## 3 Results and Discussion
It indicates that fractions with significantly higher molecular weights are present in the samples and not all polymer chains were growing with the same rate but also termination processes can be responsible for the presence of polymer chains with high molecular weight in the polymerization system. Application of smaller amounts of the catalyst system (higher molar ratio of monomer to initiator) does not allow to obtain polymers with narrow MWDs. This drawback is probably connected with a partial deactivation of the catalyst system as a result of complex formation between the polymer amide groups and the copper salt. Such a complex exhibits a low catalytic activity. [PERSON] et al. proposed the formation of such a complex as the reason for the observed difficulties in ATRP of several acrylamides [26], [PERSON] made the same suggestion for ATRP of N,N-dimethylacrylamide [27]. To study the kinetics of the process of NIPAM's polymerization, the monomer concentration was monitored using gas chromatography (GC) in short time intervals for 7 hours. Figure 3 shows the first-order kinetic plot and NIPAM's conversion vs. time of polymerization. It is clearly visible that, during the first 2 hours, this process is very fast, and the first-order kinetic plot shows significant curvature. However, after 2 hours, the polymerization slows down and during the next 4 hours the relationship is almost linear with relatively good correlation coefficient (\(R^{2}\) = 0.96). In whole range of the polymerization time relationship, conversion vs. time can be described by an exponential function with a very good correlation coefficient (\(R^{2}\) = 0.99). In view of the obtained results it seems that the polymerization rate at the first period of the reaction should be slowed down. Probably decreasing of temperature and concentration of monomer should allow to achieve a linear kinetic in whole range of the polymerization time. Figure 2: The molecular weight distribution curves from Size-Exclusion Chromatography (SEC) analyses for the prepared PNIPAMs (descriptions of the samples P1–P6 and polymerization conditions are given in Table 1). Figure 4 shows the dependence of the number-averaged molecular weight (\(M_{\rm n}\)) and polydispersity, determined from the SEC analyses, on the monomer's conversion. The linear relationship between \(M_{\rm n}\) and conversion is fairly good (\(R^{2}\) = 0.97) and the PDI values are below 1.2 in the whole analyzed range of monomer conversions (from 30% to 90%). This indicates that the contribution of termination reactions is significantly diminished, even for high conversions. The DSC and DLS corroborated that all prepared homopolymers clearly exhibit thermosensitivity with explicit LCST in their aqueous solutions. The critical solution temperatures (CSTs) determined from the DSC measurements are given in Table 2. The three temperatures have been determined: \(t_{\rm o}\) as onset of the peak, \(t_{\rm p}\) as the minimum of the peak and \(t_{\rm r}\) as the range of temperatures within which the transition occurs (under the conditions of DSC measurements). Figure 5 depicts a typical heating DSC curve, recorded for an aqueous solution of the synthesized PNIPAM (sample P1) and also shows pictures of the solution which have been taken below and above the thermal phase separation corresponding to the visible endothermic peak. As can be seen in Table 2, thermal phase separation occurs at the lowest temperatures for polymer P6. For this polymer, the  
Figure 4: Number-averaged molecular weight and polydispersity indices vs. monomer conversion. Polymerization conditions: [NIPAM]:[NCPAE]:[CuCl]:[Me\({}_{6}\)TREN]=50:1:1.1, room temperature, isopropanol as a solvent (1:2 NIPAM:solvent, _uvw_). The black and red arrows indicate a proper axis for the relationship shown in the same color. Figure 3: Conversion of monomer vs. time and first-order kinetic plot (right axis) for the Atom Transfer Radical Polymerization (ATRP) of NIPAM.