organic chemistry chapter 22 polymer chemistry

Richard F. Daley and Sally J. Daley www.ochem4free.com Organic Chemistry Chapter 22 Polymer Chemistry 22.1 Structural Characteristics of Polymers 1138 22.2 Polymer Nomenclature 1141 22.3 Types of Polymerization Reactions 1144 22.4 Chain-Growth Polymerization 1146 Synthesis of Poly(vinyl acetate) 1155 Sidebar - Natural Rubber 1155 22.5 Controlling Stereochemistry in Vinyl Polymers 1157 22.6 Nonvinyl Chain-Growth Polymerization 1160 22.7 Step-Growth Polymerization 1163 Synthesis of Poly(ethylene terephthalate) 1165 Sidebar - Plastic Recycling 1167 22.8 Copolymers 1169 Sidebar - Plasticizers 1172 22.9 Cross-Linked Polymers 1173 Key Ideas from Chapter 22 1178 Organic Chemistry - Ch 22 1134 Daley & Daley Copyright 1996-2001 by Richard F. Daley & Sally J. Daley All Rights Reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the copyright holder. www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1135 Daley & Daley Chapter 22 Polymer Chemistry Chapter Outline 22.1 Structural Characteristics of Polymers A look at the various types of polymers 22.2 Polymer Nomenclature An introduction to naming polymers 22.3 Types of Polymerization Reactions Categories of polymer forming reactions 22.4 Chain-Growth Polymerization The mechanism for the formation of vinyl chain-growth polymers 22.5 Controlling Stereochemistry in Vinyl Polymers The Ziegler-Natta polymerization catalyst for vinyl polymers 22.6 Nonvinyl Chain-Growth Polymerization Mechanisms for chain-growth polymer formation for nonvinyl polymers 22.7 Step-Growth Polymerization The mechanisms for the formation of some representative step- growth polymers 22.8 Copolymers An examination of the various types of copolymers 22.9 Cross-Linked Polymers Types of cross-linking that occur in polymers www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1136 Daley & Daley Objectives ✔ Recognize the various types of polymer structures ✔ Know how to name both source-based and nonvinyl polymers ✔ Recognize the monomers that produce polymers ✔ Write the mechanisms for cationic, anionic, and radical polymerization of vinyl monomers ✔ Know the stereochemical types of vinyl polymers ✔ Write the mechanism for representative non-vinyl chain-growth polymerizations ✔ Recognize the similarity of the step-growth polymerization reactions to those studied in earlier chapters ✔ Know the types of copolymers ✔ Recognize how cross-linking occurs in epoxy polymers Observation is a passive science, experimentation an active science. — Claude Bernard A poly of sm monomers. Polyme A polymer is a molecule made up of many smaller units called monomers. mer is a large molecule that consists of a number aller repeating units made from molecules called rs are formed by some repetitive reaction that adds these monomer units one-by-one to the growing chain of the polymer. The process of converting the monomer units to a polymer is called polymerization. A reaction forming a polymer is a polymerization reaction. Polymers, sometimes called macromolecules, affect your life in many ways. For example, plastics are synthetic polymers, and they are all around you. Industry makes plastics into such things as fibers, structural materials, and protective films. Except for fuels, more plastics are manufactured in the world than any other organic material. One-third of all industrial chemists work in the polymer industry. Another way that polymers affect your life is in the natural chemistry of the life processes. Proteins and enzymes are polyamide polymers. Proteins are an important part of the structure of all animals, and enzymes catalyze the chemical processes that make www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1137 Daley & Daley those bodies function. Cellulose and starches are polymers of individual sugar molecules. Cellulose is the structural material of plants, and starches are the energy storage medium for plants. Both RNA and DNA are polymers of individual nucleic acids. These two classes of molecules control the genetic make-up of your body. This chapter focuses primarily on synthetic polymers. Chapters 24 and 25 cover some types of natural macromolecules. Generally, the size and stereochemistry of the polymer molecule determine the properties of that molecule. This chapter examines how those features determine a polymer's physical properties. This chapter also discusses polymer synthesis. 