Thiolactone-Functional Reversible Deactivation Radical

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

Thiolactone-Functional Reversible Deactivation Radical Polymerization Agents for Advanced Macromolecular Engineering Marvin Langlais, Olivier Coutelier,* and Mathias Destarac* Laboratoire des IMRCP, Université de Toulouse, CNRS UMR 5623, Université Paul Sabatier, 118 route de Narbonne, Cedex 9 31062 Toulouse, France S Supporting Information *

ABSTRACT: The development of innovative, easy to implement strategies for polymer synthesis and modification contributes to pushing back the limits of macromolecular engineering. In this context, thiolactones were highlighted as a new powerful “click” strategy involving an amine−thiol−ene conjugation. In order to further explore the potential of thiolactone chemistry for the field of reversible-deactivation radical polymerization (RDRP), we have developed a toolbox of γ-thiolactone-based RDRP agents including xanthates, bromides, and an alkoxyamine. These RDRP agents were used for the polymerization of more activated and less activated monomers using appropriate RDRP techniques such as RAFT/MADIX, ATRP, and NMP. Well-defined thiolactone-terminated polymers were obtained and characterized for different degrees of polymerizations. An example of thiolactone−telechelic PNIPAM using a thiolactone-based xanthate and an ω-end-chain cyclization strategy was reported. The great reactivity of the thiolactone end-group for postpolymerization modification was proven using primary amines such as benzylamine or propargylamine, which ring-opened the thiolactone with subsequent thiol−thiolsulfonate reaction to scavenge the generated thiol. The original S-naphthalene ethanethiosulfonate was used to give fluorescence properties to the polymers.

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INTRODUCTION

In 2011, Du Prez and co-workers have extended the realm of PPM by reporting a new efficient one-pot multistep reaction based on five-membered ring γ-thiolactone, which can be opened with a primary amine. The resulting thiol can be further reacted with thiol scavengers such as alkenes, alkynes, or acrylates via thiol-coupling chemistries.20,21 This amine−thiol− ene conjugation was largely studied for polymer synthesis and PPM,21−24 with a recent focus on sequence-controlled polymers.25 Few thiolactone-based monomers and RDRP agents were described in the literature and used in controlled polymerizations. N-Thiolactone acrylamide and styrenic thiolactone (St-TL) monomers were respectively copolymerized with Nisopropylacrylamide (NIPAM)26 and styrene (St)27 by RAFT polymerization. St-TL was also copolymerized with methyl methacrylate (MMA) by NMP initiated by BlocBuilder MA.27 n-Butyl acrylate (BuA) was copolymerized with a thiolactonecontaining acrylate using ATRP and functionalized using a “grafting-onto approach” to produce well-defined amphiphilic macromolecules.28 ATRP of isobornyl acrylate with thiolactone-containing initiator was reported to produce poly(isobornyl acrylate) which was modified to yield α-thiolactone and ω-acrylate poly(isobornyl acrylate) for the synthesis of precision multisegmented macromolecular structures.28,29 Also,

The scope of possibilities in terms of macromolecular design has been constantly widened during the past two decades with the advent of reversible-deactivation radical polymerization (RDRP) techniques.1−3 Atom-transfer radical polymerization (ATRP),4,5 nitroxide-mediated polymerization (NMP),6 and reversible addition−fragmentation chain transfer/macromolecular design by interchange of xanthates (RAFT/MADIX) polymerization7,8 are the most common RDRP techniques enabling access to complex, functional, and well-defined polymer architectures. By using either a functional monomer, initiator, or chain transfer agent (CTA), it is possible to further modify the polymer structure by postpolymerization modification (PPM). Since the development of copper-assisted azide−alkyne cycloaddition (CuAAC)9 by Sharpless in 2001, new classes of “click” reactions have emerged and used for PPM.10,11 Among them, thiol−ene chemistry appeared as a highly efficient, metal-free alternative “click” reaction, involving a thiol and an electron-deficient double bond under stoichiometric conditions at mild temperatures.12,13 A second option is the thiol−thiosulfonate reaction, which allowed the functionalization of thiol-terminated polymers through the formation of a disulfide linkage.14−16 Azlactones were also involved in a metal-free “click” reaction in the presence of amine. Azlactone-containing initiator, CTA, or monomers were developed to produce azlactone-functionalized polymers which could further react in PPM using amines.17−19 © XXXX American Chemical Society

