B(C6F5)3-Catalyzed Group Transfer Polymerization of Acrylates Using

Article Cite This: Macromolecules XXXX, XXX, XXX−XXX

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B(C6F5)3‑Catalyzed Group Transfer Polymerization of Acrylates Using Hydrosilane: Polymerization Mechanism, Applicable Monomers, and Synthesis of Well-Defined Acrylate Polymers Yougen Chen,*,†,§ Qun Jia,† Yuansheng Ding,† Shin-ichiro Sato,§ Liang Xu,∥ Chunyu Zang,∥ Xiande Shen,∥ and Toyoji Kakuchi*,‡,§ Macromolecules Downloaded from pubs.acs.org by UNIV OF LOUISIANA AT LAFAYETTE on 01/15/19. For personal use only.

†

Institute for Advanced Study, Shenzhen University, Nanshan District, Shenzhen, Guangdong 518060, China Division of Applied Chemistry, Faculty of Engineering, and §Frontier Chemistry Center, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan ∥ Research Center for Polymer Materials, School of Materials Science and Engineering, Changchun University of Science and Technology, Weixing Road 7989, Jilin 130022, China ‡

S Supporting Information *

ABSTRACT: We demonstrated the B(C6F5)3-catalyzed group transfer polymerization (GTP) of acrylate monomers with hydrosilane by the in situ formation of silyl ketene acetals (SKAs) as the initiator by the B(C6F5)3-catalyzed 1,4hydrosilylation of acrylate monomers and hydrosilane. In addition, this new GTP method was clarified in terms of the polymerization mechanism, scope and limitation of the acrylate monomers, the livingness of the polymerization, and the synthesis of statistic and block acrylate copolymers and ωend-functionalized acrylate polymers. A mechanism involving six elementary reactions was proposed based on the specified analysis of the 1,4-hydrosilylation reaction and the usual GTP using a Lewis acid catalyst. The B(C6F5)3-catalyzed GTP using Me2PhSiH was applicable for not only various alkyl acrylates, such as the methyl, 2-ethylhexyl, cyclohexyl, and dicyclopentanyl acrylates, but also functional acrylates, such as the 2-methoxyethyl, 2-(2-ethoxyethoxy)ethyl, tetrahydrofurfuryl, allyl, triisopropylsilyl, and 2-(triisopropylsiloxy)ethyl acrylates. On the other hand, the isobornyl, tert-butyl, 2-methyl-2-adamantyl, 2(dimethylamino)ethyl, and 2-oxotetrahydrofuran-3-yl acrylates were unsuitable GTP monomers because they showed low or even no polymerization property due to the deactivation of the B(C6F5)3 catalyst or the in situ produced SKA initiator. The livingness for the GTP of suitable acrylates using Me2PhSiH was verified by the kinetic studies, which was applied to the random and block copolymerizations of two different acrylate monomers. Finally, the ω-end-functionalization of the nucleophilic propagating end of poly(n-butyl acrylate) was performed using electrophiles, such as benzaldehyde, Nbenzylidenemethylamine, and N-benzylidenebenzylamine, as terminators.

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INTRODUCTION Acrylate polymers, synthetic resins produced by the polymerization of acrylic esters, are widely used as plastic materials of notable transparency and flexibility, primarily in paints, surface coatings, adhesives, and textiles. For the industrial synthesis of acrylate polymers, the traditional radical polymerization has still been the dominant procedure due to its convenient practical operation though it cannot provide precise control over molecular weight. Nevertheless, the attempts to achieve the controlled/living polymerization of acrylate monomers have always been on the way, which offers the opportunities to tailor-make model acryalte polymers with well-defined structures of technical interest such as α,ω-end-functionalized, block, star, and graft polymers and macromonomers. Precisely for this purpose, anionic polymerization method has been the first one being intensively examined. In general, conventional anionic initiators like metal alkyls directly used for alkyl © XXXX American Chemical Society

acrylate polymerization basically yield acryalte polymers with pretty broad molecular weight distribution as well as low monomer conversion due to (1) side reactions by the nucleophilic attack of the initiator or the active chain end onto the monomer or polymer ester group and α-hydrogen in the main chain and (2) severe aggregation of the active chain end, an ester enolate structure, even in polar solvents. Hence, control over side reactions as well as aggregation−deaggregation equilibrium dynamics has been the main work for the anionic polymerization of acrylic monomers to achieve an ideal living/controlled anionic polymerization of acrylic esters in the past decades. Several effective initiating systems have been developed for the living polymerization of acrylate monomers Received: October 21, 2018 Revised: December 13, 2018

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DOI: 10.1021/acs.macromol.8b02245 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules

