The Key Laboratory of Low-carbon Chemistry & Energy Conservation of Guangdong Province/State Key Laboratory of Optoelectronic Materials and Technologies, School of Materials Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China
Institute of Chemistry, Henan Academy of Sciences, Zhengzhou 450000, China
Research Center of Green Catalysts, College of Chemistry, Zhengzhou University, Zhengzhou 450001, China
School of Chemical Engineering and Technology, Sun Yat-sen University, Guangzhou 510275, China
Authors to whom correspondence should be addressed.
Received: 27 Nov 2022
Accepted: 11 Jan 2023
Published: 30 Jan 2023
Multiblock and di-/tri-block copolymers are successfully synthesized for the first time via the metal-free terpolymerization of propylene oxide (PO), ʟ-lactide (LA) and CO2 in one-pot/one-step and one-pot/two-step protocols respectively. Firstly, triethyl borane (TEB) and bis(triphenylphosphine)iminium chloride (PPNCl) Lewis pair is employed in the ring-opening polymerization of LA, wherein the catalytic efficiency is significantly correlated to the TEB/PPNCl feed ratio. Next, a series of TEB/base pairs are selected to synthesize the PO/LA/CO2 terpolymer (PPCLA) in one-pot/one-step strategy. In PPCLA synthesis, LA exhibits the fastest reaction rate but the severe transesterification is almost unavoidable, resulting in low molecular weight products. In order to prepare high-molecular-weight terpolymers, a one-pot/two-step methodology has to be applied. By this method, the copolymerization of PO/CO2 proceeds first to form poly(propylene carbonate) (PPC) macroinitiators, which triggers the polymerization of LA to polylactide (PLA), leading to PLA-PPC or PLA-PPC-PLA block copolymers. The synthesized PLA-PPC-PLA block copolymers display an improved thermal stability compared with PPC.
Metal-free Catalysis; CO2 Utilization; Biodegradable; Multiblock copolymer; Polylactide; Polycarbonate
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Evolution of 1H NMR spectra for the copolymerization of PO/LA/PPNCl (500/100/1) catalyzed by different ratios of the TEB/PPNCl pair at 60 °C for 10 min.
(**a**) 1H NMR spectrum of PPCLA (Table 2, Entry 6); (**b**) comparison of 1H NMR spectra of PPCLA multiblock copolymer and PPC-PLA block copolymer.
Synthesis of PPC-PLA block copolymers catalyzed by TEB/PPNCl: (**a**) evolution of 1H NMR spectra of LA ROP with reaction time; (**b**) evolution of GPC traces and MWs.
(**a**) TG and (**b**) DTG curves of samples (Table 4).
Three DSC curves of PLA-PPC-PLA-2 recorded at a 10 °C/min heating rate.
Proposed mechanism of PLA synthesis catalyzed by TEB/PPNCl (1/1) pair using PO as solvent.
Synthesis of PPCLA catalyzed by different Lewis pairs.