The adsorption of se veral saturated , linea r polyesters has been studied under a varicty of conditions. The study also included di-n-butyl sebacate as a model low molecul ar weight ester and poly (met hyl m ethacrylate). The adsorbents were type E glass powder, silica, a nd a lumina. The glass powder and silica were nonporous materi als; t he alumina contained a lal'ge internal pore structure. The rate of adsorption of t he polyesters on glass was very ra pid and t he adsorpt on isotherm was irrevcrsible. Adsorption from a poor solven t was favored over adsorpt ion from a good solvent. A large number of sitcs a re available on t he adsorbent for bond format ion and the adsorbed polymer m ost proba bly extends into t he solution in a coiled configuration. Metallic ions, in a ddition to silicon , a ppear to be involved in a n electrostatic bond between t he polymer and t he glass. The Langmuir eq uation is obeyed at high-equilibrium co ncentrat ions, although t hcre is nonconformity at t he low concen trations.

A spectrophotofluorometer, suitably modified for use with plastics films, was used to study a series of cellulosic polymer films. The chemical structure of the films was found to be related to the wavelength and intensity of the fluorescence emission spectra. Saturated aliphatic esters and ethers were found to possess strong fluorescence maxima at about 350 mμ. Cellulose nitrate exhibits very weak fluorescence at 310 mμ, and a moderate fluorescence maximum appears at 440 mμ for cellulose derivatives containing double bonds or carboxyl groups. A series of experiments is described in which the modification of chemical structure was followed by measuring changes in fluorescence spectra.

The rate of formation of the donor-acceptor complex between tetracyanoethylene and hexamethylbenzene, in l-chlorobutane as solvent, has been measud at -83°C by a ternlnjratmjump method using microwave heating. Equilibrium constants have also been determined over a range of temperature. The rate constant is (1.45f0.3) x lo8 1. mol-1 s-1 (the uncertainty referring to the estimated limits of error). This is smaller by an order of magnitude than the calculated value for a diffusionantrolted reaction. The reason for this is discussed and it is concluded that there is possibly an energy barrier due to solvation changes. The rate constant in a solvent consisting of chlorobenzene+n-heptane (40-60 v-v) has also been determined, allowance being made for the parallel complex-formation between chlorobenzene and tetracyanoethylene ; at -60°C, it was found to be (8 f 3) x lo8 1. mol-I s-l.Complexes formed in solution between electron-acceptors such as trinitrobenzene, iodine or tetracyanoethylene on the one hand and electron-donors such as aliphatic amines or aromatic hydrocarbons on the other have been studied in recent years '* from various points of view-spectroscopic, structural, and thermodynamic. Kinetic investigation has lagged behind, because the reactions are extremely fast ; exploratory investigations by the ultrasonic-absorption method and by the stopped flow method at -120°C were unsuccessful, and evidence from studies of dielectric relaxation 5 * ti indicates that the rates are very high. In the most favourable cases, however, and at low temperatures, they are within the range of the temperature-jump technique, and we have used this method to determine the rate of complex-formation between tetracyanoethylene (TCNE) and hexamethylbenzene (HMB), for which the equilibrium constant and enthalpy of reaction are favourable : kf TCNE + HMB +complex.

No abstract

No abstract