Sridhar, Arun Srikanth published the artcileEffect of stoichiometry on crosslinked epoxy resin characteristics: structural heterogeneities, topological defects, properties, free volume and segmental mobility, Category: quinuclidine, the publication is Soft Matter (2022), 18(12), 2354-2372, database is CAplus and MEDLINE.
Exptl. studies have shown that changes in stoichiometry (R, ratio of amine groups to epoxy groups) cause considerable variations in the properties of epoxy-amine systems. Rationales based on free volume concepts have been routinely used to address these variations in properties but have hardly been satisfactorily substantiated. Many of these rationales remain as unverified conjectures to date. Substantiating these rationales will certainly bolster our understanding of the structure-stoichiometry-property relationship, but is difficult, due to inherent challenges involved in unambiguously characterizing the structural heterogeneities induced by changes in stoichiometry (structural heterogeneities include compositional distribution in the functionality of monomers, non-uniform dispersion of elastic chains and topol. defects). The aim of the present work is to gain mol.-level insights into this relationship and to verify the rationales that rely on free volume concepts used for addressing the variations in properties with stoichiometry, with the help of all-atom mol. dynamics (MD) simulations. Five epoxy-amine systems with varying R ranging from 0.4 to 3, including the stoichiometric system (R = 1), were considered for these purposes. The properties of interest namely d., glass transition temperature (Tg) and thermal expansion coefficient in the rubbery state (αrl) of these systems were predicted. The local structure, fractional free volume and segmental mobility of these systems were then subsequently characterized as a function of stoichiometry and the results were analyzed in detail. The role played by defects in properties and fractional free volume was then investigated. The results revealed significant insights into the compositional distribution of monomers with different functionalities as well as offered insights into the dispersion state and mobility of dangling chains, sols and elastic chains in the systems. Further, strong correlations were found between defect composition, fractional free volume at an elevated temperature (600 K) and thermomech. properties (Tg and αrl) and it was established that the key mechanism underlying these correlations was the plasticization caused by defects. Anal. based on the rule of mixture models showed that these correlations were found to be in good agreement with the interpretations based on free volume concepts. The results also revealed a strong neg. correlation between fractional free volume at room temperature and defect composition, a phenomenon typically associated with the antiplasticization effect.
Soft Matter published new progress about 1761-71-3. 1761-71-3 belongs to quinuclidine, auxiliary class Ploymers, name is 4,4-Diaminodicyclohexyl methane, and the molecular formula is C2H2N4O2, Category: quinuclidine.
Referemce:
https://en.wikipedia.org/wiki/Quinuclidine,
Quinuclidine | C7H13N | ChemSpider