Blockiness, heterogeneous

Abstract Protein-like copolymers were first predicted by computer-aided biomimetic design. These copolymers consist of comonomer units of differing hydrophilicity/hydro-phobicity. Heterogeneous blockiness, inherent in such copolymers, promotes chain folding with the formation of specific spatial packing a dense core consisting of hydrophobic units and a polar shell formed by hydrophilic units. This review discusses the approaches, those that have already been described and potential approaches to the chemical synthesis of protein-like copolymers. These approaches are based on the use of macromolecular precursors as well as the appropriate monomers. In addition, some specific physicochemical properties of protein like copolymers, especially their solution behaviour in aqueous media, are considered. 

Keywords Chemical synthesis Heterogeneous blockiness Physicochemical studies Protein-like copolymers Solution behaviour... 

The third approach (iii), the solid-phase synthesis, has not been yet implemented for the preparation of protein-like HP-copolymers with heterogeneous blockiness, although the possibility—inherent in this method—to form the macromolecular chains with a well-defined chemical sequence of monomeric units is of great interest for the problem. That is why, these possibilities will also be discussed briefly in Sect. 2.4. 

Site isomerisation also occurs in heterogeneous systems [41], A certain blockiness of the polymer tells us that this phenomenom is taking place. 

It is interesting that some heterogeneous superhigh-activity Ziegler-Natta catalysts such as MgC /TiCU/LB—AlEt3 also yield random ethylene/propylene copolymers. These copolymers, however, exhibit a blocky nature and highly isotactic propylene sequences (with no 2,1-inserted propylene units) that contribute to undesired crystallinity [68,456]. 

The chemical structure of such copolymer polysoaps can be very heterogeneous, being subject to the problems of copolymerization. Also, suitable solvents for the copolymerization reaction may be difficult to find. In fact, the choice of the solvent seems to be crucial, as it strongly influences the copolymerization parameters when using monomers of greatly differing polarity [77, 156, 188, 219-222], This effect can be exploited for the preparation of random and blocky copolymers from the same pair of monomers depending on the reaction conditions [77, 220], and thus enables an additional structural variation of polysoaps (Fig. 4). 

Table 12.5 collects literature values for r and rir2 for different catalyst systems. With vanadium-based catalysts, a correct evaluation of rir2 is hindered by the remarkable presence of regioirregularities. One could say, however, that short comonomer sequences are obtained. With heterogeneous titanium-based catalysts, blocky copolymers are prepared. A correct determination of r r2 is, however, hindered by the multisite nature of the catalyst, that is, by the presence of (many) different polymer fractions resulting from many catalyst sites with different rir2 values that could in principle be responsible for an apparent higher blockiness. 

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