On the Thermoresponsivity and Scalability of N,N‐Dimethylacrylamide Modified NIPAM Microgels

Abstract

AbstractVarious thermoresponsive copolymer microgels based on N‐isopropylacrylamide (NIPAM) and N,N‐dimethylacrylamide (DMAAm) are prepared using either precipitation polymerization (PP) or inverse emulsion polymerization (IEP). The comparison of the volume phase transition temperature (VPTT) for PNIPAMn‐co‐PDMAAmm copolymer microgels prepared by PP or IEP reveals significant differences. Empirically, PP leads to lower VPTTs than IEP for identical monomer composition, whereby the observed difference in the VPTT becomes greater the higher the DMAAm content of the monomer mixture is. Presumably this is because IEP confers a higher homogeneity of the crosslinking and polymer segmental density within the microgel particles, resulting in a linear correlation of the VPTT as a function of DMAAm. Further, the scalability of an IEP process for the synthesis of NIPAM0.86‐co‐PDMAAm0.14 containing 14% DMAAm is studied, since these microgels exhibit a VPTT in the targeted range of 37.5–38.5 °C. The study reveals that the temperature increase due to insufficient dissipation of the heat of polymerization in a batch IEP process on a larger scale affects the VPTT, leading to microgels with a VPTT of about 35.5 °C. By contrast, when conducted as semibatch IEP process with more efficient heat removal, particles with a VPTT of 38.4 °C are obtained also on larger scale.