Are polymers standard glass-forming systems? The role of intramolecular barriers on the glass-transition phenomena of glass-forming polymers

摘要: Traditionally, polymer melts have been considered archetypal glass-formers. This has mainly due to the fact that these systems can easily be obtained as glasses by cooling from melt, even at low rates. However, macromolecules, i.e. structural units of in general, are rather different standard molecules. They long objects (‘chains’) made repetition a given chemical motif (monomer) and intra-macromolecular barriers limit their flexibility. The influence properties on, for instance, glass-transition temperature polymers, is topic widely studied community almost early times science. framework glass-community, relevant chain connectivity on phenomena polymers started recognized only recently. aim this review give an overview critically revise results reported over last years. From results, it seems evident there two mechanisms involved dynamic arrest glass-forming polymers: (i) intermolecular packing effects, which dominate molecular weight systems; (ii) effect combined with connectivity. It also shown mode coupling theory (MCT) suitable theoretical discuss questions. values found central MCT parameter—the so-called λ-exponent—are order 0.9, clearly higher than (λ ≈ 0.7) where driven effects (‘standard’ glass-formers). Within MCT, signature presence competing arrest, observed short-ranged attractive colloids or component mixtures asymmetry. Moreover, recent MD-simulations ‘bead-spring’ model, but including potential strengths, confirm high λ-values barriers. Although still open questions, allow conclude fundamental difference between nature glass transition simple (standard)