Segmented polyurethanes with 4,4′‐bis‐(6‐hydroxyhexoxy)biphenyl as chain extender. Part 2. Synthesis and properties of MDI‐polyurethanes in comparison with 2,4‐TDI‐polyurethanes

Abstract

SYNOPSIS Linear segmented polyurethanes based on poly(buty1ene adipatels (PBA) of different molecular weight ( M , 2000,1000, and 600), 4,4'-diphenylmethane diisocyanate (MDI) and the mesogenic diol 4,4'-bis-(6-hydroxyhexoxy)biphenyl (BHHBP) as well as the unsegmented polyurethane consisting of MDI/BHHBP units have been synthesized and characterized by elemental analysis, 13C-NMR and SEC. The thermal behavior and the morphology were studied by DSC, polarizing microscopy, and DMA. The properties of the MDI-polyurethanes were discussed in relation to the BHHBP chain extended 2,4-TDI-polyurethanes and common 1,4-butanediol chain-extended MDI products. MDI polyurethanes based on PBA ( M , 2000) exhibit a glass transition temperature Tg of about -40°C independent of the hard segment content up to -50% hard segments. A t higher hard segment contents increasing Tgs were observed. Polyurethanes, based on the shorter polyester soft segments PBA ( M , 1000 or 600), reveal an increase in the glass transition temperatures with growing hard segment content. The thermal transitions caused by melting of the MDI/BHHBP hard segment domains are found a t 50 K higher temperatures in comparison with the analogous TDI products with mesogenic BHHBP/TDI hard segments. Shortening of the PBA chain length causes a shift of the thermal transitions to lower temperatures. Polarizing microscopy experiments indicate that liquid crystalline behavior is influenced by both the content of mesogenic hard segments and the chain length of the polyester. 0 1996 John Wiley & Sons, Inc.

Synthesis and properties of new liquid crystalline polyurethanes containing mesogenic side chain

“…Conventionally, TLCPUs have been prepared by polymerization of mesogen-containing monomers, i.e. a mesogenic diisocyanate with an aliphatic diol [15] or a mesogenic diol with an aliphatic or aromatic diisocyanate [5,7,8,11,12,16,17]. Segmented liquid crystalline polyurethanes prepared from a polymeric diol, diisocyanate, and a mesogenic diol as a chain extender are being investigated with much interest.…”

The perspective of African-American breast cancer survivor-advocates

“…The hard segment of thermoplastic PU elastomers can form a thermotropic liquid‐crystalline phase when properly selected and when diisocyanate and chain extender are used for polyaddition reaction. The hard segments prepared from 4,4′‐dihydroxybiphenyl (DHBP)/hexamethylene diisocyanate (HDI),16 4,4′‐bis(6‐hydroxyhexoxy)biphenyl (BHHBP)/4,4′‐diphenylmethane diisocyanate (MDI),17 4,4′‐bis(2‐hydroxyethoxy)biphenyl/toluene diisocyanate (TDI),18 and BHHBP/TDI19 pairs are examples of thermotropic liquid‐crystalline PUs. Furthermore, to balance the mesogenic properties and elastic nature of PU, Padmavathy and Srinivasan20 used a high‐aspect‐ratio, tetrad, hexyloxy spacer, mesogenic diol as a chain extender.…”

Studies on poly(imide-ester)s and poly(imide-urethane)s containing pyromellitimide units

“…The resonance signals around 166É3È167É3, 166É0È166É6 and 153É4È154É5 d correspond to the carbonyl carbons of imide, ester and urethane, respectively. 18,19 The methylene carbons are assigned resonance signals after considering the inÑuence of neighbouring imide and ester/urethane groups.17 X-ray di †raction studies of the polymers reveal that they are partially crystalline, and poly(imide-ester)s show better crystallinity than poly(imide-urethane)s. Among the poly(imide-ester)s IÈV, crystallinity varies with the change in number of methylene spacers. Polymers with an even number of methylene spacers show better crystallinity than those with an odd number of methylene spacers.20 However, no distinct variations are observed for poly(imide-urethane)s. The d spacings are calculated for poly(imide-ester)s using BraggÏs equation for Ðfth order reÑections.…”