Regular polymers

Polymers without configurational regularity are called atactic. Configurationally regular polymers can fonn crystalline stmctures, while atactic polymers are almost always amorjihous. Many polymers consist of linear molecules, however, nonlinear chain architectures are also important (figure C2.1.2). 

CA of Polysaccharides. Polysaccharides adopt a wide variety of shapes that depend on their composition and their environment. In solution, polymers are almost always random coils that have local regions that might be similar to conformations that are found in the solid state. The chapter by Brant and Christ discusses conformations of polysaccharides in solutions both in terms of these local regions and by the overall shape of the random coil in terms of end-to-end distance, etc. The following discussion concerns only linear (unbranched) molecules, and refers only to regular polymers, i.e., those that have repeated sequences of monomeric residues located by screw-axis (helical) symmetry. 

This term describes the phenomena of stereoisomerism observable in short chain segments. Microtacticity considerations can be applied to stereoregular polymers, to sequences of partially regular polymers, and to highly disordered polymers, both from the qualitative and quantitative points of view. This approach is the most appropriate and complete for the structural study of real polymers. 

Note In a regular polymer, a eonfigurational base unit eorresponds to the constitutional repeating unit. 

Regular polymer, the molecules of which have essentially all identical configurational repeating units. 

Regular polymer, comprising tactic macromolecules having essentially 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. 

Note As the definition above indicates, a regular polymer, the configurational base units of which contain one site of stereoisomerism only, is atactic if it has equal numbers of the possible types of configurational base units arranged in a random distribution. If the constitutional repeating unit contains more than one site of stereoisomerism, the polymer may be atactic with respect to only one type of site if there are equal numbers of the possible configurations of that site arranged in a random distribution. 

For a regular polymer containing double bonds in the main chain of the constitutional repeating units, these are the fractions of such double bonds that are in the cis and trans configurations, respectively. 

The nomenclature of regular polymers can denote stereochemical features if the CRU used is the configurational base unit [10], i.e. a CRU having one or more sites of defined stereoisomerism in the main chain of a polymer molecule [11]. Structure-based names are then derived in the usual fashion. The various stereochemical features that are possible in a polymer must first be defined. 

Irregular polymers in which polymer or oligomer chains are attached to the main chain (as in graft copolymers) are named as follows. The attached polymer or oligomer chains are considered to be substituents to the main chain and named in the same way as regular polymers [1] or irregular polymers (cf Rules 1 and 2) but without the suffix -yl. The atom in the attached chains nearest to the point of attachment to the main chain is given the locant 1. 

Note 1 A graft copolymer with poly(A) blocks grafted to the main chain of a regular polymer consisting of constitutional units Z is named... 

Rule 2.1 The formula of a regular polymer ([1], Definition 2.15) with the constitutional repeating unit ([1], Definition 1.15) —R— is given as ... 

Rule 4.1.1 Alternating and periodic copolymers, as far as possible, are treated as regular polymers. 

In those cases where copolymer moleeules ean be described by only one species of eonstitutional unit in a single sequential arrangement, copolymers are regular polymers [4] and can, therefore, be named on a structure basis [1, 2]. Examples will be quoted later in the text. 

A regular polymer is a substance composed of regular macromolecules, the structure of which essentially comprises the repetition of a single constitutional unit with all units connected identically with respect to directional sense. 

It can also be shown with related statistical arguments that the enthalpy of mixing for a regular polymer-solvent solution is given by... 

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