POSS 聚(1-卤代乙炴)：无催化剂固相聚合路线

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本文为英文原文的中文版本。English version: POSS Poly(1-Haloacetylene): Catalyst-Free Solid-State Route

多面体低聚倍半硅氧烷(POSS)基聚(1-卤代乙炴)共轭网络由弗罗茨瓦夫大学化学系的 Marta Cieplucha、Mateusz Janeta 与 Sławomir Szafert 合成,相关工作于 2025 年发表于 Materials Chemistry Frontiers。三种八官能化单体 POSS-C2Cl、POSS-C2Br 与 POSS-C2I 通过八(3-氨丙基)倍半硅氧烷与相应的 4-(卤代乙炴基)苯甲酰氯发生酰胺偶联制得,并被证明可在固相中、于无任何过渡金属催化剂的条件下发生热聚合,生成高度交联的聚(1-卤代乙炴)网络。该工作是首例报道的 1-碘乙炴衍生物聚合,也是首个完全不依赖金属引发剂实现的 1-卤代炴聚合实例。

八官能化 POSS 卤代炴单体的合成

八(3-氨丙基)倍半硅氧烷经酰胺偶联合成 POSS 卤代乙炴单体 POSS-C2Cl、POSS-C2Br 与 POSS-C2I

图 1. 1-卤代乙炴基官能化 POSS 单体的合成。八(3-氨丙基)倍半硅氧烷盐酸盐(OAS-POSS)与 4-(卤代乙炴基)苯甲酰氯(8.2 当量)及三乙胺(16.2 当量)在 N,N-二甲基甲酰胺中于 0 摄氏度反应,得到完全八取代的酰胺连接产物 POSS-C2Cl(70%)、POSS-C2Br(60%)与 POSS-C2I(71%)。

三种单体由八(3-氨丙基)倍半硅氧烷与相应的 4-(卤代乙炴基)苯甲酰氯在三乙胺存在下、于 N,N-二甲基甲酰胺中 0 摄氏度反应制备,酰胺连接的八官能 POSS 衍生物分离产率为 60% 至 71%。溶液与固态的系统表征,包括氢谱与碳-13 核磁共振、硅-29 核磁共振、氮-15 交叉极化魔角旋转核磁共振、漫反射红外傅里叶变换光谱(DRIFT)以及质谱,确认了完全八取代、合成全程 T8 倍半硅氧烷笼的完整性,以及各单体中卤代炴官能团的保留。DRIFT 谱中约 2197 cm−1 处的特征炴基伸缩振动是碳碳三键最直接的光谱标志,而硅-29 核磁共振谱中约 −66 ppm 处的单一对称共振峰证明立方笼的八个硅原子保持晶体学等价,且未发生笼结构重排。

无催化剂、氧引发的固相热聚合

POSS 卤代乙炴单体无催化剂固相聚合生成聚(1-卤代乙炴) T8 笼网络

图 2. POSS-C2X(X = Cl、Br、I)的无催化剂固相热聚合,生成高度交联的 polyPOSS-C2X 网络。八个外围 1-卤代炴基中的每一个都经历碳碳三键向双键的转化,生成锚定于刚性立方 POSS 核心并由其向外延伸的三维聚(1-卤代乙炴)网络。右侧红色片段代表连接相邻 POSS 单元的新生成聚合物主链片段。

固相热聚合的发现源于差热分析,该分析显示三种单体在约 130 至 273 摄氏度范围内各自出现明显的放热事件,而热重曲线中没有相应的质量损失,这正是固相反应而非分解过程的判据。差示扫描量热法确认了转变的不可逆性,第一次升温循环中观测到的放热峰在随后的循环中被聚合物材料特有的玻璃化转变所取代。在充氩手套箱中于严格无氧条件下进行的对照实验,经 DRIFT 光谱检测未发现任何聚合迹象,说明分子氧起到关键的引发作用,最可能的途径是高温下过氧自由基的生成。

聚(1-卤代乙炴)网络形成的光谱学确认

从单体到聚合物的结构转变由固态碳-13 交叉极化魔角旋转核磁共振、DRIFT 与拉曼光谱以及 X 射线光电子能谱(XPS)分析相互印证。在 polyPOSS-C2Br 的碳-13 CP-MAS 谱中,归属于 sp 杂化炴碳的 78.3 与 51.7 ppm 信号完全消失,取而代之的是归属于聚卤代乙炴主链 sp2 杂化烯碳的 139.0 与 135.2 ppm 两个新共振峰。聚合物的 DRIFT 谱中 2197 cm−1 处炴基伸缩振动带完全消失,而 1768 cm−1 处新出现的吸收确认了共轭 C=CBr 伸缩振动模式的形成。拉曼光谱识别出 1580 与 1555 cm−1 处反式聚卤代乙炴主链的特征谱带,XPS 数据确认溴的键合环境由单体中的 sp 碳变为聚合物中的 sp2 碳,排除了显著副反应的发生。硅-29 CP-MAS 谱保持 −66.2 ppm 处的单一对称共振峰,证明聚合全程 T8 笼完整保留。

