Your browser does not fully support modern features. Please upgrade for a smoother experience.
Subject:
All Disciplines Arts & Humanities Biology & Life Sciences Business & Economics Chemistry & Materials Science Computer Science & Mathematics Engineering Environmental & Earth Sciences Medicine & Pharmacology Physical Sciences Public Health & Healthcare Social Sciences
Sort by:
Most Viewed Latest Alphabetical (A-Z) Alphabetical (Z-A)
Filter:
All Topic Review Biography Peer Reviewed Entry Video Entry
Topic Review
Nitrile Rubber
Nitrile rubber is a copolymer of butadiene and acrylonitrile in which the unsaturated diene segments form the elastomeric network and the nitrile groups supply polarity [1]. The acrylonitrile fraction, usually between 18 and 50 percent, sets the balance: higher content raises oil resistance and the glass transition temperature, while lower content preserves flexibility in the cold [1]. Vulcanisation proceeds through the residual double bonds, and the resulting crosslink density fixes compression set and swelling [2]. Hydrogenated grades convert backbone double bonds into methylene sequences, which removes the sites at which oxidation and ozonolysis begin [3]. The nitrile dipole also makes the polymer compatible with polar plasticisers and incompatible with non-polar oils [1].
  • 3
  • 06 Nov 2026
Topic Review
Polyethylene Terephthalate (PET)
Polyethylene terephthalate is a semicrystalline thermoplastic polyester built of terephthalate units alternating with ethylene glycol residues [1]. Each repeat unit carries a rigid aromatic ring and a flexible glycol segment, so the chain is stiff enough to crystallise yet mobile above the glass transition near 78 degrees Celsius [2]. Crystallinity develops between roughly 130 and 240 degrees Celsius and governs density, barrier behaviour and clarity, which is why amorphous and crystallised grades differ in the same properties [1]. Melting near 255 degrees Celsius bounds the processing window, and the ester linkage is the point at which hydrolysis and transesterification act [3]. Copolymers that replace the glycol or the diacid segment shift both transitions and are distinguished from the homopolymer [2].
  • 3
  • 06 Nov 2026
Topic Review
Cationic Polymer
Cationic polymers are macromolecules bearing positively charged groups, usually quaternary ammonium or protonated amine functions, either along the backbone or on side chains [1]. The charge density, set by the fraction of ionisable monomers and by the degree of protonation at a given pH, governs how the chain binds to anionic surfaces of nucleic acids or cell membranes [2]. Because the charge is distributed over many repeat units, the polymer binds multivalently and condenses counter-charged macromolecules into complexes, an effect not available to a monovalent cation [3]. They differ from anionic and neutral polymers in that electrostatic attraction, rather than hydrogen bonding or hydrophobic association, dominates their interaction with dissolved polyelectrolytes [1].
  • 3
  • 09 Nov 2026
Topic Review
Oligomers
Oligomers are molecules composed of a small number of repeat units, conventionally fewer than about ten, joined by the same bonds that form a polymer, so they occupy the range between monomers and macromolecules [1]. Because the chain is short, properties that depend on entanglement or on long-range cooperative motion are absent, and the melting or softening behaviour is dominated by end groups and by the specific sequence of units [2]. Individual oligomers are discrete compounds with a defined molar mass, whereas a polymer is a distribution of chain lengths, and this distinction separates the two classes [3]. Oligomers retain the reactivity of their functional end groups, which allows them to be extended into higher polymers by further coupling [1].
  • 3
  • 09 Nov 2026
Topic Review
Magnetic Nanocomposite
Magnetic nanocomposites are multiphase solids in which magnetic nanoparticles, typically iron oxides, ferrites or metals, are dispersed in a continuous non-magnetic matrix of a polymer, silica or carbon [1]. Magnetic behaviour originates from the particle phase, while mechanical integrity and processability come from the matrix, and the two are coupled through the interfacial region [2]. The composite is superparamagnetic when the embedded particles remain single-domain and below the blocking volume, and ferrimagnetic or ferromagnetic when they are larger or exchange-coupled [3]. This distinguishes them from magnetic alloys, in which the magnetic phase and the structural phase are the same solid [1].
  • 2
  • 09 Nov 2026
Topic Review
Linear Low-Density Polyethylene
Linear low-density polyethylene is a semicrystalline ethylene copolymer in which short alkyl branches are introduced by copolymerising ethylene with an alpha-olefin, keeping the chain backbone essentially linear [1]. Branch content and branch length set the crystallinity, since the branches are excluded from the lamellae and act as defects that thin the crystals and lower the melting range [2]. The result is a density between that of low-density polyethylene, which carries long-chain branching, and high-density polyethylene, which is nearly unbranched, with a stiffness that falls as branch density rises [3]. Its melt rheology reflects the absence of long-chain branching, so the flow activation energy is lower than in a branched homopolymer of the same molar mass [2].
  • 2
  • 09 Nov 2026
Topic Review
Emulsion Templating
Emulsion templating is a fabrication route in which the dispersed droplets of an emulsion define the voids of a porous solid after the continuous phase is consolidated and the droplets are removed [1]. In the most common variant the continuous phase is a monomer mixture that is polymerised around a high-internal-phase emulsion, giving a porous polymer whose void fraction mirrors the droplet volume fraction [2]. Pore diameter follows droplet size, and interconnecting windows arise where adjacent droplets touch and the film between them ruptures during polymerisation or drying [3]. It is distinguished from porogen leaching by the fluid, deformable character of the template, which allows void fractions above three-quarters without collapse of the framework [1].
  • 2
  • 09 Nov 2026
  • Page
  • of
  • 29
Featured Entry Collections
>>

Featured Reprints

>>
Encyclopedia of Digital Society, Industry 5.0 and Smart City
Encyclopedia of Engineering
Encyclopedia of Social Sciences
Encyclopedia of Medieval Royal Iconography
Write an Entry
Feedback