Joel M. Williams

Microcellular foams: phase behaviour of poly(4-methyl-1-pentene) in diisopropylbenzene

Abstract Microcellular foams are an important component of Inertially Confined Fusion (ICF) targets. The spatial distribution of the material is critical as the target implodes. In an effort to improve the spatial uniformity, we have explored the phase separation behaviour of poly(4-methyl-1-pentene) solutions with diisopropylbenzene solvent. The cloud-point phase-separation diagram from pure solvent to pure polymer is discussed. Microstructures of the various density foams and the need for a three-dimensional phase diagram are presented.

Microstructures and properties of some microcellular foams

The microstructures of a variety of low-density (less than 0.1 g cm−3) polymeric foam materials are presented. Structures include the large, but well-defined, closed cells of commercially produced foams and a variety of finer, but often less well-defined, open cells of research foams produced from polymers, carbon, and silica. Other topics covered are the sizes and lowest densities of foams available, optical and X-ray opacity, and ease of handling.

High-density foams prepared with the styrene-divinylbenzene copolymer/heptane system

Abstract This report focuses on the production of 0.1–1.03 g cm−3 foams by taking an open, microcellular foam, saturating it with a radical-polymerizable monomer solution, polymerizing the monomers and removing the non-polymerizing diluent solvent. This study also contains information about the phase separation behaviour of divinylbenzene-crosslinked polystyrene from heptane, and about the expansion and retraction of crosslinked polystyrene. The influence of filler composition on the microstructure of the foams is presented. These two-component foams provide a new line of microporous materials, which may provide a simple alternative to the beads currently used in chromatography.

Compression moduli of some PM P microcellular foams

The elastic moduli of poly(4-methyl-1-pentene) foams made by several processes are measured. The results reveal that several terms need to be added to the currently accepted mathematical representation. Thus, the amount of noncontributing mass and the efficiency of the contributing mass must be considered along with the isotropic reduction in total mass. The mathematical equation derived gives new insight into the structure and properties of microcellular foams.

Effect of several dual solvents on the phase separation of poly(4-methyl-1-pentene)

Abstract Phase separation of isotactic poly(4-methyl-1-pentene) (PMP) from various solvents gives polymer masses which can be converted into foams that vary from crumbly powders to well-connected, strong, flexible solids. The composition of the solvent is an important parameter in determining the nature of the separated polymer phase. The influence of solvent (or non-solvent) on the temperature and character of the phase separation event and on the resulting foam structure is addressed in this paper. Thus differing ratios of two poor solvents for PMP, bibenzyl and paraffin, were found to give variable foam structures and surprising phase behaviour. Thermochromism is sometimes observed as the polymer separates.

Bromine-Containing Polymeric Foams

ow Z-element (i.e., low atomic number), low density, microcellular Lfoams are common components in targets [1-7] and plastic shells [8-11] used in laser-driven plasma physics and inertially confined fusion experiments. As those experiments become more refined, materials requirements for foam-containing target components have become more stringent. Target designers increasingly call for unusual foam geometries with novel chemical components and specific physical properties. Scientists from the University of Dundee, Scotland, and from the Atomic Weapons Establishment (AWE), Aldermaston, UK, have recently reported on the preparation and fabrication of cylindrical, microcellular foam-filled targets for laser-driven experiments [12]. This unique method of foam fabrication involves the in situ preparation of a polymer gel by UV photopolymerization of a solution of trimethylolpropanetriacrylate (TMPTA), phase separation of the polymer, and extraction of the solvent with supercritical carbon dioxide. This method manifests many advantages: (1) a broad range of foam densities (0.020-0.20 g/cm3) can be prepared, (2) small cell sizes ( < 1 /mi) can be

Diagnosis and therapy for a recalcitrant parylene coater

An in‐house built parylene coater produced coatings whose thicknesses varied 50% at the 1‐μm level, whose surfaces were rough and flapjacklike, and whose cross sections looked like foam. This paper details the product response to various equipment and operational changes. The systematic analysis showed that a balance of vacuum pressure and pyrolysis temperature is needed to produce good‐quality coatings.

Polymerization-depolymerization of 1,3-dioxolane

Abstract Poly(1,3-dioxolane) can be cleanly depolymerized to the monomer. As such, the 1,3-dioxolane system is a good one to study to learn about microscopic reversibility. Besides describing how to perform the reversible polymerization reaction, this paper also presents data on the pyrolysis-field ionization mass spectrometry (Py-f.i.m.s.) and g.p.c. of the polymer and n.m.r. characterization of the monomer and polymer. The Py-f.i.m.s. data indicate that unhydrolysed polymer fragments in a manner similar to the reverse of the polymerization sequence, i.e. the carbonium ion portion of the oxymethylene end group bites back on oxygen atoms in the backbone. Base-terminated polymer, on the other hand, appears to undergo mid-chain cleavage. A dominant peak in the Py-f.i.m.s. spectrum of either, however, corresponds to the protonated cyclic dimer, a 10-crown-4 ether. A sequestered proton structure is proposed for this protonated species.

Preparation of microcellular foam in cylindrical gold targets

The preparation of microcellular foam in submillimeter cylindrical gold targets is described. The gold cylinders were fabricated by electroplating gold onto a silicon bronze mandrel and leaching the mandrel with concentrated nitric acid. After several rinsing and cleaning steps, the cylinders were filled with a solution containing trimethylolpropanetriacrylate (TMPTA). Low density, microcellular polymeric foam was prepared by in situ photopolymerization of the TMPTA solution. Foam preparation was extremely sensitive to metal ion contaminants. In particular, copper ions left behind from ineffective leaching of the silicon bronze mandrels inhibit polymerization and must be removed in order to obtain uniform, nonshrinking foams. A procedure for the effective leaching of the mandrels is described. In addition, a study on the effects of potential contaminants and polymerization inhibitors on TMPTA photopolymerization is presented.

Effect of substituent position on the phase separation of poly(4-methyl-1-pentene) in diisopropylbenzene

Abstract The behaviour of poly(4-methyl-1-pentene) in a mixture of diisopropylbenzene isomers mimics that of the 1,4-isomer to an extent proportional to the amount of 1,4-isomer in the mixture. The 1,3-isomer gives the normal cloud-point curve behaviour, while the 1,4-isomer gives an anomalous one. This difference is reflected in the physical appearance of the foams obtained from the separated solutions. From an analysis of the solvent-to-polymer composition at the onset of this anomalous behaviour, a unique relationship is found for one 1,4-isomer molecule per methylpentene repeat unit. The observed results suggest special ordering of molecules during gelation.