Michael J. Elwell

Simultaneous studies of reaction kinetics and structure development in polymer processing.

The simultaneous time-resolved study of structure development and reaction kinetics during polymer processing is an experimental method that has great potential in developing a deeper understanding of the parameters that govern the formation of structure and therefore polymer properties. A combination of synchrotron radiation small-angle x-ray scattering and Fourier-transform infrared spectroscopy experiments have been performed on a series of model segmented block copolyurethanes. These studies confirm that the driving force for structure development in polyurethanes is the thermodynamics of phase separation rather than hydrogen bonding.

An FT i.r. study of reaction kinetics and structure development in model flexible polyurethane foam systems

Abstract Forced-adiabatic, FT i.r. spectroscopy has been employed to simultaneously monitor polymerization and microphase separation on model flexible polyurethane foam systems. The following combinations of hydroxy functional components were investigated: (1) polyether-polyol and water; (2) polyether-polyol and deuterium oxide; (3) polyether-monol and water; and (4) polyether-monol and deuterium oxide. The formation of urethane, soluble urea, soluble d -urea, hydrogen-bonded urea and associated d -urea species were monitored during their fast bulk copolymerization with a diisocyanate. The decay of isocyanate is correlated to the polymerization kinetics and the evolution of hydrogen-bonded urea/associated d -urea is analysed emphasizing the onset of microphase separation of urea hard-segment sequences. The microphase separation transition (MST) occurred at a critical conversion of isocyanate functional groups. In the deuterium oxide blown foams, there was no trace of hydrogen-bonded urethane in the spectra obtained. In the polyether-monol systems, a lower conversion of isocyanate was observed at the MST and an overall lower reaction conversion was also observed.

Structure development in multi-block copolymerisation: comparison of experiments with cell dynamics simulations

Abstract A cell dynamics simulation of phase separation in block copolymers is compared with experimental observations for two related systems, polyurethane (poly(ether-urea)) foam and poly(ether-isocyanurate). Time resolved SAXS measurements on both systems suggest a spinodal-like mechanism with kinetics following a time-dependent Ginzburg–Landau (TDGL) model. TEM micrographs from a range of sources show reactively processed multi-block copolymers to have a bicontinuous morphology, which is discussed as a non-equilibrium relic of the phase separation process. A TGDL based cell-dynamics model gives predictions of the morphology, which can be compared to TEM images and SAXS patterns. The model does not contain any reactive aspects but captures the morphology of the systems which both showed pinning of the micro-structure at early stages of microphase separation in contrast to the equilibrium structures formed by block copolymers.

A synchrotron SAXS study of structure development in a copoly(isocyanurate-urea) formed by RIM

Abstract Structure development during reaction injection moulding of a copoly(isocyanurate-urea) was studied using time-resolved, synchrotron SAXS. During the rapid copolymerization of liquid reactants, incipient microphase separation was shown to occur at a critical conversion of isocyanate groups and to proceed via the kinetics associated with spinodal decomposition. Microphase separation was halted prematurely by vitrification of the polyisocyanurate phase, thus producing a copoly(isocyanurate-urea) with a non-equilibrium, co-continuous morphology with a size scale of ≈ 100 A.

Using synchrotron radiation to study polymer processing

Abstract Recent developments in time resolved X-ray scattering from polymers are reviewed in the context of structure development in polymer processing. The use of fast SAXS/WAXS and its combination with differential scanning calorimetry (DSC) is given as an example of the use of SR in studying thermoplastics processing. A second example of SR in polymer processing concerns the in situ measurement of structure development in polyurethane foam formed by reaction injection moulding.

Combined small angle X-ray scattering (SAXS) and Fourier transform infrared (FT-IR) spectroscopy in a time resolved mode using synchrotron radiation

Abstract The simultaneous time resolved study of structure development and reaction kinetics during materials processing is an experimental method which has great potential in developing a deeper understanding of the parameters which govern the formation of various material structures and their final properties. A novel combination of synchrotron radiation small angle X-ray scattering and Fourier transform infrared spectroscopy has been developed, at Daresbury Laboratory, to enable these experiments to be conducted. Successful experiments on a series of model segmented block copoly(urethane)s have been performed and have shown that this combination of techniques is feasible, and has the potential to become a very powerful research tool for a wide variety of research fields.

A synchrotron SAXS study of the structure development kinetics during the reactive processing of flexible polyurethane foam

Abstract The kinetics of microphase separation during the reactive processing of flexible polyurethane foam have been investigated. Forced-adiabatic, time-resolved synchrotron SAXS experiments were employed to probe the evolution of polymer structure. Microphase separation was observed to occur at a critical conversion of isocyanate functional groups and shown to follow the kinetics associated with spinodal decomposition. The data have been analysed in terms of a time dependent Ginzburg-Landau model (TDGL).