Characterization of Polymers with the Kerr-Effect Alan E. Tonelli, North Carolina State University, DMR 0966478.
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A recent NSF Workshop report on Polymers concluded that “recent advances in polymer syntheses leading to elaborate and precise architectures require accompanying advances in microstructural character-ization beyond those currently available, which are collectively inadequate”.
Unlike spectroscopic probes that are only sensitive to local polymer microstructures, the birefringence observed in polymer solutions when subjected to high electric fields, ie., the directional dependence of light refracted through them, depends on the microstructural make-up of the entire polymer chain. It is the net dipole moment and direction of maximum polarizability of the entire polymer chain averaged over all conformations in solutions which determine both the magnitude and sign of its Kerr-Effect.
This is illustrated in the Figure, for 2 tri-block copolymers with polar para-bromostyrene (p-Br-S) and non-polar styrene (S) blocks located in different positions. Both tri-blocks contain the same numbers of comonomer units (60 mol% p-Br-S). Though the microstructures/architectures of A and B are indist-inguishible by any other means, the Kerr-Effect is not only sensitive to their microstructures, but also to their locations/ positions in the copolymer chain.
It would appear that the Kerr-Effect does indeed have the potential to characterize more fully the “elaborate and precise architectures “ (microstructures) of polymers, thereby increasing our ability to under-stand their behaviors and properties.
p-Br-S/S/p-Br-S(A) and S/p-Br-S/S (B) Tri-block Copolymers, whose molar Kerr constants, mK, are both predicted and observed to be different by a factor of ~2.5, with mK(A) ~ 2.5 mK(B).
Attached are photos of the Post-Doctoral, graduate, undergrad-uate, and high school students who have been and/or are current-ly supported on this grant. They have been assisting with the syntheses of model polymers and measurement and calculation of their molar Kerr constants. In addition, Prof. Brent Summerlin (SMU) and his students have become active collaborators in the syntheses of model polymers for Kerr-Effect study.
We will be describing our pre-liminary results for S/p-BrS co-polymers, including those with random, blocky, and gradient comonomer sequences, in late August at the upcoming Fall 2011 National ACS meeting in Denver.
From top-to-bottom and left-to-right are photos of Shauntrece Hardrict (Post-Doc.), Rana Gurarslan (Grad. student), Kathleen Dreifus (Undergrad. student), and High school students KaDesia Hawkins (ACS-Project SEED), and Mahi Yetukuri.