Synthetic Fibers and Polymer Tacticity Properties
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Kevlar: High-Strength Synthetic Fiber
Kevlar is a strong, lightweight synthetic fiber made from a polymer called poly-para-phenylene terephthalamide. It is formed by the polycondensation of p-phenylenediamine (C₆H₄(NH₂)₂) and terephthaloyl chloride (C₆H₄(COCl)₂). It has high strength, is lightweight, heat resistant, tough, and durable. It is used in ropes, cables, tires, sports equipment, and bulletproof vests.
Terylene (Dacron): Durable Polyester Fiber
Dacron or Terylene is a strong, wrinkle-free synthetic polyester fiber used in fabrics, ropes, and industrial materials. It is made from ethylene glycol and terephthalic acid through condensation polymerization.
Formula: [–OC–C₆H₄–CO–O–CH₂–CH₂–]ₙ
It is strong and durable, wrinkle resistant, quick drying, and water resistant. It is used in clothes, industrial belts, ropes, and tire cords.
Nylon-6: Versatile Polyamide
Nylon-6 is a synthetic fiber (polyamide) made from a single chemical called caprolactam. It is strong, elastic, and resistant to wear and tear.
Formula: [–NH–(CH₂)₅–CO–]ₙ
It is made by the ring-opening polymerization of caprolactam (C₆H₁₁NO). Its properties and applications include:
- Strong and elastic: Used for making ropes and fishing nets.
- Lightweight and tough: Used in parachutes and seat belts.
- Resistant to wear and abrasion: Used in machine parts and gears.
- Thermoplastic: Melts on heating; used in molded plastic items.
Understanding Polymer Tacticity
Isotactic Polymers
In isotactic polymers, all the side groups are present on the same side of the polymer chain. This regular arrangement makes the polymer highly crystalline and strong, giving it a high melting point. A common example of this type is isotactic polypropylene.
Atactic Polymers
In atactic polymers, the side groups are arranged randomly on either side of the chain. This irregular structure makes the polymer amorphous, soft, and rubbery because the chains cannot pack closely together. A typical example of this type is atactic polypropylene.
Syndiotactic Polymers
In syndiotactic polymers, the side groups are arranged alternately on opposite sides of the chain—one on the right, the next on the left, and so on. This orderly alternating pattern gives the polymer good flexibility, strength, and partial crystallinity. An example is syndiotactic polystyrene.