Which is the higher density of polyethylene, linear or branched? Select the choice with the best accompanying explanation
The higher density of polyethylene is typically found in linear polyethylene.
To understand why this is the case, let's first discuss the structure of polyethylene. Polyethylene is a polymer made up of repeating units of ethylene. The molecular structure of linear polyethylene consists of a long, straight chain of carbon atoms, with each carbon atom bonded to two hydrogen atoms. On the other hand, branched polyethylene contains additional side chains or branches connected to the main carbon chain.
The difference in density between linear and branched polyethylene arises from the arrangement of these molecules. In linear polyethylene, the straight chains can pack closely together, resulting in a higher density. This close packing restricts the movement of the polymer chains, leading to greater intermolecular forces such as Van der Waals forces, which hold the polymer together. As a result, linear polyethylene has a higher density compared to branched polyethylene.
In contrast, the presence of branches in branched polyethylene disrupts the regularity and close packing of the polymer chains. The branches prevent efficient packing, reducing the density of the material. Additionally, the branching in polyethylene allows for more freedom of movement, reducing the intermolecular forces and overall density.
Therefore, due to the close packing and limited chain movement, linear polyethylene generally has a higher density than branched polyethylene.