Received: April 11, 2018 Revised: May 15, 2018

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DOI: 10.1021/acs.macromol.8b00770 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Scheme 1. Synthetic Route to Thiolactone-Containing RDRP Agents for Controlled Polymerizations

Synthesis of Hydroxythiolactone (TL-OH). TL-OH was synthesized following the experimental procedure described in our previous work.31 First, monoadduct M-OH with hydroxyl group was obtained by radical addition of xanthate XA0 to 10undecen-1-ol (1:1 molar ratio) in toluene at 90 °C for 16 h, leading to monoadduct M-OH with a yield of 77%. Thermolysis of M-OH at 190 °C for 8 h with short cycles under vacuum to remove volatile byproducts yielded thiolactone TL-OH with a high yield of 91% after column purification. The formation of the desired thiolactone was confirmed by NMR spectroscopy and MS (Figures S3 and S4). Synthesis of Thiolactone-Containing RDRP Agents. The synthesis of CTAs for RAFT/MADIX polymerization, ATRP initiators, and alkoxyamine for NMP were synthesized following well-described procedures from the literature. All compounds were characterized by NMR (Figures S5−S15) and MS. TL-Br1 and TL-Br2 were synthesized by addition of bromopropionyl bromide and α-bromoisobutyryl bromide, respectively, to TL-OH in dichloromethane, in the presence of triethylamine, at room temperature for 16 h. TL-Br1 and TLBr2 were obtained with yields of 63% and 61% after purification. TL-Br1 was then used as a precursor for the synthesis of thiolactone-containing xanthates TL-XA1 and TL-XA2. Potassium ethyl xanthogenate salt was added to a solution of TL-Br1 in acetone at room temperature for 16 h, and the corresponding xanthate TL-XA1 was obtained with a yield of 74%. Xanthate TL-XA2 was obtained following the same procedure but with xanthate salt XAK, with O-alkyl group derived from the 3-methyl-2-butanol, a reagent prone to Chugaev elimination.31,33 TL-XA2 was obtained with a yield of 82%. Finally, an alkoxyamine for NMP polymerization was synthesized using a copper metal-mediated procedure.34 TLBr1 and N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide (SG1) were stirred in the presence of copper(0) powder and N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as ligand (TL-Br1/SG1/ Cu(0)/PMDETA = 1/1.1/1/1.2 molar) in acetonitrile for 16

St was polymerized using RAFT polymerization mediated by a thiolactone-based dithiobenzoate to produce cyclic polymers via disulfide bridging between the thiol resulting from aminolysis of the CTA end-group and the thiol generated from the opening of α-thiolactone.30 Most of the functional γ-thiolactones were derived from the commercially available DL-homocysteine thiolactone hydrochloride. Recently, our group reported a xanthate-mediated route to functional γ-thiolactones.31,32 This process involves two consecutive steps: (i) peroxide-induced radical addition of an O-alkyl xanthate to a substituted alkene to yield a xanthate:alkene 1:1 adduct and (ii) thermolysis of the O-alkyl xanthate group to produce a transient thiol directly undergoing a thiolactonisation with the ester group of the S-fragment of the xanthate. In order to broaden the palette of thiolactone end-functional polymers based on this new synthetic procedure, we present in this paper the use of a hydroxy-functional γ-thiolactone as a platform for the synthesis of various thiolactone-containing mediators for RDRP. The synthesis of thiolactone-functional ATRP initiators, two xanthates for RAFT/MADIX polymerization, and one SG1-based alkoxyamine for NMP will be described. We will then focus on the use of this new toolbox of RDRP agents for a wide range of monomers to produce αthiolactone-functional polymers (while γ-thiolactone refers to a 5-membered ring thiolactone, α- and ω-thiolactone will stand for a γ-thiolactone respectively located at the α-end and ω-end of the polymer chain) and one example of α,ω-thiolactonetelechelic polymer. Postpolymerization modification using primary amines and thiosulfonate reagents will be used to probe the reactivity of the thiolactone end-group and lead to a series of polymers of interest with well-defined terminal groups.