Scheme 1. B(C6F5)3-Catalyzed Group Transfer Polymerization (GTP) of Acrylate Monomers Leading to Well-Defined Homopolymers, Statistic and Block Copolymers, and ω-End-Functionalized Acrylate Polymers

mers by CRPs in the past decades. Despite this, the CRPs are still lack of preciseness when it comes to quantitative monomer conversion, very high molecular weights, very low dispersity, and very accurate control over microstructure due to the more or less radical chain transfer and biradical termination reactions. To date, the GTP catalyzed by Lewis and Brønsted acids has been one of the most efficient methods for synthesizing welldefined acrylate polymers, especially when acidic organocatalysts are used, though basic catalysts of some organic Nheterocyclic carbenes could afford moderate control over molecular weight and molecular weight distribution of alkyl acrylate polymers.5−8 The GTP of acrylate monomers using conventional Lewis acids, such as ZnX2 (X = Cl, Br, and I),9−12 organoaluminums,9,10,13 HgI2 + R3SiI,14−20 CdI2 + R3SiI,12 Yb(OTf)3,21 and Sc(OTf)3,21 produced defect-free acrylate polymers. However, a significant amount of the catalyst (10− 20 mol % relative to monomer) was required though the polymer products with low molecular weights were formed, e.g., usually no greater than 10000 g mol−1, due to the low Lewis acidity of such transition metal compounds. In contrast, the GTP of acrylate monomers using acidic organocatalysts with high Lewis and Brønsted acidities could meet all the above objectives; i.e., the amount of the catalysts used was low (0.5−5 mol % relative to initiator), the monomer conversion could be quantitative, defect-free polymer structures were achieved, and polymers with high molecular weights were produced.22 The employed acidic organocatalyst can be either an organic Lewis acid or a Brønsted acid. When a Brønsted acid is used, it first reacts with an equimolar initiator of a silyl ketene acetal (SKA) prior to the polymerization to in situ produce a silicon Lewis acid as the true catalyst for the GTP process. In this regard, Chen et al. used the organic Lewis acids of triphenylmethyltetrakis(pentafluorophenyl)borate and silylium cation to catalyze the GTP of n-butyl acrylate (nBA), producing well-defined poly(n-butyl acrylate)s with molecular

and are summarized to be three main types for achieving living polymerization of acrylic monomers. The first approach is to use various σ-type (Lewis base) and μ-type (Lewis acid) ligands, which makes the favorable aggregation−deaggregation dynamics for ligand-complexed ion pairs. The second one is to use nonmetal counterions, which includes group transfer polymerization (GTP) using a silyl ketene acetal and metalfree anionic polymerization using initiators with bulky conterions. The third one is to use coordinative anionic systems involving aluminum porphyrin and zirconocene or lanthanocene initiators. All these approaches enhance the livingness of anionic polymerization of acrylic monomers to distinct degree at temperature below 0 °C, while the conventional GTP and metal-free anionic polymerization have failed to produce adequate control that they were once thought capable of the polymerization process; on the other hand, the use of appropriate additive/ligand in combination with anionic initiator provides perfect control of the polymerization in both polar and nonpolar solvents though the initiation efficiency of each additive/ligand is strongly dependent on the steric and electronic constraints with respect to its coordination to enolate. The details have been well reviewed by Baskaran, Müller, and Ishizone.1−3 The advent of controlled radical polymerization (CRP) techniques in the mid-1990s, such as atom transfer radical polymerization (ATRP), reversible addition−fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP), has challenged the anionic polymerization of acrylic monomers later due to the simplicity in experimental operations like purification, avoidance of aggregation of active centers, and the great tolerance to polar and functional groups. For instance, Matyjaszewski et al. claimed that well-defined polyacrylates with molecular weight even up to 100000 g mol−1 and dispersity narrower than 1.10 could be accessible.4 Numerous reports have been revealed concerning the controlled polymerization of acrylate monoB


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Macromolecules weights controlled in the range of 23.1−73.1 kg mol−1 with polydispersities 99% determined by 1H NMR in CDCl3 . bM n,calcd = [nBA]0/[Me 2PhSiH or Me2PhSiD]0 × (conv) × (MW of monomer) + (MW of H (1.01) or D (2.01)) × 2. cDetermined by SEC in THF using PMMA standards. a

