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Boron‐modified polysilylcarbodi‐imides as precursors for Si–B–C–N ceramics: Synthesis, plastic‐forming and high‐temperature behavior
Author(s) -
Weinmann Markus,
Haug Rainer,
Bill Joachim,
de Guire Mark,
Aldinger Fritz
Publication year - 1998
Publication title -
applied organometallic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 71
eISSN - 1099-0739
pISSN - 0268-2605
DOI - 10.1002/(sici)1099-0739(199810/11)12:10/11<725::aid-aoc777>3.0.co;2-2
Subject(s) - chemistry , borane , hydroboration , imide , boranes , trimethylsilyl , boron , polymer chemistry , pyridine , medicinal chemistry , organic chemistry , catalysis
The synthesis, by two different reaction pathways, of boron‐modified polysilylcarbodi‐imides of general type {B[C 2 H 4 Si(R)NCN] 3 } n (R =singly bonded organic ligand) and the plastic‐forming and the thermal behavior of these polymers are described. Compounds {B[C 2 H 4 Si(R)NCN] 3 } n [ 2a , R = H; 2b , R = CH 3 ; 2c, R = (NCN) 0.5 ] can be obtained by treatment of the vinyl‐substituted polysilylcarbodi‐imides [(H 2 CCH)(R)SiNCN] n [ 1a , R = H; 1b , R = CH 3 ; 1c , R = (NCN) 0.5 ] with borane dimethylsulfide BH 3 ·S(CH 3 ) 2 . The polysilylcarbodi‐imides 1a – 1c themselves are accessible via the reaction of vinyl‐substituted chlorosilanes (H 2 C=CH)‐(R)SiCl 2 with cyanamide H 2 N‐C≡N in the presence of pyridine or by a non‐oxide sol–gel process of vinylated chlorosilanes and bis(trimethylsilyl)carbodi‐imide, (H 3 C) 3 SiNCNSi(CH 3 ) 3 . In the second method for the synthesis of 2a – 2c , hydroboration of vinyl‐substituted chlorosilanes (H 2 CCH)(R)SiCl 2 with borane dimethylsulfide, borane trimethylamide or borane triethylamide to yield the tris[(chlorosilyl)ethyl]boranes B[C 2 H 4 Si(R)Cl 2 ] 3 ( 3a , R = H; 3b , R = CH 3 ; 3c , R = Cl) is followed by treatment of the as‐obtained compounds with bis(trimethylsilyl)carbodi‐imide, which results in the formation of the hydroborated polysilylcarbodi‐imides 2a – 2c . The thermogravimetric behavior of the polymers 1a – 1c and 2a – 2c up to 2300°C is reported. It is shown that boron‐modified polysilylcarbodi‐imides are suitable precursors for the preparation of dense bulk ceramics. Therefore, the preparation of green bodies of the hydroborated polysilylcarbodi‐imides 2a – 2c by plastic forming (PF) is described. A series of experiments points to the fact that the microstructure of the as‐obtained ceramic monoliths obtained by subsequent thermolysis of the plastic‐formed green bodies is strongly influenced by the conditions during plastic forming. © 1998 John Wiley & Sons, Ltd.