Hanyang Univ. Spring 2007 Classification by Mechanism  Step – Growth  Chain – Growth Classification by Type  Condensation  Addition Classification by Bond  Radical  Ion Chap 8. Polycondensation Reactions For further details, Click next homepage. Surfing to the internet

Hanyang Univ. Spring 2007 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 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. MnMn % Conversion − Radical Living Step Growth What are differences between step and chain growth polymerizatoin?

Hanyang Univ. Spring 2007 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

Hanyang Univ. Spring 2007 Characteristics of Step-Growth Step-growth polymerization principle was used by Carothers in Synthesis of Ester 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. It seemed to him more likely that one would get long chainlike macromolecules like this

Hanyang Univ. Spring 2007 JACS (Journal of American Chemical Society, 51, P (1929)) “Polyintermolecular condensation requires as starting materials compounds in which at least two functional groups are present in the same molecule” Characteristics of Step-Growth

Hanyang Univ. Spring 2007 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 + H 2 N  R`  NH 2  polyurea Equal Functional Group Reactivity Concept

Hanyang Univ. Spring 2007 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. Equal Functional Group Reactivity Concept

Hanyang Univ. Spring 2007 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 G P = H P  TS P : this equation is the basic of understanding about polymerization, depolymerzation equilibrium Equal Functional Group Reactivity Concept

Hanyang Univ. Spring 2007  G P = G polymer  G monomer = (H P – H m ) – T(S P – S m ) =  H P – T  S P Where  H P : enthalpy change per monomer unit  S P : entropy change per monomer unit  G P < 0  Polymerization is spontaneous  G P > 0  Polymerization is not possible  G P = 0  monomer  polymer at this temperature is ceiling temperature. (for both step and chain growth) Equal Functional Group Reactivity Concept

Hanyang Univ. Spring 2007 II. Kinetic Approach “A negative  G P 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. Equal Functional Group Reactivity Concept

Hanyang Univ. Spring 2007 Step Growth Polymerization

Hanyang Univ. Spring Polyesterification by esterinterchange 2. Polyesterification and polyamidation by Schotten-Baumann Reaction O x OO R" (OCR' C O R ) OH + (2x 1)R" OH O xHO R OH +xR"OCR' C O R" Step Growth Polymerization

Hanyang Univ. Spring Amidation by thermal dehydration of ammonium salt 4. Reaction of OCN  R  NCO + HO  R’  OH  polyurethane H 2 N  R’  NH 2  polyurea n 46 H NH (CH 2 ) NH CO (CH 2 ) CO OH + (2n 1) H 2 O ++ 6 H 3 N(CH 2 ) NH 3 4 OOC(CH 2 ) COO n 4 6 n H 2 N(CH 2 ) NH 2 +n HOOC(CH 2 ) COOH Step Growth Polymerization

Hanyang Univ. Spring 2007 Well-studied, well characterized rexns Well-understood rexns at least on an empirical basis. Step Growth Polymerization For further details, Click next homepage. rvices/nylon/other/step/step.html Surfing to the internet

Hanyang Univ. Spring 2007 W. Carothers In step-growth polymerization, Carother's equation gives the number-average degree of polymerization, X n, for a given fractional monomer conversion, p.step-growth polymerization P = extent of reaction [M]= concentaration of monomer Carother’s Equation P DP n When P = DP n = 200.

Hanyang Univ. Spring 2007 Generalized Carother's Eq. Carother’s Equation f = number of average functional group per monomer N 0 = number of initial monomers N 0  f = number of initial functional group N = number of final molecules (monomer, dimer,  polymer)

Hanyang Univ. Spring 2007 ex) monomer=10, f  g= 20 final molecules= 2 Carother’s Equation For further details about W.Carothers Click next homepage. es/chemach/pop/whc.html Surfing to the internet

Hanyang Univ. Spring 2007 DP n  200 Polymer yield = 99.5% P =  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 Four Requirements of Polycondensation Exact (on known) equivalence of functional groups. Molecular Weight Control of Polycondensation Reaction Equivalence of Functional Groups.

