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Polyethylene was first synthesized by the German chemist Hans von Pechmann, who prepared it by accident in 1898 while investigating diazomethane. [12] [a] [13] [b] When his colleagues Eugen Bamberger and Friedrich Tschirner characterized the white, waxy substance that he had created, they recognized that it contained long −CH 2 − chains and termed it polymethylene.
For example, in polysiloxanes (silicone), the backbone chain is very flexible, which results in a very low glass transition temperature of −123 °C (−189 °F; 150 K). [2] The polymers with rigid backbones are prone to crystallization (e.g. polythiophenes ) in thin films and in solution .
For example, in polyethylene terephthalate (PET or "polyester"), the repeat unit is -CO-C 6 H 4-CO-O-CH 2-CH 2-O-. The polymer is formed by the condensation reaction of the two monomers terephthalic acid (HOOC-C 6 H 4-COOH) and ethylene glycol (HO-CH 2-CH 2-OH), or their chemical derivatives. The condensation involves loss of water, as an H is ...
LLDPE has penetrated almost all traditional markets for polyethylene; it is used for plastic bags and sheets (where it allows using lower thickness than comparable LDPE), plastic wrap, stretch wrap, pouches, toys, covers, lids, pipes, buckets and containers, covering of cables, geomembranes, [1] and mainly flexible tubing. In 2013, the world ...
In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron.The bond angles are arccos(− 1 / 3 ) = 109.4712206...° ≈ 109.5° when all four substituents are the same, as in methane (CH 4) [1] [2] as well as its heavier analogues.
HDPE is known for its high strength-to-density ratio. [4] The density of HDPE ranges from 930 to 970 kg/m 3. [5] Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength (38 MPa versus 21 MPa) than LDPE. [6]
An example of chain transfer in styrene polymerization. Here X = Cl and Y = CCl 3. In some chain-growth polymerizations there is also a chain transfer step, in which the growing polymer chain RM n ° takes an atom X from an inactive molecule XY, terminating the growth of the polymer chain: RM n ° + XY → RM n X + Y°.
Graft copolymers are a branched copolymer where the components of the side chain are structurally different than that of the main chain. Graft copolymers containing a larger quantity of side chains are capable of wormlike conformation, compact molecular dimension, and notable chain end effects due to their confined and tight fit structures. [1]