Shi Han, Zhuang Qixin, Zheng Anna, Guan Yong, Wei Dafu, Xu Xiang
Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology Shanghai 200237 China.
RSC Adv. 2023 Mar 6;13(11):7225-7236. doi: 10.1039/d2ra06441c. eCollection 2023 Mar 1.
In this study, the mechanism of radical polymerization was further explored by pre-dissolving different polymers and studying the kinetics of the bulk polymerization of methyl methacrylate (MMA) under shear-free conditions. Based on the analysis of the conversion and absolute molecular weight, it was found that, contrary to the shearing effect, the inert polymer with viscosity was the key factor to preventing the mutual termination of radical active species and reducing the termination rate constant . Therefore, pre-dissolving the polymer could increase the polymerization rate and molecular weight of the system simultaneously, making the polymerization system enter the automatic acceleration zone faster and greatly reducing the generation of small molecular weight polymers, leading to a narrower molecular weight distribution. When the system entered the auto-acceleration zone, decreased rapidly and greatly and entered the second steady-state polymerization stage. Then, with the increase in the polymerization conversion, the molecular weight gradually increased, while the polymerization rate gradually decreased. In shear-free bulk polymerization systems, can be minimized and radical lifetimes maximized, but the polymerization system is at best a long-lived polymerization rather than a living polymerization. On this basis, by using MMA to pre-dissolve ultrahigh molecular weight PMMA and core-shell particles (CSR), the mechanical properties and heat resistance of the PMMA with pre-dissolved polymer obtained by reactive extrusion polymerization were better than for pure PMMA obtained under the same conditions. Compared with pure PMMA, the flexural strength and impact strength of PMMA with pre-dissolved CSR were up to 166.2% and 230.5%. With the same quality of CSR, the same two mechanical properties of the samples obtained by the blending method were just improved by 29.0% and 20.4%. This was closely related to the distribution of CSR in the pre-dissolved PMMA-CSR matrix with a distribution of spherical single particles 200-300 nm in diameter, which enabled PMMA-CSR to exhibit a high degree of transparency. This one-step process for realizing PMMA polymerization and high performance shows extremely high industrial application prospects.
在本研究中，通过预溶解不同聚合物并研究甲基丙烯酸甲酯（MMA）在无剪切条件下本体聚合的动力学，进一步探索了自由基聚合的机理。基于转化率和绝对分子量的分析发现，与剪切作用相反，具有粘性的惰性聚合物是防止自由基活性物种相互终止并降低终止速率常数的关键因素。因此，预溶解聚合物可同时提高体系的聚合速率和分子量，使聚合体系更快进入自动加速区，并大大减少小分子聚合物的生成，导致分子量分布变窄。当体系进入自动加速区时，迅速大幅下降并进入第二稳态聚合阶段。然后，随着聚合转化率的增加，分子量逐渐增大，而聚合速率逐渐降低。在无剪切本体聚合体系中，可将降至最低并使自由基寿命最大化，但该聚合体系充其量只是长寿命聚合而非活性聚合。在此基础上，通过用MMA预溶解超高分子量PMMA和核壳粒子（CSR），反应挤出聚合得到的预溶解聚合物的PMMA的力学性能和耐热性优于相同条件下得到的纯PMMA。与纯PMMA相比，预溶解CSR的PMMA的弯曲强度和冲击强度分别高达166.2%和230.5%。在CSR质量相同的情况下，通过共混法得到的样品的相同两项力学性能仅提高了29.0%和20.4%。这与CSR在直径为200 - 300 nm的球形单颗粒分布的预溶解PMMA - CSR基体中的分布密切相关，这使得PMMA - CSR具有高度透明性。这种实现PMMA聚合和高性能的一步法显示出极高的工业应用前景。
