Hard Segment Structure Research Articles

Structure of polyurethane elastomers. X-ray diffraction and conformational analysis of MDI-propandiol and MDI-ethylene glycol hard segments

X-ray diffraction and conformational analysis have been used to investigate the structure of polyurethane hard segments prepared from diphenylmethane 4,4′-diisocyanate (MDI) with propandiol (PDO) and ethylene glycol (EDO) as chain extenders. The results are compared with those obtained previously for MDI-butandiol (BDO) hard segments. In the latter system, the poly(MDI-BDO) chains are fully extended with an all- trans conformation for the O(CH 2) 4O unit, and a monomer repeat of 18.95 Å. The unit cell is triclinic with a tilted base plane such that adjacent chains are staggered along the fibre axis. In contrast both poly(MDI-PDO) and poly(MDI-EDO) adopt unstaggered structures, i.e. the chains are in register and the unit cell base planes are perpendicular to the chain axis. The monomer repeats of 16.2 Å for poly(MDI-PDO) and 15.0 Å for poly(MDI-EDO) are shorter than the predicted repeats for fully-extended chains, indicating that these polymers have contracted conformations containing some gauche CH 2 groups. Conformational analysis shows that the 16.2 Å repeat for poly(MDI-PDO) can be achieved with the O(CH 2) 3O unit in the trans-gauche +- gauche +- trans or gauche +- trans-trans-gauche + conformations. Similarly the 15.0 Å repeat for poly(MDI-EDO) is predicted for the gauche +- trans-gauche − conformation for the O(CH 2) 2O unit. These conformations are of higher energy than the all- trans fully-extended chains. This may explain the higher crystalline perfection of the poly(MDI-BDO) hard segments, for which crystallization in the all- trans form will probably provide a greater driving force for phase separation.

Thermal transition behavior of polybutadiene containing polyurethanes

AbstractThe thermal transition behavior of a series of hydroxy terminated polybutadiene (HTPBD) containing segmented polyurethanes has been studied by differential scanning calorimetry (DSC) and thermal mechanical analysis (TMA). Four transition regions are observed; the soft segment Tg, at −74°C, two hard segment transitions T1, at 40°C and T2 at 103°C and a softening region by TMA at 180°C, presumed to arise from the dissociation of allophonate bonding, The low Tg, only 7°C higher than the Tg of free HTPBD, indicates nearly complete phase segregation despite the amorphous nature of the hard segment structure. The dependence of T1, on hard segment length and thermal cycling suggests that it represents domains consisting primarily of shorter hard segments units. Factors contributing to the rather low mechanical properties of HTPBD polyurethanes are also discussed.

X‐ray studies of the structure of polyurethane hard segments

Journal of Polymer Science: Polymer Letters EditionVolume 17, Issue 7 p. 447-451 Article X-ray studies of the structure of polyurethane hard segments J. Blackwell, J. Blackwell Department of Macromolecular Science, Case Western Reserve University, Cleveland, Ohio 44106Search for more papers by this authorM. Ross, M. Ross Department of Macromolecular Science, Case Western Reserve University, Cleveland, Ohio 44106Search for more papers by this author J. Blackwell, J. Blackwell Department of Macromolecular Science, Case Western Reserve University, Cleveland, Ohio 44106Search for more papers by this authorM. Ross, M. Ross Department of Macromolecular Science, Case Western Reserve University, Cleveland, Ohio 44106Search for more papers by this author First published: 12 July 1979 https://doi.org/10.1002/pol.1979.130170709Citations: 40AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume17, Issue712 July 1979Pages 447-451 RelatedInformation