Chapter 27 – Summary
27.1 Polymerization
Polymers are giant molecules that consist of long chains of units called monomers connected by covalent bonds. Polymerization is the process of linking monomers together to form a polymer. Plastic is the general term for polymers made from synthetic materials. Several important biological polymers include proteins, starch, cellulose, DNA and RNA.
27.2 Classification of Polymers
Plastics are polymers that are capable of being molded or are pliable. If they harden permanently when heated, polymers are classified as thermosetting; if they can be heated again and reformed repeatedly, they’re classified as thermoplastic (Lower & Ophardt, n.d.) Addition polymerization is when the monomer molecules bond to each other without the loss of any other atoms. Condensation polymerization requires that the monomers possess two or more kinds of functional groups that are able to react with each other in such a way that parts of these groups combine to form a small molecule (often H2O) which is eliminated from the two pieces.
27.3 Polyethylene
Polyethylene is the long chain polymer formed from ethylene (ethene) monomers. Polyethylene can be classified as HDPE, LDPE, and others based on how close the polymer chains pack together affecting its density.
27.4 Addition Polymerization
Addition polymerization is when the monomer molecules bond to each other without the loss of any other atoms. Examples of addition polymers include polyethylene, polypropylene, polystyrene, polyvinylchloride, polytetrafluoroethylene, etc. Many objects in daily use from packing, wrapping, and building materials include half of all polymers synthesized. Other uses include textiles, many electronic appliance casings, CD’s, automobile parts, and many others are made from polymers.
27.5 Rubber and Other Elastomers
The many uses of natural rubber have led to development and manufacture of synthetic rubber. Sulfur vulcanization is a chemical process for converting natural rubber or related polymers into more durable materials by heating them with sulfur or other equivalent curatives or accelerators. Three examples of synthetic rubber used in various applications are polybutadiene, polychloroprene (Neoprene), and styrene-butadiene rubber (SBR).
27.6 Condensation Polymers
Condensation polymerization (also known as step-growth) requires that the monomers possess two or more kinds of functional groups that are able to react with each other in such a way that parts of these groups combine to form a small molecule (often H2O) which is eliminated from the two pieces. The now-empty bonding positions on the two monomers can then join together. Examples of natural condensation polymers include cellulose, starch, and polypeptide chains of proteins. Several synthetic condensation polymers discussed include nylon, Kevlar, polyester, Bakelite, Melamine, polycarbonates, polyurethanes. Synthetic condensation polymers have a wide array of household, industrial, commercial, and medical uses and applications.
27.7 Properties of Polymers
The physical properties of a polymer such as its strength and flexibility depend on chain length, side groups present, branching, and cross-linking. Synthetic polymers may consist of both crystalline (more ordered, crystal-like) and amorphous (less ordered) regions; the degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with crystalline regions are generally tougher (can be bent more without breaking) and more impact-resistant than totally amorphous polymers. Due to their chemical structure, nylon, polyester, and acrylic fibers have physical properties that are comparable or even superior to natural fibers Thus, many of these fibers have a variety of uses and have replaced natural fibers in various products.
27.8 Plastics and Recycling
Plastics are found everywhere due to its low cost, versatility, ease of use etc. Plastic polymers are classified into seven groups for recycling purposes.
27.9 Plastics and the Environment
Plastics pose a threat to the environment due to residual or degradation products that contribute to air and water pollution. Plastics hazards to animals and marine life as these living creatures mistake them for food. Scientists are researching for new opportunities with plastic waste and production.
For an overall summary of Polymer Chemistry, watch Polymer Chemistry: Crash Course Organic Chemistry #35 – YouTube (13 min).
Video source: Crash Course. (2021, September 8).Polymer Chemistry: Crash Course Organic Chemistry #35 – YouTube [Video]. YouTube.
Attribution & References
Except where otherwise noted, this page is adapted by Samantha Sullivan Sauer from:
- 27.1 – “10.1: Polymerization – Making Big Ones Out of Little Ones” In Map: Chemistry for Changing Times (Hill and McCreary) by LibreTexts, CC BY-SA .
- 27.2 – “10.3: Addition Polymerization – One + One + One + … Gives One!” and “10.5: Condensation Polymers” In Map: Chemistry for Changing Times (Hill and McCreary) by LibreTexts CC BY-NC-SA 4.0.
- 27.3 – “10.2: Polyethylene – From the Battle of Britain to Bread Bags” In Map: Chemistry for Changing Times (Hill and McCreary) by LibreTexts, licensed under CC BY-SA .
- 27.4 – “10.3: Addition Polymerization – One + One + One + … Gives One!” In Map: Chemistry for Changing Times (Hill and McCreary) by LibreTexts, licensed under CC BY-NC-SA 4.0.
- 27.5 – “10.4: Rubber and Other Elastomers” In Map: Chemistry for Changing Times (Hill and McCreary) by Marisa Alviar-Agnew (Sacramento City College) & LibreTexts, licensed under CC BY-SA.
- 27.6 – “10.5: Condensation Polymers” In Map: Chemistry for Changing Times (Hill and McCreary) by Marisa Alviar-Agnew (Sacramento City College) & LibreTexts, licensed under CC BY-NC-SA 4.0.
- 27.7 – “10.6: Properties of Polymers” In Map: Chemistry for Changing Times (Hill and McCreary) by Marisa Alviar-Agnew (Sacramento City College) & LibreTexts, licensed under CC BY-NC-SA 4.0.
- 27.8 – “10.7: Plastics and the Environment” In Map: Chemistry for Changing Times (Hill and McCreary) by Marisa Alviar-Agnew (Sacramento City College) & LibreTexts, licensed under CC BY-NC-SA 4.0.
- 27.9 – “10.7: Plastics and the Environment” In Map: Chemistry for Changing Times (Hill and McCreary) by Marisa Alviar-Agnew (Sacramento City College) & LibreTexts, licensed under CC BY-NC-SA 4.0.
References
Lower, S., & Ophardt, C. (n.d.). 10.2: Polyethylene – From the Battle of Britain to Bread Bags In Map: Chemistry for Changing Times (Hill and McCreary). LibreTexts, CC BY-SA .
