Radical Copolymerization of Thionoglycolide and Derivatives for Preparation of Degradable Vinyl Polymers
Résumé
This study explores the copolymerization behavior of thionated glycolide derivatives, with a focus on thionoglycolide (TGD). It was found that TGD exhibits a nuanced reactivity profile, showing the highest compatibility with styrene and tert-butyl acrylate (tBA). Kinetic analysis of the TGD/tBA system conducted at 100°C in bulk demonstrated comparable incorporation rates for both monomers. Furthermore, RAFT copolymerization mediated by a trithiocarbonate RAFT agent resulted in well-defined copolymer with Mn = 13.4 kg mol -1 and Đ = 1.2. 2D-NMR Microstructural analysis revealed that TGD was exclusively incorporated in its ring-closed S,O-thioketal form, suggesting a selective 1,2-vinyl propagation mechanism. The degradability of the resulting copolymers was also investigated, with NaOCl, NaOMe, and benzoyl peroxide effectively cleaving S,O-thioketal linkages.
Materials and methods. The following chemicals were used as received: phosphorus pentasulfide (P4S10, 97% grade, Acros Organics), chloroacetyl chloride (98%, Sigma-Aldrich), 2-chloropropionyl chloride (97%, Sigma-Aldrich), glycolide (99%, Sigma-Aldrich), hexamethyldisiloxane (HMDSO, ≥98%, Sigma-Aldrich), α-hydroxyisobutyric acid (99%, Sigma-Aldrich), glycolide (99%, Alfa Aesar), magnesium sulfate (99.5%, Sigma-Aldrich), potassium carbonate (K2CO3, 99%, Sigma-Aldrich), 1,1'-azobis(cyanocyclohexane) (V-88, 98%, Sigma-Aldrich) and naphthalene (98%, Sigma-Aldrich)
The following chemicals were purified before use: 2,2'-azobis(2-methylproprionitrile) (AIBN, 98%, Sigma-Aldrich), was recrystallized from methanol and dried under vacuum. Vinyl acetate (VAc, >99%, Sigma-Aldrich), tert-butyl acrylate (tBA, >99%, Sigma-Aldrich), styrene (St, >99%, Sigma-Aldrich) and N,N-dimethyl acrylamide (DMA, >99%, Sigma-Aldrich), were purified by passing through neutral Al2O3 prior to use.
The following solvents were used as received: cyclohexane (Sigma-Aldrich, HPLC grade), dichloromethane (Sigma-Aldrich, HPLC grade), diethyl ether (VWR, HPLC grade), ethyl acetate (EtOAc, Sigma-Aldrich, HPLC grade), ethanol (anhydrous, Sigma-Aldrich), petroleum ether (Sigma-Aldrich, HPLC grade). Acetonitrile (MeCN, Acros, HPLC grade), and toluene (Acros, HPLC grade) were further dried using a solvent purifier (MBRAUN SP5).
NMR spectra ( 1 H, 13 C) were recorded at 25 °C on a Bruker Avance 300 MHz instrument and all 2D NMR experiments were recorded on a Bruker Avance 500 MHz spectrometer equipped with 5 mm TCI cryoprobe. 1 H NMR spectra were recorded at 300.13 MHz (500.13 MHz for 2D experiments) ± 0.5 Hz. 13 C NMR spectra were recorded at 75.47 MHz (125.75 MHz for 2D).
Size-exclusion chromatography (SEC) analyses in THF was performed on a system of an Agilent technologies guard column (PLGel20 µm, 50 × 7.5 mm) and a set of three Shodex columns (KF-805 + KF-804 + KF-802.5). Analyses were performed at 35°C and a flow rate of 1.0 mL min -1 . Detections were conducted using a Wyatt Optilab® rEX refractive index detector, a Varian ProStar 325 UV detector (dual wavelength analysis) and a Wyatt MiniDawn TREOS multi-angle light scattering (MALS) detector. Poly(methyl methacrylate) (PMMA) standards (960 -1.37 × 10 5 g mol -1 ) were used for calibration. Number-average (Mn) and weight-average (Mw) molar masses were evaluated using Waters Empower software. All SEC chromatograms have been normalised to polymer peaks.
Synthesis of 5-thioxo-1,4-dioxan-2-one TGD. Glycolide (4 g, 34.5 mmol), P4S10 (3.8 g, 8.6 mmol) and hexamethyldisiloxane (9.4 g, 58 mmol) were dissolved in 30 mL of anhydrous toluene. Then the reaction mixture was purged with argon for 15 minutes at room