Mechanically Mediated Atom Transfer Radical Polymerization

Aug 29, 2018 - A well-controlled atom transfer radicfal polymerization of methyl acrylate (MA) was realized by mechanical mediation (mechanoATRP) in ...
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Mechanically Mediated Atom Transfer Radical Polymerization: Exploring Its Potential at High Conversions Yin-Ning Zhou,†,‡ Jin-Jin Li,†,‡ Darko Ljubic,† Zheng-Hong Luo,*,‡ and Shiping Zhu*,†,§ †

Department of Chemical Engineering, McMaster University, Hamilton, ON, Canada L8S 4L7 Department of Chemical Engineering, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, China 200240 § School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, China 518172 Downloaded via UNIV OF SOUTH DAKOTA on August 30, 2018 at 01:56:55 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information *

ABSTRACT: A well-controlled atom transfer radicfal polymerization of methyl acrylate (MA) was realized by mechanical mediation (mechanoATRP) in dimethyl sulfoxide (DMSO, 50% v/v). High conversions of typically over 90% were achieved. The resulting polymers had well-controlled molecular weights and very low dispersities (Đ = 1.03−1.09). No polymerization of MA was observed under various conditions from bulk up to 33.3% DMSO (v/v) solution. It was found that adding an equivalent volume of DMSO with respect to MA activated the polymerization. This finding suggested that DMSO played a crucial role in the mechanoATRP of MA. DMSO not only improved the solubility of CuBr2 complex but also facilitated an electron transfer process in the mechanical reduction of CuBr2. For a proof of the concept, a DMSO analogue acrylate, 2-(methylsulfinyl)ethyl acrylate (MSEA), was also polymerized. In addition, the high chain-end functionality of the polymers collected at ∼95% conversion was confirmed by 1H NMR, MALDI-ToF-MS, and in-situ chain extension experiments. The extended chain polymers were characterized and found to have predicted molecular weights and low dispersities (Đ = 1.06). Chain extension in the presence of residual oxygen still yielded a well-controlled molecular weight but a slightly higher dispersity of 1.11. This work provided an in-depth insight into the mechanoATRP and demonstrated its good potential in producing well-defined polymers at high conversions.

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RAFT polymerization,28,29 offering attractive approaches in addressing the as-mentioned issues. In a large-scale application of ATRP, reducing the transition metal catalyst loading to a level of parts per million (ppm) and pushing the monomer conversion up to >85% but still possessing high end-group fidelity and low dispersity represent two important challenges.30 Currently, the ATRP variants capable of conducting polymerization with a ppm catalyst loading are distinguished by their different ways for activator regeneration, for instance, chemical reducing agents,31 free radical thermal initiators,32,33 zerovalent metals,34−37 electricity,38,39 light,40,41 and ultrasonic agitation.25−27 As shown in Scheme 1, the core of ATRP involves an activation− deactivation equilibrium between propagating radical and deactivator (transition metal complex in higher oxidation state) with dormant chain and activator (transition metal complex in lower oxidation state).42,43 Unavoidable radical termination causes an accumulation of deactivator, which can be reduced back to activator via external regulators, allowing the reaction to proceed at a low catalyst loading. The

INTRODUCTION

Over the past decades, the reversible-deactivation radical polymerization (RDRP), also known as controlled/“living” radical polymerization (CRP), has gained great attention due to its efficiency and applicability in synthesizing well-defined polymers.1,2 Three major CRP methods, i.e., nitroxidemediated polymerization (NMP),3,4 atom transfer radical polymerization (ATRP),5−7 and reversible addition−fragmentation chain transfer (RAFT) polymerization,8 are well developed. Recently, there is an increasing demand for functional polymers and their synthetic protocols. However, there are some drawbacks with the CRP methods, such as the loss of livingness and control at high conversions, the lack of temporal control, spatial control, sequential control in multiblock copolymerization, and controlled polymerization on living cell/tissue, etc. As a result, various new CRP methods have been developed, through the regulation by external stimuli, such as chemical, light, electrical, force, etc.9,10 Examples included, but not limited to, photochemically mediated ATRP,11−17 photoinduced electron transfer RAFT polymerization,18−20 electrochemically mediated ATRP,21,22 electrochemically mediated RAFT polymerization,23,24 mechanically mediated ATRP,25−27 and mechanically mediated © XXXX American Chemical Society

Received: May 31, 2018 Revised: August 11, 2018

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DOI: 10.1021/acs.macromol.8b01153 Macromolecules XXXX, XXX, XXX−XXX