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RESULTS AND DISCUSSION In this work, we provision a range of novel thiolactonecontaining RDRP agents for ATRP, RAFT/MADIX, and NMP, all of them being derived from a OH-functional thiolactone precursor (Scheme 1). B


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Macromolecules Scheme 2. Synthesis of Thiolactone-Terminated Polymers by RAFT/MADIX Polymerization

Table 1. RAFT/MADIX Polymerization Data with Xanthates TL-XA1 and TL-XA2 entry

polymer

DPn,targeted

conva (%)

Mn,theob (g mol−1)

Mn,NMRa (g mol−1)

Mn,SEC (g mol−1)

Đ

1 2 3 4 5 6 7 8 9 10 11

TL-PVP13K-XA1 TL-PVP23K-XA1 TL-PVP2.5K-XA1 TL-PVCL13K-XA1 TL-PVCL23K-XA1 TL-PVAc3K-XA1 TL-PVAc10K-XA1 TL-PNIPAM1.5K-XA1 TL-PNIPAM1.5K-XA2 TL-PNIPAM5.5K-XA1 TL-PNIPAM10K-XA1

100 200 100 100 200 50 100 10 10 50 100

97 96 16 92 97 79 77 99 99 99 98

11700 20865 2210 13240 29550 3860 7200 1555 1600 6160 11640

13370 23520 2655

13650c 23290c

1.10c 1.22c

12940c 23580c 2900d 10850d 1320e 1400e 5320e 10420e

1.10c 1.18c 1.18d 1.30d 1.24e 1.37e 1.40e 1.40e

3690 7040 1695 1690 6450 20820

Determined by 1H NMR in CDCl3. bMn,theo = ([monomer]0 × conv × Mmonomer)/[CTA]0 + MCTA; [CTA]0/[AIBN]0 = 1/0.1. cDetermined by SEC analysis in DMF + LiBr. dDetermined by SEC analysis in THF. eDetermined by SEC analysis in THF + NEt3.

a

assisted laser desorption/ionization−time-of-flight mass spectrometry (MALDI-TOF MS) analysis. MALDI-TOF MS analysis of TL-PVP2.5K-XA1 (Figure 1A) showed as main population a PVP chain capped on one side with the thiolactone fragment issued from the RAFT/MADIX agent and on the other side with a VP fragment resulting from the decomposition of the O-ethyl xanthate group under MALDI-TOF analysis conditions, as previously reported by our group.35 Nevertheless, the presence of the xanthate group at the end of the polymer was confirmed by 1H NMR analysis with a characteristic signal at 4.52−4.64 ppm ascribed to the methylene proton next to the xanthate group (Figure S19) and by the superposition of the SEC-RI and intense SEC-UV traces at 290 nm (Figure S18). The macromolecular characteristics of PVP were followed over the course of the polymerization, for a targeted DPn of 200 (Figure 2 and Table S1). Mn for low conversion (99% was determined for all polymerizations (Table 1, entries 8, 10, and 11). SEC D


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Figure 2. (A) Evolution of number-average molar mass (filled symbols) and dispersities (open symbols) vs VP conversion. (B) SEC-RI chromatograms of PVP synthesized by RAFT/MADIX using TL-XA1 at different polymerization times.

