Radical Copolymerization of Vinylidene Fluoride (VDF) with Oligo

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Radical Copolymerization of Vinylidene Fluoride (VDF) with Oligo(hexafluoropropylene oxide) Perfluorovinyl Ether Macromonomer To Obtain PVDF‑g‑oligo(HFPO) Graft Copolymers Chadron Mark Friesen*,†,‡ and Bruno Ameduri*,‡ †

Department of Chemistry, Trinity Western University, Langley, British Columbia V2Y 1Y1, Canada Ingénierie et Architectures Macromoléculaires, Institut Charles Gerhardt, Ecole Nationale Supérieure de Chimie de Montpellier (UMR5253-CNRS), 8, rue de l’Ecole Normale, 34296 Montpellier Cedex 1, France

‡

S Supporting Information *

ABSTRACT: The synthesis of PVDF-g-oligo(HFPO) graft copolymers, where VDF and HFPO stand for vinylidene fluoride and hexafluoropropylene oxide, respectively, is presented. First, an oligo(HFPO)− OCFCF2 macromonomer was prepared from two methods starting from oligo(HFPO) acyl fluoride in 34 to 54% yield. Then, the radical copolymerization of VDF with that comonomer, initiated by tert-butyl peroxypivalate (TBPPi) or perfluoro-3-ethyl-2,4-dimethyl-3-pentyl persistent radical (PPFR) was studied under various conditions. The resulting PVDF-g-oligo(HFPO) graft copolymers were produced in good isolated yields (74 to 89%). The molar percentages and molecular weights of the graft copolymers were assessed by 19F and 1H NMR spectroscopy. Molar percentages of VDF and oligo(HFPO)−OCFCF2 comonomers reached up to 99% and 11%, respectively, while the molecular weights ranged from 25 000 to 77 000 g/mol. Their thermal properties were also studied and showed: (1) satisfactory thermostability (Td) in the 410 to 494 °C range under air and (2) melting temperature (Tm) between 138 to 159 °C, while (3) the glass transition (Tg) ranged from −79 to −54 °C.

1. INTRODUCTION In order to synthesize valuable elastomers, it is worth choosing the right application and monomers to use for the copolymer system. One specific material that has been underutilized for such a purpose, but is expanding in its utility, is fluorinated liquids such as perfluoropolyalkylethers (PFPAEs). PFPAEs are valuable products that are produced on an industrial scale and have outstanding operating temperature range from −90 to +450 °C.1 Only four commercially available PFPAEs are on the market. They can be synthesized from various strategies: (i) the anionic polymerization of hexafluoropropylene oxide, (HFPO) leads to Krytox produced by Chemours, created from a chemical performance business of du Pont de Nemours and Company,2,3 or commercialized by Unimatec (formerly by NOK Corp. or Nippon Mektron Ltd.) under the Aflunox trade name; (ii) the photooxidation of perfluoroolefins (e.g., tetrafluoroethylene,4 hexafluoropropene (HFP),5 and perfluorobutadiene6) was performed by the Ausimont Company, now Solvay Specialty Polymers, yielding functional (mono- or telechelic) or nonfunctional (Fomblin Y and FomblinZ) oligomers, the molecular weights of which range from 1000 to 4000 g·mol−1;7,8 (iii) the Daikin Company commercializes Demnum oligomers, which can be inert or functional, from the ring-opening polymerization of fluorinated oxetanes followed by a fluorination to obtain thermostable oils.9 © XXXX American Chemical Society

The syntheses, properties, and applications of the PFPAEs mentioned above have been extensively reviewed by several authors.10−15 This is a special class of liquid fluoropolymers with high thermostability, excellent chemical inertness, and low surface tension. They have found various applications such as lubricants,9 elastomers,11 pump fluids, and heat transfer fluids under demanding conditions, or are involved in the development of cosmetics and barrier creams that offer a very high degree of skin protection and moisture retention. These PFPAEs are also useful for lubrication of thin film magnetic media.12,13 Some interesting characteristics are their low Tgs (lower than −50 °C) and their totally amorphous state thanks to their aliphatic structure and ether linkages.11,14 Indeed, various well-architectured materials containing PFPAEs have been reported such as telechelics and monofunctional, block and graft copolymers, briefly summarized hereafter. First, telechelic dihydroxyPFPAEs (FomblinZ-Dol) have successfully led to telechelic (meth)acrylates well reported by Bongiovanni et al.15 and also by DeSimone’s team16 from the condensation of 2-isocyanatoethyl methacrylate with Received: June 3, 2015 Revised: September 16, 2015

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DOI: 10.1021/acs.macromol.5b01199 Macromolecules XXXX, XXX, XXX−XXX

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surfaces.30 Polymer monolayer films form spontaneously from disulfide gold mediated interfacial attachment, yielding highly hydrophobic films (ca. 30 Å thick);30 (ii) the synthesis of acrylic copolymers bearing PFPAE pendant groups31 or (iii) the radical terpolymerization of VDF with hexafluoropropylene and allyl amido-oligo(HFPO) macrocomonomer leading to poly(VDF-co-HFP)-g-oligo(HFPO) graft copolymers of low molecular weights arising from a transfer to allyl group.32 Other PFPAE-macromonomer, CF 3 O−(CF 2 CF 2 O) m − (CF 2 O) n −CF 2 −CH 2 O−CONHCH 2 CH 2 −OCOC(CH 3 ) CH2, where m = n with molecular weight of 1079 g·mol−1 was reported and involved in photopolymerization. The water dynamic contact angle of the resulting polymers depends on the different amounts of such a fluoromonomer.31 The same strategy was also demonstrated from DeSimone’s team33 by using a methacrylate-based Krytox macromonomer. This was achieved from N-(3-aminopropyl) methacrylamide PFPAE macromonomer (PFPAED). Some current applications of PFPAEs based on telechelic and monofunctional block and graft copolymers have been found in fouling-release coatings,34 microfluidic35 and polymer electrolytes for lithium ion batteries (LIB) [e.g., nonflammable electrolyte composed of low molecular weight PFPAEs and bis(trifluoromethane)sulfonimide lithium salt that showed a remarkably high transference number of at least 0.91 (more than double that of conventional electrolytes),36 microlithography,37 etc. Over the years, a renaissance in the design of fluoroelastomers has been highlighted, because of tighter air emission regulations, new amine additives for motor oil to enhance oil and engine lives, and an increasing need for fluoroelastomers in cold conditions with good sealing force. Fluoroelastomer’s most crucial applications are in O-rings, gaskets, seals, and hoses found in automotive or aircraft fuel lines. Both the automotive and aerospace industries are looking for new low temperature polymers.38 Searching for low-Tg polymers is still a challenge for aerospace and automotive industries and some work has been studied to explore the compatibility of VDF with linear PFPAEs. By fine-tuning fluoroelastomers with VDF and branched PFPAE copolymers, one hopes to understand the microstructure of this fluoroelastomer for targeted low and high temperature applications. As far as we are aware, information on microstructure of copolymers of VDF with any PFPAE has not been reported nor elastomers synthesized from long-chain PFPAEs with VDF. For example, Worm39 disclosed a low Tg PVDF-g-PFPAE graft cofluorocarbon elastomers with Tg as low as −119 °C from the radical copolymerization of VDF with F2CCFO(CF2)m[(OCF2)p]nORF (where RF designates a perfluoroalkyl C1−C4 group, m = 1−4, n = 0−6, and p = 1− 2). However, the PFPAE used contains −(OCF2)− groups which is helpful for low temperature performance but are known to degrade readily in the presence of Lewis acids, thus limiting their high temperature performance.40 This patent does not claim any information on the microstructure of the final copolymers (i.e., the molar percentages of both comonomers), the defects of PVDF chaining, and the molecular weights. Hence, the objective of this present article is to understand the reactivity and to study the microstructure of a fluoroelastomeric copolymer made of VDF and a long-chained branched PFPAE macromonomer [oligo(HFPO)−OCF CF2]. This could be achieved from synthesizing copolymers

