Polymolecularity polymers

In contrast, other natural polymers, such as natural rubber (NR), cellulose, and most synthetic polymers, consist of mixtures of many members of a homologous series. These homologues contain varying numbers of units and thus have different molecular weights, and hence the polymers are said to be polydisperse or polymolecular. 

Endowing these polymolecular entities with recognition units and reactive functional groups may lead to systems performing molecular recognition or supramolecular catalysis on external or internal surfaces of organic (molecular layers, membranes, vesicles, polymers, etc.) [7.1-7.13, A.41] or inorganic (zeolites, clays, sol-gel preparations, etc.) [7.14-7.20] materials. 

It is reasonable to assume that the complementary units form the expected triply hydrogen bonded pairs, so that the entirely different behaviour of the pure compounds and of the 1 1 mixtures may be attributed to the spontaneous association of the complementary components into a polymolecular entity based on hydrogen bonding. The overall process may then be described as the self-assembly of a supramolecular liquid-crystalline polymer based on molecular recognition (Figure 40). The resulting species (TP2, TU2) is represented schematically by structure 174. 

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. 

For polymers, a number of authors have claimed that the peak width increases as the MW increases, but to discuss band broadening for polymers, several precautions are required. First, it is necessary to be sure that the injected solution is sufficiently dilute to prevent any viscous effect. (Practically no viscous effect is observable, even for narrow standards when WC < 0.1 for flexible polymers, this corresponds roughly to a concentration <1 mg/mL for MWs up to 500,000 for a higher MW, it is necessary to reduce the concentration.) Then, the real difficulty is to analyze very narrow standards for which polymolecularity is sufficiently low, so as not to participate in the peak width, or at least which polymolecularity is very precisely known. 

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. 

Recycling procedures are often used for solving the difficult separation problems, but they can also be applied to the direct determination of the polymolecularity of narrow polymer fractions [25]. 

Most polymers consist of mixtures of polymer homologous molecules of different degrees of polymerization they are polymolecular or polydisperse.t Consequently, the degree of polymerization of such polymers is always an average whose value depends on the statistical weights of the data used to obtain it. Of special importance is the number average (weighted with respect to the amount of material, n, or the equivalent number N of molecules, since nt = Nij Nl)... 

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