Terminal Anhydride Functionalized Polystyrene by Atom Transfer Radical Polymerization Used for the Compatibilization of Nylon 6/PS Blends
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6242 Macromolecules 1999, 32, 6242-6248 Terminal Anhydride Functionalized Polystyrene by Atom Transfer Radical Polymerization Used for the Compatibilization of Nylon 6/PS Blends E. G. Koulouri and J. K. Kallitsis* Department of Chemistry, University of Patras, 265 00 Patras, Greece G. Hadziioannou Department of Polymer Chemistry, Materials Science Center, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands Received January 21, 1999; Revised Manuscript Received July 2, 1999 ABSTRACT: Terminal maleic anhydride functionalized polystyrenes were synthesized using atom transfer radical polymerization (ATRP). The functionality of these polymers was determined through their reaction with poly(ethylene glycol methyl ether) (PEGM) followed by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR). Melt mixing of these reactive polystyrenes with nylon 6 resulted in blends with good mechanical properties attributed to an in situ formation of a copolymer which may be used for the compatibilization of the binary nylon 6/polystyrene. The mechanical properties of the resulting ternary blends were significantly improved with the addition of the modified polystyrene even when the molecular weight of the polystyrene used was higher than that of the respective block in the copolymer. The enhanced mechanical properties, as well as the fine PS dispersion in the nylon 6 matrix revealed by scanning electron microscopy of the compatibilized cryofractured samples, support the hypothesis that an effective compatibilization of nylon 6/PS has been achieved. Introduction termination reactions, many attempts have been made 9-14 Terminal functionalization of polymers represents an to convert radical polymerizations into living ones. interesting field of research because of their macromer Wang and Matyjaszewski reported on a “living”- character and their potential applications in several controlled radical polymerization technique, the atom technological areas, such as surface modification, adhe- transfer radical polymerization (ATRP),15-16 in which sion, lubrication, and compatibilization of polymer a catalytic amount of a Cu(I) coordination complex blends.1 These polymers can undergo chain extension reversibly abstracts an X atom (X ) Cl, Br) from the by reaction with other polymers or monomers having polymer chain ends, converting them from a dormant proper counterfunctional groups. An in situ formation to an active propagating state. Of course in this tech- of a block copolymer consisting of these functionalized nique as well as in every radical polymerization, com- polymers and another polymer bearing proper terminal plete elimination of termination reactions is not pos- groups is also possible during blending. Of the reactive sible, so it is referred to as “living” in quotations.17 pairs investigated, the ones based on the reaction of However, well-defined polymers with predetermined amines with anhydrides exhibit sufficiently fast kinetics molecular weights, low polydispersities, and terminal in the melt state to provide technologically useful, functionalities as well as block copolymers can be compatibilized polymer blends.2-5 prepared via ATRP. Various approaches for the terminal functionalization The blending of polymers for production of new tailor- of polystyrenes have been published. Among them made materials at low cost and for recycling mixed Takenaka et al. have reported a method for the syn- polymeric materials has gained great interest in recent thesis of anhydride-terminated polystyrenes and poly- years. Polyamide 6 (nylon 6) and polystyrene (PS) are dienes involving a Diels-Alder addition of maleic commodity polymers each with unique properties. Thus, 6 anhydride to a diene-terminated polymer. Park et al. a nylon 6/PS blend is expected to have commercial reported on the synthesis of hydroxy-terminated PS and interest because it could provide a combination of the subsequent esterification with trimellitic anhydride useful properties of its constituents. In practice, it is chloride (TMAC), resulting in polystyrenes having difficult to obtain such blends with good performance 7 terminal anhydride groups. Most recently Cernohous because of the immiscibility of the blend components. et al. succeeded in synthesizing polystyrene bearing a Therefore, studies aimed at enhancing the compatibility single succinic anhydride at the chain end using anionic between nylon and PS have been carried out by various 8 polymerization techniques. research groups. Most of them deal with functionalized Radical polymerizations are important for the indus- styrene copolymers capable of reacting with amine end trial production of commodity polymers but are still very groups of the polyamide during melt mixing. The result difficult to control because of the fast, irreversible is an in situ formed compatibilizer having nylon grafts termination of the growing radicals through coupling or blocks. Reactive styrene copolymers with anhy- and disproportionation reactions. Because of these drides,18-20 acrylic acid,21 ethylene oxide,22 methacrylic acid,2 glycidyl methacrylate,23 or sulfonic acid24 have * To whom correspondence should be addressed. been investigated. 