Article Cite This: Macromolecules XXXX, XXX, XXX−XXX
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Functional Diversification of Polymethacrylates by Dynamic β‑Ketoester Modification Michael B. Sims, Jacob J. Lessard, Lian Bai, and Brent S. Sumerlin* George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida, PO Box 117200, Gainesville, Florida 32611-7200, United States
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S Supporting Information *
ABSTRACT: Postpolymerization modification is a powerful strategy for the rapid generation of functional polymers, but the availability of reactions that enable fast and selective functionalization using only benign materials remains limited. We report the utility of the condensation reaction between βketoesters and primary amines for efficient polymer functionalization at room temperature. Under Brønsted acid catalysis, polymers containing pendent β-ketoesters could be functionalized with a diverse scope of primary amines containing various polar and nonpolar functional groups. The formed enaminone linkages are robust under ambient conditions but undergo dynamic transamination at elevated temperatures, enabling stimuli-responsive interchange of previously installed functional Nsubstituents. This protocol can be conducted catalyst-free at high temperature, but the addition of modest amounts of ptoluenesulfonic acid results in rapid substituent exchange, within 10 min in some cases. Furthermore, this equilibrium-controlled reaction was found to be quantitative when the initial substituent (i.e., the liberated byproduct from transamination) is either sterically hindered or electron-deficient. Overall, this postpolymerization modification complements the existing suite of oximeand hydrazone-based postpolymerization modification approaches and could similarly find utility for biologically relevant chemical modifications.
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conditions is unnecessary, among others.14 To ensure high selectivity for functionalization with sufficient rapidity, many of these reactions involve relatively reactive substrates that are not fully stable under ambient conditions (e.g., hydrolytically labile moieties such as activated esters15 and isocyanates;16 reactive heterocycles such as epoxides,17,18 chlorotriazines,19−21 and benzotrifuranones;22 powerful Michael acceptors such as maleimides;23−25 and oxidatively unstable species such as thiols26). Several concepts have been explored to stabilize a reactive polymer until the desired time for functionalization, including the use of thermally and photolytically labile protecting groups,27,28 the use of sterically hindered reactive groups,29 and catalytic generation of reactive moieties in situ.30 These strategies are indeed valuable additions to the polymer chemist’s synthetic repertoire, but it is important that they be complemented by the availability of selective modification techniques that do not require exotic catalysts or harsh external stimuli. The condensation of amines with aldehydes/ketones to yield imines is a well-known reaction that has been thoroughly explored as a tool for macromolecular engineering.31−35 The reaction typically proceeds with high selectivity at ambient temperatures, sometimes even without the need for catalysis,36 and the dynamic behavior of the resultant imine linkages can
INTRODUCTION The development of robust and user-friendly techniques for the synthesis of well-defined functional polymers (e.g., reversible-deactivation radical polymerization) has facilitated the use of these materials in increasingly sophisticated applications.1−5 Synergistically, the constantly increasing demand for smart materials continues to motivate the design of better synthetic protocols for tailor-made macromolecules. Many functional polymers can be accessed by direct polymerization due to the remarkable functional group tolerance of modern polymerization techniques.6−8 Nevertheless, some macromolecular structures remain inaccessible by direct polymerization alone due to incompatibilities between the monomer functionality and the polymerization chemistry. Additionally, some functional monomers may require tedious small molecule synthesis and purification steps that introduce undesired cost and complexity. Postpolymerization modification has consequently emerged as a powerful tool that addresses these shortcomings, enabling rapid and efficient construction of functional macromolecules.9−12 Many modern postpolymerization modification protocols have been inspired by the tenets of “click chemistry” as originally conceived by Sharpless and colleagues13 and later adapted for macromolecular substrates.14 In short, effective reactions for postpolymerization modification exhibit many of the following criteria: efficiency at near-equimolar concentrations of reactive species, very high yields on a reasonable time scale, and robustness such that fine-tuning of reaction © XXXX American Chemical Society
