Junction unit

In a cross-linked polymer, the junction units are different kinds of monomers than the chain repeat units, so these molecules might be considered to be still another comonomer. While the chemical reactions which yield such cross-linked substances are copolymerizations, the products are described as cross-linked rather than as copolymers. In this instance, the behavior due to cross-linking takes precedence over the presence of an additional type of monomer in the structure. 

In source-based nomenclature for non-linear maeromoleeules and maeromoleeular assemblies, junction units are optionally specified by their source-based names after the name of the macromolecule with the connective (Greek) v, separated by hyphens [5]. yis given a numerieal value. 

Block copolymers are named by using dashes (double-length hyphens) for the bonding of bloeks with each other and with junction units. With graft and star polymers, the grafts or the arms, respectively, are eonsidered to be substituents to the main chain, and the structure is named in the same way as a regular or irregular polymer. Table 8 lists some examples. 

Irregular polymers with regular or irregular blocks and junction units in a specific sequential arrangement are named by linking the names of the blocks and junction units with dashes ... 

A triblock copolymer consisting of a sequence of three blocks joined directly or through unspecified junction units ... 

A diblock copolymer in which the blocks are joined by a specific junction unit, as in the polymer ... 

Rule 4.3.1 The formulae of block copolymers ([1], Definition 3.35) consisting of a sequenee of regular blocks ([1], Definition 3.15) and, if known, junction units ([6], Definition Rule 5.5) in known sequential arrangement are written as, e.g.,... 

Note 2 The bonds emanating from the first and last constitutional or junction unit of an irregular block are written within the enclosing marks when it is not known to which of the units of the irregular block the other blocks or the end groups of the polymer are attached. Thus,... 

In the name of block copolymers with blocks connected by way of junction units, X, that are not part of the blocks, the name of the junction unit is inserted in the appropriate place. The connective, -block-, may be omitted. Thus,... 

A block copolymer wherein A and B blocks and junction units X are all distributed in statistical manner, as in... 

Law J. T. and Meigs P. S. (1955), Effect of water vapor on grown germanium and silicon n-p junction units , J. Appl. Phys. 26, 1265-1273. 

These connectives may be used in combination and with small, non-repeating (i.e. non-polymeric) junction units see, for example, Table 2, line 8. A long dash may be used in place of the con-... 

A long hyphen is used to separate components in names of block polymers, as in poly(A)—poly(B)—poly(C) , or poly(A) —X—poly(B) in which X is a non-polymeric junction unit, e.g. dimethylsilylene. 

The word regular in the heading is used here to mean ordinary , or, in the case of copolymers, random or statistical types with no special attributes such as nonpolymeric spacer groups (called junction units by lUPAC). As mentioned above, these are drawn usually as either structure-based, ie, —(—A—),j—, or source-based, ie, —(AB---)x-... 

This is the basic structure of rubbers. A rubbers in fact represents one huge macromolecule of macroscopic dimensions, with properties depending on the cross-link density and the functionality of the junction units. 

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