Polypropylene solution process

Eastman Chemical has utilized a unique, high temperature solution process for propylene polymerization. Polymerization temperatures are maintained above 150°C to prevent precipitation of the isotactic polypropylene product in the hydrocarbon solvent. At these temperatures, the high rate of polymerization decreases rapidly, requiring low residence times (127). Stereoregularity is also adversely affected by high temperatures. Consequentiy, the... 

Most commercial processes produce polypropylene by a Hquid-phase slurry process. Hexane or heptane are the most commonly used diluents. However, there are a few examples in which Hquid propylene is used as the diluent. The leading companies involved in propylene processes are Amoco Chemicals (Standard OH, Indiana), El Paso (formerly Dart Industries), Exxon Chemical, Hercules, Hoechst, ICl, Mitsubishi Chemical Industries, Mitsubishi Petrochemical, Mitsui Petrochemical, Mitsui Toatsu, Montedison, Phillips Petroleum, SheU, Solvay, and Sumimoto Chemical. Eastman Kodak has developed and commercialized a Hquid-phase solution process. BASE has developed and commercialized a gas-phase process, and Amoco has developed a vapor-phase polymerization process that has been in commercial operation since early 1980. 

In solution polymerization, monomers mix and react while dissolved in a suitable solvent or a liquid monomer under high pressure (as in the case of the manufacture of polypropylene). The solvent dilutes the monomers which helps control the polymerization rate through concentration effects. The solvent also acts as a heat sink and heat transfer agent which helps cool the locale in which polymerization occurs. A drawback to solution processes is that the solvent can sometimes be incorporated into the growing chain if it participates in a chain transfer reaction. Polymer engineers optimize the solvent to avoid this effect. An example of a polymer made via solution polymerization is poly(tetrafluoroethylene), which is better knoivn by its trade name Teflon . This commonly used commercial polymer utilizes water as the solvent during the polymerization process,... 

Solution polymerizafion. Highly exothermic reactions can be handled by this process. The reaction is carried out in an excess of solvent that absorbs and disperses the heat of reaction. The excess solvent also prevents the formation of slush or sludge, which sometimes happens in the bulk process when the polymer volume overtakes the monomer. The solution process is particularly useful when the polymer is to be used in the solvent, say like a coating. Some of the snags with this process its difficult to remove residual traces of solvent, if that s necessary the same is true of catalyst if any is used. This process is used in one version of a low-pressure process for high-density polyethylene and for polypropylene. 

In contrast to polyethylene production, solution polymerisation at high temperature is rarely applied for isotactic polypropylene, but some special-purpose polypropylene grades are manufactured (Figure 3.57) [51]. However, the solution process, which yields isotactic polypropylene with a very low level of impurities, is characterised by high overall costs. The solution process is being used to make atactic polypropylene, to which it seems more suited [43],... 

The phase diagram (see Figure 1) shows that there are two solution processes a low-temperature process (below 100 °C) for the production of amorphous copolymers like ethylene/propylene elastomers (EPR or EPM) [2], and a high-tempera-ture process (far beyond 100 °C) for the production of semicrystalline homo- and copolymers like high-density polyethylenes (PE-HD), linear low-density poly-ethylenes (PE-LLD) and ethylene waxes [1, 3]. Polypropylenes (PP) cannot be made in high-temperature solution processes, except for propylene waxes. 

A most significant example, which was also provided by the Symyx team, deployed the same methodology to uncover an entirely new family of isospecific propylene polymerization catalysts. The Symyx team, in collaboration with Dow Chemical, discovered and developed a new catalyst class, and a new commercial solution process for the production of isotactic polypropylene-based elastomers and plastomers. " ... 

RESS has been particularly popular for the processing of polymeric materials. According to the original report by Krukonis (55), rapid expansion of a polypropylene solution in supercritical propylene resulted in the formation of fiber-like particles. The report marked the beginning of an extensive discussion on the issue of particles vs. fibers involving the use of RESS with polymers. 

Ionic polymerizations are almost exclusively solution processes. Many Zieg-ler-Natta polymerizations are also. They can be run under conditions such that the polymer product stays in solution, as in the production of stereospecific rubbers. The crystalline polymers polyethylene and isotactic polypropylene are commonly produced at temperatures sufliciently below T so that the polymer product is a solid that grows on the catalyst particles as in gas-phase polymerizations. Such processes are known as slurry polymerizations. 

The method has severe limitations for systems where gradients on near-atomic scale are important (as in the protein folding process or in bilayer membranes that contain only two molecules in a separated phase), but is extremely powerful for (co)polymer mixtures and solutions [147, 148, 149]. As an example Fig. 6 gives a snapshot in the process of self-organisation of a polypropylene oxide-ethylene oxide copolymer PL64 in aqueous solution on its way from a completely homogeneous initial distribution to a hexagonal structure. 

Pulp-like olefin fibers are produced by a high pressure spurting process developed by Hercules Inc. and Solvay, Inc. Polypropylene or polyethylene is dissolved in volatile solvents at high temperature and pressure. After the solution is released, the solvent is volatilised, and the polymer expands into a highly fluffed, pulp-like product. Additives are included to modify the surface characteristics of the pulp. Uses include felted fabrics, substitution in whole or in part for wood pulp in papermaking, and replacement of asbestos in reinforcing appHcations (56). 

Thorough rinsing between the pretreatment steps is essential to prevent carry-over of solutions. The commonest plastic plated is ABS (acrylonitrile butadiene styrene copolymer) but procedures are also available for polypropylene and other plastics. In some proprietary processes, electroless copper solutions are used to give the initial thin conducting layer. 

In an industrial application dissolution/reprecipitation technology is used to separate and recover nylon from carpet waste [636]. Carpets are generally composed of three primary polymer components, namely polypropylene (backing), SBR latex (binding) and nylon (face fibres), and calcium carbonate filler. The process involves selective dissolution of nylon (typically constituting more than 50wt% of carpet polymer mass) with an 88 wt % liquid formic acid solution and recovery of nylon powder with scCC>2 antisolvent precipitation at high pressure. Papaspyrides and Kartalis [637] used dimethylsulfoxide as a solvent for PA6 and formic acid for PA6.6, and methylethylketone as the nonsolvent for both polymers. 

ArgoGel-MB-CHO resin (366 mg, 0.42mmol/g substitution) was placed into an Ace pressure tube (note 5). Trimethyl orthoformate (TMOF 5 mL) was added to the flask along with the primary amine (10 equiv.). The tube was capped and heated for 2h at 70°C in a rotating oven (note 6), and cooled. The TMOF solution was removed with the use of a filtration cannula, and the entire process was repeated. The resin was washed with TMOF (5 mL, lx) and anhydrous methanol (5 mL, 3 x) Anhydrous methanol (5 mL) was added to the resin, followed by the addition of sodium borohydride (133 mg, 20 equiv.). After vigorous gas evolution had ceased, the tube was capped and agitated for 8 h at room temperature. The resin was then transferred to a polypropylene reaction vessel and washed with methanol (5mL, 3 x), methanol water (1 1, 5mL, 3 x), DMF water (1 1, 5mL, 3 x), DMF (5mL, 3 x), and methylene chloride (5 mL, 3 x). 

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