Structural Changes near the Glass Transition–Neutron Diffraction on a Simple Polymer

Abstract

Using neutron diffraction, the structural change of a backbone polymer, polybutadiene, is studied when heated from the glass to the melt. On a microscopic scale the temperature dependence of the linear thermal expansion shows a discontinuity below the calorimetric glass transition temperature Tg, whereas the correlation length for monomer or chain ordering becomes independent of temperature near Tg. These effects appear in the range where we recently have observed changes in the inelastic excitation spectrum of this sample.

Modeling the principal amorphous halo in quiescent melts of polyethylene and ethylene copolymers using wide-angle X-ray scattering and its implications

“…30 For the CG plot, the value of Ϫ91°C is 26 K below the T g (onset), and 34 K below the T g defined as the midpoint of the transition. This approximates the 30 K for the T g offset found for the LAH peak value via neutron scattering measurements for poly(butadiene), 20 and is close to that for the T g (ϱ) (Ϫ30 K) found through crystallization kinetics. 31 For the indicated value of the T g onset, the experimental and kinetic determinations of T g (ϱ) differ from the Adams-Gibbs suggestion of about T g Ϫ50 K. 32 The linearity in the peak values for the two copolymer groupings in the melt shown here and elsewhere, 20 together with the extrapolated convergence angle and its relation to the T g , suggest an iso-free volume state and a free volume expansion coefficient connection as defined in the WLF equation,…”

“…Frick et al 20 used neutron scattering to show that the peak position of the LAH exhibited a linear temperature relation and a discontinuity at the thermodynamic glass transition [T g (ϱ)], whereas the second scattering maximum exhibited little temperature dependence. This temperature dependence is in accord with the results from this work, and has implications for fundamental properties of the melts of polyolefins and phase analysis, in general.…”

Study of the structure and dynamics of poly(vinyl pyrrolidone) by molecular dynamics simulations validated by quasielastic neutron scattering and x-ray diffraction experiments

“…Below Q ≈ 2 Å −1 they show two distinct peaks. One peak appears around 1.2 Å −1 , i.e., in the region where usually amorphous "simple" polymers [main-chain polymers like e.g., polybutadiene 30 or polymers with small side groups like e.g., poly(ethylene propylene)] 31 show their first or "main" structure factor peak, also called amorphous halo. At lower Qs, around 0.7 Å −1 , a "prepeak" is present.…”

Positron annihilation and relaxation dynamics from dielectric spectroscopy and nuclear magnetic resonance: Cis–trans-1,4-poly(butadiene)

“…On the other hand, the fully amorphous PBD polymer can be obtained under special synthesis conditions of anionic polymerization with the appropriate combinations of the major cis-and trans-isomer and minor vinyl-isomer microstructures giving cis-trans-1,4-poly(butadiene)s (c-t-1,4-PBD). 41 A number of structural 42 and especially, dynamic methods such as rheology, 43 dynamic neutron scattering (NS), 44 BDS, 45 and dynamic light scattering (LS) (Ref. 46) have been used in investigations of these PBD's.…”