telechelic diol PFPAEs, as precursors of photo-cross-linkable networks. The works from Bongiovanni’s team on PFPAE UV-curable derivatives are interesting: they first photopolymerized PFPAE urethane diacrylates17 and polyester acrylates,18 or polyethers achieved from DeSimone group.16 The networks displayed complex morphologies and exhibited two glass transition temperatures assigned to the PFPAE (−90 °C to −120 °C) and to the hard hydrogenated part of the network. They exhibited low surface tension (i.e., water- and oil-repellency), as well as poor adhesion, i.e., release properties. Easy-to-clean, antifingerprint, and antibiofouling properties have also been shown. PFPAEs represent interesting building blocks for surface modification: they are nonbioaccumulative, display surface tensions as low as 14 mN m−1, and their surface activity, namely water repellency in copolymerized systems, are higher than many fluoroalkylic acrylates unless a C8F17 chain was used.19 Other copolymers based on PFPAE acrylics were prepared with common photocurable acrylics of well-known reactivity (like hexanediol diacrylate). The same Italian group20 reported that hydrogenated/fluorinated mixtures were transparent up to 1:3 weight ratios and can then be photopolymerized to obtain a complex multiphasic nanostructure. The PFPAE matrix ensured low surface energy and low refractive index, while the hydrogenated counterpart enhanced the mechanical properties and polarity of the systems. Second, interesting properties were obtained by using UVcurable polysiloxanes containing methacryloxy/fluorinated side groups. Results indicated that the siloxane chain could enhance the flexibility and gloss while the fluorinated groups improved the hardness. Both functionalities increased thermal stability and water resistance.21 Third, monofunctional PFPAEs have been interesting precursors for diblock copolymers, either from polyvinylidene fluoride (PVDF) end-capping from PFPAE-Br22 or from iodine transfer polymerization of VDF in the presence of 1iodoPFPAE as the chain transfer agent.23 Original PFPAEOOPFPAE macroperoxides and peroxidic PFPAEs were obtained by oxidative polymerization of tetrafluoroethylene at low temperature in a fluorinated solvent where elemental fluorine is an efficient free radicals initiator at low temperature.24 Avataneo et al. successfully initiated the dead end polymerization of VDF or TFE25 or 2,2,4-trifluoro-5-trifluoromethoxy1,3-dioxole (TTD)26 according to a strategy well reviewed by Sawada.27 The resulting PFPAE-b-PTFE block copolymer display an amorphous behavior while the content of TTD has a crucial influence on the Tg that varied from −70 to +10 °C when the wt % TTD increased from 19 to 60 wt %. Poly(TFE-co-TTD)-b-PFPAE block copolymers of Mn up to 700 000 g·mol−1 were also produced.26 PLA-b-PFPE-b-PLA triblock copolymers (where PLA stands for polylactide) were prepared by ring-opening polymerization of lactide from telechelic diol based on PFPAE.28 Later, Smith’s group revisited that reaction and synthesized PLLA-b-PFPAE-b-PLLA segmented triblock copolymers of reasonably high molecular weights with enhanced hydrophobic properties.29 Finally, a series of copolymers that contain PFPAEs grafts and nonexhaustive approaches can be achieved from three strategies: (i) the hydrosilylation of allyl PFPAE onto hydrogenopoly(dimethylsiloxane)s to lead to perfluoropolyether-grafted siloxane copolymer bearing dithioalkyl side chains, chemisorbed from dilute solutions to fresh gold B


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Figure 1. 19F NMR spectrum of perfluorovinyl-2-poly(hexafluoropropylene oxide) perfluoropropyl ether. respectively. The experimental conditions were accomplished using TopSpin 2.1 operating at 400.13 (1H), 376.46 (19F), 100.62 (13C) MHz. Flip angle 90° for 1H and 13C and 30° for 19F NMR); acquisition time 3.96 s (1H), 0.87 s (19F), 1.36 s (13C); pulse delay 2 (1H), 4 s (19F and 13C); scans 128 (1H), 16 (19F), 6144 (13C); and pulse width of 12.50 (1H), 13.0 (19F), and 9.0 (13C) μs. The letters s, d, t, q, and sext stand for singlet, doublet, triplet, quartet, and sextet, respectively. Thermogravimetric Analyses (TGA). Thermogravimetric analyses were performed with a Texas Instrument TGA 51−133 apparatus under air (50 mL/min) at a heating rate of 10 °C·min−1 from 20 °C up to a maximum of 580 °C. The sample size varied between 10 and 15 mg. Differential Scanning Calorimetry (DSC). These measurements were conducted using a Netzsch DSC 200F3Maia instrument connected to a microcomputer. The apparatus was calibrated with indium and n-decane. After its insertion into the DSC apparatus, the sample at 20 °C was initially cooled 10 °C.min−1 until it reached −150 °C for 2 min. Then, the first scan was operated at a heating rate of 10 °C.min−1 up to 250 °C. A second scan was required for the assessment of the Tg, defined as the inflection point in the heat capacity jump, and Tm, defined as the maxima of the endothermic peak. The sample size was about 10−15 mg. 2.3. Characterization of the PPFR Initiator and Synthesis of Monomer, and Radical Polymerization. 2.3.1. Persistent Perfluoroalkyl Radical (PPFR) Initiator. Perfluoro-3-ethyl-2,4-dimethyl-3pentyl (PPFR, regarded as a persistent radical) was synthesized by known procedures.41,42 The fraction collected at 31−33 °C/25 mmHg (PPFR) was used for this investigation. Characterization. The 19F NMR data on the products (E- and Zforms of perfluoro-3-ethyl-4-methyl-2-pentene) obtained by the thermal decomposition of persistent perfluoroalkyl radical (PPFR-1; perfluoro-3-ethyl-2,4-dimethyl-3-pentyl) are as follows:

bearing labels in the end-groups that enable the integration by NMR spectroscopy. These end-labels (CF3− or (CH3)3C−) enabled the calculation of the molar amount of VDF in the polymer (including head-to-head or head-to-tail percentages). From the molar amount of VDF in the polymer and using 19F NMR spectroscopy, the molar amount of trifluorovinyl oligo(HFPO) macromonomer could be determined along with molecular weight. The best labels were obtained from • CF3 radicals, generated from a perfluorinated hyperbranched radical, capable of initiating the radical copolymerization of VDF with a macromonomer containing oligo(HFPO) units. In addition to the assessment of the molecular weights, content of comonomers and the defects of PVDF chaining, the thermal stability and glass transition temperature of the resulting copolymers were also studied.