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reaction conditions, including catalyst loading, initiator concentration (i.e., targeted chain length), BaTiO3 nanoparticles loading, and ultrasound power, were evaluated. All the cases showed excellent control over molecular weight and yielded polymers with a very low dispersity (Đ). It was of interest to find that the polymerization runs under the bulk condition and the solution conditions containing DMSO amount less than 33.3% v/v produced little polymers, while the runs with the 1:1 volume ratio of DMSO:MA proceeded smoothly. As a reference, the bulk polymerization of a DMSO analogue acrylate (MSEA) was successful. Furthermore, an insitu chain extension was performed at ∼95% conversion. The chain-end functionality was analyzed by 1H NMR and MALDI-ToF-MS. Oxygen tolerance of the system was assessed by carrying out the polymerization in a nondegassed mixture of solvent and monomer. The resulting polymers had a low Đ and high end-group fidelity, as also confirmed by successful in-situ chain extension.

Scheme 1. Proposed Mechanism of Various ATRP Techniques Conducted with a ppm Catalyst Loadinga

a

ARGET: activator regenerated by electron transfer; ICAR: initiator for continuous activator regeneration; SARA: supplemental activator and reducing agent.

molecular weight distribution in ATRP is determined by the number of dead chains (livingness) and activation/deactivation cycles (controllability) in the system. Both livingness and controllability are essential in achieving a robust ATRP that generates narrowly dispersed polymers.44−46 High conversion is challenging because of diffusion-controlled reactions (e.g., termination, deactivation, propagation, activation). In particular, the diffusion-controlled deactivation could readily cause a loss of control.47−50 Various strategies have been investigated for high conversion bulk ICAR ATRP, such as optimizing temperature profile and applying sonication enhancement.51,52 A good control over molecular weight distribution with dispersity 95% (monitored by 1H NMR), the degassed mixture of monomer and solvent (1:1 in volume) was added using a nitrogen-purged syringe. Samples were taken from the reaction mixture for the analyses of conversion, Mn, and Mw/Mn via 1 H NMR and GPC. MechanoATRP of MA in the Presence of Oxygen. The polymerization and the in-situ chain extension in the presence of oxygen were carried out according to the aforementioned procedure using a nondegassed mixture of monomer and solvent. The headspace of flask was degassed using a vacuum pump for a short time (15 s) prior to polymerization. B

DOI: 10.1021/acs.macromol.8b01153 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Table 1. Summary of MechanoATRP of MA under Different Conditionsa no.

catalyst loading (ppm)

targeted chain length

BaTiO3 (wt %)

sonication power (W)

time (h)

conv (%)

Mn,theorb (g/mol)

Mn,GPC (g/mol)

Đ (Mw/Mn)

1 2 3 4 5 6 7 8

100 150 200 150 150 150 150 150

200 200 200 100 400 200 200 200

4.5 4.5 4.5 4.5 4.5 1.5 7.5 4.5

100 100 100 100 100 100 100 70

6 4 3 3 4.5 5.5 4 5

91.3 94.1 93.9 92.4 92.7 93.0 94.4 93.0

15700 16200 16200 7950 32000 16000 16250 16000

14900 15700 15950 7700 35300 15450 15350 15700

1.04 1.05 1.05 1.05 1.09 1.03 1.05 1.03

Recipes: [MA]0:[EBiB]0:[CuBr2]0:[Me6TREN]0 = 200:x:y:8y (x = 0.5/1/2; y = 0.02/0.03/0.04), solvent: DMSO (50% v/v), temperature: 50 °C, BaTiO3 loading: 1.5/4.5/7.5 wt %, sonication power: 70 or 100 W. bCalculated from monomer conversion. Note: only one condition was varied in each experiment.

a

Figure 1. Effect of catalyst loading (100/150/200 ppm) on the mechanoATRP at 100 W and 50 °C in the presence of 4.5 wt % BaTiO3 loading. (A) Semilogarithmic kinetic plots, (B) evolutions of Mn and Mw/Mn with conversion, and (C) GPC traces of PMA at different times.

