Polymerization, of propylene

Metallocene-Catalyzed Polymerization of Propylene to Highly Isotactic Polypropylene in Organic Suspension 

Safety precautions Before this experiment is carried out, Sect. 2.2.5 must be read as weii as the materiai safety data sheets (MSDS) for aii chemicais and products used. 

Couf/on. Refiuxing of toiuene over sodium/potassium aiioy must be done under permanent supervision. 

Highiy dried toiuene is the most usefui reaction medium.lt is obtained according to the foiiowing procedure. Pre-dried toiuene (over moiecuiar sieve) is refluxed over a iiquid sodium/potassium aiioy (5-10 mi for 2 i of toluene) for 4-5 days. An alternative method is the addition of n-butyllithium in small portions (ca.10 ml for 21 toluene) which can be visualized with benzophenone as indicator. When the toluene is sufficiently dried (change of color) it is distilled off and stored under argon (The used syringes or pipettes have to be flushed prior to use with argon after use they have to be cleaned immediately with toluene). 

Couf/on. Working with MAO has to be done under rigorous safety precautions Wearing of safety goggles and protective gloves is a must. MAO is highly reactive It reacts with moisture traces on the skin. If MAO is spilled, the contaminated area has to be covered with sand to prevent a fire.Then, MAO is hydrolyzed by the careful addition of 2-propanol or ethanol,followed by water (see also Example 3-28). 

---

Polypropylene. The polymerization of propylene results in a polymer with the following structure ... 

Gas-phase polymerization of propylene was pioneered by BASF, who developed the Novolen process which uses stirred-bed reactors (Fig. 8) (125). Unreacted monomer is condensed and recycled to the polymerizer, providing additional removal of the heat of reaction. As in the early Hquid-phase systems, post-reactor treatment of the polymer is required to remove catalyst residues (126). The high content of atactic polymer in the final product limits its usefiilness in many markets. 

Fig. 2. Reaction scheme for the anionic polymerization of propylene oxide.

Polymerization to Polyether Polyols. The addition polymerization of propylene oxide to form polyether polyols is very important commercially. Polyols are made by addition of epoxides to initiators, ie, compounds that contain an active hydrogen, such as alcohols or amines. The polymerization occurs with either anionic (base) or cationic (acidic) catalysis. The base catalysis is preferred commercially (25,27). 

Polypropylene [9003-07-0] is made by the polymerization of propylene gas. Polypropylene (qv) sutures are available in clear (undyed) or blue (melt-pigmented with [phthalocyaninato(2-)] copper). Monofilament polypropylene sutures are sold under the trade names Deklene, Prolene, Surgdene, and Surgipro. 

This conceptual link extends to surfaces that are not so obviously similar in stmcture to molecular species. For example, the early Ziegler catalysts for polymerization of propylene were a-TiCl. Today, supported Ti complexes are used instead (26,57). These catalysts are selective for stereospecific polymerization, giving high yields of isotactic polypropylene from propylene. The catalytic sites are beheved to be located at the edges of TiCl crystals. The surface stmctures have been inferred to incorporate anion vacancies that is, sites where CL ions are not present and where TL" ions are exposed (66). These cations exist in octahedral surroundings, The polymerization has been explained by a mechanism whereby the growing polymer chain and an adsorbed propylene bonded cis to it on the surface undergo an insertion reaction (67). In this respect, there is no essential difference between the explanation of the surface catalyzed polymerization and that catalyzed in solution. 

Polypropylene. There is an added dimension to the catalytic polymerization of propylene, since in addition to the requirement that the catalyst be sufficiently active to allow minute amounts of catalyst to yield large quantities of polymer, it must also give predominantly polypropylene with high tacticity that is, a highly ordered molecular stmcture with high crystallinity. The three stmctures for polypropylene are the isotactic, syndiotactic, and atactic forms (90) (see Olefin polya rs, polypropylene). 

The next major commodity plastic worth discussing is polypropylene. Polypropylene is a thermoplastic, crystalline resin. Its production technology is based on Ziegler s discovery in 1953 of metal alkyl-transition metal halide olefin polymerization catalysts. These are heterogeneous coordination systems that produce resin by stereo specific polymerization of propylene. Stereoregular polymers characteristically have monomeric units arranged in orderly periodic steric configuration. 

Plastic or resin derived from the polymerization of propylene as the principal monomer. 

Low molecular weight olefins ranging from to Q, are produced by the polymerization of propylene or butylenes over a supported phosphorie acid catalyst. The product of this polymerization is a series of highly branched olefins ranging from dimers to pentamers. Some fragmentation of the polymers formed takes place in the reactor, so appreciable quantities of olefins are obtained which are not integral multiples of the monomer units. 

Polypropylene is made by the polymerization of propylene. Stronger and more rigid than... 

The properties of polymers depend not only on overall chain length, but also on the degree to which the monomers are ordered along the chain. Different methods of preparation lead to vastly different degrees of ordering. A good example is found in the polymerization of propylene. This polymerizes predominantly head-to-tail , and leads to a stereocenter ( ) at every other atom in the polymer chain. 