1.23. For a targeted DPn of 200, even though Mn values determined by SEC were slightly greater than expected, a linear evolution of Mn with MMA conversion was observed with Đ values between 1.26 and 1.31 (Table S3 and Figure S29). Nitroxide-Mediated Polymerization Mediated by a Thiolactone-Containing Alkoxyamine. Alkoxyamines based on the SG1 nitroxide are well-established control agents for NMP polymerization.6,18 Thus, a new thiolactone-functionalized alkoxyamine TL-SG1 was synthesized and evaluated in bulk NMP of St at 120 °C (Scheme 4) for targeted DPn of 100 and 200. After 5 h, conversions of respectively 82% and 90% were determined. Precipitated TL-PSt-SG1 polymers were obtained with Mn of 8700 g mol−1 (Đ = 1.22) and 12 950 g mol−1 (Đ = 1.28), and symmetrical SEC-RI traces were obtained. (Table 3, entries 1 and 2, and Figure 5). Comparison of 31P NMR analysis of TL-SG1 and precipitated TL-PSt9K-SG1 showed a shift of the signals from 24.03−24.60 ppm to 24.17−25.41 ppm and confirmed the presence of SG1 at the chain end (Figure S30). For a targeted DPn of 200, Mn increased linearly up to 60% St conversion (Table S4 and Figure S31). At higher conversions, Mn values were lower than expected and tend to level off. High dispersities were measured at the beginning of the polymerization (Đ = 1.99), which was attributed to the slow buildup of free SG1 resulting from persistent radical effect,51 and decreased with St conversion to reach Đ = 1.27 at the end of the polymerization. In summary, three different RDRP techniques have been investigated in order to introduce a thiolactone at the end of polymer chains by means of an appropriate initiator/chain transfer agent. For all polymerizations, we observed a good control in terms of molar masses and dispersities, with the presence of the expected thiolactone at the polymer α-end. The next step will be to use the thiolactone fragment for the postmodification of the polymers through an amine− thiolactone−thiosulfonate cascade reaction. Thiolactone-functionalized PVPs and PNIPAMs synthesized by RAFT/MADIX polymerization were selected to illustrate our PPM strategies in order to head for smart functional materials for waterborne applications.

Figure 3. MALDI-TOF MS analysis of (A) telechelic TLPNIPAM1.5K-TL and (B) (Bz-NH)(MeS-S)-PNIPAM1.5K-(MeSS)(Bz-NH) obtained after PPM using Bz-NH2 and MeMTS.

MMA was polymerized using TL-Br2, Cu(0), CuBr2, and PMDETA as ligand (TL-Br2/Cu(0)/PMDETA/CuBr2 = 1/1/ 1/0.05 molar) in DMSO for targeted DPn of 100 and 200. MMA conversions of 77% and 68% were respectively achieved after 6 h of reaction at room temperature (Table 2, entries 3 and 4). SEC-RI traces of the polymers showed narrow and monomodal chromatograms (Figure S28) with Đ = 1.18 and E


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Macromolecules Scheme 3. Synthesis of Thiolactone-Terminated Polymers by the ATRP Technique

Table 2. Polymerization Data with Thiolactone-Containing Initiators Using the ATRP Technique entry

polymer

initiator

ligand

DPn,targeted

conva (%)


Mn,SECc (g mol−1)

Đc

1 2 3 4

TL-PMA10K-Br1 TL-PBuA13K-Br1 TL-PMMA10K-Br2 TL-PMMA15K-Br2

TL-Br1 TL-Br1 TL-Br2 TL-Br2

Me6Tren Me6Tren PMDETA PMDETA

100 100 100 200

88 94 77 68

7970 12260 8115 13730

10150 13870 10670 14470

1.14 1.11 1.18 1.23

a Determined by 1H NMR in CDCl3. bMn,theo = ([monomer]0 × conv × Mmonomer)/[initiator]0 + Minitiator. cDetermined by SEC analysis in THF (PMMA standards).

