Univ. Limoges, CNRS, IRCER, UMR 7315, F-87000, Limoges, France.
Dalton Trans. 2018 Oct 23;47(41):14580-14593. doi: 10.1039/c8dt03076f.
Crosslinking chemistry of a liquid poly(vinylmethyl-co-methyl)silazane with an alane hydride-based complex according to Si : Al ratios varying from 5 to 2.5 has been investigated in detail through the characterization of the as-obtained polymers using solid-state NMR, FT-IR and elemental analyses. This reaction allows tailoring the chemical and physical properties of the neat liquid polysilazane while extending its processability to lead to a series of low-temperature formable aluminium-modified polysilazanes. Structural models have been established based on solid-state NMR spectroscopy. Then, pyrolysis under nitrogen occurring the conversion of polymers into ceramics has been studied by coupling TG experiments with FTIR of pyrolysis intermediates. Pyrolysis at 1000 °C leads to X-ray amorphous Al-modified silicon carbonitride materials with higher ceramic yields compared to the materials obtained from the neat polysilazane. However, the increase of the ceramic yield is minimized with the decrease of the Si : Al ratio from 5 to 2.5 in the as-obtained polymers. This is due to the introduction of -NR3 (R = CH3 and C2H5) units as side groups during the polymer synthesis which are released in the low temperature regime of the pyrolysis. The structural evolution of the amorphous network of ceramics has been studied by annealing up to 1800 °C though X-ray diffraction and Raman spectroscopy. Such studies point out that samples remain amorphous even after annealing at 1400 °C (low Si : Al ratio) and 1600 °C (high Si : Al ratio) before forming Si3N4/SiC/AlN and AlN/SiC/C composites after annealing at 1800 °C depending on the Si : Al ratio fixed in the early stage of the process. Dense pieces could be prepared from these low-temperature formable polymers. The latter, especially those containing a certain portion of -NR3 (R = CH3 and C2H5) units acting as plasticizing groups during the process, display appropriate requirements for pressing at low temperature forming dense pieces with hardness and Young's modulus as high as 21.7 GPa and 192.7 GPa, respectively.
通过固态 NMR、FT-IR 和元素分析对 Si:Al 比从 5 到 2.5 的液体聚（乙烯基甲基-共-甲基）硅氮烷与基于铝烷氢化物的络合物的交联化学进行了详细研究。该反应允许在不改变液态聚硅氮烷的化学和物理性质的情况下对其进行修饰，并扩展其加工性能，以得到一系列低温可成型的铝改性聚硅氮烷。基于固态 NMR 光谱建立了结构模型。然后，通过将 TG 实验与热解中间体的 FTIR 耦合，研究了氮气下的热解，即将聚合物转化为陶瓷。在 1000°C 下进行热解会导致 X 射线无定形 Al 改性硅碳氮化物材料，与从纯聚硅氮烷获得的材料相比，陶瓷收率更高。然而，随着聚合物中 Si:Al 比从 5 降低到 2.5，陶瓷收率的增加最小化。这是由于在聚合物合成过程中作为侧基引入了-NR3（R = CH3 和 C2H5）单元，这些单元在热解的低温区释放出来。通过 X 射线衍射和拉曼光谱研究了陶瓷非晶网络的结构演变。通过在 1800°C 退火研究表明，即使在 1400°C（低 Si:Al 比）和 1600°C（高 Si:Al 比）退火后，样品仍保持非晶态，然后在 1800°C 退火后形成 Si3N4/SiC/AlN 和 AlN/SiC/C 复合材料取决于过程早期固定的 Si:Al 比。可以从这些低温可成型聚合物中制备致密块体。后者，特别是那些在过程中含有一定比例的-NR3（R = CH3 和 C2H5）单元作为增塑剂的聚合物，显示出在低温下成型致密块体的适当要求，硬度和杨氏模量分别高达 21.7 GPa 和 192.7 GPa。
