the synthesis of new polymers by modification of existing polymers using a variety of chemical reactions 1 the esterification of cellulose crosslinking of polyisoprene hydrolysis ID: 1014388
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1. CHAPTER 9REACTIONS OF POLYMERS→ the synthesis of new polymers by modification of existing polymers using a variety of chemical reactions1) the esterification of cellulose, crosslinking of polyisoprene, hydrolysisof poly(vinyl acetate), and chlorination of polyethylene.2) polymer reactions using a polymer as a carrier or support for some component of a reaction system (polymeric brominating and Wittig reagents, the Merrifield solid-phase synthesis of polypeptides, and polymeric catalysts)
2. 9-1 PRINCIPLES OF POLYMER REACTIVITYPolymer reaction rates and conversions are usually lower than those for the corresponding low-molecular-weight homolog although higher rates are also found in some reactions9-1a Yield80% yield in the hydrolysis of methyl propanoate → pure propanoic acid is obtained in 80%80% yield in the hydrolysis of poly(methyl acrylate)→ not 80% yield of poly(acrylic acid) with 20% unreacted poly(methyl acrylate)→ but copolymer products with on the average 80% acrylic acid and 20% methyl acrylate units
3. 9-1b Isolation of Functional GroupsIn the the random reaction of a pair of neighboring functionalgroups, the maximum conversion is limited due to the isolation of single functional groups between pairs of reacted functional groups.Ex) acetal formation in poly(vinyl alcohol) by reaction with an aldehyde.EX) the dechlorination of poly(vinyl chloride)maximum conversion : 83%
4. 9-1c Concentration1% solution of poly(vinyl acetate) molecular weight 106 The overall concentration of acetate groups is about 0.11 MLarger than 0.11 M of acetate groups; larger reaction rate0 M of acetate groups : zero reaction rateThe observed overall reaction rate: an average of the rates inside and outsidethe polymer coilsThe overall rate may be the same, higher, or lower than the corresponding reaction with a low-molecular-weight homolog of the polymerdepending on the concentration of the small molecule reactant inside the polymer coils relative to its concentration outside.
5. 9-1d CrystallinityReactions of the polymers having crystalline regions→heterogeneous product because only functional groups in the amorphous regions are available for reactionEx) chlorination of polyethylene, acetylation of cellulose, and aminolysis of poly(ethylene terephthalate)9-1e Changes in Solubility
6. 9-1f CrosslinkingFor the crosslinked polymers, the concentration of small molecule reactant inside the polymer domains can be lower than outside because of a low degree of swelling.
7. 9-1g Steric EffectsPolymer reactivity can be sterically hindered,1. functional group is close to the polymer chain functional group is in a sterically hindered environment Bulky small molecule reactants are usedexamples1. hydrolysis of acrylamide copolymers with monomer IThe rate decreases sharply with decreasing value of n, although the reaction rate is not affected by the molecular weight of the copolymer
8. 2. Hydrogenation of cyclododecene using the polymeric rhodium catalyst II occurs at a rate 5 times slower than does cyclohexeneThe low-molecular-weight homolog III shows no difference in catalytic activitytoward the two cycloalkenes.3. n-C4H9I and n-C18H37I react at the same rate with pyridine, but n-C4H9I isalmost fourfold more reactive than n-C18H37I toward poly(4-vinylpyridine)
9. 9-1h Electrostatic EffectsThe conversion of uncharged functional groups to charged groups can decrease in reactivity with conversion.Acceleration of reactivity is also observedrepells hydroxide ion
10. 9-1i Neighboring-Group Effectsthe saponification of poly(methyl methacrylate) proceeds with autoacceleration when carried out with bases9-1j Hydrophobic Interactionsthe hydrolysis of various 3-nitro-4-acyloxybenzoic acid substrates (V) catalyzed by imidazole (VI) and poly[4(5)-vinylimidazole] (VII) in ethanol–water mixturesCatalysis by VII is more effective than by VIIVII for n = 11 is 30-fold larger than for n = 1, and almost 400-fold larger than for VI.
11. 9-1k Other ConsiderationsReaction between functional groups on different polymer molecules occurs - when the two polymers are sufficiently similar (polymer chain interpenetration is possible - when polymer mixing is highly exothermic (acidic and basic polymers)2. The conformation of polymer chains on the reactivity - the expanded coils (not the tight coil) can increase the accessibility of polymer functional groups and the local concentration of a small-molecule reactant.3. The functional groups in a number of polymers are not of the same reactivity.
12. 9-2a Alkyds9-2 CROSSLINKING→ unsaturated polyesters in which the unsaturation is located at chain ends instead of within the polymer chaindouble bond resides in a fatty acid component
13. Unconjugated double bonds undergo crosslinking by the initial formation of an allylic hydroperoxide followed by decomposition of the hydroperoxide.
