Article pubs.acs.org/Macromolecules
Synthesis and Remarkable Efficacy of Model Polyethylene-graf tpoly(methyl methacrylate) Copolymers as Compatibilizers in Polyethylene/Poly(methyl methacrylate) Blends Yuewen Xu,† Christopher M. Thurber,‡ Timothy P. Lodge,*,†,‡ and Marc A. Hillmyer*,† †
Department of Chemistry and ‡Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States S Supporting Information *
ABSTRACT: Polyethylene-graf t-poly(methyl methacrylate) (PE-g-PMMA) copolymers were prepared using a combination of ring-opening metathesis polymerization (ROMP), hydrogenation, and atom transfer radical polymerization (ATRP). Approximately 20 PMMA side chains per molecule with average degrees of polymerization 6, 12, and 24 were grown via a “grafting from” approach from a Br-substituted linear PE backbone with Mw = 56 000. The resulting graft copolymers were evaluated as compatibilizing agents for binary PE/PMMA homopolymer blends. The roles of PMMA side chain length and different compatibilizer concentration in the polymer blends were investigated, and the mechanical and morphological properties of blends containing 70% PE and 30% PMMA by weight were examined. The presence of the compatibilizer reduced the average PMMA droplet size substantially, even at compatibilizer loadings as low as 1%. Furthermore, the compatibilized blends exhibited significant improvements in elastic modulus, yield strength, and scratch resistance as compared to the binary blends. Adhesion testing confirmed the ability of PE-gPMMA to act as an effective PE/PMMA adhesion promoter. Remarkably, the graft copolymer with the shortest side chains was the most effective compatibilizer. This counterintuitive result is tentatively attributed to kinetic limitations in partitioning of the graft copolymers to the interface.
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merized to yield acrylate/methacrylate grafted polyethylene.29 Schneider et al. reported a quasi-living copolymerization of ethylene and functionalized norbornenes from a catalytic nickel complex, yielding functionalized PE, and in a second step, poly(methyl methacrylate) was grafted onto the backbone.30 In another example, chemical modification of poly(cis-cyclooctene) (PCOE) by hydrobromination and subsequent graft copolymerization gave a poly(ethylene)-g-poly(tert-butyl acrylate).31 In a recent study, Song et al. prepared a hydroxyl functional poly(propylene-co-ethylene) by reactive extrusion, and then PMMA was grafted by reversible addition− fragmentation chain transfer polymerization (RAFT).32 Although some synthetic advances have appeared, very limited information on the use of these materials as compatibilizers or adhesion promoters has been disclosed. Herein, we combine the advantages of ring-opening metathesis polymerization (ROMP) and controlled radical polymerization (CRP) to prepare well-defined polyethylenegraf t-poly(methyl methacrylate). ROMP allows for the synthesis of linear polymers with controlled architectures as well as hybrid polymers bearing one or more functional groups capable
rom packaging to building materials and automotive parts, polyolefins are utilized on a huge scale.1,2 The broad utility of polyolefins is due in part to their remarkable resistance to harsh environments stemming from their simple aliphatic nature.3,4 However, polyolefins exhibit relatively low compatibility and poor adhesion with other polar polymers, and this limits even broader applicability.5−8 Compatibilizers can be used to improve the properties of polyolefin blends with polar polymers. Block or graft polymers are effective compatibilizers that improve interfacial adhesion between two immiscible components in a binary blend and have proven to be very effective in the preparation of next generation of advanced polymeric materials.9−28 The use of graft copolymers as compatibilizers offers unique advantages for studying properties of heterogeneous polymer blends. They have been found to localize at the interface, reduce interfacial tension, and enhance adhesion between phases.15 Nevertheless, reports relating to poly(acrylate/ methacrylate) grafted polyolefins for compatibilizing poly(acrylate/methacrylate)/polyolefin blends are rare, although such blends are of clear technological interest. In one example, Inoue et al. employed a metallocene catalyst to copolymerize ethylene and 10-undecen-1-ol. The alcohol groups were later converted to atom transfer radical polymerization (ATRP) initiators, and acrylates and methacrylates were then poly© 2012 American Chemical Society
