Polypropenes

Mention should be made of the nomenclature for the polymer. Industrially the materially is invariably known in the English-speaking world as polypropylene. However, the lUPAC name for the monomer is propene and until 1975 the recommended lUPAC name was polypropene, a term very rarely used. The latest lUPAC rules base the name of a polymer on the constitutional repeating unit, which in this case is a propylene unit (c.f. a methylene unit for polyethylene) and this leads to the name poly(propylene) (i.e. with brackets). In this volume the more common, unbracketed but still unambiguous name will be used. 

Industrial Engineering Chemistry Research 37, No.6, June 1998, p.2316-22 DEVELOPMENT OF A CONTINUOUS ROTATING CONE REACTOR PILOT PLANT FOR THE PYROLYSIS OF POLYETHENE AND POLYPROPENE... 

Silicone rubber (Pungor) Polythene, polypropene, paraffin... 

Often a suitable potentiometric indication for Lewis titrations is not available, whereas a conductometric indication can still be applied a well known example is the Bonitz titration29 of triethylaluminium (Et3Al) with an azine, such as isoquinoline, for determination of active alkylaluminium in the precatalysts of the Ziegler synthesis of polyethene or polypropene beyond the titration parameter A of the 1 1 complex, the conductivity suddenly decreases,... 

By using the asymmetric titanocene [MeHC(Me4-Cp)(Ind)]TiCl2 (Fig. 2), Chien obtained the first elastic polypropene with a narrow molecular weight distribution [14-17],... 

Rieger B, Cobzaru C (2006) Control of ultrahigh molecular weight polypropene microstructures via asymmetric dual-side catalysts. Macromol Symp 236 151-155... 

Atactic polymethacrylate esters, glass transition temperatures of, 16 273t Atactic polypropene, 16 104 20 524 Atactic polystyrene, 10 180, 182 Atactic propylene polymers, 17 704, 705 Atactic PSSA, 20 468 Atenolol, 5 102, 160... 

Examples of important commercial products obtained by free radical polymerisation of substituted ethenes are polypropene (polypropylene). Polyphenylethene (polystyrene), poly-1 chloroethene (polyvinyl chloride) and poly 1-methoxy carbonyl-1 methylethene (polymethalmethacrylate). 

Special interest attaches to the cyclic aliphatic hydrocarbons. Cyclopropane can be converted to oligomers by cationic catalysis [75, 76], and these appear to be essentially linear but whether they are really different from the polypropenes formed under the same conditions from propene is not yet settled. The initiation most probably involves formation of a non-classical cyclopropyl ion [77], as in alkylations with cyclopropane [78],... 

Steric hindrance may hamper the correct stereochemistry required for 13-elimination, and perhaps this can be used to stabilise our metal alkyl complex. In the modem polymerisation catalysts for polypropene this feature has actually been observed, which leads to higher molecular weight polymers. This now forms part of the design of new catalysts. 

Ewen was the first to report the synthesis of stereoregular propene polymers with soluble Group 4 metal complexes and alumoxane as the co-catalyst [13], He found that Cp2TiPh2 with alumoxane and propene gives isotactic polypropene. This catalyst does not contain an asymmetric site that would be able to control the stereoregularity. A stereo-block-polymer is obtained, see Figure 10.6. Formation of this sequence of regular blocks is taken as a proof for the chain-end control mechanism. 

Using an intrinsically chiral titanium compound (rac ethylene-bis-indenyl titanium dichloride, Figure 10.7), first described by Brintzinger [14], Ewen [13] obtained polypropene that was in part isotactic. Subsequently Kaminsky and Brintzinger have shown that highly isotactic polypropene can be obtained using the racemic zirconium analogue of the ethylene-bis(indenyl) compound [15],... 

Modification of the cyclopentadienyl ligands has led to a very rich chemistry and today a great variety of microstructures and combination thereof can be synthesised as desired including isotactic polymer with melting points above 160 °C, syndiotactic polypropene [16], block polymers, hemi-isotactic polymers etc. 

Above we mentioned the results reported by Ewen [13] who found that Cp2TiPh2/alumoxane gives a polypropene with isotactic stereoblocks. Naturally, this achiral catalyst can only give chain-end control as it lacks the necessary chiral centre for site control. In the 13C NMR the stereoblocks can be clearly observed as they lead to the typical 1 1 ratio of mmmr and mmrm absorptions in addition to the main peak of mmmm pentads. These are two simple examples showing how the analysis of the 13C NMR spectra can be used for the determination of the most likely mechanism of control of the stereochemistry. Obviously, further details can be obtained from the statistical analysis of the spectra and very neat examples are known [18],... 

How the groups unravelled this phenomenon is an interesting detective story but for our purposes it is more convenient to progress directly to the conclusion. In Figure 10.19 we outlined the two modes of insertion that can occur, 1,2 and 2,1 insertion. The latter often leads to isomerisation via P-elimination and re-insertion, which will lower the stereoregularity. Another outcome, especially for catalysts that show little or no P-elimination would be to continue the polymerisation resulting in an error in the chain and hence a lower melting point of the polypropene. 

The name of a polymer is usually written with the prefix poly-(meaning many ) before the name of the monomer. Often the common name of the monomer is used, rather than the lUPAC name. For example, the common name of ethene is ethylene. Polyethene, the polymer that is made from ethene, is often called polyethylene. Similarly, the polymer that is made from chloroethene (common name vinyl chloride) is named polyvinylchloride (PVC). The polymer that is made from propene monomers (common name propylene) is commonly called polypropylene, instead of polypropene. 

A short section of the polymer polypropene is shown helow. 

The addition polymers are formed by the repeated addition of monomer molecules possessing double or triple bonds, e.g., the formation of polythene from ethene and polypropene from propene. However, the addition polymers formed by the polymerisation of a single monomeric species are known as homopolymers, e.g., polythene,... 

For many processes, how ever, it is necessary to employ a divided cell in which the anode and cathode compartments are separated by a barrier, allowing the diffusion of ions but hindering transfer of reactants and products between compartments. This prevents undesirable side reactions. Good examples of the need for a divided cell are seen in the reduction of nitjobenzenes to phenylhydroxylamines (p. 379) or to anilines (p. 376). In these ca.scs the reduction products are susceptible to oxidation and must be prevented from approaching the anode. The cell compartments can be divided with a porous separator constructed from sintered glass, porous porcelain or a sintered inert polymer such as polypropene or polytetra-... 

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