Graduate
  1. Physical Chemistry  1.1. Thermodynamics  1.1.1. Laws of Thermodynamics  1.1.2. Enthalpy and heat capacity  1.1.3. Entropy and free energy  1.1.4. Phase Equilibrium  1.1.5. Statistical thermodynamics  1.1.6. Thermodynamic cycle  1.1.7. Fugacity and activity  1.2. Quantum Chemistry  1.2.1. Principles of quantum mechanics  1.2.2. Schrödinger Equation  1.2.3. Particle in a box  1.2.4. Operators and eigenvalues  1.2.5. Atomic orbitals  1.2.6. Molecular orbital theory  1.2.7. Perturbation theory  1.2.8. Valence bond theory  1.2.9. Hybridization and chemical bonding  1.3. Chemical kinetics  1.3.1. Rate laws and reaction mechanisms  1.3.2. Collision theory  1.3.3. Transition state theory  1.3.4. Enzyme Kinetics  1.3.5. Chain Reactions and Polymerization  1.3.6. Photochemical reactions  1.4. Statistical mechanics  1.4.1. Partitioning functions  1.4.2. Molecular distribution functions  1.4.3. Boltzmann Distribution  1.4.4. Bose–Einstein and Fermi–Dirac statistics  1.5. Spectroscopy  1.5.1. Rotational Spectroscopy  1.5.2. Vibrational Spectroscopy  1.5.3. Electronic Spectroscopy  1.5.4. Nuclear magnetic resonance spectroscopy  1.5.5. Mass Spectrometry  1.5.6. Raman Spectroscopy  1.5.7. Electron paramagnetic resonance spectroscopy  1.6. Surface and colloidal chemistry  1.6.1. Absorption isotherm  1.6.2. Surface tension and wetting  1.6.3. Colloidal Stability  1.6.4. Catalysis  1.6.5. Emulsions and micelles  1.7. Electrochemistry  1.7.1. Nernst equation  1.7.2. Electrochemical cells  1.7.3. Conductivity and mobility  1.7.4. War  1.7.5. Fuel cells  1.7.6. Electrolysis
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic reactions  2.2. Spectroscopy and structural determination  2.2.1. UV-Vis Spectroscopy  2.2.2. IR Spectroscopy  2.2.3. NMR Spectroscopy  2.2.4. Mass Spectrometry  2.2.5. X-ray crystallography  2.3. Stereoscopic  2.3.1. Chirality and optical activity  2.3.2. Structural analysis  2.3.3. Geometrical isomerism  2.3.4. Dynamic Stereochemistry  2.4. Organometallic Chemistry  2.4.1. Organolithium and organomagnesium reagents  2.4.2. Palladium-catalyzed cross-coupling reactions  2.4.3. Transition Metal Complexes  2.4.4. Metal–carbon bond  2.5. Polymer chemistry  2.5.1. Polymerization mechanism  2.5.2. Polymer Characteristics  2.5.3. Biodegradable Polymer  2.5.4. Conducting polymer  2.5.5. Supramolecular polymers  2.6. Medicinal chemistry  2.6.1. Drug design and development  2.6.2. Pharmacokinetics and pharmacodynamics  2.6.3. Structure-activity relationships  2.6.4. Molecular docking and drug screening
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Crystal field theory  3.1.2. Ligand field theory  3.1.3. Spectrochemical Series  3.1.4. Chelation and stability  3.2. Organometallic Chemistry  3.2.1. Metal Carbonyls  3.2.2. Catalysis by organometallic complexes  3.2.3. Metallocenes  3.3. Bio-inorganic chemistry  3.3.1. Metalloproteins and enzymes  3.3.2. The role of metals in biological systems  3.3.3. Metal ion transport and storage  3.4. Solid state chemistry  3.4.1. Crystal Structures  3.4.2. Band theory of solids  3.4.3. Superconductors  3.4.4. Defects in the crystal  3.5. Lanthanides and Actinides  3.5.1. Electronic configuration in lanthanides and actinides  3.5.2. Coordination chemistry of the lanthanides  3.5.3. Magnetic Properties of Lanthanides
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.2. Spectroscopic Techniques  4.2.1. Atomic absorption spectroscopy  4.2.2. X-ray diffraction  4.2.3. Inductively coupled plasma spectroscopy  4.3. Electroanalytical methods  4.3.1. Potentiometry  4.3.2. Voltammetry  4.3.3. Colometry  4.4. Mass Spectrometry  4.4.1. Ionization Technique  4.4.2. Fragmentation Pattern  4.5. Chemometrics  4.5.1. Multidisciplinary analysis  4.5.2. Machine Learning in Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.1.1. Force fields and energy minimization  5.1.2. Monte Carlo simulation in molecular dynamics simulations  5.2. Quantum chemical methods  5.2.1. Hartree–Fock theory  5.2.2. Density functional theory  5.2.3. Semi-empirical methods  5.3. Computational drug design  5.3.1. Molecular Docking  5.3.2. QSAR Modeling  5.3.3. Virtual Screening
  6. Biochemistry  6.1. Enzyme Kinetics  6.1.1. Michaelis-Menten kinetics  6.1.2. Inhibition mechanism  6.2. Metabolism and Bioenergetics  6.2.1. Glycolysis  6.2.2. Citric acid cycle  6.2.3. Electron transport chain  6.3. molecular Biology  6.3.1. DNA replication and repair  6.3.2. Protein synthesis  6.3.3. Gene Regulation  6.4. Structural Biochemistry  6.4.1. Protein Folding  6.4.2. Membrane Biophysics
  7. Environmental Chemistry  7.1. Atmospheric Chemistry  7.1.1. Greenhouse gases  7.1.2. Ozone depletion  7.1.3. Air pollutants and smoke  7.2. Water Chemistry  7.2.1. pH and water hardness  7.2.2. Wastewater treatment  7.2.3. Aquatic Chemistry  7.3. Soil Chemistry  7.3.1. Heavy metal contamination  7.3.2. Soil pH and Buffering  7.3.3. Nutrient cycling  7.4. Toxicology and Chemical Safety  7.4.1. Toxicokinetics  7.4.2. Risk Assessment in Toxicology and Chemical Safety in Environmental Chemistry  7.4.3. Effects of pollutants on the environment

