Polystyrene, hypercrosslinked

First, the particles formed are too large so efficiency of noble metal usage is too low. Secondly, the catalyst synthesis is too complex, involving several stages. In our earher work we studied the formation of Co nanoparticles in nanoporous hypercrosslinked polystyrene (HPS) which showed great promise in controlling the nanoparticle size [97]. 

With respect to sweUing in non-solvents, toluene-modified styrene— DVB copolymers have much in common with hypercrosslinked polystyrenes [330]. Both are prepared in accordance with the same basic principle, the formation of rigid networks in strongly solvated state. It will be shown in detail in Chapter 7 that rigid expanded networks possess a relaxed favorable conformation only in their swollen state and, therefore, exhibit a marked tendency to acquire this state by sweUing and incorporating any liquid, even non-solvating one. 

BASIC PRINCIPLES OF FORMATION OF HYPERCROSSLINKED POLYSTYRENE NETWORKS... 

Preparation of Macronet Isoporous and Hypercrosslinked Polystyrene Networks... 

The basic principle of their suggestion was formulated as intensive crosslinking of polymeric chains, in particular, chains of polystyrene, in solution or in swollen state by rigid bridges. This approach led to the creation of a new type of polymeric materials with special structure and peculiar properties that were not characteristic of any known types of networks. Therefore, a new term was needed to characterize these new materials we have called these new polymers hypercrosslinked polystyrene. ... 

The following fundamental principles constitute the concept of hypercrosslinked polystyrene network formation. 

Trying to completely avoid the technically unpleasant process of chloromethylation, Negre et al. [48, 49] prepared a linear styrene copolymer with p-vinylbenzyl chloride and then subjected the product to self-crosslinking. Alternatively to the earlier-mentioned crosslinking of linear polystyrene with MCDE, this procedure results in local inhomogeneity of crosslinks distribution, because of the uneven distribution of the two comonomers along the initial chain (the monomer reactivity ratios of vinylbenzyl chloride and styrene are 1.41 and 0.71, respectively). Nevertheless, vinylbenzyl chloride became a popular comonomer for styrene and DVB in the preparation of beaded hypercrosslinked products [50-52]. 

Friedel-Crafts reaction can proceed in a rather limited number of inert solvents, such as aliphatic hydrocarbons, benzene, nitrobenzene, CS2, and chlorinated or fluorinated hydrocarbons. Among these solvents, however, only chlorinated hydrocarbons, particularly EDC, nitrobenzene, as well as cyclohexane at an elevated temperature, are suited for the synthesis of hypercrosslinked polystyrene, since they are thermodynamically good solvents for both the initial polystyrene and the final products of crosslinking. 

Synthesis conditions of macronet isoporous and hypercrosslinked polystyrene networks... 

Figure 6.1 FTIR spectra of (a) linear atactic polystyrene with molecular weight of 400 kDa, (b) poly(p-methylstyrene), and hypercrosslinked polystyrenes prepared by crosslinking styrene-0.5% DVB copolymer with (c) 0.3, (d) 0.5, (e) 1.0, and (0 1.5 mol of monochlorodimethyl ether per styrene repeating unit.

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