Polymer diffusion in melt blends of low and high molecular weight

• Published in: Macromolecules 1988-05, Vol.21 (5), p.1513-1517
• Main Authors: Tead, Stanley F, Kramer, Edward J
• 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/ma00183a048

Forward recoil spectrometry (FRES) was used to measure the tracer diffusion coefficient D* of deuteriated polystyrene (d-PS), of molecular weight 255 000 daltons, into a matrix blend of high and low molecular weight polystyrene (PS), as a function of the volume fraction rho of the high molecular weight polymer. The low molecular weight PS, 10 000, was too short to entangle, whereas the three different PS's of high molecular weight P = 20 000 000, 250 000, and 93 000 blended with the low molecular weight sample were well above the entanglement molecular weight M sub e of the melt at rho = 1. For the highest P, D*( rho ) proportional to rho exp --1 for rho = > 0.1 when appropriate corrections for the change in the glass transition temperature of the blend with rho are made. These results are in good agreement with the prediction of the reptation model, which predicts D* proportional to M sub e , since experimentally M sub e approx M sub e ( rho = 1)/ rho . For lower values of P, the constraint release mechanism must also be included to predict values of D* in agreement with the data. However, below a critical value of rho = rho sub c = P sub c /P where P sub c is the critical molecular weight for entanglement, the PS blend matrix becomes unentangled and D* approaches its value for the pure low molecular weight PS. 26 ref.--AA