[ Pobierz całość w formacie PDF ]
.3.Add benzoic acid (10 g, 82 mmol) to the organic extracts and stir with a glassrod to ensure complete dissolution of the acid.4.Dry the organic phase with anhydrous magnesium sulfate (ca.15 g, 30 min).103W.Hayes and S.RannardProtocol 1.Continued5.Filter the  dried organic phase at the pump through a sintered-glass filterfunnel, transfer the solution to a single-necked, round-bottomed flask(500 mL) and concentrate the solution in vacuo using a rotary evaporator.6.Dissolve the residual solid in warm THF (ca.250 mL) and concentrate the solu-tion until half of the volume of solvent remains using a rotary evaporator.7.To this concentrated solution, slowly add diethyl ether (ca.250 mL) until afine white crystalline product is observed.Filter the organic phase at thepump through a sintered-glass filter funnel and wash the product withdiethyl ether (ca.50 mL).8.Transfer the white crystalline product to a clean, dry single-necked, round-bottomed flask (100 mL) and dry using a vacuum line.Yields ca.90% aretypical.Protocol 2.GTP of methyl methacrylate (Scheme 1)Caution! Carry out all procedures in a well-ventilated fume-cupboard,wear appropriate disposable gloves, a lab-coat, and safety glasses.All vacuum-line work should be performed while standing behind a protective Perspexscreen.Polymethylmethacrylate (PMMA) possessing a degree of polymerization of190 monomer groups and Mn 19 000 has been targeted in the followingprocedure.EquipmentÏ% Ï%Dual manifold (nitrogen/vacuum) Cannula needleÏ% Ï%Vacuum source Three-necked, round-bottomed flask (250 mL)Ï% Ï%Source of dry nitrogen Rubber septaÏ% Ï%Hotplate stirrer Beaker (500 mL)Ï% Ï%Teflon-coated magnetic stirrer bar Buchner filterÏ% Ï%Contact thermocouple Buchner filter apparatusÏ% Ï%20 mL gas-tight syringe 20 cm long Filter paper (Whatman no.1)narrow bore needleMaterialsÏ%[(1-Methoxy-2-methyl-1-propenyl) oxy]trimethylsilane,a irritant0.15 ml, 0.734 mmolÏ%Freshly distilled methyl methacrylate,b causes burns, may cause sensitization15 mL, 140 mmol by inhalation and skin contactÏ%TBABB, 0.05 g, 0.103 mmol irritantÏ%Freshly distilled THF,c 50 mL irritant, highly flammable may form explosive peroxidesÏ%Methanol for precipitation, ca.700 mL toxic, flammable carcinogen,Chloroform, ca.20 mL harmful by inhalationNote: Silicone grease should not be used to seal reaction vessels used in GTP methods.Employapiezon type greases or fine teflon tape instead.1043: Controlled/ living polymerization methodsMethod1.Vacuum distil THF (50 mL) directly into a clean, dry three-necked, round-bottomed flask (250 mL) the reaction flask.Purge the flask with dry nitrogenand allow the solvent to warm to room temperature.Remove a stopper andseal with an appropriate rubber septum.2.Cannulate [(1-methoxy-2-methyl-1-propenyl)oxy]trimethylsilane (0.15 ml,0.734 mmol) from a graduated 2 mL Schlenk flask using a transfer needle (orcannula) (using this technique it is possible to add the initiator to an accuracyof 0.05 mL) by applying pressure from the nitrogen supply as shown inFigure 3.2.3.Remove the septum and add tetra n-butyl ammonium bibenzoate (seeProtocol 1) (0.05 g, 0.103 mmol) to the solution whilst maintaining a positivenitrogen pressure.Once the addition is complete, seal the flask with anappropriate rubber septum.4.Stir the solution for approximately 2 min before adding freshly distilledmethyl methacrylate (15 mL, 140 mmol) in a dropwise fashion via a cannulaor a gas-tight syringe to the reactor flask at a rate of approximately 1 mL/min.5.Monitor the exotherm using a contact thermometer (attach the contactthermometer to the side of the reactor) typical temperatures reached varybetween 45 and 60 C.6.Once the reaction has cooled to room temperature, add methanol (ca.5 mL)to the reaction mixture in order to terminate the polymerization.7.Purify and recover the resultant polymer by precipitation using drop-wiseaddition of the THF solution into the vortex walls of a rapidly stirred ten-foldexcess of cold methanol (ca.500 mL).A brilliant white fine precipitate shouldN2 N2 OutletInletneedleRubberneedleseptaRubberseptumCannulaFreshly distilledneedle[(1Methoxy-2-methyl-1-propenyl)Contactoxy] trimethylsilanethermometerxx.x°CGraduated Stirrer ReactionSchlenk tube bar flaskFig.3.2 Transfer of initiator/catalyst/solvent to reaction flask.105W.Hayes and S.RannardProtocol 2.Continuedbe produced [ Pobierz caÅ‚ość w formacie PDF ]