Polyacrylonitrile




For polyacrylonitrile at a glance, click here!

Polyacrylonitrile is used for very few products an average consumer would be familiar with, except to make another polymer, carbon fiber. Homopolymers of polyacrylonitrile have been uses as fibers in hot gas filtration systems, outdoor awnings, sails for yachts, and even fiber reinforced concrete. But mostly copolymers containing polyacrylonitrile are used as fibers to make knitted clothing, like socks and sweaters, as well as outdoor products like tents and such. If the label of some piece of clothing says "acrylic", then it's made out of some copolymer of polyacrylonitrile. Usually they're copolymers of acrylonitrile and methyl acrylate, or acrylonitrile and methyl methacrylate:

Also, sometimes we make copolymers of acrylonitrile and vinyl chloride. These copolymers are flame-retardant, and the fibers made from them are called modacrylic fibers.

But the slew of copolymers of acrylonitrile doesn't stop there. Poly(styrene-co-acrylonitrile) (SAN) and poly(acrylonitrile-co-butadiene-co--styrene) (ABS), are used as plastics.

SAN is a simple random copolymer of styrene and acrylonitrile. But ABS is more complicated. It's made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. Polybutadiene has carbon-carbon double bonds in it, which can polymerize, too. So we end up with a polybutadiene chain with SAN chains grafted onto it, like you see below.
ABS is very strong and lightweight. It is strong enough to be used to make automobile body parts, but it is so light that Wassana can lift this front bumper fascia over her head with only hand! Using plastics like ABS makes automobiles lighter, so they use less fuel, and therefore they pollute less.

ABS is a stronger plastic than polystyrene because of the nitrile groups of its acrylonitrile units. The nitrile groups are very polar, so they are attracted to each other. This allows opposite charges on the nitrile groups to stabilize each other like you see in the picture on the left. This strong attraction holds ABS chains together tightly, making the material stronger. Also the rubbery polybutadiene makes ABS tougher than polystyrene.

Polyacrylonitrile is a vinyl polymer, and a derivative of the acrylate family of polymers. It is made from the monomer acrylonitrile by free radical vinyl polymerization.

This is what the monomer acrylonitrile really looks like:

Other polymers that are used as fibers include:

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