Thermally stable and flame retardant low dielectric polymers based on cyclotriphosphazenes
作者:Ho Lim、Ji Young Chang
DOI:10.1039/b920203j
日期:——
We prepared thermally stable, low dielectric polymers by thermal polymerization of cyclotriphosphazenes bearing acetylene or styrene groups. Homosubstituted cyclotriphosphazene 1, containing acetylene groups, was synthesized by reaction of hexachlorocyclotriphosphazene with sodium salts of 4′-trimethylsilylethynyl-1,1′-biphenyl-4-ol and subsequent removal of trimethylsilyl groups under basic conditions. Heterosubstituted cyclotriphosphazene 2 was prepared using 4-phenylphenol as a cosubstituent. Cyclotriphosphazene 3 with styrene groups was prepared by reaction of hexachlorocyclotriphosphazene with sodium salts of 4-hydroxystyrene. Highly cross-linked polymers were obtained by thermal polymerization of the cyclotriphosphazenes at 200 °C for 1 and 2 and at 150 °C for 3. The 5% weight loss temperatures of the cross-linked polymers of compounds 1–3, measured by TGA, were above 470 °C. The flame-retardant property of the polymers was evaluated by measuring LOI (limiting oxygen index) values. The polymers of cyclotriphosphazenes 1–3 showed very high LOI values of 52, 50 and 49, respectively. We also prepared copolymers of cyclotriphosphazene 3 with styrene by UV irradiation in the presence of a photoinitiator (2,2-dimethoxy-2-phenylacetophenone). In the TGA thermograms, the copolymers showed good thermal stability, nearly comparable to the homopolymer of 3 when the composition of 3 was higher than 60%. The dielectric properties of the polymers were measured by a metal–insulator–metal method. The polymer obtained from acetylene-containing cyclotriphosphazene 1 showed dielectric constant and dielectric loss values of about 3.12 and 0.0016, respectively, at 1 GHz. The polymer of cyclotriphosphazene 3 showed a dielectric constant of 2.4 and a dielectric loss of 0.0014 at 1 GHz.
我们通过热聚合含有乙炔或苯乙烯基团的环三膦烯,制备出了热稳定性低介电聚合物。含有乙炔基团的均取代环三膦唑 1 是通过六氯环三膦唑与 4′-三甲基硅烷基乙炔基-1,1′-联苯-4-醇的钠盐反应合成的,随后在碱性条件下去除三甲基硅烷基。以 4-苯基苯酚为共取代基制备了异构环三膦唑 2。六氯环三磷嗪与 4-羟基苯乙烯的钠盐反应,制备出带有苯乙烯基团的环三磷嗪 3。1 和 2 在 200 ℃、3 在 150 ℃ 下进行热聚合,可获得高度交联的聚合物。通过 TGA 测量,1-3 化合物交联聚合物的 5% 失重温度高于 470 ℃。聚合物的阻燃性能通过测量 LOI(极限氧指数)值进行评估。环三膦烯 1-3 的聚合物显示出极高的 LOI 值,分别为 52、50 和 49。我们还在光引发剂(2,2-二甲氧基-2-苯基苯乙酮)存在的情况下,通过紫外线照射制备了环三唑膦 3 与苯乙烯的共聚物。在 TGA 热图中,共聚物显示出良好的热稳定性,当 3 的成分高于 60% 时,其热稳定性几乎与 3 的均聚物相当。聚合物的介电性能是通过金属-绝缘体-金属法测定的。由含乙炔的环三唑烷 1 制成的聚合物在 1 GHz 时的介电常数和介电损耗值分别约为 3.12 和 0.0016。环三磷嗪 3 的聚合物在 1 千兆赫时的介电常数为 2.4,介电损耗为 0.0014。