reaction. According to slope =

k p[Me2PhSiH]0 [B(C6F5)3 ]0 [monomer]0

, the kps for

the polymerizations of MA, nBA, EHA, CyHA, and DCyPA were calculated to be 4.549 × 105, 4.466 × 105, 0.973 × 105, 4.808 × 105, and 1.210 × 105 L mol−1 min−1, respectively, as summarized in Table 2. The polymerizations of MA, nBA, and CyHA had higher propagation rate constants, while those of EHA and DCyPA were lower. It seemed that there was no regular rule between kp and the structure of an alkyl acrylate, though we assumed in advance that the polymerization of a primary alkyl acrylate would have a higher kp than that of a secondary alkyl acrylate. The dependence of the Mn and Mw/ Mn of the resulting polymer on the monomer conversion (Figure 5b) suggested that the Mn,SEC linearly increased from 700 to 6000 g mol−1 for PMA, 1000 to 6900 g mol−1 for PnBA, 2000 to 8100 g mol−1 for PEHA, 1000 to 7700 g mol−1 for PCyHA, and 1400 to 18000 g mol−1 for PDCyPA with the increasing monomer conversion, while their Mw/Mn decreased from 1.28 to 1.05 for PnBA, 1.09 to 1.04 for PEHA, 1.19 to

completed within 9 min. The Mn,SEC of each polymer was in good agreement with its related theoretical molecular weight (Mn,calcd.) of 6400 g mol−1, and all the obtained Mw/Mns were not greater than 1.04. The MALDI-TOF MS spectra in Figure 3 provided detailed information concerning the compositional structures of these deuterium-terminated products. For each product, only one series of molecular ion peaks was observed, and the m/z interval between any two neighboring molecular ion peaks was approximately 128.08, which corresponds to the exact molecular weight of nBA as a monomer unit. In addition, the observed values of the 41-mer polymer ion peaks in the expanded spectra were 5276.30, 5277.55, 5277.42, and 5278.35 Da for the sodium-cationized H-PnBA41-H, DE


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Figure 3. MALDI-TOF MS spectra of the obtained (a) α,ω-dihydro, (b) α-hydro,ω-deuterio, (c) α-deuterio,ω-hydro, and (d) α,ω-dideuterio poly(n-butyl acrylate)s (H-PnBA-H, H-PnBA-D, D-PnBA-H, and D-PnBA-D, respectively).

propagation property (Figure 5c), from which the kps for the polymerization of EMA, EEA, THFA, and AlA (Table 2) were calculated to be 8.079 × 105, 6.407 × 105, 1.870 × 105, and 7.865 × 105 L mol−1 min−1, respectively. For the dependence of the Mn and Mw/Mn of the resulting polymer on the monomer conversion for these polymerizations, as shown in Figure 5d, the Mn,SEC of the resulting polymer linearly increased from 2300 to 7400 g mol−1 for PMEA, 2200 to 9500 g mol−1 for PEEA, 2700 to 7500 g mol−1 for PTHFA, and 900 to 7300 g mol−1 for PAlA with the increasing monomer conversion, while their Mw/Mn decreased from 1.12 to 1.04 for PMEA, 1.12 to 1.04 for PEEA, 1.16 to 1.07 for PTHFA, and 1.56 to 1.21 for PAlA. These results concluded that the new GTP method is also applicable to most of functional acrylates through the living manner. Next, the livingness of the new GTP method was used to synthesize the alkyl and functional acrylate polymers with

1.08 for PMA, 1.28 to 1.05 for PCyHA, and 1.25 to 1.07 for PDCyPA. These results strongly supported that the new GTP method is a living polymerization for these alkyl acrylate monomers. On the other hand, the polymerizations of iBOA and tBA hardly proceeded, while AdA did not polymerize at all, as shown in Table 3. The reason for this result is that B(C6F5)3 catalyzed the cleavage of the ester bond of these monomers, which in turn deactivated B(C6F5)3.29 Apart from the alkyl acrylates, the B(C6F5)3-catalyzed GTPs of the various functional acrylates, such as 2-methoxyethyl, 2(2-ethoxyethoxy)ethyl, tetrahydrofurfuryl, allyl, 2-(dimethylamino)ethyl, 2-oxotetrahydrofuran-3-yl, triisopropylsilyl, and 2-(triisopropylsiloxy)ethyl acrylates (MEA, EEA, THFA, AlA, DMAEA, GBLA, TiPSA, and TiPS-HEA, respectively), were carried out, among which no polymerization proceeded for DMAEA and GBLA. Similarly, the polymerization of MEA, EEA, THFA, and AlA showed the typical zero-order F