Received: June 25, 2018 Revised: July 26, 2018
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DOI: 10.1021/acs.macromol.8b01343 Macromolecules XXXX, XXX, XXX−XXX
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Macromolecules Table 1. Polymers Prepared by RAFT Polymerization Containing Modifiable β-Ketoestersa entry 1 2 3 4 5 6 7 8
polymerb c
PAAEMA PAAEMAc PAAEMAc PAAEMAc PAAEMA-co-PMMAd PAAEMA-co-PPEGMAe PMMA-b-PAAEMAf PAAEMA-b-PMMAg
CTAh
tempi (°C)
convj (%)
Mn,theo(g/mol)
Mnk (g/mol)
Đ
TTC DTB TTC DTB TTC TTC TTC TTC
70 70 30 30 70 70 70 70
88 90 66 74 74 91 96 83
14400 14700 11000 12200 12000 24400 15100 15500
17800 17100 17600 12400 13900 28600 15700 17000
1.08 1.03 1.11 1.01 1.08 1.15 1.06 1.10
a
AAEMA, 2-(acetoacetoxy)ethyl methacrylate; MMA, methyl methacrylate; PEGMA, poly(ethylene glycol) methacrylate, Mn = 500 g/mol; CTA, chain transfer agent. bAll polymerizations were conducted for 8 h. c[AAEMA]/[CTA]/[In] = 75.0/1.0/0.2. d[AAEMA]/[MMA]/[CTA]/[In] = 50.0/50.0/1.0/0.2. e[AAEMA]/[PEGMA]/[CTA]/[In] = 15.0/45.0/1.0/0.2 fData reported for extension with AAEMA from PMMA macroCTA with Mn = 4 860 g/mol and Đ = 1.03. gData reported for extension with of MMA from PAAEMA macroCTA with Mn = 11 400 g/mol and Đ = 1.12. hTTC = trithiocarbonate CTA, 4-cyano-4-(dodecylsulfanylthiocarbonylsulfanyl)pentanoic acid; DTB = dithiobenzoate CTA, 4-cyano-4(dithiobenzoyl)pentanoic acid. iPolymerizations at 70 °C were initiated with 2,2′-azobis(isobutyronitrile), and polymerizations at 30 °C were initiated with 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile). jConversion determined by 1H NMR spectroscopy. kNumber-average molecular weight as determined by GPC-MALLS.
reported both homo- and copolymerization of AAEMA under RAFT conditions,43−45 but molecular weight control was modest and dispersities were somewhat high in nearly all cases. We therefore conducted optimization studies on both the identity of the RAFT chain transfer agent (CTA) and polymerization temperature to determine if control over AAEMA polymerization could be improved (Table 1). Comparing the results observed for polymerization at 70 °C with either a trithiocarbonate or a dithiobenzoate CTA (entries 1 and 2), similar conversions and number-average molecular weights were achieved in both cases, but the dithiobenzoatemediated polymerization produced PAAEMA with a markedly narrower molecular weight distribution (Figure 1A). Next, reducing the polymerization temperature from 70 to 30 °C while using a dithiobenzoate CTA yielded polymers of similar dispersities (Figure 1B), but agreement between theoretical and experimental molecular weights was significantly improved for the low-temperature polymerization (entries 3 and 4). Importantly, an initiator with a 10 h halflife corresponding to the lower polymerization temperature was used to ensure the radical flux was the same as in the higher temperature polymerization. We believe that the improved molecular weight control at lower temperature results from the suppression of hydrogen abstraction from the β-ketoester α-carbon. As the radical produced by this reaction is highly stabilized by the adjacent carbonyl moieties, the associated chain transfer constant is likely quite significant, especially at elevated temperatures. Furthermore, the groups of An and Konkolewicz have both shown that radicals produced by hydrogen atom abstraction from β-diketones are reactive enough to initiate radical polymerization.46,47 Nevertheless, a well-controlled polymerization process at 30 °C was observed from kinetic studies that indicated pseudo-first-order conversion of AAEMA, linear growth of molecular weight with conversion, and uniform growth of a narrow, symmetric molecular weight distribution with time (Figure S1). Finally, AAEMA could be successfully copolymerized with hydrophilic and hydrophobic monomers as both statistical and block copolymers (entries 5−8), suggesting its versatility as a reactive moiety that can be incorporated into polymers of diverse compositions and architectures. Intriguingly, homopolymerization of methyl methacrylate (MMA) and copolymerization of AAEMA with MMA and poly(ethylene glycol) methyl ether acrylate (PEGMA) failed under the low-
