Cyanoacrylates molecular weight

These acids can be used alone or as mixtures. It is especially advantageous to use a mixture of liquid and gaseous acids. The gaseous acid will stabilize free monomer in the headspace of a container, while the liquid acid will prevent premature polymerization of the bulk monomer or adhesive. However, it is important to use only a minimum amount of acid, because excess acid will slow initiation and the formation of a strong adhesive bond. It can also accelerate the hydrolysis of the alkyl cyanoacrylate monomer to 2-cyanoacrylic acid, which inhibits the polymerization of the monomer and reduces molecular weight of the adhesive polymer. While carboxylic acids inhibit the polymerization of cyanoacrylate monomer, they do not prevent it completely [15]. Therefore, they cannot be utilized as stabilizers, but are used more for modifying the reactivity of instant adhesives. 

The molecular weights of the polymers are much larger than would be predicted from the monomer/initiator ratio, as seen in Fig. 4. However, this effect is most evident for the polymerization of ethyl cyanoacrylate alone. 

This difference in reactivity between the different classes of amines explains the difference in the primer performance on polyolefin substrates with ethyl cyanoacrylate-based adhesives [37J. Since primary and secondary amines form low molecular weight species, a weak boundary layer would form first, instead of high molecular weight polymer. Also, the polymer, which does ultimately form, has a lower molecular weight, which would lower adhesives strength [8,9]. 

Reactive adhesives Reactive adhesives are either low molecular weight polymers or monomers that solidify by polymerization and/or cross-linking reactions after application. Cyanoacrylates, phenolics, silicon rubbers, and epoxies are examples of this type of adhesive. Plywood is formed from impregnation of thin sheets of wood with resin, with the impregnation occurring after the resin is placed between the wooden sheets. 

Manufacture and Processing. The cyanoacrylic esters are prepared via the Knoevenagel condensation reaction, in which the corresponding alkyl cyanoacetale reacts with formaldehyde in the presence of a basic catalyst to form a low molecular weight polymer. The polymer slurry is acidified and the water is removed. Subsequently, the polymer is cracked and redistilled at a high temperature onto a suitable stabilizer combination to prevent premature repolymerization. Strong protonic or Lewis acids arc normally used in combination with small amounts of a free-radical stabilizer. 

The loss of the addition ability of an ion by delocalization of the electron defect in a conjugated polyene chain is documented by the observation of Subramanian et al. They polymerized monomers with C=C and C=N bonds by electroinitiation. Anionic polymerization of phenylacetylene started very easily but it rapidly died out without any external cause [109]. The polymerization of -alkyl-2-cyanoacrylate in the presence of tetracyanoethy-lene yields only low-molecular-weight products. This is due to the formation... 

M., and Kreuter, J. (2005) Molecular weights of poly(butyl cyanoacrylate) nanoparticles determined by mass specttometry and size exclusion chromatography. Eur. J. Pharmaceut. Eiopharmaceut., 60, 391-399. 

Alkyl-2-cyanoacrylates can be prepared by several synthetic procedures. The only method of importance involves the Knoevenagel condensation of an alkylcyanoacetate with formaldehyde. As this is a base-catalysed reaction, the monomer is rapidly polymerized to give a low-molecular-weight poly(alkyl-2-cyanoacrylate). The resulting polymer is retropolymer-ized by heating under controlled conditions to yield monomeric cyanoacrylate (Scheme 1). 

The second stage of cyanoacrylate polymerization, propagation, occurs after the formation of initiated monomer (8). This species attacks another monomer molecule to generate a dimeric species (9, Eq. 5), which reacts with more monomer until a high molecular weight polymer chain (10) is formed. The molecular weight of the polycyanoacrylate formed is probably... 

The ductility of polyethoxyethyl cyanoacrylate has been increased by the addition of low molecular weight polyvinyl n-butyl ether. The vinyl ether was not added to any other esters, nor was the compatibility of the two polymers described. Table VII summarizes the plasticizers reported in the patent literature. 

The moisture resistance of cyanoacrylate adhesives, like the heat resistance, is poor, and the problem is particularly apparent on metals. A cyanoacrylate bond responds in several ways to a moist environment. Polyalkyl cyanoacrylates are very susceptible to alkaline hydrolysis, which degrades the molecular weight rapidly (see Section II.F.). Corrosion products generated at the interface may catalyze this hydrolysis. Loss of adhesion due to displacement of the adhesive from the adherend by moisture is a common occurrence with many adhesives. Evidence that this mechanism... 

Use a heavy molecular weight cyanoacrylate (low bloom product)... 

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