Polymers can be assembled depending on either their physical properties or depend on their chemical nature. We will think the names of polymers based on physical groupings and present causes for these.
Physical Groupings of Polymers
Names attributed to polymers depend on their physical properties afford them to be grouped as elastomers, fibers, resins, plastics, plasticizers, thermoplastics, thermosetting, nylons, polyesters, acrylonitriles etc. Several of such will be conversed below.
Elastomers are rubber or rubber-like polymers through high degree of elasticity. The name 'Elastomers' is coined since of their elastic properties. They can be extended much more than thrice their unique length, and on liberate go back to their usual shape.
Molecules of the polymer line-up on stretching and whenever liberated aren't extended nor line up, but go back to their original random conformation that is favored via their entropy overcoming their enthalpy, along through their long polymer chain by few cross bonds, all affords them not to be extremely stiff. As well they don't have much tendency to glide from a molecular layer over the other that is through resistance to plastic flow. Elastomers are without polar groups or sites for hydrogen bonding. Instances comprise rubber.
Fibers are thin, long, threadlike, extended polymers that can be simply pulled (through tensile strength). They can be woven and spun, to impart strength on materials. When drawn the polymeric material is stretched, fiber molecules are lined-up permanently. This tendency is supported via the strong intermolecular attractions and is dependable for enthalpy overcoming entropy, unlike in Elastomers. Natural fibers include wool, cotton and silk. Rayon one of the 1st helpful fibers synthesized in the year 1865 is an instance of fibers that are long silk-like shining strands. They were recovered on via Louis Chardonnet and introduced to Paris in France in the year 1891. The word "rayon" is from ability of the fiber to shine. Another instance of synthetic fiber is vinyon, a copolymer of chloroethylene and ethenyl ethanoate. It has huge strength but of limited utilizes since of its low softening temperature of 650C.
Activity A: Through equations only illustrate the linear arrangement of copolymer shaped between monomers chloroethene and ethenylethanoate.
Resins are transparent or translucent lustrous soft solid polymers that aren't generally molded. They are extremely cross-bonded forming stiff and irregular 3-dimensional structures, therefore termed to as 'space-network polymers'. Molecules are gigantic via heavy covalent bonds that don't soften on heating, but might happen to harder, due to formation of extra cross-links. This is why they are as well termed to as "thermosetting polymers".
Activity B: Here the alternative names for given polymers: resins, fibers, Elastomers, natural rubber.
Plastics are another that is more solid polymers, they are molded polymers. A good example is celluloid one of the first plastic material invented by the British scientist A. Parke, in the year 1856, from mixing nitrocellulose and camphor; it was utilized extensively for producing piano keys and billiard balls. It was as well volatile by the presence of the nitro group, and so was modified removing the nitro group. It provided as a reprieve for elephants in addition to swapped the scarce ivory. It was significant as film for motion pictures.
Polymers by or through no cross-links but are rigid at room temperature are termed thermoplastics. They are via weak connecting forces between chains. When heated because they are stretchier, they simply soften. But on cooling it gets reversed. Therefore they are moulded when soft in liquid shape. They are subject to plastic flow, have much weaker attractive forces and soluble in organic solvents. Teflon is a steady thermoplastic via elevated softening point at 3270C. It is utilized in making non-stick cooking utensils.
They could be completed from low molecular weight compounds and could be semi-fluids. But on heating the chains become extremely cross-linked by high covalent bonds, extremely rigid materials that decrease radically their mobility. This is why thermosettings aren't utilized extensively; they are generally attained crystalline, hard, plain and insoluble. Once they are set, they can't be worked into another shape. They can only be heated to demolish their shape before building the shape one is interested in.
Rubber is obviously attained as latex, a white fluid that oozes out of wounded bark of rubber tree [Hevea brasiliensis]. It is a polymer of the diene: 2-methyl-1,3-butadiene [-(C5H8) n-] that is isoprene units, the building blocks of regular terpenes. Therefore it is as well termed to as polyisoprene or better still as polyterpene. There can be as much as 5000 isoprene units in a molecule of rubber. It is a good instance of homopolymer. Natural rubber subsists as 2 isomers (cis- and trans- forms).
Fig: Natural rubber
Structures of cis- and trans-polymethyl-1, 3-butadiene
The cis- isomer (cis-methyl-1, 3-butadiene/ cis-polyisoprene) has more elastic properties. 1,4-polymerization of the isoprene molecules pays for the double bonds to be in the cis- form. The 1,4-polymerization provide the cis- isomer that is more stable. The trans- isomer is termed gutta-percha (trans- poly methyl-1, 3-butadiene/ trans- polyisoprene). It is non-elastic, extremely helpful as coverings and for under water cables and golf-balls. The raw natural rubber has very few cross-links between the polymeric chains. This is why it is like thermoplastics which softens and joins on heating, but on cooling obtains hardened and brittle. Vulcanization eliminate this problem via heating raw rubber with Sulphur to form S-linkages [see diagram below] between the polymeric chains. This was 1st put forward by C.Goodyear in the year 1838. He heated raw rubber with 8% sulphur [See below]. Today more cold cures in vulcanization survive. This comprises (i) Utilize of 2½% solution of disulphide chloride and carbon disulphide; (ii) Calculation of accelerators in vulcanization creates possible the vulcanization procedure to take place at lower temperatures. At most temperatures properties of vulcanized rubber have higher tensile strength and elasticity, and are more durable.
Fig: Heated raw rubber
The durability of rubber materials can be improved upon by addition of additives like antioxidants that prevent auto oxidation. For example aldehyde-phenylamine condensations and addition also have accelerating action.
Synthetic rubber has been made by some scientists from derivatives of 1,3-dienes other than isoprene. One of the earliest is from polymerization of 2-chloro-1,3-butadiene also called chloroprene, which can be obtained from dimerization of ethyne, followed by its subsequent isomerization in HCl. The polymer neoprene has great resistance for chemicals and auto oxidation, but is more expensive to manufacture. Hence it isn't generally utilized in making materials industrially.
Poly [2-chloro-1,3-butadiene] as well termed neoprene rubber, is more flexible and elastic. Another is buna rubber discovered in Germany around in the year 1930 that takes its name from the major starting substances in its polymerization reaction. 1, 3-butadiene its monomer is polymerized using sodium (natrium) as the catalyst. Cold rubber or SBR (derivative of buna) is another instance of synthetic rubber discovered to replace unavailability of natural rubber during World War II. It is a copolymer of 1,3-butadiene and phenyl ethylene in ratio 7:3. The mechanism is a free-radical copolymerization. They are all-purpose synthetic rubber that can be vulcanized just as for natural rubber and are extremely durable than other synthetic rubbers, utilize for producing tyres scientifically. Rigidity of the rubber can be altered via raising the amount of phenyl ethylene in the copolymer. Other instances comprise nylons, polyesters, plasticizers, stabilizers.
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