Amorphous Microporous Polymers

Thomas S, Pinnau I, Du N et al (2009) Hydrocarbon/hydrogen mixed-gas permeation properties of PIM-1, an amorphous microporous spirobisindane polymer. J Membr Sd 338 1 ... 

Polymers confined in the nanosized spaces of the PCP channels typically show properties that are distinctly different from those shown for the same materials in the bnlk state becanse of the formation of specific molecular assemblies and conformations [19, 20]. The inclusion of polymers within crystalline microporous hosts (pore size < 2 mn) with ordered and well-defined nanochannel sfiuctures has atfiacted considerable levels of attention because, in confiast to amorphous bulk polymer systems and polymers in solution, this approach can prevent the entanglement of polymer chains and provide extended chains in resfiicted spaces. 

Conversely, in most observed cases where solidification occurs as a result of continued depletion of solvent (as described in Case B), the highly concentrated polymer layer solidifies as a relatively dense, amorphous, plasticized film. Water diffusion into this highly plasticized layer becomes prevalent (Case A) at a stage where the contraction has gone "too far" to yield even a microporous membrane structure. 

A summary of ordered macroporous materials with different compositions is given elsewhere.Many compositions have been made, ranging from oxides, polymers, " and carbons, to semiconductors and metals. The wall structures of macroporous materials can be amorphous, crystalline, with mesopores or micropores, organically modified, or with surface catalysts. ... 

As a consequence of all these properties, zeolites can be considered to be exceptional catalysts which have replaced amorphous solids in many applications. However, for the catalytic cracking of polymeric wastes, zeolites may be disadvantageous due to the steric and diffusional problems that polymer molecules may have in accessing the zeolite micropores. These drawbacks can be overcome with the use of zeolitic catalysts with very small crystal size and, therefore, with a high proportion of external surface area which is not subjected to steric hindrances for the conversion of bulky substrates. 

Solvent porogen effects for macroporous resins are often explained in terms of the degree of solvation imparted to the incipient polymer netwoik, the point at which phase separation takes place, and the resultant degree of in filling between primary particles [26]. This may play a role in some amorphous MOPs (for example, micro/ mesoporous PPV [13]) however other systems such as HCPs (Sect. 2.1) do not undergo phase separation in this way [21, 22]. This basic mechanistic difference also accounts for the apparent independence of surface area on monomer concentration for conjugated microporous PAE networks [ 19], for example, in comparison with macro-porous polymer resins where surface area may be strongly concentration dependent. 

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