2. EXPERIMENTAL SECTION 2.1. Materials. All reagents were used as received unless it is stated. 1,1-Difluoroethylene (vinylidene fluoride, VDF) and 1,1,1,3,3pentafluorobutane (Solkane 365mfc) were kindly supplied by Arkema (Pierre-Benite, France) and Solvay S.A. (Brussels, Belgium), respectively. tert-Butyl peroxypivalate and dimethylcarbonate were purchased from Akzo Nobel (TBPPi, TRIGONOX 25-C75, 75% TBPPi in isodecane) and Sigma-Aldrich, respectively, while the persistent radical was donated by Dr Taizo ONO, NIAIST, Nagoya, Japan. Hexafluoropropylene oxide and 1,1,2-trichloro-1,2,2-trifluoroethane (Freon 113) were kindly offered by DuPont (Wilmington, DE). Deuterated dimethylformamide (DMF-d7) and benzene (C6D6) were used for the NMR spectroscopy was purchased from Euroiso-top (Grenoble, France) (purity >99.8%). The 3 mm magnetic stir-bar for the Carius tube was purchased from Carl Roth Gmbh Co., Karlsruhe, Germany. 2.2. Analysis. Nuclear Magnetic Resonance (NMR) Spectroscopy. The structure of the products was determined by NMR spectroscopy at room temperature (25 °C). NMR spectra were recorded on Bruker AC-400 instruments using deuterated benzene capillary or dimethylformamide (DMF-d7) as internal references,

1 E-form: −62.9 (m, 3F), −79.4 (d, 3JFF = 29.3 Hz, 6F), −80.5 (d, 3JFF = 20.3 Hz, 3F), −81.3 (overlapped, 1F), −103.3 (m, 2F), −175.9 (m, 1F) 2 Z-form: −62.7 (d, 3JFF = 48.5 Hz, 3F), −72.1 (s, 6F), −79.1 (overlapped, 4F), −103.5 (m, 2F), −170.1 (quartet, 3JFF = 48.5 Hz, 1F) C


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Figure 2. 1H NMR spectrum of PVDF-g-oligo(HFPO) (reaction no. 4) using 50/50 by volume of 1,1,2-trichloro-1,2,2-trifluoroethane/DMF-d7 as solvents. added to the same reaction flask while stirring. A shield was placed in front of the reaction vessel. Then, the reagents were added and slowly heated to 120 °C. The temperature was held until there is was no longer a production of carbon dioxide. This was checked by turning off nitrogen flow and inspecting for any gas evolution going through the bubbler. After the reaction was completed, the total product mixture was cooled to room temperature. The product was filter through Celite using a Buchner funnel and house vacuum. The resulting product (108.9 g) was a pale yellow transparent oil. Isolated yield was 54%. Characterization. 19F−NMR (376.41 MHz, C6D6 capillary, 25 °C, Figure 1): δ = −79 to −84 (−[CF(CF3)CF2O]−), −82.03 (CF3CF2CF2O−, 2F), −83.73 (s, CF3CF2CF2O− , 3F), −117.11 (dd, −OCFc = CFaFb, 2JFaFb = 91.8 Hz, 3JFaFc = 65.4 Hz, 1F), −124.65 (dd, −OCFc=CFaFb, 2JFbFc = 112.4 Hz, 3JFbFa = 87.2 Hz, 1F), −131.69 (s, CF3CF2CF2−, 2F), −138.30 (dd, OCFc = CFaFb, 2JFcFb = 113.6 Hz, 3 JFcFa = 67.7 Hz, 1F), −146.31 (m, −[CF(CF3)CF2O]−, 5.73 x 1F); 13 C−NMR (101 MHz, C6D6 capillary, 25 °C, Figure S2): δ = 147.69 (td, −OCF = CF2, 1JCF = 278.1 Hz, 2JCF = 52.7 Hz, 1C), 129.99 (dt, −OCF = CF2, 1JCF= 269.3 Hz, 2JCF = 48.3 Hz, 1C), 117.3 (qd, −OCF(CF3)CF2−, 1JCF =288.3 Hz, 2JCF = 30.7 Hz, 8.9 × 1C), 116.86 (qt, CF3CF2CF2O−, 1JCF = 286.15 Hz, 2JCF = 32.93 Hz, 1C), 115.8 (td, −OCF(CF3)CF2O−, 1JCF =287.6, 2JCF = 28.5 Hz, 8.9 × 1C), 115.35 (tt, CF3CF2CF2O, 1JCF = 286.15, 2JCF = 34.40 Hz, 1C), 106.3 (tsex, CF3CF2CF2O−, 1JCF = 270.1, 2JCF = 40.83 Hz, 1C), 102.75 (dsext, − OCF(CF3)CF2−, 1JCF = 269.3, 2JCF = 37.3 Hz, 8.9 × 1C). 2.3.3. Radical Copolymerization of Vinylidene fluoride (VDF) with Perfluorovinyl-2-[poly(hexafluoropropylene oxide) perfluoropropyl ether] F[CF(CF3)CF2O]nCF(CF3)CF2OCFCF2. General Procedure. The radical polymerizations of VDF and the macromonomer were performed in thick borosilicate glass Carius tubes equipped with a Lshaped 3 mm Teflon coated magnetic stirrer (Carius tube dimensions =1.9 cm diameter × 13 cm length × 2 mm thickness borosilicate tube flamed sealed and rounded on one end and end-to-end joined to a 8 mm diameter × 9.5 cm × 2 mm thickness length on the other, volume 23 mL). In a typical copolymerization, an amount of the perfluorovinyl-2-(poly(hexafluoropropylene oxide)) perfluoropropyl ether (macromonomer), radical initiator, and the appropriate amount of solvent were added into the Carius tube. The Carius tube was then placed on a special metal vacuum-line manifold containing an

Thermal Decomposition Rate. This was recently published.41 The thermal decomposition rate of PPFR was examined at 90 °C monitoring the content of PPFR in the reaction mixture by gas chromatography. The peak area ratio of PPFR to the internal standard, perfluoro-tri-n-propylamine (PTFA), was plotted versus the reaction time (h). The good linear relationship showed that the thermal decomposition of PPFR followed the first order reaction (ln([PPFR]/ [PTFA]) = −0.718t + 1.479, r = 0.999). The half-life at 90 °C was assessed as 0.97 h. 2.3.2. Synthesis of Perfluorovinyl-2-[poly(hexafluoropropylene oxide) perfluoropropyl ether], F[CF(CF3)CF2O]nCF(CF3)CF2OCF CF2. Method A. Poly(hexafluoropropylene oxide) acid fluoride was slowly added (22.5810 g, 0.0176 mol, 1283 g·mol−1) to a polyethylene bottle containing 200 mL deionized water. The reaction mixture was stirred for several minutes using a Teflon coated magnetic stir bar before decanting the excess water and placing the newly formed carboxylic acid into a 50 mL round-bottomed flask. Next, 15 mL of 6.3% by mass/volume of sodium hydroxide/ethanol solution (2.5127 g of NaOH in 40 mL of 85% ethanol) were added to the carboxylic acid. The mixture was stirred and warmed to 50 °C for at least 1 h to convert the cloudy solution into a clear solution. After mixing, the ethanol was stripped at 78−90 °C using simple distillation. A shield was placed in front of the distillation and then the pressure was reduced to 10 Torr and the product was distilled over at 80−90 °C using a simple distillation system. The crude yield collected was 10.6337 g. The product was then washed with 5 mL of 1% by mass/ volume of NH4OH aqueous solution. The resulting product was a clear oil. Isolated yield was 7.1809 g (34%). Method B. A 500 mL round-bottomed flask was inspected and found to be free of defects and etching and then placed into an ice bath. The setup reactor included a mechanical stirrer, thermocouple, large bore condenser, a secondary container, and an above surface nitrogen sweep blanket. A suck-back and vapor trap were attached after the large bore condenser with a feed line running to a scrubber containing 1 L of 1 M ammonium hydroxide and several drops of universal indicator to indicate when the solution needs to be replaced. Next, 28.64 g, 37.49 mL (0.176 mol) hexamethyldisiloxane and 0.867 g (6.76 mmol) of potassium trimethysilanoate as catalyst were added into the 500 mL round-bottomed flask. Drop-wise 200 g (1365 g· mol−1, 0.145 mol) poly(hexafluoropropylene oxide) acyl fluoride was D


