Self-oligomerization

Abstract—This work studies the effects of self-oligomerization of the aminosilane coupling agent 3-aminopropyltriethoxysilane—also called y-aminopropyltriethoxysilane. 3-APS, y-APS, APS or AUOO (Union Carbide)—on the adhesion of thin polyimide films to a native-oxide silica surface under no stress, i.e. T(0) conditions, and after standard 85°C/8I%T H (temperature and humidity) stress. Techniques have been developed using both silicon and hydrogen NMR to control and monitor the degree of oligomerization in aqueous solutions at low concentrations (0.1 vol %). 

The following studies attempt to characterize the degree of self-oligomerization of aqueous APS solutions and relate such data to effects on adhesion. Of particular interest are long-term effects that are usually evaluated by T H acceleration. 

For a 50/50 monomer/dimer solution above 83wt%, there is insufficient heavy water available for complete hydrolysis of the ethyl ester and subsequent oligomerization. This fact is supported by the 87 and 95 wt % solutions shown in Fig. 3 in which the monomer NO and dimer N1 reappear, but at different chemical shifts because supporting electrolyte is now essentially APS and not heavy water. This study supports the observation that ester hydrolysis must occur before self-oligomerization (loss of monomers). 

Oligomerization in these solutions is most certainly complicated. Figure 4 shows the Si-29 NMR spectrum of 90 wt % APS in heavy water vs. time at room temperature. The Si-29 isotope is only about 4.7% of the silicons. Consequently, sensitivity suffers and recording real-time Si-29 NMR spectra is difficult. The spectra of Fig. 4 are normalized and only the NO band is prominent. The NO band is seen to decay with increasing time as the APS monomers are used up in self-oligomerizations. Because of the poor signal-to-noise, the N1 band and the... 

Highly self-oligomerized 0.1 vol% APS solutions promote adhesion as do those with very low amounts of self-oligomerization. Formation of covalent Si—O bond with the mineral surface may not even be required to promote adhesion. Possibly, only hydrogen bonding or van der Waals interactions are sufficient. Such ideas have been discussed previously [6]. 

Monosubstituted alkylidenecyclopropanes show lower regioselectivity. While /i-hexylidenecyclopro-pane (82) and the corresponding phenyl analog (83) cycloadd to cyclopentenone, acrylate or crotonate to produce mostly alkylidenecyclopentanes, a mixture of adducts is observed with diethyl fumarate (equations 74-77). Nonetheless, compared to the parent compound (79), these mono- and di-substituted alkylidenecyclopropanes often give better cycloaddition reactions with a wider range of alkenes, and are also less susceptible to self-oligomerization. 

The structural basis of DD/DD interactions involved in death receptor signaling, such as those in the Fas-FADD complex, remains largely unresolved. Although no solid experimental evidence is available, the Fas-FADD and TNF-Rl/TRADD complexes are likely to be trimeric, most likely with Fas and TNF-Rl possessing oligomerization surfaces. Therefore such complexes might comprise at least two interfaces, a self-oligomerization surface... 

Oligomeric 2-ChloroethylPhosphate. Akzo s Fyrol 99 [109640-81-5] is produced either by self-condensation of tris(2-chloroethyl) phosphate (82) or by insertion of phosphoms pentoxide into this phosphate (82) followed by ethoxylation. It is low in volatihty and useful in resin-impregnated air filters, in flexible urethane foam, rebonded foam, and stmctural foam. 

Xiong, H., Bnckwalter, B., Shieh, H.-M., and Hecht, M. H., 1995. Periodicity of polar and nonpolar amino acids is the major determinant of secondary structure in self-assembling oligomeric peptides. Proceedings of the National Academy of Sciences 92 6349—6353. 

In conclusion, the self-condensation of 2-furaldehyde promoted by heat occurs with the formation of di- and trifurylic intermediates. The functionality of the growing chain increases after each oligomerization step until gelation and precipitation of the resin occurs. Thus, the process is non-linear from the onset since the condensation product 4 possesses three sites for further attack, namely the free C-5 position and the two formyl groups. It is interestering to note that while the polycondensation of 2-furfuryl alcohol is essentially linear and cross-linking is due to side reactions, the thermal resinification of 2-furaldehyde is intrinsically non-linear and gel formation occurs at earlier conversions. 

Bizilj et at reported that disproportionation is more important for oligomeric radicals. While combination products were unequivocally identified, analytical difficulties prevented a precise determination of the disproportionation products. Accordingly, they were only able to state a maximum value of ktself reaction of 11 and <1.50 for reaction between 8 and 11. 

In contrast to the processes of Ethyl and of Chevron/Gulf, which use Ziegler catalyst in the oligomerization of the ethylenes, Shell uses a self-developed catalyst system consisting of, for example, a nickel salt, a rm-organophosphine group, and a polar solvent such as 1,4-butanediol (3) [34,35] ... 

The theories of Miller and Macosko are used to derive expressions for pre-gel and post-gel properties of a crosslinking mixture when two crosslinking reactions occur. The mixture consists of a polymer and a crosslinker, each with reactive functional groups. Both the polymer and crosslinker can be either collections of oligomeric species or random copolymers with arbitrary ratios of M /Mj. The two independent crosslinking reactions are the condensation of a functional group on the polymer with one on the crosslinker, and the self-condensation of functional groups on the crosslinker. 

Fig. 2b. The appearance of two crystal forms shows that the protein in the membrane exists in equilibrium between the protomeric aj8 unit and oligomeric (aj8>2 forms. The high rate of crystal formation of the protein in vanadate solution shows that transition to the E2 form reduces the difference in free energy required for self association of the protein. This vanadate-method for crystallization has been very reproducible [34-36] and it also leads to crystalline arrays of Ca-ATPase in sarcoplasmic reticulum [37] and H,K-ATPase from stomach mucosa [38]. 

Silylenoids R2Si(Li)Cl are unstable and easily undergo a-elimination of LiCl to form R2Si or self-condensation to form R2Si=SiR2, then oligomeric substances. 

Hunter (60) reported a self-assembled open polymer formed by a zinc porphyrin bearing one para-aniline substituent at the meso position. The ortho- and mela-analogs discussed above form closed dimers, but the geometry of the para-derivative precludes this, and polymerization is the only alternative (76, Fig. 31). Although the dilution experiments could be fitted to a non-cooperative polymerization model with a pairwise association constant (K = 190 M 1) practically identical to that found for simple aniline-zinc porphyrin complexes (K = 130 M 1), broadening of the 4H NMR spectrum at high concentrations is characteristic of oligomerization. 

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