Figure 4. (A) Evolution of number-average molar mass (filled symbols) and dispersities (open symbols) vs BuA conversion. (B) SEC-RI chromatograms of PBuA synthesized by ATRP using TL-Br1 at different polymerization times.

Postpolymerization Modification of α-ThiolactoneFunctional Polymers. As with thiolactones, xanthates are prone to react with a primary amine to form a thiol.52,53 In order to only allow the reaction of a primary amine with the terminal thiolactone, the ω-xanthate group was removed by radical reduction with lauroyl peroxide in propan-2-ol to produce a hydrogen-terminated polymer.33,53 The complete removal of the xanthate group was confirmed by SEC-UV analysis with the disappearance of its characteristic absorption at 290 nm (Figure S32). In addition, MALDI-TOF MS analysis of the TL-PVP2.5K-H (Figure 1B) and TL-PNIPAM1.5K-H (Figure S23B) confirmed that the reduction reaction was successful by showing one single population of hydrogenterminated chains. PPM of TL-terminated polymers was then considered using an amine−thiol−thiosulfonate reaction. TL-PNIPAM1.5K-H was reacted with benzylamine (Bz-NH2) to open the thiolactone, and methylmethanethiosulfonate (MeMTS) scavenged the

Scheme 4. Synthesis of Thiolactone-Terminated PSt by the NMP Technique

Table 3. Polymerization Data with Thiolactone-Containing Alkoxyamine Using the NMP Technique

a

entry

polymer

DPn,targeted

conva (%)


Mn,SECc (g mol−1)

Đc

1 2

TL-PSt9K-SG1 TL-PSt13K-SG1

100 200

82 90

8640 18920

8700 12950

1.22 1.28

Determined by 1H NMR in CDCl3. bMn,theo = ([St]0 × conv × MSt)/[TL-SG1]0 + MSG1. cDetermined by SEC analysis in THF (PSt standards). F


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Figure 5. SEC-RI chromatograms of TL-PSt-SG1 obtained by bulk NMP at 120 °C.

Figure 6. SEC-RI (solid traces) and SEC-UV (λ = 290 nm, dashed traces) chromatograms of TL-PVP13K-H (red traces) and (PPNH)(NAS-S)-PVP13K-H (blue traces) obtained after modification reaction using PP-NH2 and NAETS.

generated thiol.15,16 TL-PNIPAM1.5K-H was first solubilized in THF before 10-fold excess of Bz-NH2 and MeMTS were added. The solution was stirred at 30 °C for 2 days. MALDITOF MS analysis of the crude mixture showed only one population corresponding to the expected (Bz-NH)(MeS-S)PNIPAM1.5K-H proving the total functionalization of the polymer (Figure S23C). The same reaction was performed using the thiolactone-telechelic PNIPAM (vide supra). MALDITOF MS analysis confirmed the total bis-functionalization of TL-PNIPAM1.5K-TL to yield a (Bz-NH)(MeS-S)-PNIPAM1.5K(MeS-S)(Bz-NH) (Figure 3B). In order to consider new functionalities, the reaction was carried out using the original S-naphthalene ethanethiosulfonate (NAETS). This reagent was synthesized from 2(bromoethyl)naphthalene and S-sodium ethanethiosulfonate salt according to a protocol adapted from the literature.16 The efficient reactivity of NAETS toward thiol was proved with the functionalization of TL-PNIPAM1.5K-H to give the expected (Bz-NH)(NAS-S)-PNIPAM1.5K-H as proven by MALDI-TOF MS analysis (Figure S23D). TL-PVP2.5K-H and TL-PVP13K-H were also postfunctionalized, but with propargylamine (PP-NH2) and NAETS to obtained (PP-NH)(NAS-S)-PVP2.5K-H and (PP-NH)(NAS-S)PVP13K-H), respectively. PP-NH2 and NAETS (10-fold excess) were added to the polymer solutions in DMF and stirred at 30 °C for 2 days. (PP-NH)(NAS-S)-PVP13K-H was purified by precipitation and analyzed by SEC (Figure 6). SEC-RI traces

