UV-Light as External Switch and Boost of Molar-Mass Control in Iodine-Mediated Polymerization

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1 Supporting Information UV-Light as External Switch and Boost of Molar-Mass Control in Iodine-Mediated Polymerization Arne Wolpers and Philipp Vana Institut für Physikalische Chemie, Georg-August-Universität Göttingen, Tammannstraße 6, D Göttingen, Germany Phone: +49 (0) , Fax: +49 (0) Experimental section Materials Methyl methacrylate (MMA) (99 %, Aldrich) and n-butyl methacrylate (BMA) (99 %, Aldrich) were purified through an alumina column. 2,2 - Azobis(2-methylpropionitrile) (AIBN) ( 98.0 %, Fluka) was recrystallized from acetone and toluene. Phenylethyl iodide (PE I) was synthesized according to Matyjaszewski et al. 1 and cyanopropyl iodide (CP I) was prepared similar to Bałczewski and Mikołajczyk 2 (details see below, Preparation of cyanopropyl iodide (CP I) ). 2-Methyl-4 -(methylthio)- 2-morpholinopropiophenone (MMMP) (98 %, Aldrich), iodine (99.8 %, Aldrich), N,N,N,N,N -pentamethyldiethylenetriamine (PMDTA) (99 %, Aldrich), and toluene ( 99.5 %, Fluka) were used as received. Preparation of cyanopropyl iodide (CP I) A solution of iodine (38 mg) and AIBN (79 mg) in toluene (0.21 g) was heated under an argon atmosphere at 100 C in a thermostated block To whom correspondence should be addressed. 1

2 CN I CN CN in CDCl chemical shift / ppm Figure S1 1 -NMR spectrum of a solution of iodine and AIBN in toluene after being heated at 100 C for 1 h. heater in the absence of light. After 1 h, the slightly yellowish reaction mixture was rapidly cooled to room temperature. The solution of CP I in toluene was then used without purification. The 1 -NMR spectrum of the solution is given in Figure S1. UV/vis spectroscopy revealed that the conversion of iodine was higher than 99.8 % (via the signal at about 500 nm, see (i) in Figure S2). Photopolymerization procedure In a typical procedure, 0.13 g of the CP I solution (see above, Preparation of cyanopropyl iodide (CP I), with about 0.08 g of toluene) was added to a solution of MMMP (56 mg) in BMA (3.5 g). Prior to polymerization, the solution (ca. 4 ml in an 8 ml borosilicate-glass vial) was purged with argon for 20 min. The solution was then stirred in a thermostated water bath at 22 C. The solution was irradiated with a UV lamp (gvapor lamp with an optical bandpass filter at 366 nm, 8 W, erolab UV and Lamp) from a distance of 7 cm (intensity = 4.5 mw cm 2 ). After determined reaction times, samples were taken via syringe through a septum while purging with argon. The polymeric products were isolated by evaporation of the residual monomer and solvent. Monomer conversions were determined gravimetrically. 2

3 Instrumentation UV/vis spectroscopy Optical absorption spectroscopy was performed with a Cary 300 Scan photospectrometer in solution against the pure solvent, using ellma quartz cuvettes with a thickness of 10 mm. The spectra were recorded in the wavelength range between 280 and 900 nm in steps of 1 nm with a scan rate of 600 nm min 1 at room temperature. Size-exclusion chromatography (SEC) SEC characterization was performed using an Agilent 1260 Infinity system. It consisted of an isocratic PLC pump, an autosampler, a PSS SDV (styrene divinylbenzene copolymer-network) precolumn (8 50 mm), three PSS SDV separation columns (8 300 mm; particle size = 10 µm; pore sizes = 10 6, 10 5, and 10 3 Å), and a refractive-index (RI) detector. As the eluent, TF was used at 35 C with a flow rate of 1 ml min 1. The SEC setup was calibrated with PSS polymma standards of low dispersities (M p = kg mol 1 ) with toluene as the internal standard. The concentration of the polymer samples was 5 g L 1. Molar masses of polybma were determined according to the principle of universal calibration. 3,4 NMR spectroscopy The NMR spectrum in Figure S1 was recorded using a Varian Unity 300 system (300 Mz). It was measured at room temperature with an analyte concentration of about 40 g L 1 in CDCl 3. The residual proton signal was taken as the internal standard. Electrospray-ionization mass-spectrometry (ESI-MS) The spectrum presented in Figure S3 was measured with a Bruker Daltonik microtof ESI time of flight mass-spectrometer. The spectrum was obtained in the positive ion mode at a spray voltage of 4.5 kv and a capillary temperature of 180 C. The polymer sample was dissolved in a tetrahydrofuran methanol mixture and introduced into the electrospray interface by injection via a syringe pump of 3 µl min 1. 3

4 absorption iodine iodine & MMMP iodine & PMDTA 3 CS N O N MMMP N N O wavelength / nm PMDTA Figure S2 UV/vis spectra of solutions of (i) iodine, (ii) iodine and MMMP, and (iii) iodine and PMDTA in toluene. Reactivity of MMMP and PMDTA towards iodine UV/vis spectra were recorded of (i) a solution of iodine in toluene (1.1 mmol L 1, 1 eq) and (ii) after the addition of MMMP (8 eq) or (iii) PMDTA (8 eq) (Figure S2). In contrast to the highly active and reducing amine PMDTA, no change of the iodine signal is observed after the addition of MMMP. End-group analysis via ESI-MS A polybma sample obtained from the photopolymerization with [BMA] 0 = 6.2 mol L 1, [MMMP] 0 = 50 mmol L 1, and [CP I] 0 = 31 mmol L 1 at 22 C (12 % monomer conversion, M n = 4900 g mol 1, Ð = 1.72) was measured via ESI-MS. The resulting spectrum is shown in Figure S3 and the assigned signals are given in Table S1. Determination of C ex The program package Predici 5 7 was used to determine the transfer constant C ex = k ex /k p of CP I by modelling number-average molarmasses (M n ) as a function of monomer conversion, which had been 4

