Acrylic acid dissociated

Acrylic acid is a moderately strong carboxylic acid. Its dissociation constant is 5.5 x 10. Vapor pressure as a function of temperature is given in Table 4 for acrylic acid and four important esters (4,16—18). The lower esters form a2eotropes both with water and with their corresponding alcohols. 

While polar monomers are usually beneficial in acrylic PSA formulations, there are times when their presence is deleterious. Examples of this may be the use of acrylic acid containing adhesives for electronic applications, for adhering to some metallic surfaces, or for application to paper used in books. Higher levels of acrylic acid not only increase the acidity of the PSA but they also increase the moisture uptake in the adhesive making dissociation of the acid easier. This can increase corrosion problems in the electronic or metal applications, or severe discoloration and degradation of paper with time. The latter is often a significant concern to librarians who deal with repair and archival restoration of books. In applications such as these, acid-free adhesives are more desirable, or at the very least the amount of acid has to be low and caution has to be taken to fully incorporate the monomer into the PSA. 

This potential reflects itself in the titration curves of weak polyacids such as poly(acrylic acid) and poly(methacrylic acid) [32]. Apparent dissociation constants of such polyacids change with the dissociation degree of the polyacid because the work to remove a proton from the acid site into the bulk water phase depends on the surface potential of the polyelectrolyte. 

Fig. 15. Energy of proton dissociation (Ez) from Z times ionized polyelectrolyte molecules as function of the degree of dissociation (a). (A) - PPAL (1), PPAS (2), PPA (3), polyfmethacrylic acid) (4), copolymer of acrylic acid with ethylenesulfonic acid (50 50) in aqueous solutions (5), (B) - PPAL (1), PPAS (2), PPA in the presence of NaCl (3) ( ) INaClj = 0 (X) fNaCll = 0.25 mmol/1 (o) 0.50 mmol/1...

The two procedures give rise to different results. In both cases acrylic acid, present in the form of acrylate, readily reacts with ammonia at r.t. forming a species characterized by an intense band at 1535 cm i indicating the formation of an amide. With increasing reaction temperature (100°C), however, in the case of procedure A the band at 1535 cm shifts to 1495 cm-i and a weak band forms at 1720 cm h The latter band is characteristic of undissociated and weakly coordinated acrylic acid. This indicates that at 100°C amide dissociates with formation of the free acid. When ammonia is instead present in the gas phase (procedure B), the amide species undergoes transformation to acrylonitrile with a maximum in the intensity Fig. 6 IR spectra of 1 torr acrylic of the vcn band at 2220 cm- at an evacuation acid in contact (5 min) with Sb V=l temperature of about 300°C. and evacuation at r.t (a), and fol- Coordinated acrylic acid and ammonia thus lowing evacuations at 100 (b) and react faster at r.t. to form acrylamide, but in 200°C (c). absence of ammonia which inhibits the re-... 

In a study of the transition in conformation from random coil to stiff rod by poly(acrylic acid), it was found that the point of transition depended on a number of factors, including the nature of the solvent, the temperature, the particular counterion used and the degree of dissociation (Klooster, van der Trouw Mandel, 1984). 

Polyelectrolytes are polymers having a multiplicity of ionizable groups. In solution, they dissociate into polyions (or macroions) and small ions of the opposite charge, known as counterions. The polyelectrolytes of interest in this book are those where the polyion is an anion and the counterions are cations. Some typical anionic polyelectrolytes are depicted in Figure 4.1. Of principal interest are the homopolymers of acrylic acid and its copolymers with e.g. itaconic and maleic adds. These are used in the zinc polycarboxylate cement of Smith (1968) and the glass-ionomer cement of Wilson Kent (1971). More recently, Wilson Ellis (1989) and Ellis Wilson (1990) have described cements based on polyphosphonic adds. 

Another very interesting class of crosslinked polyelectrolytes are the so-called superabsorbents. They predominantly consist of crosslinked and (partially) neutralized poly(acrylic acid) and, hence, represent a network of flexible polymer chains that carry dissociated, ionic groups. Due to this structure they can function as water-swellable gels. Although they are hard, sandy powders in a dry... 

