Aramids, Poly-Polycarbonate, Chemistry tutorial

Aramids, Poly (methyl methacrylate) and Polycarbonate

Introduction

The different nature of polymers permit for diverse applicable usage of the materials manufactured from them.

Definitions of Aramids, Poly (methyl methacrylate) and Polycarbonate

Aramids are a family of nylons, including Nomex and Kevlar. Poly (methyl methacrylate) that lazy scientists call PMMA is a clear plastic, utilized as a shatterproof replacement for glass. Polycarbonate, or particularly polycarbonate of bisphenol A, is an obvious plastic utilized to build shatterproof windows, lightweight eyeglass lenses

Aramids

Aramids are relations of nylons, including Nomex and Kevlar. Aramids are utilized in the form of fibers. They form into even better fibers than non-aromatic polyamides, like nylon 6, 6. Kevlar is employed to build things as bullet proof vests and puncture resistant bicycle tyres. It is as well probable to create bullet proof bicycle tyres from Kevlar if one felt the require. Blends of Nomex and Kevlar are employed to make fireproof clothing. Nomex is what the monster truck remains and tractor drivers from burning to death should their fire- breathing rigs breathe a little too much fire. Polymers play another part in the monster truck illustrates in the form of elastomers from that those giant tires are made. Nomex-Kevlar blends as well protect fire fighters.

Kevlar is a polyamide, in which all the amide groups are separated by para-phenylene groups, that is, the amide groups attach to the phenyl rings opposite to each other, at carbons 1 and 4.

397_meta-linkage.jpg

Fig: meta-linkage

Nomex, on the other hand, has meta-phenylene groups, that is, the amide groups are connected to the phenyl ring at the 1 and 3 positions.

Kevlar is an extremely crystalline polymer. It took an extended time to figure out how to create anything helpful out of Kevlar since it would not liquefy in anything. So routing it as a solution was out. It would not melt below 500oC, so melting it down was out, as well. Then a scientist named Stephanie Kwolek came up through a brilliant plan.

Aramids are used in the form of fibers. They form into even better fibers than non-aromatic polyamides, like nylon 6, 6. They have the ability to adopt 2 different shapes, or conformations. The two shapes below are the same compound, in 2 different conformations. The one on the left is termed the trans conformation, and the one on the right is the cis- conformation.

1544_a cis-amide.jpg

Fig: a cis-amide

In Latin, trans means 'on the other side'. So when the hydrocarbon groups of the amide are on opposite sides of the amide bond, the bond between the carbonyl oxygen and the amide nitrogen, it's termed a trans-amide. Similarly, cis in Latin means 'on the same side', and when both hydrocarbon groups are on the similar side of the amide bond, we describe it a cis-amide.

2474_amide nitrogen.jpg

Fig: amide nitrogen

The similar amide molecule can twist back and 4th between the cis- and trans- conformations, given a little bit of energy.

The similar cis- and trans-conformations exist in polyamides, too. When all the amide groups in a polyamide, as nylon 6, 6 for instance, are in the trans conformation, the polymer is fully stretched out in a straight line. This is precisely what we want for fibers, since long, straight, fully extended chains pack more perfectly into the crystalline form that makes up the fiber. But sadly, there are always at least several amide linkages in the cis-conformation. So nylon 6, 6 chains never become fully extended.

21_nylon 6,6.jpg

Fig: nylon 6, 6

But Kevlar is dissimilar. When it tries to twist into the cis-conformation, the  hydrogens  on  the  big  aromatic  groups  get  in  the  way.  The cis conformation puts the hydrogens just a little closer to each other than they want to be. So Kevlar stays nearly fully in the trans- conformation. So Kevlar can fully enlarge to form beautiful fibers.

636_cis-conformation.jpg

Fig: cis-conformation

When Kevlar tries to form the cis-conformation, there's not sufficient room for the phenyl hydrogens.  So only the trans-conformation is frequently found.

