An analysis of data from differential scanning calorimetry and infrared spectroscopy for a series of polyurethane block polymers is presented. It is found that the DSC endotherms observed result from shortand long-range ordering of the hard segments, rather than from hydrogen-bond dissociation as previously thought.Hydrogen-bond disruption as studied by infrared spectroscopy is influenced primarily by the glass transition temperature of the hard segments. Differences in domain morphology of these materials, which are sensitive to sample thermal history, are not revealed by changes in the extent or thermal stability of the hydrogen bonds. An explanation for the lack of correlation between hydrogen-bond effects and the DSC endotherms is presented.

An analysis of hydrogen bonding in segmented polyether and polyester urethan elastomers is presented. Hydrogen bonds may form in these materials between the active hydrogen on the urethan nitrogen and either the urethan carbonyl or the prepolymer ester or ether linkage. Investigations of the infrared absorption due to the urethan N-H stretching vibration indicate that almost all of these groups are hydrogen bonded, while study of the urethan carbonyl shows that only about 60% of these groups are similarly associated. The conclusion is that substantial hydrogen bonding must occur between the urethan N-H and the appropriate prepolymer linkages. The constancy of hydrogen bonding in samples stretched to 300% indicates that changes in the extent of hydrogen bonding do not play an important part in determining observed elastic properties.t has been proposed1"3 that the elastic properties of linear urethan block copolymers arise from a twophase microstructure, in which the hard (urethan based) segments separate from the soft segment matrix to form domains. It is presumed that these hard domains act as physical cross-links, imparting the observed elastic properties.Several experimental techniques have been employedto study these materials,4 including X-ray diffraction3"7 birefringence,89 modulus-temperature,1 and dynamic thermal methods.10 It has been generally concluded that the postulated domain structure does exist, in varying degrees, and that secondary bonding is important in determining the domain structure.This paper reports investigations into the nature and behavior of hydrogen bonding in segmented polyether and polyester urethan elastomers. Literature ReviewThe extent and nature of hydrogen bonding in polyether and polyester urethans have been the subject of several recent investigations.11"13 Essentially complete * To whom correspondence should be addressed.(1) S.

The relationship was determined between sub‐Tg molecular motions and the transport of O2 and CO2 in amorphous polyesters and copolyesters based on poly(ethylene terephthalate) [PET] and poly(1,4‐cyclohexylenedimethylene terephthalate) [PCDT], Modifications of the polyester with certain acid co‐monomers restricted the molecular motions that occurred in the β‐relaxation region and in turn decreased the O2 diffusion coefficient. The solubility coefficient was unchanged by those modifications. Modification of PET with 1,4‐cyclohex‐anedimethanol increased the magnitude of the β‐relaxation and both the diffusion and solubility coefficients of O2. Similar relationships between the β‐relaxation magnitude and CO2 permeability were also found. The temperature dependence of O2 permeability followed an Arrhenius relationship, with different activation energies (Ep) above and below the β‐relaxation. The activation energy was smaller below the β‐relaxation. Values of Ep above and below the β‐relaxation did not depend on the chemical structure of the polymer.