In block copolymers structure

The standard molecular structural parameters that one would like to control in block copolymer structures, especially in the context of polymeric nanostructures, are the relative size and nature of the blocks. The relative size implies the length of the block (or degree of polymerization, i.e., the number of monomer units contained within the block), while the nature of the block requires a slightly more elaborate description that includes its solubility characteristics, glass transition temperature (Tg), relative chain stiffness, etc. Using standard living polymerization methods, the size of the blocks is readily controlled by the ratio of the monomer concentration to that of the initiator. The relative sizes of the blocks can thus be easily fine-tuned very precisely to date the best control of these parameters in block copolymers is achieved using anionic polymerization. The nature of each block, on the other hand, is controlled by the selection of the monomer for instance, styrene would provide a relatively stiff (hard) block while isoprene would provide a soft one. This is a consequence of the very low Tg of polyisoprene compared to that of polystyrene, which in simplistic terms reflects the relative conformational stiffness of the polymer chain. 

The method is based on the simple but effective idea that the pores of a host material can be used as a template to direct the growth of new materials. Historically, template synthesis was introduced by Possin (1) and refined by WilUams and Giordano (2) who prepared different metallic nanowires with widths as small as 10 nm within the pores of etched nuclear damaged tracks in mica. It was further developed by Martin s group (3-5) and followed by others (6) with the number of examples and applications (7) continually increasing. The nanoporous membranes usually employed as templates are alumina or track-etched polymeric membranes which are widely used as ultrafiltration membranes. Recently, metal nanostmctures have also been obtained using the pores created by self-assembly in block copolymer structures under the influence of electric fields and high temperatures (8,9). 

To extend the use of polyethylene, it is desirable to enhance polyethylene s polarity, toughness, adhesion and compatibility with other materials. One approach is by incorporating polyethylene in block copolymer structures (Hong et al, 2002). Polyethylene block copolymers can maintain some of the superior properties of polyethylene while introducing the desired new properties from the other copolymer segments. In this way, the utility of polyethylene can be expanded to higher value areas, especially in polymer blends or composites, the preparation of micelles and the fabrication of nanoporous membranes (Wang and Hillmyer, 2001 Chen et al, 2009 Uehara et al, 2006 Uehara et al, 2009). 

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