Step Reaction Polymerization

1. P O L Y M E R C H E M I S T R Y AN INTRODUCTION Step Reaction Polymerization Malcolm P. Stevens

2. Distinguishing features of Chain- and Step Polymerizartion Mechanisms Step Polymerizations Chain Polymerizations • Any two molecular species can react. • Monomer disappears early. • Polymer MW rises throughout. • Growth of chains is usually slow (minutes to days). • Long reaction times increase MW, but yield of • polymer hardly changes. • All molecular species are present throughout. • Usually (but not always) polymer repeat unit has • fewer atoms than had the monomer. • Growth occurs only by addition of monomer to active chain end. • Monomer is present throughout, but its concentration decreases. • Polymer begins to form immediately. • Chain growth is usually very rapid (second to microseconds). • MW and yield depend on mechanism details. • Only monomer and polymer are present during reaction. • Usually (but not always) polymer repeat unit has the same • atoms as had the monomer Introduction to Polymer Chemistry

3. Condensation vs. Addition • Carothersoriginally classified polymers based on a comparison of the atoms in the monomer to the atoms in the polymer repeat unit. • Condensation polymers had fewer atoms in the repeat unit (i.e., some small molecule was emitted during polymerization). • Addition polymers had the same atoms as their monomers. Step polymerization by addition of alcohols to diisocyanates to form polyurethanes: Chain polymerization (ring opening of heterocycle) with loss of CO2 to form polypeptide. Introduction to Polymer Chemistry

4. A. Step-Reaction Polymerization - Kinetics Step-Reaction Polymerization Introduction to Polymer Chemistry

5. A. Step-Reaction Polymerization - Kinetics Introduction to Polymer Chemistry

6. A. Kinetics of Step-Growth Polymerization Introduction to Polymer Chemistry

7. A. Kinetics of Step-Growth Polymerization Introduction to Polymer Chemistry

8. A. Kinetics of Step-Growth Polymerization Introduction to Polymer Chemistry

9. B. Stoichiometric Imbalance • These are polyethers that are processed to an oligomer stage and are subsequently converted to network polymer by appropriate reactions of terminal epoxyide groups. • With polyimides for fiber applications, molecular weight must often be limited because too high a viscosity is detrimental to extrusion of filaments through the fine holes of a spinneret. Three ways to limit M. W. in step polymerization Introduction to Polymer Chemistry

10. B. Stoichiometric Imbalance Introduction to Polymer Chemistry

11. B. Stoichiometric Imbalance Introduction to Polymer Chemistry

12. B. Stoichiometric Imbalance Introduction to Polymer Chemistry

13. C. Molecular Weight Distribution Introduction to Polymer Chemistry

14. C. Molecular Weight Distribution Nx Introduction to Polymer Chemistry

15. C. Molecular Weight Distribution Introduction to Polymer Chemistry

16. C. Molecular Weight Distribution Introduction to Polymer Chemistry

17. C. Molecular Weight Distribution Introduction to Polymer Chemistry

18. D. Network Step-Polymerization : Theory of Gelation • If monomers containing a functionality greater than two are used in step polymerization, chain branching results. • If the reaction is carried to a high enough conversion, gelation occurs. • The onset of gelation, or gel point, is accompanied by a sudden increase in viscosity such that the polymer undergoes an almost instantaneous change from a liquid to a gel. Introduction to Polymer Chemistry

