A new scheme for determination of the carrier mobility and main-chain conformation of an electroactive polymer chain by transient electric birefringence

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Abstract
A new scheme of experimental criterion is proposed for estimating the carrier mobility and main‐chain conformation of an electroactive polymer chain by the technique of transient electric birefringence (TEB). The rise response Δnr (t) and the decay response Δnd (t) in the TEB satisfy in the Kerr regime (i) Δnr (t)=Δnst ‐Δnd (t) for a polymer molecule of arbitrary conformation with an induced dipole moment alone arising from carriers highly mobile along the main chain, (ii) Δnr (t)=Δnst ‐(3/2)Δnd (t/3)+(1/2)Δnd (t) for a rodlike polymer molecule with a permanent dipole moment alone originating from carriers with low mobility, and (iii) Δnr(t)=Δnst‐2Δnd (t/2)+Δnd (t) for a random‐coiled polymer with a permanent dipole moment alone due to low‐mobility carriers, where Δnst =limt→∞ Δnr(t) . Then, comparison of the TEB rise and decay responses gives us information on the carrier mobility and main‐chain conformation. This criterion is valid also for polydispersed polymer samples. By applying the criterion to the exemplifying data of the TEB responses for soluble urethane‐substituted polydiacetylenes, it is found that the polydiacetylene molecules take a random‐coil conformation with a permanent dipole moment in a good solvent, while in a poor solvent the carrier mobility depends crucially on the solvent condition.