Polysilsesquioxanes (PSQ) containing phenyl groups as substituents on the silicon atom can form transparent, hard and glassy
materials at room temperature, which reversibly soften when heated above the glass transition temperature. Further increase in
temperature leads to irreversible curing. With this property, polyphenylsilsesquioxanes can be assigned to the so-called melting
gels. In contrast to the aromatic systems, polysilsesquioxanes with alkyl groups belonging to this class of materials are not
known. To identify structural differences between aryl and alkyl systems, polyalkylsilsesquioxanes (RPSQs with R = methyl,
ethyl, propyl, hexyl, octyl, decyl, dodecyl, hexadecyl, and octadecyl) were synthesised by a solvent-free, acid-catalysed
hydrolysis and condensation reaction of alkyltrimethoxysilanes followed by thermal treatment at 300 °C under N2 atmosphere.
The influence of the alkyl chain length on the structure built and the thermally initiated further condensation reactions were
investigated via NMR, FTIR, TGA, DSC, SEC, and XRD. Depending on the alkyl chain length, the formation of highly
crosslinked, insoluble systems (Me-PrPSQ), low molecular weight oligosilsesquioxanes in the form of cages (Hex-DecPSQ) to
semicrystalline, lamellar layers (Dodec-OctadecPSQ) were detected. A low degree of condensation, inhibition of self-assembly
and preferentially intermolecular condensation reactions were found to be crucial factors in the melting gel formation