Design of Acrylic Dispersants for Nonaqueous Dispersion Polymerization: The Importance of Thermodynamics

Abstract

Poly(acrylic) nanoparticles produced by nonaqueous dispersion (NAD) radical polymerization are important components in many automotive coating formulations. A series of experiments show that the properties of final dispersions (particle size distribution, viscosity, and stability) correlate to the thermodynamics of the NAD system, as characterized by solubility parameters and solubility distances among the continuous phase, the soluble polymeric dispersant, and the polymer particles. The insights gained have enabled the design of a macromonomer dispersant containing greater than 10 mol% 2‐hydroxyethyl methacrylate, a necessary functional comonomer addition for end‐use properties. Stable NAD products were synthesized by changing the principal component of the dispersant from butyl methacrylate to 2‐ethylhexyl methacrylate.

Synthesis and Utilization of Low Dispersity Acrylic Macromonomer as Dispersant for Nonaqueous Dispersion Polymerization

“…In addition, both macromonomers dissolve completely up to concentrations of In previous studies, a 4 h continuous feed of initiator, monomers, and dispersant solution into a 1 L reactor held at constant temperature was used to mimic the industrial process. 9 In this study, because of the small amount of low-Đ P(BMA) macromonomer synthesized, the process was scaled down to a 25 mL Schlenk tube. As well as mixing differences (impeller vs magnetic stir bar), the continuous feed was replaced by the addition of the feed in three aliquots (see Experimental Section).…”

“…The semibatch NAD procedures used in this work are adapted from those used in the previous study, , scaled to a 25 mL Schlenk tube. The initial reaction solution was prepared by dissolving P­(BMA) macromonomer (1.923 g) in a mixture of heptane (3.253 g) and mixed xylenes (1.282 g) in a 20 mL vial.…”

“…Samples were diluted in a 50/50 v/v solvent mixture of heptane and p-xylene, with the refractive index (1.444) and viscosity (0.5000 cPs) of the binary solvent mixture calculated as reported previously. 9 The weight fraction of incorporated dispersant in the NAD (W inc ) was determined by a procedure in which 2 g of NAD dispersion was added to 3.4 g of heptane and centrifuged at 6000 rpm for 10 min to separate the phases into a clear upper phase and a particle-rich denser phase. The two layers were separated, with SEC used to determine M n and Đ of the polymeric particles in the dense phase after drying.…”

“…Alternatively, macromonomer with terminal vinyl groups can be synthesized by catalytic chain transfer polymerization (CCTP), according to the mechanism in Scheme . In dispersion polymerization, the stabilization ability of the steric dispersant is affected not only by its relative affinity for the particle and continuous phases but also by the placement of the reactive functionality, as this controls the anchoring of the chains to the particle and thus the length of the dispersant chain segments that extend from the particle surface into the medium. Because of the stochastic nature of radical copolymerization in the synthesis of grafted dispersant, a significant fraction of polymer chains contain no functionality, while other chains contain multiple functional groups .…”

Modeling the Synthesis of Butyl Methacrylate Macromonomer by Sequential ATRP‐CCTP

“…In catalytic chain transfer polymerization (CCTP), a small amount of cobalt chain transfer (CCT) agent is added to radical polymerization to produce polymers containing unsaturated end groups with the so‐called macromonomer used for further post‐reaction . As the chains are produced continuously during the reaction by decomposition of a thermal initiator, the macromonomers synthesized by CCTP chemistry have a dispersity (Ð) close to 2 …”