Graduate → Organic chemistry → Polymer chemistry ↓


Polymerization mechanism


Polymerization is a chemical process that links small molecules, known as monomers, into a covalently bonded chain or network. The resulting macromolecule is called a polymer. Understanding polymerization is important in organic chemistry, as polymers play important roles in a variety of industries, from plastics to pharmaceuticals.

Addition polymerization

Addition polymerization, also known as chain growth polymerization, involves the sequential addition of monomer units to a growing chain. This type of polymerization proceeds through different mechanisms such as radical, cationic or anionic polymerization, depending on the nature of the initiator used.

Radical polymerization

Radical polymerization is one of the most common types of addition polymerization. It uses free radicals to initiate a chain reaction. This mechanism involves three main steps: initiation, propagation, and termination.

Initiation

begins with the formation of free radicals from the initiator species. For example, benzoyl peroxide can decompose to form two benzoyl radicals:

(C6H5CO)2O2 → 2C6H5CO•

Once generated, these free radicals react with monomer units to form reactive carbon radicals. For example, if styrene is the monomer:

C6H5CO• + CH2=CHC6H5 → C6H5CO-CH2-CH•C6H5

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In the propagation phase, the radical formed reacts with another monomer, joining the chain and finally forming a new radical:

C6H5CO-CH2-CH•C6H5 + CH2=CHC6H5 → C6H5CO-CH2-CH(CH2-CH•C6H5)C6H5

Closure

Termination occurs when the two parent chain ends join together, effectively ending chain growth. Various combinations can occur, including disproportionation and disproportionation:

Combination: C6H5CO-CH2-CH•C6H5 + C6H5CO-CH2-CH•C6H5 → C6H5CO-CH2-CH(CH2-CHC6H5)-CH2-CHC6H5

Here's a simple visual example:

Cationic polymerisation

Cationic polymerization involves electrophilic initiators to form polymers from monomers. Commonly used monomers include isobutylene and styrene. This type also has three main steps: initiation, propagation, and termination.

