# Smart Poly(acrylic acid)/Poly(acrylamide) Microgels with Interpenetrating Polymer Network Structure
## 2 Materials and Methods
### Methods  
#### 2.2.1 IPN MG Synthesis  
IPN MGs were synthesized via a sequential approach in an inverse miniemulsion (Scheme S2, Supplementary Materials) consisting of 81 wt. % cyclohexane as a continuous phase, 13 wt. % AOT-Brij 35 (2:1 ratio) as surfactant, and 6 wt. % aqueous phase containing both monomers AA and AAM in different volume ratios for the preparation of IPN MGswith different compositions (Table 1). In a typical experiment, a two-neck round bottom flask was charged with the whole amount of the solvent (cyclohexane) and the mixed surfactant and stirred with a magnetic stirrer (750 rpm) at 25 \({}^{\circ}\)C for 60 min. To this solution, the desired volume of AA aqueous solution was added under constant stirring at 750 rpm, and the reaction mixture was homogenized by Ultra-Turrax, IKA, Wilmington, NC, at 24,000 rpm for 5 min. The AA aqueous solution contained 10 wt. % monomer, 0.5 mol. % initiator K\({}_{2}\)S\({}_{2}\)O\({}_{8}\), and 4 mol. % crosslinking agent MBAA, with both the initiator and crosslinking agent concentrations being calculated related to the monomer (AA). After the homogenization, the AA crosslinking polymerization was performed by keeping the reaction vessel at 60 \({}^{\circ}\)C for 2.5 h.  
The next stage of the IPNs' synthesis started with the addition of the desired volume of AAM solution to the reaction vessel at room temperature. AAM aqueous solution contained 10 mol. % AAM as monomer, 0.5 mol % initiator K\({}_{2}\)S\({}_{2}\)O\({}_{8}\), and 0.1 mol % crosslinking agent MBAA, and both the initiator and crosslinking agent concentrations were calculated in relation to the AAM amount. After homogenization, the vessel was immersed in 60 \({}^{\circ}\)C water bath for 2.5 h to carry out the AAM crosslinking polymerization in situ in the PAA nanogels. The described procedure resulted in the formation of PAA/PAAM IPN MGs. By varying the volume of the aqueous solutions of both monomers AA and AAM, keeping the total aqueous phase content at 6 wt. %, IPN MGs with different PAA to PAAM weight ratios were obtained (Table 1).  
This procedure was adapted from [19] but modified in three ways: (i) PAA was synthesized at the first stage here instead of PAAM, as performed by [PERSON] et al. [19]; (ii) we used a \(\sim\)40 times higher concentration of the crosslinking agent for the 1 st network (PAA) as compared to the 2 nd network (PAAM); and (ii) Brij 35 was used instead of Brij 30.  
Using only the 1 st stage of the procedure described above, MGs from PAA and PAAM homopolymers were prepared for the sake of comparison.  
In the next step, the formed MGs were purified to remove the cyclohexane phase. For this purpose, a rotary vacuum evaporator (Laborota 4000, Heidolph Instruments GmbH & Co. KG, Schwabach, Germany) was used at 40 \({}^{\circ}\)C and a reduced pressure of 235 mbar. The solvent evaporation was followed by washing the microgels from the surfactant with 25 mL of absolute ethanol and centrifugation at 4000 rpm for 60 min (Centrifuge 5804, Eppendorf, Hamburg, Germany). The washing procedure was repeated five times. Thus, the obtained polymer microgels were resuspended in water and the solution was placed in a dialysis membrane with a cut off of 12 kDa against Millipore water, changing with fresh water twice a day in order to remove the unreacted reagents (followed by UV). The IPN MGs were then freeze-dried and used for further investigations.