Preparation of phenol-formaldehyde resins with different structures and the effect of molecular structure on the solution properties

Pheno-formaldehyde resins with different structures (NR 76, NR 88 and NR 97 : the numbers are ortho ratios) were prepared by using HCl and Zinc acetat e as catalysts. The acetylated resins (Ac 76, Ac 88 and Ac 97) were also pr epared, The relative contents of ortho-ortho' (o-o'), ortho-para' (o-p') an d para-para' (p-p') methylene linkages were determined by C-13 NMR. "Ortho ratio" was used to characterize resin structures, which means the relative reactivity of ortho position in phenolic nuclei. For solutions of NR 97 in THF at 25 degreesC, the exponent a in MHS equation and the solvation number were smaller than those of NR 76 and NR 88. On the other hand, the exponen t a in MI-IS equation of Ac 97 was slightly larger than those of Ac 76 and Ac 88. NR 97 had higher content of o-o' methylene linkages so that the hydr ogen bonding was stronger. The conformation of NR 97 in solution was more c ompact due to both branches and the hydrogen bonds between o-o' methylene l inked phenolic hydroxyl groups. Without the hydrogen bond, the conformation of Ac 97 was dependent on the molecular skeleton of high-ortho type and it was likely to expand in solution.