Polypropylene generations

Fig. 1. Positive ion ToF-SIMS spectmm from the surface of pre-treated (electrochemically oxidized) polypropylene generated by Cs+ primary ions. The intense low-mass peaks (m/z< 130) are hydrocarbon fragments from the polymer while the peaks in the region of m/z 650 are due to the antioxidant Irgaphos 168. Before pre-treatment, these peaks are not observed, showing that the antioxidant molecules migrate from the polypropylene bulk to the higher energy surface produced by electrochemical oxidation...

The relative configuration of the monomer units can be controlled by the structure of the catalyst or by the configuration of the last inserted unit. These two scenarios are called site control and chain-end control. The isotactic polypropylene generated by the types of stereodefined metallocene catalysts presented in this chapter results from site control. More sophisticated architectures are possible by site-control mechanisms than chain-end control mechanisms, as illustrated by the variety of polyolefins prepared by homogeneous catalysts. 

Isotactic-Atactic Stereobiock Polypropylene Generated from Homogeneous Catalysts... 

Experimental evidence is available to show that at room temperature diperoxides are formed in polyethylene, whereas polypropylene and polyvinyl chloride generate hydroperoxides. The temperature at which the peroxides decompose and initiate grafting depends on the type of polymer used. 

A new generation coordination catalysts are metallocenes. The chiral form of metallocene produces isotactic polypropylene, whereas the achiral form produces atactic polypropylene. As the ligands rotate, the catalyst produces alternating blocks of isotactic and atactic polymer much like a miniature sewing machine which switches back and forth between two different kinds of stitches. 

In the polymer filed, new-generation metallocenes, which are currently used in many polyethylene and polypropylene processes, can polymerize proplylene in two different modes alternating blocks of rigid isotactic and flexible atactic. These new developments and other changes and approaches related to polymerization are noted in Chapters 11 and 12. 

Occasionally the zinc electrode is wrapped in a polypropylene fleece filled with inorganic substances, such as potassium titanate, in order to reduce the solubility of zinc since the problem of dendrite growth is aggravated even by the metallization of the cellophane separator due to the aforesaid silver reduction and its promoting the generation of shorts. 

The rapid decomposition of a peroxide in the presence of MAH results in the excitation and homopolymerization of MAH. When the latter is conducted in the presence of polypropylene, the latter undergoes degradation ( 10) while polyethylene is crosslinked under the same conditions (11). This has been attributed to the presence of excited MAH which increases the radical generation on the polymer beyond that due to the radicals from the peroxide. 

In a way related are the complexes formed by Hg salts and multicrown dendrimers of different generations (dendrimers with a polypropylene amine interior of different volume and benzo[15]-crown-5 ether periphery), studied by extraction methods using radioactive 203Hg2+.210 Up to 12 Hg2+ ions were found to be bound per dendrimer molecule, obviously in the amine-dominated interior, not in the crown-ether periphery. 

At present, a fraction of the generated end-of-life FLs are being collected by the informal sector (kabadiwalas), largely from the large-scale consumers (industries and corporate sectors). The lamps are then disassembled by crude methods into useful components such as glass tubes (glass and phosphor powder), aluminum end caps, polypropylene caps, and electronic ballasts (electronic components which contain metal). The major processing hubs for the various components exist as follows ... 

The latter effect has been demonstrated by Meijer et al., who attached chiral aminoalcohols to the peripheral NH2-groups of polypropylene imine) dendrimers of different generations [100]. In the enantioselective addition of diethyl-zinc to benzaldehyde (mediated by these aminoalcohol appendages) both the yields and the enantioselectivities decreased with increasing size of the dendrimer (Fig. 28). The catalyst obtained from the 5th-generation dendrimer carrying 64 aminoalcohol groups at its periphery showed almost no preference for one enantiomer over the other. This behavior coincides with the absence of measurable optical rotation as mentioned in Sect. 3 above. The loss of activity and selectivity was ascribed to multiple interactions on the surface which were... 

Polypropylene imine) dendrimer of 3rd generation with 16 end groups... 

Microwave-assisted reactions allow rapid product generation in high yield under uniform conditions. Therefore, they should be ideally suited for parallel synthesis applications. The first example of parallel reactions carried out under microwave irradiation conditions involved the nucleophilic substitution of an alkyl iodide with 60 diverse piperidine or piperazine derivatives (Scheme 4.22) [76]. Reactions were carried out in a multimode microwave reactor in individual sealed polypropylene vials using acetonitrile as solvent. Screening of the resulting 2-aminothiazole library in a herpes simplex virus-1 (HSV-1) assay led to three confirmed hits, demonstrating the potential of this method for rapid lead optimization. 

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