Linear and Branched Macromolecules

In polymer science and technology, linear, branched and crosslinked structures are usually distinguished. For crosslinked polymers, insolubility and lack of fusibility are considered as characteristic properties. However, insoluble polymers are not necessarily covalently crosslinked because insolubility and infusibility may be also caused by extremely high molecular masses, strong inter-molecular interaction via secondary valency forces or by the lack of suitable solvents. For a long time, insolubility was the major obstacle for characterization of crosslinked polymers because it excluded analytical methods applicable to linear and branched macromolecules. In particular, the most important structural characteristic of crosslinked polymers, the crosslink density, could mostly be determined by indirect metho ds only [ 1 ], or was expressed relatively by the fraction of crosslinking monomers used in the synthesis. 

A microgel is an intramolecularly crosslinked macromolecule which is dispersed in normal or colloidal solutions, in which, depending on the degree of crosslinking and on the nature of the solvent, it is more or less swollen. Besides linear and branched macromolecules and crosslinked polymers, intramolecularly crosslinked macromolecules may be considered as a fourth class of macromolecules. 

Experimental and analytical studies over the past 25-30 years revealed that microgels are intramolecularly crosslinked macromolecules, which represent a new class of polymers besides linear and branched macromolecules and crosslinked polymers of macroscopic dimensions. In some ways microgels may be considered as a transition from molecules to larger polymer particles or macroscopic polymer materials. 

Microgels are distinguished from linear and branched macromolecules by their fixed shape which limits the number of conformations of their network chains like in crosslinked polymers of macroscopic dimensions. The feature of microgels common with linear and branched macromolecules is their ability to form colloidal solutions. This property opens up a number of methods to analyze microgels such as viscometry and determination of molar mass which are not applicable to the characterization of other crosslinked polymers. 

Thermosets are formed by crosslinking (curing) of reactive linear and branched macromolecules and can be manufactured by polycondensation, polymerization and polyaddition. Thermosets can therefore be processed once only with the application of heat and pressure to form semi-finished products or finished articles and cannot be recovered their processing is irreversible. Amongst the most familiar thermosets are the combinations of formaldehyde with phenol, resorcinol etc. (phenolics), urea, aniline, melamine and similar combinations (aminoplastics). 

The intrinsic viscosity [ry] of both linear and branched macromolecules and the branching parameter values of the star-branched copolymers were also calculated by the GPC software and are reported in Table IV. The ratio [vlhAvlim, between the intrinsic viscosity of the... 

Polymers derived from other lactams contain irregular units such as indicated in the schemes (45) and (52) so that both linear and branched macromolecules are present [134, 151, 152]. Structures (XVIII)—(XXII) containing substituted keto amide units will prevail at lower temperatures, viz. 

Poly(imines) are polymers that contain in their backbone amino nitrogens connected by single bonds to carbon atoms. Some of these polymers have a simple structure like poly(ethylene imine) or [-CH2-CH2-NH-]n. The polymer is obtained from the polymerization of aziridine, typically generating a mix of linear and branched macromolecules with about 25% primary amine groups, 50% secondary amine groups, and 25% tertiary amine groups. The polymer is used in paper industry and for various other purposes that make use of its anionic character [1]. 

Chapter 1.04 by Oleg V. Borisov deals with the main properties of concentrated polymer solutions of different kinds and architecture (linear and branched macromolecules, polyelectrolytes). Both static and dynamic properties are considered. 

A polymer comprising molecules non-uniform with respect to relative molar mass or constitution or both is termed non-imiform polymer (polydisperse) [89IUP2]. A polymer imiform with respect to either molar masses or constitution may be termed as uniform polymer (monodisperse) with respect to molar masses or constitution. A mixture of linear and branched macromolecules, both of uniform molar masses is not uniform. lUPAC recommend the use of the terms imiform for monodisperse and non-uniform for polydisperse. 

The symbol (bF) represents the mean square radius of gyration of the macromolecule. This quantity has been considered in detail for linear and branched macromolecules by Zimm and Stockmayer and is generally defined by... 

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