Diacetylene Containing Polyesters and Segmented Polyurethanes with Body Temperature Sensitive Thermochromic Transitions
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The incorporation of diacetylene groups in the soft segments of polyurethanes is also useful for mechanical studies as well. In terms of an analytical tool, lightly cross-polymerized polydiacetylenes can be used to probe the disruption and reorganization of soft segment crystallites during deformation, as well as the orientation of these crystallites throughout the deformation process. When the diacetylene groups in the soft segments are more fully crosspolymerized, soft segment crosslinking can be used to significantly enhance the mechanical properties as well as to study the deformation mechanisms active in the soft segments. Preliminary results have shown, for example, that increasing the extent of soft segment crystallite crosslinking serves to significantly extend the plateau modulus of these materials to higher temperatures. In this paper we focus on the structure-processing-property relationships in diacetylene containing polyesters and on the use of these materials as soft segments in segmented polyurethanes. We also describe new, body temperature sensitive thermochromic transitions that are possible with these materials. The mechanical and optical properties of the segmented polyurethanes will be presented in future papers. EXPERIMENTAL 10,12-docosadiyne-1,22 diol and 5,7-dodecadiyne- 1,12 diol were synthesized by oxidative coupling of 10-undecyne-1-ol and 5-hexyne-1-ol respectively as described by Hay [4]. Polyesters were synthesized by a modified version of the method described by Korshak, and Vinogradova [5]. Polyurethanes were synthesized by the two step method using hexamethylene diisocyanate as the diisocyanate and either 5,7-dodecadiyne- 1,12 diol or 1,8-octane diol as the chain extender. Soft segment : isocyanate : chain extender ratios were always 1 : 2.03 : 1. In all cases, liquids were purified by fractional distillation, solids rigorously purified and dried, solvents dried, and reactions carried out using proper vacuum/dry nitrogen techniques [1]. Polyurethanes were cast under a flow of nitrogen from toluene in a glass casting dish to form a free standing film. All diacetylenes were polymerized using a low pressure mercury arc lamp emitting 254 nm radiation. Thermal characterization was done with a Perkin Elmer DSC7. Optical absorption data was obtained using an Oriel Instaspec 250. RESULTS AND DISCUSSION Preparation of Controlled Functionality Diacetylene Containing Polyesters Diacetylene containing polyester soft segments for use in segmented polyurethanes must meet several criteria. First, one must be able to control the molecular weight within the desired range; typically between 600 and 3000 g/mol depending upon the final application. Additionally, the end groups must be functionalized almost entirely with hydroxyl groups as fully functionalized macrodiols are needed to produce high molecular weight polyurethanes. Lastly, it is desirable to control the degree of crystallinity in the soft segments in order to create materials with a full range of properties (highly crystalline polyester sof
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