Conventional and temperature-modulated differential scanning calorimetry (DSC) experiments have been carried out on miscible blends of polyisoprene (PI) and poly(4-tert-butylstyrene) (P4tBS) over a broad composition range. This system is characterized by an extraordinarily large T g difference (∼215 K) between the two homopolymers. Two distinct calorimetric glass transitions were observed in blends of intermediate compositions (25%-50% PI) by both conventional and temperature-modulated DSC. Good agreement was found between the component T g values measured by the two methods. Fitting of the component T g values to the Lodge-McLeish model gives a φ self of around 0.63 for PI in this blend and 0.03 for P4tBS. The extracted φ self for PI is comparable to reported values for PEO in blends with PMMA and is significantly larger than values reported for PI in other blends with smaller homopolymer T g differences. This observation is consistent with the presence of a nonequilibrium or confinement effect in PI/P4tBS blends, which results in enhanced dynamics of the fast component below the T g of the slow component.

Deuterium NMR at Larmor frequencies of 15.6 and 76.7 MHz was used to study the segmental dynamics of perdeuteriopoly(ethylene oxide) (d4PEO) in miscible blends with poly(vinyl acetate) (PVAc). Blends with PEO compositions of 2% and 50% were studied. The segmental dynamics of PEO are 9 orders of magnitude faster than the PVAc segmental dynamics for a 2% PEO blend near the blend T g and could be described by the Lodge−McLeish model with a self-concentration of 0.3. The segmental dynamics of PEO in blends with PVAc show a weaker temperature dependence than the terminal dynamics of PEO in the same blends. We also compare the segmental and terminal dynamics of components in several other miscible polymer blends. For the fast component in a blend, it is commonly observed that terminal relaxation has a stronger temperature dependence than segmental relaxation. This effect correlates with the difference between the T g values for the pure components and also with the ratio of the activation energies of the segmental dynamics for the two components in the blend.

Both the backbone chain rigidity of polymers as well as drug-polymer interaction can impact the free volume and glass transition behaviors of the dispersions.

Deuterium NMR at Larmor frequencies of 15.6 and 76.7 MHz was used to study the segmental dynamics of dilute perdeuteriopoly(ethylene oxide) (d4PEO) in equilibrium miscible mixtures with four low molecular weight glass-formers: indomethacin, sucrose benzoate, o-terphenyl, and toluene. Results are compared with literature data for dilute PEO in two polymer hosts: poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc). The segmental dynamics of PEO are found to strongly correlate with the dynamics of both high and low molecular weight hosts. For dilute PEO in mixtures with PMMA, PVAc, and sucrose benzoate, the Lodge–McLeish model with a ϕself (self-concentration) of 0.35 gives a good fit to the dynamics of dilute PEO, similar to previously reported dilute polyisoprene blends and dilute polystyrene blends. A smaller ϕself is obtained for dilute PEO in indomethacin, consistent with the presence of a hydrogen-bonding effect. For PEO in o-terphenyl and toluene, the implementation of the Lodge–McLeish model utilized here fails to give quantitative fits for the dynamics of the dilute PEO chains; this result is obtained because the full temperature-dependent host dynamics are not utilized in the fitting procedure.

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