From Batch to Continuous Precipitation Polymerization of Thermoresponsive Microgels

Abstract

Microgels are commonly synthesized in batch experiments, yielding quantities sufficient to perform characterization experiments for physical property studies. With increasing attention on the application potential of microgels, little attention is yet paid to the questions (a) whether they can be produced continuously on a larger scale, (b) whether synthesis routes can be easily transferred from batch to continuous synthesis, and (c) whether their properties can be precisely controlled as a function of synthesis parameters under continuous flow reaction conditions. We present a new continuous synthesis process of two typical but different microgel systems. Their size, size distribution, and temperature-responsive behavior are compared in depth to those of microgels synthesized using batch processes, and the influence of premixing and surfactant is also investigated. For the surfactant-free poly( N-vinylcaprolactam) and poly( N-isopropylacrylamide) systems, microgels are systematically smaller, while the actual size is depending on the premixing of the reaction solutions. However, by the use of a surfactant, the size difference between batch and continuous preparation diminishes, resulting in equal-sized microgels. Temperature-induced swelling-deswelling of microgels synthesized under continuous flow conditions was similar to that of their analogues synthesized using the batch polymerization process. Additionally, investigation of the internal microgel structure using static light scattering showed no significant changes between microgels prepared under batch and continuous conditions. The work encourages synthesis concepts of sequential chemical conditions in continuous flow reactors to prepare precisely tuned new microgel systems.

Inner structure and dynamics of microgels with low and medium crosslinker content prepared via surfactant-free precipitation polymerization and continuous monomer feeding approach

“…Recent publications focused on studies of the microgel properties by means of optical microscopy or light scattering to prove the homogeneous crosslinker distribution in PNIPAM microgels. [24][25][26] Such approaches do not give direct access to the internal structure and crosslinker distribution inside of the microgel. Neutron scattering methods can provide insight into the internal structure.…”

Synthesis of cross-linked poly(acrylic acid) nanogels in an aqueous environment using precipitation polymerization: unusually high volume change

“…The precipitation polymerization process, used in the synthesis of other smart polymers [48], was selected by us to obtain poly(AA-BIS) nanogels in aqueous media (scheme 1). AA and BIS were dissolved in 50 ml of deionized water and placed in a flask equipped with a reflux condenser, an inlet- and an outlet of argon and a magnetic stirrer.…”

Acrylamide precipitation polymerization in a continuous flow reactor: an in situ FTIR study reveals kinetics

“…6 a, b). An increased polydispersity in comparison to batch conditions is a common observation in continuous flow experiments, due to a lack of mixing [40]. To quantify the polydispersity of the microgels in their native state, we performed SLS experiments with the purified microgels after a residence time of 60 min in the collapsed state (Fig.…”

“…The idea of a continuous production of thermoresponsive microgels has gained popularity, due to the great potential concerning production scale-up, screening and in situ monitoring [39]. Recent work shows that a continuous flow synthesis is a suitable method to synthesize thermoresponsive microgels and points out that mixing is of great importance for narrow particle size distributions [40]. In this context, mixing inside continuous flow reactors is very challenging, as static mixers not only lead to fluid mixing, but also tend to promote fouling, coalescence, or clogging when polymer films form onto the surface.…”