Fully extended chain

Figure 36.2. Hypothetical flat sheet structure for a protein. Chains fully extended adjacent chains head in opposite directions hydrogen bonding between adjacent chains. Side chains (R) are crowded.

Intercalation of a, oo-alkyl diamines (C2-C10) follows the moving boundary model, and a number of intermediate phases appear before the intercalation is complete (74). In the final phase, the diamines form a bilayer, with the chains fully extended at an angle of 58° to the a-ZrP layer. The transformation from a layered structure to a framework structure allows for the binding of short-chain... 

Some polymer materials show good affinity towards certain solvents. As defined in polymer science, solvents that make the polymer chain fully extended are good solvents for the polymer. When the polymer is crosslinked into a polymer network, however, the polymer can no longer be dissolved . Instead, the crosslinked polymer is swollen. Namely, the solvent enters the polymer network and forms a polymer gel. Vast research efforts have been devoted to optimize the uptake capacity of crosslinked polymer networks toward certain solvents. The materials that can absorb solvents up to tens of times their weight are called super absorbents. °... 

I chains broken until fracture, II chains fully extended and contributing with chain modulus E to sample modulus E, III chains in non-extended conformation. 

Extensive discussions have focused on the conformation of the alkyl chains in the interior ". It has been has demonstrated that the alkyl chains of micellised surfactant are not fully extended. Starting from the headgroup, the first two or three carbon-carbon bonds are usually trans, whereas gauche conformations are likely to be encountered near the centre of tlie chain ". As a result, the methyl termini of the surfactant molecules can be located near the surface of the micelle, and have even been suggested to be able to protrude into the aqueous phase "". They are definitely not all gathered in the centre of tire micelle as is often suggested in pictorial representations. NMR studies have indicated that the hydrocarbon chains in a micelle are highly mobile, comparable to the mobility of a liquid alkane ... 

Syndiotactic. Substituents on the fully extended chain lie on alternating sides of the backbone. This alternation of configuration can be represented as -DLDLDLDLDLDL-. 

The c axis corresponds to both the short axis of the crystal and the axis along the molecular chain. The observed repeat distance in the c direction is what would be expected between successive substituents on a fully extended hydrocarbon chain with normal bond lengths and angles (see Sec. 1.2). 

Free rotation around each of the carbon-carbon bonds makes saturated fatty acids extremely flexible molecules. Owing to steric constraints, however, the fully extended conformation (Figure 8.1) is the most stable for saturated fatty acids. Nonetheless, the degree of stabilization is slight, and (as will be seen) saturated fatty acid chains adopt a variety of conformations. 

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. 

The exponent x is an empirical parameter to be determined from experiments. For a fully extended chain in stagnant elongational flow, x is equal to 2 whereas a value of 1 was found under transient flow conditions (Sect. 5.4). 

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 3-4. Dimensions of a fully extended polypeptide chain. The four atoms of the peptide bond (colored blue) are coplanar. The unshaded atoms are the a-carbon atom, the a-hydrogen atom, and the a-R group of the particular amino acid. Free rotation can occur about the bonds that connect the a-carbon with the a-nitrogen and with the a-carbonyl carbon (blue arrows). The extended polypeptide chain is thus a semirigid structure with two-thirds of the atoms of the backbone held in a fixed planar relationship one to another. The distance between adjacent a-carbon atoms is 0.36 nm (3.6 A). The interatomic distances and bond angles, which are not equivalent, are also shown. (Redrawn and reproduced, with permission, from Pauling L, Corey LP, Branson PIR The structure of proteins Two hydrogen-bonded helical configurations of the polypeptide chain. Proc Natl Acad Sci U S A 1951 37 205.)...

If the chain is fully extended so that all of the chain atoms lie in a plane (planar zigzag form) as in formula X... 

---