Investigating the Free‐Volume Characteristics of Regulated Dimethacrylate Networks Below and Above Glass Transition Temperature

Abstract

Studying the relationship between microstructural interactions and resulting macroscopic material properties gives a more elaborate understanding on final material performance. The microstructural arrangement with characteristic length, relaxation, and thermal expansion behavior of regulated dimethacrylate networks is studied by differential scanning calorimetry, dynamic mechanical analysis, thermomechanical analysis, and positron annihilation lifetime spectroscopy at a broad temperature range (250–380 K). The length scale ξ (Tg) of cooperative segmental rearrangement is decreased with increasing crosslinking and degree of freedom in regulated chain transfer agent (CTA)‐based networks. The macro and microscopic thermal expansion coefficients are determined in the glassy and rubbery state for three polymer systems—a dimethacrylate‐based reference (poly2M) and regulated photopolymers with CTAs (i.e., thiol, β‐allyl sulfone). The influence of CTAs on the free volume characteristics (i.e., free volume void size, the specific occupied volume V0, free volume number density per unit mass N′, and free volume fraction f) at the glass transition temperature Tg is correlated with the cooperative length, activation energy Ea,α, and mechanically effective crosslinking density. A more complex understanding of the revealed relations contributes to a more elaborate explanation of final material performance.

Temperature Dependence of the Pore Structure in Polyvinylidene Fluoride (PVDF)/Graphene Composite Membrane Probed by Electrochemical Impedance Spectroscopy

“…The finger-like pores exhibit distorted shapes after being immersed in hot water. This may contribute to the rearrangement of the polymer chains at a higher temperature [20,21]. For the PVDF/graphene membrane, there is no obvious change in the cross-section morphologies after being immersed in the water for 1 h at 50 °C.…”

“…The pore expanding during the immersing process should be attributed to the chain segments relaxation and this relaxation would be determined by temperature [20,21]. As a result, the thermal stability of the pores is related to the heat conduction of the composite membranes during the immersing process.…”

Influence of the Polarity of the Plasticizer on the Mechanical Stability of the Filler Network by Simultaneous Mechanical and Dielectric Analysis

“…Consequently, the intermolecular forces of the polymer chains and the number of free valences in the three-dimensional structure are reduced. The internal space between the polymer chains is thus larger, and the free volume that allows the polymer chains to flow above their glass transition temperature increases [ 11 , 12 , 13 , 14 , 15 ]. This new conformation of the polymer chains, in turn, increases their mobility and enhances the filler distribution in the rubber mixture [ 16 , 17 , 18 , 19 , 20 , 21 ].…”

In situinvestigation of the kinetics and microstructure during photopolymerization by positron annihilation technique and NIR-photorheology

“…23 Next, their microstructure (of CTA-based formulations) in terms of cooperative length, relaxation, thermal macro and micro expansion and free volume characteristics below and above T g were elucidated. 24 It is essential to investigate the crosslinking process more in detail, i.e. factors which inuence network formation, as well as the nal properties of materials.…”

“… 23 Next, their microstructure (of CTA-based formulations) in terms of cooperative length, relaxation, thermal macro and micro expansion and free volume characteristics below and above T g were elucidated. 24 …”