29 29-1 OrganicChemistry William H. Brown & Christopher S. Foote.
24 24-1 Organic Chemistry William H. Brown & Christopher S. Foote.
-
Upload
octavia-smith -
Category
Documents
-
view
226 -
download
2
Transcript of 24 24-1 Organic Chemistry William H. Brown & Christopher S. Foote.
2424
24-1
Organic Organic ChemChemistristry y
William H. Brown &William H. Brown &
Christopher S. FooteChristopher S. Foote
2424
24-2
Organic Organic PolymerPolymer
ChemistryChemistryChapter 24Chapter 24
2424
24-3
Organic Polymer Chem.Organic Polymer Chem. Polymer:Polymer: from the Greek, polypoly + merosmeros, many
parts• any long-chain molecule synthesized by bonding
together single parts called monomers
MonomerMonomer: from the Greek, monomono + merosmeros, single part• the simplest nonredundant unit from which a polymer
is synthesized
Plastic:Plastic: a polymer that can be molded when hot and retains its shape when cooled
2424
24-4
Organic Polymer ChemOrganic Polymer Chem Thermoplastic:Thermoplastic: a polymer that can be melted and
molded into a shape that is retained when it is cooled
Thermoset plastic:Thermoset plastic: a polymer that can be molded when it is first prepared but, once it is cooled, hardens irreversibly and cannot be remelted
2424
24-5
Notation & NomenclatureNotation & Nomenclature Show the structure by placing parens around the
repeat unit• nn = average degree of polymerization
n
StyrenePolystyrene
Cln
Poly(vinyl chloride) (PVC)
Cl
Vinyl chloride
synthesized from
synthesized from
2424
24-6
Notation & NomenclatureNotation & Nomenclature To name a polymer, prefix polypoly to the name of
the monomer from which the it 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 example poly(vinyl chloride) or poly(ethylene terephthalate)
2424
24-7
Molecular WeightMolecular Weight All polymers are mixtures of individual polymer
molecules of variable MWs• number average MW:number average MW: count the number of chains of a
particular MW, multiply each number by the MW, sum these values, and divide by the total number of polymer chains
• weight average MW:weight average MW: record the weight of each chain of a particular length, sum these weights, and divide by the total weight of the sample
2424
24-8
MorphologyMorphology 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 composed of ordered crystalline domainscrystalline domains and disordered amorphous domainsamorphous domains
2424
24-9
MorphologyMorphology High degrees of crystallinity are found in
polymers with regular, compact structures and strong intermolecular forces, such as hydrogen bonds and dipolar interactions• as the degree of crystallinity increases, the polymer
becomes more opaque due to scattering of light by the crystalline regions
Melt transition temperature, TMelt transition temperature, Tmm:: the temperature at which crystalline regions melt• as the degree of crystallinity increases, Tm increases
2424
24-10
MorphologyMorphology Highly amorphous polymers are sometimes
referred to as glassy polymers• because they lack crystalline domains that scatter
light, amorphous polymers are transparent• in addition they are weaker polymers, both in terms of
their greater flexibility and smaller mechanical strength
• on heating, amorphous polymers are transformed from a hard glass to a soft, flexible, rubbery state
Glass transition temperature, TGlass transition temperature, Tgg:: the temperature at which a polymer undergoes a transition from a hard glass to a rubbery solid
