Infrared ve raman spektroskopisi kullanılarak poliüretan sentezi üzerine kinetik çalışmalar: organik çözücünün ve reaksiyon koşullarının prepolimer reaksiyonları üzerindeki etkisi

Segmented Thermoplastic Polyurethanes (TPUs) are an important class of high performance polymeric materials. According to a recent report titled: "Polyurethanes (PU) Market: Global Industry Analysis, Size, Share and Forecast (2012-2018)", by Transparency Market Research, global PU product market revenue reached USD 43.2 billion in 2012 and is expected to reach USD 66.4 billion by 2018, growing at a compounded annual growth rate of 7.4 % from 2012 to 2018. Looking at these figures it is not surprising that there is significant interest by both academic and industrial researchers on TPUs, especially on controlling the critical factors that influence the chemical structure, microphase morphology and properties of polyurethanes. One of the critical points in TPU synthesis is the control of the primary reaction between isocyanate and urethane groups and minimize the side reactions, in order to obtain linear polymers with controlled structures. Unfortunately, this point is usually overlooked, most probably since the majority of the fundamental studies on polyurethane formation reaction kinetics and mechanisms were performed more than half a century ago. Therefore, in this research, our major goal was to investigate the effects of various reaction parameters such as; (i) the reaction solvent, (ii) diisocyanate and polyol structure, (iii) temperature and, (iv) catalyst type and (v) concentration on the reaction rate, extent of side reactions and isocyanate consumption in prepolymer formation reactions. For this purpose, a systematic investigation of the reactions between bis(4-isocyanatophenyl)methane (MDI) and various polyol oligomers (PTMO, PEO and PPO oligomers with = 1000 g/mol) have been performed. Concentrations of polymer solutions were about 25% by weight and the reaction temperatures employed were room temperature (22-25 °C) and 50 °C. Reactions were followed by monitoring the change in the strong isocyanate absorption peaks by using Fourier-Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy, which were centered at 2270 cm-1 and 1530 cm-1, respectively. As it is well documented in the literature, the reactions between isocyanate and alcohols follow second-order kinetics. Thus, results obtained were analyzed according to second-order kinetics in order to obtain the rate constant values and to understand the extent of side reactions, which resulted in deviations from the second-order kinetics. The results obtained clearly indicated the effect of solvent (especially DMF, which is a widely used solvent for the synthesis of polyurethanes in solution) on the extent of side reactions along with other parameters (concentration, temperature and catalyst). When DMF was used as the reaction solvent, the reaction rate and the observed excess isocyanate consumption levels were much higher than that of bulk or solution reactions carried out in other solvents. Moreover, in the case of DMF containing systems, a strong deviation from initial second-order linearity was also observed, indicating the presence of side reactions. Comparative reactions using MDI and HMDI clearly demonstrated that the reactivities of aromatic diisocyanate towards alcohols are significantly higher than their aliphatic counterparts (due to electron withdrawing ability of phenylene rings in MDI). On the other hand, in the case of polyol structures, no significant change is observed upon changing the oligomer structure. Reactions carried out at different temperatures also showed the effect of temperature on the polyurethane formation reactions. As expected, values of the rate constants increased with temperature. The dramatic difference between the catalytic activities of DMF and triethylamine (TEA) (a widely used catalyst in polyurethane formation reactions) were also presented in the last chapter. When compared with DMF, no significant amounts of side reactions were recorded in TEA containing systems. To conclude, the frequently utilized techniques from published studies, which significantly promoted the side reactions, were also listed in the final chapter.