Fully extended polymer

Is the average llneeur distance (angstroms), assuming a fully extended polymer chain, per acrylate group. 

A polymer that contains chiral carbons can be either atactic, isotactic, or syndio-tactic. An isotactic polymer is one in which the two different substituent groups always occur on the same side of the fully extended polymer chain. In a syndiotac-tic polymer, the groups alternate sides of the chain. In an atactic polymer, the side of the chain on which each group appears is random-there is no pattern. 

If crystallisation occurs in an oriented melt, then non-spherulitic microstructures can form, with preferred orientation of the crystals (Section 3.4.10). Fibrous nuclei, believed to contain fully extended polymer chains, can form in an oriented melt. Figure 6.7a shows several fibrous nuclei, in a polyethylene injection moulding, aligned with the flow direction. On either side of these dark nuclei is a bright layer, where lamellar crystals have grown from the nucleus. The c axes of the lamellar crystals are parallel to the fibrous nucleus the microstructure of platelet crystals skewered by a rod-like nucleus has been described as a shish kebab. The rest of the microstructure consists of small spherulites. 

A mechanophore (blue in Fig. 2a) is a strategically designed chemical entity which responds to mechanical force in a predictable and useful manner (Fig. 2d-f). The polymer strand here acts as an actuator to transmit macroscopic force to the target. For a fully extended polymer chain, the maximum tension force is at the middle point of the chain contour. So the mechanophore should be incorporated into the middle of the chain with its active bond along the chain contotu (Fig. 2a) [15, 29, 32]. Examples of mechanochemical reactions include homolytic scission of weak bonds (diazo [33]), electrocyclic ring-opening (benzocyclobutenes [29], spiropyrans [32, 34 5], gem-dichlorocyclopropanes [46-49], ge/n-difluorocyclo-propanes [30, 50], and epoxide [51]), cycloreversion reactions (cyclobutane derivatives [52-56], Diels-Alder adducts [57, 58], 1,3-dipolar adducts [59, 60], and 1,2-dioxetanes [61]), dative bond scission [62-64], and flex-activated reactions [34, 65, 66], as recently reviewed by Bielawski [67]. 

The length of molecular bmshes on surfaces was shown to be nearly equal to the length of a fully extended polymer back-bone. ° The strong extension is due to steric repulsion between the adsorbed side chains. From scaling ana-... 

Contour Length The length of a fully extended polymer chain along its backbone. 

The lamellar liquid crystalline polymer 2 has a high-temperature phase transition at about 251°C. Heating above this phase transition produces films with a smecticlike, chain-extended conformation in which the polymer chains assemble into crystalline nano-ribbons with a characteristic width of 70-80 nm, consistent with the length of the fully extended polymer chain backbone. These ribbons, separated by grain boundaries, extend over several micrometers in the direction of k-k stacking... 

Polymers in the solid state can be completely amorphous, partially crystalline, or almost completely crystaUine. Polymer crystals have the requiranent that they must accommodate the covalent axis within an ordered structure. For some time the interpretation of X-ray diffraction patterns was that individual polymer molecules were partly crystalline and partly amorphous. The longest dimension of the crystallites in polycrystalline materials is usually about 5-50 nm, which is a small fraction of the length of a fully extended polymer molecule. A graphical representation of this once popular model is shown in Figure 3.12. Here a long polymer chain wanders... 

The fully extended molecular length is not representative of the spatial extension that a molecule actually displays. The latter is sensitive to environmental factors, however, so the extended length is convenient for our present purposes to provide an idea of the spatial size of polymer molecules. 

Use the Simha equation and these data to criticize or defend the following proposition These polymer molecules behave like rods whose diameter is 16 A and whose length is 1.5 A per repeat unit. The molecule apparently exists in fully extended form in this solvent rather than as random coils. 

For materials such as rubber bands, the quantity a may be as large as five. At that point, the chains are substantially fully extended. Further stretching may break the rubber band, actually severing the polymer chains at the break point (a chemical reaction ). 

The most widely used method for preparing extended-chain crystals involves solid-phase polymerization when the monomer exists as a single crystal. The polymerization of single crystals of the monomer permits the preparation of a polymer material with a maximum orientation a polymeric single crystal composed of fully extended macromolecules. Such polymer crystals are needle-shaped22. ... 

Since the contour length of a fully extended C — C chain is lmax = Nlp, a polymer molecule can be stretched in the extreme by a factor of lmax/R or N1/2 from its equilibrium value. 

It is worth recalling that any of the molecular force laws given by Eqs. (13-16) are derived within the framework of the freely-jointed model which considers the polymer chain as completely limp except for the spring force which resists stretching thus f(r) is purely entropic in nature and comes from the flexibility of the joints which permits the existence of a large number of conformations. With rodlike polymers, the statistical number of conformations is reduced to one and f(r) actually vanishes when the chain is in a fully extended state. 

A polymorphic behavior involving packing of chains having completely different conformations has been found also for isotactic polymers. For instance, isotactic polystyrene, under suitable experimental conditions, can produce crystalline gels in which the chains assume a nearly fully extended conformation [11,12], very close to a truns-planar, rather than the classical conformation of three-fold helix [13]. The two possible conformations proposed for the two crystalline forms of i-PS are shown in Fig. 2. 

As for further analysis, curve fitting against the worm-like chain (WLC) model was conducted and indicated as a solid line in Figure 21.4. The model describes single polymer chain mechanics ranging from random-coil to fully extended forms, as follows ... 

Figure 17. Configurations of an excluded volume polymer chain with Nb = 50 for Wi > 1. The top configuration is for a polymer fully extended in the flow direction. The bottom configurations show other configurations that the polymer adopts in the shear flow. (Adapted from Fig. 2 of Ref. 88.)...

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