Article pubs.acs.org/Macromolecules
α‑Trialkoxysilyl Functionalized Polycyclooctenes Synthesized by Chain-Transfer Ring-Opening Metathesis Polymerization Abdou Khadri Diallo,†,# Xiaolu Michel,†,# Stéphane Fouquay,‡ Guillaume Michaud,§ Frédéric Simon,§ Jean-Michel Brusson,∥ Jean-François Carpentier,*,† and Sophie M. Guillaume*,† †
Institut des Sciences Chimiques de Rennes, Organometallics: Materials and Catalysis Laboratories, UMR 6226 CNRS − Université de Rennes 1, Campus de Beaulieu, F-35042 Rennes, Cedex, France ‡ BOSTIK S.A., 253, Avenue du Président Wilson, F-93211 La Plaine Saint-Denis, France § BOSTIK, ZAC du Bois de Plaisance, 101, Rue du Champ Cailloux, 60280 Venette, France ∥ Total S.A., Corporate Science, Tour Michelet A, 24 Cours Michelet − La Défense 10, 92069 Paris La Défense, Cedex, France S Supporting Information *
ABSTRACT: Ring-opening metathesis polymerization/crossmetathesis (ROMP/CM) of cyclooctene (COE) or 3-alkylsubstituted COEs (3R-COEs, R = ethyl, n-hexyl) using several trialkoxysilyl monofunctionalized alkenes as chain-transfer agents (CTAs; vinyl trimethoxysilane (1), allyl trimethoxysilane (2), and 3-(trimethoxysilyl)propyl acrylate (3)) and various Ru−carbene−alkylidene catalysts afforded several trialkoxysilyl mono- and difunctionalized polyolefins. The formation of α-monofunctional (MF), α,ω-difunctional (DF), isomerized α-monofunctional (IMF), linear nonfunctional (LNF), isomerized linear nonfunctional (ILNF), and cyclic nonfunctional (CNF) PCOEs is rationalized by a two-stage mechanism. First, formation of monofunctionalized (MF) and nonfunctionalized (LNF, CNF) macromolecules takes place through a ROMP/CM along with RCM (ring-closing metathesis) process. Subsequently, CC isomerization (ISOM) combined with a second CM process give isomerized (ILNF, IMF) and difunctionalized (DF) macromolecules. The nonfunctionalized polymers (CNF, LNF, and ILNF) were formed in minor quantities compared to the trialkoxysilyl-functionalized polymers (MF, IMF, and DF), as evidenced by NMR and MALDI-ToF MS analyses and fractionation experiments. The rate and selectivity of the reaction varied with the nature of the CTA, COE substituent, catalyst, and to a lesser extent of the solvent. The use of 1,4-benzoquinone (BZQ) as additive allowed inhibiting completely the ISOM process. Alternatively, steric hindrance in 3-RCOEs substituted monomers resulted in an ISOM-free process with selective formation of MF polymers. The reactive Grubbs’ second-generation catalyst (G2) afforded the best compromise in terms of productivity, reactivity, and selectivity. Under optimized conditions favoring the formation of MF/DF, i.e., in CH2Cl2 at 40 °C for 24 h with [COE]0/[CTA 3]0/[G2]0/[BZQ]0 = 2000:20−200:1:100, the polymerization was rather well-controlled. While CTAs 1 and 3 selectively gave mixtures of MF and DF, allyl CTA 2 resulted in a mixture of IMF, MF, and DF.
