The plasticization of polymers by addition of small molecule diluents occurs when both a - (Tg) and b - (local) relaxation peaks, at constant frequency, are shifted to lower temperatures, indicating that both these processes are being sped up. However, in some cases, an opposite effect, known as antiplasticization, occurs  where the b - relaxation peak shifts to higher temperatures even though the a - relaxation peak shifts to lower temperatures. This means that while the a - relaxation speeds up, the b - relaxation of the polymer slows down. Our inelastic neutron scattering measurements on the bisphenol A polycarbonate (BPA-PC: polymer) – Arochlor 1260 (diluent) seemed to indicate such an antiplasticization mechanism. The addition of Arochor reduced the Tg while suppressing the local motions (most likely methyl rotations) deeper in the glassy state. Such an effect was previously observed for bisphenol A polycarbonate (BPA-PC) with addition of Aroclor  or tris(2-ethylhexyl) phosphate (TOP)  (both diluents). Ourdielectric studies of the BPA-PC – Aroclor blends contradict the antiplasticization mechanism and seem to indicate a speeding up both the b - and a - relaxation processes, i.e., plasticization of the polymer. However, the b - relaxation, observed by dielectric spectroscopy reflects different motion in polymer. Moreover, it was preciously shown that different Aroclors could lead to different plasticization / antiplasticization results that also depend on their concentration . It is therefore important to further investigate the effect of this diluent.
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Mentor’s name: Jan Obrzut
Polymers Division, MSEL, Building 224, R. A323, MS 8541, x. 8647, fax: x 3928,
e-mail: firstname.lastname@example.org, not a Sigma Xi member