PolyIsoprene, description

The first alkene polymer to be used in society was polyisoprene, a natural product extracted from the sap of rubber trees. See our Box for a description of the history of rubber. The monomer from which this polymer is constructed... 

The first report on anionic polymerization appeared in the patent literature in 1910-1911. Matthews and Strange (l) in 1910 and later Harries (2) in 1911, described the preparation of polyisoprene using sodium and potassium as initiators. They mentioned the use of lithium as a possible initiator for this polymerization, but there seems to be no description of the polymer... 

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. 

For the diblock copolymer, which exhibits a flow region at longer times than pure polyisoprene, the relaxation of the isoprene sequence is treated like the relaxation of the arm of a star polymer. We have followed the description proposed by McLeish [17, 18] for star homopolymers. The distribution of relaxation times is given by Eq. (9), where Mb is the molecular weight of one branch (here the molecular weight of the polyisoprene sequence), s ranges be-... 

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