5 (a) intensity m/z (b) 1 intensity & m/z Figure S3 ESI-MS spectrum of a polybma sample (M n = 4900 g mol 1, Ð = 1.72) of the system described in the text ((a) multiple repeating units and (b) one repeating unit between m/z = 810 and 952 with peaks labeled according to Table S1). 5

6 Table S1 Polymeric species with the theoretical and the experimentally observed m/z values, (m/z) theo and (m/z) exp, respectively, and the relative intensities (rel. int.) from the ESI-MS spectrum in Figure S3b. No. species a (m/z) b theo (m/z) b exp rel. int. / % 1 CP (BMA) 5 O, Na CP (BMA) 5 I, Na CP (BMA) 4 lactone, Na CP (BMA) 5 BMA =, Na CP (BMA) 5 BMA, Na CP (BMA) 5 CP, Na CP (BMA) 5 O, K CP (BMA) 5 I, K CP (BMA) 4 lactone, K CP (BMA) 5 O, N CP (BMA) 11 O, 2 Na CP (BMA) 12 O, 2 Na a α-end-group (BMA) chain length ω-end-group, cation; b for m/z =

7 (a) [BMA] 0 x=x5p9 mol L 1 =bulk. atx60 C [AIBN] 0 x=x9p6 mmol L 1 [CP I] 0 x=x30 mmol L 1 experimentalxdata simulation (b) M n x3x1000 g mol theoreticalxline monomerxconversionx3xm Figure S4 Experimentally obtained M n values as a function of monomer conversion of the presented system and the best-fit simulation obtained for k ex = L mol 1 s 1. obtained experimentally. The simulations were performed using Predici version on an Intel Core i7-3630qm, 2.4 Gz computer. The reaction components and conditions are given in Figure S4a. The polymerization was conducted in the dark. The reactions and the respective rate coefficients implemented in the simulation are presented in Scheme S1 and Table S2. A best-fit procedure according to the leastsquares method was performed in order to obtain k ex, while the rest of the rate coefficients remained constant. The results are shown in Figure S4b. k ex was determined to be L mol 1 s 1, leading to C ex = k ex /k p = 3.6. Estimation of k hc The rate coefficient k hc of the homolytic C I-bond cleavage of CP I was determined. Therefore, a dilute solution of CP I (prepared according to Preparation of cyanopropyl iodide (CP I), see above) in toluene was saturated with air and then irradiated similarly to the polymerization experiments ( Photopolymerization procedure, see above). The formed CP reacts much more likely with the dissolved oxygen than with the free iodine (especially when iodine concentration is low), so that reversible 7

8 (a) conventional radical polymerization radical formation & initiation (I) k d AIBN f In + f In (II) irreversible termination (IV) propagation polymer (i) + polymer (j) k ini In + BMA polymer (1) (III) polymer (i) + BMA polymer (i + 1) (b) iodine-transfer polymerization pre-equilibrium degenerative chain-transfer k p k t = k t (i,i); i j δ (1 δ ) polymer dead (i) polymer dead (j) + & polymer dead (i + j) (V) polymer (i) k ex + CP I polymer I(i) + CP (VI) k ex polymer I(i) + CP polymer (i) + CP I reinitiation (VII) CP k ini + BMA polymer (1) main equilibrium degenerative chain-transfer (VIII) k ex polymer (i) polymer I(i) + polymer I(j) + polymer (j) Scheme S1 Reactions and corresponding rate coefficients implemented in the kinetic simulation. For the values of the coefficients see Table S2. Table S2 Kinetic input parameters for the simulations of ITP of BMA in bulk at 60 C. See Scheme S1 for the respective reactions. coefficient value reference k d s 1 8 f k ini 9770 L mol 1 s 1 = 10 k p k p 977 L mol 1 s 1 12 k t i 0.65 L mol 1 s 1 (i 50) i 0.20 L mol 1 s 1 (i > 50) δ ,15 k ex L mol 1 s 1 8

9 0.0 time / s ln([cp I]/[CP I] 0 ) Figure S5 Experimental data and linear best-fit according to Equation S2. The slope of the best-fit is determined to be s 1. termination with iodine is suppressed. The resulting accumulation of iodine is measured via UV/vis spectroscopy (see (i) in Figure S2), allowing to calculate the amount of decomposed CP I. The integrated rate law of the decomposition reaction gives or while [CP I] = [CP I] 0 exp( k hc t) ln([cp I]/[CP I] 0 ) = k hc t, [CP I]/[CP I] 0 = 1 [I 2 ]/[I 2 ] max, (S1) (S2) (S3) with the initial concentration of CP I, [CP I] 0, and the maximum possible [I 2 ] (for full decomposition of CP I), [I 2 ] max, which is predetermined by the amount of I 2 weighed out for the preparation of CP I. The linear best-fit in Figure S5 confirms the first-order rate law and leads to k hc = s 1. References [1] Matyjaszewski, K.; Gaynor, S.; Wang, J.-S. Macromolecules 1995, 28,

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