PMMA:

Preparation:-

• The full form of PMMA is Poly methyl methacrylate. It is a most important commercial high polymer. It comes from the acrylic class. It is also known as transparent plastic or acrylic glass. Its IUPAC name is Poly(methyl 2-methylpropenoate). Other names are Poly(methyl methacrylate) (PMMA) and methyl methacrylate resin.
• At high temperature the components of the long chain backbone of the polymer can begin to separate and react with one other to change the properties of the polymer this is the mechanism of degradation which has so many causes.

• It is of 4 types that are Heat or thermal degradation which is also of 2 types that are thermal degradation and thermal oxydative degradation causes in the presence of oxygen, light degradation called photodegradation, oxygen i.e oxydative degradation and weathering degradation generally known as UV degradation. Thermal degradation reduces the ductility and belittlement it affects on chalking, colour changes, cracking. For the neurotoxic designer drug PMMA, commonly sold as MDMA.

   

Properties:

1. The molecular formula of PMMA or Poly methyl methacrylate is$(C_5O_2H_8)_n$ .
2. It is an amorphous in nature, linear polymer valued for its hardness, rigidity in nature. it is totally visible means transparency and have properties of weathering resistance.
3. Its molecular mass always varies and it’s density is 1.18 g/cm3.
4. The refractive index value of PMMA is 1.4914 at 587.6 nm. 160 °C is it’s melting point in Fahrenheit scale it is 320 °F.
5. The standard state of PMMA is 25 °C at 100 Kpa.
6. It’s density varies in 1.17–1.20 g/cm3
7. PMMA smells and dissolved in many organic solvents
8. It is poor resistance to many other chemicals.
9. It has maximum water absorption ratio of 0.3 to 0.4 in weight, tensile strength increases with increase in water absorption.

10. It has relatively high coefficient of thermal expansion i.e.,$(5–10)×10^{−5}K^{−1}$

     

Application:

• It exploit good impact resistance and dull shards formed upon fracture that is its glazing application.
• Some of its major applications are it used in the commercial purpose like making basins, birth room fixtures, sinks used in acrylic sheet birth tubes
• It has an wide application in automotive industry i.e., used in rear lamps, light fixtures, road lines.
• It made the medical instrument more advance i.e it has wide use some of that example are used in contact lenses , bone cements, it also uses in membrane dialysis.
• Dentists are uses this in dental restoration.
• It has good degree of compatibility with human tissue and this was discovered by WWII RAF pilots, whose eyes had riddled with PMMA splinters coming from the side windows of their Super-marine spit-fire.

Kevlar:

Preparation:

• There are two main steps in making Kevlar. The first step is producing the basic plastic from which Kevlar is made which is a chemical called poly-para-phenylene terephthalamide. Second, is turning it into strong fibres.
• Just like the production of nylons, Kevlar filaments are produced by extruding the precursor through a spinneret. The rod form of the para-aramid molecules and the extrusion process make Kevlar fibres anisotropic – which means that that they are stronger and stiffer in the axial direction than in the transverse direction.Polyamides like Kevlar are polymers made by repeating amides over and over again.
• Amides are simply chemical compounds in which part of an organic (carbon-based) acid replaces one of the hydrogen atoms in ammonia (NH3). Amides are amine derivatives of carboxylic acids. So the basic way of making a polyamide is to take an ammonia-like chemical and react it with an organic acid.
• In other words, Kevlar is synthesized from the monomers 1,4-phenyl-diamine (para-phenylenediamine) and terephthaloyl chloride. The result is a polymeric aromatic amide (aramid) with alternating benzene rings and amide groups. When they are produced, these polymer strands are aligned randomly. To make Kevlar, they are dissolved and spun, causing the polymer chains to orient in the direction of the fibre.

Properties:

1. Kevlar is five times stronger than steel, yet it is extremely lightweight.
2. Kevlar does not rust or corrode and it absorbs vibrations readily.
3. Kevlar is expensive because special precautions are necessary to handle the concentrated sulfuric acid used in its production.
4. Kevlar breaks down when exposed to the ultraviolet rays in sunlight.Dry-cleaning agents bleach, and repeated washing can affect Kevlar negatively.

5. Kevlar is made in three common grades: Kevlar, Kevlar 29, and Kevlar 49. Kevlar is typically used in tires. Kevlar 29 is used in body armour, industrial cables, asbestos replacements, and brake linings. Kevlar 49 is used in applications such as plastic reinforcement for boat hulls, airplanes, and bicycles.

    

Application:-

1. Kevlar is a liquid that is converted into a fibre (called aramid fibres) and then woven into a textile material. The resulting textile material is extremely strong, lightweight, corrosion and heat resistant. It is often used in combination with other materials, forming composites.
2. Kevlar has a high tensile strength to weight ratio, far exceeding steel and even specialist metal alloys, such as magnesium alloys, used in aerospace engineering.
3. It is used extensively in the manufacture of panels and wings for fighter jets, including the Eurofighter Typhoon.

4. During the manufacture of Formula One racing cars, Kevlar is used for the bodywork and petrol tank.

    

Silicon rubber:

Preparation:

• The preparation of silicones is generally carried out by the hydrolysis of dialkyldichlorosilanes (R2SiCl2) or diaryldichlorosilanes (Ar2SiCl2), which are prepared by passing vapors of RCl or ArCl over silicon at 570 K with copper as a catalyst.

Cu, 570 K

(2RCl + Si ——————> R_2 SiCl_2)

• Silicones may be obtained in the form of oils, rubber on resins depending upon the extent of polymerization which depends upon reaction conditions and nature of alkyl groups.

   

Properties and uses:

• Silicones are water repellent and quite inert chemically. These resist oxidation, thermal decomposition and attack by organic reagents. These are also good electrical insulators and antifoaming agents. These have found the following uses:

1. Silicones have been used for making water-proof papers, wools, textiles, wood etc., after coating these articles with silicones.
2. The viscosities of silicones do not change with changes in temperature; therefore, these are used as all weather lubricants.
3. As antifoaming agent in industrial processes.
4. As a mould releasing agent in rubber industry and foundry. It avoids the sticking of the castings to the mould.
5. For making body implants in cosmetic surgery due to its inert nature.
6. Silicones are now incorporated in paints for resisting dampness and for water proofing.
7. Due to their water repellent nature and high dielectric constant, silicones are used in electrical condensers.