19. D. Network Step Polymerization Introduction to Polymer Chemistry

20. D. Network Step Polymerization Introduction to Polymer Chemistry

21. D. Network Step Polymerization Introduction to Polymer Chemistry

22. D. Network Step Polymerization Branching point Introduction to Polymer Chemistry

23. D. Network Step Polymerization Introduction to Polymer Chemistry

24. D. Network Step Polymerization Introduction to Polymer Chemistry

25. D. Network Step Polymerization Introduction to Polymer Chemistry

26. D. Network Step Polymerization Introduction to Polymer Chemistry

27. E. Step-Reaction Copolymerization Introduction to Polymer Chemistry

28. E. Step-Reaction Copolymerization Introduction to Polymer Chemistry

29. F. Step Polymerization Techniques Introduction to Polymer Chemistry

30. F. Step Polymerization Techniques Introduction to Polymer Chemistry

31. F. Step Polymerization Techniques Introduction to Polymer Chemistry

32. F. Step Polymerization Techniques Introduction to Polymer Chemistry

33. F. Step Polymerization Techniques Introduction to Polymer Chemistry

34. G. Dendritic Polymers Introduction to Polymer Chemistry

35. G. Dendritic Polymers Introduction to Polymer Chemistry

36. G. Dendritic Polymers Introduction to Polymer Chemistry

37. G. Dendritic Polymers Introduction to Polymer Chemistry

38. G. Dendritic Polymers Introduction to Polymer Chemistry

39. G. Dendritic Polymers Introduction to Polymer Chemistry

40. G. Dendritic Polymers Introduction to Polymer Chemistry

41. Commerically Important Polymers Prepared by Step-Reaction Polymerization • Carbonyl addition-elimination • Polyesters, polycarbonates, polyamides, polyimides... • Aromatic addition-elimination • Polysulfones, polysulfides, polyetherketones • Carbonyl addition-condensation • Phenol-formaldehyde and related polymers • Polymeric heterocycles • Addition to multiple bonds or epoxides • Polyurethanes • Epoxy polymers • Miscellaneous • Oxidative aromatic addition (polyphenylene oxide) • Acyclic diene metathesis (ADMET) • Aryl-aryl coupling • Reductive coupling (polysilanes) • Hydrolysis coupling (silicones) • Diels-Alder cycloaddition • Biradical coupling (polyxylylene) • Friedel-Crafts chemistry • SN2 reactions • and a host of others... Introduction to Polymer Chemistry

42. Carbonyl Addition-Elimination Step Polymerization : I. Polyester Mechanism : Structure-property relationships: I. Polyester Synthesis : Introduction to Polymer Chemistry

43. Carbonyl Addition-Elimination Step Polymerization : I. Polyester I. Polyester PBT Other commercially important polyester: PEN PET Introduction to Polymer Chemistry

44. Carbonyl Addition-Elimination Step Polymerization II. Polycarbonates III. Polyamides Introduction to Polymer Chemistry

45. Carbonyl Addition-Elimination Step Polymerization IV. Polyimide Introduction to Polymer Chemistry

46. Aromatic Addition-Elimination Polymerization Mechanism : This reaction is analogous to carbonyl addition-elimination, in that it is a two step process where the negative charge is accomodated by an electron withdrawing group. To emphasize the simularity, this example uses a ketone: Monomers : Bisphenols are most often used as the nucleophillic components. The chemistry begins when a base like NaOH or K2CO3 deprotonatea the bisphenol, as in this example for Bisphenol A: Krishnamurthy, S. J. Chem. Ed. 1982, 59, 543. Introduction to Polymer Chemistry

47. Aromatic Addition-Elimination Polymerization I. Poly(etheretherketone), ‘’PEEK’’ The most common form of PEEK is the one shown, derived from Bisphenol A. This polymer is a remarkable material, highly crystalline, thermally stable, resistant to many chemicals, very tough. It can be melt-processed at very high temperatures (>300 °C), and is useful for special applications like pipes in oil refineries and chemical plants, andparts for aerospace, where high price is not a limitation. Introduction to Polymer Chemistry

48. Aromatic Addition-Elimination Polymerization II. Polysulfone, ‘’PSF’’ Like polycarbonate, many other polysulfones could be synthesized, but the particular one shown here is by far the most common commercially, so that the general term "polysulfone" usually refers to this particular one. Worse, it is seldom called "poly(etherethersulfone)," despite its close structural similarity to PEEK Unlike PEEK, poly(etherethersulfone) is completely amorphous, probably a result of the relatively large size of the sulfonyl group, and the kink in the polymer backbone caused by the narrow C-S-C bond angle (close to 100°). Therefore, it can be processed at lower temperature than PEEK, but the material is not as resistant to heat and chemicals. Introduction to Polymer Chemistry

49. Carbonyl Addition-Condensation Polymerization III. Phenol-Formaldehyde Polymers IV. Polymeric Heterocycles Introduction to Polymer Chemistry

50. Carbonyl Addition-Condensation Polymerization • The phenol-formaldehyde polymers are the oldest commercial synthetic polymers, first introduced around 100 years ago. Their inventor, Leo Bakeland, had no idea what was happening in his reaction kettles, but he was able to work out conditions to produce a tough, light, rigid, chemically resistant solid from two inexpensive ingredients. He soon became a rich man, in the same class as the famous industrialists of the time like Alfred Nobel, Henry Ford, Andrew Carnegie, George Eastman, etc. • The actual chemistry is complicated, and still not competely understood. The polymers are usually thermosetting (i.e., crosslinked), and their insolubility limits the analytical techniques that can be brought to bear. The main reaction is the production of methylene bridges between aromatic rings, as shown below. Many side reactions also occur, and some of these give phenol-formaldehyde polymer its dark color. • Of course, these crosslinked polymers cannot be melted or dissolved, so their synthesis must be conducted in molds for the actual product. In practice, the polymerization is usually carried out to somewhere below the gel point in a separate reactor, and then the "pre-polymer" is transferred to the mold, where the reaction is completed. • Urea or melamine can be substituted for phenol. Methylene bridges can also be formed between the nitrogen atoms, giving rise to chemical relatives of the phenol-formaldehyde polymers. The urea and melamine based materials have much less color, and so are useful for decorative applications such as dinner plates and countertop materials (FormicaTM). Introduction to Polymer Chemistry