Interrelationship and common nature of the ß relaxation and the glass transition in polymers

Supercooled dynamics of glass-forming liquids and polymers under hydrostatic pressure

“…However, secondary relaxations (and other fast processes (Angell 2000)) seem to anticipate the glass transition, even though they occur earlier in time (Ngai 1998a(Ngai , 2004. This suggests that the JG process may serve as the precursor of the intermolecularly cooperative α-relaxation (Bershtein et al 1985, 1997, Bershtein and Ryzhov 1994, Ngai 1998a, Ngai and Capaccioli 2004, Roland et al 2004b. If true, investigation of the JG relaxation can potentially yield unique insights into glass formation.…”

Heterogeneity of segmental dynamics aroundtg and nanoscale compositional inhomogeneity in polyurethane/methacrylate interpenetrating networks as estimated by creep rate spectroscopy

“…Below, the spectra are analyzed in more detail. It has earlier been found in DSC 22,28 and thermally stimulated current 37 experiments that a smooth, continuous increasing of cooperativity of segmental motion (activation energy Q or parameter Z) in glassy polymers, over the range from T ␤ to T g , was observed. Unlike that, the (T) spectrum for PUR network turned out to be nonmonotonic: the ␤-and both intermediate relaxations (Z Ϸ 1, 2, or 3) were registered discretely as the steps at the expected temperatures [ Fig.…”

“…26 Significantly, the simple regular relations connecting the activation parameters of main relaxation transitions with molecular characteristics of polymers, namely, the number S of repeat monomer units in a Kuhn segment and its volume v s , cohesion energy E c , molar volume V M , internal rotation barrier B, and a solubility parameter ␦ ϭ (E c /V M ) 1/2 , have been found experimentally for a lot of flexible chain polymers. 22,23 The relation (1) found experimentally 23,27,28 is of special importance for the present research:…”

Intermolecular Interactions and Intramolecular Motions in Photomechanical Effect: Nonlinear Thermo- and Photomechanical Behaviors of Azobenzene-Functionalized Amide–Imide Block Copolymers

“…When amorphous polymers undergo several types of molecular motions in temperature cycles, the most well-known one is the glass-transition temperature ( T g or T α ), where a polymeric material changes from a rigid glassy state to being rubbery. The other event is a β-transition, one of several possible sub- T g events, and is associated with short-range segmental mobility of a polymer on a length scale comparable to the Kuhn segment. − In aromatic polyimides with a high degree of backbone rigidity, the β-transition is generally related to the rotational mobility of the benzene rings and is observed at temperatures ranging from 370 to 600 K or 97 to 327 °C . When the polyimide rigidity is mitigated by having adjacent swiveling moieties in the backbone, β relaxation is found to be related to the cooperative rotation of rigid segments of para-linked phenylenes and arylimide rings around “swivels” such as −O– and −CH 2 – in the backbone …”