be rationally tuned by altering the electronics of the amine partner.37−39 A consequence of this dynamic nature, however, is the relatively poor hydrolytic stability of imines derived from N-alkyl amines. Alternatively, the use of O-alkyl hydroxylamines can generate highly stable oxime linkages, but these reagents are often not conveniently accessible. Because of their commercial ubiquity, a postpolymerization modification protocol that utilizes functional amines in a selective and atom-economical fashion to forge a stable linkage is highly desirable. Herein, we explore the reaction between β-ketoesters and primary amines yielding enaminonesa closely related reaction to imine condensationas a tool for facile polymer functionalization. Unlike the analogous reaction between monocarbonyl compounds and amines, the initial imine product from the reaction of β-dicarbonyls and amines converts to the enamine tautomer due to the formation of a six-membered hydrogen-bonding ring that confers enhanced hydrolytic stability. While the use of these moieties for polymer functionalization has been limited thus far,40 they have been recently studied by Du Prez et al. as dynamic cross-links in vitrimers due to an ability to undergo transamination with free primary amines at elevated temperatures.41,42 We were subsequently motivated to establish this functional group as a means of achieving both efficient functionalization and stimuli-responsive functional group exchange. Using commercially available 2-(acetoacetoxy)ethyl methacrylate (AAEMA) as an inexpensive source of the β-ketoester functional group, we demonstrate that well-defined homo- and copolymers containing pendent β-ketoesters can be prepared by reversible addition−fragmentation chain transfer (RAFT) polymerization and modified under mild conditions with a variety of functional primary amines to yield stable enaminones bearing the amine substituent groups. The functional groups installed through this reaction can furthermore be exchanged for a different functionality in a single step by treatment of the enaminone with excess primary amine and modest amounts of acid catalyst at elevated temperatures.
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RESULTS AND DISCUSSION Synthesis of Well-Defined Polymers Bearing Pendent β-Ketoesters. We first sought to achieve controlled polymerization of AAEMA by the RAFT process. Several groups have B
DOI: 10.1021/acs.macromol.8b01343 Macromolecules XXXX, XXX, XXX−XXX
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Figure 2. Photoinduced end-group removal of dithiobenzoateterminated PAAEMA. A narrow molecular weight distribution was conserved (left), and GPC with UV−vis detection confirmed the absence of end-groups after reaction (right).
molecular modification. As the literature precedence for this reaction in the context of postpolymerization modification is limited, we first studied the reaction of a small molecule βketoester, ethyl acetoacetate (EtOAcAc), with benzylamine to determine the optimal reaction conditions and characterize the reaction kinetics. Using in situ 1H NMR analysis, we found that a 2-fold excess of benzylamine with 5 mol % p-toluenesulfonic acid (pTsOH) relative to EtOAcAc resulted in quantitative conversion of β-ketoester to enaminone within 3 h (Figure S5). Next, we performed kinetic studies using the same in situ NMR approach to determine the effect of amine sterics and electronics on the reaction rate (Figure 3A). Increasing the stoichiometric excess of amine to 5-fold to mimic conditions that would be used for polymer functionalization reactions, we continuously monitored the reaction between EtOAcAc and benzylamine, isopropylamine, tert-butylamine, and aniline over 75 min using 5 mol % loading of pTsOH catalyst. The steric environment surrounding the primary amino group significantly affected the observed reaction rates. Extracted pseudofirst-order rate constants indicated that the reaction between EtOAcAc and benzylamine proceeded 4 times faster than that with isopropylamine and nearly 40 times faster than with tertbutylamine. Interestingly, the reaction between EtOAcAc and aniline, an aromatic and less nucleophilic amine, proceeded at a nearly identical rate to the reaction with benzylamine. While we have not studied the origin of this result in detail, observations based on 1H NMR data suggest that benzylamine is sufficiently basic to deprotonate EtOAcAc, establishing a competitive ketone−enolate equilibrium in addition to the reaction pathway that generates the desired enaminone product (Figure 4). When EtOAcAc was treated with benzylamine or tertbutylamine, near-immediate disappearance of the α-carbon signal was observed, even though very little enaminone had been produced by that time in either reaction. In contrast, the α-carbon peak persisted throughout the reaction when aniline was used. Considering the significantly greater basicity of benzylamine [pK a (BnNH 3 + ) = 10.2] 50 versus aniline
Figure 1. Optimization of both RAFT CTA selection (A) and reaction temperature (B) for the polymerization of AAEMA. Optimal molecular weight control and dispersity were achieved with a dithiobenzoate CTA at a low polymerization temperature.
