Appendix a Synthesis of Polydimethylsiloxane Based Segmetned Polyurethane and Polyurea Copolymers

Polydimethylsiloxane (PDMS) oligomers with ranging from 900 to 7000 g/mol and which were α,ω-aminopropyl, α,ω-N-methylaminopropyl and α,ω-hydroxyhexyl terminated were obtained from Th. Goldschmidt AG in Essen, Germany. The of amine-terminated oligomers were determined by the titration of the end groups with hydrochloric acid. The of hydroxyhexyl terminated PDMS oligomers were determined by H-NMR spectroscopy. Bis(4-isocyanatocyclohexyl) methane (HMDI) with a purity of greater than 99.5% was supplied by Bayer AG. Reagent grade ethylene glycol (EG), propylene glycol (PG), 1,4-butanediol (BD), ethylene diamine (EDA) and 1,6-diaminohexane (HMDA) were purchased from Aldrich and used as received. 2-methyl-1,5-diaminopentane (Dytek) was kindly supplied by Du Pont. Chromatographic grade reaction solvents, methyl ethyl ketone (MEK), tetrahydrofuran (THF), dimethylformamide (DMF) and isopropanol (IPA) were obtained form Carlo Erba and were used without further purification. Dibutyltindilaurate (DBTDL) catalyst was obtained from Witco. The chemical structure of the precursors and the repeat unit of the segmented copolymers are presented in Scheme 4.2. All copolymers were prepared by using the two-step prepolymer method. Reactions were carried out in three-neck, round bottom flasks equipped with overhead stirrer, nitrogen inlet, and addition funnel. During the preparation of the silicone-urethane copolymers, calculated amounts of HMDI and hydroxy-terminated PDMS were introduced into the reactor, stirred and heated. When the mixture reached 80oC, 1 drop of 1 wt % DBTDL solution in toluene was added as a catalyst. Prepolymer formation was monitored by FT-IR spectroscopy, following the disappearance of the broad O-H stretching peak and formation of the N-H peak near 3450 and 3300 cm respectively. For chain extension, a stoichiometric amount of chain extender (EG, PG or BD) was added into the reactor together with MEK, as the reaction solvent and the reaction was continued at 70oC until the complete disappearance