Propylene-based polymers polymerization

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. 

Coordination polymerization Can engineer polymers with specific tacticities based on the catalyst system Can limit branching reactions Polymerization can occur at low pressures and modest temperatures Otherwise non-polymerizable monomers (e.g., propylene) can be polymerized Mainly applicable to olefinic monomers... 

The PEO salt complexes are generally prepared by direct interaction in solution for soluble systems or by immersion method, soaking the network cross-linked PEO in the appropriate salt solution [52-57]. Besides PEO, poly(propylene)oxide, poly(ethylene)suceinate, poly(epichlorohydrin), and polyethylene imine) have also been explored as base polymers for solid electrolytes [58]. Polyethylene imine) (PEI) is prepared by the ring-opening polymerization of 2-methyloxazoline. Solid solutions of PEI and Nal are obtained by dissolving both in acetonitrile (80 °C) followed by cooling to room temperature and solvent evaporation in vacuo. Polyethyleneimine-NaCF3S03 complexes have also been explored [59],... 

For the polymerization of ethylene and propylene large-scale gas-phase processes are well established. The implementation of gas-phase technology to the production of sticky polymers such as the ethylene/propylene-based rubbers EPM and EPDM was pioneered by UCC [519]. In a series of patents, UCC describes various approaches to overcome the inherent stickiness of rubber granules in the gas-phase polymerization. These approaches include the use of anti-agglomerants such as carbon black, silica, inorganic salts or appropriate catalyst supports and antistatic voltage etc. [520-535]. The addition of fluidization or anti-agglomeration aids is described by Zollner et al., silica is used in particular [536,537]. 

Chiral polymers have been applied in many areas of research, including chiral separation of organic molecules, asymmetric induction in organic synthesis, and wave guiding in non-linear optics [ 146,147]. Two distinct classes of polymers represent these optically active materials those with induced chirality based on the catalyst and polymerization mechanism and those produced from chiral monomers. Achiral monomers like propylene have been polymerized stereoselectively using chiral initiators or catalysts yielding isotactic, helical polymers [148-150]. On the other hand, polymerization of chiral monomers such as diepoxides, dimethacrylates, diisocyanides, and vinyl ethers yields chiral polymers by incorporation of chirality into the main chain of the polymer or as a pedant side group [151-155]. A number of chiral metathesis catalysts have been made, and they have proven useful in asymmetric ROM as well as in stereospecific polymerization of norbornene and norbornadiene [ 156-159]. This section of the review will focus on the ADMET polymerization of chiral monomers as a method of chiral polymer synthesis. 

Catalysts based on the Hf pyridyl amine complexes 126-128 have been used for the preparation of ethylene/ propylene co-polymers as well as of ethylene/propylene/l-octene terpolymers. These co-polymers are characterized by having at least 60 wt% propylene units, Mw around 300000, and Mw/Mn in the range 2.0-2.4. The NMR analysis of these co-polymers showed that the propylene sequences are remarkably isotactic mm > 90%) and showed the presence of regioirregularly inserted propylene units(<0.5% mol). The most interesting property of catalysts based on 126-128 is their high thermal stability.1119 Using modifications of isospecific bis(phenoxy-amine)-based catalysts, such as complex 164, the controlled synthesis of iPP- /orjf-poly/E-co-P) diblock co-poly-mers has been achieved. This is a remarkable result since iPP and PE are both polymeric materials of extreme industrial relevance.1206... 

Composition (type of polymeric components). The base polymer (which is to be modified) may be an amorphous polymer [e.g., polystyrene (PS), styrene-acrylonitrile copolymer, polycarbonate, or poly(vinyl chloride)], a semicrystalline polymer [e.g., polyamide (PA) or polypropylene (PP)], or a thermoset resin (e.g., epoxy resin). The modifier may be a rubber-like elastomer (e.g., polybutadiene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, or ethylene-propylene-diene copolymer), a core-shell modifier, or another polymer. Even smaller amounts of a compatibilizer, such as a copolymer, are sometimes added as a third component to control the morphology. 

