Synchrotron small-angle X-ray scattering (SAXS) was used to investigate the microphase structure and microphase separation kinetics of two segmented polyurethanes with 4,4'-diphenylmethyl diisocyanate (MDI) and l,4'-butanediol (BD) as the hard segment and poly(tetramethylene oxide) (PTMO) and poly (propylene oxide) end-capped with poly (ethylene oxide) (PPO-PEO) (M" ~2000) as the soft segments. A more complete phase separation was observed in the PTMO based sample although PTMO and PPO-PEO have almost identical solubility parameters. This phase separation behavior could be explained as due partially to a kinetic factor. The microphase separation kinetics from quenching a sample in the melt state to lower annealing temperatures could be described by a relaxation process. A single-relaxation time process was observed for the PTMO based sample. By variation of the soft segment molecular weight from 1000 to 2000, the relaxation time was reduced from ~103 to 64 s. This behavior strongly supports our argument that in a segmented polyurethane, hard segment mobility, system viscosity, and hard segment interactions are the three controlling factors. In the PPO-PEO-based sample a double-relaxation time process was observed. One of the relaxation times was 54 s while the other secondary process was 1.48 X 103 s.
Prior liquid chromatographic studies have shown that the reactions in epoxy resin model system phenyl glycidyl ether, p‐chloroaniline, and Monuron include amine addition to epoxy, homopolymerization of the epoxy, and a chain‐transfer reaction involving the hydroxy groups of the addition products. The present work examines the effect of variation in concentration of the accelerator Monuron, the amine‐to‐epoxy ratio, and the temperature on the competitive reaction mechanisms. The fraction of phenyl glycidyl ether reacting by homopolymerization increases with accelerator concentration and decreases with increasing amine‐to‐epoxy ratio and increasing temperature. The estimated contribution from chain transfer is much smaller and appears to parallel the homopolymerization reaction, as might be expected.
A new diisocyanate, 1,4‐eyclohexane diisocyanate (CHDI), has been used in a series of polyether‐based polyurethane elastomers. The slightly opaque samples are semicrystalline in nature with high performance properties, including high softening temperature, very good thermal stability, high tensile and tear strengths, excellent solvent resistance, and low hysteresis in compressive fatigue. Polymer properties are in part due to the small, compact, symmetrical structure of the aliphatic CHDI. Comparison of the physical, mechanical, and thermal properties of polyurethanes prepared from the aliphatic diisocyanate 4,4′‐dicyclohexylmethane dilsocyanate (H12MDI) reveal the H12MDI polymers to be more flexible and transparent elastomers with lower softening temperatures and tensile moduli and higher hysteretic heat build up. They are generally soluble in organic solvents.
Linear polyurethane elastomers are block copolymers which are elastomeric because they are phase separated. The soft block is derived from a hydroxy terminated telechelic polymer, frequently a polyether or polyester of a molecular weight less than 3000 and a glass transition temperature well below room temperature. The hard block, having a Tg above room temperature, consists of a diisocyanate and a diol. Most frequently the diisocyanate is aromatic and the diol is 1,4-butanediol. The elastomers produced are frequently opaque and then yellow in storage due to the presence of the aromatic rings. For applications where transparency and nonyellowing are important, aliphatic diisocyanates are the compounds of choice. One such diisocyanate is methylene bis(4-cyclohexyl-isocyanate), which is conveniently called H12MDI. It is prepared from the same diamine as methylene dianiline diisocyanate (MDI), but the aromatic rings are hydrogenated before phosgenation. The hydrogenation leads to a mixture of three aliphatic diamine isomers. Phosgenation leads to a diisocyanate which is a mixture of the three isomers shown in Figure 1. The isomer content is adjusted by the manufacturer, and the product received is a liquid. Another example of a diisocyanate which is marketed as a mixture is toluene diisocyanate, an 80:20 mixture of the 2,4:2,6 isomers being the most common. The aromatic diisocyanates are planar molecules or bent planar molecules like MDI. The H12MDI is also bent, but does not contain planar rings. Even if polymers from one pure diisocyanate isomer are examined, the cycloaliphatic compounds are much less likely to form highly ordered or crystalline regions in the hard-segment phase due to the greater difficulty in packing correctly. A desire to know the isomer composition of the diisocyanate and what effect the isomer composition has on the properties of the elastomers led to this study. Mixtures of the isomers varying from approximately 10% of the trans-trans isomer up to 95% (t-t) have been prepared and the properties of polyurethanes prepared from them have been studied.
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