Network polymer morphology

O2 diffusion through the membrane seems to be limited by the percolation network of the diffusion path, which is not only defined by the amount of water in the membrane, but also by the different chemical structure of the membranes. It is difficult to make comparisons of gaseous diffusion behavior among polymers with different structures because polymer morphology can change drastically without appreciable changes in density, and the presence of water and the hydrogen bonds formed between polymer-water moieties also has major effects on system properties. However, some points can be made from these particular studies. 

Lignin in the true middle lamella of wood is a random three-dimensional network polymer comprised of phenylpropane monomers linked together in different ways. Lignin in the secondary wall is a nonrandom two-dimensional network polymer. The chemical structure of the monomers and linkages which constitute these networks differ in different morphological regions (middle lamella vs. secondary wall), different types of cell (vessels vs. fibers), and different types of wood (softwoods vs. hardwoods). When wood is delignified, the properties of the macromolecules made soluble reflect the properties of the network from which they are derived. 

Ebdon JR, Hourston DJ, Klein PG (1986) Polyurethane-polysiloxane interpenetrating polymer networks 2. Morphological and dynamic mechanical studies. Polymer 27( 11) 1807—1814... 

The effect of polymer morphology on membrane structure and conductance has been shown recently. In Ref. 25 hydrogen-based graft-copolymer membranes were compared in terms of morphology and performance to random copolymer membranes with the same ion content. For the hydrated grafted membranes TEM micrographs revealed a picture of a continuous phase-separated network of water-filled channels with diameters of 5 nm. In contrast to that, the random copolymer membranes exhibit a reduced tendency toward microphase separation water is... 

There are at least four general types of combinations of crosslinked (x) and linear (1) polymers in a two-component system both components crosslinked (xx), one or the other component crosslinked (lx or xl), and both components linear (11). Where at least one of the components has been polymerized in the presence of the other, the xx forms have often been called interpenetrating polymer networks (IPN), the lx and the xl forms termed "semi-IPNs", and the last, linear or in situ blends. There are also a number of ways in which the components can be formed and assembled into a multicomponent system. Sequential IPNs are prepared by swelling one network polymer with the precursors of the second and polymerizing. Simultaneous IPNs are formed from a mixture of the precursors of both components polymerization to form each component by independent reactions is carried out in the presence of the other precursors or products. Usually, the simultaneous IPNs that have been reported are extremes in the component formation sequence the first component is formed before the second polymerization is begun. Sequential IPNs and simultaneous IPNs of the same composition do not necessarily have the same morphology and properties. 

A polyurethane (PU)/poly(n-butyl methacrylate) (PBMA) system has been selected for an investigation of the process of phase separation in immiscible polymer mixtures. Within this system, studies are made of the XX, lx, xl, and the 11 forms. In recognition of the incompatibility of PBMA with even the oligomeric soft segment precursor of the PU, no attempt was made to equalize the rates of formation of the component linear and network polymers. Rather, a slow PU formation process is conducted at room temperature in the presence of the PBMA precursors. At suitable times, a relatively rapid photopolymerization of the PBMA precursors is carried out in the medium of the slowly polymerizing PU. The expected result is a series of polymer mixtures essentially identical in component composition and differing experimentally only in the time between the onset of PU formation and the photoinitiation of the acrylic. This report focuses on the dynamic mechanical properties cf these materials and the morphologies seen by electron microscopy. 

These reactions have been explained in detail in the sections of Chapter 1 indicated and they are all identified by permanent, covalent bonds between polymeric chains. These chemical-network polymer systems are an important sub-class of network polymers and are sometimes referred to as thermoset polymers. Thermoset polymers cannot be re-melted or undergo flow under the influence of heat once they have been polymerized (i.e. they have a thermosef morphology, unlike thermoplastic polymers, which can be re-melted and flow under application of heat). Owing to their excellent properties at high temperatures (and under extreme environmental conditions) thermoset polymers are suitable for a wide variety of high-performance applications such as electronic packaging, automotive panelling and... 

Where the morphology of a network polymer corresponds to the second variant, its structure can be represented as a mixture of arbitrary polymer fractals in the vicinity of the gelation point the spectral dimension of the globule is and that of the inter-globule area is 83. The 83 value can be estimated using the relationship [61] ... 

Many theories have been proposed to account for the profound effect minute proportions of silane coupling agents at the dispersed particle interface have on the performance of composites.These include chanical bonding theory acid—base interactions formation of interpenetrating networks wetting and surface energy effects polymer morphology modification deformable layer theories restrained layer theory. 

Kumar, H., Anilkumar, A., and Siddaramaiah. 2006. Physico-mechanical, thermal and morphological behaviour of PU/PMMA semi interpenetrating polymer networks. Polymer Degradation and Stability 91 1097-1104. 

Hed Hedrick, J. L., Yilgor, I., Jurek, M., Hedrick. J. C., Wilkes, G. L., McGrath, J. E. Chemical modification of matrix resin networks with engineering thermoplastics 1. Synthesis, morphology, physical behaviour and toughening mechanisms of poly (arylene ether sulfone) modified epoxy networks. Polymer 32 (1991) 2020-2032. 

Morphological Studies of High Performance Network Polymers... 

Sellergren, B. Shea, K.J. Influence of polymer morphology on the ability of imprinted network polymers to resolve enantiomers. J. Chromatogr. 1993, 635, 31-49. 

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