Configurational unit

Whole or part of a chain comprising one or more species of configurational unit(s) in defined sequence. 

Note Configurational sequences comprising two configurational units are termed diads, those with three such configurational units triads, and so on. In order of increasing sequence lengths they are called tetrads, pentads, hexads, heptads, octads, nonads, decads, undecads, etc. 

Note Where appropriate, adjectives specifying the types of copolymer may be applied to pseudo-copolymer. The term statistical pseudo-cqpo/ywer, for instance, may be used to describe an irregular polymer in the molecules of which the sequential distribution of configurational units obeys known statistical laws. 

The absence from a formula of any one of the horizontal or vertical lines at a chiral or prochiral carbon atom (as in examples on pages 27 and 32), or of or Z designations at double bonds, indicates that the configuration of that stereoisomeric centre is not known. Also, as in our previous document [2], the convention of orienting polymer structures (and the corresponding constitutional and configurational units) from left to right is used. Thus, the two bracketted constitutional units in... 

Note Two configurational units that correspond to the same constitutional unit are considered to be enantiomeric if they are non-superposable mirror images. Two non-superposable configurational units that correspond to the same constitutional unit are considered to be diastereomeric if they are not mirror images. 

The configurational base units (1) and (2) are enantiomeric, while the configurational units (1) and (3) cannot be enantiomeric because the constitutional units are different species, according to this nomenclature. ... 

It is immaterial whether (1) or (2) is taken as the configurational repeating unit and ster corep eating unit of isotactic polypropene (see Definition 1.7) this is so because the two infinite chains, one built up of identical configurational units (1) and the other built up of... 

Structural disorder resulting from the statistical co-existence within the crystals of identical configurational units with different conformations (see Figs. 3 and 4). 

These vertically configured units use four-stage conventional atmospheric-pressure preimpactors to remove supermicrometer particles, and they also operate at 30 ilpm. All of these microorifice impactors can be used with standard low-volume rotary carbon-vane vacuum pumps. 

In this case, propagation is controlled by the selection of the site of attack on one the two asymmetric carbons by the optically active initiator. One type of configurational unit predominates in the chains, and the polymer is optically active. 

An atactic polymer is a regular polymer with macromolecules composed of a certain number of statistically distributed configurational units. The constitutional unit is a type of atom or group of atoms composing the macromolecule (e. g. —[CH2—CHPhJ- or —[CHPh— in polystyrene). The configurational unit is a constitutional unit with one or several stereoisomer-ic centres. These definitions would require a more detailed explanation. In this volume they will only rarely be used, the stereochemistry of jjolymers is a special branch of macromolecular chemistry. More information can be found in the original literature [2]. 

Other options are being investigated. One is to configure units that can run at elevated pressures as this results in a higher voltage and hence an improvement... 

No optically active centers are produced in the polymerization of achiral monomers to dissymmetric polymers. Consequently, the smallest configurational unit is the configurational diad from two monomer units. 

Configurational unit A molecular unit having one or more sites of defined stereoisomerism (lUPAC). 

Enantiomeric configurational unit n. Either of two stereoisomeric groups in a polymer that are mirror images at the plane containing the main-chain bonds. 

Classification of polymers based on the degree of stereoisomerism relative to arrangements of configurational units in a chain ... 

A major 1981 lUPAC document (9) addresses polymer stereochemistry in depth. Key chapters of this document discuss basic definitions (configurational unit, configurational base and repeating units, stereorepeating imit, 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. 

A copolymer is derived from more than one species of monomer. The term copolymer is strictly connected with the synthesis of the polymer. It does not refer to the composition of the polymers, e.g. distribution of configurational units (pseudo-copolymer). 

A monomer unit with one chiral or asymmetric center (C-atom with 4 different substituents) exists in two different stereoisomers (enantiomers). Three distinct polymer isomers can be obtained. An isotactic (it) polymer can be described by only one species of configurational unit (the same enantiomers are... 

A "stereoselective" polymerization is a process in which macromolecules containing only one type of configurational unit are formed by incorporation of one stereoisomer from a mixture into a growing polymer chain. There are as many different types of macro-molecules as different stereoisomers present in the initial monomer mixture. 

Generally the process is not as perfect and one obtains a strong predominance of one type of configurational unit in the chain. 

The direction of ring-opening is oriented by the chiral choice of the catalyst which attacks preferentially one of the asymmetric carbons with inversion of configuration of the latter. The resulting polymer is optically active due to the prevalence of one type of configurational units for example J (-RR-)> I(-SS-). ... 

Establishing expressions for the probabilities of initiating stereosequences begining with R and S configurational units. 

Deriving the equations for the probability of each pentad as the product of the probabilites for initiation with the probabilities for addition of each added configurational unit. 

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