Investigating the Effectiveness of Reactive Dispersants in Non‐Aqueous Dispersion Polymerization

Abstract

Non‐aqueous dispersion (NAD) radical polymerization is used to produce poly(acrylic) nanoparticles (<200 nm) at 60 wt% solids content by a starved‐feed semibatch process, with steric stabilization provided by a low molecular weight vinyl‐functionalized polymeric dispersant. The performance of a vinyl‐terminated BMA macromer is compared to that of a butyl methacrylate (BMA) based grafted dispersant with vinyl groups attached at random positions along the backbone. The macromer dispersant is incorporated more effectively than the randomly grafted dispersant, a result attributed to the uniform distribution of reactive double bonds across the entire dispersant molar mass distribution, although the effectiveness of the macromer dispersant decreases when methacrylates are components of the NAD recipe.

The influence of adding functionality to dispersant and particle core compositions in non-aqueous dispersion polymerization

“…[10] In contrast, MMD of the soluble polymer recovered from the dispersion produced with macromer exactly overlayed that of the initial dispersant material: with exactly one terminal double bond per chain, all macromer chains are equally likely to react, independent of chain length. [9] While the utilization of macromer as dispersant improved the NAD system (decreased particle size, with a greater fraction of the dispersant attached or adsorbed to the particles), its level of incorporation was found to be dependent on the composition of the core polymer being produced. Specifically, homopolymer particles produced using methyl acrylate (MA) were significantly smaller than copolymer nanoparticles of MA with methyl methacrylate (MMA) due to the difference in reactivity of a macromer terminal vinyl group with methacrylate and acrylate radicals [9]; while the macromer terminal double bond readily adds to acrylate radicals, it predominantly undergoes a β-scission chain transfer reaction with methacrylate radicals.…”

“…However, higher dispersant levels (~50% relative to monomer) are generally applied in the industrial process to produce dispersions with high solids content (> 50 wt%) and nanosized particles. [1], [2] Our previous work [9] showed that a poly(butyl methacrylate) macromer dispersant was more efficient than a vinyl poly(butyl methacrylate-co-methacrylic acid-glycidyl methacrylate) grafted dispersant. The latter was produced by attaching the vinyl functionality of glycidyl methacrylate (GMA) by reaction of the epoxy group with the carboxyl group of methacrylic acid (MAA) groups randomly incorporated in a copolymer consisting of predominantly butyl methacrylate (BMA) units, following a procedure reported in the patent literature.…”

“…[1] Although the two dispersants were of similar chain length (number average molar mass (M n ) of 5 000-6 000 Da) and had similar vinyl content, the macromer dispersant was incorporated into the methacrylate/acrylate copolymer NAD product at a higher level, leading to a reduction of particle size. [9] The lowered efficiency of the grafted dispersant can be attributed to the stochastic distribution of the vinyl functionality among the polymer chains, as demonstrated by comparing the molar mass distribution (MMD) of the soluble polymer recovered from the dispersion to that of the initial dispersant, combined with NMR analysis: the shorter chains were unfunctionalized and ineffective as dispersant, while the chains of longer length containing multiple vinyl groups became attached to the particles. This uneven distribution of functionality was in accord with simulations of the radical polymerization process used to synthesize the grafted dispersant.…”

Special Issue: Innovative Processes and Enabling Technologies

“…Non‐aqueous dispersions are produced commercially yet the structure and dispersity of the stabilizing agent has been shown to play a critical role in control of the particle characteristics . As with above, a key here is to minimize any ungrafted stabilizer free to diffuse post film formation.…”

Process‐Guided Product Design of Hybrid Polymer Materials

“…Hutchinson and Yang investigate the efficiency of reactive dispersants in the non‐aqueous dispersion polymerization of (meth) acrylates. The resulting dispersions are a key component of solvent borne automotive coating formulations.…”