Random Block Copolymers via Segment Interchange Olefin ...

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Random Block Copolymers via Segment Interchange Olefin Metathesis process are electrophilic transition-metal species, the process is best suited for addition-polymerizable, hydrocarbon-based, and olefinic monomers. Our interest was in producing materials with similar block distributions as the OBC materials made by chain shuttling but containing blocks with more pronounced differences in compatibility as compared to OBC. We now report random block copolymers (RBCs) which display a similar distribution of blocks and block lengths as the OBC prepared via chain shuttling. a The new RBCs are prepared via olefin metathesis in a process we call segment interchange. With the advent of olefin metathesis catalysts tolerant to polar functional groups, [4] the block composition of these new materials can be extended to contain polar functionality. Thus, the thermodynamic incompatibility of the blocks can be substantially increased such that the appropriately designed materials spontaneously assemble into ordered structures which persist at temperatures well into the liquid phase of the bulk material. Segment interchange is related to the cross-metathesis (CM) of unsaturated polymers produced by acyclic diene metathesis (ADMET). ADMET is a metathetical stepgrowth polymerization reaction which produces polymers from low molecular weight a, v-terminated diene monomers resulting in polymer product with a regular distribution of unsaturated carbon–carbon bonds with the co-production of ethylene. [5] In the segment interchange olefin metathesis process however, the substrates are base polymers which contain low levels of olefinic unsaturation. Depending on the preparation methods used, the olefinic unsaturation can be randomly distributed along the polymer backbone. The polymer units between the backbone unsaturation are segments and can be much longer than products arising from CM of polymers formed via ADMET. When the two different types of polymers, both with backbone olefinic unsaturation are treated with a compatible olefin metathesis catalyst, the various segments will interchange and, at equilibrium, result in a material with a random distribution of segments coming from both base polymers. The molecular weight of the material is neither significantly less nor greater than the average molecular weight of the reactant polymers. Because the distribution of the backbone unsaturation in the base polymers is random, then the a The OBC and RBC polymers are expected to be comprised of a random assembly of like and unlike segments, each having a most probable weight distribution. The random assembly of segments in the RBC case results from a random distribution of the backbone unsaturation. distribution of blocks in the resulting block copolymer will also be random. Experimental Part Materials Cyclooctene (Aldrich) was distilled over calcium hydride under vacuum and passed through an activated alumina column. Toluene was passed through columns containing activated alumina and Q-5 1 catalyst. Compounds bis(tricyclohexylphosphine) benzylidine ruthenium(IV) chloride and 1,3-bis- (2,4,6-trimethylphenyl)-2-imidazolidinylidene dichloro(phenylmethylene) (tricyclohexylphosphine) ruthenium (Strem), tungsten hexachloride (WCl 6) (Aldrich), and tri-n-butylmethyltin [Sn(n- Bu)3Me] (Gelest, Inc.) were used as received. Butyl vinyl ether was purged with argon and brought into the glovebox. The polyethylene reagent polymer was prepared as previously described. [6] GPC: Mw ¼ 69 kg mol 1 , Mw=Mn ¼ 2.2. 