摘要：

Ionic liquids (ILs)1have been studied as solvents for polymerization reactions.2Most recently, ILs have been shown to be good solvents for radical polymerizations.3Relatively high solvent viscosity and support for long radical lifetimes have been suggested as factors enabling the formation of polymers with high molecular weights and controllable characteristics. In most cases, separation can be facilitated by the differential solubility of the polymers and monomers in the solvent, with the polymeric materials precipitating from the IL on formation.ILs incorporated within porous polymer membranes, can act as supported polymer electrolytes.4Rather than contacting polymer membranes with the IL and relying on a ‘wetting’ action, polymer-in-salt gel membranes have been prepared directly by polymerization of vinyl monomers in ILs5and by polymerization of ILs incorporating polymerizable functions.6It seemed likely that the formation of IL-polymer gels, such as are described by Watanabe and Mizumura,5result from the plasticizing effects of the IL on the polymer matrix. The compatibility of some ILs with polymers can be advantageous in polymer processing to produce plasticized materials.ILs containing imidazolium or pyridinium cations are similar to some conventional plasticizers, containing an aromatic core and pendant alkyl groups.7Most plasticizers are based on three classes of compounds: phthalates, adipates, and trimellitates, with dioctyl phthalate (DOP) accounting for greater than 50% of all plasticizer used. Ideally, plasticizers exhibit most of the following characteristics: low volatility, low leachability, high and low temperature stability, thermodynamic compatibility with polymer, low cost and minimal health and safety concerns. ILs exhibit many of these characteristics, with performance, reproducibility, and wide thermal range being some of the greatest advantages over traditional plasticizing agents. With over 4 million tons of plasticizers produced annually,7the development of novel plasticizing agents will yield alternatives for processing, and may expand the market to include a number ofnew applications.Although the research presented here is focused on improved engineering properties of polymers, with an emphasis on high and low temperature stability imparted by the ionic liquids, the health and safety of plasticizers has been an important concern recently. Phthalate esters, including DOP, have come under scrutiny for potential health hazards,8but are currently considered safe.9Although collection of complete toxicity data for the [C4mim][PF6] ILs used in this work is still in progress, the reported LD50value for a related ionic liquid, 3-hexyloxymethyl-1-methylimidazolium tetrafluoroborate, has been reported as approximately 1400 mg kg−1in Wistar rats.10This compares with dioctyl phthalate which has an LD50value of 30 000 mg kg−1orally.The objectives of this study were to determine the effect of ILs as plasticizers on the materials properties of poly(methyl methacrylate) (PMMA), as measured through the moduli of elasticity as a function of plasticizer type and concentration, thermal stability of PMMA samples determined at high temperatures, and glass transition temperature (Tg).Polymer samples were preparedPoly(methyl methacrylate), PMMA, was synthesized using varying ratios of monomer and either DOP or [C4mim][PF6]. Free radical polymerizations were carried out at 55 °C for 24 hours using 1 wt% AIBN as the thermal initiator. Samples containing no plasticizing agent, and 10, 20, 30, 40 and 50 wt% each of the IL or DOP were synthesized. The polymers were formed between two siliconized glass sheets with Teflon®spacers to provide samples of uniform thickness for mechanical testing. No extractions were done to remove solvents after polymerization. Small pieces were collected for calorimetry and thermogravimetric analyses (TA Instruments, model 2920 MDSC and model 2950 TGA, Newcastle, DE), and dog-bone shaped samples were cut for mechanical analysis using an automated material

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