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The (bridged-cp2)Zr moiety possesses both C2Zr CATALYST discussed in SESSION 5, it WOULD be expected to produce atactic polypropylene, since the methyl group on the PROPYLENE would have no up/down preference.

The (bridged-cp2)Zr moiety possesses both C2Zr catalyst discussed in Session 5, it would be expected to produce atactic polypropylene, since the methyl group on the propylene would have no up/down preference.

"C2 symmetry" MEANS that 180o rotation about an axis through the molecule results in a geometry equivalent to the STARTING geometry. "Mirror plane symmetry" means that one half of the molecule can be PERFECTLY reflected into the other half through a symmetry plane. Molecules with mirror plane symmetry cannot be CHIRAL.

"C2 symmetry" means that 180o rotation about an axis through the molecule results in a geometry equivalent to the starting geometry. "Mirror plane symmetry" means that one half of the molecule can be perfectly reflected into the other half through a symmetry plane. Molecules with mirror plane symmetry cannot be chiral.

Molecules that are not superimposible on their mirror images are CHIRAL. Mirror IMAGE ISOMERS are called enantiomers. Enantiomers have identical PHYSICAL properties except that they rotate PLANE polarized light in opposite directions.

Molecules that are not superimposible on their mirror images are chiral. Mirror image isomers are called enantiomers. Enantiomers have identical physical properties except that they rotate plane polarized light in opposite directions.

There is no preference for the methyl group on propylene to be oriented up or down, because in each CASE it has EXACTLY the same interaction with a CP group. Since there is no up/down preference, a RANDOM (atactic) orientation of methyls along the chain RESULTS.

There is no preference for the methyl group on propylene to be oriented up or down, because in each case it has exactly the same interaction with a cp group. Since there is no up/down preference, a random (atactic) orientation of methyls along the chain results.

Each INCOMING propylene molecular orients with its methyl group in toward R, rather than out toward cp, in order to avoid unfavorable CONTACTS with the bulky cp's. When the R group migrates to propylene, it migrates to the CLOSER olefinic CARBON, which is always the one bearing the methyl group (the "b carbon").

Each incoming propylene molecular orients with its methyl group in toward R, rather than out toward cp, in order to avoid unfavorable contacts with the bulky cp's. When the R group migrates to propylene, it migrates to the closer olefinic carbon, which is always the one bearing the methyl group (the "b carbon").

Tacticity.

Tacticity.

ORIENTATION of the MONOMER UNITS ALONG the CHAIN.

Orientation of the monomer units along the chain.

The orientation of the monomer UNITS along the chain (head-to-tail, head-to-head, random) and the orientation of the methyl GROUPS with respect to the POLYMER BACKBONE (tacticity).

The orientation of the monomer units along the chain (head-to-tail, head-to-head, random) and the orientation of the methyl groups with respect to the polymer backbone (tacticity).

After the polymerization has been ALLOWED to PROCEED with monomer A, the OLEFIN FEEDSTOCK is CHANGED to B and the polymerization continues.

After the polymerization has been allowed to proceed with monomer A, the olefin feedstock is changed to B and the polymerization continues.

1. By using different monomers. For example, the incorporation of a PHENYL (C6H5) unit into the monomer LEADS to polystyrene, while the incorporation of a CHLORO (Cl) group leads to PVC, a polymer with very different properties.
2. By using different fabrication TECHNIQUES. For example, polystyrene can be glassy or foamy depending on how it is FABRICATED.

It allows the chemist to stop chain growth at a desired stage, RATHER than relying on the "NATURAL" process of b-hydride elimination. Hence, it GIVES the chemist some control over the VALUE of n.

It allows the chemist to stop chain growth at a desired stage, rather than relying on the "natural" process of b-hydride elimination. Hence, it gives the chemist some control over the value of n.

The OLEFIN USES the ELECTRONS in its p-bond to INTERACT with the METAL.

The olefin uses the electrons in its p-bond to interact with the metal.

The LIGANDS – the TWO cp's, the alkyl group, and the OLEFIN (or OPEN site) – are ORIENTED in a tetrahedral fashion around Zr.

The ligands – the two cp's, the alkyl group, and the olefin (or open site) – are oriented in a tetrahedral fashion around Zr.

Heterogeneous catalysts are insoluble in the reaction medium, while homogeneous catalysts are soluble. Since homogeneous catalysts are generally molecular SPECIES, they are more amenable to STUDY using the spectroscopic tools of chemistry. In addition, they can be chemically modified or "tailored" to PRODUCE polymers with a particular kind of structure.

Heterogeneous catalysts are insoluble in the reaction medium, while homogeneous catalysts are soluble. Since homogeneous catalysts are generally molecular species, they are more amenable to study using the spectroscopic tools of chemistry. In addition, they can be chemically modified or "tailored" to produce polymers with a particular kind of structure.

They provide a site where ORGANIC molecules can COME TOGETHER and react.

They provide a site where organic molecules can come together and react.

A catalyst reduces the energy of activation for a REACTION by providing an alternative pathway. In this way, it SPEEDS up the reaction and ALLOWS it to proceed under milder conditions.

A catalyst reduces the energy of activation for a reaction by providing an alternative pathway. In this way, it speeds up the reaction and allows it to proceed under milder conditions.

No, in the absence of a catalyst, ethylene molecules WOULD need to collide at very HIGH energy in ORDER to react with each other.

No, in the absence of a catalyst, ethylene molecules would need to collide at very high energy in order to react with each other.

The average value of n (the NUMBER of monomer units in the POLYMER) and the range in INDIVIDUAL VALUES of n.

The average value of n (the number of monomer units in the polymer) and the range in individual values of n.

Through the CHOICE of APPROPRIATE CATALYSTS and REACTION CONDITIONS.

Through the choice of appropriate catalysts and reaction conditions.

The structure (e.g., EXTENT of branching) determines how the individual polymer MOLECULES can orient (or "pack") in the SOLID state. This, in turn, influences PHYSICAL properties such as density, crystallinity, MELTING point, and strength.

The structure (e.g., extent of branching) determines how the individual polymer molecules can orient (or "pack") in the solid state. This, in turn, influences physical properties such as density, crystallinity, melting point, and strength.

• LDPE – more transparent, flexible, WAXY.
• HDPE – more opaque, RIGID, non-waxy.

The olefin MONOMERS are FLAT (two-dimensional) MOLECULES with sp2-HYBRIDIZED carbon atoms. The POLYMERS are three-dimensional molecules in which the carbon atoms are sp3 hybridized.

The olefin monomers are flat (two-dimensional) molecules with sp2-hybridized carbon atoms. The polymers are three-dimensional molecules in which the carbon atoms are sp3 hybridized.

The electrons in the WEAK p-BONDS can be USED to FORM STRONG s bonds to other monomer units.

The electrons in the weak p-bonds can be used to form strong s bonds to other monomer units.

They have DIFFERENT chemical compositions (different MONOMER units), different structures, different WAYS of being FABRICATED, etc.

They have different chemical compositions (different monomer units), different structures, different ways of being fabricated, etc.

Sandwich BAGS, carpets, nylon stockings, stackable CHAINS, MILK cartons, ETC.

Sandwich bags, carpets, nylon stockings, stackable chains, milk cartons, etc.