14. 9-2b Elastomers Based on 1,3-DienesCrosslinking is an absolute requirement for the applications as elastomers (rapidly and completely recovering from deformations).“vulcanization” is used synonymously with ‘crosslinking’ in elastomer technology.Crosslinking or vulcanization can be achieved by using sulfur, peroxides, other reagents, or ionizing radiation9-2b-1 Sulfur AloneNot the radical process but the ionic process- Neither radical initiators nor inhibitors affect sulfur vulcanization- But accelerated by organic acids, bases, and solvents of high dielectric constant.
15.
16. Vulcanization by heating with sulfur alone is not efficient ! - 40–50 sulfur atoms incorporated into the polymer per crosslink.9-2b-2 Accelerated Sulfur Vulcanizationlong polysulfide crosslinks (very large n)vicinal crosslinksintramolecular cyclic sulfide structuresTherefore commercial sulfur vulcanizations are carried out in the presence of various additives (accelerators) with a metal oxide and fatty acid (activator).Then most of the crosslinks are monosulfide or disulfide with very littlevicinal or cyclic sulfide units.How ?
17. The most used accelerators are sulfenamide derivatives such as 2-mercaptobenzothiazole2-mercaptobenzothiazole2,2’-dithiobisbenzothiazolecleavage followed by oxidative coupling.polysulfide
18. Zinc : increasing the efficiency and rate of crosslinking by chelating
19. 9-2b-3 Other Vulcanizationsby heating with p-dinitrosobenzene
20. 9-2c Peroxide Crosslinking→ compounding with a peroxide such as dicumyl peroxide or di-t-butyl peroxide and then heating the mixture.→ The crosslinks formed via peroxides are more thermally stable than those formed via sulfur vulcanization.→ peroxides more expensive than sulfur, therefore peroxides used for those polymers that cannot be easily crosslinked by sulfur,such as polyethylene and other polyolefins, ethylene–propene (no diene) rubbers (EPM), and polysiloxanes.mechanism
21. The crosslinking efficiency can be increased by incorporating small amounts of a comonomer containing vinyl groups.Ex)
22. 9-2d Other Crosslinking ProcessesCrosslinking of polymers containing fluorinated monomers such as vinylidene fluoride, hexafluoropropene, perfluoro(methyl vinyl ether), and tetrafluoroethylene→ dehydrohalogenation followed by addition of the diamine to thedouble bond with the metal oxide acting as an acid acceptor.
23. 9-3 REACTIONS OF CELLULOSE9-3a Dissolution of CelluloseFibers or films are produced by spinning or casting cellulose sodium xanthate solution10% sulfuric acid. The acid hydrolyzed the cellulose xanthic acid (XXV), is unstable and decomposes (without isolation).Then solid cellulose fiber (rayon) or film (cellophane) products are produced!
24. 9-3b Esterification of Cellulosemixed acetate–propionate and acetate–butyrate, and nitrate esters of cellulose are produced commercially9-3c Etherification of Cellulose
25. 9-4 REACTIONS OF POLY(VINYL ACETATE)Poly(vinyl alcohol) is obtained by alcoholysis of poly(vinyl acetate) with methanol:Reaction of poly(vinyl alcohol) with an aldehyde yields the corresponding poly(vinyl acetal):The two most important acetals are the formal and butyral (R = H and C3H7, respectively)
26. 9-5 HALOGENATION9-5a Natural RubberHydrochlorination at about 10 oC by electrophilic addition to give the Markownikoff product with chlorine on the tertiary carbon
27. 9-5b Saturated Hydrocarbon PolymersThe chlorination of polyethylene, poly(vinyl chloride), and other saturated polymers by a free-radical chain process catalyzed by radical initiators:The reaction of polyethylene with chlorine in the presence of sulfur dioxide yields an elastomer containing both chloro and chlorosulfonyl groupsvulcanized with metal oxides such as lead or magnesium oxide to form elastomers
28. 9-6 AROMATIC SUBSTITUTIONAromatic electrophilic substitution to produce styrene polymers withion-exchange properties
29. 9-7 CYCLIZATIONNatural rubber and other 1,4-poly-1,3-dienes are cyclized by treatment with strong protonic acids or Lewis acids
30. carbon fibers from polyacrylonitrile (PAN) (acrylic fiber)-successive thermal treatments— initially 200–300 oC in air followed by 1200–2000 oC in nitrogenFurther heating at above 2500C in nitrogen or argon for brief periods to yield carbon fibers with graphitelike morphology.
31. 9-9 GRAFT COPOLYMERSGrafting ontoGrafting fromGrafting through
32. 9-9a Radical Graft Polymerization9-9a-1 Vinyl MacromonomersPreparation of vinyl macromonomers1. Using HO-terminated polymer such as polysiloxane, polycaprolactone, or polytetrahydrofuran2. Using vinyl chloroacetate as the initiator in ATRPThen the vinyl macromonomers can be polymerized by any of the methods of radical polymerization to produce graft polymers.
