Supporting Information

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1 Supporting Information The Quest for Converting Biorenewable Bifunctional α-methylene-γ-butyrolactone into Degradable and Recyclable Polyester: Controlling Vinyl-Addition/Ring-Opening/Cross-Linking Pathways Xiaoyan Tang, Miao Hong, Laura Falivene, Lucia Caporaso, Luigi Cavallo, * and Eugene Y.-X. Chen * * Correspondence to: luigi.cavallo@kaust.edu.sa; eugene.chen@colostate.edu Table of Contents Experimental Details... 3 Table S1. Results of MBL Polymerization by La[N(SiMe 3 ) 2 ] 3 /BnOH in Toluene at 25 C Table S2. Monomer Concentration as a Function of Time at Different Temperatures Table S3. Results of Depolymerization of P(MBL) ROP in the Presence of LaCl 3 in DMSO-d Table S4. Degradation of P(MBL) ROP in 1 M NaOH, 1 M HCl and DI H 2 O Figure S1. 1 H NMR spectra (C 6 D 6, 25 C): (a) the bisphenol ligand; (b) Y(CH 2 SiMe 3 ) 3 (THF) 2 ; and (c) yttrium alkyl catalyst Figure S2. 1 H NMR spectra (C 6 D 6, 25 C): (a) the bisphenol ligand; (b) Y(CH 2 SiMe 3 ) 3 (THF) 2 ; and (c) yttrium alkyl catalyst Figure S3. MALDI-TOF spectrum of P(MBL) ROP produced with MBL/La[N(SiMe 3 ) 2 ] 3 /BnOH (100/1/3) and plot of m/z values (y) vs the number of MBL repeat units (x) Figure S4. MALDI-TOF spectrum of P(MBL) ROP produced with MBL/La[N(SiMe 3 ) 2 ] 3 / Ph 2 CHCH 2 OH (100/1/3) and plot of m/z values (y) vs the number of MBL repeat units (x).. 14 Figure S5. MALDI-TOF spectrum of P(MBL) ROP produced with MBL/La[N(SiMe 3 ) 2 ] 3 / i PrOH (100/1/3) and plot of m/z values (y) vs the number of MBL repeat units (x) Figure S6. Plot of MBL concentration as a function time during polymerization at different temperatures: Figure S7. Overlay of IR spectra of cross-linked polymer P(MBL) CLP by La[N(SiMe 3 ) 2 ] 3 /BnOH (1/1) and vinyl-addition polymer P(MBL) VAP by La[N(SiMe 3 ) 2 ] 3 at 60 C Figure S8. TGA (black) and DTG (red) curves of the cross-linked polymer P(MBL) CLP and vinyl-addition polymer P(MBL) VAP Figure S9. Overlay of DSC curve of cross-linked polymer P(MBL) CLP (a) and vinyl-addition polymer P(MBL) VAP (b) Figure S10. TGA (black) and DTG (blue) curves of P(MBL) ROP by La[N(SiMe 3 ) 2 ] 3 /ROH (1/3): S1

2 a, R = Bn; b, R = Ph 2 CHCH 2 ; c, R = i Pr; and by yttrium complex 2 (d) Figure S11. DSC curves Figure S12. DSC curves of P(MBL) ROP by yttrium complex Figure S13. Overlay of FT-IR spectra of P(MBL) ROP -hν and P(MBL) ROP Figure S14. TGA (black) and DTG (blue) curve of P(MBL) ROP -hv from P(MBL) ROP (M n = 21.0 kg/mol) prepared by Figure S15. TGA (black) and DTG (blue) curve of P(MBL) ROP -hv from P(MBL) ROP (M n = 5.5 kg/mol) prepared by 1/BnOH (1/3) Figure S C NMR spectrum of P(MBL) ROP -SR (top) and 13 C NMR (DMSO-d 6 ) spectrum of P(MBL) ROP by yttrium complex 2 (bottom) for comparison Figure S17. 1 H NMR spectra of the reaction mixture of P(MBL) ROP with La[N(SiMe 3 ) 2 ] 3 at different times. Reaction time: (a) 30 s; and (b) 3 min Figure S18. Overlay of 1 H NMR spectra (DMSO-d 6 ) the product obtained by heating the solution of P(MBL) ROP with LaCl 3 in DMSO-d 6 at 160 C for different times Computational Details Cartesian Coordinates References S2

