## 2 Materials and Methods
### Acrylic Acid Polymerisations  
A total volume of 500 mL consisting of an acrylic acid (Alfa Aesar, 98.5%, stab. with ca. 200 ppm 4-methoxyphenol (MEHQ), \(\sim\)3% dimer content) concentration of 150 g/L in isopropyl alcohol was placed inside the reactor. The inhibitor MEHQ was not removed prior to the reactions. To remove dissolved and atmospheric oxygen inside the reactor vessel, the reaction mixture was overflowed with a mild but detectable stream of nitrogen while stirring at 200 rpm for 45 min at room temperature with an anchor stirrer (defined in Section 2.1). For the heat-flow calibration (waiting time \(t=10\) min, \(T_{\mathrm{R}}=3\) K) and the subsequent polymerisation reaction, the reactor vessel was sealed, generating an excess nitrogen pressure of 0.5 bar. The vessel was further heated up to the reaction temperature (60\(-\)75 \({}^{\circ}\)C) and the stirring speed was reduced to 70 rpm. To start the polymerisation, AIBN (0.5, 1.0 and 1.5 mol% based on acrylic acid content), suspended in 20 mL isopropanol, was injected in nitrogen countercurrent without prior degassing of the suspension. To minimise any initiator residues in the syringe and the injection port, 10 mL of pre-warmed (30\(-\)40 \({}^{\circ}\)C) and degassed (5 min) isopropanol was injected subsequently. Isothermal reaction conditions were possible by using a closed-loop control (\(P\): 2, \(I\): 999999) of the reactor jacket temperature. After 2\(-\)3 h, when no significant heat-flow could be detected by the calorimeter, the final heat-flow calibration (waiting time \(t=15\) min, \(T_{\mathrm{R}}=3\) K) was performed and the reaction mixture was cooled down. An exemplary calibration is shown in Figure 1. For later size-exclusion chromatographic analysis, a sample of the slightly viscous and colourless polyacrylic acid was taken from the reactor outlet.  
Samples were also taken via the reactor outlet to determine a pH value during the reaction. Experiments involving taking samples before the end of the reaction were not used for calorimetric analysis due to the violation of the balance. The pH value was determined in each case with the pH-meter 765 Calimatic from Knick which was calibrated with regular aqueous calibration solutions.  
The reaction heat data was integrated in Mettler Toledo's iControl to use the suggested conversational proportional baseline subtraction. The integration frame was set to a point before the addition of the initiator suspension and to the point right before the end point  
Figure 1: Automatic RC1e calibration for the determination of the heat passage term _LIA_ and the heat capacity \(c_{\mathrm{p}}\) of the reactor content. This is an example of the calibration before the reaction of 150 g/L acrylic acid in isopropanol at a reaction temperature of 70 \({}^{\circ}\)C. The left axis shows the heat flow of the calibration (\(Q_{\mathrm{C}}\)) and the reaction (\(Q_{\mathrm{R}}\)), the right axis the reactor temperature (\(T_{\mathrm{R}}\)) and the jacket temperature (\(T_{\mathrm{J}}\)).  
calibration. When choosing these points, peaks in the baseline fluctuation were avoided. The insignificant drop in reaction heat due to the temperature difference of the initiator suspension was included in the integration.  
The control experiments in aqueous media were carried out under comparable conditions. However, VA-057 was chosen in place of AIBN as an initiator. When isopropanol was employed as a CTA for the polymerisation in water, the concentration of CTA/AA = 0.16 suggested by [PERSON] et al. was used [5]. In addition, the temperature range was reduced to 40 - 55 \({}^{\circ}\)C to maintain similar reaction times.