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INTRODUCTION
addition of 3-mercaptopropyl(triethoxy)silane to the CC double bonds under moisture.10,11 The living anionic polymerization of a conjugated 1,3-diene, such as isoprene, using a dimetalated (Li, Na, K) initiator, followed by in situ end-capping of both termini of the active dianionic polydiene upon quenching with a siloxane or (4vinylphenyl)dimethyl-2-propoxysilane functionality, represents another approach.2,12 Similarly, the anionic polymerization of conjugated 1,3-dienes using a monofunctional silyl ether initiator (R 1 R2 R 3SiO−A−Li, where R1−R 3 are organic substituents and A is a short chain hydrocarbon bridging group) afforded silyl polydienes.13 Other trimethoxysilyl-
Selective introduction of silyl functional groups at the chain ends of nonpolar polyolefins is of topical interest. Silyl endfunctionalized polyolefins are indeed widely used as precursors for sealings, adhesives, and coatings materials toward architectural or industrial applications.1−7 Such silyl telechelic polyolefins have been prepared following different strategies. A few examples of postpolymerization modification by hydrosilylation of unsaturated chain end groups of preformed polyolefins into silyl functions have been reported. Hydroxyl groups of a linear low-density polyethylene (PE) were thus converted under heterogeneous conditions into silyloxy groups upon quantitative reaction with chlorotrimethylsilane.8,9 Also, low molar mass dihydroxy telechelic polybutadiene (PBD) was made cross-linkable upon reaction with 3-isocyanatopropyl(triethoxy)silane, resulting in urethane linkages, or upon © XXXX American Chemical Society
Received: August 24, 2015 Revised: September 18, 2015
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DOI: 10.1021/acs.macromol.5b01863 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
Scheme 1. Tandem ROMP/CM of 3-RCOEs Catalyzed by a Ruthenium Catalyst Using a Monofunctional Trialkoxysilyl-Alkene CTA, Showing All the Possible Polymer Types Envisioneda
FG: trialkoxysilyl functional group; DF: α,ω-difunctional; MF: α-monofunctional; IMF: isomerized α-monofunctional; LNF: linear nonfunctional; ILNF: isomerized linear nonfunctional; CNF: cyclic nonfunctional. a
vinylsilane was used in this latter work in order to limit the formation of polymeric product via ADMET polymerization or ring-opening metathesis polymerization (ROMP) of COE, respectively. Recent advances in Ru- and W-catalyzed ROMP25,26 have provided new opportunities for the synthesis of functionalized polyolefins. Hence, the use of symmetric acyclic alkenes as CTAs in ROMP of a cyclic olefin enabled the selective preparation of α,ω-functionalized polymers. The ROMP and cross-metathesis (CM) reactions between the propagating center (a transition-metal alkylidene catalyst) and the CTA thus afford the chain-end functionality (vide inf ra). A variety of telechelic polyolefins were thus formed, which is of particular relevance for further reactivity. Hence, following prior work with W-based catalysts,37 dihydroxy telechelic polyenes were obtained via Ru-catalyzed ROMP of COE,38 1,5-cyclooctadiene (COD),39−41 or 1,5-dimethyl-1,5-cycloctadiene (DMCOD),42 in the presence of cis-1,4-bis(acetoxy)-2-butene as a difunctional CTA, followed by a postpolymerization deprotection step of the acetoxy end-capping groups. Similarly, the synthesis of dicarboxy and diamino telechelic PBDs was achieved from the ROMP of COD using cis-1,4-bis(2-tert-butoxycarbonyl)-2butene and cis-1,4-di-tert-butyl-2-butene-1,4-dicarbamate as difunctional CTAs, respectively.43 The preparation of α,ωdicarboxy telechelic polycyclooctene (PCOE) was described from the ROMP of COE mediated by the highly reactive Grubbs’ second generation catalyst (G2), in the presence of unprotected maleic acid as CTA.44 Also, high molar mass dicyano and dichloro telechelic PBDs were synthesized via G2catalyzed ROMP of COD in the presence of 1,4-dicyano-2butene, 1,8-dicyano-4-octene, or 1,4-dichloro-2-butene, respectively, as CTAs.45,46 The ROMP of functionalized cyclic olefins spurred a renewed interest in polymer chemistry as well. Effective ROMP of different 5- and 3-substituted R-COEs (R = CH3, C2H5, C6H13, C6H5, OH, CO, OC(O)CH3, Br) catalyzed by several Ru-, Mo-, or W-based metathesis catalysts
