Chlorination of polypropylene

The chlorination of polypropylene has been the subject of several fundamental studies and a variety of products is obtainable according to the tacticity of the original polymer and to the extent of chlorination. 

Inagaki, N., Tasaka, S., Suzuki, Y, 1994. Siuface chlorination of polypropylene film by CHCI plasma. J. Appl. Polym. Sci. 51 (13), 2131-2137. 

Chlorinations of polypropylene usually result in severe degradations of the polymer. When TiCU is the chlorination catalyst, presumably, less degradation occurs. Studies of bromination of polypropylene (atactic) show that when the reaction is carried out in the dark, in CCI4 at 60 °C, the substitution reactions proceed at the rate of 0.5% per hour. ... 

Puszyhski, A., Dwomicka, J., Chlorination of Polypropylene in Suspension, Angew. Macromol. Chem. 1986,139,123. 

Chlorination reactions. Chlorination of hydrocarbons has been carried out in Japan, chlorination of toluene in the United States, chlorination of tetrachloropentane in the former U.S.S.R. to give octachlorocy-clopentane, and chlorination of propanoic acid in France to give chloro-propanoic acid. Chlorination of methane by irradiation to give lower halomethanes was found to be cost-effective. Chlorination of various amorphous polymers such as polypropylene, polybutadiene, and PVC, has also been carried out. 

An 8000-member library of trisamino- and aminooxy-l,3,5-triazines has been prepared by use of highly effective, microwave-assisted nucleophilic substitution of polypropylene (PP) or cellulose membrane-bound monochlorotriazines. The key step relied on the microwave-promoted substitution of the chlorine atom in monochlorotriazines (Scheme 12.7) [35]. Whereas the conventional procedure required relatively harsh conditions such as 80 °C for 5 h or very long reaction times (4 days), all substitution reactions were found to proceed within 6 min, with both amines and solutions of cesium salts of phenols, and use of microwave irradiation in a domestic oven under atmospheric reaction conditions. The reactions were conducted by applying a SPOT-synthesis technique [36] on 18 x 26 cm cellulose membranes leading to a spatially addressed parallel assembly of the desired triazines after cleavage with TFA vapor. This concept was later also extended to other halogenated heterocycles, such as 2,4,6-trichloropyrimidine, 4,6-dichloro-5-nitropyrimidine, and 2,6,8-trichloro-7-methylpurine, and applied to the synthesis of macrocyclic peptidomimetics [37]. 

The solubility properties of polypropylene have been similar to that of polyethylene. Although polypropylene is insoluble at room temperature, yet it is soluble in hydrocarbons and chlorinated hydrocarbons at temperature above 80°C. 

Most properties of polypropylene are similar to polyethylene but polypropylene has higher softening point and at 140°C polypropylene still retains its shape. Polypropylene is more susceptible to oxidation by air at higher temperature. Cross-linking, chlorination and other reactions lead to degradation of Polymer chain and are not very useful commercially. 

The insertion of a certain amount of chlorine atoms into the unit cells of polyethylene and of isotactic polypropylene has been observed by PLATfe, Tran Kheu, and Shibaev (75) by chlorination of the pure homopolymers. The unit cell constants of the two pure homopolymers increase with increasing amount of bound chlorine. The amorphisation of polyethylene is reached with a chlorine content of about 50%. 

Chlorination is one of the most interesting processes for polymer modification, and is usually carried out by means of catalysts or by UV irradiation. Since 1960, radiation-induced chlorination of polyethylene and polypropylene has been studied, especially by Soviet workers (1-3). As the polymers used in that work are insoluble in the usual solvents at normal temperature, chlorination was done in the heterogeneous phase— for example, by leading continuously a stream of chlorine over the finely ground polymer or through an aqueous suspension of the polyolefin. It is, therefore, difficult to compare the results obtained under the different conditions used. 

Camino, G. Costa, L. Trossarelli, L. Thermal degradation of polymer-fire retardant mixtures Part III— Degradation products of polypropylene-chlorinated paraffin mixtures, Polymer Degradation and Stability, 1982,4(2), 133-144. 

Polymeric fibers are popular for reinforcing concrete matrices because of their low density (more number of fibers for a prescribed volume fraction), high tensile strength, ease of dispersion, relative resistance to chemicals, and relatively low cost compared to other kinds of fibers. Polypropylene and polyolefin fibers are typically hydrophobic, resulting in a relatively poor bond with concrete matrices compared to some other types of fibers. Treatment of polypropylene with an aqueous dispersion of colloidal alumina or silica and chlorinated polypropylene enhances the affinity of these fibers toward cement particles. Treatment of polypropylene fibers with a surface-active agent provides better dispersion of the fibers and a stronger bond between cement and fiber. The earlier attempts at surface treatments of polypropylene fibers have had only limited success and have not been commercially attractive. 

More than 20 aluminum alkyls are presently offered in the merchant market. As of this writing, most of the high-volume products are priced between about 5 and 10 per pound. Exceptions include trimethylaluminum (which is produced by a costly multi-step process (13)) and diethylaluminum iodide (which requires expensive iodine). Triethylaluminum (TEAL) is the most important aluminum alkyl and is sold globally in multi-million pound per year quantities. Large amounts of triethylaluminum are used in production of polypropylene. Chlorinated aluminum alkyls, such as diethylaluminum chloride (DEAC) and ethylaluminum sesquichloride (EASC), are less costly than triethylaluminum. However, DEAC and EASC do not perform well with some modern supported... 

Figure 6.3.10. Result for a Py GC/MS analysis of polypropylene chlorinated with 32% wt. chlorine. Pyrolysis done at 600° C in He, with the separation on a Carbowax type column.

OTHER COMMENTS used during deposition of metallic coatings used during synthesis of plasticizers and intermediates used in the preparation of dyes, pharmaceuticals, other chlorinating agents, and other organic chemicals used in the treatment of polypropylene before drying in manufacture of knitted fabrics. 

The plastic pipe market is dominated by PVC pipes, which hold 80% of the market. Polyethylene, principally HDPE, is used for about 12% of pipe production. Following polyethylene are other higher priced, specialty pipes made from ABS terpolymer, chlorinated PVC, polypropylene, polybutylene, and fiber-reinforced epoxy and polyester. 

Both chlorination and bromination of polypropylene and isobutylene lead to degradation of the main chain, with the loss of many useful properties. Degradation during chlorination can, however, be avoided at low temperatures by limiting the reaction to a maximum of about 2%. This procedure forms a useful commercial product. 

No reactive flame-retardants are used for polyolefins. Chlorination or sulphochlori-nation of polyethylene reduces the original flammability but they give rise to quite new products, significantly different from polyethylene. Replacement of tertiary hydrogens of polypropylene by 0.5 per cent of bromine or 3 per cent of chlorine is highly effective in flame-retardancy but the consequent impairment of thermal stability makes the products useless in practice. 

Heqing Fu. Study on grafting modification of polypropylene and chlorinated polypropylene. Guangzhou South China University of Technology, 2005. 

CH Ochiai, H., Nishihara, Y., Yamaguchi, S., and Murakami, I., Thermodynamic properties of polypropylene-chlorinated methane systems, J. Set. Hiroshima Univ., Ser. A, 41, 157, 1977. 

Table 1. Density of polypropylene, chlorinated M = 93000 g/mol, 30 wt% chlorine) in 2-butanone ...

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