2424
24-11
MorphologyMorphology Example: poly(ethylene terephthalate),
abbreviated PET or PETE, can be made with % crystalline domains ranging from 0% to 55%
OO
OO
nPoly(ethylene terephthalate)
2424
24-12
MorphologyMorphology Completely amorphous PET is formed by cooling
the melt quickly• PET with a low degree of crystallinity is used for
plastic beverage bottles
By 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
2424
24-13
Step-Growth PolymersStep-Growth Polymers Step-growth polymerization:Step-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
2424
24-14
PolyamidesPolyamides Nylon 66 (from two six-carbon monomers)
• during fabrication, nylon fibers are cold-drawncold-drawn to about 4 times their original length, which increases crystallinity, tensile strength, and stiffness
O
HOOH
OH2N NH2
Hexanedioic acid(Adipic acid)
1,6-Hexanediamine(Hexamethylenediamine)
+
O HN
NO H
heat
n
Nylon 66
2424
24-15
PolyamidesPolyamides• the raw material base for the production of nylon 66 is
benzene, which is derived from cracking and reforming of petroleum
catalyst
Cyclohexanone
catalyst
Benzene Cyclohexane
Cyclohexanol
+
3H2
HNO3
Hexanedioic acid(Adipic acid)
OH O
COOHCOOH
O2
2424
24-16
PolyamidesPolyamides• adipic acid is in turn the starting material for the
synthesis of hexamethylenediamine
catalyst
heat
4H2
O
H2N NH2
OH2N NH2
1,6-Hexanediamine(Hexamethylenediamine)Hexanediamide
(Adipamide)
OO-NH4
+
O
Ammonium hexanedioate(Ammonium adipate)
NH4+ -O
2424
24-17
PolyamidesPolyamides 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 monomer
• nylon 6 is fabricated into fibers, brush bristles, high-impact moldings, and tire cords
Caprolactam
1. partial hydrolysis2. heat n
nNH
O
NOH
Nylon 6
2424
24-18
PolyamidesPolyamides 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
+
1,4-Benzenediamine(p-Phenylenediamine)
1,4-Benzenedicarboxylic acid (Terephthalic acid)
nKevlar
+
O
NH
COHnHOC
O O
nH2N NH2
CNHC
O
2nH2O
2424
24-19
PolyestersPolyesters Poly(ethylene terephthalate), abbreviated PET or
PETE, is fabricated into Dacron fibers, Mylar films, and plastic beverage containers
heatHO
O
OH
O
HOOH
O O
OO
n
1,4-Benzenedicarboxylic acid(Terephthalic acid)
+
1,2-Ethanediol(Ethylene glycol)
+2nH2 O
Poly(ethylene terephthalate)(Dacron, Mylar)
2424
24-20
PolyestersPolyesters• ethylene glycol is obtained by air oxidation of
ethylene followed by hydrolysis to the glycol
• terephthalic acid is obtained by catalyzed air oxidation of petroleum-derived p-xylene
Terephthalic acidp-XylenecatalystHOC COHCH3
O2H3C
O O
O
CH2=CH2O2
CH2-CH2
H+, H2OHOCH2CH2OH
Oxirane(Ethylene oxide)
1,2-Ethanediol(Ethylene glycol)
Ethylenecatalyst
2424
24-21
PolycarbonatesPolycarbonates Lexan is a tough transparent polymer with high
impact and tensile strengths and retains its 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 catcher’s masks
• it is also used in the manufacture of safety and unbreakable windows
2424
24-22
PolycarbonatesPolycarbonates• to make Lexan, an aqueous solution of the sodium salt
of bisphenol A is brought into contact with a solution of phosgene in CH2Cl2 in the presence of a phase-transfer catalyst
Phosgene
+
Disodium saltof Bisphenol A
+Na-O
CH3
CH3
O-Na+
Lexan(a polycarbonate)
+
Cl Cl
O
nO
CH3
CH3
O
O
2NaCl
2424
24-23
PolyurethanesPolyurethanes A urethaneurethane, or carbamate, is an ester of carbamic
acid, H2NCH2COOH• they are most commonly prepared by treatment of an
isocyanate with an alcohol
