The structure of the hard domains in trans,trans‐HMDI‐based polyurethane elastomers

Abstract

X-ray methods have been used to investigate the structure of the hard domains in polyurethane elastomers based on trans, trans-dicyclohexylmethane 4,4'-diisocyanate (HMDI) with butanediol as the chain extender. The crystalline hard segments become oriented on stretching the films at room temperature, although the degree of crystallinity remains relatively low. The ordering is improved considerably by annealing the films for several hours at 130-190°C: the fiber diagram contains 25 sharp Bragg reflections which are indexed bya triclinicunit cell with dimensions a=5.1 A, b= 10.2 A, c =37.5 A, a = 115.2", p = 84.9", and y =94.2". The cell contains dimer units of two chains which are probably staggered along the caxis direction in the bcplane. In the samples annealed for shorter periods of time, a second less abundant crystal structure is observed that coexists with the first. This second structure is also triclinic with a more extended fiber repeat of c= 41.3 A and is slowly converted to the contracted form on further annealing. Molecular models show that in the extended form the butanediol units have the all-trans conformation, whereas in the contracted form they probably have the tg'tg-t or tg-tg+t conformations, which have lower potential energies than the all-trans form.The chains in both the extended and the contracted conformations are able to form a network of intermolecular hydrogen bonds, and in this regard the structures are very similar to those reported previously for the analogous diphenylmethane diisocyanate (MD1)-based elastomers. Thus the higher melting points for the HMDI-based hard segments are most likely due to hydrophobic interactions between the dicyclohexyl methanes that are stronger than those between the diphenyl methanes of the MDI-based elastomers.

Effect of nanotube functionalization on the properties of single‐walled carbon nanotube/polyurethane composites

“…Another way of determining the hard‐segment crystallinity is wide‐angle X‐ray diffraction. No peaks appear in the WAXS patterns in Figure 8, and this indicates that the crystalline structure is not well formed because an HMDI/PTMO/BDO polyurethane can show crystalline reflections 26. In this case then, DSC is more sensitive to crystallinity than WAXS because DSC scans clearly show hard‐segment melting.…”

“…The second feature in the DMA spectra is the drop in both E ′ and E ″ around 50 °C and the corresponding peak in tan δ. The assignment of this feature is difficult because a soft‐segment melting transition and a hard‐segment glass transition can occur in this temperature region 26. Figure 7 shows that in fact both could be occurring; DSC scans show a small and broad, but noticeable, peak that is centered around 40 °C as well as the hard‐segment glass transition that occurs around 70 °C.…”

Shape Matters: A Gold Nanoparticle Enabled Shape Memory Polymer Triggered by Laser Irradiation

“…One is located at 2 θ ≈ 17.2° to 20.2° with intensity concentrated towards the equatorial direction; and another is located at 2 θ = 10.4° with intensity concentrated towards the meridional direction. Nigar et al . performed experimental and theoretical modeling studies on the X‐ray scattering of methylene bis (p‐cyclohexyl isocyanate) (H 12 MDI) based polyurethane elastomers.…”

“…In contrast to their work, the laser irradiation experiments for EG-72D/AuNS presented previously were performed at an off-resonance meridional direction. Nigar et al [ 29,30 ] performed experimental and theoretical modeling studies on the X-ray scattering of methylene bis (p-cyclohexyl isocyanate) (H 12 MDI) based polyurethane elastomers. According to this work, we attributed the diffraction features at 2 θ ≈ 17.2° to 20.2° and 2 θ = 10.4° to the oriented hard segment (HS) domains of EG-72D that possess relatively poor crystalline order.…”

Mechanical and dynamic mechanical properties of polyurethane and polyurethane/polyurea elastomers based on 4,4?-diisocyanatodicyclohexyl methane

“…X-ray analysis of both model compounds 15 and elaspolyurethane hard segments. tomers containing this butanediol / rMDI urethane 19 have determined that this adduct is highly crystalline.…”