Polymeric resins pore structure

In addition to monomers and the initiator, an inert liquid (diluent) must be added to the monomer phase to influence the pore structure and swelling behavior of the beaded resin. The monomer diluent is usually a hydrophobic liquid such as toluene, heptane, or pentanol. It is noteworthy that the namre and the percentage of the monomer diluent also influence the rate of polymerization. This may be mainly a concentration or precipitation effect, depending on whether the diluent is a solvent or precipitant for the polymer. For example, when the diluent is a good solvent such as toluene to polystyrene, the polymerizations proceed at a correspondingly slow rate, whereas with a nonsolvent such as pentanol to polystyrene the opposite is true. 

Hi. The monomer polymerization route. Compared with the resin-functionalization route, the homo- and copolymerization of organotin-containing monomers permits one to influence the polymer resin structure to a greater extent. In principle, it is possible to prepare gel-type, macroporous, microporous or nonporous polymers. The pore structure, tin loading, solubility and other factors which influence the reactivity of the polymer-supported organotin reagents can be controlled by appropriate... 

Data of low-temperature nitrogen adsorption were used to evaluate the parameters characterizing the pore structure of the obtained polymeric materials in dry state. The BET specific surface area, Sbet, and the total pore volume, V, were estimated by applying the standard methods Sbet from the linear BET plots and F/ from adsorption at relative pressure p/po=0.975) [7]. The mesopore structure was characterized by the distribution function of mesopore volume calculated by the Barret-Joyner-Halenda (BJH) method [27]. In Table 2 the values of these parameters are given for both synthesized polymers. The melamine-formaldehyde resin MEA has a more developed pore structure (5 B 7=220mVg, F,=0.45cm /g) and narrower mesopores (D=7.3nm) in comparison to the phenolic-formaldehyde polymer PHD. 

A key factor in the development of adsorption technology for the fluid separation has been the availability of appropriate adsorbents. The most frequently used categories include crystalline materials like zeolites, and amorphous materials like activated carbons, silica and alumina gels, polymeric sorbents, and ion-exchange resins. These materials exhibit a large spectrum of pore structures (networks of micro- and mesopores of different shapes and sizes) and surface chemistry (degrees of polarity), which provide a large choice of core adsorptive properties (equilibria, kinetics, and heat) to be utilized in... 

Macroporous resins. In contrast to gel-type resins, these are prepared by polymerization in an unreactive solvent, which defines the pore structure. The functionality is largely restricted to the pore surface and is accessible even to solvents and liquid reaction media that are not good sweUing solvents. 

Resin beads are synthesized as gel or macroporous materials. The macroporous resins are polymerized in the presence of a third component that is insoluble in the polymer. After this insoluble component is removed, large pores remain that allow the ions to have improved access to the interior pore structure of the beads. Macroporous resins can be useful for large ions like proteins, but they are more expensive, have lower capacity, and are harder to regenerate than the gel resins. However, they are said to be more resistant to thermal and osmotic shock as well as to oxidation and organic fouling than the gel-type resins [4]. 

The only example of stepwise polymerization to appear in the literature is the electrosynthesis of an open pore urea-formaldehyde structure at the anode from an aqueous solution of a non etherified urea-formaldehyde resin. The structure has similar characteristics to those of a foam obtained by acidification. ... 

S. L. Regen, J. Am. Chem. Soc. 98 (1976), 6270 /. Org. Chem. 42 (1977), 875 M. Cin-quini etal, J.C.S. Chem. Comm. (1976), 394 H. Molinari et al ibid. (1977), 639 J. M. Brown and J. A. Jenkins, ibid. (1976), 458). Asymmetric reactions, with reasonable optical yields, have been attempted by this technique (S. Colonna et al, J.C.S. Perkin I (1978), 8). In particular, Chiellini and coworkers have prepared stereo-ordered macro-molecular matrices bearing ammonium groups as catalysts for use in alkylation and car-benation reactions (E. Chiellini and R. Solaro,/.C.5. Chem. Soc. (1977), 231-232 and / Org. Chem, in press E. Chiellini et al, Makromol Chemie 178 (1977), 3165-3170. Where salts of optically active amines were used, the final product displayed low but distinct optical rotation. The latter papers are to be noted because they are among the very few in this field in which attention is paid to the influence of various parameters of the macromolecular structure (polymerization degree, stereoregularity, dimension of the pores in the polymeric resins, etc) on chemical reactivity and in particular on catalysis. 

Modification of porous inorganic materials by carbon makes it possible to obtain porous carboniferous composites with high thermal and chemical stability and strength. To introduce carbon into pores, both gas phase pyrolysis and carbonization through thermochemical solid-phase reactions are employed. The formation of carbon structures depends on carbonization conditions process rate, precursor concentration, presence of catalyst, etc. [1-3]. Phenolic resins, polyimides, carbohydrates, condensed aromatic compounds are most widely used as polymeric and organic precursors[4-6]. 

The presence of insoluble materials in the polymerization mixture may have some control on the structure of the polymeric skeleton. Seidl et al. reported that the micro structure of skeletons of ion-exchange resins, based on the copolymers of styrene and DVB, can be controlled by carrying out the polymerization in presence of an inert material and by adjusting the reaction conditions and concentration of DVB. The micro structure depends on the parameter of interaction and on the molar volume of the inert material. In the case of copolymers modified by an inert component with high molar volume and interaction parameters, microstructures with small measureable surfaces and pores with relatively large radii are obtained. 

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