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Recent advances in macromolecular synthesis have been concerned with molecules containing two components in which each component is not distributed randomly as in a copolymer but segregated to a defmite part of the molecule. The provisional name of block copolymer has been applied to such a nonrandom type of structure. Linear molecules of this kind have been synthesized in two ways.' By utilizing a two-phase system of aqueous methacrylic acid and styrene it has proved possible to synthesize part of a molecule in the aqueous phase and part in the styrene phase. This method has obvious limitations since it is not easy to choose monomers which will be solely confined to the phases concerned. The second method consists in attaching to the end of a polymer (in this case polystyrene) a bromine atom, dissolving the polymer in a suitable monomer and then removing the bromine atom by photolysis. The polymer radical and the brordine atom each initiate polymerization and thus three types of polymer are present in the system. The polystyrene component can be extracted by suitable solvents and the block polymer separated from the remaining mixture by precipitation procedures using the turbidity of the solution to follow the precipitation.2Branched chain nonrandom copolymers can also be made by the process of grafting a new polymer chain to a polymer by conducting polymerization of monomer B in the presence of polymer originally made from monomer A.3 In doing this two structural features are incorporated in the molecule and therefore it is not easy to see how each of these features contributes to the properties of the resultant polymer. In attempts to deal with the branching factor methods have been developed for the synthesis of branched chain polymer and also grafting has been followed in homogeneous polymer by grafting on radioactive polymer of the same chemical composition as the original polymer.Since this new field in polymer chemistry is extensive and relatively complicated it is necessary to devise a number of new methods for the synthesis of block polymers so that a wide variety of new kinds of moleciiles may be synthesized and their properties examined. This paper describes another method for the synthesis of block polymers and incidentally another technique for measuring the lifetimes of polymer radicals.A selected monomer containing photosensitizer flows along a capillary at a defined rate into a suitable reservoir. A limited portion of the capillary is illuminated with very in- 461The principle of the method is as follows.

Polyurethane (PU) foams used in wound management are produced by a reaction between aromatic diisocyanates and polyether polyols. There is concern that residues of these starting materials, which may contain aromatic amine functionality, may leach from the finished polymer during in vivo applications. Furthermore, oligomers and additives may be leached from the PU system after the polymerization process is complete. Finished polymers have, therefore, been extracted with a range of solvents, such as water, diethyl ether and dilute HCl. The extracts were subjected to MALDI-MS (matrix-assisted laser desorption ionization mass spectrometry) analysis in an attempt to determine the amine and polyol functionality. Direct MALDI-MS analysis of the wound dressing extracts indicated the presence of components based on the polyols [corrected] used in the formulation of the foam. The spacing between the peaks identified the base monomer used in the polyol. MALDI-MS analysis of the fluorescamine derivatives of model amine compounds has demonstrated the anticipated increase in mass (278 for monoamines and 278 and 556 for diamines). Similar results were obtained from the derivatization of model polyols with phenyl isocyanate, where the mass shift (n x 119) was a direct measure of the number of active hydroxyl groups. Fluorescamine labelling of PU foams shows the colour change which could be [corrected] indicative of the presence of an amine, but the subsequent MALDI-MS analysis was unable to demonstrate the anticipated increase in mass.

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Articles you may be interested inEfficient infrared thermal emitters based on low-albedo polaritonic meta-surfaces Appl. Phys. Lett. 102, 211111 (2013); 10.1063/1.4808086 Experimental characterization and modeling of a nanofiber-based selective emitter for thermophotovoltaic energy conversion: The effect of optical properties Preliminary analyses are presented to examine how the geometric distribution of rare-earth material in a thin film selective emitter influences the net emission. The general one-dimensional equation of radiation transfer is considered under the assumption of negligible rescattering by eliminating the phase function term. Due to the large value of the absorption coefficient for the materials under discussion, the diffusion approximation to this equation is used. Homogenization techniques are applied to this diffusion approximation to define expressions for the effective absorption and scattering coefficients for a spatially distributed selective emitting film. The emitting film consists of alternating layers of emitting and nonemitting materials into a form we call stacked layers. The optical properties of the individual layers are determined experimentally. These properties are input into the effective expressions for the absorption and scattering coefficients. The effective expressions are input into the general one-dimensional equation of radiation transfer to model the net radiation obtained from these emitting structures in directions parallel and perpendicular to the stacked layers. Results show that the emissivity of the film along the parallel direction of the stacked layers exceeds that along the perpendicular direction. Further, a film consisting of stacked layers with half the volume fraction of emitting material emits radiation along the parallel direction that is quantitatively comparable to the emission from a film consisting of a single layer of only emitting material. Hence, the reduction in emitting material may lead to a drop in the weight of the device and to lower costs.