before and after modification are virtually identical with a slight shift toward higher Mn after functionalization, consistent with the small increase of the molar mass of the polymer. SEC-UV traces show an increase of the UV absorbance at λ = 290 nm after modification, indicating the presence of the naphthalene group onto the polymer and the efficient chain-end modification. The definite confirmation of the successful chain-end transformation came from the MALDI-TOF MS analysis of the crude (PP-NH)(NAS-S)-PVP2.5K-H with the expected ((PP-NH)(NAS-S)-PVP2.5K-H) as main population (Figure 1C). We studied the fluorescent properties of the PVP capped by the naphthalene group. Solutions of NAETS, TL-PVP13K-H, and (PP-NH)(NAS-S)-PVP13K-H were prepared in DMF, and the emission versus excitation wavelengths were measured for NAETS and the functionalized polymers. While NAETS has narrow emission between 350 and 370 nm when irradiated at 335 nm, (PP-NH)(NAS-S)-PVP13K-H maximal intensity emission was found to be broader and shifted to the area 415−475 nm with a corresponding excitation wavelength broader as well ranging from 345 to 380 nm (Figure S33). As a consequence, when placed under UV light at λ = 365 nm, TLPVP13K-H and NAETS solutions remained dark while the solution of (PP-NH)(NAS-S)-PVP13K-H was fluorescent with a turquoise blue color (Figure 7). We could observe that the reaction of NAETS with the thiol formed by aminolysis of the thiolactone “turned on” the fluorescence in the visible field.

Scheme 5. Postpolymerization Modification of TL-PVP-H Using PP-NH2 and NAETS To Obtain Functional and Fluorescent PVP

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AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (O.C.). *E-mail [email protected] (M.D.). ORCID

Mathias Destarac: 0000-0002-9718-2239 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the French Ministry of Higher Education and Research for a grant to M.L. Dr. Yohann Guillaneuf is warmly acknowledged for providing the SG1 nitroxide. Maxime Demazeau is acknowledged for his help on fluorescence measurements.

Figure 7. NAETS, TL-PVP13K-H, and (PP-NH)(NAS-S)-PVP13K-H in DMF under UV light at λ = 365 nm.

Fang et al. reported this “turn-on” fluorescence effect when replacing the electron-withdrawing sulfinate group of a chromophore with an electron-donating sulfide group.54

