The diacetone acrylamide crosslinking reaction and its influence on the film formation of an acrylic latex

Abstract

Waterborne colloidal polymers (i.e. latex) represent a promising alternative to organic solventbased systems in coatings applications. The development of mechanical strength and hardness is often enhanced by chemical crosslinking that creates a threedimensional network. If extensive crosslinking occurs within the particles prior to their coalescence, however, interdiffusion will be prevented. A weaker product will result. We have explored the inter-relationship between coalescence, crosslinking, and surfactant exudation in an acrylic latex containing diacetone acrylamide exploiting the ''keto-hydrazide'' crosslinking reaction. The complementary use of spectroscopic techniques on a model system determined that the crosslinking reaction yields an imine, not an enamine as has been proposed in some literature. Gel fraction measurements were used to probe the rate and amount of crosslinking and identified a slower rate in larger particles, suggesting that the transport of crosslinking agent is rate-limiting. The keto-hydrazide reaction was found to be acid catalyzed and favored at lower water concentration. Measurement of the latex pH relative to the polymer mass fraction during film formation clarified the expected point of onset for crosslinking in relation to particle packing. Atomic force microscopy was used to follow surface leveling relative to the competing influence of crosslinking. The rate and total amount of surfactant exudation were found to be influenced by crosslinking, particle deformability (as determined by the temperature relative to the polymer glass transition temperature), and the evaporation rate (as controlled by the relative humidity). There is evidence that surfactant exudation can be triggered by the particle deformation that occurs at film formation temperatures well above the glass transition temperature.

In-Situ AFM and EIS Study of Waterborne Acrylic Latex Coatings for Corrosion Protection of Carbon Steel

“…51 The SALC coating has a Tg similar to that of the SALL coating, however, because of the crosslinking system in the SALC coating, the film cohesion could be achieved after inter-particle crosslinking, which generates more cohesion even in the absence of entanglements and interdiffusion. 36,41 As reported in literature, optimal crosslinking leads to good tensile strength, dispersibility and compatibility of the coating, and enhanced barrier protection performance. 40,41,52,53 …”

“…A high Tg favors the formation of homogenous films through close particles packing, as long as an appropriate polymer interdiffusion is achieved during the film formation process. 14,16,36 For the SALH coating, the high Tg seems to be beneficial for achieving a compact and homogenous microstructure, hence the stability of the coating, even though it is not as good as the SALC coating. SALL coating.-The AFM images of the SALL coating show that the coating surface is relatively rough as compared to the SALC and SALH coatings.…”

Characterization of Molecular Structure of Emulsion Acrylic Microgels: Exploring the Impact of Molar Mass on Coating Properties of Self-Cross-Linkable Latexes

“…1. By introducing the self-crosslinkable chemistry in emulsion polymers, the physical and chemical integrity of latex films is enhanced, while the film formation process may be complicated [22]. In order to possess increased final coating properties, a balance between chemical crosslinking and polymer chain mobility resulting in sufficient inter-diffusion and entanglement of polymer chains during the particle coalescence stage has to be maintained [23,24,25].…”

Studies on the ambient temperature crosslinking of latex films based on natural rubber grafted with poly(diacetone acrylamide) using DMTA

“…The crosslinking reaction in this system occurs preferentially after the loss of water during drying [7][8][9]. Diacetone acrylamide (DAAM) has generally been the monomer of choice for providing ketone pendant groups in acrylic latexes, since the ketone carbonyl of DAAM reacts rapidly with hydrazide at ambient temperatures [10,11].…”

“…Adipic acid dihydrazide (ADH) is one of the most widely used difunctional crosslinkers in this system. The coupling reaction between a ketone group and a hydrazide is termed the keto-hydrazide reaction, and the resulting product is an imine (-C=N-) [7].…”