1 / 56

Classification by Mechanism  Step – Growth  Chain – Growth Classification by Type

Chap 8. Polycondensation Reactions. Classification by Mechanism  Step – Growth  Chain – Growth Classification by Type  Condensation  Addition Classification by Bond  Radical  Ion. Surfing to the internet. For further details, Click next homepage.

von
Download Presentation

Classification by Mechanism  Step – Growth  Chain – Growth Classification by Type

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chap 8. Polycondensation Reactions • Classification by Mechanism • Step – Growth •  Chain – Growth • Classification by Type • Condensation •  Addition • Classification by Bond • Radical •  Ion Surfing to the internet For further details, Click next homepage. http://www.pslc.ws/mactest/synth.htm

  2. What are differences between step and chain growth polymerizatoin? • Step Growth Polymerization • The growing chains react with each other. • Polymers frwo to high Mw at a slow rate. • High Mw is formed at the end of polymerization. • Long reaction time is needed to obtain high Mw and high conversion Radical − Living Mn Step Growth 100 0 % Conversion • Chain Growth Polymerization • Monomer molecules add on to a growing polymer chain one at a time. • Polymers grow to high Mw at a very fast rate • High Mw is formed at the early stage. • Monomer adds on the growing polymer chain via reactive active center.

  3. Addition versus Condensation polymerisation • Condensation polymers (C): fewer atoms in the backbone because of formation of by-products • Addition polymers (A):the repeating unit contains the same atoms as the monomer

  4. Characteristics of Step-Growth Step-growth polymerization principle was used by Carothers in 1929. Synthesis of Ester It seemed to him more likely that one would get long chainlike macromolecules like this Carothers thought about following reaction. Many scientists were sure that one would get a ring-like molecule But, if more acid and alcohol were used, ring would not form because of unstability of ring-shaped molecules more than six atom.

  5. Characteristics of Step-Growth • JACS(Journal of American Chemical Society, 51, P. 2548 (1929)) • “Polyintermolecular condensation requires as starting materials compounds in which at least two functional groups are present in the same molecule”

  6. Equal Functional Group Reactivity Concept • Extended by Flory • The reactivity of functional group is not correlated with complexity and size of molecule with functional group. • This concept is useful to polycondensation type polymerization. • ex) OCNRNCO + H2NR`NH2 polyurea

  7. Equal Functional Group Reactivity Concept • This concept also can be applied to Chain-growth polymerization. • Olefins • Vinyl monomers • Unsaturated monomers • So, double bond in vinyl monomer is considered as bifunctional.

  8. Equal Functional Group Reactivity Concept • I. Thermodynamic Approach • “In order to for a polymerization to be thermodynamically feasible, the Gibbs-Free Energy change must be negative, that is, ΔGp < 0.” • G = HTS • GP = HPTSP : this equation is the basic of understanding about polymerization, depolymerzation equilibrium

  9. Equal Functional Group Reactivity Concept • GP = Gpolymer Gmonomer • = (HP – Hm) – T(SP – Sm) • = HP – TSP • Where HP : enthalpy change per monomer unit • SP : entropy change per monomer unit • GP < 0  Polymerization is spontaneous • GP > 0  Polymerization is not possible • GP = 0  monomer polymer • at this temperature isceiling temperature. • (for both step and chain growth)

  10. Equal Functional Group Reactivity Concept • II.Kinetic Approach • “A negative GP does not necessarily mean that polymerization occurs under a particular set of reaction conditions and reaction sites” • e.g) should have •  functional group •  proper initiator •  temperature etc.

  11. Step Growth Polymerization

  12. Step Growth Polymerization • 1. Polyesterification by esterinterchange O O x HO R OH + x R"OCR' C O R" O O R" (OCR' C O R ) OH + (2 x 1)R" OH x • 2. Polyesterification and polyamidation by Schotten-Baumann Reaction

  13. Step Growth Polymerization • 3. Amidation by thermal dehydration of ammonium salt n H N(CH ) NH + n HOOC(CH ) COOH 2 2 2 2 4 6 OOC(CH ) COO 2 4 n + + H N(CH ) NH 3 2 3 6 H NH (CH ) NH CO (CH ) CO OH + (2 n 1) H O 2 2 2 6 4 n • 4. Reaction of OCNRNCO + HOR’OH  polyurethane • H2NR’NH2 polyurea

  14. Step Growth Polymerization • Well-studied, well characterized rexns • Well-understood rexns at least on an empirical basis. Surfing to the internet For further details, Click next homepage. http://www.chemheritage.org/EducationalServices/nylon/other/step/step.html

  15. Carother’s Equation • W. Carothers • In step-growth polymerization, Carother's equation gives the number-average degree of polymerization, Xn, for a given fractional monomer conversion, p. • P = extent of reaction • [M]= concentaration of monomer • P 0 0.5 0.8 0.95 0.99 0.999 • DPn 1 2 5 50 100 1000 • When P = 0.995 DPn = 200.

