Molecular weight distribution relationship

Model Networks. Constmction of model networks allows development of quantitative stmcture property relationships and provide the abiUty to test the accuracy of the theories of mbber elasticity (251—254). By definition, model networks have controlled molecular weight between cross-links, controlled cross-link functionahty, and controlled molecular weight distribution of cross-linked chains. Sihcones cross-linked by either condensation or addition reactions are ideally suited for these studies because all of the above parameters can be controlled. A typical condensation-cure model network consists of an a, CO-polydimethylsiloxanediol, tetraethoxysilane (or alkyltrimethoxysilane), and a tin-cure catalyst (255). A typical addition-cure model is composed of a, ffl-vinylpolydimethylsiloxane, tetrakis(dimethylsiloxy)silane, and a platinum-cure catalyst (256—258). 

LLDPE with narrow molecular weight distribution exhibits a lower, a sharper melting point [3], better hot tack and heat seal properties as well as higher clarity and better impact resistance (Fig. 3), tensile strength (Fig. 4) [11], and lower levels of alkane-soluble components. The most distinguishing characteristic of metallocene-based LLDPEs is that they are not restricted by the current immutable property relationships that are... 

Since the mode of termination clearly plays an important part in determining the polymer end groups and the molecular weight distribution, a knowledge of the disproportionatiomeombination ratio (ki(t/kK) is vital to the understanding of structure-property relationships. Unsaturated linkages at the ends of polymer... 

For a given initial molecular weight distribution, the weight fraction of chains incorporated into a network increases as the number of crosslinking events increases. Similarly, the number of crosslinking events required to create a network decreases as the average molecular weight increases. These relationships are illustrated schematically in Fig. 5.16. 

In Fig. 9.30 a broadening of the molecular weight distribution at increasing time of polymerization is observable which is typical for the polymerization of 2-oxazolines. Plotting the m/z value of the most intensive mass signal versus the reaction time, a strictly linear relationship is obtained (Fig. 9.30). These results are consistent with recent experimental and theoretical studies of surface-initiated... 

Narrow Molecular Weight Triacetate Calibration. A linear relationship was found when log against the elution volumes of various cellulose triacetate fractions was plotted. For narrow molecular weight distribution triacetate fractions, the GPC experimental average molecular weight, termed can be expected to conform... 

Figure 3 shows the relationships between the temperatures and molecular weight distributions for 6 successive regions of the Til profile in Figure 1. Interestingly, regions a, b and c, primarily representing the low temperature components, show relatively narrow MW distributions around M values which markedly increase with temperature. This is consistent with the proposed interpretation of the low temperature hump as a vacuum desorption and distillation process rather than as a pyrolytic process. By contrast, regions d, e and f, representing the major Til maximum in Figure 1, exhibit much broader MW...

Little is known about the chain dimensions of PPC in solution. Recently, a comparison of the hydrodynamic volume of polystyrene (PS) and PPC has been reported for tetrahydrofuran (THF) as solvent in connection with a size exclusion chromatography (SEC) analysis [78, 79]. The basis for the calculation was the assumption of an immortal PO/CO2 alternating copolymerization, and thus that absolute values of Mn relate to starter and PO/CO2 ratios. Narrow molecular weight distributed PPCs with various molecular weights were prepared from adipic acid as starter. The absolute molecular weight has a relationship of K = K(ps)... 

The molecular weight distribution and/or PDI has been described for several cases where the assumption of equal reactivity of functional groups is not valid. Unequal reactivity is easily handled by the Macosko-Miller method. For the A—A + B—B + B B system described in the previous section, we simply redefine the relationship between P and y by... 

Here, too, the deviation of this ratio Jromunity may be taken as a measure of polydisper-sity. The relationship between the ratio MJMn and the standard deviation of the molecular weight distribution is easily seen as follows. From Equation (16), it is clear that... 

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