Resin

Lore & Background

Resins protect plants from insects and pathogens and are secreted in response to injury. They repel herbivores, insects, and pathogens, while volatile phenolic compounds may attract benefactors such as predators of insects that attack the plant. Most plant resins are composed of terpenes, including α-pinene, β-pinene, limonene, and others; some also contain resin acids. Rosin is a solidified resin from which volatile terpenes have been removed by distillation, consisting of resin acids such as abietic acid and pimaric acid.

Reader's Guide

Resins have been valued by humans for millennia, with documented use in ancient Greece, Rome, and Egypt, particularly for frankincense and myrrh in religious rites. The oldest known use of plant resin comes from the late Middle Stone Age in Southern Africa, where it was used as an adhesive for hafting stone tools. Plant resins are used in varnishes, adhesives, food glazing agents, incense, and perfumes. Hard transparent resins like copals and dammars are used for varnishes, while softer oleo-resins like frankincense and myrrh are used for food and incense. Animal-derived resins such as shellac and lac have been used for sealing wax and lacquerware. Synthetic resins, including epoxy and alkyd resins, are produced via conversion to solids and used in paints, varnishes, and glues. The term 'resin' has been applied to nearly any liquid that sets into a hard lacquer or enamel-like finish, such as nail polish.

Did You Know?

• Resins protect plants from insects and pathogens and are secreted in response to injury.
• Amber is fossil resin from coniferous and other tree species.
• Rosin is obtained from pines and some other plants, mostly conifers.
• The word 'resin' comes from French resine, from Latin resina, which either derives from or is a cognate of the Greek ῥητίνη rhētínē 'resin of the pine'.

Origins of the Concept

The word polymer carries a straightforward Greek lineage: polus meaning many and meros meaning part, a fitting name for a molecule built from countless repeating fragments. Yet the term's history is far from simple. Staudinger then devoted the following decade to gathering the experimental evidence needed to convince his skeptical colleagues. Today, the study of these materials spans polymer chemistry, polymer physics, biophysics, and materials science and engineering, with a growing frontier in supramolecular polymers held together not by covalent bonds but by weaker, non-covalent interactions.

The Natural and Synthetic Spectrum

Polymers are everywhere in the material world, split broadly into those that nature assembles and those that human industry manufactures. On the natural side, materials like hemp, shellac, amber, wool, silk, and rubber have served civilizations for centuries, while cellulose quietly forms the backbone of wood and paper. Even space has yielded a polymeric surprise: hemoglycin, once called hemolithin, stands as the first polymer of amino acids ever identified inside meteorites. In biology, virtually every major macromolecule—proteins, nucleic acids, polysaccharides—is polymeric in nature. On the synthetic side, the global demand list reads like a household inventory: polyethylene, polypropylene, polystyrene, polyvinyl chloride, Bakelite, nylon, silicone, and dozens more. Most plastic backbones are carbon-based, though silicon gives rise to Silly Putty and plumbing sealants, and oxygen appears in the chains of polyethylene glycol, polysaccharides, and DNA.

The Art of Polymerization

At its core, polymerization is the act of stitching thousands of small monomer molecules into a single covalently bonded chain or network. The process is not always a simple concatenation. In making PET polyester, for instance, terephthalic acid and ethylene glycol join together while shedding two molecules of water per repeat unit, so the final polymer is not a literal sum of its parts. Synthetic routes fall into two broad families. Chain polymerization adds monomers to a growing chain one at a time, as in polystyrene production. Step-growth polymerization, by contrast, allows partially built chains to fuse with one another directly, as in polyester synthesis, and can be further split into polycondensation, which releases a small by-product at every step, and polyaddition. Newer techniques like plasma polymerization resist tidy classification. In living cells, entirely different machinery takes over: DNA polymerase catalyzes the copying of genetic material, and a cascade of enzyme-mediated steps transcribes and translates that information into functional proteins.

Structure, Properties, and Scientific Reach

What makes a polymer behave so differently from a small-molecule compound is, in large part, sheer scale. The enormous molecular mass relative to ordinary chemicals gives rise to a distinctive toolkit of physical properties: remarkable toughness, high elasticity, viscoelasticity, and a marked preference for forming amorphous or semicrystalline arrangements rather than well-ordered crystals. Describing a polymeric material's structure requires a hierarchy of length scales, stretching from the sub-nanometer level of individual bonds up to the macroscopic dimensions of a finished product, with each level providing the foundation for the next. This multi-scale complexity is why polymers sit at the intersection of several scientific disciplines. Polymer science encompasses both chemistry and physics, while biophysics and materials science and engineering each contribute their own analytical lenses. An emerging branch, supramolecular polymer chemistry, shifts the focus from covalent linkages to the weaker non-covalent interactions that can also assemble repeating units into functional macromolecular architectures.