3 Experimental Details Materials and Methods. All syntheses and manipulations of air- and moisture-sensitive chemicals and materials were carried out in flamed Schlenk-type glassware on a dual-manifold Schlenk line, on a high-vacuum line, or in an inert gas (Ar or N 2 )-filled glovebox. NMR-scale reactions were conducted in NMR tubes sealed with Precision Seal rubber septa caps. HPLC-grade organic solvents were first sparged extensively with nitrogen during filling 20 L solvent reservoirs and then dried by passage through activated alumina (for dichloromethane, DCM) followed by passage through Q-5 supported copper catalyst (for toluene, TOL, and hexanes) stainless steel columns. HPLC-grade tetrahydrofuran (THF) was degassed and dried over Na/K for 3 days, followed by distillation. HPLC-grade N,N-dimethylformamide (DMF) was degassed and dried over CaH 2 overnight, followed by vacuum distillation (CaH 2 was removed before distillation). Dimethyl sulfoxide-d 6 (DMSO-d 6 ) was degassed and dried over CaH 2 overnight, followed by vacuum distillation. Benzene-d 6 was dried over sodium/potassium alloy and filtered, whereas CD 2 Cl 2 and CDCl 3 were dried over CaH 2, vacuum-distilled and stored over activated Davison 4 Å molecular sieves. NMR spectra were recorded on a Varian Inova 400 MHz spectrometer (400 MHz, 1 H; 100 MHz, 13 C) or a 500 MHz Bruker spectrometer. Chemical shifts for 1 H and 13 C spectra were referenced to internal solvent resonances and are reported as parts per million relative to SiMe 4. Fourier transform infrared (FT-IR) spectroscopy was performed on a Thermoscientific (Nicolet is50) FT-IR spectrometer equipped with a diamond attenuated total reflectance (ATR) at room temperature in the range of cm 1. α-methylene-γ-butyrolactone (MBL) was purchased from TCI America, dried over CaH 2 overnight, vacuum distillated, and stored over activated Davison 4 Å molecular sieves in a brown bottle inside a S3

4 freezer of the glovebox for further use. Tri[N,N-bis(trimethylsilyl)amide] lanthanum(ш) La[N(SiMe 3 ) 2 ] 3, lanthanum chloride LaCl 3, yttrium chloride YCl 3, and (trimethylsilyl)methyllithium (SiMe 3 ) 2 CH 2 Li solution in pentane were purchased from Sigma-Aldrich Chemical Co. and used as received. 2,2-Diphenylethanol, diphenylmethanol, and triphenylmethanol were purchased from Sigma-Aldrich Chemical Co., which were purified by dissolving in toluene over CaH 2, filtering after stirring overnight, and removing the solvent. Isopropanol and benzyl alcohol were purchased from Fisher Scientific Co. and Alfa Aesar Chemical Co., respectively, which were purified by distillation over CaH 2 and stored over activated Davison 4 Å molecular sieves. 4-tert-Butylbenzylmercaptan was purchased from Alfa Aesar and used as received. 2,2-Dimethoxy-2-phenylacetophenone (DMPA) was purchased from Acros Organics and used as received. Yttrium complexes 2 and 3 were prepared according to literature procedures. 1 General Polymerization Procedures. Polymerizations were performed in 25 ml flame-dried Schlenk tubes interfaced to a dual-manifold Schlenk line using an external cooling bath. The reactor was charged with a predetermined amount of catalyst and/or initiator and solvent (as specified in the polymerization tables) in a glovebox. The reactor was sealed with a septum, taken out of the glovebox, and immersed in the cooling bath. After equilibration at the desired polymerization temperature for 10 min, the polymerization was initiated by rapid addition of MBL via a gastight syringe. After a desired period of time, the polymerization was quenched by addition of 5 ml methanol acidified with HCl (5%). The quenched mixture was precipitated into 100 ml of cold methanol, filtered, washed with methanol to remove any unreacted monomer, and dried in a vacuum oven at room temperature to a constant weight. The results were summarized in Tables 1 and S1. S4