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diverse molecular weights by tuning the initial monomer-toMe2PhSiH ratio ([M]0/[Me2PhSiH]0), and Tables 3 and 4 summarize the polymerization results. Except for the polymerization of iBOA, tBA, and AdA, all the polymerizations of the alkyl acrylates proceeded with quantitative monomer conversions within the respective stated polymerization times. The GTPs of MA, EHA, CyHA, and DCyPA with the [M]0/ [Me2PhSiH]0s of 30−150, 30−200, 30−200, and 25−50 produced the poly(methyl acrylate)s (PMAs), poly(2-ethylhexyl acrylate)s (PEHAs), poly(cyclohexyl acrylate)s (PCyHAs), and poly(dicyclopentanyl acrylate)s (PDCyPAs) with the Mn,SECs in the ranges of 2900−13100, 6000−27800, 4400− 27700, and 5400−13700 g mol−1, respectively, and all their Mw/Mns were 99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 17.3 23.2 99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 99 >99 >99 >99 >99 >99 60.0 0

10700 15600 14100 16700 12900 15800 14200 7300

12600 14400 38600 48600 16200 14500 16100 59000

1.05 1.04 1.20 1.28 1.05 1.06 1.12 1.42

Ar atmosphere; [nBA + CoM]0 = 1.0 mol L−1 in CH2Cl2; [nBA]0/ [CoM]0 = 50/50; rt; convnBA > 99%. bDetermined by 1H NMR in CDCl3. cMn,calcd = [nBA]0/[CoM]0 × (convnBA) × (MW of nBA) + [nBA]0/[CoM]0 × (convCoM) × (MW of CoM) + (MW of H) × 2. d Determined by SEC in THF using PMMA standards. a

Table 6. Block Copolymerizations of MA with nBA, nBA with MA, EHA with nBA, nBA with EHA, MEA with nBA, nBA with MEA, EEA with nBA, and nBA with EEA by the B(C6F5)3-Catalyzed GTP Using Me2PhSiHa run 48 49 50 51 52 53 54 55

first second first second first second first second first second first second first second first second

nBA and comonomer (CoM)

time (min)

convb (%)

Mn,calcdc (g mol−1)

Mn,SECd (g mol−1)

MA nBA nBA MA EHA nBA nBA EHA MEA nBA nBA MEA EEA nBA nBA EEA

20 2880 9 60 45 90 9 60 6 50 9 60 8 150 9 60

>99 0 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99

4300

6100

1.08

6400 10700 9200 15600 6400 15600 6500 12900 6400 12900 9400 15800 6400 15800

7100 12900 8100 8400, 27100 6900 15400 7400 15900 7400 8200, 18300 9500 20500 7000 7900, 20900

1.03 1.09 1.04 1.04, 1.07 1.04 1.03 1.04 1.04 1.03 1.06, 1.03 1.04 1.08 1.03 1.05, 1.05

Mw/Mnd

Ar atmosphere; [nBA + CoM]0= 1.0 mol L−1 in CH2Cl2; [nBA]0/[CoM]0 = 50/50; rt. bDetermined by 1H NMR in CDCl3. cMn,calcd = [nBA]0/ [CoM]0 × (convnBA) × (MW of nBA) + [nBA]0/[CoM]0 × (convCoM) × (MW of CoM) + (MW of H) × 2. dDetermined by SEC in THF using PMMA standards. a

I


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Scheme 5. Synthesis of ω-End-Functionalized PnBAs by the B(C6F5)3-Catalyzed GTP with Me2PhSiH Using the Electrophiles of Benzaldehyde (BzA), N-Benzylidenemethylamine (BMA), and N-Benzylidenebenzylamine (BBA) as the Terminating Agents

Table 7. Synthesis of ω-End-Functionalized PnBAs by the B(C6F5)3-Catalyzed GTP of nBA Using Me2PhSiH and Benzaldehyde (BzA), N-Benzylidenemethylamine (BMA), and N-Benzylidenebenzylamine (BBA) as Electrophilic Terminatorsa run 56 57 58

terminator (T) BzA BMA BBA

convb (%) >99 77.1 >99

time (h) 0.3 1.5 2

Mn,calcdc (g mol−1) e

6500 5000e 6600e

Mn,SECd (g mol−1)

Mw/Mnd

ω-end-functionalization

7500 5800 7500

1.04 1.15 1.03

quantitative almost quantitative quantitative

a Ar atmosphere; [nBA]0 = 1.0 mol L−1 in CH2Cl2; room temperature; polymerization time, 9 min; [nBA]0/[Me2PhSiH]0/[B(C6F5)3]0/[T]0 = 50/ 1/0.05/10. bDetermined by 1H NMR in CDCl3. cMn,calcd = [nBA]0/[Me2PhSiH]0 × (conv) × (MW of nBA) + (MW of H) × 2. dDetermined by SEC in THF using PMMA standards. eMn,calcd = [nBA]0/[Me2PhSiH]0 × (conv) × (MW of nBA) + (MW of H) × 2 + (MW of terminator; BzA = 106.12, BMA = 119.17, BBA = 195.26).