Received: October 19, 2012 Revised: December 4, 2012 Published: December 12, 2012 9604
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Scheme 1. Synthesis of PE-Br Macroinitiator and PE-g-PMMAa
a Reagents and conditions: (i) G2, cis-4-octene, CHCl3, 40 °C; (ii) TsNHNH2, o-xylene, 140 °C; (iii) MMA, CuBr, PMDETA, toluene, 100 °C. αbromoisobutyrate 3-COE was prepared from a reported procedure.54
geometry was utilized. Polymer samples were pressed into films (∼1 mm) by compression molding and then mounted on an aluminum puck. A normal force was applied on the polymer surface at a constant rate of increase with respect to distance (from 0 to 40 mN). The indenter moved on the surface laterally for 600 μm, and the force was first applied at the distance of 100 μm. Adhesion Test. 180° peel tests were performed to investigate the capabilities of synthesized graft copolymers as adhesion promoters. The MINIMAT tensile tester was also utilized in this experiment. PMMA and PE were pressed into films by compression molding at 210 °C. PMMA films were dipped into a solution of benzene containing PE-g-PMMA for a few seconds and then air-dried. The coated PMMA film and a premade PE film were pressed into bilayer and laminated for 120 s at 180 °C.49,50
of initiating another polymerization.33−38 Also, like ROMP, most CRP methods are functional group tolerant and thus can be useful for the polymerization of various monomers.39−48 In this manner, we developed a route to polyethylene containing α-bromoisobutyrate groups by ROMP and hydrogenation, and then graft copolymers were synthesized from the macroinitiator by ATRP. The graft copolymers were utilized as compatibilizers in highly incompatible PE/PMMA blends. The morphology and material properties of these blends were explored, and the utility of PE-g-PMMA as an adhesion promoter was assessed.
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EXPERIMENTAL SECTION
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Materials and Molecular Characterization. Polyethylene (LLDPE, Exxon LL 3003) and PMMA (Plexiglas MI-7) homopolymers were provided by Exxon and Altuglas International, respectively. cis-Cyclooctene (95%) purchased from Acros Organics for monomer synthesis was purified by vacuum distillation. Grubbs’ catalyst second generation (G2) was used as received from Sigma-Aldrich. Chain transfer agent cis-4-octene (97%) was purchased from GFS Chemicals and purified by vacuum distillation. Methyl methacrylate (MMA) was purified by passing through a neutral alumina column to remove any stabilizer and dried over molecular sieves. CHCl3 for polymerization was purified by passing thorough a basic Al2O3 plugged column and distillation over CaH2 prior to polymerization. Toluene for ATRP polymerization was refluxed over sodium/benzophenone and distilled under nitrogen before use. Other chemicals were used as received. 1H and 13C NMR spectra were recorded on Varian Inova 300/500 spectrometers, respectively. Polymer molar mass distributions were measured using a high-temperature SEC system PL-GPC 220 (Agilent Systems) with 1,2,4-trichlorobenzene as the mobile phase (1.0 mL/ min at 135 °C). The column was calibrated with polystyrene standards. Differential scanning calorimetry was conducted on a TA Instruments Discovery Series DSC. Preparation of PE/PMMA Blends. Polymer blends were prepared using a recirculating, conical twin-screw extruder (DACA Instrument, 4 g capacity) at 150 rpm and a temperature of 210 °C. For compatibilized blends, the graft copolymer was introduced simultaneously with the PE and PMMA homopolymers and mixed for 5 min before blends were extruded and collected. Scanning Electron Microscopy (SEM). All polymer blends were subjected to cryo-microtoming at −140 °C and sputter-coated with platinum (100 Å thickness) prior to SEM analysis. SEM images were taken with JEOL 6500 and 6700 scanning electron microscopes. Particle size analysis was performed with ImageJ software. Tensile Test. Tensile properties were investigated using a MINIMAT tensile tester (Rheometric Scientific) with an extension rate of 1 mm s−1. PE, PMMA, and blended materials (with and without graft copolymer added) were processed by compression molding into dogbone shapes (12 mm gauge length, 0.5 mm gauge thickness, 3 mm gauge width). All samples were dried in a vacuum oven at room temperature overnight before tensile testing. Nanoscratch Test. A Nano Indenter (MTS System Co.) was used to perform scratch tests. A diamond indenter with 90° conical
