Question

Peroxide initiated polymerizations occur via (a) hydrocarbon combustion (b) natural process synthesis (c) isomeric saponification (d) free radical chain propagation

Short answer

(d) free radical chain propagation

Step-by-step solution

Understanding Peroxide Initiated Polymerization

Peroxide initiated polymerizations occur by first decomposing the peroxide to form free radicals. The free radicals are the key players in initiating the polymerization process. These free radicals then react with monomer molecules to start a chain reaction of polymerization.

Identifying Free Radical Chain Propagation

The process of polymerization initiated by free radicals involves the growth of a polymer chain by successive additions of monomer units. The radical generated in the initial decomposition step adds to a monomer, forming a new, larger radical, which then reacts with another monomer.

Matching the Description with the Options

From the provided choices, the process of peroxide initiated polymerizations closely matches with (d) free radical chain propagation, as it describes the process by which polymer chains grow due to the action of free radicals.

Key concepts

Free Radical Polymerization

When people talk about peroxide initiated polymerizations, they are discussing a process known as free radical polymerization. This fascinating chemical reaction plays a key role in creating polymers like plastics and resins.
To start, a compound called a peroxide decomposes into smaller fragments known as free radicals. These radicals aren't terribly stable, but they are incredibly reactive. Their job is to initiate the polymerization process by attaching to monomer molecules—these are the small building blocks of larger polymers.
Because the radicals are so reactive, they quickly grab onto a monomer molecule, creating a new radical at the end of that monomer. This newly formed radical then continues to react with additional monomers, perpetuating the process until the polymer chain is fully formed. This type of polymerization is crucial in industrial applications due to its simplicity and ability to rapidly produce large quantities of polymer material.

Chain Reaction

Polymerization via free radicals is an example of a chain reaction. These reactions are an exciting dance of molecules, where one step naturally leads to the next. In peroxide initiated polymerizations, the chain reaction is divided into three stages:

• Initiation: As explained before, this step begins with the formation of radicals. These radicals add to monomers, thus forming the first links in the polymer chain.
• Propagation: This stage sees the rapid growth of the polymer chain as each radical keeps adding monomer units. It's the heart of the chain reaction, where the polymer builds to its final length.
• Termination: Eventually, the addition of monomers halts when two radicals meet and join to form a stable non-radical product, thus ending the chain growth.

Each stage is crucial to ensure a successful polymerization process. The beauty of chain reactions is how automatic and self-perpetuating they are, continuing once started without needing additional energy or substances.

Radical Formation

Radical formation is at the heart of understanding peroxide initiated polymerizations. Peroxides are generally unstable molecules predisposed to breaking down easily under heat or light. When they decompose, they split into two identical radical fragments.
These radicals are characterized by an odd number of electrons, often making them highly reactive. They strive to pair up their unpaired electron, and this drive is what kicks off the polymerization chain reaction.
In simpler terms, think of radicals as eager party-goers looking for dance partners. They rapidly react with monomers, attaching themselves and creating a new radical to continue the sequence. Radical formation is fundamental because without radicals, the chain reaction of polymer formation wouldn't even get the chance to start.