Block Copolymers Based on Ethylene and Methacrylates Using a Combination of Catalytic Chain Transfer Polymerisation (CCTP) and Radical Polymerisation

Abstract Two scalable polymerisation methods are used in combination for the synthesis of ethylene and methacrylate block copolymers. ω‐Unsaturated methacrylic oligomers (MMAn) produced by catalytic chain transfer (co)polymerisation (CCTP) of methyl methacrylate (MMA) and methacrylic acid (MAA) are used as reagents in the radical polymerisation of ethylene (E) in dimethyl carbonate solvent under relatively mild conditions (80 bar, 70 °C). Kinetic measurements and analyses of the produced copolymers by size exclusion chromatography (SEC) and a combination of nuclear magnetic resonance (NMR) techniques indicate that MMAn is involved in a degradative chain transfer process resulting in the formation of (MMA)n‐b‐PE block copolymers. Molecular modelling performed by DFT supports the overall reactivity scheme and observed selectivities. The effect of MMAn molar mass and composition is also studied. The block copolymers were characterised by differential scanning calorimetry (DSC) and their bulk behaviour studied by SAXS/WAXS analysis.

of 200 µL were analyzed at concentrations of 3 mg mL −1 . The Omnisec software was used for data acquisition and data analysis. The molar mass distributions (MMD) were calculated by means of a conventional calibration curve on the basis of linear polyethylene standards from 300 to 130 000 g mol −1 (Polymer Standards Service).
Gas chromatography (GC) analyses were conducted on a GC HP instruments 6890 equipped with a flame ionization detector (FID) and an Agilent 19091J-413 HP-5 column (30 m × 320 µm × 0.25 µm). Injector and detector temperatures were set to 250 °C. The initial and final column temperatures were respectively 40 °C and 250 °C with a heating rate of 20 °C min -1 and a final isotherm of 2 min at 250 °C. The internal standards used was dodecane.
DSC analyses were performed on a Mettler Toledo DSC 3. Measurements were carried out by two successive heating and cooling cycles (5 K min -1 for the first cycle) with temperatures ranging from 10 to 220 °C. Crystallization, melting and glass transition temperatures were recorded on the second cycle.
Small-angle X-ray scattering (SAXS) measurements were made using a Xenocs Xeuss 2.0 equipped with a micro-focus Cu Kα source collimated with Scatterless slits. The scattering was measured using a Pilatus 300k detector with a pixel size of 0.172 mm x 0.172 mm. The wide angle x-ray scattering (WAXS) data was collected using a Pilatus 100k mounted at an angle of 36 º from the beam and a distance of 162(2) mm from the sample. The distance between the detectors and the sample was calibrated using silver behenate (AgC22H43O2). The magnitude of the scattering vector (q) is given by q = (4π sin(θ))⁄λ, where 2θ is the angle between the incident and scattered X-rays and λ is the wavelength of the incident X-rays. This gave a q range for the SAXS detector of 0.005 Å -1 and 0.16 Å -1 . A radial integration of the 2D scattering profile was performed using FOXTROT software and the resulting data corrected for the absorption, sample thickness and background. When required, samples were mounted between sticky Kapton windows.
Geometry optimization of reactants and transition states were carried out without any symmetry restrictions at the DFT level of theory using the global hybrid meta-GGA functional MPWB1K. [2,3] For each compound, a conformational sampling has been performed by hand. Only the most stable conformers are reported. All atoms were represented by all electron polarized def2-TZVP basis sets. [4] Solvation by DMC was implicitly represented during optimization using dibutylether as a model (similar r) and for which parameters are available for the SMD method. [5] According to previous benchmark studies no dispersion correction was added. [6][7][8] Analytical frequency calculations were carried out to verify the nature of the extrema (minimum or transition state). Gibbs energies have been computed within the harmonic approximation and estimated at 298.15 K and 1 atm. Standard state conversion has been applied and evaluated at 343K. [9] Additionally, energy barriers have been corrected by reaction symmetry numbers in order to account for the statistic degeneracy of transitions states. [10] Criteria for SCF convergence, geometry optimization, and integration grids are set to default values. All these computations have been performed with the gaussian09 suite of programs. [11] General procedure for the preparation of poly(methyl methacrylate) ω-functional oligomers (MMAn,) via catalytic chain transfer polymerisation (CCTP) Four different ω-functional oligomers were prepared either by solution or emulsion polymerization according to described protocols. [12,13] For a CCTP carried out in solution, bis[(difluoroboryl)dimethyl glyoximato]cobalt(II) (CoBF, 0.09 mg, 5 ppm relative to monomer) or bis[(difluoroboryl)dimethyl phenyl-glyoximato]cobalt(II) and a stirring bar were charged into a 100 mL round bottom flask. The flask was purged with nitrogen for one minute. Subsequently, 10 mL of methyl methacrylate (MMA), previously deoxygenated for 30 minutes by bubbling with nitrogen, were added to the flask via a deoxygenated syringe. The mixture was stirred under a nitrogen atmosphere until dissolution of the catalyst. Meanwhile, dimethyl-2,2′-azobis(2-methyl propionate) (V601, 107 mg, 1 mol% relative to monomer) was dissolved in 10 mL toluene (1/1 v/v to monomer) and this solution charged into a 50 mL round bottom flask and bubbled with nitrogen for 30 min. Subsequently, the 100 mL flask with the monomer and catalyst was heated to 75 °C under an inert nitrogen atmosphere. When the temperature of the catalyst solution reached 75 °C, the initiator solution was added. The reaction was allowed to continue for 6 hours with continuous stirring. MMA dimer (MMA2) was recovered after distillation whereas poly(methyl methacrylate) with higher molar mass (1100 g mol -1 , MMA11) was recovered by precipitation in methanol. MMA2 after distillation is composed of three products, MMA dimer (97%), trimer (3%), which were analysed with 1 H and 13 C NMR spectroscopy as well as Gas Chromatography (GC) ( Figure S1 and Table S1) as the percentage of each oligomer in the mixture could play a role in the synthesis of copolymers.  For a CCTP in emulsion, 22.4 mg of CoBF and a stirring bar were charged into a 100 mL round bottom flask. The flask was purged with nitrogen for at least one minute. Subsequently, MMA (96.3 mL) and optionally MAA (10.7 mL) when copolymers were targeted, previously deoxygenated for at least 30 min, were added to the flask via a deoxygenated syringe. The mixture was stirred under a nitrogen atmosphere until the total dissolution of the solids. Meanwhile, 4,4'-azobis(4-cyanovaleric acid) (ACVA, 1.35 g), sodium dodecyl sulfate (SDS, 2.1 g) and 250 mL of deionized water were charged into a threeneck, 500 mL double jacketed reactor, equipped with a thermometer and an overhead stirrer. The mixture was bubbled with nitrogen for at least 30 min. Subsequently, the mixture was heated under inert atmosphere. When the temperature of the mixture reached 75 °C, the addition of the solution of monomer and cobalt complex is performed with a syringe pump (feeding rate = 1.866 mL min -1 , feeding time = 60 min). After the end of the addition, stirring continued for another 60 min under the same temperature and stirring rate. The final products (MMA35 and MMA12MAA2) were recovered by lyophilisation using the freeze-dryer.

