Supramolecular functionalized polybenzoxazines from azobenzene carboxylic acid/azobenzene pyridine complexes: synthesis, surface properties, and specific interactions

Abstract

Supramolecular complex of azobenzene carboxylic acid/pyridine functionalized benzoxazine system featured significantly lower curing temperatures and maintain high water contact angles.

Corrosion Resistance of Mild Steel Coated with Phthalimide-Functionalized Polybenzoxazines

“…The uncoated MS had a hydrophilic surface with a WCA of 70 • ± 1 • , suggesting that it would readily be attacked by corrosive agents. The curing temperature had a slight influence on the WCA of the prepared coating samples, but all of the coated samples had hydrophobic surfaces (WCAs: >90 • ), which we attribute to the low surface free energies of PBZ coatings [25,[42][43][44]. Hydrophobic phthalimide-functionalized PBZ coatings have been demonstrated previously to decrease the wettability of corrosive media and provide strong barrier effects [34].…”

In(NO3)3 catalyzed curing reaction of benzoxazine

“…For B-In, the peak at 750 cm −1 corresponding to monosubstituted benzene 10 decreases, and the characteristic peak of 1,4-disubstituted benzene (820 cm −1 ) 10,30 increases with extended stirring time at 35°C, indicating that an arylamine Mannich bridge structure (structure I in Figure 4(a)) formed. Meanwhile, the characteristic peak (1660 cm −1 ) representing C=N bond 31 increases, and that of C-N-C bond (1180 cm −1 ) 30,32 decreases with prolonged stirring time. In the ring opening process, benzoxazine produces iminium-ion (C=N + ) intermediate and carbonium-ion ( + C–N) intermediate, and the structure transforms from + C–N to C=N + , 33 which was herein verified by increase in the peak intensity of the N-H bond stretching vibration (3320 cm −1 ) 10,34,35 assigned to the secondary amine.…”

“…The intensity of the peak representing 1,4-disubstituted benzene at 820 cm −1 soars, but those of the peaks representing monosubstituted benzene at 750 and 690 cm −1 plummets, suggesting that the para position of the aniline ring became the main site for cross-linking reaction. Given the disappearance of a band representing 1,2,4,6-tetrasubstituted benzene at 1484 cm −1 , 10,33 and the appearance of a band representing 1,2,4-trisubstituted benzene at 1499 cm −1 , 31 the arylamine Mannich bridge structure was the main cross-linked structure in poly B-In. In the presence of In(NO 3 ) 3 , the intensity of the band at 1174 cm −1 originating from C–N–C bond in the phenolic Mannich bridge structure greatly reduces.…”

“…33,36 –38 For BA-a (a*), the two strong signals at 5.33 and 4.58 ppm correspond to –CH 2 – groups on the oxazine ring. 10,31 Compared with the monomer, the signal of –CH 2 – groups shifts downfield after addition of In(NO 3 ) 3 . Besides the signals at 5.40 and 4.61 ppm from the oxazine ring, new small signals appear at 5.37 and 4.55 ppm, which can be attributed to the reduction of electron density of the methylene group as a result of the coordination of metal ion with dimer.…”

“…In the ring opening process, benzoxazine produces iminium-ion (C=N + ) intermediate and carbonium-ion ( + C–N) intermediate, and the structure transforms from + C–N to C=N + , 33 which was herein verified by increase in the peak intensity of the N-H bond stretching vibration (3320 cm −1 ) 10,34,35 assigned to the secondary amine. The peak intensity of C–O–C bond (1230 cm −1 ) 30 –33 drops, suggesting that the N, O-acetal-type bridge structure (structure II in Figure 3(c)) existed and gradually decreased.…”