Thermoresponsive polymers bear a large potential for drug delivery applications, however, the influence of small molecules on the phase transition is a critical issue. Our work investigates the effects of different additives such as benzene derivatives, employed as model drugs, on the phase transition behaviour of crosslinked Poly(N-isopropylacrylamide)/N,N′-methylenebisacrylamide (PNiPAM/BIS) microgels. While the homopolymer PNiPAM has already been studied earlier in the presence of various aromatic additives, in the present work the influence of a selection of additives (dihydroxybenzenes, dihydroxybenzaldehydes) on the VPTT of PNiPAM microgels is determined. NMR Spectroscopy, Differential Scanning Calorimetry (DSC), Isothermal Titration Calorimetry (ITC) and Dynamic Light Scattering (DLS) are employed to determine the characteristic Volume Phase Transition Temperature (VPTT), transition widths and critical transition-inhibiting concentrations of additives. All additives investigated induce a shift of the VPTT to lower temperatures, consistently observed in all temperature-dependent characteristic parameters. It is observed that some microgel architectures are more sensitive towards aromatic cosolutes, as the VPTT shift depends on crosslinking density. Furthermore, as a result from temperature dependent 1H-NMR spectra, this work proofs the existence of an incorporated additive fraction at T &gt; VPTT. A quantification of the incorporated additive fraction is achieved. By investigation of the transverse spin relaxation rates R2 of the aldehyde protons, additive molecular dynamics below and above the collapse temperature of the microgels are clarified.

Influence of aromatic additives on the phase transition behaviour of thermoresponsive Poly(N-isopropylacrylamide) microgels with different cross-linker densities

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.