1 H NMR showed there was 0.66 mol-% internal C–C doublebonds. Methods A Haake MiniLab Compounder, Rheomex CTW5 Type 557-2200, with co-rotating screws was used in the melt blend experiments. This unit uses 4–5 g of material and was used with the nitrogen purge to minimize detrimental effects of air on the polymer– polymer metathesis reaction. The chamber was warmed to the desired reaction temperature and calibrated at 100 rpm. Gel Permeation Chromatography (GPC) was performed on an Agilent 1100 Series LC System containing two PLgel 300 7.5 Mixed C columns (5 mm, Polymer Laboratories) kept at 35 8C with tetrahydrofuran (THF) as the eluent. The columns were calibrated with narrow molecular weight polystyrene standards (Polymer Laboratories). Samples for GPC analysis were prepared in THF (1 mg mL 1 ) and run at 1.0 mL min 1 . An Agilent 1100 Series Refractive Index detector was used. Data were analyzed using Agilent Technologies ChemStation GPC Data Analysis Software. Transmission electron microscopy (TEM) was performed with a JEOL JEM-1230 TEM running at an accelerating voltage of 120 kV. The polymer powders were pressed between two glass slides to form a film which was then clamped in a chuck for ultramicrotomy. The films were then polished with a diamond knife using a Leica UC6:FC6 cryo-ultramicrotome at 100 8C and stained with RuO4 vapors for 3 h at room temperature. After staining, thinsections of approximately 90 nm are collected at room temperature. Images are recorded digitally using a Gatan Multiscan CCD camera, Model 749 and postprocessed with Adobe Photoshop CS2 to adjust the contrast and resize the image. The WAXS/SAXS simultaneous differential scanning calorimetry (DSC)/wide and small angle X-ray scattering (WAXS and SAXS) experiments were conducted at the Advanced Photon Source (APS), DND-CAT, 5-ID-D beamline. The standard APS Undulator A was used as the x-ray source, with the x-ray energy set at 15 keV (l ¼ 0.82656 A˚ ). Two-dimensional scattering patterns were collected on a MARUSA, Inc. CCD camera (SAXS), and a Roper Macromol. Rapid Commun. 2008, 29, 1438–1443 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.mrc-journal.de 1439
1440 Scientific CCD camera (WAXS) with data acquisition time set at 1 s. The sample to detector distance was set at 531.9 cm for the SAXS experiments and at 23.01 cm for the WAXS experiments. Twodimensional scattering patterns were reduced to one-dimensional datasets of scattering intensity versus scattering angle by radial integration of the 2-D images, using a data visualization and analysis package developed by Dow on the PV-WAVE platform. Reduction and analysis of the one-dimensional patterns were performed using the commercial software package JADE 1 . Approximately 5–15 mg portions of samples were loaded into aluminum DSC pans. Sample pans were sealed with an aluminum lid. DSC experiments were performed using a Linkam DSC cell. Samples were heated from 20 to 300 8C at108C min 1 , and then cooled back to 20 8C at108C min 1 . WAXS and SAXS patterns were collected simultaneously, during the thermal cycle, at 2 8C intervals. Preparation of Polycyclooctene Reactions were performed in a dry nitrogen atmosphere using a glovebox. A lower molecular weight polymer was prepared by mixing cyclooctene (2.1 g, 0.019 mol) and 1,7-octadiene chaintransfer agent (0.12 g, 0.0011 mol) in 20 mL toluene in a jar equipped with a stir bar. A portion of bis(tricyclohexylphosphine) benzylidine ruthenium(IV) chloride catalyst (0.079 g, 0.096 mmols) was added. The capped jar was heated in a block heater with stirring at 55 8C for 2 h. An aliquot of butyl vinyl ether (1.3 mL) was added to terminate catalyst activity. The jar was removed from the glovebox, and the polymer was precipitated by adding methanol, filtered, and dried under vacuum at 60 8C overnight. GPC: Mw ¼ 8.6 kg mol 1 , Mw=Mn ¼ 2.3. A higher molecular weight polymer was prepared by reducing the catalyst concentration to 0.10 wt.-%. GPC: Mw ¼ 197 kg mol 1 , Mw=Mn ¼ 1.74. Preparation of Polycarbonate The polycarbonate reagent polymer was prepared as previously described. [8] A jacketed reactor was temperature controlled by a water bath at 35 8C. Aqueous alkaline bisphenol-A solution [bisphenol-A (6.2 g, 27 mmol) dissolved in 50 mL of a 1.5 M sodium hydroxide solution] was added to a nitrogen-flushed reactor and stirred at 300 rpm. After 20 mL of dichloromethane was added, the pH was adjusted to 13 ( 0.1) by the addition of 32% aqueous HCl. Within 2 min, 27 mL of the triphosgene solution [4.5 g bis(trichloromethyl)carbonate] in 45 mL dichloromethane was added and the mixture stirred for 30 min. The pH was again adjusted to a value of 9 by the addition of 15% aqueous HCl followed by the addition of 0.46 g fumaryl chloride using a special syringe. After 10 min, the pH was increased to a value of 12.5 by the addition of 20 wt.