STERIC EFFECTS IN PHOTOCHROMIC POLYSILOXANES WITH SPIROOXAZINE SIDE GROUPS

Synthesis and properties of linear and cyclic polysiloxanes with photochromic spirooxazine side groups were investigated. The photochromic groups were connected to the main chains through a flexible (CH2)n spacer. The number of photochromic groups that can be incorporated in the polymer by a polymer analogous reaction is restricted for the short spacer (CH2)3 to approximately 50%, while the photochromic groups with the longer spacer (CH2)6 can be added to practically each polymer unit. The rates of the thermal decoloration reactions are also determined by the spacer lengths and the spirooxazine content. At high content, a deviation from first-order kinetics was observed for the color decay. The effects are explained by the steric interactions of the bulky photochromic groups. Computer simulation of the molecular movement in the macromolecules confirmed the explanation.