# Smart Poly(acrylic acid)/Poly(acrylamide) Microgels with Interpenetrating Polymer Network Structure
## 3 Results
### Asymmetrical Flow Field-Flow Fractionation (AF4)  
AF4 measurements were carried out using Light Scattering Detection to determine the average molar masses and sizes of the particles in pure water at pH-7. Depending on the composition of the MG, these molecular parameters of the IPNs changed (see Table 2). IPN MGs with a low amount of PAA (PC25) possess properties similar to those of the neat PAA particles (PC100). As the PAAM content increased, the particles became progressively smaller and more spherical. In the case of PC50, the highest dispersity can be observed. The detector signals (RI and LS, see Figure 10A) of the AF4 measurements show multimodality. Obviously, there was a second fraction of non-crosslinked polymers with significantly lower molar masses and another conformation than the main particle fraction.  
PC75 shows a very high void peak that can be assigned to very large particles or agglomerated structures that are not well separated. By optimizing the AF4 parameters (method B, see Section 2), a separation of IPN particles from large agglomerates is possible (see Figure 10B) and the average molar mass and radii can be determined. Nevertheless, overloading and slight co-elution was observed. PC100 particles were significantly larger and possessed higher molar masses than the other samples (Figure S4, Supplementary Materials). The size increase was previously revealed by batch DLS with increasing pH.  
AF4-LS was used to determine both the averages of the hydrodynamic radius and the radius of gyration. The absolute \(\mathrm{R_{h}}\) values increased with increasing PAA content in the IPN MGs. The ratio \(\mathrm{\rho=R_{g}/R_{h}}\) delivers information about the molecular conformation (see Table 2). Most of the MGs had a very compact, spherical shape close to a hard sphere (theoretical value \(\mathrm{\rho=0.778}\)); meanwhile, the homopolymer MGs (PC100 and PC0) possessed a more open and heterogeneous shape, as typical for polymer coils [27].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Sample**} & **dn/dc** & **M\({}_{\mathrm{w}}\)** & **D** & **R\({}_{\mathrm{g}}\)** & **R\({}_{\mathrm{h}}\)** & \(\mathrm{\rho}\) \\  & **(mL/g)** & **(kg/mol)** & **(M\({}_{\mathrm{w}}\)/M\({}_{\mathrm{n}}\))** & **(nm)** & **(nm)** & **(R\({}_{\mathrm{g}}\)/R\({}_{\mathrm{h}}\))** \\ \hline PC0 & 0.142 & 48,700 & 1.02 & 261 & 168 & 1.55 \\ \hline PC25 & 0.140 & 50,900 & 1.02 & 289 & 203 & 1.42 \\ \hline PC33 & 0.136 & 6940 & 3.47 & 198 & 280 & 0.71 \\ \hline PC50 & 0.132 & 7560 & 3.37 & 233 & 294 & 0.79 \\ \hline PC66 & 0.129 & 7530 & 1.33 & 175 & 272 & 0.64 \\ \hline PC75 * & 0.128 & 15,900 & 1.42 & 421 & 244 & 1.73 \\ \hline PC100 & 0.126 & 503,000 & 4.51 & 400 & 243 & 1.65 \\ \hline \end{tabular}
*fraction without void peak, ** calculated by [PERSON] plot (2 nd order).  
\end{table}
Table 2: dn/dc values and AF4-LS results for IPN MGs.  
Figure 9: Hydrodynamic radius (\(\mathrm{R_{h}}\)) temperature dependence at pH-5, as revealed by DOSY (**A**) and DLS (**B**) for sample PC66.  
These findings are in line with the strong complexation described above between PAA and PAAM when they are in stoichiometric 1:1 ratio. The IPN MGs with a composition close to this ratio have the most compact structure, as revealed by the \(\rm{R_{g}/R_{h}}\) value (Table 2). Thus, AF4 results confirm that the IPN MGs' composition strongly influences their structure and properties.