Condensation polymers
In condensation polymerisation, monomers with two functional groups join and release a small molecule (H₂O or HCl). Polyesters: diol + dicarboxylic acid (or diacyl chloride), e.g. PET from benzene-1,4-dicarboxylic acid and ethane-1,2-diol, linked by –COO–. Polyamides: diamine + dicarboxylic acid, e.g. nylon-6,6 (hexane-1,6-diamine + hexanedioic acid) and Kevlar, linked by –CONH–; hydrogen bonds between chains give strength. Proteins are natural polyamides. Unlike poly(alkenes), condensation polymers can be hydrolysed at their polar links (acid or alkali), making some biodegradable (e.g. PLA).
≈ 45 minAddition polymers
In addition polymerisation, many alkene monomers open their C=C π bonds and join into a long saturated chain; no other product forms. The repeat unit is drawn by turning C=C into C–C with extension bonds through brackets: ethene → poly(ethene), chloroethene → poly(chloroethene) (PVC), propene → poly(propene). Poly(alkenes) are unreactive (saturated, non-polar C–C and C–H bonds), so they're non-biodegradable. Disposal: landfill (lasts centuries), incineration (energy recovery but CO₂ and, for PVC, HCl and dioxins), recycling, or biodegradable alternatives.
≈ 35 min