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.The solution is maintained175 D.J.Walton et al.Protocol 7.Continuedunder a continuous stream of nitrogen and held at 20 1 C in a thermostatted water-bath.Copper (II)perchlorate hexahydrate, Cu(ClO4)2 6H2O (0.74 g, 2 mmol) is dissolved in acetonitrile (8 10 mL) andadded drop-wise to the monomer solution.A black precipitate is formed immediately in the clear solu-tion.The mixture is stirred for a minimum of 90 min and then filtered.The solid polymer is thenwashed under filtration with copious amounts of water followed by acetonitrile, in order to removeunreacted monomer and oxidant.Finally, the polymer is washed with hot acetonitrile using a Soxhletextractor, for up to 6 8 h.Drying in vacuo for a further 6 8 h yields poly 3-[6-(4 -cyanobiphenyl-4-yloxy)hexyl]pyrrole as an amorphous black solid.bSubsequent manipulations of solvents are performed with nitrogen-purged syringes and/or acannula, through degassed, flasks fitted with septa (see text).The presence of the mesogenic side-chains allows for the developmentof orientation in films prior to polymerization.If the monomer is then poly-merized in this aligned state, it would be expected that the orientationimparted on the pyrrole units by association with the mesogens wouldbecome incorporated into the polymer.High levels of anisotropy may lead,for example, to new applications that can exploit the different conductingmechanisms along and orthogonal to the polymer chains.16 The apparatusfor polymerizing the substituted pyrroles as an aligned film consists of areaction cell through which bromine vapour (the oxidant) can be passed.Thisapparatus is designed to fit within the cavity of a polarizing microscope, andcontains an aperture for viewing the sample to ensure the requiredphase/alignment state.Protocol 8.Polymerization of 3-[6-(4 -cyanobiphenyl-4-yloxy)hexyl]pyrroleas an aligned filmEquipmentÏ% Ï%Type K Chromel Aluminel thermocouple Vacuum ovenÏ% Ï%Temperature controller Glass slideÏ% Ï%Glass reaction cell with inlet and outlet for Aluminium heating block designed for usenitrogen and oxidant vapour with the reaction cellÏ% Ï%Optical microscope Power supplyÏ% Ï%Source of dry nitrogen 2 Dreschel bottlesMaterialsÏ%3-[6-(4 -cyanobiphenyl-4-yloxy)hexyl]pyrrole, treat as harmfulca.50 mg, 1.3 mmolÏ%Acetonitrile highly flammable, toxic by inhalation, incontact with skin, and if swallowedÏ%Nitrogen gas asphyxiation hazardÏ%Dimethylformamide potentially teratogenic, harmful in contactwith skin, irritating to eyes176 6: Conducting polymers from heterocyclesÏ%Bromine very toxic by inhalation, causes severe burnsÏ%Probimide® 32 irritating to eyes, skin, and respiratory systemÏ%Sodium thiosulfate solution (saturated)Method1.A glass slide (ca.1 cm 1 cm) is spin-coated with a solution of Probimide®32 in dimethylformamide.a The coated slide is annealed at high temperatures(ca.200 C), followed by unidirectional rubbing with a soft cloth, to yield ahard, inert, rubbed polymer film, suitable for enticing homogeneousalignment of a mesophase.2.The sample to be polymerized (15, ca.50 mg) is deposited on the glass slideand placed in a reaction cell cavity.b The reaction cell is connected on oneside to a reservoir of bromine in a glass tube fitted with both gas inlet andoutlet valves (such that nitrogen can be passed through the tube, but withoutbubbling through the bromine).Between the bromine reservoir and the cellis a three-way tap, which is connected to a separate nitrogen inlet and allowsthe passage of bromine free- nitrogen through the cell as required.On theopposite side, the cell is connected to two Dreschel bottles arranged in seriescontaining a saturated solution of sodium thiosulfate to destroy the effluentbromine vapour.c3.The cell is placed in an aluminium heating block shaped out to contain thecell and fitted with four heating elements, connected to a 10-A power supply,and placed in the cavity of a polarizing microscope.d The cell is then purgedwith a continuous stream of nitrogen and heated to the approximate requiredtemperaturee for polymerization in the liquid crystalline region; this involvesheating to ca.80 C such that the sample becomes isotropic and then coolingfairly rapidly to 60 C or until an optical texture typical of a liquid crystallinephase is observed.f4.With the sample in the required phase, the nitrogen is passed over the tubecontaining bromine and this tube warmed with a beaker containing hot waterto speed up evaporation of bromine [ Pobierz caÅ‚ość w formacie PDF ] |
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