Zirconocene dichloride 121 derived from (l-phenylethyl)cyclopentadienyl ligand is formed as a mixture of diastereomers from which the racemic form can be isolated by fractional crystallization. This complex was studied by X-ray diffraction methods and revealed a virtually chiral C2-symmetrical conformation in which the chiral ring-substituents are arranged in a synclinal position relative to the five-membered ring. It was proposed that this conformation is preserved in solution. Using 121 as catalyst the influence of double stereodifferentiation during isospecific polymerization of propylene (Eq. 32) was demonstrated for the first time [142],... 

Provided that the uncomplexed species is suceptible to destruction, while the complex is protected, the lifetime of living polymer increases at higher monomer concentrations. Cationic polymerization of propylene induced by AlBr3. HBr studied by Fontana and Kidder22) exemplifies perhaps such a system. 

The kinetic models for the gas phase polymerization of propylene in semibatch and continuous backmix reactors are based on the respective proven models for hexane slurry polymerization ( ). They are also very similar to the models for bulk polymerization. The primary difference between them lies in the substitution of the appropriate gas phase correlations and parameters for those pertaining to the liquid phase. 

Table II summarizes the yields obtained from the CONGAS computer output variable study of the gas phase polymerization of propylene. The reactor is assumed to be a perfect backmix type. The base case for this comparison corresponds to the most active BASF TiC 3 operated at almost the same conditions used by Wisseroth, 80 C and 400 psig. Agitation speed is assumed to have no effect on yield provided there is sufficient mixing. The variable study is divided into two parts for discussion catalyst parameters and reactor conditions. The catalyst is characterized by kg , X, and d7. Percent solubles is not considered because there is presently so little kinetic data to describe this. The reactor conditions chosen for study are those that have some significant effect on the kinetics temperature, pressure, and gas composition.

An optimal reaction-temperature of 65°C was claimed. The blackish brown TiSCl is very sensitive to oxygen and humidity. As no X-ray measurements have been made, additional work is needed. Titanium sulfide halides have also been claimed as catalysts for the polymerization of propylene (363). 

Co/Zn double metal cyanide catalyzed ring-opening polymerization of propylene oxide effect of cocataiysts on polymerization behavior... 

Polymerizations of propylene oxide were rarried out by using 1 L autoclave (Parr) at... 

Initial studies of the polymerization of propylene with transition metal allyl compounds suggested that this monomer could not be polymerized by any of the soluble catalysts available. Subsequent work (16) has revealed, however, that the propylene polymerization is much more susceptible to impurities, in particular traces of ether which compete with the monomer for the coordination sites. When this and other impurities are removed, weak activity is detected. These results are summarized in Table XIII. 

Polymerization of Propylene by Transition Metal Alkyl Compounds Toluene as Solvent, Temperature 65°C. Ethylene Pressure 10 atm (IS, 16)... 

It has been suggested however that isotacticity derives from polymerization occurring on colloidal particles formed by thermal decomposition of the catalysts. As stated previously, in the presence of the monomer even the allyl compounds are stable at 65°C and none of the thermal decomposition products (black to yellow solids) could be detected. As a check on these results a polymerization of propylene was carried out with Zr (benzyl) 4 in toluene at 0°C in a sealed tube. The reaction was very slow and analytical quantities of polymer could be obtained only after 312 hr. NMR analysis showed peaks assignable to isotactic sequences, and these were much stronger than the peaks assignable to syndiotactic diads. It was concluded... 

Polymerization of Propylene with Benzyl Derivatives of Titanium (36) at 2Cl°C in Benzene ... 

Head-to-tail polymerization of propylene produces a polymer in which every other atom is a stereocenter. 

Variation in the substituents at the nitrogen donor atom has also been examined,126 and in one case isoselective polymerization of propylene was described (mmmm pentad = 56% using (31)).127 Syndioselective propylene polymerization with an rr triad content of 63% has been reported using (32)/MAO, although residual Me3Al must be removed from the MAO in order to suppress chain transfer to aluminum.128... 

Zirconium bis(amides) such as (35) and (36) display moderate ethylene polymerization activities.133,134 Complex (37) containing a chelating diamide ligand has been shown to initiate the living polymerization of a-olefins such as 1-hexene (Mw/Mn= 1.05-1.08) with activities up to 750gmmol-1 h-1.135-137 The living polymerization of propylene using this system activated with... 

When mixed with Et2AlCl, the vanadium(III) complex (87) polymerizes propylene at —78 °C in a living manner.241,242 Poor initiator efficiency ( 4%) and low activities were improved by employing complex (88) activities of lOOgmmol h bar 1 were reported and the polymerization of propylene remained living (Mw/Mn= 1.2-1.4) up to 40 °C.243 244 The synthesis of end-functionalized PP and PP copolymers has also been achieved using these initiators. 

Cationic complexes, such as 55 and 56, catalyze the polymerization of propylene oxide, cyclohexene oxide, and of e-caprolactone with substantially higher activities than neutral zinc complexes. 

---