Structurally, it's a vinyl polymer, and is similar to polyethylene, only that on every other carbon atom in the backbone chain has a methyl group attached to it. Polypropylene can be made from the monomer propylene by Ziegler-Natta polymerization and by metallocene catalysis polymerization.
This is what the monomer propylene really looks like:
Wanna know more? Research is being conducted on using metallocene catalysis polymerization to synthesize polypropylene. Metallocene catalysis polymerization can do some pretty amazing things for polypropylene. Polypropylene can be made with different tacticities. Most polypropylene we use is isotactic. This means that all the methyl groups are on the same side of the chain, like this: But sometimes we use atactic polypropylene. Atactic means that the methyl groups are placed randomly on both sides of the chain like this: However, by using special metallocene catalysts, it's believed that we can make polymers that contain blocks of isotactic polypropylene and blocks of atactic polypropylene in the same polymer chain, as is shown in the picture: This polymer is rubbery, and makes a good elastomer. This is because the isotactic blocks will form crystals by themselves. But because the isotactic blocks are joined to the atactic blocks, the little hard clumps of crystalline isotactic polypropylene are tied together by soft rubbery tethers of atactic polypropylene, as you can see in the picture on the right. To be honest, atactic polypropylene would be rubbery without help from the isotactic blocks, but it wouldn't be very strong. The hard isotactic blocks hold the rubbery isotactic material together, to give the material more strength. Most kinds of rubber have to be crosslinked to give them strength, but not polypropylene elastomers. Elastomeric polypropylene, as this copolymer is called, is a kind of thermoplastic elastomer. However, until the research is completed, this type of polypropylene will not be commercially available. The polypropylene that you can buy off the shelf at the store today has about 50 - 60% crystallinity, but this is too much for it to behave as an elastomer. Other polymers used as plastics include: Other polymers used as fibers include: Polyethylene Polyethylene Polyesters Polyesters Polystyrene Nylon Polycarbonate Kevlar and Nomex PVC Polyacrylonitrile Nylon Cellulose Poly(methyl methacrylate) Polyurethanes Return to Level Two Directory Return to Macrogalleria Directory Copyright ©2005 Polymer Science Learning Center Department of Polymer Science The University of Southern Mississippi
Research is being conducted on using metallocene catalysis polymerization to synthesize polypropylene. Metallocene catalysis polymerization can do some pretty amazing things for polypropylene. Polypropylene can be made with different tacticities. Most polypropylene we use is isotactic. This means that all the methyl groups are on the same side of the chain, like this:
This polymer is rubbery, and makes a good elastomer. This is because the isotactic blocks will form crystals by themselves. But because the isotactic blocks are joined to the atactic blocks, the little hard clumps of crystalline isotactic polypropylene are tied together by soft rubbery tethers of atactic polypropylene, as you can see in the picture on the right.
To be honest, atactic polypropylene would be rubbery without help from the isotactic blocks, but it wouldn't be very strong. The hard isotactic blocks hold the rubbery isotactic material together, to give the material more strength. Most kinds of rubber have to be crosslinked to give them strength, but not polypropylene elastomers.
Elastomeric polypropylene, as this copolymer is called, is a kind of thermoplastic elastomer. However, until the research is completed, this type of polypropylene will not be commercially available.
The polypropylene that you can buy off the shelf at the store today has about 50 - 60% crystallinity, but this is too much for it to behave as an elastomer.
Copyright ©2005 Polymer Science Learning Center Department of Polymer Science The University of Southern Mississippi