A polymer is generally defined as a long chain of repeating units derived from monomers. This characteristic distinguishes it from small molecules or alloys and is central to polymer science.

Monomers are small molecules that chemically bond to form long polymer chains. They are the fundamental units in polymer synthesis and understanding them is key to mastering polymer science.

Polymer chains are most commonly held together by covalent bonds, which provide strong linkage between monomer units. Ionic, hydrogen, or metallic bonds are not typically responsible for the main chain structure in polymers.

Polyethylene is a well-known synthetic polymer used widely in plastic products. While cellulose, protein, and DNA are also polymers, they are naturally occurring rather than synthetic.

The process of linking monomers into a long chain is called polymerization. This term distinguishes the formation of polymers from physical processes such as crystallization, sublimation, or oxidation.

Free radical polymerization is initiated by free radicals, making it a fundamental mechanism for synthesizing many polymers. This method differs from ionic and condensation polymerizations in its reaction pathway.

Thermoplastic polymers can be melted and reshaped, facilitating recycling and reprocessing. In contrast, thermoset polymers form irreversible cross-links during curing, which prevents them from being remelted.

Amorphous materials have polymer chains arranged in a random, disordered manner without long-range order. This contrasts with crystalline structures, specific tacticities, or cross-linked networks that exhibit higher levels of organization.

Tacticity refers to the stereochemical arrangement of side groups along the polymer chain and affects how closely chains can pack, influencing melting temperature and crystallinity. It does not dictate catalyst choice, molecular weight, or solubility directly.

Step-growth polymerization is characterized by the gradual formation of polymers through reactions between any two reactive species, whether monomers or oligomers. This differs from chain-growth mechanisms where initiation occurs at a specific reactive center.

Polydispersity describes the variation in molecular weights among the chains in a polymer sample. This distribution affects many of the polymer's physical properties and is essential for understanding its behavior.

Longer polymer chains typically enhance mechanical strength due to increased entanglement, which improves load distribution. While other properties may be influenced by chain length, color and conductivity are dictated by other structural features.

Catalysts work by lowering the activation energy required for a reaction, thereby accelerating polymer synthesis. They do not become part of the final polymer structure and are not exclusively linked to free radical mechanisms.

Cross-linking involves creating chemical bonds between different polymer chains, which typically enhances the strength and thermal stability of the material. It is a distinct process from crystallization, degradation, or blending.

Addition polymerization involves the direct linking of monomers without the formation of byproducts, while condensation polymerization typically releases small molecules like water. This fundamental difference affects both the reaction mechanism and the properties of the resulting polymer.

A higher degree of polymerization indicates longer chain lengths, which typically lead to enhanced viscosity and tensile strength due to greater chain entanglement. These improved mechanical properties are a direct result of the extended network of polymer chains.

Gel permeation chromatography (GPC) is a widely used analytical technique for determining the molecular weight distribution and polydispersity of polymers. Unlike XRD, FTIR, or SEM, GPC separates polymer chains based on their size and provides crucial information about chain length distribution.

Plasticizers are additives that, when introduced to a polymer, reduce the intermolecular forces between chains. This reduction increases the flexibility of the material rather than increasing brittleness, thermal conductivity, or melting point.

Polymers with higher isotactic or syndiotactic regularity have more uniformly arranged side groups, permitting tighter packing and greater crystallinity. In contrast, irregular tacticity hinders efficient packing and typically results in an amorphous structure.

Chemical degradation involves the breakdown of polymer chains into smaller molecules as a result of chemical reactions, often initiated by reagents or environmental factors. This process is essentially the reverse of polymerization and is distinct from cross-linking or crystallization processes.