Optically-active hyperbranched poly(n-alkyltriferrocenylsilanes): 2. Thermal transition and optical activity

A class of hyperbranched poly(n-alkyltriferrocenylsilanes) is synthesized and characterized. These polymers have a sterically-crowding induced perturbation to the achiral chromophores resulting in the formation of a negative helix structure or a twisted screw sense of chiralty, therein a fisrt negative Cotton effect, which is arising from the intra-repulsion and twisting behavior of the hyperbranched structure in space. The length of the n-alkyl chain at silicon can effectively encumber the Si atom from the nucleophilic attack to favor the formation of hyperbranched structure. Two transition temperatures, T_g and T_m when the length of alkyl chain at silicon exceeds a certain value (12 carbons).