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.This is done by distillation under reduced pressure.1.Place the 4-cyanophenyl-4 -(6-propenoyloxyhexanoxy) benzoate (1 g,2.5 mmol) and 2-hydroxyethylacrylate (18 mg, 0.15 mmol) in the polymeriza-tion tube.Add AIBN (4 mg, 0.03 mmol) and finally add chlorobenzene(20 mL).Place a protective netting over the tube to minimize danger fromglass should the tube shatter.Attach the tube to the manifold and close theYoung s tap at the top of the tube.2.Carry out the freeze thaw degassing programme outlined in Chapter 2, toensure all oxygen is removed from the system.Isolate the tube from themanifold by closing the Young s tap while the system is under vacuum.3.Place the tube in a thermostatted water-bath at 55 C for 24 h.This procedureshould be carried out behind a blast screen.4.Remove the tube from the water-bath and allow to cool to room temperature5.Transfer the resulting polymer solution into a round-bottomed flask (100 mL)and remove the majority of the chlorobenzene using a rotary evaporator.Then re-dissolve the polymer in the minimum volume of dichloromethaneand drop the resulting viscous solution into cold methanol (150 mL) in anErlenmeyer flask (500 mL).The flask is allowed to stand for 30 min and theliquid decanted.The solid is allowed to dry in the fume-cupboard and thenre-dissolved in dichloromethane (minimum volume).Once again the polymersolution is precipitated, this time into diethyl ether.The polymer is then isolatedas above and a further precipitation into ether undertaken.The polymer is224 9: Liquid Crystalline polymersthen placed in the vacuum oven and dried at 50 C for several hours to removeany residual solvent and water.The polymers are subsequently characterizedby differential scanning calorimetry (DSC) to determine the phase transitiontemperatures.3.The hydrosilylation reaction: a useful procedure for thepreparation of a variety of side-chain polymersThe main structural features of a side-chain polymer are given in Figure 9.3 andalthough the polymer backbone and flexible spacer group are important in deter-mining the thermal and physical properties of these polymers, potential applica-tions are determined mainly by the side-group.For example, if the side-chainpolymer is to be used as a non-linear optical (NLO) device then the structure ofthe side-group might be as shown in Figure 9.3(a), for liquid crystal displaydevice applications structures such as shown in Figure 9.3(b) or (c) may be used.Grafting of the side-group onto a preformed polymer backbone has been avery useful and highly productive way of making a large variety of side-chainpolymers for display device applications.Such polymers should have lowglass transition (Tg) temperatures, and for that reason many of these side-chainliquid crystalline polymers are prepared from preformed poly(siloxane) back-bones.The polymer backbones come in a variety of different forms examples ofwhich are shown in Figure 9.4.The procedure described here involves thepreparation of a ferroelectric side-chain liquid crystal of structure 13, in thiscase a cyclic siloxane tetramer, however, this procedure can be simply adapted toprepare a range of side-chain liquid crystalline poly(siloxanes) and elastomers(see later).The procedure is performed using the hydrosilation reaction ofthe preformed cyclic siloxane tetramer 11 with the mesogenic side-group 10in anhydrous toluene in the presence of the catalyst platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex 12 at room temperature.(a)X (CH2)6 O N N NO27O(b)NOX (CH2)10 O O*NO8CH3(c)X (CH2)10 O CO2 CO2CHCO2Et9Fig.9.3 The main structural features of a side-chain polymer.225 S.I.Patel et al.(a)CH3 CH3CH3 SiO SiO Si(CH3)3CH3 Hn(b)CH3 CH3 CH3CH3 SiO SiO SiO Si(CH3)3CH3 H CH3mn(c)CH3SiOHnFig.9.4 Different types of polymer backbone: (a) homopolymers; (b) copolymers; (c) cyclicpolymers.Protocol 5.Use of the hydrosilylation reaction to form a side-chain liquidcrystalline cyclic tetramer (Scheme 5)Caution! Carry out all procedures in a well-ventilated fume-cupboard, wearappropriate disposable gloves, a lab-coat, and safety glasses.Never use flat-bottomed flasks with rotary evaporators.EquipmentÏ% Ï%Dual manifold (nitrogen/vacuum) Source of dry nitrogenÏ% Ï%Three-necked, round-bottomed flask (100 mL) Rotary evaporatorÏ% Ï%Pressure-equalizing dropping funnel TLC plates (silica gel)Ï% Ï%Rubber septa Teflon-coated magnetic stirrer barÏ% Ï%Inlet tube Disposable syringe filter (PTFE, 0 [ Pobierz caÅ‚ość w formacie PDF ]
