Oligomers synthesis procedures

Si NMR spectroscopy reveals that the silicon monomers and dimers start to bind into higher silicon oligomers at the very beginning of the Ti-Beta synthesis procedure. After... 

Efficiency of the deprotection and coupling reactions are critical to the success of any iterative solid-phase synthesis. Shown in Scheme 1 is a triad of reactions for phenylacetylene oligomer synthesis trimethylsilyl deprotection,28 29 triazene unmasking of an iodobenzene,30 and the Sonogashira coupling of a terminal acetylene with an aryl iodide.31-33 Representative procedures for each step in this sequence are included at the end of this chapter. 

The synthesis of high-molar-mass PLA and PGA by two-step polycondensations of lactic and glycolic acids, respectively, has recently been reported.374,375 It involves the formation of a low-molar-mass oligomer followed by a polycondensation step either in the solid state374 or in the melt under vacuum.375 The procedures are detailed in Section 2.4.1.5.2. 

Detailed procedures for the synthesis ofa,o>-organofunctionally terminated siloxane oligomers with well defined structures have been given 50,66-67). Tables 6 and 7 provide the data on the synthesis and characteristics of aminopropyl and hydroxybutyl terminated polydimethylsiloxane oligomers prepared via anionic and cationic ringopening polymerization of octamethylcyclotetrasiloxane (D in the presence of appropriate disiloxanes, respectively. 

An interesting procedure has been proposed for the synthesis of amylose-b-PS block copolymers through the combination of anionic and enzymatic polymerization [131]. PS end-functionalized with primary amine or dimethylsilyl, -SiMe2H groups were prepared by anionic polymerization techniques, as shown in Scheme 56. The PS chains represented by the curved lines in Scheme 56 were further functionalized with maltoheptaose oligomer either through reductive amination (Scheme 57) or hydrosilyla-tion reactions (Scheme 58). In the first case sodium cyanoborohydride was used to couple the saccharide moiety with the PS primary amine group. 

Synthesis of a Urethane Vinyl Ether Oligomer. A urethane vinyl ether oligomer was prepared by the procedure discussed by Lapin.15 Reacting a hydroxyalkyl vinyl ether, an oligomeric diol and a diisocyanate gave and oligomer that had a Brookfield viscosity of 3.7 million mPa-s and a theoretical equivalent weight of 1000 g per vinyl ether double bond. 

Synthesis and characterization of well-defined, a,w-terminated difunctional siloxane oligomers are discussed. Detailed procedures on the preparation of primary amine- and hydroxy-terminated oligomers are given. Control of the average molecular weight (Mn) and also the possible variations in the backbone structure and composition are explained. The effect of these variations on the physical, thermal and chemical properties of the resulting materials are discussed. Characterization of these oligomers by FT-IR, NMR and UV spectroscopy, potentiometric titration and DSC are summarized. 

In this paper we will discuss the synthesis of a, urhydroxybutyl terminated polydimethylsiloxane oligomers by cationic routes and a,u-aminopropyl terminated poly(dimethy1-diphenyl)siloxane oligomers by anionic methods respectively. Detailed procedures for the synthesis of aminopropyl, carhoxypropyl and glycidoxypropyl terminated polydimethylsiloxane oligomers have already been described elsewhere(1 1). ... 

While the extracts of SPMDs are generally less difficult to purify than are extracts of tissue or sediment, certain interferences can be problematic for some types of analyses. The most important of these potential interferences are codialyzed polyethylene oligomers (i.e., the so-called polyethylene waxes), oleic acid, and methyl oleate. The latter two interferences are residual from the synthesis of the triolein. Also, oxidation products of triolein may be present in dialysates of SPMDs that have been exposed (especially in the presence of light) to air for periods exceeding 30 d. For a standard 1-mL triolein SPMD, the mass of all these interferences in dialysates is generally <30 mg or about 6 mg g of SPMD (Huckins et al., 1996). Another potential interference is elemental sulfur, which is often present in sediment pore water and is concentrated by SPMDs. However, both polyethylene waxes and elemental sulfur are readily removed using the previously described SEC procedure. 

An example for the synthesis of poly(2,6-dimethyl-l,4-phenylene oxide) - aromatic poly(ether-sulfone) - poly(2,6-dimethyl-1,4-pheny-lene oxide) ABA triblock copolymer is presented in Scheme 6. Quantitative etherification of the two polymer chain ends has been accomplished under mild reaction conditions detailed elsewhere(11). Figure 4 presents the 200 MHz Ir-NMR spectra of the co-(2,6-dimethyl-phenol) poly(2,6-dimethyl-l,4-phenylene oxide), of the 01, w-di(chloroally) aromatic polyether sulfone and of the obtained ABA triblock copolymers as convincing evidence for the quantitative reaction of the parent pol3rmers chain ends. Additional evidence for the very clean synthetic procedure comes from the gel permeation chromatograms of the two starting oligomers and of the obtained ABA triblock copolymer presented in Figure 5. 

Synthesis and characterization of polyols. The procedure described above yields PHBA-modifled oligomers, apparently with minimal side reactions. The odor of phenol was barely detectable in the products, indicating that little phenol had been formed. p-TSA catalyst plays a crucial role. When p-TSA was not used in the 30/70 PHBA/diol reaction only 75% of theoretical distillate was collected, and the product smelled strongly of phenol. Solvent plays an important role by helping control temperature and by facilitating removal of water. If desired, the products can be purified as described to remove small amounts of unreacted PHBA and phenol. 

Conventional liquid phase synthesis suffers from the limitation that each product or intermediate has to be separated from the other components of the reaction mixture. An elegant answer to this problem is to use a solid phase synthesis (SPS) approach. In such an approach the compounds are synthesized on a solid support and simple washing steps replace the laborious work up and isolation procedures. At the end of the synthesis the product is released from the solid support. The SPS of oligomers of amino acids or nucleotides is well estabilished and task chemists are facing now is the development of SPS routes for small organic molecules. 

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