Branch length dependence, physical properties

While the basic chemical structure of a synthetic polymer is usually well understood, many physical properties depend on such characteristics as chain length, degree of chain branching, and molar mass, which are not easy to specify exactly in terms of a molecular formula. Moreover the macromolecules in a given sample are seldom uniform in chain length or molar mass (which for a linear polymer is proportional to chain length) thus the nature of the distribution of molar masses is another important characteristic. 

Figure 45 shows another example of the dependence of polymer physical properties on the branch length. Copolymers were made with Cr/silica catalyst to have the same approximate density and MI. Various comonomers were used, ranging from propylene to 1-octene. The ESCR of each polymer was then determined and is plotted against the number of carbon atoms in the comonomer. There is a clear advantage associated with longer branch lengths. 

Stoddard solvent is a mixture of hydrocarbons derived by refining crude oil its environmental fate is dependent on the physical and chemical properties of the individual components. The hydrocarbon chain length ranges from C to C12, although a form of Stoddard solvent called 140 flash contains Cs and Ce hydrocarbons as well. These hydrocarbons consist primarily of linear and branched alkanes (also called paraffins) (30-50% of the total mixture), cycloalkanes (30 40%), and aromatics (10-20%). 

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