temperature, dithiobenzoate-mediated conditions we established for AAEMA homopolymerization. While we were not able to identify a reasonable cause of this, we nevertheless were able to achieve successful copolymerization by instead using a trithiocarbonate CTA at 70 °C. Under these conditions, relatively narrow molecular weight distributions and good molecular weight control were observed (Figure S2). While retention of the thiocarbonylthio end-group enables preparation of block copolymers and other architectures, we were concerned that aminolysis during functionalization could lead to deleterious side reactions such as chain−chain coupling. We therefore explored strategies for substitution of this end-group with a more inert functionality. Treating the polymer with excess radical initiator48 led to broadening of the molecular weight distribution (Figure S3), but clean thiocarbonylthio displacement could be achieved by employing the photoinduced end-group removal method recently developed by our group (Figure 2).49 Gel permeation chromatography (GPC) analysis of the polymer before and after the reaction revealed nearly perfectly overlaid traces, confirming that chain cleavage or branching reactions are largely absent in this process. Spectroscopic characterization additionally confirmed quantitative removal of dithiobenzoate groups (Figure S4), which was corroborated by GPC with ultraviolet−visible (UV−vis) detection at the dithiobenzoate visible absorption wavelength. Amine Modification of β-KetoestersSmall Molecule Model Studies. Having established conditions for the synthesis of well-defined PAAEMA, our next objective was to evaluate the efficacy of the enaminone reaction for macroC
DOI: 10.1021/acs.macromol.8b01343 Macromolecules XXXX, XXX, XXX−XXX
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Figure 3. (A) Kinetic analysis of the reaction between ethyl acetoacetate and amines bearing sterically and electronically differentiated substituents depicting progressively slower reactions as steric bulk is increased. (B) Functionalization of PAAEMA-H with benzylamine and characterization by 1 H NMR spectroscopy. (C) Summary of substrate scope studies for the functionalization of PAAEMA at room temperature. Characterization data are presented in the Supporting Information. aReaction was conducted for 3 days. bReaction was conducted for 14 days. cReaction was conducted in water keeping other conditions constant.