RESULTS AND DISCUSSION Preparation of PE-Br Macroinitiator. The linear polyethylene multifunctional macroinitiator was prepared by ROMP of cis-cyclooctene (COE) and α-bromoisobutyrate functionalized cis-cyclooctene (3-BrI-COE), with subsequent hydrogenation of the resulting polycyclooctene copolymer (poly(COE-co-BrCOE)). The molar mass of the resulting poly(COE-co-BrCOE) was controlled by utilizing cis-4-octene as a chain transfer agent (CTA) with ([COE] + [3-BrI-COE])/ [CTA] = 150. At the low catalyst loadings used (([COE] + [3BrI-COE])/:[Ru] ≈ 4000), the initiating fragments from the catalyst should have very little impact on the number-average degree of polymerization.51 Subsequent chemical hydrogenation of poly(COE-co-BrCOE) using p-toluenesulfonhydrazide successfully yielded the linear polyethylene macroinitiator (Scheme 1).52,53 Approximately 9.1 mol percent bromoester group was incorporated into the polyethylene backbone (x:y = 1:10.1, Figure S1). The 1H NMR spectrum of PE-Br shows a broad signal at 1.36 ppm assigned to the polyethylene backbone, a pentet at 5.04 ppm characteristic of a methine proton adjacent to an ester group, and the methyl end group from the CTA (−CH3) as a triplet at 0.89 ppm (Figure 1a).29,30 1H NMR end-group analysis revealed that PE-Br macroinitiator possessed a number average molar mass (Mn) of 30 kg mol−1, which indicates that ∼21 bromoester initiating groups are distributed along each polymer chain. With a ROMP reaction time of 20 h and a molar mass dispersity of 2.0 (Table 1), we expect that the monomer sequence distribution (bromoester initiating groups) should be randomized along the polymer backbone through secondary metathesis.55 Polyethylene is a semicrystalline polymer at ambient temperatures with a typical melting temperature range of approximate 60−130 °C, depending on the branching and/or density of material.3 The ROMP of COE and 3-BrI-COE and 9605
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Figure 2. Differential scanning calorimetry (DSC) thermograms of macroinitiator and graft copolymers. The heating portion represents the second heating cycle after the thermal history of samples was standardized by first heating to 200 °C followed by cooling to −85 °C at 10 °C min−1 and then heating to 200 °C at 10° min−1.
The degree of polymerization on each PMMA graft site was controlled by varying the polymerization time and determined by 1H NMR spectroscopy, assuming 100% initiation efficiency for each bromoester. The total molar masses of the graft copolymers were further analyzed by high-temperature SEC in 1,2,4-trichlorobenzene at 135 °C (Table 1). These three graft copolymers were selected as candidates for compatibilizers, since their molar masses were comparable with PE and PMMA model systems used in this study. The graft copolymer structure was confirmed by 1H NMR spectroscopy (Figure 1b). The signal of PE segments remained at the same chemical shift (1.36 ppm) after grafting, as a broad peak. The signals associated with −OCH3, −CH2−, and −CH3− in the PMMA grafts appeared at 3.4−3.5, 2.0, and 1.2 ppm, respectively.29,30 More than one signal was observed for the ester methyl resonance at 3.4−3.5 ppm due to the enhanced syndiotacticity of PMMA prepared by ATRP.57,58 Absorptions at 1730 and 1150 cm−1 in the infrared spectrum correspond to the stretching modes of ν(CO) and νa(C− O−C) in the methyl methacrylate functionality (Figure S9).59,60 With increasing amounts of methyl methacrylate grafted onto the PE backbone, the graft copolymer displayed improved solubility in chloroform, dichloromethane, and toluene. Thermal Characteristics of the Graft Copolymers. After grafting methyl methacrylate on the PE backbone, decreased PE crystallinity was observed, as summarized in Table 1 (32%, 19%, and 2% based on PE content for PE-g-PMMA-6, PE-gPMMA-12, and PE-g-PMMA-24, respectively). The glass
Figure 1. (a) 1H NMR spectrum of PE-Br macroinitiator. (b) Representative 1H NMR spectrum of a graft copolymer (PE-g-PMMA12). Toluene-d8 at 95 °C; asterisk denotes signals from the solvent.