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Characterization. Monomer conversions were monitored by 1H NMR spectra acquired on a Bruker AV200 MHz NMR spectrometer. 1 H NMR spectra of the resulting polymers for end-group analysis were recorded on a Bruker AV600 MHz NMR spectrometer. The number-average molecular weight (Mn) and the dispersity (Mw/Mn or Đ) of PMA were analyzed by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as effluent at a fixed flow rate of 1 mL/ min at 35 °C. The GPC (Waters 2690 separation module) was equipped with autoinjector, three linear columns in series (Waters Styragel HR 2, 3, and 4), and a 2410 RI detector. The Mn and Mw/Mn of PMSEA were analyzed by a Polymer Laboratories PL-GPC 50 Plus Integrated System, comprising three Phenogel columns connected in series (guard, 104, 500, and 100 Å), and a differential refractive index detector using N,N-dimethylformamide (DMF) with 0.03 wt % LiBr as an eluent at 20 °C with a flow rate of 0.35 mL min−1. A series of narrow molecular weight distribution poly(methyl methacrylate) samples were used as standards for both PMA and PMSEA samples. UV−vis−NIR spectra were recorded on Agilent Cary 5000 spectrophotometer. The glass transition temperature (Tg) was measured by a DSC 2910 (TA Instruments) under a nitrogen atmosphere. Samples were first heated from room temperature to 120 °C at 50 °C/min and kept isothermal for 5 min to eliminate thermal history. The temperature was then cooled to −20 °C at a rate of 10 °C/min, maintained at −20 °C for 5 min, and heated to 120 °C at 10 °C/min again. The second heating curve was used to analyze Tg through Universal Analysis 2000 software. MALDI-ToF mass spectra were acquired on Bruker UltrafleXtreme MALDI ToF mass spectrometer in positive ion mode performed using an accelerating voltage of 25 kV. Saturated solutions of dithranol in THF and sodium acetate (NaAcetate) in isopropyl alcohol were used as the matrix and cationization agent, respectively. The samples were prepared in THF, the concentration was 1 mg/mL, and the ratio of matrix:polymer:cationization agent was 10:5:1. An amount of 1 μL was spotted on a plate. An external standard PEG was used for calibration.

RESULTS AND DISCUSSION Challenges with ATRP, as well as any other controlled radical polymerization, are the high end-group fidelity and low dispersity of the polymers yielded at high conversion. Table 1 summarizes the experiments performed under various conditions. To account for possible loss of the catalyst−ligand complex due to dissociation under sonication, an excess of ligand Me6TREN with high complexation ability was employed.26,27,56,57 The ratio of ligand to Cu salt was fixed to 8:1. The temperature of the water bath was found to increase from 25 to 45 °C and fluctuated slightly in a few hours of sonication. To avoid the influence of temperature on the polymerization at the initial stage, the water bath was preheated to 50 °C prior to polymerization. The temperature fluctuation was controlled within ±1 °C. All the polymer samples collected over 90% conversion under different reaction conditions showed negligible tailing on GPC traces (Figures S1−S4 and S6−S8) and had their dispersities ranged from 1.03 to 1.05, except for the polymer with a targeted chain length (DPn) of 400 (sample 5). All the molecular weights obtained by GPC were in a good agreement with their theoretical values. A noticeable shoulder peak was found in the GPC curve (Figure S5) of PMA with the targeted DPn = 400, which was attributed to the both autoacceleration in the polymerization rate and bimolecular termination occurring at high conversion, leading to an increased Mn and higher dispersity (Đ = 1.09). Further insight into the polymerization kinetics will be discussed in the following sections. Effect of Catalyst Loading. Initially, the mechanoATRP using three different catalyst loadings at a ppm level was C

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Figure 2. Effect of initiator concentration (DPn = 100/200/400) on the mechanoATRP at 100 W and 50 °C in the presence of 150 ppm catalyst loading and 4.5 wt % BaTiO3 loading. (A) Semilogarithmic kinetic plots, (B) evolutions of Mn and Mw/Mn with conversion, and (C) GPC traces of PMA at different times.

Figure 3. Effect of BaTiO3 loading (1.5/4.5/7.5 wt %) on the mechanoATRP at 100 W and 50 °C in the presence of 150 ppm catalyst loading. (A) Semilogarithmic kinetic plots, (B) evolutions of Mn and Mw/Mn with conversion, and (C) GPC traces of PMA at different times.