General procedure for the polymerisation of ethylene
The reaction was conducted in a stainless-steel reactor (160 mL, from Parr Instrument Co.) equipped with a thermometer, a pressure sensor, a mechanical stirring apparatus, and safety valves. In a typical polymerisation procedure, AIBN (50 mg, 0.30 mmol) was dissolved in degassed DMC (50 mL). The solution was later introduced into an injecting chamber. The chamber was then pressurised at 30 bar of ethylene, and open into a preheated autoclave at 70 °C. Ethylene gas was then introduced to the reactor until the desired pressure of 80 bar was reached. The reaction medium was stirred at 600 rpm. In order to manage the polymerisation safely over 50 bar of ethylene, we use a 1.5 L intermediate tank.
The tank is cooled at -20°C during a filling step with the ethylene bottle. After isolation, it is then heated back and connected to the reactor to get the desired pressure. This tank was used to charge the reactor and to maintain a constant pressure of ethylene in the reactor by successive manual ethylene additions. After the desired time, the stirring was slowed down, and the autoclave was cooled with iced water. When the temperature inside the autoclave dropped below 25 °C, the remaining pressure was carefully released. The contents of the reactor were collected with acetone or toluene. The evaporation of the solvent gave the polymeric product

General procedure for the copolymerisation of methacrylic oligomers with ethylene
In a typical polymerisation procedure, a solution of methacrylic oligomers (0.30 mmol) and AIBN (50 mg, 0.30 mmol) in DMC (50 mL) was degassed by bubbling with argon for 30 minutes. The remainder of the procedure was the same as previously described for ethylene polymerisation.

