X-ray investigations concerning the physical structure of cross-linking in urethane elastomers. II. Butanediol as chain extender

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Abstract
The elastomers investigated are cross-linked partly by primary and partly by secondary valencies, i.e., by allophanate, biuret, and cyanurate bonds, on the one hand, and by hydrogen bridges and other intermoiecular interactions, on the other. The so-called physical cross-linking effected by secondary valencies is associated with a segregation of the hard segments, whereby statistically defined systems of hydrogen bridges are formed within the segregation areas. These systems lead to quasiperiodical, paracrystalline arrangements of the hard segments within the segregation areas. Under certain conditions true crystallization of the hard segments can be observed.