Undergraduate
  1. General chemistry  1.1. Introduction to Chemistry  1.2. Atomic Structure  1.2.1. Subatomic particles  1.2.2. Atomic Model  1.2.3. Quantum numbers  1.2.4. Electron Configuration  1.2.5. Periodic trends  1.2.6. Isotopes and their applications  1.3. Chemical bond  1.3.1. Ionic bond  1.3.2. Covalent bonds  1.3.3. Metal Bond  1.3.4. Hybridization  1.3.5. Molecular geometry and VSEPR theory  1.3.6. Bond polarity and dipole moment  1.4. Stoichiometry  1.4.1. Mole concept  1.4.2. Empirical and molecular formula  1.4.3. Limiting reactant and excess reactant  1.4.4. Percent Yield and Purity  1.4.5. Dilution calculation  1.5. States of matter  1.5.1. Gas Laws  1.5.2. Matter and Intermolecular Forces  1.5.3. Solid and Crystal Structures  1.5.4. Phase diagram  1.5.5. Plasma and supercritical fluid  1.6. Chemical reactions  1.6.1. Types of Chemical Reactions  1.6.2. Balancing Chemical Equations  1.6.3. Thermochemical reactions  1.6.4. Reaction energy profiles  1.7. Solutions and Mixtures  1.7.1. Concentration units  1.7.2. Syndrome properties  1.7.3. Solubility and Solubility Rules  1.7.4. Henry's Law and Raoult's Law  1.7.5. Partition coefficient  1.8. Chemical equilibrium  1.8.1. Law of mass action  1.8.2. Le Chatelier's principle  1.8.3. Reaction quotient  1.8.4. To use this online calculator for Equilibrium Constant, enter Equilibrium Constant (Eq.) and hit the calculate button. Here is how the Equilibrium Constant calculation can be explained with given input values -> 0.05 = 0.05/0.  1.8.5. Acid-base balance  1.9. Acids and bases  1.9.1. Arrhenius, Brønsted–Lowry, and Lewis definitions  1.9.2. pH and pOH  1.9.3. Acid-base titration  1.9.4. Buffer Solution  1.9.5. Acid-base indicator  1.9.6. Polyprotic Acids and Bases  1.10. Electrochemistry  1.10.1. redox reactions  1.10.2. Galvanic and Electrolytic Cells  1.10.3. Nernst equation  1.10.4. Electrolysis  1.10.5. Faraday's laws of electrolysis  1.11. Thermodynamics  1.11.1. Laws of Thermodynamics  1.11.2. Enthalpy, entropy and Gibbs free energy  1.11.3. Spontaneity of reactions  1.11.4. Thermodynamic cycles (Hess's law, Carnot cycle)  1.12. Kinetics  1.12.1. Rate law and reaction order  1.12.2. Activation Energy and Catalyst  1.12.3. Collision theory  1.12.4. Reaction mechanism  1.12.5. Transition state theory
