Abstract
Polyhedral oligomeric silsesquioxanes (POSSs), Am-POSS(x,y), prepared by hydrolytic condensation, contains two types of ammonium side-chain groups, where the numbering of x and y represents the type of ammonium ions in the POSS structure, corresponding to primary (1), secondary (2), tertiary (3), and quaternary (4) ammonium ions. Mixtures of the two starting materials selected from organotrialkoxysilanes containing primary, secondary, and tertiary amines and a quaternary ammonium salt [(RO)3Si(CH2)3R′, R = CH3 or CH2CH3, R′ = NH2, NHCH3, N(CH3)2, and N(CH3)3Cl] were dissolved in dimethyl sulfoxide (DMSO). The hydrolytic condensation was performed in the presence of bis(trifluoromethansulfonyl)imide (HNTf2) and water. All Am-POSS(x,y) structures consisted of a cage-type octamer (T8-POSS), as confirmed by 29Si NMR spectrometry and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses indicated that Am-POSS(1,3), Am-POSS(1,4), and Am-POSS(2,4) had amorphous structures. These POSSs have two or three differences in the number of methyl groups between the two types of ammonium side-chains. Conversely, Am-POSS(1,2), Am-POSS(2,3), and Am-POSS(3,4) had crystalline structures. The difference in the number of methyl groups between the two types of ammonium side-chains in these POSSs is only one. Therefore, the crystalline-amorphous structure of Am-POSS(x,y) is controlled by the side-chain group combinations. Furthermore, Am-POSS(1,3), Am-POSS(1,4), and Am-POSS(2,4) are protic ionic liquids with relatively low flow temperatures.
Highlights
Polyhedral oligomeric silsesquioxanes (POSSs), which are generally prepared by the hydrolytic condensation of trifunctional silane compounds, such as organotrialkoxysilanes and organotrichlorosilanes, have attracted much attention in recent years as compounds having both inorganic and organic characteristics
In our previous studies on the preparation of ammonium-functionalized POSSs using superacid catalysts, the solvent water was yielded a mixture of cage-type octamer and decamer [20], while applying the solvent dimethyl sulfoxide (DMSO) selectively provided only a cage-type octamer in higher yield at short reaction times [21]
Am-POSS(x)s were prepared in DMSO by the hydrolytic condensation of
Summary
Polyhedral oligomeric silsesquioxanes (POSSs), which are generally prepared by the hydrolytic condensation of trifunctional silane compounds, such as organotrialkoxysilanes and organotrichlorosilanes, have attracted much attention in recent years as compounds having both inorganic and organic characteristics. In addition to the remarkable thermal and chemical stability derived from siloxane-bond frameworks, good dispersibility and solubility are provided due to regulated cage structures and suitable side-chain groups [1,2,3,4]. POSSs are, in great demand as dispersible inorganic compounds for the development of organic—inorganic hybrid materials [5,6,7,8,9,10]. Well-known POSSs are typically crystalline, cage-type octamers, because of their isotropic cubic structure. The amorphization of POSSs is one of the recent interesting topics in basic research and material applications. Amorphous POSS dimers [11] and polymers [12,13,14] are prepared
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