5 NMR data for the ROP product P(MBL) ROP. 1 H NMR (400 MHz, DMSO-d 6, 298K): δ 6.09 (s, 1H, =CH 2 ), 5.71 (s, 1H, =CH 2 ), 4.20 (t, J = 6.1 Hz, 2H, -CH 2 O-), 2.58 (t, J = 6.0 Hz, 2H, -CH 2 -). 13 C NMR (100 MHz, DMSO-d 6, 298K): δ (C=O), (=CH 2 ), (C=CH 2 ), (-CH 2 O-), (-CH2-). Polymer Characterizations. The resulting polymers were initially characterized by 1 H NMR to determine the polymer type. P(MBL) VAP and P(MBL) ROP can be clearly distinguished by their 1 H NMR spectra (c.f., Figure 1), while P(MBL) CLP cannot dissolve in any common organic solvents. From the solubility test of the polymer, the presence of P(MBL) CLP can be confirmed. Polymer weight-average molecular weight (M w ), number-average molecular weight (M n ), and molecular weight distribution or polydispersity index (Đ = M w /M n ) were measured by gel permeation chromatography (GPC) analyses carried out at 40 ºC and a flow rate of 1.0 ml/min, with DMF as the eluent on a Waters University 1500 GPC instrument equipped with one PLgel 5 µm guard and three PLgel 5 µm mixed-c columns (Polymer Laboratories; linear range of MW = 200 2,000,000). The instrument was calibrated with 10 PMMA standards, and chromatograms were processed with Waters Empower software (version 2002). Melting transition (T m ) and glass transition (T g ) temperatures of the resulting polymers were measured by differential scanning calorimetry (DSC) on an Auto Q20, TA Instrument. All T m and T g values were obtained from a second scan after the thermal history was removed from the first scan. The second heating rate was 10 C/min and the cooling rate was 10 C/min. Decomposition onset temperatures (T onset ) and maximum rate decomposition temperatures (T max ) of the polymers were measured by thermal gravimetric analysis (TGA) on a Q50 TGA Analyzer, TA Instrument. Polymer samples were heated from ambient temperature to 700 C at a heating rate of 10 C/min. Values of T max S5

6 were obtained from derivative (wt.%/ C) vs. temperature ( C), while T onset values (initial and end temperatures) were obtained from wt.% vs. temperature ( C) plots. The isolated low molecular weight sample was analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI TOF MS). The experiment was performed on a Microflex-LRF mass spectrometer (Bruker Daltonics, Billerica, MA) in positive ion, reflector mode using a 25 kv accelerating voltage. A thin layer of a 1% NaI solution was first deposited on the target plate, followed by 0.6 µl of both sample and matrix (dithranol, 10mg/mL in 50% ACN, 0.1% TFA). The mixture was spotted on top of the NaI layer and allowed to air dry. External calibration was done using a peptide calibration mixture (4 to 6 peptides) on a spot adjacent to the sample. The raw data was processed in the FlexAnalysis software (version 3.4.7, Bruker Daltonics). Dynamic mechanical analysis (DMA) was performed on P(MBL) ROP thin films (ca mm) with an RSAG2 analyzer (TA Instruments) in the tension film mode at a maximum strain of 0.3% and a frequency of 1 Hz. The sample was heated from 100 ºC to 40 ºC at a heating rate of 3 ºC/min. The DMA T g was selected as the temperature at the maximum (peak) value of the loss modulus. Thermodynamic Studies. In a glovebox under an argon atmosphere, a NMR tube was charged with La[N(SiMe 3 ) 2 ] 3 (18.6 mg, 0.03 mmol), Ph 2 CHCH 2 OH (17.8 mg, 0.09 mmol) and 0.34 ml of CD 2 Cl 2. The NMR tube was sealed with a Precision Seal rubber septum cap and taken out of the glovebox. After completion of alcoholysis in 5 min with occasional shaking, the NMR tube was immersed in a cooling bath at 78 ºC (at which temperature MBL was frozen and not polymerized). After equilibration at 78 ºC for 10 min, MBL (0.294 g, 3.0 mmol, MBL/La/Ph 2 CHCH 2 OH = 100/1/3) was S6

