Blocky bromination of syndiotactic polystyrene via post-polymerization functionalization in the heterogeneous gel state
Blocky bromination of syndiotactic polystyrene via post-polymerization functionalization in the heterogeneous gel state
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DOI：
10.1039/c8py01008k
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发表时间：
2018-10
影响因子：
4.6
通讯作者：
Kristen F. Noble;A. M. Noble;S. Talley;R. Moore
中科院分区：
文献类型：
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作者：
Kristen F. Noble;A. M. Noble;S. Talley;R. Moore
这项工作展示了使用在非均相凝胶状态下进行的后聚合官能化方法，成功地对含有 6-30 mol% 对溴苯乙烯单元的间规聚苯乙烯 (sPS-co-sPS-Br) 共聚物进行了嵌段溴化。为了进行比较，使用均相（溶液态）反应条件制备了一组匹配的随机溴化 sPS-co-sPS-Br 共聚物。使用 1H 和 13C 核磁共振 (NMR) 光谱评估溴化程度和共聚物微观结构。凝胶态（块状）和溶液态（无规）共聚物的 NMR 谱在 6 mol% Br 以上表现出显着不同的共振频率和峰强度，并提供了直接证据，表明凝胶态官能化产生具有非无规“块状”微观结构的共聚物。使用超小角 X 射线散射 (USAXS) 和小角 X 射线散射 (SAXS) 分析的块状共聚物的淬火膜显示出微相分离的形态，这进一步支持了块状共聚物包含不同的纯 sPS 片段和随机溴化 sPS 片段，这与完全随机的类似物不同。使用差示扫描量热法 (DSC) 检查共聚物的结晶行为，表明与无规类似物相比，嵌段共聚物在较低的过冷度下更容易结晶且结晶更快。基于 10 w/v% sPS/CCl4 凝胶的半结晶形态开发了嵌段共聚物的计算机模拟，以合理化异质官能化对共聚物微观结构和结晶行为的影响。模拟发现与基于 NMR 结果的微观结构分析一致，并证实限制溴化试剂对从凝胶网络的结晶部分中充分去除的单体的可及性产生的共聚物具有更普遍的长、不间断的 sPS 均聚物序列。因此，嵌段微观结构有利于保持所得嵌段共聚物所需的结晶性。
This work demonstrates the successful blocky bromination of syndiotactic polystyrene (sPS-co-sPS-Br) copolymers containing 6–30 mol% p-bromostyrene units, using a post-polymerization functionalization method conducted in the heterogeneous gel state. For comparison, a matched set of randomly brominated sPS-co-sPS-Br copolymers was prepared using homogeneous (solution-state) reaction conditions. The degree of bromination and copolymer microstructure were evaluated using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. The NMR spectra of gel-state (Blocky) and solution-state (Random) copolymers exhibit strikingly different resonance frequencies and peak intensities above 6 mol% Br and provide direct evidence that functionalization in the gel state produces copolymers with non-random “blocky” microstructures. Quenched films of the Blocky copolymers, analyzed using ultra-small-angle X-ray scattering (USAXS) and small-angle X-ray scattering (SAXS), show micro-phase separated morphologies, which further supports that the Blocky copolymers contain distinct segments of pure sPS and segments of randomly brominated sPS unlike their completely Random analogs. Crystallization behavior of the copolymers, examined using differential scanning calorimetry (DSC), demonstrates that the Blocky copolymers are more crystallizable and crystallize faster at lower supercooling compared to their Random analogs. Computer simulations of the blocky copolymers were developed based on the semicrystalline morphology of a 10 w/v% sPS/CCl4 gel, to rationalize the effect of heterogeneous functionalization on copolymer microstructure and crystallization behavior. The simulations were found to agree with the microstructural analysis based on the NMR results and confirm that restricting the accessibility of the brominating reagent to monomers well removed from the crystalline fraction of the gel network produces copolymers with a greater prevalence of long, uninterrupted sPS homopolymer sequences. Thus, the blocky microstructure is advantageous for preserving desired crystallizability of the resulting blocky copolymers.