Development of the new aluminum-based macroinitiator for use in the synthesis of high molecular weight biodegradable poly(ε-caprolactone) (PCL) was presented. The macroinitiators were prepared via solvent-free ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) initiated by different concentrations of aluminum tri-s-butoxide (Al(OsBu)3) (2, 4, 8, and 12 mol%), yielding soft solid macroinitiators denoted as ALCL2, ALCL4, ALCL8, and ALCL12, respectively. From Fourier-transform infrared (FT-IR) and proton-nuclear magnetic resonance (1H-NMR) spectroscopic analyses confirmed that the ALCL macroinitiators contained Al-O active centers capable of initiating subsequent ROP of ε-CL. From gel permeation chromatography (GPC) analysis revealed that the chain length and molecular weight of macroinitiators decreased in following order ALCL2 > ALCL4 > ALCL8 > ALCL12. From thermogravimetric analysis (TGA), ALCL2 showed higher thermal stability than ALCL4, ALCL8, and ALCL12. The effectiveness of the ALCL macroinitiators for PCL synthesis was evaluated under solvent-free conditions using conventional heating. The results demonstrated that ALCL12 produced PCL with number average molecular weight (Mn) in the range of 1.58 × 104 − 3.63 × 104 g/mol and weight average molecular weight (Mw) in the range of 3.38 × 104 − 6.97 × 104 g/mol, with dispersity (Đ) of 1.92–2.34. At a synthesis temperature of 150 οC for 48 h, ALCL12 produced PCL with a higher Mw (6.11 × 104 g/mol) than ALCL8 (5.53 × 104 g/mol), ALCL4 (4.94 × 104 g/mol), and ALCL2 (1.84 × 104 g/mol). Furthermore, ALCL12 yielded PCL with the lowest Đ (2.02) and the highest yield (93%). Under facile and green solvent-free conditions using microwave (MW) heating, all ALCL macroinitiators effectively produced PCL, with ALCL8 showing particularly superior performance at MW power of 450 W and an irradiation time of 30 min. Under these conditions, ALCL8 produced PCL with Mw up to 5.10 × 104 g/mol and high yield of 84–90%. Moreover, upon reducing the initiator loading in MW-assisted synthesis, ALCL8 remained more effective than the other macroinitiators and could be efficiently utilized at very low concentration (0.0625–0.250%wt), producing high molecular weight PCL with Mw values in the range of 9.78 × 104 − 1.10 × 105 g/mol. Based on mechanistic considerations, the ROP of ε-CL initiated by the ALCL macroinitiators is proposed to proceed via a coordination-insertion mechanism. Graphical abstract

Designing of effective aluminum-based macroinitiators for the solvent-free ring-opening polymerization of ε-caprolactone via the facile and green process

期刊论文
发表日期：

2026年4月15日

查看全文

Watcharee Funfuenha,
Puttinan Meepowpan,
Nathaporn Cheechana,
Winita Punyodom,
Wanich Limwanich

摘要

Development of the new aluminum-based macroinitiator for use in the synthesis of high molecular weight biodegradable poly(ε-caprolactone) (PCL) was presented. The macroinitiators were prepared via solvent-free ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) initiated by different concentrations of aluminum tri-s-butoxide (Al(OsBu)₃) (2, 4, 8, and 12 mol%), yielding soft solid macroinitiators denoted as ALCL2, ALCL4, ALCL8, and ALCL12, respectively. From Fourier-transform infrared (FT-IR) and proton-nuclear magnetic resonance (¹H-NMR) spectroscopic analyses confirmed that the ALCL macroinitiators contained Al-O active centers capable of initiating subsequent ROP of ε-CL. From gel permeation chromatography (GPC) analysis revealed that the chain length and molecular weight of macroinitiators decreased in following order ALCL2 > ALCL4 > ALCL8 > ALCL12. From thermogravimetric analysis (TGA), ALCL2 showed higher thermal stability than ALCL4, ALCL8, and ALCL12. The effectiveness of the ALCL macroinitiators for PCL synthesis was evaluated under solvent-free conditions using conventional heating. The results demonstrated that ALCL12 produced PCL with number average molecular weight (M_n) in the range of 1.58 × 10⁴ − 3.63 × 10⁴ g/mol and weight average molecular weight (M_w) in the range of 3.38 × 10⁴ − 6.97 × 10⁴ g/mol, with dispersity (Đ) of 1.92–2.34. At a synthesis temperature of 150 ^οC for 48 h, ALCL12 produced PCL with a higher M_w (6.11 × 10⁴ g/mol) than ALCL8 (5.53 × 10⁴ g/mol), ALCL4 (4.94 × 10⁴ g/mol), and ALCL2 (1.84 × 10⁴ g/mol). Furthermore, ALCL12 yielded PCL with the lowest Đ (2.02) and the highest yield (93%). Under facile and green solvent-free conditions using microwave (MW) heating, all ALCL macroinitiators effectively produced PCL, with ALCL8 showing particularly superior performance at MW power of 450 W and an irradiation time of 30 min. Under these conditions, ALCL8 produced PCL with M_w up to 5.10 × 10⁴ g/mol and high yield of 84–90%. Moreover, upon reducing the initiator loading in MW-assisted synthesis, ALCL8 remained more effective than the other macroinitiators and could be efficiently utilized at very low concentration (0.0625–0.250%wt), producing high molecular weight PCL with M_w values in the range of 9.78 × 10⁴ − 1.10 × 10⁵ g/mol. Based on mechanistic considerations, the ROP of ε-CL initiated by the ALCL macroinitiators is proposed to proceed via a coordination-insertion mechanism.

Graphical abstract