Poly(acrylic acid) is a typical polyelectrolyte and shows a dissociation reaction. When pH is high, the polymer chain is charged negatively and extends itself due to coulombic repulsion and thermal motion of counter ions which pull the charged side chains. 

When the polymer is charged, the repulsive forces of the charges prevent an approach of the radicals, and the lifetime of the radicals increases dramatically. In the case of poly(acrylic acid), for example, the decay of the poly(acrylic) acid radicals is fast and follows the same kinetics as any radical derived from neutral polymers as long as the polymer is fully protonated (low pH) (Ulanski et al. 1996c). With increasing pH and concomitant dissociation of the polymer, however, the polymer assumes a rod-like shape, its segments become less flexible, and repulsive forces increasingly prevent their approach. Some radicals survive even for hours under such conditions. 

The results obtained for reaction of acrylic acid (200 /iM) with tetrasulfide (1.25 mM 5 mM) as well as bisulfide (5 mM) are shown in Figurel. In the reaction with HS, the concentration of 3-MPA did not noticeably increase after treatment with TBP. If polysulfide ion was the actual reactive species in this reaction, then TBP treatment should have caused a significant increase of 3-MPA, in comparison to that without TBP. Therefore, these results indicate that HS was the reactive species in the sulfide medium. However, in the reaction of acrylate with the polysulfide ion, S42, determination of 3-MPA concentration after TBP treatment revealed a large increase, indicating that S42 reacted with acrylate to produce 3-tetrasulfidopropionic acid. The reactivity of tetrasulfide with acrylate was much higher than that of bisulfide. Similar results were also obtained for reaction of acrylonitrile with HS and S42 (Figure 2). The kinetic data are summarized in Table I. In the polysulfide senes low concentrations of 3-MPA were also observed without TBP treatment. It is possible that this 3-MPA was formed from uncatalyzed dissociation of the polysulfide addition product... 

The initially formed rhodium/substrate (B) complex of the hydrogenation of Z-OC-(acyl-amino)acrylic acid in Figure 17.77 possesses structure C (Figure 17.78). The reaction starts with the reversible dissociation of two MeOH ligands from the central atom Rh(I). The two now... 

The relatively small values of acrylic acid in the presence of ethanol as well as acetic acid can be caused by a partial ester formation and a small amount of dissociation along with a high partial pressure over the solution. 

Steps 1-3 of the catalytic cycle correspond to various steps of other catalytic cycles already discussed in Chapter 13. Step 1 tt-complex formation by combination of the aryl triflate and a sufficiently valence-unsaturated and thus sufficiently reactive Pd(0) species. Step 2 oxi-dative addition of the aryl triflate to Pd with formation of a Cspi—Pd(II) bond. Steps 3a and 3b exchange of a PPh3 ligand by an acrylic acid methyl ester via a dissociation/addition mechanism. The newly entered acrylic acid ester is bound as a 77 complex. 

The electrostatic attraction would be used more effectively by employing carboxylic acid groups whidi completely dissociate under most solvolytic conditions. Cr olymers of vinylimidazole and acrylic acid (VIm-AAc, 34) were first prepared by the Overberger group (80,81). This polymer catalyst diows a substrate... 

PAA and PVP do not react in DMF. The PMAA-PVP compact complex formed in DMF gradually dissociates upon the addition of DMSO (Fig. 16, curve 4). The behavior of the free poly(acrylic acid) and poly(methacrylic acid) in mixtures of organic solvents (methanol - DMSO for PAA and DMF - DMSO for PMAA) markedly differs from that in the complex (Fig. 16). This also supports the binding of PAA and PMAA with PVP in organic solvents (in methanol and DMF, respectively). 

In NaOH solution, parts of acrylic acid groups in starch/acrylic acid copolymers are neutralized with NaOH, and sodium acrylates formed dissociate easily... 

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