Thermal properties of polymethylvinylborosiloxanes

Abstract

New branched polymethylvinylborosiloxanes (PMVBSs) with random structures were prepared, and their chemical structures were studied by spectroscopic methods (FTIR, 1 H-, 29 Si-, and 11 B-NMR) and elemental analysis (% C, % H, % Si, and % B). Average molecular weights M w and M n were determined by a size exclusion chromatography (SEC), and dynamic viscosities were measured in Brookfield cone-plate reoviscometer HBDV-II?cP. Thermal properties of PMVBSs were studied under air and under nitrogen atmosphere. Thermal curves were interpreted from the point of view of physical and chemical transitions, taking place during the heating process of PMVBSs. Parameters of their thermal stabilities and glass transition temperatures (T g ) were determined. The synthesized PMVBSs are characterized by low glass transition temperatures (T g : from -122 to -137°C) which depend on their chemical structures. It was concluded that gaseous products (such as volatile siloxanes, silanes, CO 2 , H 2 O, CH 2 O, methanol, and formic acid), which could be liberated during the heating process of PMVBSs, promote ceramization processes, leading to the formation of the ceramics of a type SiBCO-a borosilicate glass and silica.

Synthesis of hyperbranched polymethylvinylborosiloxanes and modification of addition‐curable silicone with improved thermal stability

“…A strong peak at 0.17 ppm corresponded to hydrogens in Si―CH 3 . Strong peaks at 5.83 (q, J 1 = 23.3 Hz, J 2 = 11.3Hz, 1H) and 6.02 ppm (m, J 1 = 23.3 Hz, J 2 = 11.3Hz, J 3 = 2.1Hz, 2H) corresponded to hydrogens in Si―CH═CH 2 groups . A weak peak at 2.09 ppm corresponded to hydrogen in B―OH groups .…”

“…This observation indicated that most silicon atoms were connected through ―O―B linkages at both sides. Moreover, a medium peak at −34.60 ppm may correspond to the middle silicon in the Si―O―Si―O―Si linkages, as shown in Fig. (c, structure (c)), which were formed from the reaction between CH 3 O―Si― and HO―Si groups.…”

“…These polymers, named polyborosiloxanes (PBSs), contain high‐energy B―O and Si―O bonds with corresponding bond energies of 537.6 and 422.5 kJ mol −1 , respectively . PBSs are widely used as active modifiers for thermosetting resins to improve their thermal stability, non‐halogenated flame retardants, heat‐resistant painting and ceramic precursors . Several methods have been described for the synthesis of PBSs from di‐ and tri‐functional silicon compounds as well as boron‐containing compounds, such as boric acid (BA), boron trioxide, boron trichloride and borate esters .…”

“…synthesized PBS through the reaction of BA with vinyltriethoxysilane and cyclotetrasiloxane. Chruściel et al . prepared polymethylvinylborosiloxane (PMVBS) through the reaction of BA with Me 2 SiCl 2 in ether solution, followed by co‐polycondensation of the ethereal solution with MeViSiCl 2 .…”

“…[1] PBSs are widely used as active modifiers for thermosetting resins to improve their thermal stability, non-halogenated flame retardants, heat-resistant painting and ceramic precursors. [2][3][4][5][6][7][8] Several methods have been described for the synthesis of PBSs from di-and tri-functional silicon compounds as well as boron-containing compounds, such as boric acid (BA), boron trioxide, boron trichloride and borate esters. [9][10][11][12] BA is the cheapest source of boron used to prepare PBSs.…”