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 _gs) of near-infinitely dilute (0.1 wt %), well-dispersed polystyrene (PS) components in seven blend partners using intrinsic and extrinsic fluorescence. The PS T _gs span a 150 °C range when PS is dispersed in partners with T _gs of -6 to 150 °C. We calculate self-concentrations for PS (β _self ^PS) of ∼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 β _self ^PS calculations, correlate with partner fragility rather than partner T _g, with higher fragility partners resulting in higher β _self ^PS 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 β _self ^PS = 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 (β _self ^PS ∼ 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 β _self ^PS. In PVC, β _self ^PS decreases from 0.72 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 ∼0.45 nm of the backbone.