The pyrolysis of tetraiodopyrrole in an inert atmosphere at temperatures from 120-700� yields black, infusible, amorphous polymers insoluble in solvents. Depending on the pyrolysis temperature, iodine may be present in the polymers as iodine of substitution and as chemisorbed molecular iodine, which is very tenaciously held. As a first approximation, the structure may be regarded as a three-dimensional network of pyrrole rings cross-linked in a nonplanar fashion by direct carbon to carbon linkages. The secondary nitrogen atoms form a hydroquine type system which may be oxidized by iodine or molecular oxygen under alkaline conditions. The extent of oxidation depends on the hydroxyl ion concentration. The nonplanarity of the oxidized quinonoid system renders it unstable but stability is enhanced, as in the triphenylmethane dyestuffs, by the formation of a carbinol. Despite their nonplanarity polypyrroles are relatively good conductors of electricity. The resistivity ranges from 1-200 ohm cm depending on the temperature of pyrolysis.

The electron spin resonance absorption and electrical resistivity have been measured under rigorous conditions for a series of polypyrroles prepared over the temperature range 120-500�. When plotted as a function of pyrolysis temperature the resistivity shows a maximum in the region 200-300�. Although the resistivity of the polymers prepared at 120� and 500� is roughly similar, their e.s.r. behaviour is quite different. The low-temperature polymer, containing much complexed iodine, shows a very broad signal arising from an excited state probably associated with a polypyrrole-iodine charge-transfer complex; the high temperature polymer, containing no iodine, shows a strong narrow signal arising from the ground state of the polymer. The changes in conductivity of the polymers following the adsorption of electron acceptor or donor molecules have been measured. It is concluded that, depending on the relative amounts of electron donating or attracting chemisorbed species in relation to the concentration of donor nitrogen atoms in the polypyrrole, the polymer may behave as an intrinsic or extrinsic semiconductor with n- or p-type characteristics. Charge-transfer complexes of strength sufficient to cause partial ionization induce extrinsic behaviour by changing the ratio of the number of electrons to the number of holes. Substituent groups such as the hetero atoms which interact with the π-electron system inductively or through resonance affect only the relative mobility of the charge carriers and induce intrinsic behaviour.

Multistage column experiments have been performed using a mixed bed of finely divided weakly acidic and weakly basic ion-exchange resins with thermal regeneration of the resins at 80�. A product water fraction with a concentration of 200- 250 p.p.m. can be obtained using such a column from a feed water containing 1000 p.p.m. of sodium chloride. When the same feed water is used as the regenerant at 803 an effluent having a peak concentration of about 5000 p.p.m. can be obtained. A solution of 1000 p.p.m. magnesium sulphate can be similarly demineralized. The performance of the resin column is highly dependent on the pH value to which it has been buffered by prior treatment with acid or alkali. It is also shown that thermal regeneration is feasible when the resins are used in a softening cycle.

Weakly basic ion-exchange resins have been synthesized by treating crosslinked chloromethylated polystyrene beads with primary and secondary amines and with polyamines. Titration curve data show that such resins may be either homofunctional and possess flat titration curves, or heterofunctional and possess sloping titration curves, depending on whether the basic sites within the resin have the same or different basicities. A comparison of the titration curves determined at c. 20' or 80" reveals that all amine resins become weaker bases when heated, but the maximum effect is shown by the resins with homofunctional structures; e.g. the plateau-shaped curves at c. 20' and 80" of a polyvinylbenzyldiethylamine resin differ by about 1.2 of a p H unit at half neutralization. The ~ffect is fully reversible.The influence of amino group substituents, crosslinking, salt concentration, sulphate ions, and temperature on the titration curves of weakly basic amine resins has been studied. Titration curves of a variety of commercial amine resins have been determined a t c. 20' and 80" and show t h a t a t least two resins with homofunctional structures are commercially available.In the first paper in this series1 it was shown, from an analysis of the factors influencing the salinity of water supplies, that the production of municipal and industrial waters in the future will need a cheap method of demineralization for use in conjunction with conventional methods of water supply, if locally available waters are to be used and reused extensively. There is therefore a major need developing for a method of removing at low cost small amounts (500 p.p.m.) of salinity from waters of marginal quality. An analysis of the principles of demineralizatiod reveals that the process with the greatest potential for this purpose would use adsorbents, such as ion-exchange resins, which can be regenerated with heat rather than chemicals. Such an ion-exchange process, which will be designated the "Sirotherm" process,$ is being developed in these laboratoriea and is the subject of this and the following papers.The Sirotherm process uses weakly basic ion-exchange resins in admixture with weakly acidic resins for the adsorption of salts from an aqueous solution in a thermally variable manner. Weakly basic resins may be made with different basicities,

The pyrolysis of 2,4,5-triiodoimidazole and 1,2,4,5-tetraiodoimidazole yields polymers whose poor conductivity is attributed to the presence of two types of nitrogenous centres with electron-donating and electron-accepting properties respectively. Nitrogenous polymers produced by passing mixtures of chlorine and pyridine through a silica tube heated to 800� have low resistivities (0.03 to 15 ohm cm), indicating that the polymers have a highly conjugated structure. The increase of resistivity with chlorine content, together with the decrease in resistivity observed on adsorption of the electron donor ethylene, suggest that the nitrogen centres are donor rather than acceptor type. The properties of the polymers suggest that the latter are probably substituted polypyridines. The results support the following guide to synthesis: organic polymers of good conductivity can be prepared by directly crosslinking small aromatic or heterocyclic units into three-dimensional non-planar structures in which the number of crosslinks should be as large as possible. Either electron-donating or electron-accepting structures, but not both, may be present in the one polymer.