sup (13) NMR Structural Studies of a Soluble Polydiacetylene Poly(4BCMU).

The chromism of a soluble polydiacetylene, poly(4BCMU), whose side chain substituents are -(CH sub 2) sub 4- O-o over (||) over C- under | under CH sub 2-=O over (||) over C-O- (CH sub 2) sub 30CH sub 3, was studied by use of nigh resolution, solid state sup (13) C NMR. The solid state thermochromic transition (104C; DSC at 10C/min.) resulted in a more localized electronic state for the backbone, extended side chains with more trans bond character, and retention of the hydrogen-bonding network between side chains, results similar to those observed for the thermochromic transition of poly(ETCD). Unlike poly (ETCD), the thermochromic transition observed in poly(4BCMU) was irreversible, and poly(4BCMU) cooled from the red phase or molten state to room temperature displayed two distinct backbone structures.