Six diblock copoly(oxybutylene/oxyethylene)s (Eg2B7, E50B73, E4, B, , E50B4, E24B10 and E27B5, where E represents oxyethylene and B represents oxybutylene) have been prepared by sequential anionic copolymerisation and their micellisation in aqueous solution investigated. Surface tension, static and dynamic light scattering and gel permeation chromatography techniques were used to study solutions at temperatures in the range 20 to 50°C over a wide concentration range from dilute to 100 g dm-3. The micellar properties reported are critical micelle concentrations, micellar molar masses and radii. The thermodynamics of micellisation of E , B , diblock copolymers is discussed in relation to that of related triblock copolymers ( E, , . , B, E, and E , P , E , , where P represents oxypropylene).
Thermoelastic measurements at constant volume are reported for a series of natural rubber samples. The energy component of the stress supported by the network is more or less independent of the network cure at a value of &/f= 0.1240.02. The energy component of the stress is independent of whether the measurements are made in the dry or in the swollen state, despite the fact that the dry rubbers have non-Gaussian equations of state and that the swollen rubbers approach Gaussian behaviour. Flory's analysis of rubber elasticity which includes hindered internal rotation in the main polymer chain, is compared with experimental results. To a first approximation it gives the correct order of magnitude for the energy component of stress. Measurements have also been made of the pressure coefficient of stress, from which the dilation coefficient of the rubber has been calculated as a function of strain. Flory's analysis does not appear to'predict this coefficient satisfactorily.
The changes in molecular structure of high density polyethylene which can take place during processing have been studied using a nitrogen blanketed Brabender plastograph to simulate processing conditions. At high melt temperatures (> 290°C) decreases in melt viscosity and a narrowing of molecular weight distribution were observed, while at lower melt temperatures an increase in melt viscosity was observed. The increase in melt viscosity arises from a molecular enlargement reaction which is mainly attributable to the formation of long chain branches (LCB) which were detected using intrinsic viscosity measurements as well as by a novel method involving the measurement of melt elasticity on a Weissenberg rheogoniometer. The scission and enlargement reactions are not mutually exclusive but competitive, and a basic reaction scheme is proposed to explain the experimental results. The effect on this basic reaction scheme of mechanical shear, polymer unsaturation, and oxygen content has been investigated. The presence of excess oxygen promoted the scission reaction, the extent of molecular weight reduction increased with decreasing temperature as would be expected for a shear induced reaction. However, it was found that under nitrogen the effect of mechanical shear at low melt temperature (<290°C) was to increase the melt viscosity and extent of LCB when compared to the corresponding reactions performed at the same melt temperatures but in the absence of shear; an explanation of this effect which involves the breakdown by shear of a radical cage is proposed. The observation that polymers having a high vinyl content undergo extensive increases in melt viscosity and LCB at all melt temperatures and in the presence or absence of shear has also been explained on the basis of the proposed reaction scheme.
A number of polyurethane anionomers based on isophorone diisocyanate, polytetrahydrofuran, and cyclohexane dimethanol were prepared as aqueous dispersions. The dispersions were stabilized by the use of an internal emulsifier. The principal ionic moiety used was dimethylol propanoic acid, but dimethylol butanoic acid and an experimental suphonate diol sodium salt were also used. The consequence of the neutralization step, the degree of neutralization, the type of ionic component, and the type of counterion were investigated for their effect on the mechanical and colloidal properties of the polyurethanes. Dynamic mechanical thermal analysis, tensiometry, solvent spot testing, and swelling studies were used for the characterization of the materials.
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