  16. Carother’s Equation • f = number of average functional group per monomer • N0 = number of initial monomers • N0f = number of initial functional group • N = number of final molecules (monomer, dimer,  polymer) • Generalized Carother's Eq.

  17. Carother’s Equation • ex) monomer=10, fg= 20 • final molecules= 2 Surfing to the internet For further details about W.Carothers Click next homepage. http://www.chemheritage.org/EducationalServices/chemach/pop/whc.html

  18. Four Requirements of Polycondensation • DPn 200 • Polymer yield =99.5% • P = 0.995 • Highly efficient Reaction • Absent of side Reactions • that is, a 99.5% consumption of functional group does not necessarily a 99.5% polymer yield or 99.5% yield of interunit linkages • Ex) • High monomer purity • Exact (on known) Stoichiometry Exact (on known) equivalence of functional groups. Molecular Weight Control of Polycondensation Reaction Equivalence of Functional Groups.

  19. Kinetics (ref. chap 11 in book) A. Types of monomer   a. AB type  b. AA and BB type  c. Three functional groups for crosslinked polymers

  20. Kinetics (ref. chap 11 in book) B. Condensation of difunctional monomers. a. H+ HOCH2CH2OH (-H2O)  b. ∆ H2NCH2CH2CH2CO2H (-H2O)

  21. Kinetics (ref. chap 11 in book) Polyesterfication as an example of polycondensation k - d[COOH] / dt = k [COOH][OH][acid] Assumption : without strong acid catalyst condition, pure monomer and correct equivalent - d[COOH] / dt = k3[COOH]2[OH] -COOH is considered as acid catalyst - d[COOH] / dt = k3[COOH]3 [COOH] = [OH] integral eqn 1 / [COOH]2 = 1 / [COOH]02 +2k3t 1 / (1-P)2 = 1+2[COOH]02k3t P = 1 – [COOH] / [COOH]0

  22. Kinetics (ref. chap 11 in book) Assumption : with strong acid catalyst condition, pure monomer and correct equivalent • - d[COOH] / dt = [COOH]2(k3[COOH] + kcat[H +] ) • kcat » k3 k3 can be neglected. • d[COOH] / dt = k2[COOH]2 k2 = kcat[H+] • integral eqn • 1 / (1-P) = 1 + k2[COOH]0 · t [COOH] = [COOH]0 (1-P) If you know the value of K2, you can calculate DPn at any time

  23. Kinetics (ref. chap 11 in book) ex) k 2 10 –2 l mole1sec1 , C0 3 mole  sec  l1 , DPn =50 ( k2 = kcat[H+] ) Reaction time = ? if k 2 10 –4 l mole1sec1 Reaction time = ? less than 30 min about 45 hr

  24. Kinetics Mw distributions of linear condensation polymers • Assumption : Independence between reaction time and molecular size • P: fraction of functional groups that have reacted in time t • 1-P : fraction of functional groups remaining at time t • x-mer:randomly selected polymer molecule containing exactly x structural units. • Probability finding a reacted carboxyl group in molecules = P Probability finding (x-1) number of reacted carboxyl group in molecules = P x1 • Probability finding a unreacted carboxyl group in molecules = 1P • Probability findingx-mer = P x1(1-P)

  25. 0.045 P=0.95 Nx 0.020 P=0.98 0.010 P=0.99 Kinetics • If there are N number of molecules, total x-mer number is • N x = N  P x1(1-P) • N = N 0 (1 P) •  N x = N 0 P x1(1P) 2 • Mw distributions of linear condensation polymers. 100 220

  26. Kinetics 2.0 MWD

  27. Molecular Weight Control Target Molecular weight DPn is time – dependent 1) Quench (cooling) the polymerization at pre- determined time heating unstable react as heating  undesirable

  28. Molecular Weight Control • 2) Regulation of monomer concentration • nonstoichiometric condition or adding monofunctional reactant. • Stable Polymer • No more reaction. • can control & limit MW

  29. Molecular Weight Control Nylon 66: Adding lauric acid or acetic acid, MW control Possible melt spinning through viscosity control melt viscosity undesirable mw