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Figure 3. 19F NMR spectrum of PVDF-g-oligo(HFPO) graft copolymer (reaction no. 5, Tables 1 and 2) using 50/50 by volume of 1,1,2trifluorotrichloroethane (Freon 113)/THF solvents and a C6D6 capillary. Reaction No. 4. In a Carius tube, 0.7466 g of oligo(HFPO)− OCFCF2, 9.0190 g of 1,1,2-trichloro-1,2,2-trifluoroethane, 1.5 g of VDF, and 3 drops of PPFR (0.0170 g) were added. After the reaction and drying, a white solid polymer was formed. During heating the Carius tube ruptured. The little remaining content was analyzed by NMR. No isolated yield was obtained. Reaction No. 5. In a Carius tube, 0.5191 g of oligo(HFPO)− OCFCF2, 8.9977 g of 1,1,2-trichloro-1,2,2-trifluoroethane, 1.0 g of VDF, and 3 drops of PPFR (0.0301 g) were added. After the reaction and drying, a white solid polymer was formed. The isolated yield was 1.1306 g. Reaction No. 6. In a Carius tube, 0.2505 g of oligo(HFPO)− OCFCF2, 8.9977 g of F113, 0.5 g of VDF, and 3 drops of PPFR (0.0412 g) were added. After the reaction and drying, a white solid flake polymer was formed. The isolated yield was 0.5517 g. Characterization. 1H NMR (DMF-d7/CClF2CFCl2) δ (ppm) (Figures 2 and S3−S5 in the Supporting Information): 0.86−1.5 ((CH3)3CCH2CF2− or (CH3)3CCF2CH2− or CH3CH2CF2−), 3.3 (CF3−CH2−CF2, regioselective addition of •CF3 radical onto CH2 of VDF); 3.0 (CH2−CF2 of VDF, normal VDF−VDF addition); 2.4 (CF2−CH2−CH2−CF2 reverse addition of VDF). 19F NMR (C6D6 capillary THF/CClF2CFCl2) or (DMF-d7/CClF2CFCl2) δ (ppm) (Figure 3 and S6−S10 in Supporting Information): −61.3 (CF3 chain end), −79 to −84 (−[CF(CF3)CF2O]−), −82.03 (CF3CF2CF2O−, 2F), −83.73 (s, CF3CF2CF2O−, 3F), −91.5 (CF2 of VDF, normal addition head-to-tail); −113 and −116 (CH2−CF2−CF2−CH2 reverse addition of VDF, head to head). −131.69 (s, CF3CF2CF2O−, 2F), −146.31 (m, −[CF(CF3)CF2O]−, 5.73 × 1F).

intermediate cylinder from which the drop of pressure was beforehand calibrated with the amount (in g) of vinylidene fluoride (VDF). The contents of the tube were degassed by at least three freeze−thaw cycles to remove oxygen. Finally, the appropriate amount of VDF was vacuum transferred into the Carius tube frozen in liquid nitrogen. The 8 mm diameter end of the tube was flamed sealed under dynamic vacuum while the bottom of the tube was still located in liquid nitrogen. After warming up to room temperature, the Carius tube was then placed in a silicon oil bath, magnetically stirred, and heated to a temperature suitable for the radical initiator used. The reaction was carried out for approximately 14−24 h at constant temperature (75 or 90 °C for TBPPi or PPFR, respectively). The colorless liquid solution turned into a white waxy thick turbid product after 3−4 h (as evidenced by pictures of Carius tubes in Figure S25). After the reaction was complete, the total product mixture was frozen in liquid nitrogen, and finally opened. The resulting copolymers were isolated by evaporation of the solvent, and then dried at 50 °C under vacuum (10 mbar). The copolymers obtained were then weighed to assess the yield. For characterizations using nuclear magnetic resonance (NMR), the polymers were dissolved in a 50/50 mixture of DMF-d7 and 1,1,2trichloro-1,2,2-trifluoroethane when TBPPi was used as the initiator and a 50/50 mixture of THF and 1,1,2-trichloro-1,2,2-trifluoroethane containing a capillary of C6D6 when PPFR was used as the initiator. Reaction No. 1. In a Carius tube, 1.9105 g of oligo(HFPO)− OCFCF2, 3.810 g of dimethylcarbonate, 3.0320 g of 1,1,1,3,3pentafluorobutane, 0.31 g of VDF, and 2 drops of TBPPi (0.0269 g) were added. After the reaction and drying, an opaque white tacky but waxy polymer was formed. The isolated yield was 1.9553 g. Reaction No. 2. In a Carius tube, 2.3490 g of oligo(HFPO)− OCFCF2, 3.857 g of dimethylcarbonate, 2.4340 g of 1,1,1,3,3pentafluorobutane, 0.57 g of VDF, and 2 drops of TBPPi (0.0390 g) were added. After the reaction and drying, a white opaque viscous polymer was formed. The isolated yield was 2.6088 g. Reaction No. 3. In a Carius tube, 0.5789 g of oligo(HFPO)− OCFCF2, 9.0829 g of 1,1,2-trichloro-1,2,2-trifluoroethane, 1.00 g of VDF, and 3 drops of TBPPi (0.0199 g) were added. After the reaction and drying, a white powdered solid polymer was formed. The isolated yield was 1.4052 g.

3. RESULTS AND DISCUSSION 3.1. Synthesis of Perfluorovinyl-2-(poly(hexafluoropropylene oxide) Perfluoropropyl Ether (F[CF(CF 3 )CF 2 O] n CF(CF 3 )CF 2 OCFCF 2 ) [oligo(HFPO)− OCFCF2) and Its Copolymerization with Vinylidene Fluoride (VDF). First, the synthesis of the macromonomer (oligo(HFPO)−OCFCF2) required several steps (Scheme 1). The polymerization of HFPO was first carried out in our research laboratory. After the polymerization, two routes have E


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CF2]o) molar ratios. The temperatures were chosen so that the half-lives of these above initiators were ca. 1 h, i.e., 74 °C for TBPPi while the reactions initiated by PPFR were carried out at 90 °C (see Experimental Section, part 2.3.1) for ca. 14−24 h to be sure that all the initiators decomposed into their corresponding radicals (Scheme 3).

