Lifetime heterogeneous polymeric systems

Since the 1960s position annihilation lifetime spectroscopy (PALS) has been used to measure free-volume cell size and/or its content in liquids or solids. The three chapters of Part III discuss correlations between the PALS experimental values and those computed from the S-S theory. Chapter 10, by Consolati and Quasso, considers free volume in amorphous polymers Chapter 11, by Dlubek, its distribution from PALS and Chapter 12, by Jamieson et al., the free volume in heterogeneous polymer systems. These state of the art texts offer intriguing observations on the structure of polymeric systems and its variation with independent variables. In all cases, good correlation has been found between the free-volume quantity measured by PALS and its variability computed from the S-S equation of state. 

The different organomagnesium species present may propagate at different rates and with different stereochemistries. Their persistence during the lifetime of the polymer chains is thought to be responsible for the multimodal molecular weight distributions and heterogeneity of tacticity observed in many systems [34]. Accordingly, one could view the polymerization process as an amplifier. ... 

Some coordination polymerizations also exhibit the character of a living polymerization process. For example, Natta32 described a heterogeneous catalyst yielding block polymers when the initially present monomer was replaced by another one. In that system, the lifetime of a growing polymer exceeds one-half hour, i.e. the termination caused by the hydride transfer to the catalytic center was very slow. Similar results were reported by Bier33 and by Kontos et al.34. ... 

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