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Pore structure crosslinked polymer

Polymer-based, synthetic ion-exchangers known as resins are available commercially in gel type or truly porous forms. Gel-type resins are not porous in the usual sense of the word, since their structure depends upon swelhng in the solvent in which they are immersed. Removal of the solvent usually results in a collapse of the three-dimensional structure, and no significant surface area or pore diameter can be defined by the ordinaiy techniques available for truly porous materials. In their swollen state, gel-type resins approximate a true molecular-scale solution. Thus, we can identify an internal porosity p only in terms of the equilibrium uptake of water or other liquid. When crosslinked polymers are used as the support matrix, the internal porosity so defined varies in inverse proportion to the degree of crosslinkiug, with swelhng and therefore porosity typically being more... [Pg.1500]

Characterization of the crosslinked polymer in the dry state [apparent density (16), surface measurement by N2-ad sorption (17,18), Hg-intrusion for measurement of the pore volume (iS)] is not conclusive for the properties as polymeric reagent, However, extensive knowledge about the porous structure and the accessibility of different regions in the polymer network can be obtained by gel-permeation chromatography (GPC) (20). GPC is used in an inverse mode. Well-characterized samples are keys for the pore structure. [Pg.3]

The schematic structure of a microball is shown in Fignre 5.14. The outermost layer of a microball is a hydration layer that makes the microball stable in water so that it will not precipitate. The middle, crosslinked polymer layer gives the microball some elasticity and deformabiUty. The inner layer is a core that gives the microball some strength when it blocks a pore throat (Snn et al., 2006). [Pg.126]

First, the lyotropic phase is used as a template for the preparation of a bicontinuous silica structure, from which the polymer is removed by calcination or extraction. In the second step the porous inorganic structure is filled with monomer and crosslinker which is polymerized to form a bicontinuous organic polymer network from which the silica template is removed by treatment with hydrofluoric acid. An example for the preparation of hierarchical structures is the synthesis of bicontinuous pore structures by using two templates simultaneously [115]. In this case a liquid crystalline lyotropic phase of an amphiphilic block copolymer is used as a template together with suspended latex particles. The sol-gel process with subsequent calcination leads to a bicontinuous open pore structure with pores of 300 nm and 3 nm. [Pg.24]

The applicability of nanocasting as an analytical tool has been demonstrated [38] by comparing the silica structures obtained from the lyotropic phase, which has been crosslinked using y-rays, in order to provide sufficient mechanical stability to allow thin-sectioning, with those of a silica nanocast obtained from a lyotropic phase of the same composition (Fig. 7). The similarity between the structures is striking. A reference sample was prepared by filHng the pore system of the crosslinked polymer gel with sihca and subsequent calcination. The pictures prove without doubt that the sol-gel process indeed does not have any structurally disrupting effect on the hquid crystalhne phase [38]. [Pg.39]

Scheme 1 a-c Synthesis and structure of macroporous resins, a Polymer network forming b porogen phase acts as pore template c dry macroporous resin with large interconnected pores. (1) Porogen and network start to phase separate (2) porogen phase removed to yield pores (hatched area=crosslinked polymer, dofs=porogen phase)... [Pg.4]

The monomer 1 was copolymerized by free radical initiation in the presence of an inert solvent with a large amount of a bifunctional crosslinking agent. Under these conditions, macroporous polymers were obtained which possessed a permanent pore structure, a high inner surface area, and good accessibility. Additionally, low polymer swellability would imply limited mobility of the polymer chains. From a polymer of this type, 40 to 90% of template molecules can be split off by treatment with water or alcohol (see Figure 3 ). If this polymer is... [Pg.189]


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See also in sourсe #XX -- [ Pg.120 ]




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