Polyurethanes consist of flexible polyester or polyether units (blocks) alternating with rigid urethane units (blocks)• the rigid urethane blocks are derived from a
diisocyanate
+An isocyanate A carbamate
RNHCOR'RN=C=O R'OH
O
2424
24-24
PolyurethanesPolyurethanes• the more flexible blocks are derived from low MW
polyesters or polyethers with -OH groups at the ends of each polymer chain
Low-molecular-weightpolyester or polyether
2,6-Toluenediisocyanate
+
n
A polyurethane
CH3
CNH NHCO-polymer-OCH3
N=C=OO=C=N
O
nHO-polymer-OH
O
2424
24-25
Epoxy resinsEpoxy 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
polymeric materials, and epoxy resins are produced in forms ranging from low-viscosity liquids to high-melting solids
2424
24-26
Epoxy ResinsEpoxy Resins• the most widely used epoxide monomer is the
diepoxide prepared by treating 1 mole of bisphenol A with 2 moles of epichlorohydrin
O
CH3
CH3
OOO
A diepoxide
OCl Na+-O
CH3
CH3
O-Na+
the disodium salt of bisphenol A
Epichlorohydrin
+
2424
24-27
Epoxy ResinsEpoxy Resins• treatment of the diepoxide with a diamine gives the
resin
H2NNH2
A diamine
O
CH3
CH3
O
An epoxy resin
HN
OH OH
NH n
O
CH3
CH3
OOO
A diepoxide
2424
24-28
ThermosetsThermosets Baelekite was one of the first thermosets
OH
+ CH2OOH
OH
OH
OH
OH
Baekelite
Phenol Formaldehyde
2424
24-29
Chain-Growth PolymersChain-Growth Polymers Chain-growth polymerization:Chain-growth polymerization: a polymerization
that involves sequential addition reactions, either to unsaturated monomers or to monomers possessing other reactive functional groups
Reactive intermediates in chain-growth polymerizations include radicals, carbanions, carbocations, and organometallic complexes
2424
24-30
Chain-Growth PolymersChain-Growth Polymers We concentrate on chain-growth polymerizations
of ethylene and substituted ethylenes
• on the following two screens are several important polymers derived from ethylene and substituted ethylenes, along with their most important uses
R
An alkene
R
n
2424
24-31
PolyethylenesPolyethylenes
CH2=CH2
CH2=CHCH3
CH2=CHCl
CH2=CCl2
MonomerFormula
Common Name
Polymer Name(s) andCommon Uses
Ethylene
Propylene
Vinyl chloride
1,1-Dichloro-ethylene
Polyethylene, Polythene;break-resistant containersand packaging materials
Polypropylene, Herculon;textile and carpet fibers
Poly(vinyl chloride), PVC;construction tubing
Poly(1,1-dichloroethylene), Saran; food packaging
2424
24-32
PolyethylenesPolyethylenesCH2=CHCN
CF2 =CF2
CH2=CHC6 H5
CH2=CHCOOEt
CH3
CH2=CCOOCH3
Acrylonitrile
Tetrafluoro-ethylene
Styrene
Ethyl acrylate
Methylmethacrylate
Polyacrylonitrile, Orlon;acrylics and acrylates
Poly(tetrafluoroethylene), PTFE; nonstick coatings
Polystyrene, Styrofoam;insulating materials
Poly(ethyl acrylate); latex paintsPoly(methyl methacrylate), Plexiglas; glass substitutes
2424
24-33
Radical Chain-GrowthRadical Chain-Growth Among the initiators used for radical chain-
growth polymerization are diacyl peroxides, which decompose as shown on mild heating
ΔO
O
O
O
Dibenzoyl peroxide
O
O
2 + 2CO2
A phenyl radical
A benzoyloxy radical
2
2424
24-34
Radical Chain-GrowthRadical Chain-Growth Another common class of initiators are azo
compounds, which also decompose on mild heating or with absorption of UV light
Azoisobutyronitrile (AIBN)
Δ or hνN NN
C
N
C NN CN
+2
Alkyl radicals
•: : ::
2424
24-35
Radical Chain-GrowthRadical Chain-Growth Radical polymerization of a substituted ethylene
• chain initiation
• chain propagation
In-In
In
Δ or hυ 2 In
In
RR+
In
RR
In
RR
etc.
