Molecular elongation index

Figure 12.8 shows the (PPE) curves (see 12.3.3) for the rotation of flat molecules, (in the rigid environment approximation). An elongation index is defined as D /D (see 12.2.3.1), the ratio of the two molecular dimensions in the molecular plane. The rotation is severely hindered if the elongation index exceeds about 1.3. A large molecule such as coronene rotates easily in the crystal, due to its very small elongation index. For these molecules, the ease of molecular rotation in the solid depends more on molecular shape than on details of the crystal structure. 

Fig. 12.8. (PPE) profiles for molecular rotation in crystals of some aromatic hydrocarbons. 1 anthracene (elongation index 1.57) 2 pyrene (1.27) 3 naphthalene (1.24) 4 benzene (1.10) 5 cor-onene (1.00)...

The values of X calculated from Eq. 26 are given in Table 8. It should be pointed out that the classical rubber theory does not account for a dependence of molecular orientation on the considered length scale, as found for sample C in Fig. 29. Therefore the simplistic approach presented here should in principle be restricted to samples A and B for which the principal directions for the low-q SANS data (I and II) are close to the principal directions for the refractive index. The data in Table 8 actually show a satisfactory agreement between calculated and experimental mean square chain dimensions for samples A and B. For sample C, the agreement is less satisfactory in the direction perpendicular to the chain elongation, but one must be aware that for this sample, the directions in which Rg j and Rg jj measured... 

The effect of microwave irradiation on chemical reactions is usually described by comparing time needed to obtain a desired yield of final products compared with conventional thermal heating. Research in the area of chemical synthesis has shown potential advantages in the ability not only to drive chemical reactions but to perform them more quickly. In polymer synthesis other factors can be considered, for example molecular weight, polydispersity index, crystallinity, mechanical properties (i.e. strength, elongation, modulus, toughness), and thermal properties... 

When we move on therefore, to a partially oriented semi-crystalline polymer such as HOPE and PP for which there are as yet many unsolved problems regarding the initial morphology, it is somewhat surprising that the simple scheme for molecular reorientation is applicable. It is not clear how a simple morphology of alternating crystalline and amorphous regions could always reform so that the direction of maximum refractive index was parallel to the direction of maximum elongation, for all specimen orientations and initial draw ratios, as is required by this scheme (Fig. 12). 

Damage can be noticed when melt flow index tests are performed and the reduction in molecular weight causes a higher melt flow value. Also, damage can be noticed when tensile tests are performed and decreases in ultimate elongation are noticed. The intention of this research is to derive a new Qio constant for the Arrhenius Equation to better predict shelf life of medical polymers. 

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