1、Introduction to Organic Chemistry 2 ed William H. Brown,Organic Polymer Chemistry,Chapter 15,Organic Polymer Chem.,Polymer: from the Greek, poly + meros, many parts. Any long-chain molecule synthesized by linking together single parts called monomersMonomer: from the Greek, mono + meros, single part
2、. The simplest nonredundant unit from which a polymer is synthesizedPlastic: a polymer that can be molded when hot and retains its shape when cooled,Organic Polymer Chem,Thermoplastic: a polymer that can be melted and molded into a shape that is retained when it is cooledThermoset plastic: a polymer
3、 that can be molded when it is first prepared, but once it is cooled, hardens irreversibly and cannot be remelted,Notation & Nomenclature,Show the structure by placing parens around the repeat unit n = average degree of polymerization,Notation & Nomenclature,To name a polymer, prefix poly to the nam
4、e of the monomer from which the polymer is derived if the name of the monomer is one word, no parens are necessary for more complex monomers or where the name of the monomer is two words, enclose the name of the monomer is parens, as for examplepoly(vinyl chloride)poly(ethylene terephthalate),Morpho
5、logy,Polymers tend to crystallize as they precipitate or are cooled from a melt Acting to inhibit crystallization are their very large molecules, often with complicated and irregular shapes, which prevent efficient packing into ordered structures As a result, polymers in the solid state tend to be c
6、omposed of ordered crystalline domains and disordered amorphous domains,Morphology,High degrees of crystallinity are found in polymers with regular, compact structures and strong intermolecular forces such as hydrogen bonds as the degree of crystallinity increases, the polymer becomes more opaque du
7、e to scattering of light by the crystalline regions Melt transition temperature, Tm: the temperature at which crystalline regions melt as the degree of crystallinity increases, Tm increases,Morphology,Highly amorphous polymers are sometimes referred to as glassy polymers because they lack crystallin
8、e domains that scatter light, amorphous polymers are transparent in addition, they are weaker polymers, both in terms of their high flexibility and low mechanical strength on heating, amorphous polymers are transformed from a hard glass to a soft, flexible, rubbery state Glass transition temperature
9、, Tg: the temperature at which a polymer undergoes a transition from a hard glass to a rubbery solid,Morphology,Example: poly(ethylene terephthalate) (PET) can be made with % crystalline domains ranging from 0% to 55%,Morphology,Completely amorphous PET is formed by cooling the melt quickly PET with
10、 a low degree of crystallinity is used for plastic beverage bottlesBy prolonging cooling time, more molecular diffusion occurs and crystalline domains form as the chains become more ordered PET with a high degree of crystallinity can be drawn into textile fibers and tire cords,Step-Growth Polymers,S
11、tep-growth polymerization: a polymerization in which chain growth occurs in a stepwise manner between difunctional monomers We discuss five types of step-growth polymers polyamides polyesters polycarbonates polyurethanes epoxy resins,Polyamides,Nylon 66 (from two six-carbon monomers)during fabricati
12、on, nylon fibers are cold-drawn to about 4 times their original length, which increases crystallinity, tensile strength, and stiffness,Polyamides,The raw material base for the production of nylon 66 is benzene, which is derived from cracking and reforming of petroleum,Polyamides,Adipic acid is in tu
13、rn the starting material for the synthesis of hexamethylenediamine,Polyamides,Nylons are a family of polymers, the two most widely used of which are nylon 66 and nylon 6 nylon 6 is synthesized from a six-carbon monomernylon 6 is fabricated into fibers, brush bristles, high-impact moldings, and tire
14、cords,Polyamides,Kevlar is a polyaromatic amide (an aramid)cables of Kevlar are as strong as cables of steel, but only about 20% the weight. Kevlar fabric is used for bulletproof vests, jackets, and raincoats,Polyesters,Poly(ethylene terephthalate) (PET) is fabricated into Dacron fibers, Mylar films
15、, and plastic beverage containers,Polyesters,ethylene glycol is synthesized from ethyleneterephthalic acid is synthesized from p-xylene, which is obtained from petroleum refining,Polycarbonates,Polycarbonates,Lexan is a tough transparent polymer with high impact and tensile strengths and retains its