Figure 6. MALDI-TOF MS spectra of (a) BzA, (b) BMA, and (c) BBA ω-end-functionalized PnBAs.

J


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Figure 7. 1H NMR spectra of (a) BzA, (b) BMA, and (c) BBA ω-end-functionalized PnBAs in CDCl3 at room temperature.

summarizes the ω-end-functionalization results. After nBA was quantitatively consumed within the shortest time of 9 min, the polymerization was terminated by adding BzA, BMA, or BBA with the [BzA, BMA, or BBA]0/[Me2PhSiH]0 ratio of 10. All the polymerizations were well controlled to produce PnBAs with the predicted molecular weights and narrow polydispersities. The ω-end-functionalized polymer products were then subjected to a TBAF solution in THF/MeOH to remove the still bonded dimethylphenylsilyl group, affording PnBAs with a hydroxyl, a secondary amino, and benzyl-protected secondary amino group at the ω-end. In addition, the PnBA with the benzyl-protected secondary amino group at the ω-end could be further transformed into a primary amino ω-end-functionalized product by deprotecting the benzyl group using the Pd/ C catalyst. These reactive functionalities are very useful to carry out the postmodification of PnBA. The detailed information about the ω-end-functionalization and chain structure of these polymer products was sequentially evaluated by MALDI-TOF MS and 1H NMR measurements. For the BzA-terminated PnBA, the MALDI-TOF MS spectrum exhibited only one population of molecular ion peaks, as shown in Figure 6a. The distance between any two neighboring molecular ion peaks was 128.12, corresponding to the exact mass of nBA, 128.08, as the repeating unit. In addition, the m/z value of each observed molecular ion peak was consistent with the calculated monoisotopic molecular weight when PnBA had the BzA residue (Bz−OH) at the ωend. For instance, one of the observed polymer ion peak at 5894.95 Da well agreed with the calculated value of 5894.81 Da when the polymer had a sodium-cationized 45-mer structure of [H-(nBA) 45 -Bz−OH + Na]+ . This result conclusively indicated that every PnBA ω-end was bonded

nBA, the second GTP of nBA did not proceed at all, suggesting that the isomerization of the SKA at PMA end quickly occurred. All these results strongly implied that the isomerization of the terminal SKA moiety, which was derived from a primary acrylate monomer, readily occurred after its complete homopolymerization, while that of the SKA moieties derived from MEA and EEA was difficult to take place even after all the MEA or EEA was consumed, probably because the nucleophilic ether group stabilized the electrophilic silyl group. As a short summary, the isomerization of the terminal SKA moiety should be carefully considered and paid much attention for preparing structurally defect-free homopolymers. In addition, this realization, in turn, provides rather meaningful knowledge when designing acrylate statistic and block copolymers. Synthesis of ω-End-Functionalized Acrylate Polymers. We previously reported the α, ω, and α,ω-endfunctionalizations of PMMA and PnBA by the t-Bu-P4- and MeSiNTf2-catalyzed GTPs.27,36 Functional SKAs were used for the α-end-functionalization for both GTP methods, while benzaldehyde (BzA) was used for the t-Bu-P4-catalyzed GTP and functional α-phenyl acrylates for the MeSiNTf2-catalyzed GTP as terminating agents for the ω-end-functionalization. In this study, the livingness of the B(C6F5)3-catalyzed GTP of nBA using Me2PhSiH was applied to synthesize the ω-endfunctionalized PnBAs based on a termination approach using the electrophiles of BzA, N-benzylidenemethylamine (BMA), and N-benzylidenebenzylamine (BBA) as terminators, as shown in Scheme 5. The reason why these electrophiles were used is that B(C6F5)3 could efficiently catalyze both the Mukaiyama aldol reaction of an SKA with an aldehyde and the Munnich reaction of an SKA with an imine. Table 7 K


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with one BzA, i.e., the ω-end-functionalization was stoichiometric. For the BMA- and BBA-terminated PnBAs, both of their MALDI-TOF MS spectra showed two populations of molecular ion peaks, as shown in Figures 6b and 6c, respectively. In the case of the BMA-terminated PnBA, the main polymer ion peaks were assignable to the sodiumcationized ω-end BMA-functionalized PnBA. The subpeaks were attributed to the PnBA bearing a Me2PhSi group, which was the SKA terminal isomerized product. This meant that a very small proportion of PnBA was not ω-end-functionalized by BMA. However, we firmly believe that the quantitative ωend-functionalization using BMA can be achieved under careful experimental operation. In the case of the BBAterminated PnBA, the main and submolecular ion peaks belonged to the desilylated and silylated BBA ω-endfunctionalized PnBAs, respectively, which meant that the ωend-functionalization using BBA stoichiometrically proceeded. The ω-end-functionalization of PnBA was successfully proven by the1H NMR spectra, as shown in Figure 7. In greater detail, the characteristic signals were clearly observed at 7.20−7.60 and 4.82, 6.60−7.68, and 6.60−7.67 ppm due to the aromatic and methine protons of the BzA residue, aromatic protons of BMA residue, and aromatic protons of BBA residue in the polymer products, respectively.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b02245.

