Infrared study of the hydrogen bonding association in polyamides plasticized by benzenesulfonamides. Part I: Self-association in amide and sulfonamide systems; Part II: Amide-sulfonamide interaction

The molecular associations of N-(n-hexyl)hexanamide (PA-12MC) and N-(n-buty l)benzenesulfonamide (BBSA), taken as model compounds for polydodecamide (P A-12) and benzenesulfonamide plasticizers, respectively, were examined by F ourier transform infrared spectroscopy. In solution, the amide is distribut ed between a self-associated form, involving intermolecular hydrogen bondin g, and isolated species. Dissociation is favored in an electron donor solve nt due to hydrogen bonding between the amide and the solvent. Comparatively , BBSA has much less tendency to dissociate. Molecular modeling suggests th at BBSA dimer associations exist in the condensed state thanks to intermole cular hydrogen bonds, while gasphase infrared spectroscopy supports a stabi lizing intramolecular interaction between the sulfonamide proton and the su lfonyl lone pairs for isolated molecules. Mixtures of the amide model compo und with BBSA show the creation of a strong S-N-H . . .O=C hydrogen bond be tween the sulfonamide proton and the amide's carbonyl lone pairs. The amide N-H groups liberated from the former amide-amide interaction find themselv es involved in a weaker C-N-H . . .O=S hydrogen bond ("free N-H") with the plasticizer's sulfonyl lone pairs, the concentration of these bonds being m aximum at mid-composition. For polyamide/BSAs mixtures, the accessibility o f the amide and sulfonamide groups can restrict these associations. Mixture s of AAPA, an aliphatic amorphous polyamide, with a plasticizer bearing a b ranched alkyl chain, generate a low free N-H concentration and cause phase separation to occur, which confirms the steric sensibility of their interac tion. A bifunctional benzenesulfonamide plasticizer appears to be less effi cient than BBSA and leads to an increased dispersion in hydrogen bond distr ibution, both of which could be ascribed to the bulk of this molecule. Inco rporation of BBSA in semicrystalline PA-12 leads to a behavior identical to that of AAPA/BBSA mixtures.