Dipole moment characterization of phenol–, o‐cresol–, and p‐cresol–formaldehyde resins

Dipole moments and their temperature dependence have been measured in p ‐dioxane for fractionated novolac phenol–, o ‐cresol–, and p ‐cresol–formaldehyde polymers. The phenol–formaldehyde fractions covered a molecular weight range of 200 to 6100, and the limiting dipole moment ratio 〈μ 2 〉/ xm 2 is 1.48. The p ‐cresol–formaldehyde dipole‐moment ratio at a DP of 4 is 2.47, whereas the phenol–formaldehyde dipole‐moment ratio is 1.40. That for o ‐cresol–formaldehyde is intermediate in value. The dipole‐moment temperature coefficients are positive for p ‐cresol chains and negative for the phenol–formaldehyde chains. These results indicate that the hydroxyl groups along the p ‐cresol–formaldehyde polymer are highly ordered, with the aromatic rings closer to the sterically hindered planar position than in the phenol–formaldehyde polymers.