Design of a Series of Preceramic B-Tri(methylamino)borazine-Based Polymers as Fiber Precursors:  Shear Rheology Investigations

Abstract

Oscillatory shear flow of poly[B-(methylamino)borazine] was studied for suitability as a melt-spinnable material. Shear rheology experiments show that viscosity of molten poly[B-(methylamino)borazine] is temperature dependent following an Arrhenius-type equation. The high value of the flow activation energy is caused by the presence of branched chains and cross-linked portions in the polymer network which supply an intrinsic rigidity to the molecular architecture. Dynamic rheological properties of polymers were measured at their spinning temperatures as a function of the oscillatory frequency. The frequency dependence of the storage and loss moduli as well as the damping factor shows that an appropriate ratio of viscosity to elasticity, i.e., 1 < tan δ < 2.3, is necessary to allow for extrusion while a specific range of elasticity, i.e., 104 < G‘ [Pa] < 3 × 104, is required for drawing the emerging molten fibers as they solidify into fine-diameter solid filaments without loss of cohesion.

Precursor Based on Polyborylborazine for BN Fiber: Preparation and Rheology Properties

“…It is reasonable to suggest that γ 0 = 10% represents an appropriate value to maintain constant dynamic moduli with deformation amplitude. [28] The good thermal stability of the precursor polymer in the melt was confirmed by such experiments, since values of G , G , and η * remain unchanged for short times. So this preceramic polymer exhibited non-Newtonian behavior during extrusion in the first stage.…”

“…[28] The determination of the linear viscoelastic region is an important step in dynamic rheological characterization testing. In this controlled-strain test, samples are heated and then deformed in oscillatory shear flow up to a maximum strain γ 0 , which must be small enough to be in the linear regime.…”

Thermal behaviour of a series of poly[B-(methylamino)borazine] for the preparation of boron nitride fibers

“…As an illustration, Fig. 5 shows the general thermo-mechanical behaviour of a polymer prepared at Table 1 Proportion of -N(CH 3 )-and -N(H)CH 3 units as a function of T thermolysis measured by 13 It is clearly observed that polymer swelling is reduced when the load used during TMA experiments is increased from 0.01 to 0.5 N.…”

“…Such results can be linked to rheological experiments which have been achieved for the same polymeric systems. 13 …”

“…3 In our group, we showed that preceramic polymers of the type poly[B-(methylamino)borazine] are well suited to fill the requirements for the preparation of boron nitride fibers. [7][8][9][10][11][12][13][14] However, a lack of reproducibility in the mechanical performances of these fibers can be encountered if the viscoelastic and thermal properties of polymers are not defined.…”