolyzed and subsequently condenses with the elimination of water to give a mixture of straight-chain and cyclic oligo-dimethyl-siloxanes. A second step is needed to convert the reaction mixture to high-molecular-... 

Nifantiev et al have studied the conformational behaviour of a series of linear and cyclic oligo-(l->6)-p-glucosamines and their N-acetylated... 

There are various systems that fulfill the different conditions, namely thermoplastic PU, anionic ring-opening polymerization of polyamide, entropy driven ring-opening polymerization of cyclic oligo-esters. 

Free-radical ROP of cyclic oligo(thioarylene)s (9) in the presence of a small amount of an initiator (elemental sulfur or MBTS) in melt at 300°C has been studied (14). 

Ring-opening polymerization of cyclic oligo(ether-sulfone)s... 

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