Polymer chemistry Polymer chemistry

Chapter 1 Introduction to Polymer Science 1.1 Concept and History 1.2 Classification and Nomenclatur 1.3 Clssification of Polymerization reaction 1.4Molecular-Weight Distribution 1.5Microcosmic Structure of polymer 1.6 Microcosmic shape 1.7 Polymer Morphology and Thermal Transition

1.1 Concept and History Brief Introduction Polymers are made up of many many molecules all strung together to form really long chains (and sometimes more complicated structures, too).

Property Remember that polymers are very very long chains. These long chains: can bend and twist and get all tangled up, can stick to each other, move much slower because they're so big. Let's see how each of these affects how polymers act.

Polymer Chains Tangle Up (Chain Entanglement) The longer a polymer chain is, the more tangled up it can get. Since the chains are harder to pull out or separate, that can make things made out of polymers stronger. Some polymers are more straight and stiff than others. These won't tangle up as much, but they're strong for a different reason - stiff chains can pack together and stick to each other.

Polymer Chains Stick to Other Polymer Chains (Summationof Intermolecular Forces): Think of molecules as being like magnets. Some are like very weak magnets, and some are like strong magnets. So, some can be pulled apart easily, but others take a lot more energy to pull them apart. Polymer chains are like this too, but remember that they're much much longer than molecules. When the chains stick together very strongly, it can be really tough to pull them apart. If the chains happen to be straight and stiff and all lined up next to each other, it can be REALLY hard to pull them apart. A great example is cellulose in wood. The chains lay next to each other, straight and sticky (like strong magnets). That makes trees (and lots of houses!) strong and tall.

Polymer Chains Move Slower than Molecules (Time Scale of Motion) We can see what happening when polymers dissolve in a liquid. Those long chains move around so slowly that they make the solution flow much slower. The longer the chains, the slower the flow. If we measure how long it takes for a polymer solution to flow through a special tube, we can learn more about how big the polymer chains are.

Polymers in life

Poly(styrene-butadiene-styrene), or SBS, is a hard elastomer that's used for things like the soles of shoes, tire treads, and other places where durability is important. It's a copolymer called a block copolymer made of three segments. The first is a long chain of polystyrene, the middle is a long chain of poly butadiene, and the last segment is another long chain of polystyrene.

Certain polymers, such as proteins, cellulose, and silk, are found in nature, while many others, including polystyrene, polyethylene, and nylon, are produced only by synthetic routes. In some cases, naturally occurring polymers can also be produced synthetically. An important example is natural rubber, known as polyisoprenein its synthetic form.

Polymers that are capable of high extension under ambient conditions find important applications as elastomers. In addition to natural rubber, there are several important synthetic elastomers including nitrileand butyl rubber.

Other polymers may have characteristics that permit their formation into long fibers suitable for textile applications. Other polymers may have characteristics that permit their formation into long fibers suitable for textile applications. The synthetic fibers, principally nylon and polyester, are good substitutes for naturally occurring fibers such as cotton, wool, and silk. The synthetic fibers, principally nylon and polyester, are good substitutes for naturally occurring fibers such as cotton, wool, and silk.

1.1.2Concept polymer （ Macromolecules, High Polymer ） The word polymer is derived from the classical Greek words poly meaning "many" and meres meaning "parts." Polymers are substances consisting of many structural units connected by covalent bonds. Simply stated, a polymer is a long- chain molecule that is composed of a large number of repeating units of identical structure.

Monomer; Structure unit degree of polymerization Poly- means "many" and -mer means "part" or "segment". Mono means "one". So, monomers are those itty bitty molecules that can join together to make a long polymer chain. Monomer : material employed in the preparation of the polymer. Many many many MONOmers make a POLYmer!

Structure units are connected to one another in the polymer molecule, or polymeric structure, by covalent bonds. repeat unit: The atoms that make up the backbone of a polymer chain come in a regular order, and this order repeats itself all along the length of the polymer chain. For example, look at polypropylene : Its backbone chain is made up of just two carbon atoms repeated over and over again. One carbon atom has two hydrogen atoms attached to it, and the other carbon atom has one hydrogen atom and one pendantmethyl group (CH 3 ).

This is called the repeat structure or the repeat unit. To make things simple, we usually only draw one unit of the repeat structure, like this: The repeat unit is put inside brackets, and the subscript n just stands for the number of repeat units in the polymer chain.

Another example: styrene monomers join together to make polystyrene:

Degree of polymerization: refers to the number average obtained by dividing the total number of structural units by the total number of molecules. Polymer molecular weight: M 0 ： molecular weight of repeating unit DP ： Degree of polymerization, M  DP × M 0

History

H ． Standinger