A structural interpretation of the two components governing the kinetic fragility from the example of interpenetrated polymer networks

• Published in: Journal of polymer science. Part B, Polymer physics Vol. 56; no. 20; pp. 1393 - 1403
• Main Authors: Araujo, Steven, Batteux, Florian, Li, Wenlong, Butterfield, Lena, Delpouve, Nicolas, Esposito, Antonella, Tan, Li, Saiter, Jean‐Marc, Negahban, Mehrdad
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 15.10.2018; Wiley Subscription Services, Inc; Wiley
• Subjects: Condensed Matter; cooperativity; Differential scanning calorimetry; Divergence; Dynamic mechanical analysis; Fragility; Glass; glass transition; Interpenetrating networks; Materials Science; Physics; Polymers; Relaxation time; Rigidity; Temperature dependence; thermosets; Time dependence
• ISSN: 0887-6266; 1099-0488
• DOI: 10.1002/polb.24722

ABSTRACT Kinetic fragility and cooperativity length, two major characteristics of the relaxation dynamics at the glass transition, are, respectively, investigated by dynamic mechanical analysis and modulated temperature differential scanning calorimetry in a series of interpenetrated polymer networks based on acrylate and epoxy systems. The relaxation dynamics are impacted by two variables: the rigidity of the network, and the structural heterogeneity resulting from blending. However, the fragility and the cooperativity do not vary similarly. The glass transition progressively broadens as the mass fractions of acrylate and epoxy become equivalent, leading to a strong decrease in cooperativity. On the other hand, under the same conditions, the fragility transitions between the lower value of pure acrylate and the higher value of pure epoxy. This divergence helps concluding that the variations in the temperature dependence of the relaxation time are not purely related to the more or less cooperative nature of the glass transition. By splitting the fragility index in a volume contribution and an energetic contribution, it is shown that the contribution of cooperativity to the variations of the relaxation time with temperature is increased under two structural conditions: low backbone rigidity and high intermolecular interactions. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1393–1403 Interpenetrated polymer networks were obtained by simultaneous ultraviolet‐photocuring acrylate and epoxy resins with highly different crosslink densities and chain rigidities. From the investigation of the kinetic fragility, it is proposed to provide a structural representation of its thermal and volume components: the first is related to the rigidity of the polymer backbone, and the second depends on the nature and amount of intermolecular interactions.