  30. Molecular Weight Control Assume B-B unit slightly in excess NA : number of A functional group Nb : number of B functional group r = NA / Nb = feed ratio P : rate of A group at t rP : rate of B group at t Initial total number of molecules = (NA + NB) / 2 Number of unreacted A= NA(1―p) Number of unreacted B= NB(1―rP) Number of total chain end = Number of unreacted A and B → Number of total molecules after t = (Number of total chain end )/2 = [NA(1―p)+ NB(1―r p)]/2

  31.   Network Step Polymerization A. Greater than two functionality polymers. a. Alkyd-type polyester :   b. Phenol-formaldehyde resin :  c. Melamine-formaldehyde resin : 

  32.   Network Step Polymerization B. Gelatin : High conversion of greater than two functionality. a. Gel point : onset of gelatin.         sudden increase in viscosity.         change from liquid to gel.        bubbles no longer rising.         impossible stirring.

  33.   Network Step Polymerization C. Gel point conversion.    : critical reaction conversion.  : average functionality.

  34.   Network Step Polymerization D. Examples of gel point conversion. 3mol of 1 2mol of 4 Gel point conversion : 77% (Experiment)                         83% (Calculate)

  35. Carother’s Equation • where DPn ∝ • = critical extent of reaction at gel point • In case of ex. • Pc = 2/2.4 = 0.833 • DPn ∞ • Ni:Monomer have functional group, f i • ex) 2mole Glycerol 6OH • 3mole Phthalic Acid 6COOH • total 5 mole 12 f.g • N, No , No favg=total functional group • 2( No- N) = number of functional • group after reaction

  36. Example of condensation polymerization • Polyester • (Dacron, Mylar) ester interchange rexn is faster thandirect esterification. • It is difficult to purify diacid. • Methyl ester is used commonly. • For termination, alcohol is removed by distillation of reaction mixture. Surfing to the internet For further details about Polyester Click next homepage. http://www.pslc.ws/mactest/pet.htm

  37. Example of condensation polymerization 1. 2.

  38. Example of condensation polymerization B. Nylon 66 • . • nylon salt Surfing to the internet For further details about Nylon Click next homepage. http://www.pslc.ws/mactest/nysyn.htm http://www.pslc.ws/mactest/nylon.htm

  39. Example of condensation polymerization C. Aromatic Polyamide • Kevlar poly(p-phenylene terephthalamide) • -high strength Surfing to the internet For further details about Kevlar and Nomex Click next homepage. http://www.pslc.ws/mactest/aramid.htm

  40. Example of condensation polymerization • Nomex poly(m-phenylene isophthalamide) • -very good high temperature resistance • The electron density of NH2 is reduced by aromatic ring. So, the nuclephilicity of aromatic amine is reduced by –COOH. • High temperature is needed. • For faster reaction, diacid chloride is used. * Coordinated covalent bond by using Li ion

  41. Example of condensation polymerization D. Aromatic Polyimides

  42. Example of condensation polymerization • Two step polymerization is used because precipitation is occured before high molecular • aromatic polyimide was formed. • In first step, poly(amic acid) is formed at -70oC • The poly(amic acid) is cyclized over 150 oC. • Aromatic polyimide is very high heat resistance, Kapton, H-film • To improve solubility of poly(amic acid), CH2 group is introduced in aromatic amine or • isocyanate is used instead of amine. Surfing to the internet For further details about Polyimides Click next homepage. http://www.pslc.ws/mactest/imide.htm

  43. Example of condensation polymerization E. Aromatic Polysulfone • amorphous polymer, good strength, good oxidation resistance, engineering plastic, membrane material • AMOCO PERFORMANCE Co. UDEL. • .

  44. Example of condensation polymerization F. Polybenzimidazole (PBI)

  45. Example of condensation polymerization

  46. 1961 Synthesized by Marvel • Some problems : • stoichiometric problems, side reactions, oxidatio,… • Celanese Co. (http://www.celanese.com) • not burn easily, self-extinguishing, but still expensive $45/lb in 1985

  47. Example of condensation polymerization G. Epoxy Prepolymers Structoterminal propolymer (epoxy end-group)

  48. Example of condensation polymerization X-linking • In this case, epoxy prepolymer is structure pendant prepolymer (OH terminated)

  49. Example of condensation polymerization Curing Agnet maleic anhydride pyromellitic anhydride phthalic anhydride • or • amines • Properties and Applications • Thermoset, high Chemical and solvent resistance, adhesion to many • substrates, impact resistance, structural applications

  50. Example of condensation polymerization H. Unsaturated Polyesters

More Related