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Monomer Purification
In polymer synthesis and organic synthesis, the purity of monomers directly affects the rate of polymerization reaction, molecular weight distribution, degree of polymerization, and properties of the final material.
Even trace amounts of impurities (such as polymerization inhibitors, moisture, peroxides, metal ions, etc.) may cause reaction failure or product performance degradation. Therefore, the purification of monomers is one of the key steps for the success of the experiment.
Ⅱ. Common types of impurities in monomers and their effects on reactions
The presence of these impurities not only affects the stability of experimental results, but may also increase safety risks during process scale-up (especially the risks of thermal runaway and self-aggregation).
Ⅲ. Common methods for monomer purification
Commonly used laboratory methods are shown in the following table:
Each method has its applicable scenarios and limitations, and usually needs to be used in combination to achieve the required purity and safety.
Ⅳ. Examples
Example 1: Purification of styrene
Styrene often contains phenolic polymerization inhibitors, which can be removed by alkaline alumina columns.
Operation steps:
1. Prepare the chromatography column and fill it with basic alumina (200–300 mesh);
2. Moisten the column with a dry inert solvent (such as cyclohexane);
3. Slowly pass styrene through the column and control the flow rate;
4. Collect the effluent and pass it through nitrogen protection to avoid oxidation;
5. It can be further dried with CaH₂ and distilled under reduced pressure to obtain high-purity styrene.
The following figure is a schematic diagram of the chromatography column device:
Example 2: Purification of acrylic acid
Acrylic acid is easy to polymerize and often contains polymerization inhibitors, so it needs to be distilled and purified under reduced pressure.
Operation steps:
1. Add a small amount of hydroquinone as a distillation stabilizer;
2. Start the vacuum distillation system and keep it sealed;
3. Temperature control 60–70°C, pressure 10–15 mmHg;
4. Collect the fractions and seal them with nitrogen for storage.
Example 3: Purification of methyl methacrylate (MMA)
Operation steps:
1. Stir MMA with a small amount of CaH₂ overnight to remove water;
2. After filtering, put it into the vacuum distillation device;
3. Collect fractions at 40–50°C, 15–20 mmHg;
4. Store the distillate with molecular sieves to prevent moisture absorption.
Ⅴ. Conclusion
Monomer purification is a seemingly "pre-treatment" operation, but it is a key operation related to reaction controllability and product quality. Clean monomers are the starting point for precise polymerization. Scientific purification procedures and safety regulations are the solid experimental cornerstone for every chemist.
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