4.7 Article

Glass engineering of aminotriazine-based materials with sub-ambient Tg and high kinetic stability

Journal

CRYSTENGCOMM
Volume 22, Issue 25, Pages 4275-4288

Publisher

ROYAL SOC CHEMISTRY
DOI: 10.1039/d0ce00500b

Keywords

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Funding

  1. Natural Sciences and Engineering Research Council of Canada (NSERC) [RGPIN-2015-04014]
  2. Canadian Defence Academy Research Programme (CDARP) from RMC
  3. Canada Foundation for Innovation

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A challenge in glass engineering is the design of molecular glasses combining a high glass kinetic stability (GS) of the amorphous phase with a low (sub-ambient) glass transition temperature (T-g). Triazine derivatives with arylamino substituents readily form glassy phases that can show outstanding resistance to crystallization. In the present study, a series of 12 analogous compounds incorporating phenylamino and cyclohexylamino groups was synthesized, and their thermal properties and intermolecular interactions were studied. All compounds possess an excellent glass-forming ability, a lowT(g)ranging from 32 degrees C to as low as -19 degrees C, and a high GS. While the cyclohexyl derivatives show higherT(g), the phenyl derivatives possess a higher GS with some compounds remaining completely amorphous for over three years despite their sub-ambientT(g). X-ray diffraction, infrared spectroscopy and DFT calculations reveal that the higher volume occupancy and rotational energy barrier of cyclohexyl groups are the main factors responsible for the compounds' higherT(g)values but that they also contribute to their higher propensity to crystallize. In counterpart, the planarity of phenyl groups leads to poorer packing and enhances their GS while keeping theirT(g)well below ambient. The formation of hydrogen bonds or competing interactions provides an additional handle to tune theT(g)of the compounds. Taken together, these studies provide guidelines for the design of molecular glasses with readily tunable thermal properties in view of their functionalization.

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