Second generation polypropylene

Polyamines, such as second-generation polypropylene imine dendrimers and polyethyleneimine have been used as cross-linkers increasing the cross-link density above the level obtained with CL alone. Polyethyleneimine-functionalized single-walled carbon nanotubes (SWNTs) have been also used as macromolecular cross-linking agents (Homenick et al., 2010). 

As the demand of polypropylene increased, it was necessary to increase the plant capacity and to use continuous processes, this was possible thanks to second-generation catalysts with increased yield (6000-15 000 kg-PP per kg catalyst) and isotacticity, but not yet to an extent that allowed simplification of the production process. Several different processes were developed slurry, solution, bulk, gas phase. 

The second generation of polymers was introduced during 1950—65 and includes a number of engineering plastics such as high-density polyethylene, isotactic polypropylene, polycarbonates, polyurethanes, epoxy resins, polysulphones and aromatic polyesters, also used for films and fibres. New rubber materials, acrylic fibres made of polyacrylonitrile and latex paint were also introduced. 

Wilhelmy advancing force data for flame-treated polypropylene. To generate this data, a scratch was made directly above a downstream primer port while a second downstream primer port located 5 mm away from the scratch was also plugged. 

Radicals, generated in polypropylene fibers during irradiation as well as the transition frcan these reidicals (R ) to peroxy radicals (ROa ) are monitored by electron spin resonance spectroscopy. Experimental data exhibit an anomaly in the temperature dependence of RO, concentration, around the glassy transition temperature (Tq). The dependence of RO, concentration on temperature, around T, is described by a Hil-liam-Landel-Perry equation rather than by an Arrhenius one. Consequently, the transition consists of two steps the first is associated with diffusion processes and the second with the proper chemical reaction. 

In addition to the formation of stereoblock polypropylenes by exchange of the polymer chain from one site to another within one catalyst, stereoblock polypropylenes have been generated by the exchange of the polymer chain from one catalyst to another. Thus, mixtures of two different catalysts can be used to form stereoblock polypropylene if polymer chains can be exchanged between two different metal centers. Often trialkylalu-minum additives are used as the chain transfer agents. The polymer chain transfers from the transition metal catalyst to aluminum to a second transition metal catalyst. 

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