[pKa(PhNH3+) = 3.8],50 we believe that this acid−base reaction considerably reduces the concentration of EtOAcAc in the former reaction, counteracting the greater nucleophilicity of benzylamine in terms of the reaction rate. Postpolymerization Amine Modification of PAAEMA. Using PAAEMA bearing hydrogen end-groups (PAAEMA-H) as the macromolecular substrate, we screened amines featuring a wide variety of aliphatic and aromatic substituents to probe the scope of this modification strategy. 1H NMR spectroscopy was used to determine the reaction efficiency by observing the appearance of characteristic resonances associated with the newly installed functional groups, as exemplified by the appearance of aromatic proton peaks after the reaction of PAAEMA-H with benzylamine (Figure 3B). Successful functionalization was also confirmed by FTIR spectroscopy via observation of an attenuated CO stretching peak at 1720 cm−1 and appearance of N−H bending and CC stretching peaks at 1650 and 1600 cm−1, respectively (Figure S6). Using these same conditions, we achieved virtually quantitative functionalization of PAAEMA-H with a diverse library of primary amines bearing saturated, unsaturated, aromatic, and polar functional groups (Figure 3C), including fluorescent moieties like anthracene (Figure S7). While extended reaction times were necessary to achieve high conversions when more sterically hindered amines such as isopropylamine were used, complete functionalization was possible without the need for more forcing conditions (e.g., heat or higher catalyst loading). Electron-deficient aromatic amines such as p-bromoaniline and p-nitroaniline proved challenging to install through this reaction, although the observation of partial conversion over 6 h suggests complete functionalization with p-bromoaniline could be achieved by employing longer reaction times. Additionally, while 1H NMR spectroscopy suggested quantitative functionalization of PAAEMA with p-aminophenol, significant discoloration observed over the course of the reaction may be evidence of oxidation. We are therefore skeptical of the fidelity of this particular reaction and
encourage caution if this strategy is attempted with other hydroxyanilines. Interestingly, this approach could also be used for the functionalization of a water-soluble copolymer, P(AAEMA0.25co-PEGMA0.75) (entry 6 in Table 1), with a biologically relevant compound, D-biotin, under aqueous conditions. Moderate functionalization (75%) was observed in this caselikely a consequence of the hydrolytic instability of the imine intermediate, although it is possible that extended reaction times could improve this result. Nevertheless, the product enamine linkage is sufficiently stable to largely withstand multiple days of aqueous dialysis. When considered with the fact that both β-ketoesters and primary amines are largely innocuous reagents and the byproduct of their reaction is water, we believe this chemistry holds significant potential as a bioconjugation strategy. Dynamic Substituent Exchange of Functionalized PAAEMA. Our final objective was to adapt the exchange reaction that enaminone-containing vitrimers have been shown to undergo at elevated temperatures41,42 for dynamic Nsubstituent modification of functional polymers. We began this investigation with a series of kinetic studies on a small molecule model compound to identify the range of conditions under which this reaction is practically operative. Using variable-temperature NMR spectroscopy with in situ monitoring to track the reaction in real time, ethyl 3-(aminohexyl)-2butene (i.e., the enaminone adduct between EtOAcAc and hexylamine) was treated with a 5-fold excess of benzylamine at different temperatures (Figure 5A) and pTsOH catalyst loading (Figure S8). As expected, the reaction was extremely slow at room temperature, even in the presence of catalyst. However, we found that relatively rapid substituent exchange occurred when the temperature was increased to 60 °C in the presence of 5 mol % pTsOH, a significantly lower and more accessible temperature than the 100−140 °C reported previously using the lower loading of 1 mol % pTsOH.41,42 Similar to these reports, conducting reactions at higher D
DOI: 10.1021/acs.macromol.8b01343 Macromolecules XXXX, XXX, XXX−XXX
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ance of aromatic peaks in the 1H NMR spectrum after polymer purification (Figure 5B). Progressively greater conversion of benzyl groups was observed with increasing hexylamine concentration, although quantitative conversion was never observed due to the similar reactivity of benzylamine and hexylamine. However, we found that when PAAEMA bearing N-phenyl groups (PAAEMA-Ph) derived from aniline was treated with hexylamine under identical conditions, virtually quantitative conversion of phenyl groups to hexyl groups was observed with only a 2-fold molar excess of hexylamine. This result is attributed to the lesser nucleophilicity of liberated aniline introducing a thermodynamic driving force for full functionalization. We observed similar results when PAAEMA bearing isopropyl groups was treated with benzylamine (Figure S9), in which case the liberated amine is less reactive due to the greater steric bulk of the isopropyl substituent relative to the benzyl substituent. Finally, we could again modify the operative equilibrium by employing a volatile amine, allylamine, as the original substituent and conducting the exchange reaction open to air (Figure S10). This time, the liberated amine is selectively removed from the reaction due to its greater volatility than hexylamine, which drives exchange toward the hexyl substituent. In summary, we have confirmed that the enaminone N-substituent can be dynamically exchanged at elevated temperatures by treatment with a second functional primary amine, and this “refunctionalization” can be driven to high conversions when the original amine is either less reactive (sterically or electronically) than the second amine or is selectively purged from the reaction (Table S1).
