Process modeling of the low‐temperature evolution and yield of polycarbosilanes for ceramic matrix composites

Abstract

The volatilization of polycarbosilanes is important to the processing and performance of polymer infiltration and pyrolysis‐based ceramic matrix composites. Low molecular weight (MW) polycarbosilane is often present in preceramic polymers and enhances viscosity for the purpose of composite infiltration. Due to the volatility of low MW chains, a model was developed to semi‐empirically determine the MW distribution and then predict the mass yield and evolution of the MW distribution as a function of temperature and time for StarPCS™ SMP‐10. The enthalpy of vaporization, the temperature dependence of the enthalpy of vaporization, the temperature dependence of the normal boiling point and a representation of the molecular weight distribution were fit using a series of thermogravimetric measurements, involving isothermal holds on a particular batch of SMP‐10. Once calibrated for SMP‐10 in this fashion, the molecular weight distribution of different batches of SMP‐10 could be fit using a thermogravimetric measurement involving a reduced temperature‐time series. The model was then predictive of mass loss over time for temperatures below the onset of curing (>90°C). Understanding this volatilization enables improved SiC yield, reduced processing time and minimizing void/bubble formation.

Effect of high‐pressure carbon dioxide on thermal conversion process of polydimethylsilane to Si–C backbone polymers

“…The polymer yield was always above 85%. 26,27 The resulting ceramic yield of the 420°C condensate is higher than that of the 380°C condensate. Figure 6B shows a photoimage of condensates obtained at 400°C and 420°C after immersing in toluene.…”

“…This TG curve feature of the 380°C condensate is similar to that of allylhydridopolycarbosilane (AHPCS) (SMP-10, Starfire® Systems, Inc. ), which is liquid in nature and is reported to contain a considerable amount of short chains (MW range of 800-5000), although absolute ceramic yield of AHPCS is high (about 80%) because of the effect of cross-linkable allyl groups. 26,27 The resulting ceramic yield of the 420°C condensate is higher than that of the 380°C condensate. The TG curve, however, shows two-step mass losses at 200-400°C and 400-600°C with an interval plateau region.…”

Grignard coupling-based synthesis of vinyl-substituted hydridopolycarbosilane: effect of starting material and polymerization behavior

“…The Grignard coupling-based synthesis of polycarbosilanes has already been investigated in terms of mechanism, structural characteristics, kinetics, and side reactions; [8][9][10][11] however, out current understanding of polycarbosilane growth via this method is very limited. 12,13 For example, Guodong and Jang analyzed and discussed the change in the properties of polycarbosilane with the growth behavior of the polymer, but it is limited to the Yajima method. 14,15 In other cases, molecular weight was analyzed only to evaluate individual synthesis conditions, and the studies related to polymer growth were very insignicant.…”

“…13 C NMR spectra of (a) P1-1, (b) P2, and (c) P3.© 2021 The Author(s). Published by the Royal Society of Chemistry RSC Adv., 2021, 11, 11771-11778 | 11773 Paper RSC Advances Open Access Article.…”

A polymer infiltration and pyrolysis (PIP) process model for ceramic matrix composites (CMCs)

“…For example, see Refs [39–42]. Pyrolysis of polycarbosilane polymer has been modeled by Key et al 43 …”