Polypropylene, chain type

How does the type and level of tacticity of the polypropylene chain affect the degree of crystallinity of the solid polymer ... 

Effect of Substrate. Again, polyethylene and ethylene-propylene copolymers are better substrates for block formation than polypropylene (Table XI). Polyethylene is better than polypropylene, and a polyethylene-polypropylene-polyethylene type of block polymer is better than polyethylene. This agrees with what has been found for AFR polymers containing methylvinylpyridine and acrylonitrile. It also supports our belief that AFR polymers are formed by the growing of a free radical polymer onto active ends of anionic polymer chains. If it were a random grafting reaction, it would be hard to explain why a propylene polymer with a more vulnerable tertiary hydrogen should give a lower... 

Figure 2 Types of polypropylene chains produced with metallocene catalysts.

Polypropylene (PP) fibers contain, according to ISO 2076, minimally an 85% portion of macromolecular polypropylene chains and maximally 15% of another fiber-forming polymer, the content of nonfiber-forming substance being unlimited. Of the stereoregular isomers, only isotactic PP is used for fiber preparation. Nowadays, new types of PP (s)mdio-tactic, metallocene based) have been developed for fiber and film production. The first industrial company that launched the production of PP fibers was Montecatini Co. (1959), then after 1960 l.C.l., Celanese, Hercules, etc. Japanese companies started the production of bicomponent fibers. Ciurently, the global production amounts to 4200 kt of PP fibers in wide assortment of textile, industrial and special typ>es. Table 1 presents a survey of the world production of PP fibers in 1992-1995. 

In the case of stereoregular polymers, such as isotactic and syndiotac-tic polypropylene, chain tacticity is the main factor affecting crystallizability. Crystaf can also be used to measure the distribution of tacticity. Since the distribution of tacticity is often modeled with pseudo binary copolymerization models (i.e. the meso and racemic insertions stand for the comonomer type in the case of a copolymer), the following discussion for copolymers can be easily modified to describe the tacticity distribution of stereoregular polymers. 

Another man of genius, G. Natta at Milano Polytechnic, soon extended that type of catalysis to the stereoselective polymerization of propylene into isotactic (and also syndiotactic) stereoregular polypropylene chains (highly cristalline fiber-forming material, m.p. close to 170 °C). 

Figure 1.2 shows sections of polymer chains of these three types the substituent R equals phenyl for polystyrene and methyl for polypropylene. The general term for this stereoregularity is tacticity, a term derived from the Greek word meaning to put in order. ... 

Oxidative degradation of polypropylene chemically incorporates oxygen to the polymeric chains. Why would an isotactic polypropylene be less susceptible to this type of degradation than one that is atactic ... 

Meijer et al [6] reported on inverted unimolecular micelle type dendrimers (Figure 13.4) which have a hydrophilic interior and a hydrophobic shell, synthesized by modifying the end groups of hydrophilic polypropylene imine) dendrimer with alkyl chains. It was shown that these dendrimers could host... 

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