Constitutional unit

Interestingly, since all constitutive units and linkages can be distributed at random within a polymer, the number of possible isomers increases expo-... 

The polyethylene obtained (the already cited HDPE) is more highly crystalline and more rigid and dense and has a much more regular structure than the one previously known and obtainable at very high temperature and pressure and which had been industrially produced in the previous 15 years (now called low-density polyethylene, LDPE). The latter shows macromolecules with both long and short branches and is consequently less crystalline than the almost completely linear HDPE. It is obvious that polyethylene does not present tertiary carbon atoms in its constitutional unit, hence it does not show problems of stereoisomerism. 

Molecule which can undergo polymerization, thereby contributing constitutional units to the essential structure of a macromolecule. 

Macromolecule, the structure of which essentially comprises the repetition of a single constitutional unit with all units connected identically with respect to directional sense. 

Largest constitutional unit contributed by a single monomer molecule to the structure of a macromolecule or oligomer molecule. 

Macromolecule or oligomer molecule capable of entering, through reactive groups, into further polymerization, thereby contributing more than one constitutional unit to at least one type of chain of the final macromolecules. 

Smallest constitutional unit, the repetition of which constitutes a regular macromolecule, a regular oligomer molecule, a regular block, or a regular chain. 

Constitutional unit having at least one site of defined stereoisomerism. 

Tactic macromolecule, essentially comprising only one species of configurational base unit, which has chiral or prochiral atoms in the main chain in a unique arrangement with respect to its adjacent constitutional units. 

Whole or part of a macromolecule, an oligomer molecule, or a block, comprising a linear or branched sequence of constitutional units between two boundary constitutional units, each of which may be either an end-group, a branch point, or an otherwise-designated characteristic feature of the macromolecule. 

Arbitrarily chosen contiguous sequence of constitutional units, in a chain. 

Note The term subchain may be used to define designated subsets of the constitutional units in a chain. 

Chain that comprises constitutional units connected in such a way that adjacent constitutional units are joined to each other through two atoms, one on each constitutional unit. 

Note A spiro chain is a double-strand chain with adjacent constitutional units joined to each other through three atoms, two on one side and one on the other side of each constitutional unit. 

Note A chain that comprises constitutional units joined to each other through n atoms on at least one side of each constitutional unit is termed an n-strand chain, e.g., three-strand chain. If an uncertainty exists in defining n, the highest possible number is selected. 

Sequence of atoms in the constitutional unit(s) of a macromolecule, an oligomer molecule, a block, or a chain, which defines the essential topological representation. 

Highly ramified macromolecule in which essentially each constitutional unit is connected to each other constitutional unit and to the macroscopic phase boundary by many permanent paths through the macromolecule, the number of such paths increasing with the average number of intervening bonds the paths must on the average be co-extensive with... 

Note 1 Usually, and in all systems that exhibit rubber elasticity, the number of distinct paths is very high, but, in most cases, some constitutional units exist which are coimected by a single path only. 

Portion of a macromolecule, comprising many constitutional units, that has at least one constitutional or configurational feature which is not present in the adjacent portions. 

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

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

Macromolecule in which a substantial portion of the constitutional units has ionizable or ionic groups, or both. 

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