2334_trans conformation.jpg

Fig: Trans conformation

Poly (methyl methacrylate), PMMA

Poly (methyl methacrylate), or PMMA, is a clear plastic, used as a shatterproof replacement for glass. The barrier at the ice rink which keeps hockey pucks from flying in the faces of fans is made of PMMA. The chemical company Rohm and Haas makes windows out of it and calls it Plexiglas. Ineos Acrylics also makes it and calls it Lucite. Lucite is used to make the surfaces of hot tubs, sinks, and the ever popular one piece bathtub and shower units, among other things.

When it comes to making windows, PMMA has another advantage over glass. PMMA is more transparent than glass. When glass windows are made too thick, they become difficult to see through.  But PMMA windows can be made much thicker and they are still perfectly transparent. This makes PMMA a wonderful material for making large aquariums, whose windows must be thick in order to contain the high pressure due to millions of gallons of water. In fact, the largest single window in the world, an observation window at California's Monterrey

Bay Aquarium, is made of one big  piece of PMMA which is 54 feet long, 18 feet high, and 13 inches thick (16.6 m long, 5.5 m high, and 33 cm thick).

PMMA is as well establishing in paint. Acrylic 'latex' paints frequently enclose PMMA suspended in water. PMMA doesn't dissolve in water, so dispersing PMMA in water requires another polymer to build water and PMMA compatible through each other. But PMMA is more than just plastic and paint. Often lubricating oils and hydraulic fluids tend to obtain really viscous and even gummy when they obtain really cold. This is a genuine pain when we are trying to control heavy equipment in really cold weather. But when a little bit PMMA is dissolved in these oils and fluids, they don't obtain viscous in the cold, and machines can be activated down to -100oC (-150oF), that is, presuming the rest of the machine can obtain that type of cold!

PMMA is a vinyl polymer, made via free radical vinyl polymerization from the monomer methyl methacrylate.

2454_methyl methacrylate.jpg

Fig: methyl methacrylate  

Polycarbonate

Polycarbonate, or particularly polycarbonate of bisphenol A, is an obvious plastic utilized to create shatterproof windows, lightweight eyeglass lenses, and similar products. Universal Electric makes this stuff and sells it as Lexan.

763_carbonate group.jpg

Fig: carbonate group

Polycarbonate gets its name from the carbonate groups in its backbone chain. It is recognized as polycarbonate of bisphenol A since it is made from bisphenol A and phosgene. This begins out through the reaction of bisphenol A by sodium hydroxide to get the sodium salt of bisphenol A.

The sodium salt of bisphenol A is then reacted through phosgene, a right nasty compound that was a favorite chemical weapon in World War I, to manufacture the polycarbonate.

743_sodium salt of bisphenol.jpg

Fig: sodium salt of bisphenol

But there is an additional polycarbonate. This is the polycarbonate that is employed to make ultra-light eyeglass lenses. For people by really bad eyesight, if the lenses were made out of glass, they would be so thick that they would be too heavy to wear. But this new polycarbonate changed all that. Not only is it a lot lighter than glass, but it has a much higher refractive index. That means it bends light more than glass.

1619_allyl group.jpg

Fig: allyl group

It has 2 allyl groups on the ends. Such allyl groups have carbon-carbon double bonds in them. This means they can polymerize via free radical vinyl polymerization. Of course, there are 2 allyl groups on each monomer. The 2 allyl groups will happen to parts of different polymer chains. In this way, all the chains will become tied mutually to form a cross connected substance. The carbonate-containing groups (shown in blue) form the cross links between the polymer chains (shown in red). This cross linking makes the substance very strong, so it would not break nearly as easily as glass will. This is actually significant for kids' glasses!

There is a fundamental difference in the 2 kinds of polycarbonate described here. Polycarbonate of bisphenol A is a thermoplastic. This means it can be molded when it is hot. But the polycarbonate employed in eyeglasses is a thermoset. Thermosets don't melt, and they can't be reshaped. They are utilized to build things that require being really strong and heat resistant.

2164_heat resistant.jpg

Fig: heat resistant

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