Chemistry · Ch 15 — Chemistry in Everyday Life
Classification of Polymers
Classification of Polymers
A single polymer can carry four independent labels at once, because the unit's classification chart sorts polymers along four completely separate axes.
By source of availability: natural polymers come straight from plants or animals (cellulose, silk); semisynthetic polymers start as a natural polymer that is then chemically modified (viscose rayon, cellulose diacetate); synthetic polymers are built entirely from man-made chemicals (polythene, PVC).
By structure: linear polymers form one long continuous chain (HDPE, PVC); branched polymers have a main chain with smaller side chains hanging off it (polypropylene, LDPE); cross-linked (network) polymers have their chains directly linked to one another (bakelite, melamine formaldehyde).
By the molecular forces holding chains together: elastomers are held together loosely enough to be soft and stretchy (neoprene, buna-S, buna-N); fibres are held together tightly by hydrogen bonding between chains, giving them high tensile strength (Nylon-6,6, Terylene); thermoplastics soften on heating and re-harden on cooling, so they can be remoulded repeatedly (polythene, PVC, polystyrene); thermosetting polymers do the opposite -- they do not soften again once heated, instead setting permanently into an infusible mass the first time they are heated (bakelite, melamine formaldehyde). …
By source: Natural polymers, obtained from plants/animals -- e.g. cellulose, silk. Semisynthetic polymers, natural polymers modified by chemical treatment -- e.g. viscose rayon, cellulose diacetate. Synthetic polymers, man-made from chemicals -- e.g. polythene, PVC.
By structure: Linear, a long continuous chain -- e.g. HDPE, PVC. Branched, one main chain with smaller chains as branches -- e.g. polypropylene, LDPE. Cross linked/network, chains linked to each other -- e.g. bakelite, melamine formaldehyde.
By molecular forces: Elastomers, soft and stretchy -- e.g. neoprene, buna-S, buna-N. Fibres, chains held together by hydrogen bonding into high-tensile-strength threads -- e.g. Nylon-6,6, Terylene. Thermoplastics, soften on heating and harden on cooling and so can be remoulded -- e.g. polythene, PVC, polystyrene. Thermosetting polymers, do not soften on reheating and instead set irreversibly to an infusible mass on first heating -- e.g. bakelite, melamine formaldehyde. …