10.1021/ma990087c CCC: $18.00 © 1999 American Chemical Society Published on Web 08/26/1999 Macromolecules, Vol. 32, No. 19, 1999 Terminal Anhydride Functionalized Polystyrene 6243 Scheme 1 n n Table 1. GPC Characterization of Synthesized The compositions of the binary blends prepared under these Polystyrenes conditions were 95/5, 90/10, 85/15, 80/20, and 75/25 nylon sample M M I (M /M ) 6/maleic anhydride terminated PS. Ternary blends of 75% n w w n nylon 6 with 25% PS and maleic anhydride terminated PS PS-18 18 100 21 300 1.18 were also prepared. The maleic anhydride terminated PS PS-15 15 200 17 600 1.16 varied from 0 to 15% in the blends. Since PS had very poor PS-13 12 700 14 900 1.17 mechanical properties, the selected compositions were those PS-11 11 300 13 400 1.19 of a high concentration of nylon 6 so as to certify the latter as PS-6 6000 7000 1.17 the matrix. Although these compositions are not typical for PS-3 2500 2800 1.13 studying the compatibilization effect, they were selected in order to explore the limits of the increase of the ultimate In this article, we describe the synthesis of polysty- properties. Films were made by compression molding between renes functionalized with maleic anhydride by ATRP Teflon sheets at 250 °C and 70 kg cm-2, pressure release, and and their subsequent reaction with polyamides in the quenching to 0 °C. melt, aiming at the formation of a potential compatibi- Polymer and Blend Characterization. Molecular weights lizer for the incompatible nylon 6/PS blends. The ef- of the polymers were determined by GPC with a refractive fectiveness of the functionalization was determined with index detector using chloroform as eluent and PS standards GPC and NMR after derivatization with PEGM. Char- for calibration. acterization of the blends prepared was performed using SEM was carried out with a JEOL 6320 F field emission dynamic mechanical analysis (dma), tensile testing, scanning electron microscope on cryofractured and etched specimens. differential scanning calorimetry (dsc), scanning elec- Dsc measurements were carried out in an inert atmosphere tron microscopy (SEM) and Fourier transform infrared using the DSC plus of Rheometrics Scientific. Sample weight spectroscopy (FTIR) as well as extraction experiments. was ca. 10 mg and heating rate 10 °C min-1. Samples were heated to 250 °C and quenched to -50 °C, followed by heating Experimental Section to 250 °C. The second heating run was recorded. Tensile tests were performed according to ASTM D882 at Materials. Styrene (Merck) was washed with 5% NaOH in 23 °C using a J.J. Tensile Tester type T5001 and film strips order to remove the stabilizers, followed by distillation over with dimensions 4.0 cm × 0.65 cm × 0.025 cm. Data reported finely powdered CaH before polymerization. Diphenyl ether 2 were obtained at a cross-head speed of 10 cm.min-1. (Merck), used as solvent, was stored over molecular sieves and purged with argon for 30 min before polymerization. Maleic Dynamic mechanical analysis was performed with a solid- anhydride (Merck) was recrystallized twice from dry chloro- state analyzer RSA II, Rheometrics, at 10 Hz. Specimen × × 3 form. CuBr (Aldrich) was purified according to the literature dimensions were 3.0 0.5 0.01 cm . procedure.25 R,R′-Dibromo-p-xylene (Acros) was recrystallized FTIR spectra were obtained using a Perkin-Elmer 1600 from toluene, and 2,2′-bipyridine (bipy) (Merck) was used as spectrometer. received. Extraction experiments were performed in chloroform at room temperature for 24 h. Nylons 6 and nylon 11 were obtained from BDH while general-purpose PS (Styron 648) from DOW Plastics. All polymers were dried in a vacuum oven at 80 °C for 48 h to Results and Discussion remove sorbed water before processing. Synthesis and Characterization of the Maleic Synthesis of Maleic Anhydride Terminated Polysty- Anhydride Terminated Polystyrene. The polysty- rene. Polystyrenes of various molecular weights were syn- renes obtained by the ATRP polymerization had molec- thesized according to the procedure described by Matyjaszew- × 4 15,16 ular weights up to 2 10 and polydispersities ranging ski and the results are presented in Table 1. The terminal from 1.13 to 1.19 as shown in Table 1. These polysty- functionalization of polystyrene was carried out in a previously dried flask equipped