Figure 4. Spectroscopic evidence of ethyl acetoacetate enolization by benzylamine and tert-butylamine. The α-carbon (orange labeled peak) almost completely disappears only 5 min after treatment with excess benzylamine (left spectra) and tert-butylamine (middle spectra), but the continued presence of the initial O-ethyl CH2 peak (blue labeled peak) indicates that very little ethyl acetoacetate was converted to enamine. When a less basic amine such as aniline (right spectra) is used, virtually no change in the α-carbon peak is observed. aListed pKa values were obtained for the protonated ammonium ion in DMSO from ref 47. bA literature value for the pKa of tert-butylammonium was unavailable so the pKa value of n-butylammonium was used instead.
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CONCLUSIONS We have demonstrated a robust and selective technique for the room-temperature ligation of primary amines to macromolecules under highly accessible conditions. This reaction exhibits many of the hallmarks of a “click” reaction, requiring only innocuous starting materials, modest catalyst loadings, and reasonable reaction times, which we believe will render it highly useful for the synthesis of tailor-made macromolecules. Importantly, the reactive β-ketoester moieties are derived from a commercially available, inexpensive methacrylic monomer that could be both homopolymerized and copolymerized to yield well-defined polymers of diverse microstructures. While only side-chain functionalizations were explored in this work, AAEMA could also feasibly be installed at chain ends of RAFT polymers by thiol−Michael chemistry to open the door for facile end-group functionalization with primary amines. A second major feature of this modification strategy is that the installed functional groups can be exchanged in a subsequent heat-activated transamination step with no evidence of polymer degradation, and the reaction equilibrium can be biased exclusively toward products for substrates bearing electron-deficient or sterically hindered N-substituents. This dynamic process is most efficient in the presence of an acid catalyst but can also be activated solely using elevated temperatures, joining reactions like the heat-activated exchange of Diels−Alder adducts51,52 and thiol−Michael adducts.53 Critically, an enormous diversity of functional primary amines are readily available, enabling access to a vast library of functional materials from a single polymer feedstock. From a synthetic perspective, the ability to wholly recycle a previously functionalized macromolecule could reduce material waste and improve the economy of experimental designs. This strategy could furthermore impact approaches toward material
temperatures resulted in extremely rapid functional exchange, reaching equilibrium within 10 min in some cases. These results indicate that facile functional exchange is possible under a broader range of conditions than previously suggested, with higher catalyst loadings allowing lower temperatures for adequate reaction kinetics. While one could plausibly imagine that amidation is a competing side reaction to transamination, no evidence of amidation was observed to occur at the ester portion of either the vinylogous urethane or the methacryloyl backbone units during these NMR studies. As shown in the kinetic plot, a limiting factor in this modification approach is the establishment of an equilibrium prior to quantitative functional exchange. When the reactant and byproduct amines are similarly reactive, the forward and reverse reactions are effectively degenerate and the reaction efficiency is dictated by the molar excess of reactant amine. We therefore sought to both confirm this behavior on polymeric substrates and formulate strategies to overcome this equilibrium. Exchange reactions were first performed on PAAEMA bearing N-benzyl substituents (PAAEMA-Bn) at 100 °C in the presence of 5 mol % pTsOH for 8 h to ensure that equilibrium was reached. Using hexylamine as the reactant amine at a range of molar excess values from 1.1 to 10 per N-benzyl group, we could monitor the reaction efficiency through the disappearE
