Expanding the monomer scope of linear and branched vinyl polymerisations via copper- catalysed reversible-deactivation radical polymerisation of hydrophobic methacrylates using anhydrous alcohol solvents

The use of anhydrous alcohols for Cu-catalysed reversible-deactivation radical polymerisation of a wide range of hydrophobic methacrylates has been explored in detail.

Characterisation 1 H and 13 C nuclear magnetic resonance (NMR) spectra were recorded in CDCl 3 using a Bruker Avance spectrometer operating at 400 and 100 MHz respectively. Triple detection size exclusion chromatography (SEC) was conducted using a Malvern Viscotek instrument equipped with a GPCmax VE2001 auto-sampler, two viscotek T6000 columns (and a guard column), a refractive index (RI) detector VE3580 and a dual 270 detector (light scattering and viscometer). SEC was performed at a flow rate of 1 mL min -1 using THF containing 2 v/v % of TEA as the mobile phase. Fluorescence spectra were obtained using a Shimadzu RF-5301PC spectrofluorophotometer. Emission spectra for pyrene were recorded between 350 and 500 nm. An excitation wavelength of λex = 335 nm was used for all studies as well as an excitation slit width of 2.5 nm and an emission slit width of 2.5 nm with a scan rate of 60 nm min -1 .

Experimental Details Preliminary Feasibility Studies
Monomer-solvent miscibility studies were conducted at a monomer concentration of 50 weight percent (50 wt %) with respect to the total mass of the monomer-solvent mixture. Solvent miscibility was assessed visually at both ambient (20 ℃) and elevated (60 ℃) temperatures. In a typical experiment, MMA (1.00 g, 9.99 mmol) and anhydrous methanol (1.00 g, 1.26 mL) were added to a glass vial and sealed. The vial was agitated gently in order to give ample opportunity for mixing, after which monomer-solvent miscibility at ambient temperature was assessed visually. A magnetic stirrer bar was then added, the vial was re-sealed with a rubber septum and placed in an oil bath at 60 ℃ under magnetic stirring. After 10 minutes, the vial was withdrawn from the oil bath and monomeralcohol miscibility at an elevated temperature was assessed visually.

Fluorescence Emission Spectroscopy
Pyrene emission fluoresence spectroscopy was conducted at a pyrene concentration of 10 nM.
Solutions were prepared containing pyrene dissolved in: neat methacryllic monomers, common organic solvents, monomer-MeOH mixtures and monomer-IPA mixtures. As in the miscibility studies described above, monomer-alcohol mixtures were prepared at a monomer concentration of 50 wt %.
In a typical experiment, an stock solution of pyrene in acetone was added to a glass vial (300 µL, 0.1 mg mL -1 ). The vial was left in a low velocity fumehood overnight, allowing complete evaporation of acetone, to give a known quantity of solid pyrene (0.03 mg, 1.48 x 10 -4 mmol). Following addition of the MMA-MeOH mixture (14.8 mL, 50 wt %), the vial was sealed and placed on an orbital mixer to ensure full dissolution of pyrene. The solution (ca. 1.00 mL) was added to a quartz cuvette and placed in a Shimadzu RF-5301PC spectrofluorophotometer. A fluorescence emission spectrum was recorded between 350 nm and 500 nm following excitation at 335 nm. The polarity of all pyrene solutions were determined using the I 1 /I 3 ratio, by comparison of the relative intensities of the first (I 1 , ca. 373 nm) and third (I 3 , ca. 384 nm) vibrational bands of the pyrene fluorescence emission ( Figure S2, Table S1).
Benzyl alcohol (5.00g, 46.2 mmol), anhydrous TEA (7.02g, 69.4 mmol) and DMAP (0.565g, 4.62mmol) were added to an oven dried round bottomed flask containing a magnetic stirrer bar and was equipped with a pressure equalising dropping funnel. The round bottom flask was purged with nitrogen followed by addition of anhydrous THF (100 mL) and the solution was cooled to 0 ℃ in an ice bath. α-bromo isobutyryl bromide (13.8 g, 7.43 mL, 60.1 mmol) and anhydrous THF (25.0 mL) were added dropwise over 30 minutes via the pressure equalising dropping funnel and the reaction could be observed immediately by the formation of the of a white precipitate. After one hour the ice bath was removed and the reaction was allowed to proceed for a further 23 hours. The precipitate was removed by filtration and the THF was removed in vacuo. The product was then extracted using diethyl ether and dried in vacuo to give a colourless oil. The pure product was isolated by silica gel column chromatography using a hexane/ethyl acetate mobile phase (95/5 volume %), Rf = 0.44, giving a colourless oil (71%). 1 H NMR (400 MHz, CDCl 3 ) δ ppm 7.40 -7.30 (m, 5H), 5.21 (s, 2H), 1.95 (s, 6H). 13 C NMR (100 MHz, CDCl 3 ) δ ppm 171. 5, 135.4, 128.6, 128.4, 127.9, 67.6, 55.7, 30.8   Cu(I)Cl (48.5 mg, 0.489 mmol) was added rapidly to the flask, instantly forming a brown coloured solution. The reaction was then purged with N 2 for a further 60 seconds, sealed and quickly submerged into an oil bath preheated at 60 ° C. In some cases (MMA, tBMA and nBMA) the reaction mixture remained homogeneous throughout the reaction and phase separation only occurred on cooling following removal from the oil bath at 60 ° C. In all other cases (nHMA, CHMA, EHMA, LMA and SMA) phase separation occurred during the early stages of polymerisation and the reaction proceeded as a biphasic mixture. The reaction was stopped after 24 hours by dilution with CDCl 3 until a homogeneous blue/green solution was obtained, at this point a sample (ca. 500 μL) was taken for quantification of monomer conversion by 1 H NMR ( Figure S6).