-% NaOH solution followed immediately by the addition of 10 mL of the terminator solution [para tertiary butylphenol (PTBP) (0.281 g, 1.87 mmol) dissolved in 50 mL dichloromethane]. Within 2 min, 11 mL of the triphosgene solution was added and the mixture stirred for 30 min. Subsequently, 30 mL of triethyl amine solution (2.0 g in 150 mL dichloromethane) and 3 mL of 30% NaOH solution were added and stirred an additional 10 min, during which time the pH-value was kept at 12.5 by the addition of further 20 wt.-% NaOH solution. The lighter aqueous phase was decanted and the mixture was added to a 250 mL separating N. L. Wagner, F. J. Timmers, D. J. Arriola, G. Jueptner, B. G. Landes funnel and mixed vigorously two times with 100 mL of 2 M aqueous hydrochloric acid. The polymer was then washed four times with 100 mL deionized water. The resulting pure polymer solution was added to an aluminum pan and warmed on an electrical heating disk to completely remove the dichloromethane by evaporation. The resulting solid polymer disk was dried at 100 8C at 10 mbar for 12 h. GPC: Mw ¼ 31 kg mol 1 , Mw=Mn ¼ 1.7. 1 H NMR showed there was 10.5 mol-% C–C double bonds. Solution Metathesis Reactions Inside a glovebox, a 50:50 w/w mixture of the low and high molecular weight polycyclooctene polymers was added to a 12 oz jar and dissolved in toluene at 35 8C to make a 5% (g polymer/mL toluene) solution. Bis(tricyclohexylphosphine) benzylidine ruthenium(IV) chloride catalyst (1 mol-% with respect to polymer double bonds) was added. The viscosity of the polymer mixture noticeably decreased within 1 min. The catalyst mixture was stirred for 2 h, taken out of the glovebox, precipitated in methanol, filtered, and dried under vacuum at 45 8C. GPC: Mw ¼ 18 kg mol 1 , Mw=Mn ¼ 2.5. Similarly, either 50:50 or 80:20 w/w of polycarbonate and polyethylene polymers were heated to 105 8C followed by the addition of [1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene] dichloro (phenylmethylene) (tricyclohexylphosphine) ruthenium) (2.8 mL of 4 10 3 M stock solution) and the capped reaction mixture stirred at 105 8C for 1 h. The polymer was isolated as described above. TEM and SAXS analysis were performed on the product. Melt Metathesis Reaction A mini twin-screw extruder was heated to 80 8C at which time 2.5 g each of the low and high molecular weight polycyclooctene polymers were added to the feed chamber. The temperature was increased to 125 8C and the polymers blended at 100 rpm for 10 min under a nitrogen purge. Bis(tricyclohexylphosphine) benzylidine ruthenium(IV) chloride catalyst was added (1 mol-% with respect to polymer double bonds) through the feed chamber. The nitrogen purge was momentarily turned off during catalyst addition. Within 1 min, the viscosity readings on the instrument panel dropped to zero presumably indicating the polymer– polymer metathesis reaction was complete. The melt mixture was blended for 10 min at 125 8C and cooled to room temperature. GPC: Mw ¼ 17 kg mol 1 , Mw=Mn ¼ 2.0. Results and Discussion To demonstrate the viability of this approach, two compositionally identical unsaturated polymers, polycyclooctene, which differ only in molecular weight, were prepared via ROMP. When these two polymers are combined, either in solution with benzylidene-bis(tricyclohexylphosphine)dichlororuthenium or with a tungsten catalyst system, WCl6-(n-C4H9)3SnMe, [7] or in the melt with benzylidene-bis(tricyclohexylphosphine)dichlororuthenium, the bimodal distribution of molecular weights collapses into a single narrow peak that is the weighted average of the starting base polymer molecular Macromol. Rapid Commun. 2008, 29, 1438–1443 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/marc.200800344
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Page 5 and 6: 1442 Figure 2. TEM images of polyet

Random Block Copolymers via Segment Interchange Olefin ...

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