Question

We saw how intramolecular chain transfer in radical polymerization of ethylene creates a four-carbon branch on a polyethylene chain. What branch is created by a comparable intramolecular chain transfer during radical polymerization of styrene?

Short answer

During the intramolecular chain transfer in the radical polymerization of styrene, a one-carbon branch bearing a new radical site on the carbon atom is created. This is different from the four-carbon branch created in the radical polymerization of ethylene.

Step-by-step solution

Understand the radical polymerization process

Radical polymerization involves the formation of a polymer by adding monomer units sequentially, initiated by a radical species. This process relies on the creation of free radicals and their propagation. Free radicals are formed by homolytic cleavage of a covalent bond, leaving each of the involved atoms with an unpaired electron.

Identify the monomer structure

The monomer unit of styrene is \[ C_6H_5CH=CH_2 \]. It consists of a benzene ring (phenyl group) attached to a vinyl group.

Consider the intramolecular chain transfer reaction

Intramolecular chain transfer is a process in which a growing radical polymer chain reacts with itself or another part of its chain, leading to branching. The chain transfer process would involve a hydrogen atom in the phenyl group of styrene monomer unit. This can be represented as: \[ C_6H_5CH\cdotCH_2 + H \to C_6H_5C\cdotHCH_3 \]

Determine the branch created

During the intramolecular chain transfer, the hydrogen atom from the phenyl group of the styrene monomer reacts with the radical site on the vinyl group, creating a one-carbon branch with a new radical site on the carbon atom: \[ C_6H_5\cdot + CH=CH_2 \to C_6H_5CH\cdotCH_3 \] So, the resulting branch created during the intramolecular chain transfer in radical polymerization of styrene is a one-carbon branch bearing a new radical site on the carbon atom.