Figure S6
Quantification of the monomer conversion achieved in for the polymerisation of nHMA by 1 H NMR analysis of the reaction mixture after 18 hours (CDCl 3 , 400 MHz).
The solution was further diluted in CHCl 3 , passed over a neutral alumina column to remove the copper catalyst and dried in vacuo. The polymer was re-dissolved in a minimum amount of THF and precipitated twice from THF into cold methanol to give p(nHMA) as a clear viscous liquid. The polymer was then dried in vacuo at 40 ° C for 48 hours and characterised using 1 H NMR in CDCl 3 ( Figure S7) and triple detection SEC using a THF/TEA eluent (98/2 v/v %) using a narrow poly(styrene) standard calibration. ( Figure S8).

Figure S7
Quantification of the number average degree of polymerisation of p(nHMA) by analysis of the purified p(nHMA) using 1 H NMR spectroscopy (CDCl 3 , 400 MHz).

Figure S9
Kinetic studies on the Cu-catalysed RDRP of nHMA at 60 ℃ in anhydrous methanol. a) Monitoring the rate of polymerisation using 1 H NMR spectroscopy to construct plots of monomer conversion and semi-logarithmic plots against time. b) Analysis of the evolution of number average molecular weight (M n ) and polymer dispersity (Đ) with monomer conversion.

Figure S10
TD-SEC analysis of linear homopolymers generated using Cu-catalysed RDRP at 60 ℃ in IPA. Overlaid refractive index (RI, red solid lines) and right-angle light scattering (RALS, blue dotted lines) chromatograms obtained from (a) p(MMA), (b) p(tBMA), (c) p(CHMA), (d) p(LMA), (e) p(SMA).  Cu(I)Cl (48.5 mg, 0.978 mmol) was added rapidly to the flask, instantly forming a brown coloured solution. The reaction was purged with N 2 for a further 60 seconds and quickly submerged into an oil bath preheated at 60 ° C. The reaction was stopped after 24 hours by dilution with CDCl 3 until a homogeneous blue/green solution was obtained, at this point a sample (ca. 500 μL) was taken for quantification of monomer conversion by 1 H NMR ( Figure S6). The solution was further diluted in CHCl 3 , passed over a neutral alumina column to remove the copper catalyst and dried in vacuo. The polymer was re-dissolved in a minimum amount of THF and precipitated twice from THF into cold methanol to give a viscous clear liquid. Polymers were then dried in vacuo at 40 ° C for 48 hours and characterised by 1 H NMR in CDCl 3 ( Figure S7) and triple detection SEC using a THF/TEA eluent (98/2 v/v %) using a narrow poly(styrene) standard calibration.

Figure S13
Quantification of the DP n of the primary chains of which branched statistical copolymers, in this case p(nHMA 65 -co-EGDMA 0.98 ), are constructed. Analyses were conducted via 1 H NMR spectroscopy of branched copolymers following purification (CDCl 3 , 400 MHz). The M n of constituent primary chains (M n (pc)) were subsequently calculated as M n (pc) = (DP n x Mr(monomer)) + Mr (Initiator).

Table S3
Good and bad solvents identified for purification of linear homopolymers and branched statistical copolymers.

Polymer
Polymer

Equation S1
Calculation of the number of primary chains per macromolecule where M = absolute molecular weight of the species contributing towards the cum. ω f and M n (LH) = the number average molecular weight of the linear homopolymer generated in the absence of EGDMA under identical polymerisation conditions.

Table S4
Calculation of the differences in initiator ([I] 0 ) and methacrylate group ([M] 0 ) concentrations which arises as a result of the increased contribution of the pendant side group to the overall monomer mass.

Figure S18
Spartan simulations of pendant group and repeat unit protrusion distances in p(MMA) and p(LMA) oligomers (DP = 10) containing one EGDMA unit per chain. Distances were measured between the polymer backbone and the: a) pendant methacrylate group in p(MMA 10 -co-EGDMA 1 ), b) pendant CH 3 of a p(MMA) repeat unit, c) pendant methacrylate group in p(LMA 10 -co-EGDMA 1 ), b) terminal CH 3 of a p(LMA) repeat unit.

Table S6
Calculated pendant group and repeat unit protrusion distances from the methacryllic polymer backbone using Spartan molecular modelling software.