Phenols dielectric behavior

Van Beek, L. K. H. Dielectric behavior of curing phenolic-formaldehyde resins, J. Appl. Polym. Sci., 8,2843 (1964)... 

When the blend of polyesterimide and phenol-formaldetyde resin is heated in air, it forms a crosslinked product. Cross-linking reaction is facilitated at about 300 C and 150 C for no-volac and resole, respectively. The onset of crosslinking reaction by heating the polyblend has been suggested on the baisis of solvibility, thermal and dielectric behavior of the heated blend. 

A second type of study that corroborates the basic assumption is any measurement which specifically shows that the H bonded species are cyclic. Infrared data can offer such evidence, provided the only important species over a wide concentration range are monomers and dimers. For such a system the peak intensities of absorption by the monomer (Im) and dimer (Id) are simply related the ratio IdIIm is a constant. Such behavior has been observed and cited in favor of cyclic dimers of S-valerolactam and of -caprolactam by Tsuboi (2050), and of y-bu-tyrolactam by Klemperer et al. (1117). However, no such deduction can be made for other amides (e.g., see 1117), phenols (e.g., see 411), or alcohols (e.g., see 1375 and 1150). There is much evidence in favor of cyclic dimers of carboxylic acids in the gas phase (1081), and some referring to solutions (1652 and 445). On the other hand, the IR data for liquid formic acid are more complicated. Ghapman (373) concludes that the liquid contains a mixture of cyclic dimers and chain polymers. Dielectric data have been interpreted to show that formic acid is not entirely dimeric (1046). By use of thermo-electric osmometry Davies and Thomas have measured AH of dimerization of several amides and have concluded that trichloroacetamide and A -methyltrichloroacet-amide form cyclic dimers, whereeis iV-methylaceteunide, iV-methylform-... 

Bruce and Harlow have presented additional evidence for this type of behavior. They did titrations in benzene, toluene, and gasoline. Figure 6 shows conductometric titrations in a solvent of very low dielectric constant. One of these phenols gives a conductometric curve with a very sharp peak at the point where half an equivalent of base has been added. The reason for the enhanced conductivity is that in solvents of low dielectric constant, these association complexes between the two molecules are greatly protonated. In the case ofthe other phenol, which is substituted in the 2,6- positions, this sort of association is sterically hindered. 

---