Polymolecularity macromolecules

Early on, before the existence of macromolecules had been recognized, the presence of highly crystalline structures had been suspected. Such structures were discovered when undercooling or when stretching cellulose and natural rubber. Later, it was found that a crystalline order also existed in synthetic macromolecular materials such as polyamides, polyethylenes, and polyvinyls. Because of the polymolecularity of macromolecular materials, a 100% degree of crystallization cannot be achieved. Hence, these polymers are referred to as semi-crystalline. It is common to assume that the semi-crystalline structures are formed by small regions of alignment or crystallites connected by random or amorphous polymer molecules. 

Preliminary data on MMD of our samples are given in Table IV. It is evident that equimolar concentrations of activator and initiator produce PCL polymers characterized by a regularly decreasing polymolecularity index Q, from ca. 2.6 to 2.0. In Figure 1 the number of polymer molecules formed per acyllactam molecule is plotted as a function of initiator concentration. The actual values should be compared to the theoretical value of 1, which corresponds to the assumption that the number of macromolecules would be equal to the number of acyllactam molecules (26J, as in the ideal case of a step-addition of lactam anions to a constant number of growth centers. 

Figure 9-8. Dependence of the dissymmetry coefficient z of scattered light at angles of 45° and 135° on the ratio of >/X for spheres (sph), unimolecular random coils cm)y polymolecular (Mn) = 2) random coils Cp), and rods (r). Here Xo is the wavelength of light in the medium of refractive index n, and D corresponds to the diameter of the spheres, the length of the rods, and the chain end-to-end distance of coiled macromolecules.

As mentioned above, polymers synthesised by chemistry are not identical but form a family of macromolecules of different lengths that can be characterised by a size distribution with a mean value of the molecular weight. A typical distribution graph of the size of polymer chains present in a sample and constituting a polymolecular population is illustrated in Figure 2.1. 

H. Polymolecularity Correction Factors for the Determination of the Dimensions of Macromolecules... 

Deteimination of Unperturbed Dimensions of Macromolecules VII / 241 TABIE 70. POLYMOLECULARITY CORRECTION FACTORS AND FOR BURCHARD-STOCKMAYER -FIXMAN PROCE-... 

Star-shaped polymers have gained increasing interest because of their compact structure and high segment density, and because very efficient synthetic methods have made possible the functionalization of the outer branch ends. Until recently, anionic polymerization was one of the best methods to obtain well-defined star-shaped polymers of predetermined branch molar mass. This technique provided the long lifetime for the active sites necessary to allow the formation of star-shaped macromolecules. Anionic polymerization also limited the polymolecularity of the samples. Given the appropriate reaction conditions, the functionality of the core can be controlled in advance. 

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