Synthesis and Characterization of Novel Urethane-Siloxane Copolymers with a High Content of PCL-PDMS-PCL Segments Marija V. Pergal, 1 Vesna V. Antic ´, 2 Milutin N. Govedarica, 1 Dejan Goðevac, 1 Sanja Ostojic ´, 3 Jasna Djonlagic ´ 4 1 Center of Chemistry, Institute of Chemistry, Technology and Metallurgy, University of Belgrade, Belgrade 11000, Serbia 2 Faculty of Agriculture, University of Belgrade, Belgrade, Zemun 11080, Serbia 3 Holding Institute of General and Physical Chemistry, Belgrade 11000, Serbia 4 Faculty of Technology and Metallurgy, University of Belgrade, Belgrade 11000, Serbia Received 6 September 2010; accepted 11 December 2010 DOI 10.1002/app.33926 Published online 29 June 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: Novel polyurethane copolymers derived from 4,4 0 -methylenediphenyl diisocyanate (MDI), 1,4-buta- nediol (BD) and a,x-dihydroxy-[poly(caprolactone)-poly (dimethylsiloxane)-poly(caprolactone)] (a,x-dihydroxy- (PCL-PDMS-PCL); M n ¼ 6100 g mol 1 ) were synthesized by a two-step polyaddition reaction in solution. In the syn- thesis of the polyurethanes, the PCL blocks served as a compatibilizer between the nonpolar PDMS blocks and the polar comonomers, MDI and BD. The synthesis of thermo- plastic polyurethanes (TPU) with high soft segment con- tents was optimized in terms of the concentrations of the reactants, the molar ratio of the NCO/OH groups, and the time and temperature of the polyaddition reaction. The structure, composition, and hard MDI/BD segment length of the synthesized polyurethane copolymers were deter- mined by 1 H, 13 C-NMR, and two-dimensional correlation (COSY, HSQC, and HMBC) spectroscopy, while the hydro- gen bonding interactions in the copolymers were analyzed by FT-IR spectroscopy. The influence of the reaction condi- tions on the structure, molecular weight, thermal, and some physical properties was studied at constant composi- tion of the reaction mixture. A change in the molar ratio of the NCO/OH groups and the reaction conditions modified not only the molecular weight of the synthesized polyur- ethanes, but also the microstructure and therefore the ther- mal and physical properties of the copolymers. It was demonstrated that only PCL segments with high soft seg- ment contents crystallize, thereby showing spherulitic morphology. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 2715–2730, 2011 Key words: segmented polyurethanes; synthesis; structure; a,x-dihydroxy-[poly(caprolactone)-poly(dimethylsiloxane)- poly(caprolactone)]; thermal properties INTRODUCTION Segmented thermoplastic polyurethane elastomers (TPUs) are an important class of polymeric materials consisting of thermodynamically incompatible hard and soft segments. The soft segments usually con- sists of polyether or polyester macrodiols of moder- ate molecular weight (1000 to 5000 g mol 1 ), whereas the hard segments consist of the diisocya- nate component and a low molecular weight chain extender (usually a diol or diamine). The thermody- namic incompatibility of the hard and soft segments at low temperatures results in phase separation and, consequently, in a domain structure. The hard seg- ments form glassy or crystalline domains, which act as physical crosslinking points among the flexible soft segment chains. The two-phase microstructure of TPUs imparts excellent mechanical properties. The properties of TPUs depend on many variables, such as the chemical structure of each type of seg- ment, the molecular weight of the soft segments, the hard/soft segment content ratio, etc. 1–4 In addition, it is well known that the polymerization method and preparation conditions affect the microstructure and the mechanical properties of TPUs. 5–12 Biocompatibility, unique chemistry and process- ability make polyurethanes ideal for numerous med- ical applications. Polyether- and polyester-based thermoplastic polyurethanes were the first to be used in biomedical applications; however, it is well known that they are susceptible to degradation by oxidation or hydrolysis. 2 Siloxane-containing TPUs have been studied dur- ing the last 30 years. 13 Polyorganosiloxanes were chosen as the soft segments because of their good thermal and oxidative stability, water repellency, low glass transition temperature, low surface energy, Correspondence to: J. Djonlagic ´ (jasna@tmf.bg.ac.rs). Contract grant sponsor: Ministry of Science and Technological Development of the Republic of Serbia; contract grant number: 142023. Journal of Applied Polymer Science, Vol. 122, 2715–2730 (2011) V C 2011 Wiley Periodicals, Inc.