Abstract:The substance under investigation is taken as a model for hard segments consisting of MDF) and 1,4-butane diamine. It crystallizes in the triclinic space group P I with a = 4.6297; b = 5.8259; c = 25.286 A; c~ = 90.721; ~ = 91.580; y = 102.90 degrees and Z = 1. Bond distances and angles are given, together with some data on the conformation.The most significant finding is that neighbouring molecules in one and the same plane are linked to one another by means of bifurcated hydrogen bonds.A comparison with the corresponding data for an analogous bis-urethane provides a plausible explanation of the main differences between diamine and glycol extension in polyurethane elastomers.
Single‐crystal x‐ray diffraction analysis is performed on a model compound (bisurethane of diphenylmethane‐4–monoisocyanate and butanediol‐1,4) for the thermoplastic polyurethane (TPU) hard segment formed from diphenylmethane‐4,4′‐diisocyanate and butanediol‐1,4. The resulting structure is compared to structure models of corresponding TPU hard segments, especially to the structure proposed by Blackwell and Ross. Our results confirm this structure model showing a planar zigzag of the (CH2)4 group and planar hydrogen bonding between the urethane groups of adjacent molecules. X‐ray diffraction analyses of polymeric TPU hard segments and of TPU elastomers with noncrystallizing soft segments lead to a revision of the dimensions of the proposed lattice cell, resulting in a more plausible value of 1.3226g/cm3 for the crystal density.
Polyurethane elastomers extended with aliphatic glycols or diamines, show a characteristic fluctuation in their thermal and hydrothermal properties which is dependent on the number of CH 2 grofips in the chain extender ("even" or "odd"). The causes of this behavior are examined in the following report using X-ray crystallographic analyses of single crystals of model urethanes. These model compounds were prepared by reaction between diphenylmethane -4-mono-isocyanate and glycoles of the HO-(CH2) ,-OH structure with n = 2 to 6. Whilst strain-free hydrogen bonds can form between neighboring molecules in urethanes with "even" chain extenders, significant strains occur in urethanes containing "odd" chain extenders which result in reduced stability of the physical crosslinking system.
A description of irreversible quasi-isothermal deformation of PUR-elastomers to large strains is developed on the basis of the classical thermodynamics of irreversible processes. This approach is shown by representing stress-strain cycles at different constant strain rates and at two temperatures.The discussion implicates the description of birefringence data and first stretchingcalorimetric results.
SynopsisThe deformation behavior of polyurethane elastomers depends strongly on physical interactions.In this paper the stress-induced crystallization of the polyester or polyether segments is investigated in several polyurethane elastomer system having different chemical structure for the soft segments. The correlation between the tensile properties (hysteresis loss, extension set, modulus) and the stress-induced crystallization is discussed.
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