subsequent hydrogenation resulted in the PE-Br macroinitiator with a melting transition (Tm,E) at 111 °C and a degree of crystallinity (XE) of 39% (calculated from XE = ΔHm/ΔH0m, ΔH0m = 293 J g−1; Figure 2).3,56 Preparation of PE-g-PMMA. The PE-Br had limited solubility in common organic solvents, and thus we performed the ATRP in toluene at elevated temperature (100 °C). The initial MMA monomer concentration was limited to 0.9 M to avoid any gel formation.29 Grafting from the PE macroinitiator was conducted using [MMA]0/[I]0/[CuBr]0/[PMDETA]0 = 200/1/1/1. Under these conditions, conversion of monomers proceeded to ∼50% after 18 h (Figure S10). The characteristics of the polymers used are collected in Table 1. Table 1. Polymer Molecular Characteristics sample
Mna (kg mol−1)
Mwa (kg mol−1)
Đa
Tm (°C)
PE PMMA PE-Br PE-g-PMMA-6d PE-g-PMMA-12 PE-g-PMMA-24
50 45 28b 34 40 50
199 81 56 62 77 88
3.9 1.8 2.0 1.8 1.9 1.8
124
Tg (°C)
Tc (°C)
XEc (%)
114
43
102 101 97 76
39 32 19 2
104 111 112 109 112
124 122
Measured using an RI detector on an SEC instrument with 1,2,4-trichlorobenzene at 135 °C. bMn = 30 kg mol−1 from 1H NMR end-group analysis. XE = degree of crystallinity, calculated based on PE content. dNumbers after dash (6, 12, and 24) indicate the degree of polymerization of graft chains. PMMA wt % in copolymers are 29.6%, 45.7%, and 62.7% for PE-g-PMMA-6, PE-g-PMMA-12, and PE-g-PMMA-24, respectively. a c
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copolymer samples, the PMMA domain sizes were significantly reduced. Interestingly, the polymer blend with the shortest side chain copolymer (PE-g-PMMA-6) adopted the smallest domain size (dn = 2.3 μm, Figures 3 and 4a), and the domain size increased with the increasing side chain length of graft copolymer. As the side chain became longer, the dispersed PMMA phases also adopted more irregular shapes (Figure 3b− d). It is plausible that the graft copolymer with relatively short side chains possesses more chain mobility and is more apt to localize at the interface at the time scale of melt blending. As a consequence, it anchors the two phases more effectively and improves compatibility.63 On the other hand, if the side chain length was extremely short (as with the PE-Br), one might expect that the two phases would not be anchored efficiently by the compatibilizer. Nevertheless, some compatibilization effect was observed even using PE-Br (Figure 4a and Figure S15). Since the graft copolymer with shortest side chains gave the most homogeneous dispersion and smallest PMMA particle size, we investigated the impact of the amount of graft copolymer (PE-g-PMMA-6) on the morphology of the PE/ PMMA blends. Figure 4b illustrates that increasing the amount of PE-g-PMMA-6 in the polymer blend (1, 2.5, and 5 wt %) does not dramatically reduce the domain size.64 Significant particle size reduction was achieved with an addition of as little as 1 wt % of this graft copolymer. Modulus and Yield Strength. Tensile tests were performed to evaluate the mechanical properties of the blends and the impact of added compatibilizer. Compatibilizers can improve the mechanical properties of polymer blends both by reducing interfacial tension and by enhancing adhesion between two immiscible components.62,65−72 As expected, the polymer blends exhibited noticeable increases in elastic modulus and yield strength upon addition of graft copolymer (Table 2) as compared to PE and the uncompatibilized blend. The yield strength of the blend containing 5% PE-g-PMMA-6 surpassed the uncompatibilized blend by nearly 100% (Figure 5a). As a control, the PE-Br macroinitiator (5 wt %) was blended with PE/PMMA (70/30), and its mechanical behavior was also tested. Modulus and yield strength were increased as compared to the PE/PMMA (70/30) blend, however, not nearly as significantly as those with graft copolymers. This slight property improvement was attributed to a reduction in
transition temperature of PMMA (Tg,M) occurred between 122 and 124 °C and was only observed for the PE-g-PMMA-12 and PE-g-PMMA-24 samples. The relative magnitude of crystallinity (XE) and glass transition (Tg,M) for graft copolymers was consistent with the compositional change (degree of polymerization of graft chains) observed from SEC and 1H NMR spectroscopy.