22.1 Structural Characteristics of Polymers The composition of polymers is a sequence of repeating monomer units that are covalently bonded together. The reactions that connect these repeating units can involve any of the functional groups discussed previously. The functional group on the repeating unit provides the reactive site for the connecting reaction. The repeating units of polymers have a variety of possible structures. When all the repeating units in a particular polymer have the same structure, that polymer is called a homopolymer. In a homopolymer, all the repeating units are identical. n A AAAAAAAA A n or An example of a homopolymer is polyvinyl chloride. or n CH 2 CH Cl CH 2 CH Cl CH 2 CHCH 2 CHCH 2 CHCH 2 CHCH 2 CH Cl Cl Cl Cl Cl Polyvinyl chloride When different repeating units make up the polymer chain, the polymer is called a copolymer. There are three types of copolymers: 1) alternating copolymers, 2) block copolymers, and 3) random copolymers. If you designate the repeating units as A and B, the following illustration shows representations of these three types of copolymers. A copolymer contains more than one type of monomer unit. Alternating copolymer ABABABAB n A + n B www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1138 Daley & Daley m A + n B AAAAABBB Block copolymer Random copolymer ABBBAABB m A + n B An example of the alternating copolymer is Nylon 66. n H 2 N(CH 2 ) 6 NH 2 n ClC(CH 2 ) 4 CCl OO NH(CH 2 ) 6 NHC(CH 2 ) 4 C OO + Nylon 66 n All the above examples are linear polymers. Some polymers contain additional covalent links to repeating units at various locations on the backbone. Such polymers are called branched polymers. Linear or branched polymer chains can be connected by some additional covalent links. These polymers are called cross- linked polymers. A linear polymer is a molecule with a series of connected repeating units with no branching. A branched polymer has bonds branching from the backbone of a linear polymer. Cross-linked polymers are linear polymer molecules joined by a branching connection. Polymer End Groups The structural drawings of all the polymers discussed in this chapter show a bond extending out of the brackets that enclose the repeating unit. The functional groups on the ends of the polymer chains are left unspecified because the end groups are an insignificant portion of the total chain. These groups have very little effect on the physical properties of the polymer. In a given sample of polymer, a variety of end groups may be present depending on how the polymer was synthesized. The physical properties of a specific polymer are the result of two molecular characteristics: 1) the length of the molecule and 2) the functional group associated with the repeating units. To determine the length of a polymer chain, chemists use the molecular weight of the polymer. Different polymers of the same chain length have similar physical properties regardless of the functional group present unless the functional group can hydrogen bond or disrupt the intermolecular van der Waals forces. These two interactions are more important in determining the physical properties of the polymer than is the molecular weight. The physical properties of interest to a consumer are those that show how well the polymer performs in response to various stresses. These responses include compressive, flexural, and tensile strength, as well as impact resistance. Compressive strength is a measure of how much compression a sample can tolerate before it Compressive, flexural, and tensile strength, as well as impact resistance are measures of the mechanical strength of a polymer. www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1139 Daley & Daley fails. Flexural strength is a measure of resistance to breaking or snapping when the sample is bent. Tensile strength is a measure of resistance to stretching. Impact resistance is a measure of how well a sample resists damage from a sudden impact. Some polymers have the characteristics of a crystalline solid. Crystalline polymers have chains that tend to orient themselves in a regular way, similar to the way the molecules in a crystalline solid orient themselves. The chains are held together in this regular orientation by hydrogen bonds or dipole alignments. These polymers generally have characteristic melting points, are strong, and nonelastic. Linear polyethylene is an example of such a crystalline polymer. The molecules of a crystalline polymer line up in a regular way similar to the smaller molecules in a crystal. Orientation of the chains of a crystalline polymer Amorphous polymers are similar to glassy solids. Amorphous polymers do not have a characteristic melting point. Instead, they often make an indistinct transition from the glassy solid to a viscous liquid called the glass transition temperature. These polymers do not have a regular orientation in the solid state. Amorphous polymers are generally not particularly strong and tend to be quite elastic. Rubber is an example of an amorphous polymer. The molecules