In
R
In
RRn
R
Rn+
+
2424
24-36
Radical Chain-GrowthRadical Chain-Growth• chain termination
InRR
InRR
InR R
InRR
InRR
H
2
+
n n
nn
n
radicalcoupling
dispropor-tionation
2424
24-37
Radical Chain-GrowthRadical Chain-Growth Radical reactions with double bonds almost
always gives the more stable (the more substituted) radical• because additions are biased in this fashion,
polymerizations of vinyl monomers tend to yield polymers with head-to-tail linkages
head-to-tail linkages
R R R R R R R
R R R
head-to-tail linkages head-to-head linkage
R R R R R R R
R R R
2424
24-38
Radical Chain-GrowthRadical Chain-Growth Chain-transfer reaction: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 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 then continues from the 2° radical
2424
24-39
Radical Chain-GrowthRadical Chain-Growth
A six-membered transition state leading to 1,5-hydrogen abstraction
H H
n
nCH2=CH2
2424
24-40
Radical Chain-GrowthRadical Chain-Growth The first commercial 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 transparent
• approx. 65% is fabricated into films for consumer items such as baked goods, vegetables and other produce, and trash bags
2424
24-41
Ziegler-Natta PolymersZiegler-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 4B transition metal halide such as TiCl4, and an alkylaluminum compound
nCH2=CH2
TiCl 4/ Al(CH2CH3)2Cl
MgCl2Ethylene Polyethylene
2424
24-42
Ziegler-Natta PolymersZiegler-Natta Polymers Mechanism of Ziegler-Natta polymerization
Step 1: formation of a titanium-ethyl bond
Step 2: insertion of ethylene into the Ti-C bond
Ti Cl Ti+ +
Mg Cl2 / TiCl4particle
Diethylaluminumchloride
AlCl
Cl
AlCl
Ti Ti+ CH2 = CH2
2424
24-43
Ziegler-Natta PolymersZiegler-Natta Polymers Polyethylene from Ziegler-Natta systems is
termed high-density polyethylene (HDPE)• it has a considerably lower degree 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!
2424
24-44
Polymer StereochemistryPolymer Stereochemistry There are three alternatives for the relative
configurations of stereocenters along the chain of a substituted ethylene polymer
HR RH HR RH HR
Syndiotactic polymer(alternating configurations)
HR HR HR HR HR
Isotactic polymer (identical configurations)
HR HR HR HR RH
Atactic polymer(random configurations)
2424
24-45
Polymer StereochemistryPolymer Stereochemistry In general, the more stereoregular the
stereocenters are (the more highly isotactic or syndiotactic the polymer is), the more crystalline it is• the chains of atactic polyethylene, for example, do not
pack well and the polymer is an amorphous glass• isotactic polyethylene, on the other hand, is a
crystalline, fiber-forming polymer with a high melt transition
2424
24-46
Ionic Chain-GrowthIonic Chain-Growth May be either anionic or cationic polymerizations
• cationic polymerizations are most common with monomers with electron-donating groups
• anionic polymerizations: most common with monomers with electron-withdrawing groups
OR SR
Styrene IsobutyleneVinyl ethersVinyl thioethers
StyreneCOOR COOR CN COOR
CN
Alkyl methacrylates
Alkyl acrylates
Acrylonitrile Alkylcyanoacrylates
2424
24-47
Anionic chain-GrowthAnionic chain-Growth Anionic polymerization can be initiated by
addition of a nucleophile, such as methyl lithium, to an activated alkene
R'
R LiR
R'R'
R
R' R'
etc.