the monomer conversion reached ∼43% in the first hour, with a linear increase in the semilogarithmic plot observed. A higher radical concentration at an early stage of the polymerization was expected as the more initiator was used. Notably, it could be found that their steady-state polymerization rates were independent of the initiator concentration, as evident from their approximately equal slopes after the induction period. The steady-state radical concentration in the low-ppm system was related to the rates of CuIX regeneration and radical termination. The experimental Mn increased linearly and the molecular weight distribution narrowed with conversion, as shown in Figures 2B and 2C. In the cases of targeted DPn = 100 and 200, the dispersities remained as low as 1.04 at 90% conversion. However, an unfavorable secondary peak appeared, when the conversion was >90% in the DPn = 400 experiment, which could be ascribed to both autoacceleration in rate and bimolecular termination occurred in a system of high viscosity. Our previous work on highly viscous ATRP systems demonstrated that diffusion-controlled deactivation, rather than diffusion-controlled termination, was mainly responsible for the loss of control of molecular weight at high conversion.47,48,51,52 At the point where the polymerization reached a high conversion with the increased polymer chain length, the diffusion of Cu(II) species for radical deactivation in the polymer matrix became constrained. That is to say, the diffusion-controlled deactivation dramatically decreased the number of activation/deactivation cycles and increased the radical concentration under the highly viscous condition,44,45,48 resulting in high molecular weight and high dispersity. Further

performed until the conversion reached 90% or higher. As seen in Figure 1A, all the polymerization runs experienced a mechanically induced reduction period and followed by an increased reaction rate. This was caused by a mismatch between slow reduction rate and rapid propagation rate. There was no significant difference in the induction period, lasting for about 1 h with all the catalyst loadings. As shown in Figure 1A, the conversions in the first hour reached 11.5%, 11.0%, and 8.5% in the reactions with 200, 150, and 100 ppm catalyst loadings, respectively. Increasing the catalyst loading led to an increased reaction rate, which is a common feature as observed in other low catalyst loading ATRP systems with activator regeneration, such as ARGET ATRP and eATRP. Faster polymerization rate (Rp) means higher radical concentration in the system, resulting from the more generated activator. Figure 1B shows the evolution of Mn and Mw/Mn with conversion. The Mn increased linearly with conversion, while the dispersity decreased. Higher catalyst concentrations yielded polymers with lower dispersity. Even at 94% conversion, the dispersity was as low as 1.05. All the GPC curves (Figure 1C) were unimodal and shifted progressively to the higher molecular weight region. Effect of Initiator Concentration. By varying the initiator concentration while retaining the catalyst loading at 150 ppm, we performed the mechanoATRPs of MA with targeted DPn 100, 200, and 400. Significant differences were observed in their kinetic plots (Figure 2A). Higher initiator concentration shortened the induction period or even eliminated this period, as evident from the polymerization of DPn = 100. In this case, D

DOI: 10.1021/acs.macromol.8b01153 Macromolecules XXXX, XXX, XXX−XXX

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Figure 4. Effect of sonication power (70/100 W) on the mechanoATRP at 50 °C in the presence of 150 ppm catalyst loading and 4.5 wt % BaTiO3 loading. (A) Semilogarithmic kinetic plots, (B) evolutions of Mn and Mw/Mn conversion, and (C) GPC traces of PMA at different times.

Figure 5. Effect of DMSO on the mechanoATRP at 70 W and 50 °C in the presence of 150 ppm catalyst loading and 4.5 wt % BaTiO3 loading. (A) Reaction scheme, (B) Semilogarithmic kinetic plot, (C) evolution of Mn and Mw/Mn with conversion, and (D) GPC traces of PMA at different times.

1.04, were found. All the polymerization runs gave uniform polymer chains up to 93% conversion and monomodal GPC curves (Figure 3C). A very small fraction of tailing was found in the two cases with 4.5 and 7.5 wt % loadings as the polymerization proceeded to the conversion >94%. Effect of Sonication Power. The kinetic behaviors of the polymerization under different sonication powers were examined as well. Interestingly, the polymerization proceeded smoother when a lower sonication power (70 W) was utilized (Figure 4A). Compared to a higher sonication power (100 W) system, the polymerization under 70 W exhibited a short induction period within 0.5 h, suggesting a good matching between the reduction and propagation rates. Stronger ultrasonic agitation might cause higher dissociation of ligand from the Cu complex and piezoelectric NPs surface. The lack of free ligand postponed the process of electron transfer and therefore caused the longer induction period. Although a shorter induction period was gained, the monomer conversion reached only 92% in 4 h, a steady-state rate slower than the reaction under 100 W ultrasound agitation (96% conversion at 4 h). As seen in Figure 4B, the molecular weight evolutions followed the theoretical lines very well in both cases. The

