Cross-linking poly[(vinyl acetate)-co-N-methylolacrylamide] latex adhesive performance part I: N-methylolacrylamide (NMA) distribution

Three poly[(vinyl acetate)-co-N-methylolacrylamide] (VAc–NMA) latex adhesives were synthesized, each containing the same total amount of NMA. In each of the three co-polymerizations, the NMA was fed into the reactor according to a unique feed profile. NMA distribution in the latexes, as determined via both 13C and 15N variable temperature solution nuclear magnetic resonance (NMR) spectroscopy, differed among the three adhesives. When NMA monomer was added via injections (latex I), predominantly surface-NMA (62.7%) was detected, with significant amounts of water-phase NMA (20.8%) and core NMA (16.5%). Delayed NMA injections (latex DI) led to a very high proportion of surface NMA (82.3%) with less core (10.6%) and water-phase NMA (7.1%). A continuous feed of NMA (latex C) gave predominantly core NMA (84.7%), some surface NMA (13.4%) and very little water-phase NMA (1.9%). NMA distribution findings from 15N-NMR and 13C-NMR analyses were consistent.