Stereorepeating units

Regular macromolecule essentially comprising only one species of stereorepeating unit. 

Unless otherwise stated, the drawings of configurational base units, configurational repeating units, stereorepeating units, etc., provide information regarding relative configurations. 

Polymerization of 1 -benzofuran with an optically active initiator gives the optically active polymer, poly[(27 ,35)-2,3-dihydro-l-benzofuran-2,3-diyl], containing predominantly one type of stereorepeating unit. 

Thus, not only the kind of configurational monomeric units, but also their mutual bonding to what are called stereorepeating units are important with polymers. The three simplest stereorepeating units in stereoregular poly(propylene) are... 

Here it is immaterial whether II-1 or II-2 is chosen as the simplest stereorepeating unit. Infinitely long poly(propylene) molecules from II-l, of course, differ from those from II-2 only in the orientation of the repeating units. Thus, chains consisting of II-l and II-2 are not enantiomeric to each other, which is in contrast to their configurational monomeric units. 

Stereoblock polymers are defined analogously to constitutional block polymers each block has a different species of stereorepeating unit to the block preceding it, but has the same constitutional monomeric units. Tactic... 

Stereoregular polymer n. A regular polymer whose molecules can be described by only one species of stereorepeating unit in a single sequential arrangement. A stereoregular polymer is always a tactic polymer, but a tactic polymer need not have every site of stereoisomerism defined (ISO). 

Stereorepeating unit n. A configurational repeating unit having defined configuration at all sites of stereoisomerism in the main chain of a polymer molecule (lUPAC). In stereoregular polypropylene, the two simplest possible stereorepeating units are ... 

A major 1981 lUPAC document addresses polymer stereochemistry in depth. Key chapters of this document discuss basic definitions (configurational unit, configurational base and repeating units, stereorepeating unit, different types of tacticity, tactic block polymers, and stereoblock polymers) sequences conformations and supplementary definitions. Most of the illustrations use the rotated Fischer projections, but some three-dimensional representations are included. 

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