Cyclic oligomerization

Oligomeric Cyclic Phosphonates. Albright Wilson s Antiblaze 19 and 1045 are mixtures of the material shown where x = 1 has the CAS... 

It is well known that D3 cyclic has a Si NMR signal at — 9 ppm, (5) and that higher oligomeric cyclic compounds (D4 to DJ and linear dimethylsiloxy units appear between —19 and —22 ppm. When samples of T2D3 and T2D4 were examined by the Jancke group their results unequivocally identified structures [25] and [27] (chemical shifts in Table XIII). 

Homo and copolymers of tetrahydrofuran (THF) and alkylene oxides (AO) are used as soft segment glycols in the preparation of polyurethanes. In the process of producing the THF-AO homo and copolymers certain oligomeric cyclic ethers are also produced and can comprise 7-15 % of the polymer. These cyclic ethers are undesirable because when the polymers are used to prepare polyurethane the cyclic ethers tend to degrade the polyurethane s properties. 

Copelin, H. B. 1981. Method for reducing oligomeric cyclic ether content of a polymerizate. U.S. Patent 4,306,058. 

The most studied system is the (Me2SiO) family because of its commercial importance. Although the neat system is ca. 83 % polymeric, dilution of the system to ca. 20% Me2SiO with solvents (e.g., THF, toluene) precludes linears at equilibrium. The equilibrium cyclics are predominantly tetramer and pentamer, with decreasing amounts of the larger oligomeric cyclics. The abundances parallel their probabilities, determined by the same factors that are operative in other cyclic distributions. The distribution of tetramers, pentamers, hexamers, etc., may vary with the substituents (i.e., polarity, bulk), but this has not been studied definitively. 

Many biologically active compounds contain cyclic ureas, including inhibitors of human immunodeficiency virus (HIV) protease and HIV replication [70]. Kim et al. [71] presented an illustration of the synthesis of oligomeric cyclic ureas as nonnatural biopolymers. Applying the libraries from libraries [72] concept, triamines [65] such as those described earlier were used as templates for the generation of different heterocyclic compounds such as cyclic ureas, cyclic thioureas, and bicyclic guanidines [65]. The cyclizations to obtain the five-membered ring cyclic ureas and cyclic thioureas were... 

Poly(phosphoric acid) is the high-molar-mass condensation product of orthophosphoric acid. The corresponding salts are called polyphosphates. The oligomeric, cyclic metaphosphate compounds, as they are called, are often also classified as polyphosphates. 

One of the analogues is calix arenes which are oligomeric cyclic analogues of novolac resin derived through the condensation of p-alkyl phenols with formaldehyde. Quite re-... 

Kuo, C. M. Clarson, S. J., An Investigation of the Thermodynamic Interactions of Oligomeric Cyclic Methylphenylsdoxanes in Siloxane Melts and Blends. Polymer 2000,41, 5993-6002. 

Oligomeric Cyclic Phosphonates. AMGARD CU or CT, also Clariant s EX-OLIT OP 910, and AMGARD 1045 are mixtures of the diphosphonate and triphos-phonate with the following structures (CgH 2oOeP2 [41203-81-0], and C15H31O 9P3 [42595-49-9]). 

J/° K-mole),3 these reactions do not proceed to 100% completion, and monomer recoveries of 5-30% are typical. The removal of unreacted monomer may be a limitation if a finished part is to be formed by ring-opening polymerization. Virtually all ring-opening polymerization reactions which involve ring-chain equilibration form measurable quantities of monomeric or oligomeric cyclics." ... 

The ring-opening polymerization of the oligomeric cyclic dimethylsiloxane tetramer seems to be an unusual example, in that the entropy actually increases during polymerization.5 This increase in entropy is the driving force for the reaction, since the enthalpy is near zero. Nonetheless, the anionic polymerization is an equilibrium reaction, and significant amounts of cyclics remain after polymerization (18.3% for dimethylsiloxane,6 Equation 5). 

Figure 1. HPLC trace of oligomeric cyclics formed via hydrolysis/ condensation using Et3N.

Figure 4. GPC of oligomeric cyclics (bottom) and high Mw polymer (top). 

The structure of methylaluminoxane (MAO) was generally recognized as an oligomeric (cyclic or linear) chain with [—O—Al(Me)—] units as shown in Fig. 4 [13], although the structure of MAO has not yet been clearly determined. 

Scheme 11.11 Synthesis of oligomeric cyclic ketone 31 from 5-thexylborocane 29.

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