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On the networking mechanisms of additives‐accelerated phenol–formaldehyde polycondensates
Author(s) -
Pizzi A.,
Garcia R.,
Wang S.
Publication year - 1997
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/(sici)1097-4628(19971010)66:2<255::aid-app6>3.0.co;2-v
Subject(s) - formic acid , formaldehyde , phenol , polymer chemistry , chemistry , condensation polymer , methylamine , hydrolysis , formamide , alcohol , organic chemistry , polymer , materials science
Determination by thermomechanical analysis (TMA) of the average number of degrees of freedom of polymer segments between crosslinking nodes of phenol‐formaldehyde (PF) resin‐hardened networks indicate that additive‐accelerated PF resin polycondensations and hardening presented several different acceleration mechanisms. Some additives such as sodium carbonate appear to present purely an acceleration effect on the polycondensation reaction. Other additives such as propylene carbonate appear to present an acceleration effect by also inducing an increase in the average functionality of the system, due to alternate crosslinking reactions to which the accelerator itself does participate, leading to a tighter final network. These alternate crosslinking reactions can be of a different nature. In the propylene carbonate case, the reaction is related to a Kolbe–Schmitt reaction. In formamide, instead, it is related to its hydrolysis to formic acid and ammonia with the subsequent rapid reaction of the latter with two or more hydroxybenzyl alcohol groups of PF resols. The rapid reaction of the—NH 2 group of formamide with two hydroxybenzyl alcohol groups of PF resols, a reaction which is also characteristic of urea and methylamine, also appears likely to occur. Both liquid‐ and solid‐phase 13 C‐NMR supporting evidence of the mechanisms proposed is also presented. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 255–266, 1997