Polymerization and molecular weight

Reaction conditions should usually be chosen such that the fraction of initiator-derived chains (should be greater than or equal to the number of chains formed by radical-radical termination) is negligible. The expressions for number average degree of polymerization and molecular weight (eqs. 13 and 14) then simplify to eqs. 15 and 16 ... 

In this manuscript we review the principles of bulk and solution polymerization with particular emphasis on high conversion (high polymer concentrations) rate of polymerization and molecular weight development. 

Molecular weight from osmotic pressure measurements Degree of polymerization and molecular weight distribution Excluded volume from osmotic pressure measurements Theta temperature from second virial coefficient data Evaluation of charges on macroions from osmotic pressures... 

Dehydrogenative Coupling. Transition-metal catalyzed polymerization of silanes appears to hold promise as a viable route to polysilanes. A number of transition-metal complexes have been investigated, with titanium and zirconium complexes being the most promising (105—108). Only primary silanes are active toward polymerization, and molecular weights are rather low. The dehydrogenative polymerization is depicted in reaction 11, where Cp = cyclopentadienyl ... 

Berry, K. L., and J. H. Peterson Tracer studies of oxidation-reduction polymerization and molecular weight of Teflon tetrafluoroethylene resin. J. Am. Chem. Soc. 73, 5195-5197 (1951). 

Synthetic polymers are often produced with a range of degree of polymerization and molecular weight. As shown next, a molecular weight determined for such a polymer by measurement of osmotic pressure is a number-average molecular weight. 

Figure 3.1 Relationship between initial rate (wt%/h) of styrene polymerization and molecular weight at various temperatures. Reproduced with permission from Encyclopedia of Polymer Science and Engineering, Mark (Ed.), John Wiley Sons, NY. Copyright John Wiley Sons...

Detailed equations describing the rate of polymerization and molecular weight development can be found in Dhib et al. [31]. Yoon et al. [33] also calculated the molecular weight distribution in styrene batch thermal polymerization. 

This term refers to the number of repeating units in the polymer molecule. We shall use the abbreviation DP for the degree of polymerization defined in this way. The subscript n used on the parentheses in the foregoing structural formulas for polymers, represent this DP. The relation between degree of polymerization and molecular weight M of the same macromolecule is... 

Polyethylene (also known as polythene) was synthesized by accident in 1932 when scientists at Imperial Chemical Industries (ICI) investigated the reaction between ethylene and various compounds at high pressure. Polyethylene is generally commercially polymerized from monomer ethylene gas under high pressure (1000—3000 atmospheres) and at temperatures of 80-300°C (Brydson, 1999). A free radical initiator such as benzoyl peroxide, azodi-isobutyronitrile or oxygen is added. The reaction is exothermic and must be cooled to control the rate of polymerization and molecular weight. 

Another application of NRs is in polymer science. Polymerization in the interior cavity of NR can be used for controlling the rate of polymerization and molecular weight of the resultant polymer. Fnrthermore, the development of self-healing polymers can be achieved by using NRs. Herein, three representative examples have been presented to disclose the utility of NRs in this research field. 

Taking the above points into consideration, when deciding the type of binder to use, it is necessary to determine the degree of polymerization and molecular weight besides the sort of polymer. 

For example, the polymerization of vinyl monomers initiated by benzoyl peroxide (BPO) and 2,2 -azobisisobutyronitrile (AIBN) in ionic liquids has been reported. It is interesting to note that the rate of the radical polymerization and molecular weight of resulting polymer in ionic liquids were much larger than those in a conventional organic solvent. 

Rp and MW are the rate of polymerization and molecular weight of polymer, respectively. 

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