Block copolymer structure

Fig. 5. Representative block copolymer structures, (a) Routes to SIS i, coupling reaction ii, sequential, (b) Three and four-arm SI stars, (c) (Sllih radial, (d) (SEB)2B2 radial.

Fig. 5.5 (A) Alginate block copolymer structure with random sequences (B) divalent cations induced gelation of alginate (formation of egg-box structure).

Upon copolymerization of each novolac with the PDMSX oligomers, both and increased as expected, although not in a strictly additive manner since we have not formed a single block copolymer structure (7) but are measuring... 

Block copolymer Structure Morphology Orientation method Ref. 

Hoogenboom R, Schubert US, van Camp W et al. (2005) RAFT polymerization of 1-ethoxy ethyl acrylate a novel route toward near-monodisperse poly(acrylic add) and derived block copolymer structures. Macromolecules 38 7653-7659... 

If both r and ri are greater than unity (and therefore, also r ri > 1) there is a tendency to form a block copolymer (structure II ) in which there are blocks of both monomers in the chain. This type of behavior is rarely encountered. 

Even though the products are not block copolymer structures, the work of Kadokawa and colleagues should be mentioned here. In a process that the authors named vine-twining polymerization (after the way that a vine plant grow helically around a support rod), the enzymatic polymerization of amylose is performed in the presence of synthetic polymers in solution, and the authors showed that the grown amylose chains incorporate the polymers into its helical cavity while polymerizing [184-191]. 

The higher the initial polymer molecular weight and the monomer tendency to terminate by combination, the more complex the block copolymer structure. 

The living nature of the poly(styryl)anion allows one to prepare block copolymers with a great deal of control of the block copolymer structure. The preparation of diblock, triblock, and other types of multiblock copolymers has been reviewed [29-32]. Several of these block copolymers are in commercial use. The basic concept involves first preparing polystyrene block [RSt StLi—see Eq. (2)] and then adding a new monomer that can be added to start another growing segment. 

The equivalence ratio can be calculated from the Mark-Houwink coefficient, K, of component homopolymers. The composition distribution in the chromatogram of a block copolymer is negligible. The peak point of a block copolymer chromatogram corresponds to the average structure of the polymer. Thus, analysis of block copolymers is reduced to analysis of the peak point. Analyses of anionic block copolymer structures have been successfully accomplished by this peak analysis technique with the aid of equivalence ratio. 

Copolymerization Initiators. The copolyineri/ution of styrene and dienes in hydrocarbon solution wilh alkyllithium initiators produces a tapered block copolymer structure because of the large differences in monomer reactivity ratios lor styrene (r, < 0.11 and dienes (rj > 10). In urder to obtain random copolymers of styrene and dienes, it is necessary to either add small amounts of a Lewis base such us tetrahydrofuran or an alkali metal alkoxide (MtOR. where Ml = Na, K. Rb, or Cs>. 

Aiba S-i (1991) Studies on chitosan 3. Evidence for the presence of random and block copolymer structures in partially N-acetylated chitosans. Int J Biol Macromol 13(l) 40-44... 

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