  2. Organic chemistry  2.1. Structure and relationships  2.1.1. Hybridisation in Carbon Compounds  2.1.2. Resonance and aromatization  2.1.3. Molecular orbitals  2.1.4. Inductive and mesomeric effects  2.2. Hydrocarbons  2.2.1. Hydrocarbons  2.2.2. Alkene  2.2.3. Alkynes  2.2.4. Aromatic compounds  2.2.5. Cycloalkanes and Conformation  2.3. Functional Group  2.3.1. Alcohols and phenols  2.3.2. Ethers and epoxides  2.3.3. Aldehyde and ketone  2.3.4. Carboxylic acids and derivatives  2.3.5. Amin  2.3.6. Esters and amides  2.3.7. Thiols and sulfides  2.4. Stereoscopic  2.4.1. Isomerism in Stereochemistry  2.4.2. Chirality and optical activity  2.4.3. Structural analysis  2.4.4. Diastereomers and Enantiomers  2.5.1. Substitution reactions  2.5.2. Elimination reactions  2.5.3. Addition reactions  2.5.4. Radical reactions  2.5.5. Rearrangement reactions  2.5.6. Pericyclic Reactions  2.6. Spectroscopy and structural analysis  2.6.1. Infrared Spectroscopy  2.6.2. Nuclear magnetic resonance spectroscopy  2.6.3. Mass Spectrometry  2.6.4. UV-visible spectroscopy  2.6.5. X-ray crystallography  2.7. Polymer chemistry  2.7.1. Addition and Condensation Polymers  2.7.2. Polymerization mechanism  2.7.3. Biodegradable Polymer  2.7.4. Conducting and smart polymers
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Ligands and coordination compounds  3.1.2. Crystal field theory  3.1.3. Molecular Orbital Theory in Coordination Compounds  3.1.4. Jahn–Taylor distortion  3.2. Main Group Chemistry  3.2.1. Alkali and alkaline earth metals  3.2.2. Halogens and Noble Gases  3.2.3. Transition metals and their complexes  3.2.4. Lanthanides and Actinides  3.3. Solid state chemistry  3.3.1. Crystal lattices and unit cells  3.3.2. Defects in solids  3.3.3. Electrical and magnetic properties  3.3.4. Superconductivity  3.4. Bio-inorganic chemistry  3.4.1. Metal ions in biology  3.4.2. Enzymatic reactions with metals  3.4.3. Metal poisoning and detoxification  3.4.4. Metalloproteins and Metalloenzymes
  4. Physical chemistry  4.1. Quantum Chemistry  4.1.1. Wave–particle duality  4.1.2. Schrödinger Equation  4.1.3. Quantum Numbers and Orbitals  4.1.4. Atomic and molecular spectroscopy  4.2. Statistical mechanics  4.2.1. Maxwell–Boltzmann distribution  4.2.2. Partitioning functions  4.2.3. Bose–Einstein and Fermi–Dirac statistics  4.3. Chemical thermodynamics  4.3.1. Gibbs Free Energy  4.3.2. Phase transition  4.3.3. Thermodynamic efficiency  4.4. Surface chemistry  4.4.1. Absorption and Catalysis  4.4.2. Colloids and Emulsions
  5. Analytical Chemistry  5.1. Classical methods  5.1.1. Gravimetric Analysis  5.1.2. titrimeter  5.2. Instrumental methods  5.2.1. Chromatography  5.2.2. Spectroscopy  5.2.3. Electroanalytical methods  5.2.4. X-ray diffraction
  6. Industrial Chemistry  6.1. Petrochemistry  6.2. Chemical engineering principles  6.3. Green Chemistry  6.4. Pharmaceuticals and Drug Synthesis
  7. Biochemistry  7.1. Carbohydrates  7.2. Proteins and enzymes  7.3. Lipids and membranes  7.4. Nucleic acids  7.5. Metabolism and Bioenergetics  7.6. Enzyme kinetics and mechanism

