Crosslinking systems and film properties for surfactant-free latexes based on anhydride-containing polymers

In this paper, we report novel crosslinking systems for surfactant-free artificial latexes based on anhydride-containing polymers. Surfactant-free latexes with average particle diameters of about 150 nm and a ζ-potential of −70 mV have been successfully obtained from anhydride-containing polymers with various Tgs and polarities, including poly(octadecene-alt-maleic anhydride) (POMA) and maleinized polybutadiene (PBDMA). When adipic dihydrazide (ADH), a water-soluble crosslinker, was added to these latexes, no differences in particle size or ζ-potential were found; the presence of ADH did not affect the latex stability. In contrast, when 1,6-diaminohexane (DAH) was added to these latexes, it was found to interact with the polymer particles, indicated by a decrease in absolute ζ-potential for the latex particles and even gelation in the case of POMA. From 1H NMR and LC–MS studies, it has been shown that no free DAH was present after being added to the latex, while free, unreacted ADH was present in aqueous phase upon its addition to the latex. Kinetic studies revealed that irreversible imide formation between anhydride and ADH took place at temperatures of 90 °C and above. In comparison, DAH only formed imides with the copolymers at significantly higher curing temperatures, i.e. >130 °C. Furthermore, the film formation of these latexes was studied; for the different copolymer latexes, curing at temperatures above the Tg of the respective copolymers led to homogeneous film formation. These systems based on surfactant-free latexes crosslinked with ADH have displayed promising properties for future coating applications.