ABSTRACT
Stereoblock polypropylenes are complicated, intriguing, and challenging polymers. It may be worthy to open this chapter by recalling that, according to the IUPAC Glossary of Basic Terms in Polymer Science,1 a block is “a portion of a macromolecule comprising many constitutional units, that has at least one feature which is not present in the adjacent portions”; a block macromolecule is “a macromolecule which is composed of blocks in linear sequence”; a stereoblock macromolecule is “a block macromolecule composed of stereoregular, and possibly non-stereoregular, blocks.” On paper, applying these definitions to propylene polymers is straightforward with the notable exception of the “stereoblock-isotactic” case, which will be discussed specifically in the last part of this section. On the other hand, demonstrating that these structures exist for a real polypropylene sample is a formidable microstructural problem; in fact, of the many cases claimed in the scientific and patent literature, those rigorously proven to be stereoblock polypropylenes can be counted on the fingers of one hand.
