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.Aragrag et al.Protocol 11.Continuedfiltration at the water pump.This procedure is then repeated twice and thepolymer dried using a vacuum desiccator or vacuum oven.ea As an alternative, a two-necked Schlenk tube can be used (see Chapter 3, Figure 3.4).b At this stage the mixture can be degased using the freeze–pump–thaw–purge method (outlined in Protocol 1).c Care must be taken to ensure that the initiator is injected directly into the cold, stirring solution.Initiator that touches the sides of the polymerization tube first may be liable to react with styrene residue, thus not initiating the solution effectively.d At this stage an aliquot may be removed for analysis to check the percentage conversion of monomer to polymer.e The precise procedure for purification will be determined by the composition of the copolymer, if the material is soft at room temperature then filtration will not be possible and draining the majority of the non-solvent off will be sufficient.This method for the preparation of poly(styrene- b-tBuA) is based upon the procedure described by Jerôme et al.44 Teyssie and co-workers45,46 demonstrated that the addition of LiCl can be effective in the living anionic polymerization of the acrylic monomers, because a ␮-type complex47 is formed between LiCland the growing site.This complex prevents the occurrence of side-reactions at the propagating site, thus markedly narrowing the molecular weight distribution.Protocol 12.Synthesis of poly(styrene- b-tBuA) diblock copolymerCaution! Carry out all procedures in a well-ventilated fume-hood, wear appropriate disposable gloves, a lab-coat, and safety glasses.All vacuum-line work should be performed while standing behind a protective Perspex screen.Never use flat-bottomed flasks with rotary evaporators.Equipment● Dual manifold (nitrogen/vacuum)● Source of dry nitrogen● Two-necked round-bottomed flask (100 and 50 mL)● Beakers and Erlenmeyer flasks (various)● Gas-tight syringe (10 mL)● Hotplate stirrer● Gas-tight syringe (50 mL)● Nitrogen gas inlet● Gas-tight syringe(2 mL)● Syringe needles (various)● Magnetic stirrer bar● Rubber septa● Dry ice-bath● Apparatus for filtration, Buchner funnel,● Rotary evaporatorflask, and water pump● Vacuum ovenMaterials● Freshly distilled styrene, a 6.6 mL, 58 mmolflammable, harmful by inhalation● Freshly distilled tert-butyl acrylate, bhighly flammable, irritating to eyes skin and respiratory4.57 mL, 31 mmolsystem.very toxic to aquatic organisms, may causelong-term adverse effects in an aquatic environment● Lithium chloride, 0.02 g, 0.5 mmolharmful if swallowed, irritating to eyes, skin, andrespiratory system● ␣-Methylstyrene, 0.05 mL, 0.38 mmolflammable irritant802: General procedures in chain-growth polymerization● sec-Butyllithium, 1.3 M, 0.5 mL, 0.65 mmolhighly flammable, reacts violently with water,spontaneously flammable in air, causes burns,harmful by inhalation● THF 50 mLhighly flammable, may form peroxides, irritating to eyesand respiratory system● Acetone for cooling bathhighly flammable● Solid CO2 for cooling bathextremely cold solid, vapour can cause rapid suffocation● Methanol, ca.150 mLtoxic, highly flammableMethodInitiator preparationThe monofunctional initiator [(␣-methylstyryl)-lithium (␣-MeSt⫺Li⫹)] is prepared by reacting sec-BuLi with a slight molar excess of ␣-MeSt at room temperature in dry THF.1.Flush nitrogen through a pre-dried two-necked round-bottomed flask (50 mL) equipped with a magnetic stirrer bar and sealed with two septa.2.Freshly distilled THF (10 mL) is added directly via a gas-tight syringe through the side-arm of the flask.3.sec-Butyllithium 1.3 M (0.5 mL, 0.65 mmol) is then added at room temperature directly via a gas-tight syringe through the side-arm of the flask.4.␣-Methylstyrene (0.05 mL, 0.38 mmol) is then added to the stirred mixture, at room temperature, via a gas-tight syringe through the side-arm of theflask.The colour of the solution should turn and stay dark red.cPolymerization reaction5.Into a dry two-necked, round-bottomed flask (100 mL) equipped with a magnetic stirrer bar, a septum cap, and a nitrogen gas inlet attached to thedouble manifold, add lithium chloride (0.02 g, 0.5 mmol) under a flow ofnitrogen.Freshly distilled THF (50 mL) is added directly via a gas-tight syringe through the side-arm of the flask.6.The initiator solution is transferred into the flask by means of a syringe.7.Cool down the mixture to ca.⫺78⬚C using a dry ice/acetone bath and add freshly distilled styrene (6.6 mL, 57 mmol).The solution should turn a redcolour.8.Allow the solution to warm to room temperature and stir for 30 min.Cool down the content of the flask to ca.⫺78⬚C and then add freshly distilledtert-butyl acrylate, (4.57 mL, 31 mmol).Stir the mixture for a further 30 min at room temperature.9.Methanol (5 mL) is then added to the polymerization flask and the contents of the flask is stirred for a further 30 min.10.The solution is then transferred to a single-necked round-bottomed flask (250 mL) and the THF removed on the rotary evaporator.The crude mixtureis then dissolved in a minimum amount of acetone and the dissolved mater-ial precipitated into a solution of 7 : 3 methanol : water.81N.Aragrag et al.Protocol 12.Continued11.The precipitated material is collected, dissolved it in acetone and precipitated it once again.The dissolution/precipitation step must be done at least three times to ensure the elimination of any traces of unreacted initiator.12.The precipitated polymer (white solid) is filtered using a Buchner filter and dried under vacuum.a Styrene should be washed with 10% NaOH (aq.), dried over Na2SO4 and then filtered in order to remove any stabilizer.The resultant pre-dried styrene should then be directly distilled carefully under high vacuum and used immediately.b Methacrylate monomers should be passed through a basic alumina column directly into a Schlenk flask containing CaH2 and stored in the fridge.The monomer should be directly distilled carefully from the CaH2 under high vacuum and used immediately.c Loss of colour suggests that traces of water are present, if the colour disappears rapidly then the system should be investigated for sources of adventitious water.These should be removed and the procedure repeated.The block copolymer produced in the above protocol can be hydrolysed toproduce an acrylic acid containing system [ Pobierz całość w formacie PDF ]