The Role of Density and Temperature in the Dynamics of Polymer Blends

• Published in: Macromolecules 2005-10, Vol.38 (21), p.8729-8733
• Main Authors: Roland, C. M, Casalini, R
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Structure, morphology and analysis
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma051481f

The relative effect of volume and thermal energy on the local segmental dynamics, as reflected in the ratio of the isochoric, E V , and isobaric, E P , activation enthalpies, is determined for blends of polystyrene (PS) with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and with poly(vinyl methyl ether) (PVME). We find that neat PPO near T g has the lowest value of E V /E P = 0.25 ± 0.02 reported for any polymer, indicating volume-dominated dynamics. Addition of the lower T g PS alleviates constraints on local motion, resulting in a weaker volume effect. The opposite situation prevails with PS/PVME blends. PS has a higher T g, and in blends segmental relaxation of the PVME becomes more controlled by volume than for neat PVME. We also show herein that the relaxation times for the PVME/PS blends measured at various T and P superpose when plotted vs Tυγ, where υ is the specific volume and γ is a material constant. This scaling, which has previously been demonstrated for various neat glass-formers and is reported herein for the first time for a blend, enables E V /E P to be determined at T g in the absence of actual measurements near T g.