Scheme 1. Strategies in the Synthesis of Oligo(HFPO)− OCFCF2 Macromonomer from Oligo(hexafluoropropylene oxide) Acyl Fluoride

Scheme 3. Initiators Able to Generate either tert-Butoxyl and tert-Butylcarboxyl Radical from tert-Butyl Peroxypivalate (TBPPi) or a Trifluoromethyl Radical from Perfluoro-3ethyl-2,4-dimethyl-3-pentyl Persistent Radical (PPFR)

been studied. In the first one, the HFPO oligomer was then reacted with water to convert the terminal acyl fluoride into a carboxylic acid. The next step deals with the reaction of the acid with a caustic solution of NaOH in ethanol to generate the corresponding sodium carboxylate. The salt was thermally cracked and then distilled resulting in a perfluorovinyl endgroup. If the material is not washed in a weakly basic solution after distillation, such as aqueous ammonium hydroxide, any residue HF will add to the perfluorovinyl end-group resulting in a hydrogen-end-cap (−OCFHCF3). A second alternative to the formation of the vinyl ether end-group is the thermal cracking of trimethylsilyl ester at a minimum temperature of 120 °C. However, if the temperature becomes too high, 2 + 2 cycloadditions can take place with the newly formed perfluorovinyl end-groups. In either method, the perfluorovinylether was characterized by 19F NMR and 13C NMR spectroscopies. Three vinyl fluorine atoms, shown as doublets of doublets, are evident at −117, −124, and −138 ppm in the 19 F NMR spectra (Figures 1 and S1 in the Supporting Information) corresponding to the Fa, Fb, and Fc in the vinyl group, respectively (oligo(HPFO)−OCFcCFaFb). The 13C NMR spectrum (Figure S2) shows a triplet of doublets and a doublet of triplets centered at 148 and 130 ppm assigned to  CF2 and −OCF groups, respectively. Then, the radical copolymerization of VDF with perfluorovinyl-2-(poly(hexafluoropropylene oxide)) perfluoropropyl ether macromonomer (F[CF(CF 3 )CF 2 O] n CF(CF 3 )CF2OCFCF2, oligo(HFPO)−OCFCF2), was initiated either by •C(CH3)3 (from tert-butyl peroxypivalate) or a • CF3 radical (generated from perfluoro-3-ethyl-2,4-dimethyl-3pentyl (PPFR) regarded as a persistent radical at room temperature, Scheme 2). The copolymerizations were carried out under different initiator concentrations and various initial [PPFR]o or [TBPPi]o /([VDF]o + [oligo(HFPO)−OCF

Scherer et al.42 and Ono et al.43 synthesized PPFR persistent radical and also reported that the thermal degradation of PPFR occurred via a β-scission to yield a trifluoromethyl radical and perfluoro-4-methyl-3-ethyl-2-pentene (E/Z forms in 8/3 ratio; Scheme 3). 1,1,1,3,3-Pentafluorobutane,44 1,1,2-trichloro-1,2,2-trifluoroethane, or dimethylcarbonate45 were used as the reaction medium due to their high solubility toward the starting fluorinated monomers and because they do not induce any chain transfer reactions. An effectiveness of the persistent radical has been first attempted for the radical homopolymerization of VDF46 and its copolymerization with a series of different fluorinated monomers.47 However, no study has been reported on the radical copolymerization of VDF with oligo(HFPO)−OCFCF2 macromonomer (Scheme 2). The results are summarized in Table 1. 3.2. Characterization of the Microstructure of PVDF-goligo(HFPO) Graft Copolymers by 1H NMR and 19F NMR Spectroscopy. After purification, the PVDF-g-oligo(HFPO) copolymers were characterized by 1H NMR (Figures 2 and S3− S5) and 19F NMR (Figures 3 and S6−S10) spectroscopy.

Scheme 2. Radical Copolymerizations of Vinylidene Fluoride (VDF) with Oligo(HFPO)−OCFCF2 Macromonomer Initiated by •CF3 Radical Generated by a Perfluorinated Branched Persistent Radical (PPFR) at 90 °C for 14-24 h or by tert-Butyl Peroxypivalate (TBPPi) at 74 °C (EG Stands for End-Group)

F


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Table 1. Experimental Conditions and Isolated Yields for the Radical Copolymerization of VDF with Oligo(HFPO)−OCF CF2 Initiated by tert-Butyl Peroxypivalate (TBPPi) and Perfluoro-3-ethyl-2,4-dimethyl-3-pentyl Persistent Radical (PPFR)a reacn

initiator

pHFPO−CFCF2 (g)

pHFPO−CFCF2 (mmol)

VDF (g)

VDF (mmol)

initiator (g)

initiator (mmol)

isolated yield (g)

1 2 3 4 5 6

TBPPI (63%) TBPPI (63%) TBPPI (75%) PPFR (52%) PPFR (52%) PPFR (52%)

1.911 2.349 0.579 0.747 0.519 0.251

1.549 1.905 0.470 0.606 0.421 0.203

0.310 0.570 1.000 1.500 1.000 0.500

4.841 8.902 15.618 23.427 15.618 7.809

0.027 0.039 0.020 0.017 0.031 0.041

0.097 0.141 0.086 0.019 0.034 0.046

1.9553 2.6088 1.4052 N/A 1.1306 0.5517

a

Reaction conditions: reactions 1−2 used 1,1,1,3,3-pentafluorobutane and dimethylcarbonate; reactions 3−6 used ca. 9 g of 1,1,2-trichloro-1,2,2trifluoroethane; reaction temperature: 74−90 °C; reaction time: 14−24 h; N/A = not available.

complementary. The 19F NMR spectra display the presence of: (i) the characteristic signals assigned to VDF in normal head to tail addition VDF-VDF dyads and reversed head to head dyads at −92 ppm, −113, and −116 ppm, respectively; (ii) the expected signals assigned to oligo(HFPO) chain centered at −80 and −144 ppm, and the signal centered at −110, −120, and −127 ppm assigned to CF2 of VDF and CF2 and CF of macromonomer in the VDF-oligo(HFPO) dyad (Figures 3 and S6−S10). The 1H NMR spectra were used to find the mole relationship between the tert-butyl starting group, arising from the decomposition of TBPPi, to the VDF in the polymer. Once the molar amount of VDF is determined from 1H NMR and the mole% of VDF in relationship with the oligo(HFPO)− OCFCF2 monomer is known from 19F NMR, the molecular weight can thus be determined. The molecular weight using TBPPi as the initiator was assessed using the following equations below.