terminated PBDs were prepared from silylation of poly(butadienyllithium) using 3-chloropropyl(trimethoxy)silane.14 Direct introduction of reactive silyl end groups toward telechelic polyolefins was also effectively achieved through direct in situ end-functionalization via the use of silylfunctionalized chain-transfer agents (CTAs). 15 Lanthanides-16,17 and early transition metals (Ti, Zr)18−24-catalyzed (co)polymerizations of α-olefins enabled to prepare various silyl-end-capped polyolefins along with the control of the molar mass values. For instance, primary alkylsilanes (n-BuSiH3, PhCH2SiH3) and arylsilanes (PhSiH3) CTAs efficiently terminated growing polyethylene chains.16,17 Selective organotitanium-mediated silanolytic (PhSiH3, PhMeSiH2, Me2SiH2, Et2SiH2) chain transfer in the homogeneous polymerization and copolymerization of a variety of α-olefins (ethylene, propylene, 1-hexene, styrene) afforded silyl-capped and silyllinked polyolefins.18,19 Also, the possibility of forming silylterminated highly branched polyolefins by coupling an α-olefin with a CTA as one comonomer was first established with the polymerization of ethylene using Ti−alkyl precatalysts and a primary alkenylsilane (RSiH3) comonomer/CTA.20,21 More commonly, among metathesis reactions,25−27 acyclic diene metathesis (ADMET) polymerization, as pioneered by Wagener,28,29 also enabled the formation of silyl-terminated polyolefins.3,30−36 Oligo(oxyethylene) α,ω-dienes were crosslinked via ADMET upon exposure to moisture of latent trimethoxysilyl chain-end or chain-internal functionalities.31−33 In an elegant example, mass-tailored disilyl telechelic PBDs were synthesized via ADMET depolymerization of 1,4-PBD and allylsilanes (CH2CHCH2SiMe2R, R = Me, Cl)34,35 or bis(tert-butyldimethoxysiloxy)-3-hexene36 in the presence of Mo− or W−alkylidenes catalysts. Also, the metathesis of divinyltetraethoxydisiloxane with 1,9-decadiene and cyclooctene (COE), catalyzed by Cl2(PCy3)2RuCHPh, provided a mixture of the monosilyl derivative, a bis-silyl-substituted diene, and polymeric product.30 A large excess (ca. 10-fold) of B
DOI: 10.1021/acs.macromol.5b01863 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules afforded the corresponding functionalized PRCOEs.47−49 Subsequent hydrogenation of these PRCOEs gave precision linear low density polyethylenes (LLDPEs) featuring R substituents on every eight backbone carbons. Within a general strategy to produce non-isocyanate polyurethanes (NIPUs) through the carbonate/amine reaction, we recently reported the synthesis of α- and α,ω-cyclocarbonate telechelic PCOE and PE, using vinyl or acryloyl glycerol carbonate CTAs in the G2-catalyzed ROMP and ROMP/hydrogenation of COE, respectively.50−53 To our knowledge, no example of trialkoxysilyl-functionalized polyolefins prepared from ROMP of a cycloolefin in the presence of a trialkoxysilylalkene CTA has been reported. Taking advantage of the reactivity of trialkoxysilyl-bearing olefins in Ru-catalyzed metathesis,54−58 we now report herein a novel route to trialkoxysilyl-functionalized polyolefins using monofunctionalized alkenes as CTAs (1, 2, 3) in the Ru-catalyzed ROMP of COE and other 3-alkyl-substituted COEs (3-RCOEs; Scheme 1). Insights into the ROMP/CM mechanism are first addressed. The influence of the solvent, catalyst, CTA, and additives is next investigated so as to optimize the polymerization efficiency.