16、 shape over a wide temperature range it is used in sporting equipment, such as bicycle, football, and snowmobile helmets as well as hockey and baseball catchers masks it is also used in the manufacture of safety and unbreakable windows,Polyurethanes,A urethane, or cabamate, is an ester of carbamic a
17、cid, H2NCH2CO2H they are most commonly prepared by treatment of an isocyanate with an alcoholPolyurethanes consist of flexible polyester or polyether units (blocks) alternating with rigid urethane units (blocks) the rigid urethane blocks are derived from a diisocyanate,Polyurethanes,the more flexibl
18、e blocks are derived from low-molecular-weight polyesters or polyethers with -OH groups at the ends of each polymer chain,Epoxy resins,Epoxy resins are materials prepared by a polymerization in which one monomer contains at least two epoxy groups within this range, there are a large number of polyme
19、ric materials and epoxy resins are produced in forms ranging from low viscosity liquids to high melting solids the most widely used epoxide monomer is the diepoxide prepared by treating 1 mol of bisphenol A with 2 mol of epichlorihydrin,Epoxy Resins,Epoxy Resins,Chain-Growth Polymers,Chain-growth po
20、lymerization: a polymerization in which monomer units are joined together without loss of atoms. For example:,Polyethylenes,Polyethylenes,Radical Chain-Growth,Among the initiators used for radical chain-growth polymerization are organic peroxides, which decompose as shown on mild heating,Polymerizat
21、ion,Radical: a molecule or ion containing one or more unpaired electrons Fishhook arrow: a curved and barbed arrow used to show the repositioning of a single electron To account for the polymerization of alkenes in the presence of peroxides, chemists propose a three-step radical chain mechanism,Poly
22、merization,Step 1: chain initiationChain initiation: a step in a radical chain reaction characterized by the formation of radicals from nonradical compounds,Polymerization,Step 2: chain propagationChain propagation: a step in a radical chain reaction characterized by the reaction of a radical and a
23、molecule to give a new radical Chain length, n: the number of times the cycle of chain propagation steps repeats in a chain reaction,Polymerization,Step 3: chain terminationChain termination: a step in a radical chain mechanism that involves destruction of radicals,Radical Chain-Growth,The first com
24、mercial polyethylenes produced by radical polymerization were soft, tough polymers known as low density polyethylene (LDPE) LDPE chains are highly branched due to chain-transfer reactions because this branching prevents polyethylene chains from packing efficiently, LDPE is largely amorphous and tran
25、sparent approx. 65% is fabricated into films for consumer items such as baked goods, vegetables and other produce, and trash bags,Radical Chain-Growth,Chain-transfer reaction: the reactivity of an end group is transferred from one chain to another, or from one position on a chain to another position
26、 on the same chain polyethylene formed by radical polymerization exhibits a number of butyl branches on the polymer main chain these butyl branches are generated by a “back-biting” chain transfer reaction in which a 1 radical end group abstracts a hydrogen from the fourth carbon back polymerization
27、then continues from the 2 radical,Radical Chain-Growth,Polymerization,Propylene and other substituted ethylene monomers can also be polymerized under a variety of experimental conditions radical polymerization of propylene involves 2 radical intermediates to give polypropylene, with methyl groups re
28、peating on every other carbon,Ziegler-Natta Polymers,Ziegler-Natta chain-growth polymerization is an alternative method that does not involve radicals Ziegler-Natta catalysts are heterogeneous materials composed of a MgCl2 support, a group IVB transition metal halide such as TiCl4, and an alkylalumi
29、num compound,Ziegler-Natta Polymers,Step 1: formation of a titanium-ethyl bond,Ziegler-Natta Polymers,Step 2: insertion of ethylene into the titanium-carbon bond,Ziegler-Natta Polymers,Polyethylene from Ziegler-Natta systems is termed high-density polyethylene (HDPE) it has a considerably lower degr
30、ee of chain branching than LDPE and, a result, has a higher degree of crystallinity, a higher density, a higher melting point, and is several times stronger than LDPE appox. 45% of all HDPE is blow-molded into containers with special fabrication techniques, HDPE chains can be made to adopt an extended zig-zag conformation. HDPE processed in this manner is stiffer than steel and has 4x the tensile strength!,Recycling Codes,Recycling Codes,End Chapter 15,Organic Polymer Chemistry,