Hanyang Univ. Spring 2007 A. Types of monomer a. AB type b. AA and BB type c. Three functional groups for crosslinked polymers Kinetics (ref. chap 11 in book)

Hanyang Univ. Spring 2007 B. Condensation of difunctional monomers. a. b. HOCH 2 CH 2 OH H+H+ (-H 2 O) H 2 NCH 2 CH 2 CH 2 CO 2 H ∆ (-H 2 O) Kinetics (ref. chap 11 in book)

Hanyang Univ. Spring 2007 Kinetics (ref. chap 11 in book) Polyesterfication as an example of polycondensation - d[COOH] / dt = k [COOH][OH][acid] Assumption : without strong acid catalyst condition, pure monomer and correct equivalent - d[COOH] / dt = k 3 [COOH] 2 [OH] -COOH is considered as acid catalyst - d[COOH] / dt = k 3 [COOH] 3 [COOH] = [OH] integral eqn 1 / [COOH] 2 = 1 / [COOH] k 3 t 1 / (1-P) 2 = 1+2[COOH] 0 2 k 3 t P = 1 – [COOH] / [COOH] 0 k

Hanyang Univ. Spring d[COOH] / dt = [COOH] 2 (k 3 [COOH] + k cat [ H + ] ) k cat » k 3 k 3 can be neglected. -d[COOH] / dt = k 2 [COOH] 2 k 2 = k cat [H + ] integral eqn 1 / (1-P) = 1 + k 2 [COOH] 0 · t Kinetics (ref. chap 11 in book) [COOH] = [COOH] 0 (1-P) If you know the value of K 2, you can calculate DP n at any time Assumption : with strong acid catalyst condition, pure monomer and correct equivalent

Hanyang Univ. Spring 2007 Kinetics (ref. chap 11 in book) ex) k 2  10 –2 l mole  1 sec  1, C 0  3 mole  sec  l  1, DP n =50 ( k 2 = k cat [H + ] ) Reaction time = ? if k 2  10 –4 l mole  1 sec  1 Reaction time = ? less than 30 min about 45 hr

Hanyang Univ. Spring 2007 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 finding x -mer = P x  1 (1-P) Kinetics Mw distributions of linear condensation polymers

Hanyang Univ. Spring 2007  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 P=0.95 P=0.98 P=0.99 NxNx Kinetics

Hanyang Univ. Spring MWD Kinetics

Hanyang Univ. Spring 2007 Target Molecular weight DP n is time – dependent 1) Quench (cooling) the polymerization at pre- determined time heating unstable react as heating  undesirable Molecular Weight Control

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

Hanyang Univ. Spring 2007 Nylon 66: Adding lauric acid or acetic acid, MW control Possible melt spinning through viscosity control melt viscosity mw undesirable Molecular Weight Control

Hanyang Univ. Spring 2007 Assume B-B unit slightly in excess N A : number of A functional group N b : number of B functional group r = N A / N b = feed ratio P : rate of A group at t rP : rate of B group at t Initial total number of molecules = (N A + N B ) / 2 Number of unreacted A= N A (1―p) Number of unreacted B = N B (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 = [N A (1―p)+ N B (1―r p)]/2 Molecular Weight Control

Hanyang Univ. Spring 2007 A. Greater than two functionality polymers. a. Alkyd-type polyester : b. Phenol-formaldehyde resin : c. Melamine-formaldehyde resin : Network Step Polymerization

Hanyang Univ. Spring 2007 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. Network Step Polymerization

Hanyang Univ. Spring 2007 C. Gel point conversion. : critical reaction conversion. : average functionality. Network Step Polymerization

Hanyang Univ. Spring 2007 D. Examples of gel point conversion. 3mol of 12mol of 4 Gel point conversion : 77% (Experiment) 83% (Calculate) Network Step Polymerization

