•Zero-VOC colloidal unimolecular polymer particles with sulfonate groups on the surface were prepared.•Unlike carboxylate functional CUPs, the sulfonate functional CUPs are stable in water containing 50 ppm calcium ions.•These CUP systems catalyzed the crosslinking of hydroxyl and carboxyl functional acrylics with melamine resin.•Commercial catalyst leached out of the crosslinked acrylic-melamine film but the CUP catalyst did not.Colloidal unimolecular polymer particles (CUPs) based on poly(methyl methacrylate-co-2-acrylamido-2-methylpropane sulfonic acid) were synthesized and characterized and its potential for use as a blocked acid catalyst for curing of acrylic-melamine based resin systems were evaluated. These CUPs were synthesized by the process of water reduction of acrylic copolymers and had zero volatile organic content (VOC). The curing performance of CUPs was evaluated by way of pencil hardness, micro-indentation hardness and solvent resistance measurements. These sulfonic acid containing CUPs catalyzed the curing of acrylic-melamine systems effectively and were found to provide final resin properties comparable to the commercially used blocked acid catalysts. On a molar equivalent basis, the amount of CUP catalyst required for the final cured film properties was lower than the commercial blocked acid catalyst. NMR analysis confirmed that the commercial acid catalyst leached out of the cured film when exposed to water for 24 h while the CUP catalyzed coating did not.

Cationic colloidal unimolecular polymer (CUP) particles were prepared by using a lower concentration of the quaternary ammonium functional copolymers during the process of water reduction. True nanoscale (diameter 3–9 nm), zero-volatile organic content (VOC), spheroidal CUP particles, and self-stabilized via electro-repulsion of surface cationic groups were obtained. The viscosity of the cationic CUP systems was influenced by the electroviscous effects arising from the surface charge and the associated surface water layer. The density of surface water was 1.6 % greater than the bulk water density which was attributed to the structuring of water around charged quaternary ammonium groups. The equilibrium surface tension values decreased linearly with increasing concentration and surface charge density of CUP particles due to a greater reduction in surface energy. The rate of surface tension reduction determined by maximum bubble pressure method decreased with increasing concentration and the molecular weight of the CUP due to diffusion effects.

The formation of colloidal unimolecular polymer (CUP) particles from single polymer strands was investigated as a function of molecular weight. The CUP particle size was correlated with the absolute molecular weight and its distribution. The characteristics of the particles were evaluated with respect to viscosity, acid number, size distribution, and stability. The particle size varied from less than 3 nm to above 8 nm representing polymers with molecular weight in the range of 3000–153,000. Lower molecular weight polymers were found to be unstable. Particle size measurements using dynamic light scattering technique indicated a normal distribution which corresponded to the molecular weight distribution of the copolymer. The statistical distribution of the acid groups in the polymer chains played a significant role in the stability of low molecular weight polymers.

Colloidal Unimolecular Polymer, CUP, particles were synthesized and characterized as a potential new and useful spheroidal polymer conformation for a variety of applications. Also known as single chain nanoparticles, these nanomaterials are gaining in popularity. The route to CUP particle formation is an innovative approach utilizing a small number of hydrophilic groups along a hydrophobic polymer backbone which transitions from a random coil conformation in organic solvent to a hard sphere in water through a slow gradient with subsequent solvent removal. The CUP particles have diameters which are proportional to their molecular weights and range typically from 3 nm to over 9 nm. These CUP particles were stable in water and free of solvent or surfactants. The sodium or potassium salts of CUP particles are spheroidal and are able to be dried then re-dissolved in water with no aggregation, unlike the original polymer. The diameters of the CUP particles correlate with the absolute number average molecular weight (Mn) and distributions from the GPC. Molecular weights from 28K to 122K are reported here and are based on an acrylic copolymer having a molar ratio of 9:1 MMA:MAA.

Polymers were synthesized with a 1:7 or 1:8 ratio of acrylic acid to acrylate monomers to produce an acid-rich resin. The polymers were water-reduced and solvent-stripped to produce colloidal unimolecular polymers (CUPs). These particles are typically 3–9 nm in diameter, depending upon the molecular weight, and have different rheological behavior from micelles, polyelectrolytes, fullerenes, and latex particles, due to their charged surface and large surface areas. They were then formulated into ambient cure clearcoatings with aziridine crosslinking. These aziridine-cured acrylic CUPs were either solvent-free or very low VOC. The coatings were evaluated for their MEK resistance, adhesion, hardness, gloss, flexibility, wet adhesion, and abrasion and impact resistance properties.

The rheological characteristics of anionic colloidal unimolecular polymer (CUP) particles in water were investigated. The intrinsic viscosities were determined for CUPs with different molecular weights as a function of volume fraction. The specific viscosities were measured and fit with models considering hydrodynamic interaction and electroviscous effects. The rheological characteristics were consistent with a surface layer of water which increases with the particle size or molecular weight of CUPs. The effective charges on the surface of particle were calculated and correlated with the rheological behavior of the CUP particles from the dilute to semidilute range, a volume fraction of 0.0001–0.08.

The gel point of a colloidal unimolecular polymer (CUP) aqueous suspension was determined. The zero-shear viscosities of suspensions were measured by capillary viscometer and cone-and-plate rheometer. The relative viscosities were fit to the Krieger-Dougherty equation \( {\upeta}_{\mathrm{r}}={\left[1-\frac{\phi }{\phi_{\max }}\right]}^{-\left[\upeta \right]{\phi}_{\max }} \) to determine the maximum packing volume fraction ϕmax. The gel point was found to be much lower than the anticipated random close packing (~0.63) or hexagonal packing (~0.74). The gel point was attributed to the effect of surface water, and subsequently the thickness and density of water layer were calculated. The CUP results were compared with the rheological behavior of commercial waterborne suspension with particle size 25 and 77 nm. The packing volume fraction of colloids with different particle sizes was predicted considering the effect of surface water.