Location of the antiplasticizer in cross-linked epoxy resins by ²H, ¹⁵N, and ¹³C REDOR NMR

Carbon-13 rotational-echo double-resonance (REDOR) NMR with ¹⁵N or ²H dephasing, combined with ¹⁵N REDOR NMR with ¹³C dephasing, has been obtained for a fully cross-linked epoxy resin prepared from a nominally uniform mixture of two parts of diglycidyl ether of Bisphenol A, one part of hexamethylenediamine, and 19% (by weight) antiplasticizer made from a carbonyl-¹³C-labeled aromatic acetamide. The antiplasiticizer contains the hydroxypropyl ether moiety of the epoxy repeat unit. A partially cross-linked resin was formed from five parts of epoxide, one part of hexamethylene-diamine, three parts of hexylamine, and 19% (by weight) antiplasticizer. Labels were introduced into the resin by replacing both methyl groups of the isopropylidene moiety of Bisphenol A with CD₃ groups and by using [¹⁵N₂]hexamethylenediamine and [¹⁵N]hexylamine (and their unlabeled counterparts) in various combinations. The antiplasticizer ¹³C-carbonyl carbon is 4.9 ± 0.5 Å from an amine ¹⁵N (with no preference for free or cross-linked sites) and 6.7 ± 1 Å from a quaternary carbon of the isopropylidene moiety.