脂肪族聚酯是一种重要的聚酯材料,具有良好的生物相容性和降解性,它可以通过环氧化物和酸酐的开环交替共聚(ROAC)合成。在这里,密度泛函理论(DFT)用于探索环氧化物(环氧丙烷(PO)、氧化苯乙烯(SO),表氯醇(ECH),和二(三苯基膦)氯化铵(PPNCl)和脲催化的氧化环己烷(CHO)和邻苯二甲酸酐(PA)。发现环氧化物的开环聚合(ROP)是速率控制步骤,苯甲醇(BnOH)作为引发剂对聚合活性影响不大,这与以前的实验结果是一致的。由四种不同尿素催化的CHO/PA的ROAC活性的计算比较表明,随着尿素的Lewis酸度的增加,共聚的能障增加,活性降低。主要原因是强的氢键相互作用稳定了速率控制步骤的关键中间体并抑制了随后的单体插入。基于此,通过引入供电子取代基,设计了一系列具有更高催化活性的新型脲。在SO聚合中,增加尿素的路易斯酸度可以提高SO区域选择性。此外,具有CH2Cl的单体ECH比PO和SO显示更高的ROAC活性,这可以归因于以下事实:强吸电子Cl原子使速率控制步骤中的过渡态稳定并降低了反应能垒。
Aliphatic polyester is an important polyester material with good biocompatibility and degradability, which can be synthesized through ring-opening alternating copolymerization (ROAC) of epoxides and anhydrides. Herein, density functional theory (DFT) is used to explore the mechanism of ROAC of epoxides (propylene oxide (PO), styrene oxide (SO), epichlorohydrin (ECH), and cyclohexane oxide (CHO)) and phthalic anhydride (PA) catalyzed by bis(triphenylphosphine) ammonium chloride (PPNCl) and ureas. It was found that the ring-opening polymerization (ROP) of epoxides is the rate-controlling step, and the benzyl alcohol (BnOH) as the initiator has little effect on the polymerization activity, which was consistent with previous experimental results. Calculated comparisons of the ROAC activity of CHO/PA catalyzed by four different ureas indicate that as the Lewis acidity of the urea increased, the energy barriers of the copolymerization increased and the activity decreased. The main reason was that the strong hydrogen-bonding interactions stabilized the key intermediate of the rate-controlling step and inhibited subsequent monomer insertion. Based on this, a series of new ureas with higher catalytic activity were designed by introducing electron-donating substituents. In SO polymerization, increasing the Lewis acidity of urea can improve the SO regioselectivity. In addition, the monomer ECH with CH2Cl shows higher activity of ROAC than PO and SO, which could be ascribed to the fact that the strong electron-withdrawing Cl atom stabilizes the transition state in the rate-controlling step and reduces the reaction energy barrier.