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.This is done by distillation under reduced pressure.1.Place the 4-cyanophenyl-4 -(6-propenoyloxyhexanoxy) benzoate (1 g,2.5 mmol) and 2-hydroxyethylacrylate (18 mg, 0.15 mmol) in the polymeriza-tion tube.Add AIBN (4 mg, 0.03 mmol) and finally add chlorobenzene(20 mL).Place a protective netting over the tube to minimize danger fromglass should the tube shatter.Attach the tube to the manifold and close theYoung s tap at the top of the tube.2.Carry out the freeze thaw degassing programme outlined in Chapter 2, toensure all oxygen is removed from the system.Isolate the tube from themanifold by closing the Young s tap while the system is under vacuum.3.Place the tube in a thermostatted water-bath at 55 C for 24 h.This procedureshould be carried out behind a blast screen.4.Remove the tube from the water-bath and allow to cool to room temperature5.Transfer the resulting polymer solution into a round-bottomed flask (100 mL)and remove the majority of the chlorobenzene using a rotary evaporator.Then re-dissolve the polymer in the minimum volume of dichloromethaneand drop the resulting viscous solution into cold methanol (150 mL) in anErlenmeyer flask (500 mL).The flask is allowed to stand for 30 min and theliquid decanted.The solid is allowed to dry in the fume-cupboard and thenre-dissolved in dichloromethane (minimum volume).Once again the polymersolution is precipitated, this time into diethyl ether.The polymer is then isolatedas above and a further precipitation into ether undertaken.The polymer is224 9: Liquid Crystalline polymersthen placed in the vacuum oven and dried at 50 C for several hours to removeany residual solvent and water.The polymers are subsequently characterizedby differential scanning calorimetry (DSC) to determine the phase transitiontemperatures.3.The hydrosilylation reaction: a useful procedure for thepreparation of a variety of side-chain polymersThe main structural features of a side-chain polymer are given in Figure 9.3 andalthough the polymer backbone and flexible spacer group are important in deter-mining the thermal and physical properties of these polymers, potential applica-tions are determined mainly by the side-group.For example, if the side-chainpolymer is to be used as a non-linear optical (NLO) device then the structure ofthe side-group might be as shown in Figure 9.3(a), for liquid crystal displaydevice applications structures such as shown in Figure 9.3(b) or (c) may be used.Grafting of the side-group onto a preformed polymer backbone has been avery useful and highly productive way of making a large variety of side-chainpolymers for display device applications.Such polymers should have lowglass transition (Tg) temperatures, and for that reason many of these side-chainliquid crystalline polymers are prepared from preformed poly(siloxane) back-bones.The polymer backbones come in a variety of different forms examples ofwhich are shown in Figure 9.4.The procedure described here involves thepreparation of a ferroelectric side-chain liquid crystal of structure 13, in thiscase a cyclic siloxane tetramer, however, this procedure can be simply adapted toprepare a range of side-chain liquid crystalline poly(siloxanes) and elastomers(see later).The procedure is performed using the hydrosilation reaction ofthe preformed cyclic siloxane tetramer 11 with the mesogenic side-group 10in anhydrous toluene in the presence of the catalyst platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex 12 at room temperature.(a)X (CH2)6 O N N NO27O(b)NOX (CH2)10 O O*NO8CH3(c)X (CH2)10 O CO2 CO2CHCO2Et9Fig.9.3 The main structural features of a side-chain polymer.225 S.I.Patel et al.(a)CH3 CH3CH3 SiO SiO Si(CH3)3CH3 Hn(b)CH3 CH3 CH3CH3 SiO SiO SiO Si(CH3)3CH3 H CH3mn(c)CH3SiOHnFig.9.4 Different types of polymer backbone: (a) homopolymers; (b) copolymers; (c) cyclicpolymers.Protocol 5.Use of the hydrosilylation reaction to form a side-chain liquidcrystalline cyclic tetramer (Scheme 5)Caution! Carry out all procedures in a well-ventilated fume-cupboard, wearappropriate disposable gloves, a lab-coat, and safety glasses.Never use flat-bottomed flasks with rotary evaporators.EquipmentÏ% Ï%Dual manifold (nitrogen/vacuum) Source of dry nitrogenÏ% Ï%Three-necked, round-bottomed flask (100 mL) Rotary evaporatorÏ% Ï%Pressure-equalizing dropping funnel TLC plates (silica gel)Ï% Ï%Rubber septa Teflon-coated magnetic stirrer barÏ% Ï%Inlet tube Disposable syringe filter (PTFE, 0 [ Pobierz caÅ‚ość w formacie PDF ]