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Synthetic details of deuteriodimethylphenylsilane (Me2PhSiD), triisopropylsilyl acrylate (TiPSA), 2(triisopropylsiloxy)ethyl acrylate (TiPS-HEA), and Nbenzylidene benzylamine (BBA), polymerizations, SEC profiles of acrylate homopolymers and acrylate random and block copolymers (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Toyoji Kakuchi: 0000-0002-1882-8418 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by National Natural Science Foundation of China (No. 21604057), Natural Science Foundation of SZU (No. 000215), Shenzhen Science and Technology Research Grant (No. JCYJ20160422154131724), Shenzhen University-National Taipei University of Technology Joint Research Program (2018004), and the MEXT Grant-in-Aid for Scientific Research on Innovative Areas “Advanced Molecular Transformation by Organocatalysts”.

CONCLUSION

On the basis of the pioneering investigation of the B(C6F5)3catalyzed GTP of nBA using Me2PhSiH, we determined the polymerization mechanism in light of elementary reactions and analyzed the polymerization behaviors based on the kinetic studies. The 1,4-hydrosilylation and polymerization reactions of nBA were found to simultaneously occur prior to the complete consumption of Me2PhSiH because the 1,4-hydrosilylation, initiation, and propagation rates were comparable to each other. After the 1,4-hydrosilylation, the propagation process proceeded in a living fashion and turned out to be a zero-order reaction, which was supported by both the theoretical deviation and analysis of the polymerization kinetics. The current GTP method could be applied to most of the acrylate monomers, including both the alkyl and the functional acrylates, except for some susceptible ones. In addition, statistic and diblock acrylate copolymers could be synthesized by carefully selecting the comonomers. Very importantly, the isomerization of the SKA moiety as the propagating end during the propagation should be paid special attention to obtain defect-free polymers, not only for the copolymers but also for the homopolymers. Nevertheless, the high nucleophilicity of the propagating end of the SKA moiety was in turn used to react with the electrophiles of benzaldehyde, N-benzylidenemethylamine, and N-benzylidenebenzylamine as terminators to achieve the ω-end-functionalization of the acrylate polymers, i.e., to obtain the hydroxyl and amine ω-end-functionalized PnBAs. These reactive functional groups are useful for the postmodification of the acrylate polymers. In conclusion, we strongly believe that this study provides an extremely elemental and in-depth understanding of the current new GTP methodology, which provides a significantly useful means for designing and synthesizing well-defined acrylate polymers.

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REFERENCES

(1) Baskaran, D. Strategic Developments in Living Anionic Polymerization of Alkyl (Meth)acrylate. Prog. Polym. Sci. 2003, 28 (4), 521−581. (2) Baskaran, D.; Müller, A. H. X. In Anionic Vinyl Polymerization Controlled and Living Polymerizations; Müller, A. H. X., Matyjaszewski, K., Eds.; Wiley-VCH: Verlag GmbH & Co. KGaA: Weinheim, 2009; pp 1−56. (3) Ishizone, T.; Kosaka, Y.; Goseki, R. In Anionic Polymerization of Polar Vinyl Monomers: Vinylpyridines, (Meth)acrylates, (Meth)acrylamides, (Meth)acrylonitrile, Phenyl Vinyl Sulfoxide, Benzofulvene, and Other MonomersAnionic Polymerization: Principles, Practice, Strength, Consequences and Applications; Hadjichristidis, N., Hirao, A., Eds.; Springer: Tokyo, 2015; pp 127−189. (4) Matyjaszewski, K.; Xia, J. Atom Transfer Radical Polymerization. Chem. Rev. 2001, 101 (9), 2921−2990. (5) Raynaud, J.; Ciolino, A.; Baceiredo, A.; Destarac, M.; Bonnette, F.; Kato, T.; Gnanou, Y.; Taton, D. Harnessing the Potential of NHeterocyclic Carbenes for the Rejuvenation of Group Transfer Polymerization of (Meth)acrylics. Angew. Chem., Int. Ed. 2008, 47 (29), 5390−5393. (6) Scholten, M. D.; Hedrick, J. L.; Waymouth, R. M. Group Transfer Polymerization of Acrylates Catalyzed by N-Heterocyclic Carbenes. Macromolecules 2008, 41 (20), 7399−7404. (7) Raynaud, J.; Gnanou, Y.; Taton, D. Group Transfer Polymerization of (Meth)acrylic Monomers Catalyzed by N-Heterocyclic Carbenes and Synthesis of All Acrylic Block Copolymers: Evidence for an Associative Mechanism. Macromolecules 2009, 42 (16), 5996− 6005. (8) Raynaud, J.; Liu, N.; Gnanou, Y.; Taton, D. Expanding the Scope of Group Transfer Polymerization Using N-Heterocyclic Carbenes as L