When observing the characterization data more closely, the H NMR spectra (Figures 2 and S3−S5) of PVDF-goligo(HFPO)−OCFCF2 copolymer displayed the expected broad signals centered at 3.0 ppm (as a quintet) and at 2.4 ppm for the assigned normal (head to tail −CH2CF2−CH2CF2−) and reversed (or tail to tail (−CF2CH2−CH2CF2)) VDF-VDF dyads, respectively. A negligible triplet of triplets centered at 6.3 ppm was also noted and justifies the presence of ∼CH2CF2−H end-group arising from either the transfer to monomer or copolymer or branching.48 The tert-butyl group at the end of the polymer which is used to calculate the moles of VDF in the polymer was evidenced from the signals centered between 0.86 and 1.2 ppm.49 As these copolymers were insoluble in common organic solvents (THF, DMF, chloroform), the determination of the molecular weights was not possible. In addition, appropriate standards for these copolymers are not available. For the same reason, viscosimetry was not used. However, it was of interest to use both 1H and 19F NMR spectra that are 1

mol % of VDF calculated from 19F NMR spectroscopy −96 −111 −117 CF2(VDF) + CF2(VDF) + CF2(VDF)) −90 −109 −113 −111 −117 −125 CF2(VDF) + CF2(VDF) + CF2(oligoHFPO − OCFCF2)) −109 −113 −122

(∫ = (∫

−96

−90

∫

CF2(VDF) + ∫

∫

∫

× 100

∫

mol % of oligo(HFPO)−OCFCF2 = 100 − mol % VDF

average M n copolymer initiated by tert ‐butyl peroxypivalate (TBPPi)

(

g

64 mol × [mol % VDF] + 1230

=

g mol

⎡ ∫ 2.6 CH2 + ∫ 3.3 CH2 ⎤ 2.8 ⎥ × [mol % oligoHFPO−OCFCF2] × ⎢ 2.2 2 ⎦ ⎣

)

1.2

∫0.86 CH3(TBPPi)

g ⎞ ⎛ ⎟ + ⎜2 × 57 ⎝ mol ⎠

18

Figure 3 (as well as Figures S6−S10) exhibits a typical 19F NMR spectrum of copolymers made using VDF and oligo(HFPO)−OCFCF2. First, this spectrum displays the quasi disappearance of the three complex signals assigned to the three fluorine atoms in the trifluorovinyl group of the macromonomer (Figure 1). As expected, the difluoromethylenes of normal head-to-tail and reversed head-to-head VDF-VDF dyads can easily be identified by characteristic signals ranging between −91 and

−96 ppm and −113 and −117 ppm, respectively45−50 while the central position of − CH2CF2−CF2CFO[oligo(HFPO)]− led to a complex signal between −109 and −111 ppm. The characteristic signals assigned to CF2O and CF3 in HFPO units are located between −76 ppm and −88 ppm whereas the peaks centered at −145 and −130 ppm are assigned to tertiary fluorine in the −[CF(CF3)CF2O]− group and difluoromethylene in CF3CF2 at the end of the oligo(HFPO) chain of the macromonomer.51,52 The signals ranging between −122 G


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Macromolecules Table 2. Experimental Conditions and Results for the Radical Copolymerization of VDF with Perfluorovinyl-2(poly(hexafluoropropylene oxide) Perfluoropropyl Ethera VDF(mol %) reaction 1 2 3 4 5 6

mol % initiator b

1.5 1.3b 0.5b 0.1c 0.2c 0.6c

feed (%)

copolymers (%)

yield (%)

Mn (g mol‑1) by 1H/19F NMR

Tm (°C)

Tg (°C)

Td50% (°C)

76 82 97 97 97 97

93 89 98 99 98 98

88 89 89 N/A 74 74

25 000 39 000 77 000 58 000 50 000 45 000

144 138 160 N/A 159 157

−74 −59 −54 N/A −77 −79

410 435 470 475 494 475

a Reaction conditions: reactions 1−2 used 1,1,1,3,3-pentafluorobutane and dimethylcarbonate; reactions 3−6 used ca. 9 g of 1,1,2-trichloro-1,2,2trifluoroethane. btert-Butyl peroxypivalate as the initiator. cPerfluoro-3-ethyl-2,4-dimethyl-3-pentyl persistent radical (PPFR) as the initiator; reaction temperature = 74−90 °C; reaction time= 14−24 h. N/A = not available.

and −124 ppm and −127 and −128 ppm represent the −CF2CF(ORf)CH2− and −CF2CF(ORf)CH2− groups, respectively. Previous work using perfluoromethyl vinyl ether (PMVE) as a model for such a macromonomer, showed expected signals centered at −122.5 and −126.8 ppm representing −CF2CF(ORf)CH2− and −CF2CF(ORf)CH2−, respectively in poly(VDF-co-PMVE) copolymers are also present in a similar manner in PVDF-g-oligo(HFPO) copolymers.53 An additional feature is the presence of characteristic quintet (3JFH = 4JFF = 10 Hz) assigned to trifluoromethyl end-group in CF3−CH2CF2− centered between −60.5 to −62.0 ppm as

noted in previous works (Figure 3).46,47,54 Although it cannot be determined in the NMR spectra (ca. −83 ppm), we believed there are no trifluoromethyl end-groups in CF3-CF2CFO(oligo(HFPO)− or CF3−CF(O(oligo(HFPO)CF2− groups since highly electrophilic •CF3 radical can not react onto electrophilic CF2 and hindered CFO sites of the macromonomer. Since macroradicals terminated by VDF55 recombine exclusively, it can be anticipated that the resulting copolymers contain CF3 group at both extremities, i.e. CF3−PVDF-g-oligo(HFPO)-CF3. Hence, the average molecular weight (Mn) of the polymers can be determined from the following equation:

average M n copolymer initiated by persistent perfluoroalkyl radical (PPFR) ⎡ (∫ −96 CF2(VDF) + ∫ −111 CF2(VDF) + ∫ −117 CF2(VDF)) ⎤ ⎡ (∫ −125 CF2(oligo(HFPO)) ⎤ g g −90 −109 −113 ⎢ ⎥ + 1230 mol × ⎢ −122 2 64 mol × ⎥ 2 ⎦ ⎣ ⎣ ⎦ g ⎞ ⎛ ⎟ = + ⎜2 × 69 −62 ⎝ (∫ CF3(PPFR)) mol ⎠ −60 6

where ∫ −j −iCF2 stands for the integral of the signal assigned to difluoromethylene group centered from −i to −j in the 19F NMR spectrum. The results are listed in Table 2. The radical copolymerization initiated by •CF3 generated from the branched persistent radical (PPFR) led to a 97% yield with a range of molecular weights from 45,000 to 58,000 g·mol−1. Unlike the use of TBPPi where the molecular weight range was 25 000−77 000 g·mol−1. From the 19F NMR spectroscopy, the −96 defects of the polymer can be determined. The ∫ −90 CF2 integral is the normal head-to-tail portion (normal addition in −111 the VDF-VDF dyad) of the VDF, ∫ −109 CF 2 integral corresponds to the VDF units next to the −CF2− backbone of the −CF2CF(oligo(HFPO))− macromonomer unit the oligo(HFPO) macromonomer, while the ∫ −117 −113CF2 integral is the head-to-head portion (or reversed VDF−VDF dyad) of the VDF in the graft copolymer. The reversed amount of VDF− VDF dyad (or defect of chaining) was ca. 5%. 3.3. Polymerization Conditions That Affect Comonomer Incorporation, Yields, and Molecular Weights of PVDF-g-oligo(HFPO) Copolymers. Table 1 summarizes the conditions for the radical polymerization of VDF with the oligo(HFPO)−OCFCF2 macromonomer, and Table 2 provides the yields, molecular weights, and properties of the copolymers such as melting points, decomposition temperature, and glass transitions. Although reactions 1 and 2 were under the same solvent conditions of 1,1,1,3,3-pentafluorobutane and dimethylcarbonate, the molecular weight of the copolymer