Li ++ +
2424
24-48
Anionic Chain-GrowthAnionic Chain-Growth An alternative method for initiation involves a
one-electron reduction of the monomer by Li or Na to form a radical anion which is either reduced or dimerized to a dianion
+
A radical anion
A dianion
Butadiene
Li +
Li +
Li +
Li
Li
A dimer dianion
radical couplingto form a dimer
Li +Li +
2424
24-49
Anionic Chain-GrowthAnionic Chain-Growth To improve the efficiency of anionic
polymerizations, soluble reducing agents such as sodium naphthalide are used
• the naphthalide radical anion is a powerful reducing agent and, for example, reduces styrene to a radical anion which couples to give a dianion
THF
Sodium naphthalide(a radical anion)
Na+Na+
Naphthalene
:
2424
24-50
Anionic Chain-GrowthAnionic Chain-Growth
• the styryl dianion then propagates polymerization at both ends simultaneously
A styrylradical anion A distyryl dianion
Styrene
Na+
Na+Na+
Na+
2424
24-51
Anionic Chain-GrowthAnionic Chain-Growth propagation of the distyryl dianion
Na+
Na+
1. 2n
2. H2O
A distyryl dianion
Polystyrene
nn
2424
24-52
Anionic Chain-GrowthAnionic Chain-Growth Living polymer:Living polymer: a polymer chain that continues
to grow without chain-termination steps until either all of the monomer is consumed or some external agent is added to terminate the chains• after consumption of the monomer under living
anionic conditions, electrophilic agents such as CO2 or ethylene oxide are added to functionalize the chain ends
2424
24-53
Anionic Chain-GrowthAnionic Chain-Growth• termination by carboxylation
:nNa+
CO2H3 O+n
COO- Na +
nCOOH
2424
24-54
Cationic Chain-GrowthCationic Chain-Growth The two most common methods for initiating
cationic polymerization are • reaction of a strong protic acid with the monomer• abstraction of a halide from the organic initiator by a
Lewis acid
Initiation by a protic acid requires a strong acid with a nonnucleophilic anion in order to avoid addition to the double bond• suitable acids include HF/AsF5 and HF/BF3
2424
24-55
Cationic Chain-GrowthCationic Chain-Growth• initiation by a protic acid
• Lewis acids used for initiation include BF3, SnCl4, AlCl3, Al(CH3) 2Cl, and ZnCl2
H3CR
R
H+BF4-
+ BF4-R
R
R
R
n BF4-
H3C R
R R R R R
+
2424
24-56
Cationic Chain-GrowthCationic Chain-Growth• initiation
• propagation
Cl + SnC l4 +
2-Chloro-2-phenylpropane
SnCl5-
n +
+
2-Methylpropene
++
+
n
2424
24-57
Cationic Chain-GrowthCationic Chain-Growth• chain termination
OH+
+SnCl5
-
H2O
H+SnCl5-
n
n
2424
24-58
Prob 24.5Prob 24.5Name each polymer, and draw the structure of the monomer(s) that might be used to make it.
(a) (b)nO
n (c)O
n
O
(d) CFCF2
CF3n
On
(e) (f) OO
O O
n
n(g)
CH2Cl
HN
NH
O
On
(h)
2424
24-59
Prob 24.7Prob 24.7Draw a structural formula for the polymer formed in each reaction.
(a) + HO OH H+OMe
O
MeO
O
(b) + HO OHOH
H+
OMe
O
MeO
O
(c) (d)O CF3SO3H O
KOH
2424
24-60
Prob 24.8Prob 24.8Propose reagents and experimental conditions for the conversion of furan to hexamethylenediamine.
Furfural
oat hulls, corn cobs, sugar cane stalks, etc
Furan Tetrahydrofuran (THF)
(2)(1)
Zn-Cr-Mo catalyst
O CH
O
O
O
H2 SO4
H2 O
1,4-Dichloro- butane
Hexanedinitrile (Adiponitrile)
1,6-Hexanediamine(Hexamethylenediamine)
(3)
(4)C(CH2 )4CN
Cl(CH2)4Cl
H2 N(CH2)6NH2N
2424
24-61
Prob 24.9Prob 24.9Propose reagents for the conversion of 1,3-butadiene to hexamethylenediamine.
1,6-Hexanediamine(Hexamethylenediamine)
Butadiene 1,4-Dichloro-2-butene
3-Hexenedinitrile
(1) (2)
(3)
CH2=CHCH=CH2 ClCH2CH=CHCH2 Cl
H2 N(CH2)6NH2N CCH2CH=CHCH2C N
2424
24-62
Prob 24.10Prob 24.10Propose reagents and experimental conditions for the conversion of butadiene to adipic acid.
HOOCCOOH
1,3-Butadiene Hexanedioic acid(Adipic acid)
?
2424
24-63
Prob 24.12Prob 24.12Propose a mechanism for the step-growth reaction in this polymerization.
Ethylene glycol
Poly(ethylene terephthalate)
Dimethyl terephthalate
+n
+n 275°C
COCH2CH2OC 2nCH3OH
nHOCH2CH2OH
Methanol
O O
COCH3
OCH3OC
O
2424
24-64
Prob 24.13Prob 24.13Identify the monomer(s) required for the synthesis of each step-growth polymer.