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Macromolecules Catalysts: Application to Miscellaneous (Meth)acrylic Monomers and Kinetic Investigations. Macromolecules 2010, 43 (21), 8853−8861. (9) Sogah, D. Y.; Hertler, W. R.; Webster, O. W.; Cohen, G. M. Group Transfer Polymerization-Polymerization of Acrylic Monomers. Macromolecules 1987, 20 (7), 1473−1488. (10) Hertler, W. R.; Sogah, D. Y.; Webster, O. W.; Trost, B. M. Group-Transfer Polymerization. 3. Lewis Acid Catalysis. Macromolecules 1984, 17 (7), 1415−1417. (11) Eggert, M.; Freitag, R. Poly-N,N-diethylacrylamide Prepared by Group Transfer Polymerization: Synthesis, Characterization, and Solution Properties. J. Polym. Sci., Part A: Polym. Chem. 1994, 32 (5), 803−813. (12) Ute, K.; Tarao, T.; Hongo, S.; Ohnuma, K.; Hatada, K.; Kitayama, T. Preparation of Disyndiotactic Poly(methyl crotonate) by Stereospecific Group Transfer Polymerization. Polym. J. 1999, 31 (2), 177−183. (13) Ute, K.; Ohnuma, H.; Shimizu, I.; Kitayama, T. Stereospecific Group Transfer Polymerization of Methyl Methacrylate with LewisAcid Catalysis-Formation of Highly Syndiotactic Poly(methyl methacrylate). Polym. J. 2006, 38, 999−1003. (14) Webster, O. W. Group Transfer Polymerization: A Critical Review of Its Mechanism and Comparison with Other Methods for Controlled Polymerization of Acrylic Monomers. Adv. Polym. Sci. 2003, 167, 1−34. (15) Dicker, I. B. Group Transfer Polymerization (GTP) of Acrylates Catalyzed by Mercuric Iodide. Polym. Prepr. 1988, 29 (2), 114−115. (16) Zhuang, R.; Müller, A. H. E. Kinetics and Mechanism of Group Transfer Polymerization of n-Butyl Acrylate Catalyzed by Hgl2/ (CH3)3Sil in Toluene. Macromol. Symp. 1994, 85 (1), 379−392. (17) Zhuang, R.; Müller, A. H. E. Group Transfer Polymerization of n-Butyl Acrylate with Lewis Acid Catalysts. 1. Kinetic Investigation Using HgI2 as a Catalyst in Toluene. Macromolecules 1995, 28 (24), 8035−8042. (18) Zhuang, R.; Müller, A. H. E. Group Transfer Polymerization of n-Butyl Acrylate with Lewis Acid Catalysts. 2.1 Kinetic Investigation Using the HgI2/Me3SiI Catalyst System in Toluene and Methylene Chloride. Macromolecules 1995, 28 (24), 8043−8050. (19) Ute, K.; Tarao, T.; Nakao, S.; Kitayama, T. Preparation and Properties of Disyndiotactic Poly(alkyl crotonate)s. Polymer 2003, 44 (26), 7869−7874. (20) Ute, K.; Tarao, T.; Kitayama, T. Enhanced Stereocontrol in Disyndiotactic-specific Group Transfer Polymerization of Methyl Crotonate-Stereochemical Evidence of Group Transfer. Polym. J. 2005, 37 (8), 578−583. (21) White, D.; Matyjaszewski, K. Controlled Polymerization of Acrylates Activated by Lanthanoid Triflates. Polym. Prepr. 1995, 36 (2), 286. (22) Fuchise, K.; Chen, Y.-G.; Satoh, T.; Kakuchi, T. Recent Progress in Organocatalytic Group Transfer Polymerization. Polym. Chem. 2013, 4 (16), 4278−4291. (23) Zhang, Y.; Chen, E. Y.-X. Structure-Reactivity Relationships in Bimolecular-Activated Monomer Polymerization of (Meth)acrylates Using Oxidatively Activated Group 14 Ketene Acetals. Macromolecules 2008, 41 (17), 6353−6360. (24) Zhang, Y.; Lay, F.; García-García, P.; List, B.; Chen, E. Y.-X. High-Speed Living Polymerization of Polar Vinyl Monomers by SelfHealing Silylium Catalysts. Chem. - Eur. J. 2010, 16 (34), 10462− 10473. (25) Takada, K.; Fuchise, K.; Chen, Y.; Satoh, T.; Kakuchi, T. Controlled Polymerization of Methyl Acrylate for High-molecularweight Polymers by Pentafluorophenylbis(triflyl)methane-promoted Group Transfer Polymerization Using Triisopropylsilyl Ketene Acetal. J. Polym. Sci., Part A: Polym. Chem. 2012, 50 (17), 3560−3566. (26) Takada, K.; Ito, T.; Kitano, K.; Tsuchida, S.; Takagi, Y.; Chen, Y.-G.; Satoh, T.; Kakuchi, T. Synthesis of Homopolymers, Diblock Copolymers, and Multiblock Polymers by Organocatalyzed Group Transfer Polymerization of Various Acrylate Monomers. Macromolecules 2015, 48 (3), 511−519.