Hanyang Univ. Spring 2007 DPn  ∞ N i :Monomer have functional group, f i ex) 2mole Glycerol 6OH 3mole Phthalic Acid 6COOH total 5 mole 12 f.g N, N o, N o f avg =total functional group 2( N o - N) = number of functional group after reaction Carother’s Equation where DPn  ∝ = critical extent of reaction at gel point In case of ex. P c = 2/2.4 = 0.833

Hanyang Univ. Spring 2007 A.Polyester (Dacron, Mylar) ester interchange rexn is faster than direct esterification. It is difficult to purify diacid. Methyl ester is used commonly. For termination, alcohol is removed by distillation of reaction mixture. Example of condensation polymerization For further details about Polyester Click next homepage. Surfing to the internet

Hanyang Univ. Spring Example of condensation polymerization

Hanyang Univ. Spring  nylon salt B. Nylon 66 For further details about Nylon Click next homepage. Surfing to the internet Example of condensation polymerization

Hanyang Univ. Spring 2007 Kevlar poly(p-phenylene terephthalamide) -high strength C. Aromatic Polyamide For further details about Kevlar and Nomex Click next homepage. Surfing to the internet Example of condensation polymerization

Hanyang Univ. Spring 2007 Nomex poly(m-phenylene isophthalamide) -very good high temperature resistance The electron density of NH 2 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. Example of condensation polymerization * Coordinated covalent bond by using Li ion

Hanyang Univ. Spring 2007 D. Aromatic Polyimides Example of condensation polymerization

Hanyang Univ. Spring 2007 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 -70 o C The poly(amic acid) is cyclized over 150 o C. Aromatic polyimide is very high heat resistance, Kapton, H-film To improve solubility of poly(amic acid), CH 2 group is introduced in aromatic amine or isocyanate is used instead of amine. For further details about Polyimides Click next homepage. Surfing to the internet Example of condensation polymerization

Hanyang Univ. Spring 2007 amorphous polymer, good strength, good oxidation resistance, engineering plastic, membrane material E. Aromatic Polysulfone AMOCO PERFORMANCE Co. UDEL.. Example of condensation polymerization

Hanyang Univ. Spring 2007 F. Polybenzimidazole (PBI) Example of condensation polymerization

Hanyang Univ. Spring 2007 Example of condensation polymerization

Hanyang Univ. Spring Synthesized by Marvel Some problems : stoichiometric problems, side reactions, oxidatio,… Celanese Co. ( not burn easily, self-extinguishing, but still expensive $45/lb in 1985

Hanyang Univ. Spring 2007 Structoterminal propolymer (epoxy end-group) G. Epoxy Prepolymers Example of condensation polymerization

Hanyang Univ. Spring 2007 X-linking In this case, epoxy prepolymer is structure pendant prepolymer (OH terminated) Example of condensation polymerization

Hanyang Univ. Spring 2007 phthalic anhydride maleic anhydridepyromellitic anhydride Curing Agnet Example of condensation polymerization or amines Properties and Applications Thermoset, high Chemical and solvent resistance, adhesion to many substrates, impact resistance, structural applications

Hanyang Univ. Spring 2007 H. Unsaturated Polyesters Example of condensation polymerization

Hanyang Univ. Spring 2007 brittleness, softness depends on X-linking densityh. Applications: bowling ball, helmet, auto part, air con Example of condensation polymerization

Hanyang Univ. Spring 2007 Lexan  from GE Tm = 270°C, Tg=150°C high impact resistance, transparency, packaging, phone dial ring, process similar to polyester synthesis 2stage, ① vaccum at 200°C ② 300°C I. Polycarbonate Example of condensation polymerization

Hanyang Univ. Spring 2007 J. Poly urethane Example of condensation polymerization

Hanyang Univ. Spring 2007 diamine in water Polymer film forming at the interface diacid chloride in organic solvent Interfacial Polymerization

Hanyang Univ. Spring 2007 Nylon-6,6

Hanyang Univ. Spring 2007 Since the reactants are in different phases, they can only react at the phase boundary. Once a layer of polymer forms, no more reaction occurs. Removing the polymer allows more reaction to occur. Nylon-6,6