Undergraduate → Organic chemistry → Polymer chemistry ↓


Polymerization mechanism


Polymerization is a chemical process that links small molecules called monomers into a covalently bonded chain or network. These larger molecules are called polymers. The conversion of a monomer into a polymer involves a series of chemical reactions, and this process can occur through different mechanisms. Polymerization can be broadly classified into two types: addition polymerization and condensation polymerization.

Addition polymerization

Addition polymerization, also known as chain-growth polymerization, involves the addition of monomers with unsaturated bonds (such as double bonds) without the loss of any small molecule byproducts. This is typical for monomers such as alkenes, which contain carbon-carbon double bonds.

1. Free radical polymerization

Free radical polymerization is one of the most common types of addition polymerization. It involves three primary steps: initiation, propagation, and termination.

Initiation

This step involves the formation of free radicals, which are highly reactive species with unpaired electrons. This can be achieved by using an initiator, a compound that decomposes when heat or light is applied. A common initiator is benzoyl peroxide, which decomposes to form two benzoyl radicals:

(C_6H_5CO)_2 → 2 C_6H_5CO•

Propagation

Once the free radicals are produced, they react with a monomer to form a new free radical. This step is repeated many times, growing the polymer chain:

R• + CH_2=CHX → R-CH_2-CHX•

Here, X can be a substituent like -Cl or -CH_3.

Termination

Termination can occur in several ways, either by combination or by disproportionation. In combination, two active chain ends combine to form a non-active end:

R-CH_2-CHX• + R'-CH_2-CHX• → R-CH_2-CHX-CH_2-R'

In disproportionation, a hydrogen atom is transferred from one radical to another:

R-CH_2-CHX• + R'-CHX-CH_2• → R-CH_2-CHX + R'-CH=CH_2

2. Cationic polymerization

Cationic polymerization is initiated by a cation and typically involves monomers that have electron-rich double bonds. This mechanism is used for the polymerization of isobutylene and other alkenes.

Initiation

The reaction is usually initiated by a strong acid such as HClO_4:

HClO_4 + CH_2=CH-R → HClO_4^− + CH_2^+-CH-R

Propagation

The positively charged monomer can react with another monomer to extend the chain:

CH_2^+-CH-R + CH_2=CH-R → CH_2-CH(R)-CH_2^+-CH-R

Termination

Termination may occur via proton transfer or other reactions that stabilize or inactivate the polymeric species.

3. Anionic polymerization

In anionic polymerization, a negatively charged ion (anion) initiates the polymerization. It is used for polymers such as polyisoprene and acrylates.

Initiation

Anionic polymerization can be initiated using alkali metals such as sodium or lithium. For example:

Na + CH_2=CHCN → Na^+ + CH_2=CHCN^−

Propagation

Similar to the other mechanisms, the reaction continues by adding monomers to the end of the active chain:

CH_2=CHCN^− + CH_2=CHCN → CH_2-CH(CN)-CH_2=CHCN^−

Termination

Anionic polymerization can be terminated in a variety of ways, including reaction with water or solvents.

Condensation polymerization

In condensation polymerization, molecules join together and lose smaller molecules as byproducts such as water or methanol. This type of polymerization is common in the manufacture of polyesters and polyamides.

Step-growth polymerization

Condensation polymerization can also be described as step-growth polymerization because it involves reactions between functional groups of the monomers. It differs from chain polymerization in the sense that any monomer can react with any other molecule, leading to the growth of the polymer.

Polyester construction

Polyester is formed by the reaction between a diacid and a diol.

n HOOC-R-COOH + n HO-R'-OH → [—OR'-OOC-R-COO—]_n + 2n H_2O

The small molecule product in this case is water.

Polyamide construction

Polyamides, such as nylon, are made from diacids and diamines.

n H_2N-R-NH_2 + n HOOC-R'-COOH → [—NH-R-NHCO-R'-CO—]_n + 2n H_2O

Comparison of mechanisms

In brief, the addition polymerization mechanism is characterized by a chain that grows during the polymerization process due to the presence of active sites, whereas condensation polymerization involves the formation of polymers in multiple steps from multifunctional monomers that react to form relatively small oligomers that eventually form long chains upon interlinking.

Examples of polymer structures

Here are some simplified examples of polymer structures:

-CH_2-CH_2- Ethylene -NH-(CH_2)_6-NH-CO-(CH_2)_4-CO- Nylon 6,6

These examples represent common polymer bases, such as polyethylene and nylon, which are derived from their respective polymerization processes.

Conclusion

Polymerization is a fundamental aspect of materials science and chemistry, allowing the creation of versatile and essential polymeric materials found in almost every aspect of daily life. Understanding the mechanisms behind polymerization helps in the development of new materials with desired properties for specific applications.


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Polymerization mechanism

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