Chain structure dangling chains

Figure 9.2 Main elements constituting the structure of a polymer network (1) crosslink point, (2) elastically active chain, (3) dangling chain, (4) loop or cycle, (5) multiple connection between two crosslink points, and (6) permanent chain entanglements between two adjacent crosshnks.

Despite its simplicity, the statistical method has been quite successful in predicting the effect of various chemical variables on network formation (cf. e.g. [29, 30, 34-37]). Since the internal structure of the gel can be characterized to a certain degree by the statistical method (e.g. average size of dangling chains and weight fraction of material in them), these methods offer a basis for correlations between structure and viscoelastic properties. 

Figure 5.12 Structure of a polyurethane network with dangling chains prepared from F1 + F2 + F3 components...

A nonideal network may be obtained as in the previous case but using different nonstoichiometric molar ratios or arresting the polymerization at different conversions, to modify the structure. In these cases, the presence of a sol fraction and dangling chains will introduce an additional plasticization effect, surimposed on the new architecture (Vallo et al., 1993). 

In polyesters, the existence of an osmotic cracking process (see below), gives importance to other structural factors, especially the concentration of dangling chain ends. 

Mechanical properties of crosslinked elastomers are influenced not only by the volume-average crosslink density but also by network heterogeneity. The influence of structural defects (such as residual sol, dangling chains, chain loops and the heterogeneity of the junction distribution) on the viscoelastic properties and the equilibrium swelling data is still under discussion. Local methods which probe molecular properties are very suitable for the determination of the degree of network heterogeneity [11]. 

Scheme 5.8b depicts a saturated fatty acid, called palmitic acid, which is represented in the implicit cartoon with a skeleton without explicit notation of the C and H atoms. The term saturated means that there are no double bonds in the chain, and as can be seen beneath the structure, the chain is constructed from a click of one singleconnector HgC to 14 double-connector H2C fragments. The dangling connectivity of the last CH2 is in turn clicked to a single-connector COOH fragment. Palmitic acid is the most common fatty acid found in mammals, plants, and microorganisms. Excess carbohydrates in the body are converted to palmitic acid, and as a result, it is a major body component. As we drew it, the chain of palmitic acid is extended in shape, and therefore the many molecules of the acid can pack nicely together and... 

In 1987 Ovchinnikov et al. announced the discovery of the first ferromagnetic organic polymer based on polydiacetylene chain with dangling nitroxyl radicals [8,9]. The compound was obtained by bulk polymerization of stable paramagnetic biradical BlPO initiated by light. The chemical structure of this compound is shown below. 

Since dangling chains are imperfections in a network structure, their presence should have a detrimental effect on ultimate properties such as the tensile strength, as gauged by the nominal stress, f, at rupture, f. ... 

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