基于 Kissinger 法的聚合动力学与活化能

以时间分辨拉曼光谱在等温条件下监测的聚合动力学表明,三种单体均遵循准二级模型。对于 POSS-C2Br,在 165 摄氏度下前 10 分钟内转化率即超过 47%,6 小时内实现完全转化。对于 POSS-C2Cl(145 摄氏度)与 POSS-C2I(175 摄氏度),完全转化分别需要 24 与 25 小时。由非等温差热分析实验经 Kissinger 法测定的表观活化能分别为 POSS-C2Br 179 kJ/mol、POSS-C2Cl 209 kJ/mol 与 POSS-C2I 217 kJ/mol,显著高于乙烯基单体经典自由基聚合的数值,反映出固相约束下三键活化所需克服的更高能垒。

交联网络的热稳定性、不溶性与光学带隙

三种聚合物在常见有机溶剂中完全不溶,其分解起始温度分别为 polyPOSS-C2Br 267 摄氏度、polyPOSS-C2Cl 287 摄氏度与 polyPOSS-C2I 309 摄氏度。立方 POSS 骨架强制形成的三维交联拓扑,即每个笼上八个炴基同时参与聚合,是所得网络具有优异不溶性与力学坚固性的原因。氯代、溴代与碘代聚合物的玻璃化转变温度分别为 51、140 与 211 摄氏度,证明三种材料在室温下均表现为玻璃态固体。

polyPOSS-C2Cl、polyPOSS-C2Br 与 polyPOSS-C2I 直接与间接光学带隙柱状图,由固态紫外可见吸收光谱经 Tauc 作图法确定

图 3. 由固态紫外可见吸收光谱经 Tauc 作图法确定的 polyPOSS-C2Cl、polyPOSS-C2Br 与 polyPOSS-C2I 的直接带隙(蓝柱)与间接带隙(深红柱),每列下方给出相应重复单元的结构片段。直接带隙由 2.79 eV(Cl)经 2.74 eV(Br)系统降至 2.38 eV(I),反映出直接引入聚合物主链的卤素取代基极化率的增加。

通过固态紫外可见光谱与 Tauc 作图法研究的光学性质表明,polyPOSS-C2Cl、polyPOSS-C2Br 与 polyPOSS-C2I 的直接光学带隙分别为 2.79、2.74 与 2.38 eV。三个数值均落在被认为对光伏与光电应用最为有利的 1 至 3 eV 可见光区间内。所有聚合物的吸收谱相对其单体显著展宽并红移,与聚卤代乙炴主链上形成扩展 π 共轭体系相一致。带隙由氯代聚合物到碘代聚合物的系统性收窄,反映了卤素极化率的增加及其对共轭链电子结构的影响。此外还确定了间接带隙,polyPOSS-C2Cl 为 2.19 eV,polyPOSS-C2Br 为 1.57 eV,polyPOSS-C2I 为 1.47 eV,使碘代聚合物的光学响应延伸至近红外区。

综合而言,该工作确立了制备杂化共轭聚合物网络的新合成范式,即利用立方 POSS 骨架的几何刚性与热稳定性,通过无催化剂、氧引发的固相过程引导聚(1-卤代乙炴)链的三维交联。所得材料兼具卤代聚乙炴的半导体特性与倍半硅氧烷杂化结构的优异热稳定性与结构精确性,是有机光伏、场效应晶体管、化学传感器与电致变色器件领域值得探索的候选材料。该研究延续并拓展了弗罗茨瓦夫大学 Janeta 与 Szafert 课题组关于功能化 POSS 杂化材料的整体研究计划,此前的工作涵盖用于超分子组装与碘捕获的亚胺功能化 POSS、用于催化二氧化碳环加成的锌-POSS 配合物,以及用于硫醚选择性氧化为亚砜的二氟硼-POSS 光催化剂。

原始文献

Cieplucha, M.; Janeta, M.; Szafert, S. Hybrid inorganic–organic polyhedral oligomeric silsesquioxane-based poly(1-haloacetylene)s: thermal, solid-state polymerization. Materials Chemistry Frontiers 2025, 9, 3034. DOI: 10.1039/d5qm00583c | View at RSC Publishing

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