7 added via a gastight syringe and the NMR tube was brought into a 500 MHz NMR probe precooled to the desired polymerization temperature ( 55, 60, and 65 ºC, respectively). The conversion of the monomer was monitored by 1 H NMR at different time intervals until the conversion remained constant. The results were summarized in Table S2. Post-Polymerization Photocuring and Film Formation. P(MBL) ROP (300 mg) and DMPA (2 wt.%) was dissolved in 3.0 ml chloroform, and the subsequent solution was filtered through a plastic frit (0.45 µm pore size) to eliminate any undissolved polymer particle. The solution was then transferred into PTFE molds (2 0.5 inches) with a syringe. Each solution (~1 ml) was allowed to slowly evaporate for at least 1 h at room temperature in the dark, after which a translucent and colorless film was formed. The mold was located in the photoreactor chamber (Luzchem, LZC-4 photoreactor with top-irradiation configuration, UVA lamps centered at 350 nm) and irradiated for 10 minutes, after which a gel was formed. The gel was allowed to dry slowly under ambient laboratory conditions overnight and then thoroughly dried in a vacuum oven at room temperature to a constant weight. Post-Functionalization by the Thiol-Ene Click Reaction. In a typical reaction by a radical photoinitiation, an isolated polymer (100 mg, produced by MBL/2 = 100/1) was dissolved in 1.5 ml of degassed chloroform inside a glovebox. This solution was filtered through a plastic frit (0.45 µm pore size) to eliminate any possible undissolved polymer particles, and charged in a 20 ml glass vial containing a magnetic stirrer, 0.2 equiv of DMPA, and 5 equiv of p-tert-butylbenzyl mercaptan. The reactor was then taken out of the glovebox, and placed inside a photoreactor (Luzchem, LZC-4 photoreactor with a horizontal UVA lamp configuration, radiation centered at 350 nm) where it was stirred at room S7