Furukawa et al. explored the use of methanol and ethanol as additives for diethylzinc-based epoxide polymerization systems, and found that both the yield and crystallinity of the resulting polymers were inferior to those for polymers synthesized with the ZnEt2/H20 system. The use of achiral alcohols as cocatalysts was revisited in 1994 when Kuran and Listos reported the polymerization of propylene oxide and cyclohexene oxide (a meso molecule) with ZnEt2/polyhydric phenol (such as 4-tert-butyl-catechol), phenol, or l-phenoxy-2-propanol. The poly(propylene oxide) formed from these systems contained mostly isotactic dyads (72% m), whereas the poly(cyclohexene oxide) contained mostly syndiotactic dyads (80% r) (Scheme 24.8). 

Prior to the mid-1980 s, catalysts formed using achiral CpaMCb precursors were found to produce only atactic polypropylene (which, incidentally cannot be obtained in the pure form directly from heterogeneous catalysts). In 1984, Ewen reported the use of metallocene-based catalysts for the isospecific polymerization of propylene.38 The polymerization of propylene at -45°C using a Cp2TiPh2 (I,Fig.4) / MAO catalyst system produced a partially isotactic polymer with an mmmm pentad content of 52% (versus 6.25% for a purely atactic polymer). NMR analysis of the polymer revealed the stereochemical errors mmmr and mmrm in the ratio of 1 1, which is indicative of a stereoblock microstructure (Fig.5). Such a structure is consistent with a chain-end control mechanism,39 where the stereocenter of the last inserted monomer unit provides... 

It was during the 1940s that the base-initiated polymerization of propylene oxide began to be used to produce products that are still in use today (14). In a series of patents by H. R. Rife and F. H. Roberts (15), poly (propylene oxide)s are described that are initiated in the presence of alcohols to produce ether propoxylates. These liquid polymers had methoxy or butoxy groups on one end of the poly ether chain and were used as lubricants and hydraulic fluids. This work was quickly followed by other derivatives, which included esters and mixed alkoxylates of propylene oxide and ethylene oxide (16). Uses included antifoams and emulsifiers, coating solvents, ceramic glazes and binders, and synthetic lubricants for internal combustion engines (17). 

The base polymer for this t5q>e of sealant exists in the form of an emulsion of micron- and submicron-sized partides of the polymer suspended in water. The base polymer formed by free radical polymerization may be a homopolymer of an acrylic monomer but is more likely to be a copolymer of a number of different monomers chosen to provide the correct balance of properties. The polymer latex has to be made more permanent and therefore a nonionic surfactant such as a nonyl phenol/ polyethylene oxide is added to help stabilize the emulsion. Other additives to the sealant formulation include plastid-zers, fillers, solvents, and silanes. A plasticizer is added to the formulation in order to improve upon or maintain the flexibility of the sealant. Solvents (usually a small amount) are added to improve the tooling of the sealant after it is applied. In addition, a solvent could be a material such as ethylene or propylene glycol which can improve the resistance of the packaged sealant to temperatures below freezing. The most widely used filler for this type of sealant is calcium carbonate. Silanes are often added to acrylics to improve the wet adhesion of the sealant to glass. Other additives include antimildew agents (for tub and tile applications) and clay for rheological control. 

Emulsion polymerizations of vinyl acetate in the presence of ethylene oxide- or propylene oxide-based surfactants and protective coUoids also are characterized by the formation of graft copolymers of vinyl acetate on these materials. This was also observed in mixed systems of hydroxyethyl cellulose and nonylphenol ethoxylates. The oxyethylene chain groups supply the specific site of transfer (111). The concentration of insoluble (grafted) polymer decreases with increase in surfactant ratio, and (max) is observed at an ethoxylation degree of 8 (112). 

Ethylene reacts by addition to many inexpensive reagents such as water, chlorine, hydrogen chloride, and oxygen to produce valuable chemicals. It can be initiated by free radicals or by coordination catalysts to produce polyethylene, the largest-volume thermoplastic polymer. It can also be copolymerized with other olefins producing polymers with improved properties. Eor example, when ethylene is polymerized with propylene, a thermoplastic elastomer is obtained. Eigure 7-1 illustrates the most important chemicals based on ethylene. 

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