Block copolymers with complex molecular architecture

2 Block copolymers with complex molecular architecture 

The synthesis concepts for linear structures outlined in Section 7.2.1 have been extended in the recent years to the preparation of block copolymers with complex architectures 

With the significant progress in the living polymerization techniques , in the design of multifunctional initiators and the control in coupling reactions a large variety of block copolymers with sophisticated architecture became available such as cyclic, H and star shaped, multiarm and pahn-tree or dumbell structures, dendritic blocks linked to linear blocks, etc. 

In the following typical examples of these new amphiphilic structures will be outlined, by considering at first block copolymers with poly A/polyB sequences and then those comprising poly A/poly B/poly C blocks. In both cases only copolymers having at least one water-soluble block will be considered. Further details and informations especially on star-block copolymers can be found in the excellent review articles recently published by Hadjichristidis etal. [13], Hirao etal. [77] and Quirk etal. [78]. 

/ Block copolymers with poly A/poly B sequences 

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A wide range of functionalized block copolymers also became available by anionic polymerization, with the specific functionality either at the junction of the A and B block, or as end-standing functionality. Of special interest for micellization studies is the functionalization of block copolymers, for example PS-PEO diblocks with fluorescent labels like anthra-cenyl or phenanthrenyl groups built in at the junction of the two blocks [ 54]. Furthermore, anionic polymerization is of special interest for the preparation of block copolymers with complex molecular architecture, as shown in the review articles of Almdal [23] and Hadjichristidis etal. [13]. 

Reversible addition-fragmentation chain transfer (RAFT) polymerization has proven to be a powerful tool for the synthesis of polymers with predetermined molecular weight and low polydispersity [11, 12], In recent years, synthesis of polymers with complex molecular architecture, e.g. block and star copolymers, via the RAFT process have been reported [13],... 

In 1998, Chiefari et al. [10] attempted to combine the convenience of radical polymerization with the many benefits of living polymerization, e.g. control of the molecular weight and polydispersity and the possibility of synthesizing block copolymers of complex architecture. They used free-radical polymerization reagents of formula (I) to produce a sequence of reversible addition-fragmentation in which the transfer of the S=C (Z) S moiety between active and dormant chains serves to maintain the living character of the polymerization ... 

Using the repoited data on the experimentally derived values of glass transition temperature, Tg, degree of crystallinity, Vickers indentation microhardness, H, and blend compositions for homopolymers, block copolymers, blends of polyolefins, or of polycondensates, blends of miscible amorphous polymers and copolymers (some of them with rather complex molecular architecture), all of them containing a soft component and/or phase at room temperature, an attempt is undertaken to look for the reasons for the frequently reported drastic deviations of the experimentally derived H values from the calculated ones by means of the additivity law assuming that the contribution of the soft component and/or phase is negligibly small. 

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