in an amorphous polymer do not have any preferred alignment. A glassy solid is a solid that is often hard and brittle. Orientation of the chains of an amorphous polymer The glass transition temperature is the temperature at which a polymer transforms from a glass to a viscous liquid Many polymers are neither completely crystalline nor completely amorphous. Segments of the chains lie parallel to each other in regions called crystallites. Other segments of the chains are not ordered. Such polymers are called semicrystalline polymers. These polymers have much of the strength of a crystalline polymer along with much of the flexibility of an amorphous polymer. Nylon is an example of a semicrystalline polymer. Ordered regions among the amorphous regions in a semicrystalline polymer are called crystallites. www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1140 Daley & Daley Semicrystalline polymers are polymers with regions of disorder and crystallites. Orientation of the chains of a semicrystalline polymer Crystalline regions (Crystallites) Amorphous region Crystalline polymers generally are opaque, but amorphous polymers generally are transparent. Thus, increasing the number of crystallites in a polymer normally reduces the transparency of the polymer. An example is polystyrene. Amorphous polystyrene is found in a number of transparent, brittle "plastic" items, such as drinking cups. 22.2 Polymer Nomenclature The IUPAC has proposed some logical rules for naming polymers, but polymer chemists seldom use them because many polymers are so branched and cross-linked that their names are very complex. Thus, this section is only an introduction to the fundamentals of naming polymers. Many polymer chemists use source based naming. They name the monomer then add the poly- prefix. A complication with this method is that chemists use the common names of the monomers more often than their IUPAC names. For example, the common name for ethenylbenzene is styrene, so chemists call the polymer of styrene polystyrene. In addition to using common names, chemists refer to many polymers by their trade names. They use the trade name Teflon ® more frequently than the IUPAC name of polytetrafluroethylene. Vinyl polymers are among the easiest polymers to name when following the common name method. Simply use the monomer's common name with the prefix poly If the monomer's name includes more than one word, or if a letter or number precedes the name, enclose the monomer's name in parentheses. Thus, the polymer of 1- pentene is poly(1-pentene). Table 22.1 lists a few common names for vinyl polymers. www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1141 Daley & Daley Monomer Monomer Name Polymer Polymer Name CH 2 CH 2 Ethylene CH 2 CH 2 n Polyethylene CH 2 CHCH 3 Propylene n CH 2 CH CH 3 Polypropylene CH 2 CHCN Acrylonitrile n CH 2 CH CN Polyacrylonitrile CH 2 C CH 3 COOCH 3 Methyl methacrylate CH 2 C CH 3 COOCH 3 n Poly(methyl methacrylate) CH 2 CH O OCCH 3 Vinyl acetate n CH 2 CH OCCH 3 O Poly(vinyl acetate) CH 2 CHCl Vinyl chloride n CH 2 CH Cl Poly(vinyl chloride) CH 2 CH Styrene n CH 2 CH Polystyrene CF 2 CF 2 Tetrafluoroethylene n CF 2 CF 2 Polytetrafluoroethylene Table 22.1. Representative names for some vinyl polymers. Nonvinyl polymers generally have some atom other than carbon as a part of the backbone of the polymer. As with the vinyl polymers, the nomenclature of these polymers is often source based or based on their trade names. Nylon is an example of a family of compounds that chemists call by their trade names. To name them, use the word Nylon followed by a number for the number of carbons in the monomer(s) for that Nylon. Nylon 6 is a polymer made from monomers that consist of a single cyclic amide with six carbons. The monomers in Nylon 68 are diamines with six carbons and dicarboxylic acids with eight carbons. www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1142 Daley & Daley Nylon 68 From an 8 carbon carboxylic acidFrom a 6 carbon amine n NHCH 2 CH 2 CH 2 CH 2 CH 2 CH 2 NHCCH 2 CH 2 CH 2 CH 2 CH 2 CH 2 C OO Table 22.2 lists a few representative nonvinyl polymer names. Monomer Monomer Name Polymer Polymer Name O CH 2 CH 2 Ethylene oxide n CH 2 CH 2 O Poly(ethylene oxide) O O Propiolactone n OCH 2 CH 2 C O Polypropiolactone HOCH 2 CH 2 OH + COHHOC OO Ethylene glycol + Terephthalic acid COCH 2 CH 2 OC OO n Poly(ethylene terephthalate) NH O Caprolactam n NH(CH 2 ) 5 C O Polycaprolactam Nylon 6 H 2 N(CH 2 ) 6 NH 2 + HOOC(CH 2 ) 6 COOH Hexamethylenedi- amine + Sebacic acid NH(CH 2 ) 6 NHC(CH 2 ) 6 C OO n Poly(hexamethylene sebacate) Nylon 68 Table 22.2. Representative names for some nonvinyl polymers. Exercise 22.1 Name the following polymers and draw structural formulas for the monomers that form each of the polymers. a) n CH 2 CH CH 2 CH 3 b) n OCH 2 CH 2 CH 2 C O c) CH 2 CH OH n www.ochem4free.com 5 July 2005 [...]