Swollen polymer-network gels usually exhibit notable spatial inhomogeneity of their crosslinking density. The effect of this inhomogeneity on the permeability of the gel to small particles is of major importance in many applications such as those in analytical separation technology. To systematically address this effect, we mimic inhomogeneous polymer-network gels by dense-packed pastes of sub-micrometer-sized microgel building blocks with two distinctly different crosslinking degrees. The diffusive mobility of rigid nanoparticle tracers within these inhomogeneous pastes that contain purposely imparted densely and loosely cross-linked local domains is studied by spatially resolved dual-focus fluorescence correlation spectroscopy on a sub-micrometer length scale. The outcome of this investigation is that the sub-micrometer-scale tracer diffusivity of the tracers is not affected by the gel-matrix crosslinking density, and hence, also not by its spatial inhomogeneity. Instead, the tracer diffusion is dominantly hindered by the high density of polymer segments in the deswollen gel matrixes.

•Polymers from secondary and tertiary amides are compared.•Thermoresponsive polyacrylamides with amide proton show cononsolvency.•Thermoresponsive polyacrylamides without amide proton do not show cononsolvency.•Tertiary poly(N-vinylcaprolactam) behaves like tertiary polyacrylamides.•Calculations reproduce the experimental results.In this comparative study we investigate the influence of the side chain substitution pattern on the volume phase transition temperature (VPTT) of thermo-sensitive polymer microgels. We especially focus on cononsolvency of water and methanol. We compare literature data for poly(N-isopropylacrylamide) (PNIPAM) that shows cononsolvency to experimental data for secondary amide poly(N-n-propylacrylamide) (PNNPAM) as well as tertiary poly(N,N-diethylacrylamide) (PDEAAM) and poly(N-vinyl-caprolactam) (PVCL). As methods we apply size determination by dynamic light scattering (DLS) as well as differential scanning calorimetry(DSC) and theoretical calculations using COSMO-RS (conductor-like screening model for real solvents). Clear differences are found for PDEAAM and PVCL in comparison to PNIPAM and PNNPAM. We ascribe the significant differences between PNIPAM and PNNPAM on the one hand and PDEAAM and PVCL on the other hand to the amide proton, which is present in PNIPAM and PNNPAM but not in the other two polymers.