Evaluation of the processability of boron‐containing organosilazane polymers based on shear rheology

Abstract

The shear rheology of boron-containing organosilazane polymers has been investigated in detail with a double objective. The first objective was to evaluate their processability to form fibers by melt-spinning, and the second objective was to predict their molecular structure. We focused on a representative type of boron-containing organosilazane polymers called boron-modified polysilazanes (BmPSs) with the ideal structure [B(C 2 H 4 SiCH 3 NCH 3 ) 3 ] n (C 2 H 4 ¼ CHCH 3 , CH 2 CH 2 ). Characterization tools showed that their viscous and elastic properties are strongly affected by molecular parameters fixed during synthesis and in particular by the methylamine (MA) : tris(dichlorosilylethyl)borane (TDSB) molar ratio imposed during their synthesis. In the spinning domain, the frequency dependences of the storage and loss moduli showed that the prerequisite conditions for obtaining polymer fibers are fulfilled with samples having 9.0 MA : TDSB molar ratios 9.7. However, the presence of thickening in the computed extensional viscosity function and the loss of cohesion of filament derived from samples with MA : TDSB ratio > 9.2 during drawing put in evidence the best potential of polymers with 9 MA : TDSB ratio 9.2 to generate fine-diameter solid filaments in a stable process. Based on rheological tests, the molecular structure of BmPSs has been tentatively predicted in relation with the MA : TDSB ratio. The increase of the latter favored the disentanglement of the polymer framework, and we postulated that it lowered the molecular weight.

Polymer-Derived Boron Nitride: A Review on the Chemistry, Shaping and Ceramic Conversion of Borazine Derivatives

“…The intermediate curing step results in an increased cross-linking of the polymer and hence in the formation of an infusible polymer fiber necessary for the shape retaining thermal conversion into the ceramic material. Many examples of polymer-derived ceramic fibers have been reported through reviews or specific articles [25,26,28,29,36,37,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113], in particular on BN fibers by our group [101,102,103,104,105,106,107,108,109,110,111,112,113]. …”

Facile synthesis of a novel transparent melt‐spinnable polysilazane

“…When storage and loss modulus as a function of frequency, it can be seen that the magnitude of G′ and G″ demonstrates a positive correlation with the oscillatory frequency since molecular viscosity responses require higher energy. [ 29 ] These results suggest that the polysilazane is highly spinnable.…”

Polymer-derived ceramics route toward SiCN and SiBCN fibers: from chemistry of polycarbosilazanes to the design and characterization of ceramic fibers

“…Indeed a ratio between 9 and 9.2 of MA:TDSB is needed in order to obtain a polymer with suitable rheological properties and stability for melt-spinning. 89) Through a detailed investigation of the polymer-to-ceramic conversion, 164) fibers with average diameter of 12.1¯m, tensile strength of 1.4 GPa and Young's modulus of 120 GPa were obtained through the optimization of the synthesis procedure.…”