Hard segments photochromic

MACRODIOL+DIISOCYANATE, NO CHAIN EXTENDER ) PHOTOCHROME( ) IN THE "HARD SEGMENT"(—) ... 

Figure 7. Molecular structure of soft and hard segment of photochromic polyester urethane with partly photochromic soft segments.

Figure 12. The UV absorption spectra of 4,4 -di(phenylurea)azobenzene (Curves 1 and 2) and polyurethane with photochromic hard segment (Curves 3 and 4) in DMF solution before (1,3) and after (2,4) irradiation at k — 405 nm Curve 5 pure poly(tetramethylene adipate urethane) (12).

As compared to the systems discussed in the previous section, due to the absence of a chain extender (EDA) in the synthesis of these polyurethanes, the length of the carbamate units is not sufficient to enable phase separation consequently, the small amount of photochromic hard segments here exist in a medium similar to isolated hard segments in the soft-phase of two-phase polyurethanes. 

The fact that in these bulk polymer samples no photoisomerization could be detected has to be attributed only to the severe restrictions of the local chain segmental mobility around the chromophore, i. e., it is due to the predominant incorporation of the azochromophoric units in the hard phase the mobility of chain segments within the hard domain is widely suppressed in this system, cousing a nearly complete immobilization of the chromophore in the hard phase. This behaviour is comparable to systems where the photochrome was incorporated in highly crystalline polyamide or polyimide (2,20,21). 

Cyanophenyl)-[3-[9-[2-(2-methacryloyloxy-propanoyloxyethyl] carbazolyl]] diazene [(5)-MLECA] chiral monomer containing the carbazole moiety is a novel optically active photochromic polymer. After study of chiroptical, thermally and spectroscopic properties shows the presence of dipolar interaction characteristics between chromophores and chiral confirmation of prevailing helical hardness for chain segments of macromolecules. 

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