Junhua Bai

In this study, the homopolymerization of 2,2‐dimethyltrimethylene carbonate (DTC) and its copolymerizations with ε‐caprolactone (CL) were carried out in detail using the isothiourea‐based Lewis pairs comprised 2,3,6,7‐tetrahydro‐5H‐thiazolo(3,2‐a)pyrimidine and magnesium halides (MgX₂) with benzyl alcohol (BnOH) as the initiator. The copolymerization of DTC and CL via one‐pot addition produced randomly sequenced copolymers. On the other hand, a well‐defined linear poly(ε‐caprolactone)–block–poly(2,2‐dimethyltrimethylene carbonate) (PCL‐b‐PDTC) diblock copolymer was prepared by simple sequential ring‐opening polymerization of CL and DTC. In addition, poly(ω‐pentadecalactone)–block–PDTC diblock copolymer was successfully prepared by the same strategy. Moreover, PDTC–poly(ethylene glycol) (PEG)–PDTC triblock copolymer was synthesized in the presence of PEG 2000. The effects of different polymerization conditions on the polymerization reactions have been systematically discussed. The resulting polymers were characterized by the ¹H and ¹³C NMR spectra, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐ToF MS). The block copolyester structures were confirmed by the ¹³C NMR spectroscopy and DSC characterizations. These results indicated that the supposed mechanism was a dual catalytic mechanism. The proposed mechanism involved activation of the monomer via coordination to the MgX₂, and the initiator alcohol was deprotonated by base. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2349–2355

In this study, the catalytic behavior of dual catalysis based on isothioureas (ITUs) for ring‐opening polymerization (ROP) of macrolactone ω‐pentadecalactone (PDL) and its copolymerization with ε‐caprolactone (CL) has been investigated in detail. In the presence of benzyl alcohol (BnOH) initiator, 2,3,6,7‐tetrahydro‐5H‐thiazolo[3,2‐a]pyrimidine (THTP) acted as a representative organic compound, which coupled with magnesium halides (MgX₂) as cocatalysts and catalyzed the polymerization in toluene at 70 °C. Under suitable conditions, an array of polymers with controlled molecular weights and relatively narrow molecular weight distributions were synthesized. The formation of homopolymers and copolymers with different architectures was verified using GPC, DSC, NMR, and matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐ToF) mass. The MALDI‐ToF mass spectrometry (MS) analysis of poly(ω‐pentade‐calactone) (PPDL) provided direct evidence for the successful initiation of ROP of PDL using BnOH to obtain linear PPDL with a very small amount of oligomer. The NMR analysis indicated that the arrangements of PDL and CL units in the copolymer chains were completely random. The thermal stability of copolymers was composition dependent and increased with the increase in the content of PDL unit. Furthermore, the proposed polymerization mechanism is a dual catalytic mechanism. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019

In this study, three isothioureas (ITUs), 2,3,5,6-tetrahydroimidazo[2,1-b]thiazole (ITU 1), 2,3,6,7-tetrahydro-5H-thiazolo-[3,2-a]pyrimidine (ITU 2) and 3,4,7,8-tetrahydro-2H,6H-pyrimido[2,1-b][1,3]thiazine (ITU 3) were prepared. These ITUs coupled with magnesium halides (MgX₂) as the cocatalysts, cooperatively promoted the ring-opening polymerization (ROP) of several common lactones (including δ-valerolactone, ε-caprolactone, ε-decalactone and even of macrolactone ω-pentadecalactone) and 2,2-dimethyltrimethylene carbonate. These cocatalysts were found to exhibit suitable activities and ITU 2 emerged as the most active organic component. The order of activities for the magnesium halides was found to be lying in the following order: MgI₂ > MgBr₂ > MgCl₂. The polymerizations attained high conversions (>90%) under optimal conditions, and produced linear polyesters having predictable molecular weights, narrow polydispersity indices (PDIs < 1.20) and defined end groups, which were derived from the benzyl alcohol initiator. The resulting polymers were characterized using GPC, IR, DSC, NMR and MALDI-ToF mass. The kinetic and chain extension experiments showed that the ITUs/MgX₂-cocatalyzed ROPs of ε-caprolactone proceeded a living polymerization characteristics. Furthermore, the proposed polymerization mechanism was supposed to be a dual catalytic mechanism, and involved the activation of monomers through coordination to Lewis acids, while the initiator was activated by bases.

Dihydroxyl capped biodegradable poly(ε-caprolactone)–poly(ethylene glycol)–poly(ε-caprolactone) (PCL–PEG–PCL) triblock copolymer and poly(L-lactide)–poly(ε-caprolactone)–poly(ethylene glycol)–poly(ε-caprolactone)–poly(L-lactide) (PLLA–PCL–PEG–PCL–PLLA) pentablock copolymer have been synthesized by using benzo-12-crown-4-imidazole carbene (B-12-C-4imY) as a catalyst, and PEG and PCL–PEG–PCL copolymer as macroinitiators, respectively. We focused on the influence of the varied reaction time, temperature and monomer/catalyst molar ratio on the copolymerizations. Chemical structures and physical properties of the block copolymers were studied through the characterization of ¹H, ¹³C NMR, GPC and DSC. The NMR spectral data of the copolymers displayed the chemical structures without random placement. Therefore, the pure triblock and pentablock copolymers have been synthesized successfully.