Figure 3. Scanning electron microscope images of different blends. Scale bar represents 10 μm.
Morphology of PE/PMMA Blends. PE/PMMA (70/30) blends formed unevenly dispersed droplets of PMMA (number-average particle diameter dn = 8.1 μm; dn = ∑nidi/ ∑ni) in the PE matrix (Figure 3a), characteristic of a low level of compatibility.61,62 Upon addition of the PE-g-PMMA
Figure 4. Average particle size for (a) PE/PMMA (70/30) blend and that with various copolymers added as compatibilizers (5 wt % for each) and (b) PE/PMMA (70/30) blended with PE-g-PMMA-6 at different mass ratios. Approximately 150 particles were measured for each blend; a relatively large standard deviation for the uncompatibilized blend is likely due to particle coalescence. 9607
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distance of 100 μm. The force increased linearly as the indenter moved laterally for another 500 μm. The PE/PMMA (70/30) blend presented a significantly lower resistance to scratching as indicated by depth of the scratch at a scratch length of 600 μm. By introducing the graft copolymer as a compatibilizing agent into polymer blends (PE-g-PMMA-6, 1% weight ratio), better resistance to the applied force was observed (Figure 6). It was
Table 2. Modulus and Yield Strength for the Homopolymers and Blends sample PMMA PE PE/PMMA (70/30) PE/PMMA/PE-Br (70/30/5) PE/PMMA/PE-gPMMA-24 (70/30/5) PE/PMMA/PE-gPMMA-12 (70/30/5) PE/PMMA/PE-gPMMA-6 (70/30/5)
modulus (MPa) 2100 106 155 202
± ± ± ±
76 9 14 18
yield strength (MPa) 63 10 7.2 8.4
± ± ± ±
1.3 0.4 0.2 0.2
elongation at break (%) 49 1280 620 610
± ± ± ±
9 55 43 39
240 ± 15
11 ± 0.7
121 ± 10
250 ± 18
13 ± 0.2
110 ± 21
255 ± 15
14 ± 0.3
96 ± 9
interfacial tension because of the polar bromoester group along the polyethylene macroinitiator backbone. The PE-g-PMMA-6 was selected and blended with PE/ PMMA (70/30) at 1%, 2.5%, and 5%. Upon addition of the compatibilizing agent, both modulus and yield strength were improved as shown in Figure 5b. The modulus increased by 32% with as little as 1 wt % of this graft copolymer added, suggesting that only a trace amount of compatibilizer is necessary for significant property improvements. Nanoscratch Tests. There has been a long-standing need to improve the scratch resistance of polyolefins in applications where surface quality control is crucial. Some studies have attempted to correlate scratch behavior and material properties in polymeric materials.73−76 Properties such as Young’s modulus, yield strength, and friction coefficient were found to be responsible for determining scratch resistance. In this study, the friction coefficient refers to that between PE/PMMA blends and the diamond indenter; the compatibilizers should have more impact on the elastic modulus and yield strength of blends as compared to the friction coefficient. Shear yielding is the main damage mechanism during scratching for elastomers,32 and this correlates with our observations; better scratch resistance was observed in blends that possessed higher modulus and yield strength. A certain level of modulus may build rigidity in the polymer blend and maintain a small scratch depth when the material is subjected to plastic flow scratch damage; a high yield strength is believed to reduce the yield zone size that also leads to smaller plastic flow scratch damage.73 In this nanoscratch test,77−83 a conical tip was pressed into the polymeric sample and a normal force was applied at a lateral
Figure 6. Penetration depth vs scratch distance in nanoscratch tests of PE, PMMA, PE/PMMA binary blends, and PE/PMMA blends with 1% PE-g-PMMA-6 graft copolymer.
