No abstract

A novel diisocyanate, 1,2-bis(isocyanate)ethoxyethane (TEGDI), whose backbone is ether bonds was used for the preparation of polyurethane elastomers (PUEs). 1,6-Hexamethylene diisocyanate (HDI) was also used as a control. The PUEs were prepared with either TEGDI or HDI, poly-(oxytetramethylene) glycol (PTMG), and curing agent by a prepolymer method. Differential scanning calorimetry, infrared spectroscopy, and wide-angle X-ray diffraction revealed that the phase separation of the network TEGDI-based PUEs was much weaker compared with that of the HDI ones. Highly softened TEGDI-based PUEs were successfully prepared on account of flexibility of TEGDI itself and weaker phase separation.

A series of eight aliphatic polycarbonate (PC) glycols with various methylene numbers (HO−[(CH2) m OC(O)O] n −(CH2) m −OH, m = 3, 4, 5, 6, 7, 8, 9, and 10) were employed as a soft segment for a synthesis of polyurethane elastomers (PUEs). First of all, viscosity, glass transition temperature, melting point, and crystalline structure of these new PC-glycols were investigated. The PC-glycol-based PUEs were synthesized using the PC-glycols, 4,4′-diphenylmethane diisocyanate, and 1,4-butanediol by a one-shot method. Differential scanning calorimetry and small-angle X-ray scattering measurements revealed that the degree of microphase separation of the PC-glycol-based PUEs became first weaker and then stronger with increasing number of methylene groups of PC-glycols. The threshold carbon number for the degree of microphase separation was six. In the tensile testing, Young’s modulus of the PUEs decreased and increased with an increase in the methylene number, which can be explained by the degree of microphase separation. Tensile strength and elongation at break of the PC-glycol-based PUEs increased and decreased with increasing the number of methylene groups. These results are associated with the ease of packing of the PC-glycol chains.

Molecular arrangement of polymerized n-octadecyltrichlorosilane (OTS, CH3(CH2)17SiCl3) monolayer transferred onto hydrophilic substrate by an upward drawing method was investigated with a transmission electron microscope (TEM) and an atomic force microscope (AFM). The electron diffraction (ED) pattern of the OTS monolayer revealed that the OTS molecules were regularly arranged in a hexagonal array with a (10) spacing of ca. 0.42 nm. The high-resolution AFM image of the OTS monolayer in a scan area of 10 × 10 nm 2 exhibited the individual methyl group of which packing was a hexagonal array in a similar molecular arrangement concluded on the basis of the ED study. Also, the point defect in the crystalline OTS monolayer was successfully observed for the first time.

A comparative study in molecular arrangements of the n-octadecyltrichlorosilane (OTS) monolayer prepared by the Langmuir method and the chemisorption methods were carried out on the basis of grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XR) measurements. The OTS molecules in the Langmuir OTS monolayer uniformly tilt ca. 8-10°to the surface normal and packed in a hexagonal lattice with the (10) spacing of 0.412 nm. On the other hand, the OTS molecules in the chemisorbed OTS monolayer tilt ca. 15-17°to the surface normal and also crystallite orient randomly in the two-dimensional plane. The average magnitude of the (10) spacing of the chemisorbed OTS monolayer was ca. 0.417 nm. Direct evidence that the packing density of the Langmuir OTS monolayer was higher than that of the chemisorbed OTS monolayer was obtained by GIXD and XR measurements for the first time.

Randomly copolymerized poly(carbonate) glycols were employed as starting materials for the synthesis of polyurethane elastomers (PUEs). The poly(carbonate) glycols had hexamethylene (C 6 ) and tetramethylene (C 4 ) units between carbonate groups in various composition ratios (C 4 /C 6 ϭ 0/100, 50/50, 70/30, and 90/10), and the number-average molecular weights of these poly(carbonate) glycols were 1000 and 2000. The PUEs were synthesized with these poly(carbonate) glycols, 4,4Ј-diphenylmethane diisocyanate, and 1,4-butanediol by a prepolymer method. Differential scanning calorimetry measurements revealed that the difference between the glass-transition temperature of the soft segment in the PUEs and the glass-transition temperature of the original glycol polymer decreased and the melting point of the hard-segment domain increased with an increasing C 4 composition ratio. The microphase separation of the poly(carbonate) glycol-based PUEs likely became stronger with an increasing C 4 composition ratio. Young's modulus of these PUEs increased with an increasing C 4 composition ratio. This was due to increases in the degree of microphase separation and stiffness of the soft segment with an increase in the C 4 composition ratio. The molecular weight of poly(carbonate) glycol also influenced the microphase-separated structure and mechanical properties of the PUEs. The addition of different methylene chain units to poly(carbonate) glycol was quite effective in controlling the microphase-separated structure and mechanical properties of the PUEs.

Polyurethane elastomers (PUEs) containing trans-1,4-bis­(isocyanato­methyl)­cyclohexane (1,4-H6XDI) have been synthesized by polymerizing 1,4-H6XDI with poly­(oxytetra­methylene) glycol and 1,4-butanediol. The molecular aggregation state and mechanical properties of these PUEs have been compared with those exhibited by PUE analogues made of MDI and diols. The hard segment chains in the 1,4-H6XDI-based PUEs are found to readily crystallize and form strong hydrogen bonds due to a high symmetry of 1,4-H6XDI molecule. Consequently, the 1,4-H6XDI-based PUEs exhibit well-organized hard segment domains. This leads to their generally superior mechanical properties as compared to those of the well-known MDI-based PUEs. 1,4-H6XDI’s lack of aromatic moieties is expected to greatly enhance color stability of resulting PUEs. All the above features suggest 1,4-H6XDI could replace MDI in a range of applications.

Mechanical properties of thermoplastic polyurethane elastomers based on either polyether or polycarbonate (PC)-glycols, 4,4’-dipheylmethane diisocyanate (1,1’-methylenebis(4-isocyanatobenzene)), 1,4-butanediol, were controlled by restriction of crystallization of polymer glycols. For the polyether glycol based-polyurethane elastomers (PUEs), poly(oxytetramethylene) glycol (PTMG), and PTMG incorporating dimethyl groups (PTG-X) and methyl side groups (PTG-L) were employed as a polymer glycol. For the PC-glycol, the randomly copolymerized PC-glycols with hexamethylene (C6) and tetramethylene (C4) units between carbonate groups with various composition ratios (C4/C6 = 0/100, 50/50, 70/30 and 90/10) were employed. The degree of microphase separation and mechanical properties of both the PUEs were investigated using differential scanning calorimetry, dynamic viscoelastic property measurements and tensile testing. Mechanical properties could be controlled by changing the molar ratio of two different monomer components.