(27) Takada, K.; Fuchise, K.; Kubota, N.; Ito, T.; Chen, Y.-G.; Satoh, T.; Kakuchi, T. Synthesis of α-, ω-, and α,ω-End-Functionalized Poly(n-butyl acrylate)s by Organocatalytic Group Transfer Polymerization Using Functional Initiator and Terminator. Macromolecules 2014, 47 (16), 5514−5525. (28) Fuchise, K.; Tsuchida, S.; Takada, K.; Chen, Y.-G.; Satoh, T.; Kakuchi, T. B(C6F5)3-Catalyzed Group Transfer Polymerization of nButyl Acrylate with Hydrosilane through In Situ Formation of Initiator by 1,4-Hydrosilylation of n-Butyl Acrylate. ACS Macro Lett. 2014, 3 (10), 1015−1019. (29) Chen, Y.-G.; Kitano, K.; Tsuchida, S.; Kikuchi, S.; Takada, K.; Satoh, T.; Kakuchi, T. B(C6F5)3-catalyzed Group Transfer Polymerization of Alkyl Methacrylates with Dimethylphenylsilane through in situ Formation of Silyl Ketene Acetal by B(C6F5)3-catalyzed 1,4Hydrosilylation of Methacrylate Monomer. Polym. Chem. 2015, 6 (18), 3502−3511. (30) Kikuchi, S.; Chen, Y.-G.; Kitano, K.; Sato, S.-I.; Satoh, T.; Kakuchi, T. B(C6F5)3-Catalyzed Group Transfer Polymerization of N,N-Disubstituted Acrylamide Using Hydrosilane: Effect of Hydrosilane and Monomer Structures, Polymerization Mechanism, and Synthesis of α-End-Functionalized Polyacrylamides. Macromolecules 2016, 49 (8), 3049−3060. (31) Chen, J.; Chen, E. Y.-X. Elusive Silane-Alane Complex [Si-H··· Al]: Isolation, Characterization, and Multifaceted Frustrated Lewis Pair Type Catalysis. Angew. Chem., Int. Ed. 2015, 54 (23), 6842− 6846. (32) Xu, T.; Chen, E. Y.-X. Silylium Dual Catalysis in Living Polymerization of Methacrylates via In Situ Hydrosilylation of Monomer. J. Polym. Sci., Part A: Polym. Chem. 2015, 53 (16), 1895−1903. (33) Parks, D. J.; Piers, W. E. Tris(pentafluorophenyl)boronCatalyzed Hydrosilation of Aromatic Aldehydes, Ketones, and Esters. J. Am. Chem. Soc. 1996, 118 (39), 9440−9441. (34) Parks, D. J.; Blackwell, J. M.; Piers, W. E. Studies on the Mechanism of B(C6F5)3-Catalyzed Hydrosilation of Carbonyl Functions. J. Org. Chem. 2000, 65 (10), 3090−3098. (35) Houghton, A. Y.; Hurmalainen, J.; Mansikkamaki, A.; Piers, W. E.; Tuononen, H. M. Direct Observation of a Borane-silane Complex Involved in Frustrated Lewis-pair-mediated Hydrosilylations. Nat. Chem. 2014, 6 (11), 983−988. (36) Chen, Y.-G.; Takada, K.; Kubota, N.; Eric, O.-T.; Ito, T.; Isono, T.; Satoh, T.; Kakuchi, T. Synthesis of End-functionalized Poly(methyl methacrylate) by Organocatalyzed Group Transfer Polymerization Using Functional Silyl Ketene Acetals and α-Phenylacrylates. Polym. Chem. 2015, 6 (10), 1830−1837.

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