A Study of Aliphatic Polyurethane Elastomers Prepared from Diisocyanate Isomer Mixtures

Abstract

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.

Physical and chemical cross-linking effects in polyurethane elastomers

“…Taking into account that the urethane C=O groups form stronger H-bonds than the ester C=O groups [9], and considering the results both from N-H and -t0o C=O peak absorbances, it may be concluded that: The number and average strength of the H-bonds formed, either between hard segments or hard-soft segments, substantially decreases as the NCO/OH ratio increases from 0.9 to 1.2. Consequently, in the case of the NCO/OH being equal to 1.2, the most homogeneous network is obtained.…”

Influence of filming process on macromolecular structure and organization of a medical segmented polyurethane

“…This has been described for polyamide, 6 poly(etherurethane)s, or poly(ether–urethane urea)s 31; these authors have detailed up to four different bands in the amide I region originating from the carbonyl groups in various environments. 32 We have assigned the bands at 1660 and 1701 cm −1 to bonded CO with different environments. Our experiments and arguments confirming this hypothesis are presented in the and clearly evidence the noncovalent nature of the chemical modification responsible for this absorption.…”

Amines, Cycloaliphatic

“…The cyclohexylamine derivative is preferred over tert-butylamine [75-64-9] and morpholine sulfenamide analogues because of lower amine volatility and less nitrosamine risk respectively. Polyurethane physical properties are dependent on the diamine geometric isomer composition used for the derivative diisocyanate which reacts with diol (89).…”