increased with a decrease in the amount of TBPPi radical initiator (25,000 to 39,000 g·mol−1). Also, as the VDF mole% feed increased from 76% to 82% respectively, the mole% VDF in the copolymer decreased from 93% to 89%. Using 1,1,2trichloro-1,2,2-trifluoroethane as the solvent and using the same initiator (TBPPi), but increasing the mole% of the initiator, led to a large increase in molecular weight of the final polymer from 25,000 to 77,000 g·mol−1. A higher VDF mole% in the copolymer was also evident, 98% versus 74%. Using a different initiator, PPFR, in the same halogenated solvent (1,1,2trichloro-1,2,2-trifluoroethane) led to a lower molecular weight but higher consumption of oligo(HFPO)−OCFCF2 macromonomer (see Figures S6−S8 versus Figures 3 and S9−S10). The mole% of VDF in the feed and the copolymer remained relatively constant. 19F NMR spectroscopy was useful in identifying changes to the polymer when the amount of PPFR initiator was reduced. As expected, when PPFR concentration was reduced, the molecular weight increased (Table 2). The reactivity rate of VDF was apparent with the type of solvent. VDF was more reactive than the oligo(HFPO) macromonomer when 1,1,1,3,3-pentafluorobutane and dimethylcarbonate were used as the solvents and TBPPi as the initiator. In all other cases with TBPPi or PPFR in 1,1,2trichloro-1,2,2-trifluoroethane, this tendency was not so stressed since VDF only showed a 1−2% increase in the copolymer compared to the original mol % VDF in the feed. H


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achieved by using the persistent radical (PPFR) or the TBPPi initiator with other VDF-based polymers. In particular, the efficiency of this persistent radical was already tested in previous studies.46,47 It was reported that the molecular weights and thermostability of the resulting PVDF homopolymer46 or copolymers of VDF with hexafluoropropylene, trifluoroethylene, 3,3,3-trifluoropropene, and 2-trifluoromethacrylic acid increased with the lower initiator concentration.47 In addition, it was also reported that •CF3 radical’s attack was selective onto the methylene site of VDF, as underlined by Tedder and Walton’s team.56 Within that present study, it was possible to confirm that PPFR initiator was successful to initiate radical copolymerization reactions to form thermostable PVDFg-oligo(HFPO) graft copolymers. As expected, the molecular weight was found to increase with a decrease in the percentage of PPFR initiator (reactions 4−6, Table 2, Figure 5) and that CF3 acted as an original label to determine the number of VDF and oligo(HFPO)−OCFCF2 units.

The yields of the resulting copolymers were generally 88− 89% and 74% using TBPPi and PPFR, respectively. 3.4. Thermal Properties of PVDF-g-oligo(HFPO) Copolymers. In comparison to PVDF or poly(VDF-co-PMVE) copolymers, a significant improvement in Tg and Td values was observed for PVDF-g-oligo(HFPO) copolymers. PVDF has a typical glass transition (Tg) around −40 °C,38 a melting temperature (Tm) of 170 °C, and a decomposition temperature (Td) of ca. 450 °C if Mn > 400 000 g·mol−1.38 Poly(VDF-coPMVE) copolymers (Mn = 1,250 to 24 000 g/mol) have Tg values ranging between −66 and −40 °C53 and Td(10%) varying from 305 to 205 °C, but the PMVE amount copolymerized with VDF was in a much higher percentage (8−46%) than those in the copolymers presented in this article. As seen in Table 2, a higher thermostability (Td50%) values ranged from 475 to 494 °C, Figures S11−S15) was achieved by using PPFR as the radical initiator. The best Td(50%) (470 °C) from TBPPi is shown in Figure 4.

Figure 5. Relationship between molecular weight of PVDF-goligo(HFPO) graft copolymer versus the inverse molar amount of radical initiator: tert-butyl peroxypivalate, TBPPi (blue line), or perfluoro-3-ethyl-2,4-dimethyl-3-pentyl persistent radical, PPFR (red line).

Figure 4. Thermal gravimetric analysis under air of PVDF-goligo(HFPO) graft copolymer (reaction no. 3, in Table 1) initiated by TBPPi, Td (470 °C).

The difference of slopes in both lines may arise from the efficiency of the initiators, or their solubility in the medium, with a higher one for TBPPi. Deeper kinetics studies are required to go further in the understanding of these efficiencies.

Glass transitions temperatures (Tgs) were ranging from −79 to −54 °C (Figures S16−S24), which is even lower than those of poly(VDF-co-PMVE) copolymers brought from the efficient contribution of oligo(HFPO) side chains to lower such values. Melting points (Tm) were also shown to be 138−160 °C (Figures S16−S24) since VDF molar percentages were quite high (89−99%) and support the observation that the higher the VDF molar percentage, the higher the melting temperature. Though a fair amount of oligo(HFPO) macromonomer was incorporated, oligo(VDF) between oligo(HFPO) graft could crystallize and confirm similar behavior as those of poly(VDFco-HFP) and poly(VDF-co-PMVE) copolymers.38 The radical copolymerization of VDF with linear fluorinated ethers was first disclosed by the Dyneon company in 2000.39 However, branched fluorinated ethers such as oligo(HFPO) macromonomers were never used and their work displayed a limited understanding of how the nature of the initiator affected the polymerization and the properties of the polymer. It was shown that the persulfate initiated copolymerization starting from 60 mol % feed of VDF resulted in a copolymer that contained 80 mol % VDF, hence demonstrating a higher reactivity of VDF. It is worth comparing the molecular weight and thermostability of the PVDF-co-oligo(HFPO) graft copolymer

4. CONCLUSIONS For the first time, R-PVDF-g-oligo(HFPO)-R graft copolymers that bear distinct R end-groups were synthesized and characterized. The nature of the end-groups arose from the radical initiator used (either tert-butyl peroxypivalate (TBPPi) or perfluoro-3-ethyl-2,4-dimethyl-3-pentyl persistent radical (PPFR) leading to either C(CH3)3− or CF3− end groups, respectively). These PVDF-g-oligo(HFPO) graft copolymers, as potential thermoplastic elastomers, endowed with very low Tg values (as low as −79 °C), were prepared in satisfactory yields by radical copolymerization of VDF with a trifluorovinyl oligo(hexafluoropropylene oxide) macromonomer, with an almost complete conversion of the oligo(HFPO) macromonomer, especially when using PPFR. Varying solvents and feed amounts of both monomers enabled to control over the copolymer composition by governing the intake of the comonomers. Since the resulting graft copolymers were not soluble in common organic solvents for characterization by size exclusion chromatography (SEC) or viscosimetry, 19F NMR spectroscopy was the most convenient method to determine I