also found that the graft copolymer with shorter side chains exhibited better improvement in scratch resistance, again suggesting an improved compatibilization effect. As a control study, the scratch resistance of polymer blends with an addition of PE macroinitiator was also investigated, which showed almost as weak resistance as unblended polyethylene (Figure S20a). We also examined the effect of weight ratio of graft copolymer on the scratch resistance of the polymer blends (Figure S20b). It appeared that by incorporating more PE-gPMMA-6 in the blends (1%−5%) the scratch resistance did not increase significantly. Thus, a small amount of graft copolymer in the polymer blends appeared to be sufficient to reduce debonding and cracking of the scratched polymer surface. Adhesion. Because of the incompatibility of polyolefins and PMMA, the interfacial width between them should be small; consistent with this, virtually no adhesion between poly(propylene-co-ethylene) and poly(methyl methacrylate) was observed by Song et al.32 To test our material, we first examined PE-Br coated on a PMMA film for 180° peel test as a
Figure 5. (a) Representative stress−strain curve of PE/PMMA (70/30) binary blend and PE/PMMA/PE-g-PMMA-6 (70/30/5). (b) Modulus and yield strength for PE/PMMA (70/30) blended with PE-g-PMMA-6 at different mass ratios (1, 2.5, and 5%). 9608
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control. The adhesion value reached 42 N m−1; this slight improvement can be attributed to the polar bromoester group on the polyethylene backbone, as noted previously. However, when graft copolymers were coated on PMMA, the adhesion between PE and PMMA exhibited a significant enhancement. The greatest enhancement was achieved when PE-g-PMMA-6 was applied, with a peel strength of 376 ± 29 N m−1. As the side chain length increased, the adhesion between two polymers decreased. We hypothesize that the graft copolymer with the shortest side chains was capable of inducing a larger interfacial width between the two polymers, thereby leading to enhanced adhesion; this is consistent with the reduced droplet size in Figures 3 and 4. As with the mechanical properties, we speculate that the PE-g-PMMA-6 was better able to migrate to the interface more effectively on the time scale of lamination (120 s) due to higher mobility. Such a result was consistent with our previous observations, as the PE-g-PMMA-6 leads to the most promising material properties. Nevertheless, it is remarkable that such short, oligomeric side chains can have such a profound beneficial effect.
polymer blends. The performance of this material as an adhesion promoter was also evaluated, and it exhibited great potential in bridging incompatible polyolefins and polar polymers.
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ASSOCIATED CONTENT
S Supporting Information *
Synthetic procedures of all polymers prepared, 1H NMR, 13C NMR, and FTIR spectra, kinetic plots of ATRP polymerization, complete SEM images of all blends used, and representative stress−strain curves. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected] (T.P.L.);
[email protected] (M.A.H.). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was funded by The Dow Chemical Company. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program (Award DMR-0819885). We acknowledge Dr. Louis Pitet for his work on αbromoisobutyrate functionalized COE monomers. We also thank Zhen Ren for some assistance in SEM and Prof. Chris Macosko and Dr. Craig Silvis for helpful insights into this project.