DOI: 10.1021/acs.macromol.8b01343 Macromolecules XXXX, XXX, XXX−XXX
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Figure 5. (A) Kinetics of enaminone exchange in the presence of 5 equiv of benzylamine and 5 mol % pTsOH catalyst at room temperature (orange markers), 60 °C (green markers), 80 °C (red markers), and 100 °C (blue markers) with overlaid 1H NMR spectra depicted for the 80 °C experiment. (B) Overlaid 1H NMR spectra depicting N-substituent exchange of benzyl-functionalized PAAEMA (left) and phenyl-functionalized PAAEMA (right) at 100 °C in the presence of variable equivalents of hexylamine and 5 mol % pTsOH. (3) Moad, G.; Chen, M.; Haussler, M.; Postma, A.; Rizzardo, E.; Thang, S. H. Functional polymers for optoelectronic applications by RAFT polymerization. Polym. Chem. 2011, 2, 492−519. (4) McKenzie, T. G.; Fu, Q.; Uchiyama, M.; Satoh, K.; Xu, J.; Boyer, C.; Kamigaito, M.; Qiao, G. G. Beyond Traditional RAFT: Alternative Activation of Thiocarbonylthio Compounds for Controlled Polymerization. Adv. Sci. 2016, 3, 1500394. (5) Ouchi, M.; Sawamoto, M. 50th Anniversary Perspective: MetalCatalyzed Living Radical Polymerization: Discovery and Perspective. Macromolecules 2017, 50, 2603−2614. (6) Hill, M. R.; Carmean, R. N.; Sumerlin, B. S. Expanding the Scope of RAFT Polymerization: Recent Advances and New Horizons. Macromolecules 2015, 48, 5459−5469. (7) Grubbs, R. B.; Grubbs, R. H. 50th Anniversary Perspective: Living PolymerizationEmphasizing the Molecule in Macromolecules. Macromolecules 2017, 50, 6979−6997. (8) Perrier, S. 50th Anniversary Perspective: RAFT PolymerizationA User Guide. Macromolecules 2017, 50, 7433−7447. (9) Gauthier, M. A.; Gibson, M. I.; Klok, H.-A. Synthesis of Functional Polymers by Post-Polymerization Modification. Angew. Chem., Int. Ed. 2009, 48, 48−58. (10) Sumerlin, B. S.; Vogt, A. P. Macromolecular Engineering through Click Chemistry and Other Efficient Transformations. Macromolecules 2010, 43, 1−13. (11) 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. (12) Blasco, E.; Sims, M. B.; Goldmann, A. S.; Sumerlin, B. S.; Barner-Kowollik, C. 50th Anniversary Perspective: Polymer Functionalization. Macromolecules 2017, 50, 5215−5252. (13) 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. (14) Barner-Kowollik, C.; Du Prez, F. E.; Espeel, P.; Hawker, C. J.; Junkers, T.; Schlaad, H.; Van Camp, W. Clicking” Polymers or Just Efficient Linking: What Is the Difference? Angew. Chem., Int. Ed. 2011, 50, 60−62.
fabrication by enabling on-demand repurposing of previously fabricated materials that complements existing techniques for commodity polyacrylate modification.30
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b01343. Materials, experimental procedures, supporting figures, and characterization data (PDF)
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AUTHOR INFORMATION
Corresponding Author
*(B.S.S.) E-mail
[email protected]fl.edu; Fax +1 352 392 9741. ORCID
Jacob J. Lessard: 0000-0003-2962-6472 Brent S. Sumerlin: 0000-0001-5749-5444 Funding
This material is based upon work supported by the National Science Foundation (DMR-1606410) (B.S.S.) and the National Science Foundation Graduate Research Fellowship (DGE-1315138) (M.B.S.). Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Matyjaszewski, K. Atom Transfer Radical Polymerization (ATRP): Current Status and Future Perspectives. Macromolecules 2012, 45, 4015−4039. (2) Moad, G.; Rizzardo, E.; Thang, S. H. RAFT Polymerization and Some of its Applications. Chem. - Asian J. 2013, 8, 1634−1644. F
DOI: 10.1021/acs.macromol.8b01343 Macromolecules XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.macromol.8b01343 Macromolecules XXXX, XXX, XXX−XXX
