Understand Why Ethylene Glycol Cannot Undergo Addition Polymerization

Understanding the limitations of certain monomers like ethylene glycol in undergoing addition polymerization is crucial in the field of polymer science. Ethylene glycol, commonly used in antifreeze solutions and other industrial applications, cannot undergo addition polymerization due to several key factors. This article will explore the reasons behind this limitation and provide a detailed explanation of the mechanisms involved.

Key Reasons for Ethylene Glycol's Inability to Undergo Addition Polymerization

One of the primary reasons why ethylene glycol cannot undergo addition polymerization is its structural characteristics. Ethylene glycol, also known as ethane-12-diol, contains two hydroxyl (-OH) groups, but it lacks the necessary carbon-carbon double bonds required for addition polymerization to occur. This absence of unsaturated bonds means that no CC double bonds are available to initiate the polymerization process.

1. Absence of Suitable Double Bonds

Addition polymerization typically requires monomers that possess unsaturated bonds, such as double bonds (CC), which can open up and form long polymer chains. Ethylene glycol, however, has no carbon-carbon double bonds, making it unable to undergo addition polymerization under normal conditions.

2. Reactivity of Hydroxyl Groups

The hydroxyl groups in ethylene glycol are highly reactive and can participate in condensation reactions, leading to the formation of polyesters or polyethers. These reactions are fundamentally different from the addition polymerization process, where small molecules are eliminated as byproducts. Condensation reactions form covalent bonds between monomers, releasing small molecules such as water, which is not the case in addition polymerization.

3. Stability of the Product

Another critical reason why ethylene glycol cannot undergo addition polymerization is the lack of structural features required for stable addition polymers. Addition polymers typically have a backbone of carbon-carbon single bonds, which are essential for their stability and longevity. The product formed from the polymerization of ethylene glycol through condensation mechanisms, known as polyethylene glycol, lacks these necessary carbon-carbon single bonds and therefore does not meet the criteria for addition polymers.

4. Polymer Type

The typical polymerization of ethylene glycol results in the formation of polyethylene glycol (PEG) through condensation mechanisms, not addition mechanisms. This process involves linking the glycol units together while releasing small molecules like water as byproducts. This is fundamentally different from the addition polymerization process, which does not involve the elimination of byproducts.

Initiation and Propagation in Addition Polymerization

For benzoyl peroxide, a common initiator in polymerization processes, to be effective, it must undergo a specific sequence of reactions leading to the formation of a polymer. However, when applied to ethylene glycol, the process does not yield a viable polymeric chain. Instead, it generates a mixture of unstable organic peroxides, which can be hazardous.

Initiation:

C6H5COO::OCOO::C6H5 — C6H5COO° radical initiator

C6H5COO° HO-CH2CH2-OH — O-CH2CH2OH radical intermediate

Propagation:

The propagation of the polymer does not effectively add to the ethylene glycol molecule to create a viable polymeric chain. Instead, it generates a random mixture of various organic aliphatic and aromatic peroxides. These peroxides are not useful as polymers and, due to their explosive nature, pose a significant safety hazard.

Conclusion

In summary, the inability of ethylene glycol to undergo addition polymerization is primarily due to its lack of carbon-carbon double bonds and the reactivity of its hydroxyl groups. The absence of suitable monomer structures and the formation of unstable byproducts through condensation mechanisms highlight why this process is not viable for ethylene glycol. Understanding these limitations is essential for researchers and industrial chemists seeking to develop new polymers and polymerization processes.