analysis on the GPC result (pink curve) showed that PMA generated at >95% conversion possessed Mn of 29500 g/mol and Đ = 1.08. The molecular weights (Mp) of the main peak and shoulder were Mp1 = 30100 g/mol and Mp2 = 54000 g/ mol, respectively. The fraction of the dead polymer chains of the shoulder peak was about 8%. Effect of BaTiO3 Loading. As shown in the mechanism of mechanoATRP (Scheme 1), the activator is (re)generated from the deactivator through mechanically mediated electron transfer from piezoelectric nanoparticles to CuII compelex.27 Figure 3 shows how BaTiO3 loading affected the polymerization kinetics. When a higher BaTiO3 weight percentage was used, the polymerization became faster. Rapid reduction of the deactivator led to more activator and thus caused higher radical concentration. A nearly linear first-order kinetic plot was obtained with the 7.5 wt % loading system, as displayed in Figure 3A. With 1.5 wt % loading, the monomer conversion reached 21% in 2 h, much lower than 40% and 78% with 4.5 and 7.5 wt % loadings, respectively. Despite their different kinetic behaviors, the molecular weights increased linearly as a function of conversion and agreed well with their theoretical values (Figure 3B). Very low dispersities, ranging from 1.09 to E

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about 950 nm, as well as a downward trend of absorption band between 450 and 800 nm, were found in the 1:1 MA/DMSO mixture (Figure S12A), while there was no obvious change in the 2:1 MA/DMSO mixture (Figure S12B). As indicated in the UV−vis−NIR spectrum of CuBr/Me6TREN (Figure S12C), the change of light absorption was caused by the reduction of CuBr2/Me6TREN. A similar trend was also observed in Esser-Kahn’s and Qiao’s works.25,54 These findings suggested that DMSO played a crucial role in the mechanoATRP of MA because of not only improving the solubility but also facilitating the electron transfer process in the mechanical reduction of the CuBr2 complex. Inspired by the fact that an in-situ addition of DMSO (1:1 ratio) induced mechanoATRP, the bulk polymerization of a DMSO analogue acrylate (MSEA) was conducted, as depicted in Figure 6. An identical reaction recipe was adopted first as

dispersity of the resulting polymers prepared by 70 W sonication decreased gradually from 1.07 to 1.03. Near-perfect GPC curves were obtained with a clear shifting toward the higher molecular weight region (Figure 4C). The above kinetic studies under various reaction conditions elucidated the characteristics of the solution mechanoATRP at high conversion. The polymerization runs exhibited very good control over molecular weight and dispersity, except for the case of very high viscosity. Importance of DMSO. In general, bulk ATRP with low catalyst loading remains to be challenging. ARGET and ICAR ATRP are the two systems which have been conducted under bulk conditions and achieved reasonably good control.47,58 Other analogues, such as Cu(0)-mediated ATRP, photoATRP, and eATRP, encounter difficulties because of limited activation or/and electron transfer in the absence of favorable solvents. The above well-controlled polymerization behaviors encouraged us to try the bulk mechanoATRP. In Figure 5A, a similar reaction condition of 70 W sonication power was adopted for the bulk polymerization of MA. Without solvent DMSO, the polymerization did not occur, even with a prolonged reaction time of 3 h. However, the polymerization was initiated when an equivalent volume of DMSO was added into the system, which yielded PMA with Mn = 14000 g/mol and Đ = 1.05 at 91.7% conversion after 2.5 h (Figure S9). The kinetics was studied, as shown in Figures 5B−5D. In the first 2 h, no monomer conversion was detected through 1H NMR analysis. The reaction rate was zero, as displayed in Figure 5B. An insitu addition of DMSO (1:1 ratio in volume corresponding to MA) at the second hour initiated the polymerization, exhibiting a first-order polymerization kinetics. The monomer conversion reached 92% in 2.5 h. The reaction rate was even higher than that shown in Figure 4. The Mn linearly increased and Đ (1.09−1.05) gradually decreased with conversion (Figure 5C). Their unimodal GPC curves are illustrated in Figure 5D. Through visual observation and UV−vis−NIR analysis (Figure S10), it was found that no polymerization could be attributed to an insufficient amount of catalyst complex under the bulk condition. The initial CuBr2-containing MA solution appeared brown and transparent. The solution quickly turned into light green within 1 min upon adding Me6TREN. Some colloid particles were observed after the Me6TREN amount reached 8 equiv. Finally, an almost colorless and transparent solution was obtained with light green catalyst complex precipitating out (inset figure). UV−vis spectra showed an obvious decrease in absorbance between 600 and 1100 nm, indicating an extremely low content of CuBr2/Me6TREN complex in the solution. As has been reported, the normal bulk ATRP of MA was heterogeneous due to the accumulation of the CuBr2/Me6TREN complex.59 Surprisingly, another trial with 33.3% (v/v) DMSO did not generate any polymer either, even after 3 h of sonication. Subsequently, with additional DMSO added to match a 1:1 volume ratio, the reaction produced PMA having Mn = 15200 g/mol and Đ = 1.05 at 93.5% conversion after 2.5 h (Figure S11). In this case, CuBr2 was soluble in the MA/DMSO mixture (2:1 in volume). We speculated it was caused by severe limitation of mechano-induced electron transfer in the presence of insufficient DMSO, even if the catalyst complex was soluble in the system. UV−vis−NIR analysis was carried out for both 1:1 and 2:1 MA/DMSO mixtures (Figure S12). In contrast, an increase and a blue-shift of the absorption band at

