30: Synthetic Polymers
- Page ID
- 429806
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- 30.2: Stereochemistry of Polymerization- Ziegler-Natta Catalysts
- An efficient and stereospecific catalytic polymerization procedure was developed by Karl Ziegler (Germany) and Giulio Natta (Italy) in the 1950's. Ziegler-Natta catalysts are prepared by reacting certain transition metal halides with organometallic reagents. The catalyst formed by reaction of triethylaluminum with titanium tetrachloride is commonly used. Ziegler-Natta catalysts allowed for the first time, the stereochemically controlled synthesis of polymers with virtually no branching.
- 30.3: Copolymers
- Homopolymers are made with a single monomer and are made up of identical repeating units. Copolymers is made when two or more different monomers are polymerized together to create a polymer with variable repeating units. For example the monomers hexafluoropropene and vinylidene fluoride can be polymerized together to create the copolymer vitron which is used to create durable gaskets.
- 30.4: Step-Growth Polymers
- Often, the reactions used to link these monomers include multiple nucleophilic acyl substitutions. Step-growth polymerizations usually use two different monomers, neither of which would undergo polymerization on its own. The two monomers are multifuntional and complementary to each other, such that each provides the other with a reactive partner. In this section, we will be focusing on monomers which are difunctional, meaning they contain two of the same reactive functional group.
- 30.6: Polymer Structure and Physical Properties
- To account for the physical differences between the different types of polymers, the nature of the aggregate macromolecular structure, or morphology, of each substance must be considered. Because polymer molecules are so large, they generally pack together in a non-uniform fashion, with ordered or crystalline-like regions, called crystallites, mixed together with disordered or amorphous domains. In some cases the entire solid may be amorphous, composed entirely of tangled macromolecules.