Synthesis and Characterization of methylene bis (p-cyclohexyl isocyanate)-poly (tetramethyl oxide) based Polyurethane Elastomers

摘要

This research concerns the development and characterization of methylene bis (p-cyclohexyl isocyanate/butanediol) (HMDI/BD) based polyurethanes used in connection with surface-active anti-microbial polyurethanes. Previously studied polyurethanes having an isophorone diisocyanate/butanediol (IPDI/BD) hard block contaminated water during dynamic contact angle (DCA) analyses. This contamination by unknown species confounds results from biocidal studies and jeopardizes the use of the polyurethane as a matrix polyurethane. By contrast, polyurethanes with methylene bis (p-cyclohexyl isocyanate)/butanediol hard block showed no contamination during DCA analysis. For this reason, further study of HMDI/BD/PTMO polyurethanes was conducted. HMDI/BD polyurethanes were synthesized with 15-50wt% hard block and a soft block of PTMO-2000 or PTMO-1000 where PTMO-2000 is poly (tetramethylene oxide) with a molecular weight of 2000g/mol and PTMO-1000 has a molecular weight of 1000g/mol. Characterization was performed with FT-IR and 1H NMR spectroscopy to verify polyurethane composition as well as hard block percentage. Thermal characterization was performed with modulated differential scanning calorimetry (MDSC). From MDSC, the glass transition temperatures of the soft and hard block for polyurethanes with PTMO-2000 as the soft block were -80°C and 86°C, respectively. For corresponding polyurethanes containing PTMO-1000 as the soft block, the measured Tgs for the soft and hard segments were -55°C and 65°C, respectively. The disparity between the respective soft and hard segment Tgs of these polyurethanes of differing soft block molecular weights is due to increased phase mixing that causes an increase in soft block Tg and a decrease in hard block Tg for the PTMO-1000 polyurethanes. From dynamic contact angle analyses of HMDI/BD/PTMO polyurethanes, the advancing and receding contact angles gradually decreased with each cycle but approached 80° and 60°, respectively. Results from force-distance curves with flamed glass slides obtained before and after immersion of the polyurethane coatings indicated that no water contamination occurred. Tensile tests demonstrated that hard block percentage, soft block molecular weight, and the amount of chain extender influences mechanical properties. For example, increasing hard block weight percentage increases the modulus. HMDI/BD(30)/PTMO-2000 (PU-1), HMDI/BD(25)/PTMO-2000, (PU-2) and HMDI/BD(35)/PTMO-2000 (PU-10) exhibited the best elastomeric properties. As the final outcome, lack of contamination and good mechanical properties made PU-2 and PU-9 (HMDI/BD(50)/PTMO-1000) suitable candidates as polyurethane matrices for polymer surface modifier evaluation.