C C-O-CH2 CH2 OO O
nKodel
(a polyester)
(a)
C(CH2)6CO
NHO
CH2 NHn
(b)
Quiana(a polyamide)
2424
24-65
Prob 24.14Prob 24.14Draw a structural formula for the repeating unit of Nomex.
+
1,3-Benzenediamine 1,3-Benzene-dicarbonyl chloride
NH2H2N ClCl
O O
polymerizationNomex
2424
24-66
Prob 24.15Prob 24.15Propose a mechanism for this Beckmann rearrangement which converts cyclohexanone oxime to caprolactam, the monomer from which nylon 6 is synthesized.
NOH
O
NH2OH H2SO4 NH
O
Cyclohexanone Cyclohexanone oxime
Caprolactam
2424
24-67
Prob 24.17Prob 24.17Propose a mechanism for the formation of this polycarbonate.
F F
O
O
O
+
n+
An aromaticdifluoride
O
Sodium carbonate
O
A polycarbonate
Na2CO3
2NaF
2424
24-68
Prob 24.18Prob 24.18Propose a mechanism for the formation of this polyurea. To simplify, consider the reaction of one -NCO group with one -NH2 group.
NCOOCN H2NNH2
NH
NH
NH
HN
OO
n
+
1,2-Ethanediamine
Poly(ethylene phenylurea)
1,4-Benzene-diisocyanate
2424
24-69
Prob 24.19Prob 24.19When equal molar amounts of these two monomers are heated, they form an amorphous polyester. Under these conditions, polymerization is regioselective for the 1°-OH groups. Draw a structural formula for the repeat unit of this polyester.
O
O
O
HO OHOH
+heat a polyester
Phthalicanhydride
1,2,3-Propanetriol (Glycerol)
2424
24-70
Prob 24.21Prob 24.21Propose a mechanism for formation of this polymer.
H2N
O
NH2
O O O
N Nn
base+
2424
24-71
Prob 24.22Prob 24.22Draw a structural formula for the polymer resulting from base-catalyzed polymerization of each monomer. Will the polymer by optically active?
O
O
O
O
(a) O
(R)-Propylene oxide
(b)
(S)-(+)-Lactide
2424
24-72
Prob 24.23Prob 24.23The polymer on the left is an insoluble, opaque material that is difficult to process into shapes. The polymer on the right is an transparent material that is soluble in a number of organic solvents. Explain the difference in physical properties between the two in terms of their structural formulas.
O O O
O O O
n n m
Poly(3-hydroxybutanoic acid) Poly(3-hydroxybutanoic acid -3-hydroxyoctanoic acid) copolymer
2424
24-73
Prob 24.25Prob 24.25Draw a structural formula for the repeat unit of the polymer formed in each reaction.
(a)O
OAIBN
70°C(b)
CN
Li
2424
24-74
Prob 24.26Prob 24.26Select the member of each pair that is more reactive toward cationic polymerization.
(a)OCH3
or (b)OCH3 OCCH3
or
(d)
(c) or
orCH3O
O
2424
24-75
Prob 24.33Prob 24.33Natural rubber is the all-cis polymer of isoprene. Draw a structural formula for the repeat unit of natural rubber.
Poly(2-methyl-1,3-butadiene) (Polyisoprene)
2424
24-76
Prob 24.34Prob 24.34Radical polymerization of styrene gives a linear polymer. Show by drawing structural formulas how incorporation of a few percent 1,4-divinylbenzene in the polymerization mixture gives a cross-linked polymer.
+
Styrene 1,4-Divinylbenzene
a copolymer of styreneand divinylbenzene
2424
24-77
Prob 24.37Prob 24.37From what two monomer units is this polymer made?
C C NN
2424
24-78
Prob 24.38Prob 24.38Draw a structural formula for the repeat unit in the polymer formed by ring-opening metathesis polymerization of each monomer.
(a) (b) (c) (d)O
O
2424
24-79
OrganicOrganicPolymerPolymer
ChemistryChemistryEnd Chapter 24End Chapter 24