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REFERENCES

(1) Controlled Radical Polymerization: Mechanisms; Matyjaszewski, K., Sumerlin, B. S., Tsarevsky, N. V., Chiefari, J., Eds.; ACS Symp. Ser. 1187; American Chemical Society: 2015. (2) Controlled Radical Polymerization: Materials; Matyjaszewski, K., Sumerlin, B. S., Tsarevsky, N. V., Chiefari, J., Eds.; ACS Symp. Ser. 1188; American Chemical Society: 2015. (3) Pearson, S.; St Thomas, C.; Guerrero-Santos, R.; D’Agosto, F. Opportunities for dual RDRP agents in synthesizing novel polymeric materials. Polym. Chem. 2017, 8, 4916−4946. (4) Matyjaszewski, K. Atom Transfer Radical Polymerization (ATRP): Current Status and Future Perspectives. Macromolecules 2012, 45, 4015−4039. (5) Boyer, C.; Corrigan, N. A.; Jung, K.; Nguyen, D.; Nguyen, T. K.; Adnan, N. N.; Oliver, S.; Shanmugam, S.; Yeow, J. Copper-Mediated Living Radical Polymerization (Atom Transfer Radical Polymerization and Copper(0) Mediated Polymerization): From Fundamentals to Bioapplications. Chem. Rev. 2016, 116, 1803−1949. (6) Nicolas, J.; Guillaneuf, Y.; Lefay, C.; Bertin, D.; Gigmes, D.; Charleux, B. Nitroxide-mediated polymerization. Prog. Polym. Sci. 2013, 38, 63−235. (7) Moad, G.; Rizzardo, E.; Thang, S. H. Living Radical Polymerization by the RAFT Process - A Third Update. Aust. J. Chem. 2012, 65, 985−1076. (8) Perrier, S.; Takolpuckdee, P. Macromolecular design via reversible addition-fragmentation chain transfer (RAFT)/xanthates (MADIX) polymerization. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 5347−5393. (9) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Click Chemistry: Diverse Chemical Function from a Few Good Reactions. Angew. Chem., Int. Ed. 2001, 40, 2004−2021. (10) Goldmann, A. S.; Glassner, M.; Inglis, A. J.; Barner-Kowollik, C. Post-Functionalization of Polymers via Orthogonal Ligation Chemistry. Macromol. Rapid Commun. 2013, 34, 810−849. (11) Sumerlin, B. S.; Vogt, A. P. Macromolecular Engineering through Click Chemistry and Other Efficient Transformations. Macromolecules 2010, 43, 1−13. (12) Hoyle, C. E.; Bowman, C. N. Thiol-Ene Click Chemistry. Angew. Chem., Int. Ed. 2010, 49, 1540−1573. (13) Lowe, A. B. Thiol-ene “click” reactions and recent applications in polymer and materials synthesis: a first update. Polym. Chem. 2014, 5, 4820−4870. (14) Parsons, T. F.; Buckman, J. D.; Pearson, D. E.; Field, L. Organic Disulfides and Related Substances. XIV. Aspects of the Reaction of Thiolsulfonates with Thiols. J. Org. Chem. 1965, 30, 1923−1926. (15) Roth, P. J.; Kessler, D.; Zentel, R.; Theato, P. A Method for Obtaining Defined End Groups of Polymethacrylates Prepared by the RAFT Process during Aminolysis. Macromolecules 2008, 41, 8316− 8319.

CONCLUSIONS We reported the synthesis of new thiolactone-based RDRP agents for the synthesis of end-functional and well-controlled polymers from a single hydroxy thiolactone synthesized by a xanthate-mediated procedure. This hydroxy thiolactone was modified into bromide, xanthate, and alkoxyamine RDRP agents which were further used in RAFT/MADIX polymerization of N-vinylpyrrolidone, N-vinyl caprolactam, vinyl acetate, and N-isopropylacrylamide, ATRP of methyl and butyl acrylates as well as methyl methacrylate, and finally NMP of styrene. The efficiency of this library of thiolactonefunctional RDRP agents was evidenced through the successful synthesis of a large selection of polymers of controlled Mn and low dispersities, bearing thiolactone end-groups. Good chainend fidelity was highlighted by NMR, SEC, and MALDI-TOF MS analysis. One example of thiolactone-telechelic PNIPAM was reported via RAFT/MADIX polymerization mediated with a thiolactone-based xanthate, followed by thermal elimination of the xanthate and intracyclization of the generated thiol onto the penultimate NIPAM unit. The reactivity of the thiolactone group at the end of the polymer chains was demonstrated by postpolymerization modification with an amine−thiol−thiosulfonate reaction. Polymers were functionalized using primary amines such as benzylamine or propargylamine to open the thiolactone, and the generated thiol was used to introduce another functional group such as S-naphthalene ethanethiosulfonate. Fluorescence properties of the initial S-naphthalene ethanethiosulfonate and functionalized polymer were compared and showed a “turn-on” fluorescence system. Thanks to the efficiency of the amine−thiolactone−thiosulfonate end-modification strategy and the myriad of well-defined polymers which can be produced by RDRP techniques, thiolactone-based RDRP agents pave the way for new synthetic possibilities for simply or doubly end-functional polymers. ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b00770. Materials, general techniques, experimental procedures, NMR spectra, SEC chromatograms, and supplementary results (PDF) H


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