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Oxazine Ring-Substituted 4th Generation Benzoxazine Monomers & Polymers: Stereoelectronic Effect of Phenyl Substituents on Thermal Properties
Macromolecules ( IF 5.1 ) Pub Date : 2021-10-07 , DOI: 10.1021/acs.macromol.1c01582 Sourav Mukherjee 1 , Nagarjuna Amarnath 2 , Bimlesh Lochab 1
Macromolecules ( IF 5.1 ) Pub Date : 2021-10-07 , DOI: 10.1021/acs.macromol.1c01582 Sourav Mukherjee 1 , Nagarjuna Amarnath 2 , Bimlesh Lochab 1
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Oxazine ring-substituted benzoxazine monomers inherit a smart architecture to cater intriguing properties offered by this upcoming latest generation of polybenzoxazines. It is therefore encouraging to study the regio-effect of oxazine ring substitution on ROP (ring-opening polymerization) temperature, thermal stability of the monomers and polymers to guide future designing of structures. Herein, we report a systematic analysis on the thermal properties with variation in the number and position of substituent (2- and/or 4-) in phenyl-substituted benzoxazines. Successful syntheses of monomers and structural characterization were confirmed using 1D NMR (nuclear magnetic resonance spectroscopy), HRMS (high-resolution mass spectrometry), and XRD (X-ray diffraction). Polymerization behavior and thermal stability was studied by DSC (differential scanning calorimetry), FTIR (Fourier transform infrared) spectroscopy, and TGA (thermogravimetry analysis). In-depth structural analysis by 2D NMR [1H – 1H COSY (correlation spectroscopy), 1H – 13C HSQC (heteronuclear single quantum correlation), and HMBC (heteronuclear multiple bond correlation)] experiments, crystal data, TGA–GC–MS (thermogravimetry analysis-gas chromatography–mass spectrometry), and DFT (density functional theory) calculation provided mechanistic insights of the effect of substitution on thermal behavior of monomers. It is found that besides the molecular mass of monomers and intermediates, the stereo-electronic effect of substituents at the 2- and/or 4-positions governs both the evaporation of monomer/cleaved intermediates and ring-opening reaction. Activation energy (Ea) of polymerization depends upon the position and degree of phenyl substituent(s). Among the studied varieties, the 2,4-substituted benzoxazine monomer showed the lowest ROP temperature with the least mass-loss during polymerization, the lowest Ea value of polymerization. Additionally, the resultant 2,4-substituted polybenzoxazine showed the highest thermal stability and char yield. An astute choice of selective positioning of groups in the oxazine ring can be a guiding principle for the structural designing of monomers to advocate a wide variety of applications.
中文翻译：
恶嗪环取代的第四代苯并恶嗪单体和聚合物：苯基取代基对热性能的立体电子效应
恶嗪环取代的苯并恶嗪单体继承了智能架构，以迎合即将到来的最新一代聚苯并恶嗪提供的有趣特性。因此，研究恶嗪环取代对 ROP（开环聚合）温度、单体和聚合物的热稳定性的区域效应以指导未来的结构设计是令人鼓舞的。在此，我们报告了对苯基取代的苯并恶嗪中取代基（2-和/或 4-）的数量和位置变化的热性能的系统分析。使用 1D NMR（核磁共振光谱）、HRMS（高分辨率质谱）和 XRD（X 射线衍射）证实了单体的成功合成和结构表征。通过DSC（差示扫描量热法）、FTIR（傅里叶变换红外）光谱和TGA（热重分析）研究聚合行为和热稳定性。通过 2D NMR 进行深入的结构分析 [1 H – 1 H COZY（相关光谱）、1 H – 13 C HSQC（异核单量子相关）和 HMBC（异核多键相关）] 实验、晶体数据、TGA-GC-MS（热重分析-气相色谱-质谱）和 DFT（密度泛函理论）计算提供了取代对单体热行为影响的机械见解。发现除了单体和中间体的分子量外，2-和/或4-位取代基的立体电子效应控制着单体/裂解中间体的蒸发和开环反应。活化能 ( E a) 的聚合取决于苯基取代基的位置和程度。在所研究的品种中，2,4-取代的苯并恶嗪单体在聚合过程中表现出最低的ROP温度和最小的质量损失，最低的聚合E a值。此外，所得的 2,4-取代聚苯并恶嗪显示出最高的热稳定性和炭产率。对恶嗪环中基团选择性定位的精明选择可以成为单体结构设计的指导原则，以促进广泛的应用。
更新日期：2021-11-09
中文翻译：
恶嗪环取代的第四代苯并恶嗪单体和聚合物：苯基取代基对热性能的立体电子效应
恶嗪环取代的苯并恶嗪单体继承了智能架构，以迎合即将到来的最新一代聚苯并恶嗪提供的有趣特性。因此，研究恶嗪环取代对 ROP（开环聚合）温度、单体和聚合物的热稳定性的区域效应以指导未来的结构设计是令人鼓舞的。在此，我们报告了对苯基取代的苯并恶嗪中取代基（2-和/或 4-）的数量和位置变化的热性能的系统分析。使用 1D NMR（核磁共振光谱）、HRMS（高分辨率质谱）和 XRD（X 射线衍射）证实了单体的成功合成和结构表征。通过DSC（差示扫描量热法）、FTIR（傅里叶变换红外）光谱和TGA（热重分析）研究聚合行为和热稳定性。通过 2D NMR 进行深入的结构分析 [1 H – 1 H COZY（相关光谱）、1 H – 13 C HSQC（异核单量子相关）和 HMBC（异核多键相关）] 实验、晶体数据、TGA-GC-MS（热重分析-气相色谱-质谱）和 DFT（密度泛函理论）计算提供了取代对单体热行为影响的机械见解。发现除了单体和中间体的分子量外，2-和/或4-位取代基的立体电子效应控制着单体/裂解中间体的蒸发和开环反应。活化能 ( E a) 的聚合取决于苯基取代基的位置和程度。在所研究的品种中，2,4-取代的苯并恶嗪单体在聚合过程中表现出最低的ROP温度和最小的质量损失，最低的聚合E a值。此外，所得的 2,4-取代聚苯并恶嗪显示出最高的热稳定性和炭产率。对恶嗪环中基团选择性定位的精明选择可以成为单体结构设计的指导原则，以促进广泛的应用。
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