Initiation

In cationic polymerization, a strong acid donates a proton to the monomer, forming a carbocation:

H+ + CH2=CHC6H5 → CH3-CH+CH2-C6H5

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The carbocation connects the double bond of the subsequent monomers:

CH3-CH+CH2-C6H5 + CH2=CHC6H5 → CH3-CH(CH2-CH+CH2-C6H5)-CH2-C6H5

Closure

Termination may occur by combination with anions or through internal rearrangement:

CH3-CH+CH2-C6H5 + X- → CH3-CHXCH2-C6H5

Anionic polymerisation

Anionic polymerization is characterized by the use of a nucleophile as an initiator. It is particularly effective with electron-withdrawing monomers such as styrene. This method also follows the steps of initiation, propagation, and termination.

Initiation

In anionic polymerization, a nucleophile such as an organolithium compound initiates the process:

C4H9Li + CH2=CHC6H5 → C4H9-CH2-CH-LiC6H5

Publicity

The anion attaches to the double bond of the next monomer, continuing chain growth:

C4H9-CH2-CH-LiC6H5 + CH2=CHC6H5 → C4H9-CH2-CH(CH2-CH-LiC6H5)-CH2-C6H5

Closure

Anionic polymerization can be controlled to minimize termination events, often resulting in "living" polymers that continue to grow until a termination step, such as protonation, occurs.

C4H9-CH2-CH-LiC6H5 + CH3OH → C4H9-CH2-CH(OH)-CH2-C6H5

Condensation polymerization

Condensation polymerization, also called step-growth polymerization, involves linking monomer units through a reaction that typically releases a small molecule such as water or methanol. These reactions often involve bi-functional or tri-functional monomers.

Polyester construction

A classic example of condensation polymerization is the production of polyester. The reaction of a diol with a diacid usually forms a polyester and water:

HO-R-OH + HOOC-R'-COOH → H[ORO-OC-R'-COO]nH + (n-1)H2O

Polyamide construction

Polyamides such as nylon are another example. They are formed through the reaction between a diamine and a diacid:

H2N-R-NH2 + HOOC-R'-COOH → [NH-R-NHC(O)R'-C(O)]n + (n-1)H2O

This process can be summarized in a visual sequence:

Ring-opening polymerization

Ring-opening polymerization involves the opening of cyclic monomers to form linear polymers. It can be considered a form of chain-growth polymerization, especially when initiated by radicals or ionic species.

Examples of ring-opening polymerization

A typical example involves the polymerization of ethylene oxide to form polyethylene glycol:

CH2CH2O (cyclic) → (-CH2CH2O-)n (linear)

Mechanism

This mechanism is initiated by breaking the rings under specific conditions, allowing the chain to grow as each ring opens up and connects to the end of the chain.

Copolymers

Copolymers are polymers derived from two or more different monomer species. Examples include styrene-butadiene rubber, which benefits from the properties of both compounds.

Types of copolymers

  • Random copolymer: The monomers are arranged in random order.
  • Block copolymer: Large blocks of each type of monomer are linked together.
  • Alternating copolymers: The monomers alternate in sequence.
  • Graft copolymer: A main chain of one type of monomer is grafted onto the main chain of another type.

For example, a block copolymer:

(AAABBB)n

A simple representation of a block copolymer:

Block A Block B

Summary

Polymerization is a key process in organic chemistry, essential for the production of many materials. Understanding the different mechanisms helps design tailored polymers for specific applications. Different polymer types, such as homopolymers and copolymers, allow for the customization of materials properties, which has profound implications across industries.


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Polymerization mechanism

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