8 temperature for 2 h. At this point, 0.1 ml of the solution was withdrawn and quenched into a 1.5 ml vial containing 0.6 ml of CDCl 3 for conversion quantification by 1 H NMR. The remaining mixture was precipitated into 100 ml of methanol; the white sticky product was separated and redissolved in 5 ml of CHCl 3. Any insoluble particles were removed by filtration and the filtrate was precipitated in methanol. The product was filtered, washed with methanol, and dried in a vacuum oven to a constant weight. NMR data for P(MBL) ROP -SR. 1 H NMR (400 MHz, CDCl 3, 298 K): δ (m, 4H, Ar-H), (m, 2H, -OCH 2 -), 3.65 (s, 2H, -SCH 2 Ar), 2.65 (m, 2H, CHCH 2 S-), (m, 1H, CHCH 2 S-), (m, 2H, CHCH 2 CH 2 O-), 1.28 (s, 9H, -C(CH 3 ) 3 ). 13 C NMR (100 MHz, CDCl 3, 298 K): δ , , , , , 62.59, 42.52, 36.37, 34.61, 33.27, 31.49, Reaction of P(MBL) ROP with La[N(SiMe 3 ) 2 ] 3. P(MBL) ROP (200 mg, produced by MBL/2 =100/1) was dissolved in 0.6 ml CH 2 Cl 2. A solution of La[N(SiMe 3 ) 2 ] 3 [28.9 mg, La/P(MBL) ROP (mol/mol) = 1/50] in CH 2 Cl 2 (0.4 ml) was added to the above solution under vigorous stirring. After the measured time interval, a 0.1 ml aliquot was taken from the reaction mixture via syringe and quickly quenched into a 1.5 ml vial containing 0.6 ml of undried wet DMSO-d 6 with 250 ppm of benzoic acid. The quenched aliquots were later analyzed by 1 H NMR to obtain the conversion data. After 3 min, the solution became very viscous, and the polymer product precipitated after about 5 min. On the basis of the 1 H NMR spectra of the reaction mixture, about 64% P(MBL) ROP was depolymerized to MBL in 30 seconds. However, the lanthanum complex can also initiate VAP of the MBL generated by depolymerization of P(MBL) ROP, so the vinyl-addition polymer P(MBL) VAP was also produced during this process. The reaction was quenched with MeOH/HCl after 2 h, and the isolated product was the mixture of P(MBL) VAP and some cross-linked polymer. S8

9 Depolymerization of P(MBL) ROP Solution in the Presence of Catalyst. P(MBL) ROP (produced by MBL/2 = 100/1) was dissolved in 0.45 ml wet DMSO-d 6 in a NMR tube, and the resulting solution was heated to the desired temperature (60, 100 or 130 C). The degradation reaction was started by rapid addition of a La[N(SiMe 3 ) 2 ] 3 solution [0.05 ml wet DMSO-d 6, P(MBL) ROP /La (mol/mol) = 100/1] to the above solution. After the desired time, the resulting solution was analyzed by 1 H NMR to obtain the conversion data. The results were summarized in Table 2. Owing to the fact that P(MBL) ROP can undergo crosslinking by heating the bulk polymer, the depolymerization was carried out in solution in the presence of catalyst La[N(SiMe 3 ) 2 ] 3. However, in dry DMSO-d 6, a mixture of MBL (50.5%) and vinyl-addition polymer P(MBL) VAP (49.5%) was obtained by heating the polymer solution with an initial concentration of 0.2 M at 130 C for 1 h. To inhibit the vinyl-addition polymerization of MBL, a trace amount of water was added to the DMSO-d 6 (3.5 mm). Under such conditions, P(MBL) ROP can be completely recycled back to its monomer MBL. At lower temperature of 60 C, the depolymerization took a longer time (24 h), but nonetheless it reached quantitative conversion to MBL. The depolymerization was also investigated with a simple catalyst, LaCl 3, which is incapable of reinitiating the vinyl-addition polymerization of MBL generated. P(MBL) ROP (produced by MBL/2 = 100/1) was dissolved in 0.45 ml DMSO-d 6 in a NMR tube, and the resulting solution was heated to the desired temperature (130 or 160 C). The degradation reaction was started by rapid addition of a LaCl 3 solution (0.05 ml DMSO-d 6 ) to the above solution. After the desired time, the resulting solution was analyzed by 1 H NMR to obtain the conversion data. The results were summarized in Table S3. S9