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REFERENCES
(1) Piringer, O. G.; Baner, A. L. Plastic Packaging: Interactions with Food and Pharmaceuticals, 2nd ed.; Wiley-VCH: Berlin, 2008. (2) Coates, G. W. Chem. Rev. 2000, 100, 1223. (3) Peacock, A. J. Handbook of Polyethylene: Structure, Properties, and Applications; Marcel Dekker, Inc.: New York, 2000. (4) Chu, J.; Xiang, C.; Sue, H. J.; Hollis, R. D. Polym. Eng. Sci. 2000, 40, 944. (5) Kobayashi, S.; Song, J.; Silvis, H. C.; Macosko, C. W.; Hillmyer, M. A. Ind. Eng. Chem. Res. 2011, 50, 3274. (6) Song, J.; Ewoldt, R. H.; Hu, W.; Silvis, H. C.; Macosko, C. W. AIChE J. 2011, 57, 3496. (7) Boaen, N. K.; Hillmyer, M. A. Chem. Soc. Rev. 2005, 34, 267. (8) Chung, T. C. Functionalizaiton of Polyolefins; Academic Press: New York, 2002. (9) Jung, W. C.; Park, K. Y.; Kim, J. Y.; Suh, K. D. J. Appl. Polym. Sci. 2003, 88, 2622. (10) Cassu, S. N.; Felisberti, M. I. J. Appl. Polym. Sci. 2001, 82, 2514. (11) Torres, N.; Robin, J. J.; Boutevin, B. J. Appl. Polym. Sci. 2001, 81, 2377. (12) Gersappe, D.; Irvine, D.; Balazs, A. C.; Liu, Y.; Sokolov, J.; Rafailovich, M.; Schwarz, S.; Peiffer, D. G. Science 1994, 265, 1072. (13) Lee, Y.; Char, K. Macromolecules 1994, 27, 2603. (14) Norton, L. J.; Smigolova, V.; Pralle, M. U.; Hubenko, A.; Dai, K. H.; Kramer, E. J.; Hahn, S.; Berglund, C.; Dekoven, B. Macromolecules 1995, 28, 1999. (15) D’Orazio, L.; Guarino, R.; Manchrella, C.; Martuscelli, E.; Cecchin, G. J. App. Polym. Sci. 1997, 66, 2377. (16) Jannasch, P.; Wesslen, B. J. Appl. Polym. Sci. 1997, 65, 2141. (17) Dong, L.; Xiong, C.; Wang, T.; Liu, D.; Lu, S.; Wang, Y. J. Appl. Polym. Sci. 2004, 94, 432. (18) Charoensirisomboon, P.; Inoue, T.; Weber, M. Polymer 2000, 41, 6907.
Figure 7. Peel force/sample width for adhesion between PE and PMMA. PE-Br and PE-g-PMMA were coated on the PMMA film. PE and coated PMMA films were pressed and laminated for the 180° peel test.
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CONCLUSIONS Polyethylene-graf t-poly(methyl methacrylate) copolymers were prepared by combining ROMP of cis-cyclooctene and αbromoisobutyrate functionalized cyclooctene and ATRP of methyl methacrylate. ROMP was performed first, and subsequent hydrogenation gave a polyethylene macroinitiator with control of molar mass in the presence of a chain transfer agent. ATRP of methyl methacrylate monomers resulted in a copolymer with polar segments grafted on the nonpolar semicrystalline polyethylene chain. This strategy has relevance in controlling crystallinity as well as in developing nanostructured graft copolymers with controlled side chain lengths and molar masses. These graft copolymers were further employed as compatibilizers for highly incompatible PE/ PMMA blends. Material properties such as dispersed phase droplet size, elastic modulus, yield strength, and scratch resistance revealed significant improvements in the presence of this graft copolymer. The graft copolymer with the shortest side chains studied displayed the most promising behavior. This compatibilizer was found to be very efficient, in that it exerted a significant positive effect at as low as 1% mass ratio in the 9609
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dx.doi.org/10.1021/ma302187b | Macromolecules 2012, 45, 9604−9610
