Major Roles of Blend Partner Fragility and Dye Placement on Component Glass Transition Temperatures: Fluorescence Study of Near-Infinitely Dilute Species in Binary Blends

We measure the glass transition temperatures (T(g)s) of near-infinitely dilute (0.1 wt %), well-dispersed polystyrene (PS) components in seven blend partners using intrinsic and extrinsic fluorescence. The PS T(g)s span a 150 degrees C range when PS is dispersed in partners with T(g)s of -6 to 150 degrees C. We calculate self-concentrations for PS (phi(self) (PS)) of similar to 0 to 0.72 via the Lodge-McLeish model, the largest range ever reported for a blend component. Our study reveals that perturbations to PS T-g, which may be quantified by phi(PS)(self) calculations, correlate with partner fragility rather than partner T-g, with higher fragility partners resulting in higher phi(PS)(self) values. In particular, for 0.1 wt % PS in poly(vinyl chloride) (PVC), the partner with the highest reported fragility but an intermediate T-g, the PS T-g is only weakly perturbed with phi(PS)(self) = 0.72. These results indicate that partner fragility plays a key role in determining the strength of T-g perturbations to a blend component. Also noteworthy is 0.1 wt % PS in poly(4-vinylpyridine) (P4VP) where the PS T-g is slaved to that of P4VP (phi(PS)(self) similar to 0). Fluorescent label location on the backbone does not significantly influence the measured T-g. However, the distance separating a label from the backbone is crucial in determining T-g and thereby phi(PS)(self). In PVC, phi(PS)(self) decreases from 0.72 to similar to 0 when a dye is attached to the PS backbone by a methyl ester or butyl ester group, respectively, indicating a highly heterogeneous environment within similar to 0.45 nm of the backbone.