## 3 Results and Discussion
### Effects on Molecular Weight  
Since the polymerisation of AA was carried out in a chain-transferring solvent, it is to be expected that polymers with low molecular weights were produced. At the end of each of the performed reactions, a sample was taken from the reactor outlet and analysed via size exclusion chromatography (SEC). In addition, polymerisations in water with the addition of 2-propanol (IPA/AA = 0.16) as a chain-transferring agent (CTA) were carried out for comparison purposes. A reaction in pure water (without CTA) was also meant to serve as a further comparison, but under comparable conditions a highly viscous reaction mass was produced in the batch reactor. Because of this, neither the stirrer could ensure reliable mixing, nor could the Raman spectra provide trustworthy spectra, since the measurements could only show one spot in an unevenly mixed medium. Comparative literature data from AA polymerisation in water or in water with the addition of a CTA were used but these were mostly carried out in a continuous or semi-batch process with different initiators and concentrations. Moreover, in contrast to the literature, here the molecular weight was considered after close to complete conversion for the most part. Figure 11: Comparison of reaction conversion curves of acrylic acid polymerisations in isopropyl alcohol (150 g/L, 1.0 mol% AIBN) acquired from Raman spectroscopy (solid lines) and reaction calorimetry (dashed lines). In the following Figure 12, first the influence of the initiator concentration, as well as the solvent on the molecular weight is shown. First, it is shown in Figure 12a that the number-average molecular weight is relatively low at 1.5 \(\times\) 104 g/mol. No effect of initiator concentration was observed here for different initiator concentrations of 0.5, 1.0 and 1.5 mol% of the AIBN. The right part of the figure shows the corresponding molar mass distribution. The reaction in pure isopropanol led to a distribution with an average PDI of 1.64 \(\pm\) 0.05 (1.67 in Figure 12b). This is compared to different solvents under similar reaction conditions. The polymerisation in water with the addition of isopropanol as the CTA (IPA/AA = 0.16) is not much broader with an average PDI of 2.06 \(\pm\) 0.31 (1.77 in Figure 12b), but the molecular weight is 25 times higher (\(M_{\rm n}\) = 3.8 \(\times\) 105 g/mol) than the molecular weight of the polymers made in pure isopropanol. The molar mass distribution of the reaction in pure water could not be directly compared with the other results here, as it did not show a completely unimodal distribution. Additionally, the observations during the reaction and sample preparation indicated a very high gel fraction, which presumably was adhered to the guard column during the SEC measurement due to reduced solubility in the eluent. In the literature, values for \(M_{\rm n}\) range up to 2 \(\times\) 106 g/mol during AA polymerisation in water [10]. Figure 13 shows the effect of temperature and initial monomer concentration on molecular weight. Figure 12: (**a**) Influence of different AIBN initiator concentrations on the weight and number average of molecular weight during polymerisation of acrylic acid in 2-propanol (150 g/L, 65 \({}^{\circ}\)C). (**b**) Molar mass distribution during polymerisation of acrylic acid in pure isopropanol, water with isopropanol as the CTA (IPA/AA = 0.16) and pure water at 0.5 mol% initiator, respectively. Molecular weights were determined after a conversion of about 95%. Figure 13: (**a**) Effect of temperature on the number- and weight-average molecular weight during the polymerisation of acrylic acid in 2-propanol (150 g/L, 1 mol% AIBN). (**b**) Corresponding influence of the initial monomer concentration at a constant reaction temperature of 65 \({}^{\circ}\)C. Molecular weights were determined after a conversion of about 95%. In both graphs an expected linear dependence can be observed.