Mercaptoester

Figure 2. Ethylene mercaptoester polymeric coupling agent (EME) the reaction product of random ethylene/viny alcohol co-polymers with mercaptoacetic acid. The number after the EME (e.g. EME 47) refers to the weight percent of mercaptoester units along the chain. Essentially no vinyl alcohol units remain.

Figure 3. Effect of EME 58 (58 wt% mercaptoester units co-polymer) coupling agent concentration on the peel strength of flexible epoxy (amine-cured)/AD = acetone-degreased steel test panels following (a) I day and (b) 3 day exposure to 57°C condensing humidity. See Appendix 4 for epoxy resin and cure description.

Effect of the coupling agent mercaptoester concentration on the peel adhesion and corrosion protection of epoxy/EME/steel test panels [7]... 

W(% mercaptoester in EME Peel strength" (g/cm) (after 1 h in 57 C water) Relative corrosion protection (in water at 57°C). Time to form 3 corrosion pits (h)... 

Figure 6. Influence of EME co-polymer coupling agent mercaptoester unit concentation on (a) the dry peel strength and (b) the time in 57 C water until the presence of visible corrosion products was observed for epoxy/steel peel test panels. From ref. 6.

Figure 7. Effect of air exposure time on the solid surface tension of an EME 58 (58 wt% mercaptoester unit co-polymer) thin film.

Figure 8. Shear strength durability in a 57°C water immersion of epoxy/steel torsional joints with and without EME 90 (90 wt% mercaptoester unit co-polymer) coupling agent pretreatment. From ref. 6. Adhesive diglycidyl ether of bisphenol A (Epon 828) cured with a stoichiometric amount of methylene dianiline for I h at 120°C followed by 2 h at 150°C.

Figure 10. Peel strength durability in a 5TC condensing humidity of acetone-degreased and EME 67 (67 wt% mercaptoester unit copolymer) coupling agent treated 1010 carbon steel/epoxy peel test panels. The epoxy top-coat formulation is given in Appendix 4.

As an example, both monofunctional and multifunctional polymeric mercapto-esters were deposited onto optically smooth silicon wafers coated with vapor-deposited copper. The copper had been oxidized to Cu20, as verified by XPS. Infrared reflectance (RAIRS) at 81° (4 cm-1 resolution, 2000 scans) using an MCT detector yielded information on both the nature and the durability of the mercaptoester bond to the metal oxide film. A 16 cm l shift (1740— 1724 cm-1) was observed in the carbonyl absorption of stearyl thioglycolate (STG) deposited onto the Cu20 mirror. The absorption spectrum of the carbonyl region is illustrated in Fig. 11, both for the pure STG and the reacted monolayer. 

The STG was cast from alx 10 3 M solution into which the mirror had been immersed for from 10 to 20 min (see Appendix 1). The presence of a monolayer was confirmed by ellipsometry (18 A). The spectral data agreed with data gathered on a similar system in a powder form. In this case, CuzO powder was immersed in a 0.01 M solution of isooctyl thioglycolate (OTG) in isopropanol for from 1 to 10 min, washed with pure isopropanol, dried in air, and analyzed via infrared transmission in a KBr dispersion pellet (see Appendix 2). A similar spectral shift of approximately 15 cm 1 (1739— 1724 cm-1) was observed and the lack of two distinct carbonyl absorbances suggested the formation of a monolayer. In both cases, the formation of a copper-mercaptoester salt may be responsible... 

Synthesis of 12- and 13-membered sulfur-containing lactones by homolytic macrocyclization of mercaptoacetic esters and alkynes has been investigated [95S307]. Reaction of the mercaptoester 245 with alkynes using triethyl borane radical initiation gave the macrolactones 247 and 248 in low yield [95TL2293], Remote asymmetric induction is observed during the cyclization. 

To the above mercaptoester (3.0 g, 19 mmol) in ethanol (20 ml) is added a wet suspension of freshly prepared Raney nickel [26] in ethanol ( 5 g). The mixture is heated under reflux and monitored by TLC on silica (ethyl acetate). The desulfurization is complete in about 1 h. The suspension is then treated with activated charcoal, filtered (Celite) and washed with a little ethanol, and then the filtrate is rotary evaporated. Recrystallization of the residue from aqueous ethanol gives methyl imidazole-4-carboxylate (1.27g, 53%), ra.p. 149°C. 

Problem 4.16. Upon mixing an A-chloroaniline and an a-mercaptoester, a nucleophilic substitution occurs, followed by a [2,3] sigmatropic rearrangement. An ortho-alkylated aniline is ultimately obtained. Draw the mechanism for this reaction. 

Organometallics as stabilisers Dibutyl tin(IV) mercaptides, dibutyl tin(IV) mercaptoesters, dibutyl tin(IV) dilaurates Sn... 

Larson and Harpp have prepared the bis(triazole) 13 and found that it undergoes cycloaddition with 1,3-dienes to afford stable adducts in high yields (Scheme 5-XIII).38 These adducts, on treatment with dry methano-11c HC1, can be opened to mercaptoesters [Eq. (16)]. 

The serious drop in strength of epoxy bonded carbon steel structural joints exposed to humid environments for extended periods of time is greatly reduced by surface treating the bond surfaces with polyfunctional mercaptoester coupling agents. 

Adhesion performance was evaluated by accelerated aging of torsion joints in water at 57°C. Surface treatment involves preactivation of the steel surface with aqueous ammonium citrate solution and treatment with the mercaptoester in organic solution. 

Several factors are thought to be involved in the mechanism of durability improvement. The objective of this study was to examine compounds which are capable of interacting chemically with the steel surface. In addition, reaction with the epoxide resin is also desirable. The polyfunctional mercaptoester compounds meet both of these requirements in that the mercaptoester moiety provides a means of chelating iron cations and in addition is very reactive towards the epoxide group in the presence of an amine. The polyfunctional nature of this compound enables it to attach to the steel surface at more than one site and provides a group which can chemically attach to the resin. The dramatic improvement in bond durability supports such a hypothesis. 

Polyfunctional mercaptoester chelators have been synthesized and evaluated as potential coupling agents for the adhesion of epoxy resins to steel. The adhesive systems were evaluated by subjecting torsional joints to shear failure after accelerated immersion testing in distilled water. 

DeNicola and Bell have reported attempts to improve durability of epoxy-bonded steel joints using coupling agents containing )8-diketone and polyfunctional mercaptoester chelating groups. The success of this approach again depends on the hydrolytic stability of the chemical bonds formed with the oxide surface. 

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