Polymers: Types, Properties, and Applications
Polymers: Types, Properties, and Uses
A polymer is a macromolecule composed of long chains in repeated units known as monomers.
Classification of Polymers
According to their source:
- Natural: Found in nature, formed by living things (e.g., proteins and cellulose).
- Artificial: Obtained from natural polymers through chemical modification (e.g., celluloid).
- Synthetic: Result from human design and manufacture (e.g., polyvinyl chloride or PVC).
According to their physical properties:
- Elastomers: Possess high elasticity (e.g., rubber).
- Plastics: Irreversibly deform under force (e.g., most polymers).
- Thermosets: Substances of high hardness and stiffness (e.g., bakelite).
According to their response to heat:
- Thermoplastics: Become liquid and flow at high temperatures, hardening upon cooling.
- Thermosets: Do not fuse with heat; they break down at a certain temperature, losing their chemical structure.
Natural and Artificial Polymers
Natural Polymers: Their chemical composition is diverse. The monomers of proteins are amino acids, cellulose’s monomer is glucose, and rubber’s is isoprene. Cellulose is the most widely used natural polymer.
Major artificial polymers include:
- Nitrocellulose (obtained by treating cellulose with nitric acid)
- Rayon (a very flexible cellulose polymer)
- Vulcanized rubber (obtained by heating a mixture of natural rubber and sulfur)
Synthetic Polymers
Most synthetic polymers are derived from petroleum. They are electrical and heat insulators and can be easily shaped. The most commonly used include:
- Nylon: A synthetic polymer composed of long chains of monomers linked by amide bonds.
- Polystyrene: A group of thermoplastics available in three forms: impact polystyrene, glass, and expanded.
- Polyurethane: Synthesized through the condensation of polyesters.
- Polyesters: Polymers with ester bonds.
- PVC: A thermoplastic polymer available in two varieties: rigid (e.g., for doors) and flexible (e.g., for cables).
- Polyethylene: One of the most common plastics, derived from ethylene, in long linear chains.
- Methacrylate: Notable for its high rigidity and transparency.
New Technology Products
New Electrical Equipment
Advances in physics have led to the development of new electrical equipment groups:
- Semiconductors: Materials whose resistance to electricity flow depends on factors like temperature, mechanical stress, or illumination.
- Superconductors: Materials with zero resistance to electric current (e.g., titanium, copper).
- Piezoelectric Materials: Materials that convert mechanical energy into electricity and vice versa.
Nanotechnology
Nanotechnology encompasses fields of science and technology where materials, substances, and devices are studied and manipulated at the nanometer scale.
Nanotubes: Tubular structures with diameters of a few nanometers, made of carbon. Their physical properties include semiconductor and superconductor electrical performance, high resistance to mechanical tension, and excellent heat conductivity.
Other New Materials
Significant Groups:
- Silicones: Polymers with chains formed from silicon instead of carbon.
- Smart Materials: Materials capable of responding reversibly and controllably to external chemical or physical stimuli. Shape-memory materials are a special case, capable of “remembering” their spatial structure and returning to it after deformation.
- Hybrid Materials: Composed of a base material (matrix) with added fibers. The matrix provides stability and strength, while the fibers provide greater elasticity.