Figure 6. Reaction scheme and GPC traces of PMSEA prepared via the bulk mechanoATRP of DMSO analogue acrylate (MSEA) at 70 W and 50 °C in the presence of 150/1500 ppm catalyst and 4.5 wt % BaTiO3 loadings.

the bulk polymerization of MA (Figure 5): 70 W, 50 °C, [MSEA]0:[EBiB]0:[CuBr2]0:[Me6TREN]0 = 200:1:0.03:0.24, and 4.5 wt % BaTiO3 loading. A rapid polymerization was observed with 75% conversion reached within 2 h, yielding PSEMA having Mn,GPC = 22500 g/mol and Đ = 1.78. The experimental Mn was close to the theoretical value (Mn,theor = 24300 g/mol) estimated from the initial monomer/initiator ratio based on conversion. The control of molecular weight distribution was somewhat poor, which could be attributed to diffusion-controlled deactivation, as discussed before. It is noteworthy that the diffusion limitation on deactivation under the bulk condition was more severe and came earlier than that of the solution polymerization. Even if temperature was set higher than Tg of PSEMA (Tg = 17 °C, Figure S13), the system became solid with evenly dispersed BaTiO3 NPs. To tackle this issue, a polymerization with 10-fold catalyst loading (i.e., 1500 ppm) was carried out. As confirmed by the GPC result, the higher catalyst loading provided a better control over the reaction process, generating a polymer sample (collected at ∼74% conversion) having Mn,GPC = 21500 g/mol and Đ = 1.55. These results strongly suggested an important role of F

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Figure 7. End-group fidelity investigation of PMA-Br prepared via the mechanoATRP at 70 W and 50 °C in the presence of 150 ppm catalyst loading and 4.5 wt % BaTiO3 loading. (A) GPC traces of in-situ chain extension from PMA-Br, (B) 1H NMR spectrum, (C) MALDI-ToF-MS analysis, and (D) zoom-in of MALDI-ToF spectrum.

be 84%, suggesting a good retention of the chain-end fidelity at ∼95% conversion. In addition, MALDI-ToF-MS was used to acquire accurate information about the resulting polymers. Figure 7C shows a unimodal distribution of PMA chains initiated from EBiB. Zoom-in of the MALDI-ToF spectrum (Figure 7D) clearly shows a series of well-separated peaks with an interval of ∼86 m/z, corresponding to a single MA unit. The observed mass of the main peak at 15779.7 m/z agreed well with the expected mass of 15800.3 m/z, corresponding to the Na+-ionized PMABr (denoted as red star at the top of Figure 7). However, a noticeable shoulder peak with an ∼17 m/z shift was found along with each of the main peak, possibly attributed to the nonfunctionalized PMA chains resulted from biomolecular termination (denoted as a navy dot at the top of Figure 7). However, the MALDI-ToF spectrum was unable to quantify the ratio of dead chains for high molar mass polymers due to a low resolution. The PMA sample having 84% chain-end fidelity was employed for in-situ chain extension in a well-degassed mixture of MA and DMSO (1:1 in v:v). As confirmed by the GPC results in Figure 7A, an extended PMA with Mn,GPC = 22200 g/mol and Đ = 1.06 was obtained. Furthermore, the

DMSO played in the mechanoATRP under the current conditions. Although this finding did not mean that DMSO is indispensable for the mechanoATRP, a solvent or monomer that facilitates electron transfer process and improves solubility of the catalyst complex is required. Chain-End Fidelity Analysis and in-Situ Chain Extension. The retention of chain-end fidelity represents another important feature of the resulting polymers prepared by ATRP. In general, a high end-functionality (e.g., >80%) could be maintained by stopping the reaction at a medium conversion (e.g.,