... completing the polymer synthesis www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1162 Daley & Daley Exercise 22. 6 One of the difficulties associated with the anionic lactam polymerization that forms Nylon 6 is that a proton transfer sometimes occurs within the polymer chain This proton transfer leads to polymer chain branching Show this reaction Exercise 22. 7 Tetrahydrofuran polymerizes in... CH2 n H Exercise 22. 5 Draw the structure for the product of the polymerization of styrene with TiCl4 and AlEt3 22. 6 Non-Vinyl Chain-Growth Polymerization Although many of the most common commercial polymers are vinyl polymers, industry does make some important non-vinyl polymers Several of these polymers form from cyclic compounds that undergo ring-opening reactions via chain-growth polymerization The... molecules to branch off the main polymer chain www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1148 Daley & Daley • • y x y x Exercise 22. 2 A polymerization reaction involving 1,3-butadiene and a radical initiator forms two different repeating polymer units Account for the formation of these two units CH2 CH CH CH2 CH2 CH CH CH2 Cationic polymerization is similar to radical polymerization in that both... starting point for the polymer formation As the polymer forms, the anion reacts with additional molecules of styrene at each end of the distyryl sodium to form a polymeric dianion Propagation step www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1152 • • Daley & Daley •• • • •• Repeat •• •• x x Each polymer chain grows at a remarkably similar rate Thus, the process produces the polymeric dianions... to the formation of radicals, most chain-growth polymerization reactions proceed via radical intermediates Some monomers do polymerize with ionic initiators, but that number is far fewer than those that polymerize with a radical initiator Chain-growth polymerization reactions usually form vinyl polymers One such vinyl polymer is polystyrene Polystyrene polymerizes under radical, cationic, and anionic... stereochemical relationship of the substituents present on the polymer backbone The arrangement of the substituents on the backbone of the polymer is called the tacticity of that polymer The three possible arrangements of substituents can be shown using polypropylene www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 The tacticity of a polymer is the stereochemical relationship among the side groups.. .Organic Chemistry - Ch 22 1143 d) Daley & Daley e) f) CH3 n O CHCH n NH(CH2)6NHC(CH2)4C CH2CH3 Sample solution b) Polybutyrolactone O O 22. 3 Types of Polymerization Reactions Chain-growth polymerization adds monomer units with the same functional group to the chain In step-growth polymerization, one functional group at the end of the chain... hydride from another polymer molecule All three of these steps are typical carbocation termination reactions Termination step www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1150 H Daley & Daley n Nu • • -H Nu H R n H H H n H n The removal of the hydride from another polymer chain can lead to branching of the polymer chain similar to the branching in the radical reaction Exercise 22. 3 What product... CO2 As the polymer forms, it traps the bubbles of carbon dioxide that are also forming These carbon dioxide bubbles give the polyurethane a foamy texture as the polymer hardens Generally, during the early part of the polymerization process, the manufacturers vigorously stir the polymer mixture to encourage the formation of smaller bubbles www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1166 Daley... number of polymers that form The reaction has no important termination reactions The dianion is relatively stable until a source of protons is added to the solution www.ochem4free.com 5 July 2005 Organic Chemistry - Ch 22 1153 Daley & Daley HCl •• •• x CH3OH x H x x H Exercise 22. 4 Predict the order of reactivity of styrene, p-chlorostyrene, and pmethoxystyrene in radical, cationic, and anionic polymerization . Organic Chemistry Chapter 22 Polymer Chemistry 22. 1 Structural Characteristics of Polymers 1138 22. 2 Polymer Nomenclature 1141 22. 3 Types of Polymerization Reactions 1144 22. 4. Organic Chemistry - Ch 22 1135 Daley & Daley Chapter 22 Polymer Chemistry Chapter Outline 22. 1 Structural Characteristics of Polymers A look at the various types of polymers. formation of vinyl chain-growth polymers 22. 5 Controlling Stereochemistry in Vinyl Polymers The Ziegler-Natta polymerization catalyst for vinyl polymers 22. 6 Nonvinyl Chain-Growth Polymerization