Dynamics, fragility, and glass transition of low-molecular-weight linear homopolymers

Abstract

Analysis of the dynamics of low-molar-mass linear homopolymers is important when trying to understand the mechanisms driving structural relaxation properties from molecular liquids to polymers. Theoretical models assume, in general, the same mobility of the different moieties of the macromolecule, but this hypothesis fails for low-molar-mass polymers. Therefore, isofrictional comparisons are necessary to interpret experimental data with theoretical models. In this work, the molar-mass dependence of the glass transition temperatures T _g, fragility indexes, and dynamic moduli of unentangled poly(ethyl acrylate) (PEA) melts are studied and discussed. All the results are interpreted in a coherent framework developed from the free-volume concept. The predictive power of this framework is also tested to fit theoretical and experimental master curves, introducing an ‘inverse’ isofrictional correction.

Keywords:

• glass transition
• polymers
• fragility
• molecular weight
• free volume

Acknowledgement

We thank Regione Toscana POR OB3 D4 for partial financial support of this work.

Notes

Note

1. The volume ratio f _r is defined as v _f /(v _f + v _o ) being respectively v _f the free volume and v _o the occupied volume at the temperature T _r .