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The molar mass values of the polymers samples were determined by H NMR analysis in CDCl3 (Mn,NMR) from the integral value ratio of the signals of end-groups hydrogens (typically δ 6.98 (H7)) to internal olefin hydrogens (δ 5.41 (H10)) (Figure 5). DOSY spectra were acquired at 23 °C in CDCl3 with the stebpgp1s pulse program from Bruker topspin software. All spectra were recorded with 32 K time domain data points in the t2 dimension and 32 t1 increments. The gradient strength was logarithmically incremented in 32 steps from 2% up to 95% of the maximum gradient strength. Diffusion times of 100 ms and the maximum bipolar gradient pulse length of 1.8 ms were used in order to ensure full signal attenuation. The data were processed using an SI F2 and SI F1 of 32 K. The diffusion dimension of the 2D DOSY spectra was processed by means of Bruker topspin software (version 3.0). The DOSY maps were obtained with the Bruker topspin software (version 3.0). The average molar mass (Mn,SEC) and dispersity (ĐM = Mw/Mn) values were determined by size exclusion chromatography (SEC) in THF at 30 °C (flow rate = 1.0 mL min−1) on a Polymer Laboratories PL50 apparatus equipped with a refractive index detector and a set of two ResiPore PLgel 3 μm MIXED-E 300 × 7.5 mm columns. The polymer samples were dissolved in THF (2 mg mL−1). All elution curves were calibrated with 12 monodisperse polystyrene standards (Mn range = 580−380 000 g mol−1). Mn,SEC values of polymers were uncorrected for their possible difference in hydrodynamic volume vs polystyrene. The SEC traces of the polymers all exhibited a monomodal and symmetrical peak (Figures S6 and S21). MALDI-ToF mass spectra were recorded at the CESAMO (Bordeaux, France) on a Voyager mass spectrometer (Applied Biosystems) equipped with a pulsed N2 laser source (337 nm, 4 ns pulse width) and a time-delayed extracted ion source. Spectra were recorded in the positive-ion mode using the reflectron mode and with an accelerating voltage of 20 kV. A freshly prepared solution of the polymer sample in THF (HPLC grade, 10 mg mL−1) and a saturated solution of trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (10 mg, DCTB) in THF (1 mL, HPLC grade) were prepared. A MeOH solution of the cationisation agent (NaI or AgTFA, 10 mg/mL) was also prepared. The solutions were combined in a 10:1:1 v/v of matrix-to-sample-to-cationization agent. 1−2 μL of the resulting solution was deposited onto the sample target and vacuum-dried. General ROMP Procedure. All polymerizations were performed according to the following typical procedure (Table 1, entry 10). The only differences lie in the nature of the solvent, catalyst, CTA, and its initial concentration ([CTA]0), and the presence of additives in some cases. Under argon atmosphere, a 20 mL Schlenk flask, equipped with a magnetic stir bar, was charged sequentially with dry CH2Cl2 (5.0 mL), COE (1.56 mL, 1.32 g, 12.0 mmol), and CTA 3 (0.13 mL, 140 mg, 0.60 mmol). The resulting solution was placed at 40 °C, and the polymerization was started upon addition, via a cannula, of a dry CH2Cl2 solution (2.0 mL) of G2 (5.0 mg, 5.3 μmol). The reaction mixture turned highly viscous within 2 min. The viscosity then slowly decreased over the next 10 min. After the desired reaction time (typically 24 h), the volatiles (solvent and ethylene) were removed under vacuum. The polymer was then recovered upon precipitation in excess methanol (50 mL) (thereby allowing removal of the catalyst), filtration, and drying at 25 °C under vacuum (95% yield). All polymers were recovered as white powders, readily soluble in chloroform and THF and insoluble in methanol (Tables 1−3). Separation of Nonfunctionalized (NF) Polymers from Functionalized Polymers. NF (i.e., LNF, ILNF, and CNF) polymers were separated by column chromatography on silica gel 60 acidified with HCl (37%) until pH < 2 using CH2Cl2 as eluent. Functionalized polymers (MF, IMF, DF) thus remained grafted onto the acidified silica, while NF polymers were isolated from the eluted solution (Table 3). 1
EXPERIMENTAL SECTION
Materials. All syntheses and manipulations of air- and moisturesensitive materials were performed under inert atmosphere (argon,
