Radiation reactivity diacetylenes

Finally, reference should be made to copolymerization in this series. The diacetylene 142 is (homo)-polymerizable by high-energy radiation, whereas 143, though structurally very similar, is not. This difference in reactivity is apparently due to the difference between the crystal axial lengths in the direction in which polymerization would be expected to proceed this length is 4.37 A for 142 and 4.55 A for 143 (216). The two monomers are miscible in all proportions in the... 

While diacetylene polymerization is justifi U3ly regarded (18) as better investigated and imderstood than any other polymerization reaction, several fundamental uncertainties remain. With respect to initiation emd propagation, the lack of thermal reactivity of certain monomers (e.g., urethanes) which require radiation for polymerization contrasts with a monomer such as PTS (la), which polymerizes both thermally and with radiation. Equally... 

Under favourable packing conditions, diacetylene single crystals exposed to heat, radiation, or pressure react to form high quality polydiacetylene single crystals. Structural aspects of monomer reactivity are fairly well understood (at least at a qualitative level) via models based on least motion principles. However, there remain many unanswered questions regarding the detailed chemistry and physics of reaction initiation, propagation, and termination. 

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