10 Degradation Study. The hydrolytic stability of P(MBL) ROP and P(MBL) VAP in 1 M NaOH, 1 M HCl and DI H 2 O was examined according to the following procedures. Three parallel sheet specimens of P(MBL) ROP (typical dimensions mm, ~ 40 mg), prepared by spreading the polymer solution in chloroform into PTFE molds and evaporating slowly and then dried in a vacuum oven overnight at room temperature), and P(MBL) VAP (typical dimensions mm, ~ 90 mg), prepared by compression molding at 250 ºC for 5 min), were immersed in the above three different aqueous solutions (10 ml each) and allowed to sit undisturbed under ambient conditions. At each time point the specimens were removed from the solutions, dried in a vacuum at room temperature oven overnight, and weighed. And then the specimens were reimmersed in the same aqueous solutions again, and such a process was repeated at each time point. The results were summarized in Table S4. Table S1. Results of MBL Polymerization by La[N(SiMe 3 ) 2 ] 3 /BnOH in Toluene at 25 C a Run # Initiator (I) [MBL]/[La] /[I] Time (min) Polymer (mg) Yield b (%) M n c (kg/mol) Ð c (M w /M n ) Polymer type 1-100/1/ Vinyl addition 2 BnOH 100/1/ Vinyl addition 3 BnOH 100/1/ Vinyl addition 4 BnOH 100/1/ Vinyl addition a Conditions: MBL = 0.49 g (5 mmol), [MBL] = 5.0 M, toluene as the solvent, V solvent = 0.56 ml, 7 min, the La catalyst and initiator amount varied according to the [MBL]/[cat]/[I] ratio. b Isolated polymer yield. c M n and Ð determined by GPC at 40 C in DMF relative to PMMA standards. Table S2. Monomer Concentration as a Function of Time at Different Temperatures a Time (min) 55 C 60 C 65 C 65 C [MBL] t (mol/l) Time (min) [MBL] t (mol/l) Time (min) [MBL] t (mol/l) Time (min) [MBL] t (mol/l) S10

11 a Conditions: MBL/La[N(SiMe 3 ) 2 ] 3 /Ph 2 CHCH 2 OH = 100/1/3, MBL = g, MBL = 5.0 M in CD 2 Cl 2. Note that raising the temperature and lowering the temperature beyond the current temperature range resulted in negligible ROP and competing vinyl-addition polymerization (higher temperature) or polymer precipitation (lower temperature), respectively, thus limiting the temperature window applicable for this measurement. Table S3. Results of Depolymerization of P(MBL) ROP in the Presence of LaCl 3 in DMSO-d 6 a [P(MBL) ROP ]/[LaCl 3 ] = 100 T = 130 C [P(MBL) ROP ]/[LaCl 3 ] = 100 T = 160 C [P(MBL) ROP ]/[LaCl 3 ] = 50 T = 160 C Time (h) Conv. (%) to MBL Time (h) Conv. (%) to MBL Time (h) Conv. (%) to MBL a Conditions: [P(MBL) ROP ] 0 = 0.2 M, the amount of LaCl 3 varied according to [P(MBL) ROP ]/[La] molar ratio, V solvent = 0.5 ml. Table S4. Degradation of P(MBL) ROP and P(MBL) VAP in 1 M NaOH, 1 M HCl and DI H 2 O Time (day) P(MBL) ROP (Weight [%]) P(MBL) VAP (Weight [%]) 1 M NaOH 1 M HCl DI H 2 O 1 M NaOH 1 M HCl DI H 2 O S11

12 Figure S1. 1 H NMR spectra (C 6 D 6, 25 C): (a) the bisphenol ligand; (b) Y(CH 2 SiMe 3 ) 3 (THF) 2 ; and (c) yttrium alkyl catalyst 2. Figure S2. 1 H NMR spectra (C 6 D 6, 25 C): (a) the bisphenol ligand; (b) Y(CH 2 SiMe 3 ) 3 (THF) 2 ; and (c) yttrium alkyl catalyst 3. S12

13 Figure S3. MALDI-TOF spectrum of P(MBL) ROP produced with MBL/La[N(SiMe 3 ) 2 ] 3 /BnOH (100/1/3) and plot of m/z values (y) vs the number of MBL repeat units (x). S13

14 Figure S4. MALDI-TOF spectrum of P(MBL) ROP produced with MBL/La[N(SiMe 3 ) 2 ] 3 /Ph 2 CHCH 2 OH (100/1/3) and plot of m/z values (y) vs the number of MBL repeat units (x). S14