33. 9-9a-2 Chain Transfer and Copolymerizationthe radical polymerization of a monomers in the polymer solutions produce a mixture of homopolymerization and graft polymerizationCopolymerizationchain transferHigh-impact polystyrene (HIPS): styrene polymerized in the presence of poly(1,3 butadiene)], ABS and MBS: styrene–acrylonitrile and methyl methacrylate–styrene, respectively, copolymerized in the presence of either poly(1,3-butadiene) or SBR
34. 9-9a-3 Ionizing RadiationThe polymer is swollen by monomer but does not dissolve in the monomer.Ex) poly(ethylene-graft-styrene can be produced from polyethylene/styrene mixture
35. 9-9a-5 Living Radical PolymerizationUsing ATRPUsing NMPA halogen-containing monomer such as vinyl chloroacetate or p- chloromethylstyrene is reacted with an HO containing alkoxyamine to yield a vinyl alkoxyamine, then (co)polymerization of the vinyl macromonomer produces the graft copolymer.Using RAFT
36. 9-11 POLYMERS AS CARRIERS OR SUPPORTSThree classes of polymer supports polymer reagentsa polymer containing a functional group that acts as the reagent to bring about a chemical transformation on some small (i.e., low-molecular-weight) molecule2. polymer catalystsHaving a group that performs a catalytic function in some reaction—usually a reaction between small molecules3. polymer substrateshaving an attached molecule on which some transformation is carried out using a small-molecule reagent
37. 9-11a Synthesis a polymer reagent, catalyst, or substrateTwo approachesFunctionalization of polymer approach the required functional group, for the reagent, catalyst, or substrate function, is attached to the polymer. 2. functionalization of monomer approach an appropriate monomer with the desired functional group is synthesized and then polymerized or copolymerized.9-11a-1 Functionalization of Polymerpolymer rhodium catalyst
38. polystyrenes containing OH, COOH, B(OH)2, RSnCl2, and P2 groups can be prepared by reaction with ethylene oxide, CO2, B(OR)3, MgBr2 followed by RSnCl3, and 2PCl, respectively.polymer reagent
39. 9-11a-2 Functionalization of MonomerThe approach of synthesizing a monomer containing the desired functional group followed by (co)polymerizationthe sequence of reactions starting from histidine(XXXVII) to yield 4(5)-vinylimidazole (XXXVIII)
40. 9-11b Advantages of Polymer Reagents, Catalysts, and SubstratesAn insoluble polymer reagent, catalyst, or substrate can be easily separatedfrom the other (i.e., the small molecule) components of a reaction system by filtration.Small-molecule reagents, catalysts,or substrates that are highly reactive, toxic, or malodorous can be handled much more safely and easily in the form of the corresponding polymers.disadvantagesFunctional polymers are more expensive than their smallmolecule analogs.Filtration of a polymer reagent, catalyst, or substrate is often not easy.Then, multistep sequential reactions and automated parallel combinatorial synthesis to produce libraries of compounds is possible
41. The epoxidation of an alkene by a polymer peracid (polymer reagent)9-12 POLYMER REAGENTSPreparation of polymer peracidThe application of polymer peracidfiltrationRegeneration of polymer peracid
42. Oxidation of alcohols to aldehydes or ketones : anion-exhange resin,Polymer reducing agentsobtained bycomplexing AlH3 or BH3 with poly(4-vinylpyridine)
43. a chiral polymer for an asymmetric synthesisstereoselective reduction of acetophenone to (R)-1-phenylethanol in 76–97% enantiomeric excess using the chiral supporthalogen addition to alkenes and -substitution on aldehydes and ketonesSmall molecular weight Pyridinium bromide is dangerous to handle.halogenating reagents
44. Polymer Wittig reagents : the conversion of an aldehyde or ketone to an alkenePolymer scavengers8-hydroxyquinoline group for chelating nickel, cobalt, and copper ionschiral groups are for resolving racemic mixtures into the individual enantiomersthe copper(II) complex of this polymer (either the R- or S-enantiomer) resolves racemates of amino acids by the formation of a pair of diastereomeric complexes with the two enantiomers.
45. 9-13 POLYMER CATALYSTShydrogenation by the polymer rhodium catalystester hydrolysis by poly[4(5)-vinylimidazole]
46. 9-14 POLYMER SUBSTRATES(substrate)insoluble
47. 9-14a Solid-Phase Synthesis of PolypeptidesSynthesis of glycylalanine requires that the amine and carboxylends of glycine and alanine, respectively, be protected.Boc (protecting group) formed by reacting the amino acid with 2-(t butoxycarbonyloxyimino)-2-phenylacetonitrile.
48. Solid-phase synthesis of polypeptide