Geoffrey Allen

Thermodynamics of oligomeric binary mixtures of polyethylene glycol and polypropylene glycol methylethers

Abstract Measurements are reported of the heats of mixing and cloud point curves of binary mixtures of methoxylated polyethylene glycol with methoxylated polypropylene glycol. The data are discussed in terms of the Flory equation of state theory and it is shown that both a temperature and concentration dependent X12 parameter and a Q12 term are required.

Graded block and randomized copolymers of butadiene-styrene

Abstract Graded block and randomized copolymers of butadiene-styrene were prepared anionically by polymerizing a mixture of butadiene and styrene with n-BuLi, in the absence and in the presence of t-BuOK respectively. Determination of the monomer composition and microstructure of the poly-butadiene sequence was achieved by 300 MHz 1 H n.m.r. and infra-red spectroscopy. 1 H n.m.r. equations developed previously for butadiene-styrene copolymers were modified and extended. In this way, cis, trans butadiene contents were determined from the aliphatic region of the n.m.r. spectra. The monomer sequence distribution of the copolymers has been investigated by examination of the morphology and their dynamic mechanical properties. The experimental conditions have been established for the preparation of random copolymers with inter- and intramolecular composition distribution.

Molecular dynamics of poly(ethylene oxide) in concentrated solution

Abstract Incoherent quasi-elastic neutron scattering measurements on aqueous poly(ethylene oxide) solutions show that as the concentration of water is increased to 1:1 mole ratio of water to ethylene oxide monomer units, the polymer chain mobility is not enhanced. Increased mobility is only observed when the water content is increased beyond this ratio. The activation energy for viscous flow shows a similar behaviour, it is unchanged as the system is diluted from the melt to the 1:1 solution and as more water is added it falls sharply. Similar studies on the system poly(ethylene oxide)/toluene show that chain mobility is enhanced and the activation energy for viscous flow falls continuously, at all concentrations. The difference is attributed to the formation of polymer-water hydrogen bonded complexes in aqueous solution. High resolution data for the aqueous systems suggest that the molecular dynamics obey the scattering law predicted for the Zimm model. In the melt the behaviour changes towards the limit given by the Rouse model.

Temperature dependence of chain dimensions

The dimensions of linear atactic polystyrene (Mw = 75 700) in cyclohexane have been determined at a series of temperatures using small-angle neutron scattering. Three solutions were examined: dilute (2% polymer), semi-dilute (19% polymer) and concentrated (47% polymer). End-to-end distances obtained from the data were compared with current theories of polymer solutions. For the semi-dilute solution results agreed with scaling law predictions, whereas results from the concentrated solution agreed with the formula obtained by Edwards. Furthermore, the latter results gave a characteristic ratio (C∞) of 9.5 ± 0.7 for polystyrene.

Toughened polystyrene containing block, graded block and randomized copolymers of butadiene-styrene

Abstract During the polymerization of styrene in the presence of a block, graded block, or randomized copolymer of butadiene-styrene, new morphologies of dispersed rubber particles are observed (i.e. cylindrical-type, coreshell, lamellar). These morphologies are the result of (i) polymer-polymer interactions between the copolymer and the ‘ in situ ’ formed polystyrene, (ii) an intramolecular phase separation within the polybutadiene and polystyrene sequences of the copolymer, and (iii) the mechanical treatment during the polymerization process. Elucidation of the structural characteristics of these morphologies has been achieved by following the phase changes during the polymerization and the changes in the intramolecular phase separation of the copolymers with respect to variation of their composition. The randomized copolymers were capable of forming toughened polystyrene blends with similar morphology to those containing polybutadiene rubber, but with enhanced adhesion between the rubber and polystyrene matrix. The structural characteristics of such randomized copolymers have been established.

Small-angle neutron scattering from a polymer coil undergoing stress relaxation

Abstract Small-angle neutron scattering measurements have been made on samples of polystyrene in which the stress has been allowed to relax at a constant strain. The radii of gyration parallel and perpendicular to the stretch direction have been measured as a function of time after the strain has been applied. After an initial rapid change, the radii of gyration tend towards asymptotic values which are close to those for the undeformed chain. The deformation appears to behave as if the affine deformation theory holds only for distances separating effective crosslinks. It is proposed that after the initial change in radii of gyration the stress is relieved by reorientation of the chain segments.

A small-angle neutron scattering study on poly(ethylene oxide) crystals

Abstract Small-angle neutron scattering measurements were made on poly(ethylene oxide) (PEO) crystallized from the melt. Samples with the deuterated species (DPEO) as a matrix present distinct Bragg peaks from which the lamella spacings can be determined. As a result of strong void-scattering, quantitative analysis of the low-angle regime of these scattering curves is not possible. Samples with the protonous species as a matrix, for which void-scattering is expected to be negligibly small, present unusual scattering curves indicating that they consist of two components, i.e. the intramolecular and intermolecular interference terms. A quantitative analysis of these curves indicates: (1) the solute DPEO molecules are embedded in the crystalline structure of the matrix, assuming rod-like conformations but (2) forming essentially homogeneous aggregates of a few to tens of the DPEO molecules, depending on the crystallization temperature and the DPEO concentration; (3) the DPEO molecules or aggregates are distributed in space in a non-random manner that corresponds to the presence of inhomogeneous ‘domains’ having root-mean-square radii of about 250 A, and each containing about 100 DPEO molecules.

The molecular basis of rubber elasticity

This paper reviews experimental work designed to test the molecular basis of the kinetic theory of rubber elasticity. Neutron scattering experiments have been used to test the essentially amorphous character of a rubber network and aspects of chain conformation in the network and in the uncrosslinked state. Networks of controlled topology have been synthesized in solution and in the dry state to examine the form of the shear modulus of the system, predicted by the kinetic theory.

Small-angle neutron scattering from polymer solutions: 3. Semi-dilute solutions near the lower critical solution temperature

Abstract Measurements of the radius of gyration and the screening lengths have been made for semi-dilute solutions of polystyrene near the lower critical solution temperature. From these data two regions of behaviour are clearly discerned. By analogy with similar data near the upper critical solution temperature, a ‘phase diagram’ has been drawn from the results around the lower critical solution temperature.