Arrangement of Molecular Chains

During the 1940 s it was proposed that partially crystalline polymers consisted of regions where the molecular chains where gathered in an ordered 

Appropriately, this was called the Folded Chain Theory and is illustrated in Fig. A.ll. There are several proposals to account for the co-existence of crystalline and amorphous regions in the latter theory. In one case, the structure is considered to be a totally crystalline phase with defects. These defects which include such features as dislocations, loose chain ends, imperfect folds, chain entanglements etc, are regarded as the diffuse (amorphous) regions viewed in X-ray diffraction studies. As an alternative it has been suggested that crystalline 

Twisted tolded chain growth Irom nucleus 

The ease with which a polymer will form into crystalline regions depends on the structure of the molecular chain. It can be seen, for example, that if the polyethylene molecule has a high degree of branching then it makes it difficult to form into the ordered fashion shown in Fig. A.9. Also, if the side 

The following type of differential equation is encountered in the text, for example, in the analysis of the models for viscoelastic behaviour  

Twisted folded choin growth from nucleus 

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A complete definition of the fine structure of cellulose would entail a knowledge of the exact distribution of the size and shape of these ordered and disordered regions, a position which has not yet been achieved. However, a report claims that four types of material which differ in the degree of orderly arrangement of molecular chains can be distinguished in both native and regenerated celluloses, although quantitative measurements have only been made on one viscose-rayon fiber. These four types of material are ... 

When we consider the arrangement of molecular chains with respect to each other there are again two largely separate aspects, those of molecular orientation and crystallinity. In semicrystalline polymers this distinction may at times be an artificial one. 

Initially the name and general information for a given fiber is set forth followed by an outline of the stmctural properties, including information about chemical structure of the polymer, degree of polymerization, and arrangement of molecular chains within the fiber. Physical properties... 

Figure 14.10 Arrangement of molecular chains in a unit cell for polyethylene.

Epitaxy between Linear Polymers The epitaxy between linear polymers usually sums up to the parallel arrangement of molecular chains, evidently more favorable when lattice spacing is comparable. As an illustration, PE and aliphatic polyesters have nearly similar unit-cell parameters (in c-axis projection) PE and polyamides have interchain distances that are close to 0.5 nm (0.48 nm for polyamides, 0.5 nm for PE in the be plane) [11]. 

Figure 37 Representation of arrangement of molecular chains in shish kebab structure. (From Ref 88.)...

Figure 8-6 (A) Molecular packing of 2,3-dimyristoyl-D-glycero-l-phosphocholine dihydrate. The two molecules in the asymmetric unit are labeled 1 and 2. The position of the water molecules is indicated either by W1-W4 or by small open circles. Hydrogen bonds are represented by dotted lines. From Pascher et al.66 (B) Two-dimensional "orthorhombic" arrangement of hydrocarbon chains in a crystalline alkane. The a-b plane corresponds to the plane of the bilayer surface the long axes of the acyl chains project from the page. From Cameron et al.67...

The dense arrangement of the chains points to the action of other forces that can control the molecular conformation of adsorbed macromolecules in addition to the interaction with the substrate. Capillary forces and dewetting during evaporation of the solvent can cause condensation and dense packing of the molecules in monolayer patches,147 148 150 For large molecules with a diameter of ca. 5 nm, capillary forces are in the range of a few nN, which is sufficient to... 

Proteins are linear condensation products of various a-L-amino acids (a.a.) that differ in molecular weight, charge, and nonpolar character (Table 7.1), bound by trans-peptide linkages. They differ in number and distribution of various a.a. residues in the molecule. The chemical properties, size of the side chain, and sequence of the a.a. affect the conformation of the molecule, i.e., the secondary structure containing helical regions, [3-plcalcd sheets, and [3-tunis the tertiary structure or the spatial arrangement of the chain and the quaternary structure — the assembly of several polypeptide chains. 

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