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(6) Sianesi, D.; Pasetti, A.; Belardinelu, G. US Patent 4,451,646, 1969 (assigned to Montefluos). (7) Sianesi, D.; Marchionni, G.; De Pasquale, R. J. Organofluorine chemistry: principles and commercial applications, Banks, R. E., Ed., Plenum Press: New York, 1994; pp 431−460. (8) Tonelli, C.; Gavezotti, P.; Strepparola, E. J. Fluorine Chem. 1999, 95, 51−70. (9) Yohnosuke, O.; Takashi, T.; Shogi, T. European Patent 148,482, 1983 (assigned to Daikin). (10) Slinn, D. S.; Green, S. W. Fluorocarbon fluids for the use in the electronic industry. In preparation, properties and industrial applications of organofluorine compounds, Banks, R. E., Ed., Ellis Horwood Ltd. Publ.: Chichester, U.K, 1982; Vol. 2, pp 45−82. (11) Gilson, R.; Grundy, P. J. Fluorine compound lubrication of thin film magnetic media. In Fluorine in Coatings I Conference; Paint Research Association Ed: Salford, U.K., 1994. (12) Turri, S.; Scicchitano, M.; Tonelli, C. J. Polym. Sci., Part A: Polym. Chem. 1996, 34, 3263−3275. (13) Scheirs, J. Perfluoropolyethers, in Modern Fluoropolymers; Scheirs, J., Ed.; J. Wiley & Sons: New York, 1997; pp 435−483. (14) Scicchitano, M.; Turri, S. J. Fluorine Chem. 1999, 95, 97−103. (15) (a) Priola, A.; Bongiovanni, R.; Malucelli, G.; Pollicino, A.; Tonelli, C.; Simeone, G. Macromol. Chem. Phys. 1997, 198, 1893− 1907. (b) Bongiovanni, R.; Malucelli, G.; Pollicino, A.; Tonelli, C.; Simeone, G.; Priola, A. Macromol. Chem. Phys. 1998, 199, 1099−1105. (c) Bongiovanni, R.; Malucelli, G.; Lombardi, V.; Siracusa, V.; Tonelli, C.; Di Meo, A. Polymer 2001, 42, 2299−2305. (16) Rolland, J. P.; Quake, S. R.; Schorzman, D. A.; Van Dam, R. M.; DeSimone, J. M. J. Am. Chem. Soc. 2004, 126, 2322−2323. (17) Bongiovanni, R.; Medici, A.; Zompatori, R.; Tonelli, C.; Garavaglia, S. Polym. Int. 2012, 61, 65−73. (18) Bongiovanni, R.; Malucelli, G.; Messori, M.; Pilati, F.; Priola, A.; Tonelli, C.; Toselli, M. J. Appl. Polym. Sci. 2000, 75, 651−659. (19) Bongiovanni, R.; Priola, A.; Tonelli, C.; Di Meo, A.; Pollicino, A. React. Funct. Polym. 2008, 68, 189−200. (20) Vitale, A.; Priola, A.; Tonelli, C.; Bongiovanni, R. Polym. Int. 2013, 62, 1395−1401. (21) Tang, C.; Liu, W.; Ma, S.; Wang, W.; Hu, C. Prog. Org. Coat. 2010, 69, 359−365. (22) (a) Marchionni, G.; Spataro, G.; De Pasquale, R. J. J. Fluorine Chem. 1990, 49, 217−24. (b) Moggi, G.; Modena, S.; Marchionni, G. J. Fluorine Chem. 1990, 49, 141−149. (23) Gelin, M. P.; Ameduri, B. J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 160−171. (24) Sianesi, D.; Marracini, A.; Marchionni, G. US Patent 5,258,110, 1993 (assigned to Ausimont). (25) Avataneo, M.; Guarda, P. A.; Marchionni, G.; Maccone, P.; Boccaletti, G. World Patent 2008/1065163, (assigned to SolvaySolexis S.p.A). (26) Avataneo, M.; Navarrini, W.; De Patto, U.; Marchionni, G. J. Fluorine Chem. 2009, 130, 933−937. (27) Sawada, H. Polym. Chem. 2012, 3, 46−65. (28) Ren, Y.; Lodge, T. P.; Hillmyer, M. A. Macromolecules 2001, 34, 4780−4787. (29) Haynes, D.; Naskar, A. K.; Singh, A.; Yang, C. C.; Burg, K. J.; Drews, M.; Harrison, G.; Smith, D. W. Macromolecules 2007, 40, 9354−9360. (30) Wang, W.; Castner, D. G.; Grainger, D. W. Supramol. Sci. 1997, 4, 83−99. (31) Casazza, E.; Mariani, A.; Ricco, L.; Russo, S. Polymer 2002, 43, 1207−1214. (32) Gelin, M. P.; Ameduri, B. J. Fluorine Chem. 2003, 119, 53−58. (33) Yarbrough, J. C.; Rolland, J. P.; DeSimone, J. M.; Callow, J. A.; Finlay, J. A.; Callow. Macromolecules 2006, 39, 2521−2528. (34) Wang, Y.; Betts, D. E.; Finlay, J. A.; Brewer, L.; Callow, M. E.; Callow, J. A.; Wendt, D. E.; DeSimone, J. M. Macromolecules 2011, 44, 878−885. (35) Vitale, A.; Quaglio, M.; Marasso, S. L.; Chiodoni, A.; Cocuzza, M.; Bongiovanni, R. Langmuir 2013, 29, 15711−15718.

their microstructures and molecular weights (molecular weights reached up to 77 000 g·mol−1). These graft copolymers possess interesting thermal properties. The maximum stability measured was 494 °C under air and they also displayed low Tg values that ranged between −79 and −54 °C depending upon the amount of macromonomer in the copolymer. From the data, various features have been highlighted: (1) PPFR was the only initiator to react more completely with the macromonomer; (2) as expected, VDF showed a higher reactivity over the macromonomer, regardless of solvent; (3) the highest molecular weight of copolymer was demonstrated using TBPPi in 1,1,2-trichloro-1,2,2-trifluoroethane; (4) TBPPi enhanced the yields of copolymer 14−15%; (5) the molecular weights of the copolymers increased with a decrease in initiator concentration; (6) PPFR led to copolymers possessing higher decomposition temperatures (475−494 °C).

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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.5b01199. 13 C and 19F NMR spectra of perfluorovinyl-2-oligo(hexafluoropropylene oxide) macromonomer and 1H and 19F NMR spectra of PVDF-g-oligo(HFPO) graft copolymers, TGA analysis thermograms, DSC thermograms of PVDF-g-oligo(HFPO) graft copolymers, and picture of Carius tubes for run 3(PDF)

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AUTHOR INFORMATION

Corresponding Authors

*(C.M.F.) Telephone: +01-604-513-2121 (3220). E-mail: chad. [email protected]. *(B.A.) Telephone: +33-467-144-368. Fax: + 33-467-147-220. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Chaire Balard “Fundation Total” for sponsoring Prof. Chadron M. Friesen’s stay at ICGM, Dr. Taizo Ono from National Institute of Advanced Industiral Scinece and Technology (AIST) for supplying the gift of persistent radical, Dr. Jon Howell from E. I. DuPont for their gift of hexafluoropropylene oxide and 1,1,2-trichloro-1,2,2trifluoroethane (Freon 113), Mr. Thibaut Soulestin for doing additional DSC work, Mr. Gerard Jacob Puts for providing assistance with VDF transfers into frozen Carius tubes, and Dr. Alice van der Ende and Mr. Sebastian Temple for their former works with perfluorovinyl ethers.

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REFERENCES

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