Oligomer preparation

Decafluorobiphenyl [434-90-2] C F C F (mol wt, 334.1 mp, 68°C bp, 206°C), can be prepared by I Jllmann coupling of bromo- [344-04-7] chloro- [344-07-0] or iodopentafluorobenzene [827-15-6] with copper. This product shows good thermal stabiHty decafluorobiphenyl was recovered unchanged after 1 h below 575°C (270). Decafluorobiphenyl-based derivatives exhibit greater oxidative stabiHty than similar hydrocarbon compounds (271). Therm ally stable poly(fluorinated aryl ether) oligomers prepared from decafluorobiphenyl and bisphenols show low dielectric constant and moisture absorption which are attractive for electronic appHcations (272). 

The effect of the initiation and termination processes on compositional heterogeneity can be seen in data presented in Figure 7.3 and Figure 7.4. The data come from a computer simulation of the synthesis of a hydroxy functional oligomer prepared from S, BA, and HEA with a thiol chain transfer agent. The recipe is similar to those used in some coatings applications. 

Linear novolac resins prepared by reacting para-alkylphenols with paraformaldehyde are of interest for adhesive tackifiers. As expected for step-growth polymerization, the molecular weights and viscosities of such oligomers prepared in one exemplary study increased as the ratio of formaldehyde to para-nonylphenol was increased from 0.32 to 1.00.21 As is usually the case, however, these reactions were not carried out to full conversion, and the measured Mn of an oligomer prepared with an equimolar phenol-to-formaldehyde ratio was 1400 g/mol. Plots of apparent shear viscosity versus shear rate of these p-nonylphenol novolac resins showed non-Newtonian rheological behavior. 

The polymerization of 1,3,3-trimethyl-2,7-dioxabicyclo[2.2.1 Jheptane 35 was carried out in methylene chloride, toluene, and 1-nitropropane at temperatures between —78 and 0 °C32l Boron trifluoride etherate, triethyloxonium tetrafluoro-borate, antimony pentachloride, and iodine were used as initiators. Irrespective of the solvents and initiators employed, the products obtained at 0 °C were white powders with melting points of 50—55 °C, while those obtained at tower temperatures were sirups. The number average molecular weight of the unfractionated products ranged from 400 to 600. The molecular weight distribution of the oligomers prepared at 0 °C was broad, in contrast to the relatively narrow distribution of those obtained at -40 °C. 

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. 

Figure 4. (Phenylene ethynylene)-based conjugated oligomers prepared in solution using a bi-direction growth approach with in situ deprotection and coupling.

Figure 3.2 Periluorocyclobutane ring containing periluoroalkyl ether oligomers prepared by Beckerbauer.

Nadic anhydride was also used to terminate an amic acid oligomer prepared from the reaction of 3,3 , 4,4 -benzophenonetetra-carboxylic dianhydride and 3,3 -methylenedianiline where the... 

Cured ethynyl-terminated ester oligomers prepared from the reaction of hydroxy-termi nated ester oligomers with 4-ethynyl benzoyl chloride exhibited higher Tgs and better solvent resistance than comparable unendcapped polymers (50). Biphenylene end-caps have been placed on imide (40, 51), quinoline (52, 53) and quinoxaline (53) oligomers. High temperatures (> 316°C"J are required to cure... 

Coating Applications. The compositions and the performance coatings are described in Table I. The coatings are prepared by the same procedure as described in the oligomer preparation. 

Nickel oligomers prepared in the presence of PA (Amax = 540 nm) (Section 20.4.2) may also act as catalysts for the reduction of Ni by hypophosphite ions. This requires, as shown by pulse radiolysis, a critical nuclearity, while free Ni cannot be reduced directly by H2PO2. Very low radiation dose conditions, just initiating the formation of a few supercritical nuclei, will lead to large particles of nickel [96]. 

Template copolymerization seems to be applied to the synthesis of copolymers with unconventional sequences of units. As it was shown, by copolymerization of styrene with oligomers prepared from p-cresyl-formaldehyde resin esterified by methacrylic or acrylic acid - short ladder-type blocks can be introduced to the macromolecule. After hydrolysis, copolymer with blocks of acrylic or methacrylic acid groups can be obtained. Number of groups in the block corresponds to the number of units in oligomeric multimonomer. Such copolymers cannot be obtained by the conventional copolymerization. 

Some types of compound are also well suited to being screened as mixtures. This is, for instance, possible for peptides, which often either bind very strongly or not at all to a given receptor. In this instance, the most potent peptide can be identified by deconvolution, and tagging of the support particles is not required. As shown in Figure 1.2, oligomers prepared by the mix-and-split method can contain positions with... 

Another example of oligomer preparation by C-C bond formation is outlined in Figure 16.30. In this synthesis, nitroalkyl phenyl selenides are converted into nitrile oxides in the presence of support-bound terminal alkenes, forming isoxazolines. Oxidative elimination of the selenide yields a new alkene, which can then be subjected to further 1,3-dipolar cycloaddition with a new nitrile oxide. Although this synthesis is short and easy to perform, the cycloadditions proceed with low diastereoselectivity... 

Oligomers prepared by radical polymerization of 2-vinylpyridine could be separated into tactic isomers on a silica column (250 x 4.6 dQ = 10 nm dP = 10 pm) with a gradient pentane/methanol (concave 10 to 40% in 30 min). The experiments were... 

The degree of polymerization of bischloroformate oligomers prepared in the pyridine system is controlled primarily by the molar ratio of phosgene to bisphenol-A, as long as the ratio is greater than 1. Increas-... 

Boiling hexane-soluble fraction of a bisphenol-A oligomer prepared in aqueous caustic... 

Table III. CPC Data on Bisphenol-A Carbonate Oligomers Prepared in Pyridine...

Although related SiN precursor systems have been developed, the above sets of reactions provide launch points for synthesizing the majority of SiN-containing precursors studied to date. Various groups have learned to manipulate oligomers prepared as above to develop useful precursors. We begin by discussing those that provide phase pure silicon nitride. 

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