15 Figure S5. MALDI-TOF spectrum of P(MBL) ROP produced with MBL/La[N(SiMe 3 ) 2 ] 3 / i PrOH (100/1/3) and plot of m/z values (y) vs the number of MBL repeat units (x). S15

16 Figure S6. a, Plot of MBL concentration as a function time during polymerization at different temperatures: ( ) = 55 ºC; ( ) = 60 ºC, ( ) = 65 ºC. Conditions: MBL/La[N(SiMe 3 ) 2 ] 3 / Ph 2 CHCH 2 OH = 100/1/3, [MBL] 0 = 5.0 M in CD 2 Cl 2. b, Van t Hoff plot of ln[mbl] eq vs. reciprocal of the absolute temperature (T -1 ). Figure S7. Overlay of FT-IR spectra of cross-linked polymer P(MBL) CLP by La[N(SiMe 3 ) 2 ] 3 /BnOH (1/1) and vinyl-addition polymer P(MBL) VAP by La[N(SiMe 3 ) 2 ] 3 at 60 C. S16

17 Figure S8. TGA (black) and DTG (red) curves of the cross-linked polymer P(MBL) CLP by La[N(SiMe 3 ) 2 ] 3 /BnOH (1/1) (top) and vinyl-addition polymer P(MBL) VAP by La[N(SiMe 3 ) 2 ] 3 at 60 C (bottom). S17

18 Figure S9. Overlay of DSC curve of cross-linked polymer P(MBL) CLP by La[N(SiMe 3 ) 2 ] 3 /BnOH (1/1) (a) and vinyl-addition polymer P(MBL) VAP by La[N(SiMe 3 ) 2 ] 3 at 60 C (b). S18

19 Figure S10. TGA (black) and DTG (blue) curves of P(MBL) ROP by La[N(SiMe 3 ) 2 ] 3 /ROH (1/3): a, R = Bn; b, R = Ph 2 CHCH 2 ; c, R = i Pr; and by yttrium complex 2 (d). Figure S11. DSC curves: (a) MBL/La[N(SiMe 3 ) 2 ] 3 /BnOH = 100/1/3 (M n = 5.5 kg/mol); (b) MBL/La[N(SiMe 3 ) 2 ] 3 /Ph 2 CHCH 2 OH = 100/1/3 (M n = 5.8 kg/mol); (c) MBL/La[N(SiMe 3 ) 2 ] 3 / i PrOH = 100/1/3 (M n = 4.7 kg/mol); (d) MBL/yttrium complex 2 = 100/1 (M n = 18.3 kg/mol). S19

20 Figure S12. DSC curves of P(MBL) ROP by yttrium complex 2. Figure S13. Overlay of FT-IR spectra of P(MBL) ROP -hν and P(MBL) ROP. S20

21 Figure S14. TGA (black) and DTG (blue) curve of P(MBL) ROP -hv from P(MBL) ROP (M n = 21.0 kg/mol) prepared by 2. Figure S15. TGA (black) and DTG (blue) curve of P(MBL) ROP -hv from P(MBL) ROP (M n = 5.5 kg/mol) prepared by 1/BnOH (1/3). S21

22 Figure S C NMR spectrum of P(MBL) ROP -SR (top) and 13 C NMR (DMSO-d 6 ) spectrum of P(MBL) ROP by yttrium complex 2 (bottom) for comparison. S22

23 Figure S17. 1 H NMR spectra of the reaction mixture of P(MBL) ROP with La[N(SiMe 3 ) 2 ] 3 at 30 s (a) and 3 min (b). S23

24 Figure S18. Overlay of 1 H NMR spectra (DMSO-d 6 ) the product obtained by heating the solution of P(MBL) ROP with LaCl 3 in DMSO-d 6 at 160 C for different times: (i) 1 h; (ii) 2 h; (iii) 3 h; (iv) 4 h; (v) 6 h. S24

