Dumbbell-shaped polyhedral oligomeric silsesquioxanes/polystyrene nanocomposites: The influence of the bridge rigidity on the resistance to thermal degradation

Abstract

A comparative study concerning the resistance to the thermal degradation of polystyrene-based nanocomposites loaded with five novel aromatic dumbbell-shaped polyhedral oligomeric silsesquioxanes was carried out in dynamic heating conditions. The fillers were formed by two identical silicon cages R 7 (SiO 1.5 ) 8 (R ¼ isobutyl) linked to several aromatic bridges (Ar, Ar-Ar, Ar-O-Ar, Ar-S-Ar and Ar-SO 2 -Ar) where Ar ¼ p-C 6 H 4 . Nanocomposites were prepared by in situ polymerization of styrene in the presence of 5% of appropriate polyhedral oligomeric silsesquioxanes. The actual filler content in the products obtained, which was checked by 1 H NMR spectroscopy, resulted in all cases slightly higher than that in starting mixtures. Glass transition temperature (T g ) was determined by differential scanning calorimetry. Thermogravimetric (TG) and differential thermogravimetric (DTG) analysis were carried out in both flowing nitrogen and static air atmosphere, and temperatures at 5% mass loss (T 5% ) were determined to investigate the resistance to the thermal degradation. The results obtained were compared with each other and discussed. The resistance to the thermal degradation showed modest increments in respect to neat polystyrene, differently from analogous nanocomposites containing as fillers aliphatic bridged polyhedral oligomeric silsesquioxanes, as supported by scanning electron microscopy measurements which evidenced polyhedral oligomeric silsesquioxanes auto-aggregation phenomena. This behaviour was interpreted as due to the rigidity of polyhedral oligomeric silsesquioxane's aromatic bridges, which leads to low miscibility between filler and polymeric matrix.

Synthesis and Thermal Behaviour of Novel Aliphatic/Aromatic Hepta-Cyclopentyl Bridged Polyhedral Oligomeric Silsesquioxanes (POSSs)/Polystyrene (PS) Nanocomposites

“…In the next Fig. 4a, b the DT 5 % values of the here studied nanocomposites prepared with cyclopentyl POSSs (solid circles and squares) are compared with those previously obtained for the nanocomposites prepared with the corresponding isobutyl POSSs (empty circles and squares) [33,34]. Since we would compare the increments in thermal stability between nanocomposites containing POSSs with the same bridge and different (cyclopentyl or isobutyl) periphery, isobutyl compounds are indicated on the x axis by the same numbers of the corresponding cyclopentyl derivatives.…”

“…Comparable residue values (in the 4-9 % range) among various nanocomposites were found, which were slightly higher for the degradations in nitrogen and for aromatic 4-7 nanocomposites in respect to aliphatic 1-3 compounds, in agreement with higher difficulty of aromatic bridges to be decomposed [34]. The IR spectra of the residues at 700°C from various nanocomposites were thus performed, aiming to have some information about the degradation process.…”

“…Their thermal decomposition was studied and higher thermal stability was evidenced for cyclopentyl derivatives than for the isobutyl ones. The bridged PS based nanocomposites of isobutyl POSSs were thus prepared, that exhibited averagely only little improvements of thermal stability in respect to neat PS [33,34]. We studied here the thermal decomposition of PS nanocomposites containing aliphatic and aromatic bridged polyhedral silsesquioxanes with cyclopentyl peripheries.…”

Thermal characterization of a series of novel hepta cyclopentyl bridged POSS/PS nanocomposites

“…Since the effective modification of polymer with POSSs depends, to a large extent, on the successful dispersion of the nanoparticles within the matrix, we studied, in these years, the influence of filler percentage [13], of the electron-donor or electron-withdrawing character of the substituents on silicon cage [14,15], of symmetry/asymmetry [16] and rigidity/flexibility [17][18][19] of the nanoparticles structure on the dispersion/aggregation in the polymer matrix. On continuing the study in this field, we report here the synthesis and thermal behavior of a bridged POSS/PS system whose molecular structure is reported in Fig.…”

Photoresponsive Bridged Silsesquioxane Nanoparticles with Tunable Morphology for Light-Triggered Plasmid DNA Delivery

“…[1][2][3][4][5][6][7][8][9] Nonetheless, it remains a challenge to control the kinetic in sol-gel processes, which generally lead to macroscaled nonporous BS functional materials. [10][11][12] Their design involves kinetically-controlled sol-gel processes of bis-or multiorganoalkoxysilanes which yield to hybrid materials with very high organic contents depending on the type of organic groups.…”