Film Formation of Waterborne 2K Polyurethanes: Effect of Polyols Containing Different Carboxylic Acid Content

Abstract

While the interaction of NCO with carboxylic acids has been documented, a comprehensive knowledge of its effect on the film formation in a two-component waterborne polyurethane (2K-WPU) system is lacking. In this work, we synthesized a series of carboxylfunctional acrylic polyols (M n ≈ 5000 g/mol, Đ ≈ 2.7, T g ≈ 15 °C) of uniform diameter (120 nm) with varying amounts of methacrylic acid introduced into the latex. For 2K-WPU dispersions with a molar NCO/ OH ratio of 1.3:1, we monitored particle size by dynamic light scattering and NCO consumption by FTIR. In the dispersion, we found that the particle size remained nearly constant, and the NCO was almost completely consumed after 2 days. Incorporating COOH in the polyol latex accelerated the consumption of NCO. We synthesized polyol samples labeled with donor and acceptor dyes for fluorescence resonance energy transfer (FRET) studies of polymer diffusion and molecular mixing. In films formed from the polyol latex in the absence of hmPIC, the COOH content of the polyols had no significant effect on the rate or extent of polymer diffusion. In contrast, in films formed from the 2K-WPU dispersions with a stoichiometric NCO/OH ratio (1.3:1), the extent of ET rapidly increased to the maximum value, showing that the full extent of molecular mixing of the two components can be accomplished in films. Thus, the hmPIC acts as a reactive plasticizer. In parallel experiments in which the hmPIC was labeled with the donor dye, we found evidence for partial mixing of the PIC and polyol in the dispersed state. We also showed that the rate of mixing of the hmPIC and the polyol in the films cast from these dispersions was accelerated by −COOH groups in the polyol.

Amphiphilic Block-Random Copolymers: Shedding Light on Aqueous Self-Assembly Behavior

“…The quenching of emission by the acceptor fluorophore only occurs when the donor and acceptor molecules are within ∼10 nm. In polymer systems, this has commonly been used to study the mixing of polymer chains as a function of time − and evaluate the exchange dynamics of amphiphilic polymer chains between aggregates. ,, In combination with measurements from dynamic light scattering (DLS), static light scattering (SLS), and transmission electron microscopy, it is evident that BRCs in the composition range of interest self-assemble into low chain number aggregates (below 40–50 chains; an order of magnitude lower than analogous block copolymers), as opposed to self-folding into single-chain nanoparticles as previously suggested. By developing a fundamental understanding of BRC solution properties, the full potential of these materials can be reached, and their behavior in emulsion polymerization systems, where the initial morphology and exchange dynamics of polymeric stabilizers will impact nucleation mechanisms, will be more thoroughly understood.…”

Biodegradable, Stretchable and Transparent Plastic Films from Modified Waterborne Polyurethane Dispersions

“…Alternatively, in the one-component system, the crosslinker is activated during the drying process of the dispersion, after application. Waterborne PU dispersions can be used to cast polymer films with ease, however, certain technical issues such as poor miscibility or poor homogeneous distribution between the polyol and polyisocyanate can lead to poor aesthetics and appearance and even a loss of transparency [ 21 , 22 ]. In fact, a very recent review by Madbouly [ 23 ] extensively covered and discussed the important variables that control the thermomechanical properties and biodegradation aspects, as well as antimicrobial and biocompatibility performances of waterborne PU dispersions and their cast films that are developed for certain industrial and biomedical applications.…”