25 Computational Details. All the density functional theory (DFT) calculations were performed using the Gaussian09 package. 2 Geometry optimizations were performed using the BP86 GGA functional of Becke and Perdew. 3 The electronic configuration of the molecular systems was described by the split-valence basis set with a polarization function of Ahlrichs and co-worker (SVP basis set in Gaussian09), for main group atoms. 4 For the metals we used the small-core, quasi-relativistic Stuttgart/Dresden effective core potential basis set, with the associated valence basis set (SDD ECP and basis set in Gaussian09). 5 Geometry optimizations were performed without symmetry constraints. All the geometries discussed in this work were confirmed as minima or TSs by frequency calculations. Single-point energy calculations in solution were performed with the triple-ζ plus one polarization function basis set proposed by Ahlrichs (TZVP keyword in Gaussian) basis set for main group atoms and again the same SDD pseudopotential for the metals. Solvent effects were included with the polarizable continuum solvation model PCM using toluene and THF as the solvent. 6 Reported energies are M06/TZVP//BP86/SVP electronic energies corrected with ZPEs, thermal energies, and entropy effects calculated at T= K using the BP86/SVP method. S25

26 Cartesian coordinates of species reported in Schemes 5 and 7. MBL O C C C C O C H H H H H H La-M La(OMe) 3 O C C C C O La O C C O C O C H H H H H H H H H H H H H H H ROP La(OMe) 3 O C C C C La O O C C O C O C H H H H H H H H H H H H H H H ROP La(OMe) 3 La S26

27 O O O C O C C C C H H H H H H O C H H H C H H H C H H H ROP La(OMe) 3 C O C C C La O C H H H H H H O O O C H H H C H H H C H H H ROP La(OMe) 3 La O O O C O C C C C H H H H H H O C H H H C H S27

28 H H C H H H ROP La(OMe) 3 C O C C C O La O C C O C O C C C C O C C O H H H H H H H H H H H H H H H H H H H H H ROP La(OMe) 3 C O C C C La O C O O C C O C H H H H H H H H H H H H H C H C H H S28

29 C C H H O O C H H H ROP La(OMe) 3 C C C C O La O C O C O C O C H H H H H H H H H H H H H H C C H H C C H H O O C H H H VAP La(OMe) 3 La O O O O C C C C H H H H O C H H C H H H C H H H C H H S29

30 H VAP La(OMe) 3 O C C C C La O C O O O H H H H H H C H H H C H H H C H H H VAP La(OMe) 3 La O O O C O C C C C O C C C C H H H H O C H H O H H H H H H C H H H C H H H C H H H VAP La(OMe) 3 O C C C C O La S30

31 O C C O C O C C C C O C O C H H H H H H H H H H H H H H H H H H H H H VAP La(OMe) 3 O C C C O C C O La O O O C C C C O C H H H H H H H H H H H H C H H H C H H H C H H H S31

32 1-La-M La[N(SiMe 3 ) 2 ] 3 La N N N O Si Si Si Si Si Si C C C C C C C C C C C C C C C C C C C O C C C C H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H S32

33 H H H H H H H H H H H H H H ROP La[N(SiMe 3 ) 2 ] 3 La N N N O Si Si Si Si Si Si C C C C C C C C C C C C C C C C C C C O C C C C H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H S33

34 H H H H H H H H H H H H H H H H H H H H H H H H H H H H ROP La[N(SiMe 3 ) 2 ] 3 La N N N O Si Si Si Si Si Si C C C C C C C C C C C C C C C C C C C O C C C C H H H H H H H H H H H H H H H H H H S34

35 H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H ROP La[N(SiMe 3 ) 2 ] 3 C O C C C La Si C O C N Si C N Si C Si C C C C C C C C C N Si C Si C C C C C H H H H S35

36 H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H ROP La[N(SiMe 3 ) 2 ] 3 C C O C C La Si C O N Si C C Si C N Si C N Si C C C C C S36