Polymer Science Cheat Sheet
The core ideas of Polymer Science distilled into a single, scannable reference — perfect for review or quick lookup.
Quick Reference
Polymerization
The chemical process by which monomers are linked together to form polymer chains. The two main types are addition (chain-growth) polymerization, where monomers add one at a time to a growing chain, and condensation (step-growth) polymerization, where monomers react with the loss of a small molecule such as water.
Molecular Weight Distribution
Unlike small molecules, synthetic polymers consist of chains with a range of lengths. The distribution of molecular weights in a polymer sample is characterized by number-average (Mn) and weight-average (Mw) molecular weights. The ratio Mw/Mn, called the dispersity (formerly polydispersity index), measures the breadth of the distribution.
Glass Transition Temperature (Tg)
The temperature at which an amorphous polymer transitions from a hard, glassy state to a soft, rubbery state. Below Tg, polymer chains lack sufficient thermal energy for large-scale segmental motion; above Tg, they become mobile and the material becomes flexible.
Crystallinity
The degree to which polymer chains are organized into ordered, closely packed regions. Polymers can be fully amorphous (no long-range order), semicrystalline (containing both crystalline and amorphous regions), or, rarely, highly crystalline. Crystallinity affects density, mechanical strength, optical transparency, and barrier properties.
Copolymer
A polymer formed from two or more different types of monomers. Copolymers can be classified by the arrangement of monomers: random (irregular sequence), alternating (ABAB), block (AAABBB), or graft (side chains of one monomer attached to a backbone of another).
Cross-Linking
The formation of covalent bonds between polymer chains, creating a three-dimensional network structure. Cross-linked polymers cannot dissolve (they swell instead) and cannot be melted and reshaped, making them thermosets rather than thermoplastics.
Viscoelasticity
The property of materials that exhibit both viscous (liquid-like) and elastic (solid-like) behavior when deformed. Polymers are inherently viscoelastic because their long chains can both store energy elastically and dissipate energy through chain slippage and friction.
Thermoplastic vs. Thermoset
Thermoplastics are polymers that can be melted and reshaped repeatedly because their chains are held together by weak intermolecular forces. Thermosets, once cured, form permanent cross-linked networks and cannot be remelted -- they decompose before melting.
Degree of Polymerization
The number of monomer repeat units in a single polymer chain. It is directly related to molecular weight: the molecular weight of the polymer equals the degree of polymerization multiplied by the molecular weight of the repeat unit.
Polymer Degradation
The deterioration of polymer properties due to chemical or physical changes in the polymer structure. Degradation can occur through thermal decomposition, photodegradation (UV light), oxidation, hydrolysis, or biodegradation, and it leads to chain scission, cross-linking, or chemical modification.
Key Terms at a Glance
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