General procedure for precipitation of the copolymer of MMA2 and ethylene
The polymer (100 mg) was dissolved in 10 mL of toluene at 90°C and stirred for two hours. The solution was subsequently poured in 100 mL of methanol or acetone, and a white solid precipitated. The solid was filtered and dried under vacuum to afford a white powder. The solid was analyzed by 1 H NMR and HT-SEC.
Copolymerisation of methacrylic dimer (MMA 2 ) with ethylene  Determination of structure formed during the ethylene copolymerization with MMA 2 via NMR studies Figure S4. 1 H-1 H COSY NMR from run 8 in Table 2 in TCE/C6D6 at 90°C. Isobutyronitrile stems from the chain-ends of the PE initiated from AIBN.  Table 2 in TCE/C6D6 at 90°C. Figure S7. 1 H-13 C HMBC NMR from run 8 in Table 2 in TCE/C6D6 at 90°C.

Molecular modelling
Energy profiles Scheme S1. Gibbs Energy profiles computed at the MPWB1K DFT level. Thermodynamics is in red, kinetics in blue. Gibbs Energy variation are relative to starting reactants. Green values refer to the Gibbs energy barrier of the quoted elementary step.
Transfer with vinyl terminated PMMA chain transfer: (C2H4)PE and C2H4 are both referring to ethylene species with identical molar masses in the same system, hence volume of solvent. The fraction in Equation 5 can thus be also given in terms of mass in grams. ( (1) °C and 80 bar. [16,17] The chain transfer constant is determined by linear regression from Equation 7.
DSC of the different copolymers synthesized Figure S16. DSC of experiments presented in Table 1, Table 2 and Table 3. a-e) heating and f-j) cooling for the copolymerisation carried out in the presence of MMA 2 , MMA 11 Figure S17. Comparison of melting temperatures, measured by DSC, depending on the number of carbons per PE chain, as measured by 1 H NMR, for the different copolymers. [18] SAXS/WAXS analysis of the different copolymers

SAXS analysis of polyethylene
In the low q-range (q < 0.04 Å −1 ), the scattering intensity fits the Porod law (I(q) ∝ q −4 ) corresponding to the amorphous PE bulk. The peak around 0.055 Å −1 has been fitted with a Broad Peak model [20,21] characteristic of a two-component system (with a crystalline and an amorphous phase).
A second broad peak of lower intensity is discernible at higher q-range (d ≈ 54 nm and ξ ≈ 6 nm). The decorrelation of the diffraction peaks gives many useful information. The area of diffraction peaks and the amorphous halo (fitted using a Gaussian function) allowed estimating a crystallinity index (ic): ic (%) = Apeak/(Apeak+Ahalo )×100 Where Apeak and Ahalo are the area of the (110) crystalline peaks (blue peak in Figure S17) and the amorphous halo (green curve in Figure S17), respectively. The characteristic domain size (τ) perpendicular to the reflecting plane of each peak can be obtained from the Scherrer equation: [22] τ = Kλ/(β cos θ) Where K is a dimensionless shape factor of about 0.9 under the assumption of a Gaussian line shape, λ is the X-ray wavelength, β is the line broadening at half the maximum intensity (full width at half maximum, FWHM), after subtracting the instrumental line broadening in radians and θ is the Bragg angle also in radians. Figure S17. Diffraction pattern of PE and gaussian peak fitting for the determination of the crystallinity index and the characteristic domain size of bulk PE. [23]  Here the low q-range (q < 0.02 Å −1 ) exhibit a q −4 slope, followed by a peak around 0.03 Å −1 (ξ ≈ 80 nm and d ≈ 200 nm), the high q-range show two wavelets characteristic of a cylindrical form factor (R = 56 nm and L = 35 nm).   Figure S21. Diffraction pattern of PE and gaussian peak fitting of PE-b-MMA11 block copolymer