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What are polyolefins

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What are polyolefins

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    1. June 13, 2012 Polyolefins 1 What are polyolefins?

    2. June 13, 2012 Polyolefins 2 Cracking furnace

    3. June 13, 2012 Polyolefins 3 Polyethylene

    4. June 13, 2012 Polyolefins 4 Free-radical polymerization mechanism

    5. June 13, 2012 Polyolefins 5 Free-radical polymerization mechanism

    6. June 13, 2012 Polyolefins 6 Free-radical polymerization mechanism

    7. June 13, 2012 Polyolefins 7 Free-radical polymerization mechanism

    8. June 13, 2012 Polyolefins 8

    9. June 13, 2012 Polyolefins 9 Rate laws

    10. June 13, 2012 Polyolefins 10 Chain transfer reactions

    11. June 13, 2012 Polyolefins 11 Mayo Equation

    12. June 13, 2012 Polyolefins 12 Example… Listed below are data generated by the experimental polymerization of methyl methacrylate (MMA). The initial concentration of MMA, [M]o, is assumed to be 9.35 mol/l. The %-CTA is the mole percent chain transfer agent (CTA) with respect to monomer. Using the data in the table below, calculate CCTA.

    13. June 13, 2012 Polyolefins 13 Solution…

    14. June 13, 2012 Polyolefins 14 Long-chain branching

    15. June 13, 2012 Polyolefins 15 Long-chain branching

    16. June 13, 2012 Polyolefins 16 Short-chain branching

    17. June 13, 2012 Polyolefins 17 Short-chain branching

    18. June 13, 2012 Polyolefins 18 Life cycle of polyolefin materials

    19. June 13, 2012 Polyolefins 19 High-density polyethylene (HDPE) Made with Ziegler-Natta catalyst Has lower degree of branching (0.5-3 vs. 15-30 side chains/500 monomer units), why?. Higher crystallinity compared to LDPE. HDPE has greater rigidity than LDPE. It has higher tensile strength, stiffness, and chemical resistance, BUT lower permeability, and resistance to stress crack.

    20. June 13, 2012 Polyolefins 20 Linear low-density polyethylene (LLDPE) A copolymer of ethylene and a-olefins, generally 1-butene, 1-ohexene, or 1-octene. It is equivalent to LDPE. LDPE is supplemented by LLDPE; BUT not always. It is produced in gas-phase reactors (T ~ 80 ŗC and P ~ 20 bar).

    21. June 13, 2012 Polyolefins 21 Polyethylene

    22. June 13, 2012 Polyolefins 22 Polypropylene Second most important commercial polyolefin. Isotactic PP density (0.90-0.91 g/mL). High crystalline melting point (165-175 ŗC). Ziegler-Natta catalyst is used to produce it.

    23. June 13, 2012 Polyolefins 23 Polyethylene

    24. June 13, 2012 Polyolefins 24

    25. June 13, 2012 Polyolefins 25 PE and PP consumption

    26. June 13, 2012 Polyolefins 26 POs vs. other plastics

    27. June 13, 2012 Polyolefins 27 Tacticity

    28. June 13, 2012 Polyolefins 28 Pendant groups Small chains of atoms attached to the backbone. Just have few atoms.

    29. June 13, 2012 Polyolefins 29 Definitions Stereoisomers are molecules whose atomic connectivity is the same but whose atomic arrangement in space is different. Stereocenter is any atom in a molecule bearing groups such that an interchanging of any two groups lead to stereoisomer.

    30. June 13, 2012 Polyolefins 30

    31. June 13, 2012 Polyolefins 31 Factors controlling stereo-arrangement The degree of branching. The pendant methyl sequence. Stereoselectivity.

    32. June 13, 2012 Polyolefins 32 Random PP copolymers It contains up to 6% of ethylene or other comonomers The introduction of comoner(s) results in discontinuity that reduces PP crystallinity. Random copolymers are used where clarity, lower melting point or lower modulus is required. MWD play similar role for the properties of the random copolymers.

    33. June 13, 2012 Polyolefins 33 Impact (heterophasic) copolymers Contains up to 40 % ethylene-propylene rubber (EPR) regularly distributed inside the PP matrix. It improves impact properties of the polymer. It gives a good balance between stiffness-impact strength. The relationship between the structure and PP heterophasic copolymer properties is complex.

    34. June 13, 2012 Polyolefins 34 Ziegler-Natta catalyst The catalyst consists of two components: Transition metal salt, TiCl4 Main-group metal alkyl, cocatalyst. Z-N catalysts could be: Homogeneous. Heterogeneous, usually supported on MgCl2. What are the possible effects???

    35. June 13, 2012 Polyolefins 35 Z-N catalysts Cocatalysts Triethyl-Aluminum (TEA) Triiso-butyl-Aluminum (TIBA) Used for: Electro donors Donors effect: Increases catalyst activity Improve the crystallinity of the produced polyolefin Affect on MWD.

    36. June 13, 2012 Polyolefins 36 Mechanisms proposed for the action of donors Lewis base coordinates to a Mg ion neighboring a less isoselective Ti site. It influences the active site via both steric and electronic effects. By the addition of the donor, the isotacticity of the highly isotactic site is improved. Part of a less isotactic sites are transformed to a highly isotactic sites. The activity of less isotacitic sites decreases.

    37. June 13, 2012 Polyolefins 37 Z-N generations

    38. June 13, 2012 Polyolefins 38 Pentad (mmmm)

    39. June 13, 2012 Polyolefins 39

    40. June 13, 2012 Polyolefins 40 Philips catalyst Based on Cr (IV) supported on silica and alumina. It is true structure is not well-understood. Active sites are created by the mixture CrO3/SiO2. Active sites are produced by thermal activation at high temperatures, ~ 600 ŗC. Hydrogen is not chain-transfer agent and it has negative effect on catalyst reactivity.

    41. June 13, 2012 Polyolefins 41 Metallocene catalysts

    42. June 13, 2012 Polyolefins 42 Metallocene catalysts

    43. June 13, 2012 Polyolefins 43 Metallocene catalysts

    44. June 13, 2012 Polyolefins 44 Metallocene catalysts

    45. June 13, 2012 Polyolefins 45 Metallocene catalysts Advantages: Narrow MWD. More sensitive to hydrogen. Produce polymers with very high melt index. Disadvantages: Low activity.

    46. June 13, 2012 Polyolefins 46

    47. June 13, 2012 Polyolefins 47 Mechanism of polyolefin polymerization

    48. June 13, 2012 Polyolefins 48 Insertion mode

    49. June 13, 2012 Polyolefins 49 Chain termination Chain transfer with hydrogen

    50. June 13, 2012 Polyolefins 50 Chain termination ß-hydride elimination

    51. June 13, 2012 Polyolefins 51 Bimetallic polymerization mechanism

    52. June 13, 2012 Polyolefins 52 Catalyst deactivation Over-reduction of active centers, Ti3+. The formation of dormant sites. Reaction of active sites with polar impurities. Physical deactivation. Formation of a stable complex.

    53. June 13, 2012 Polyolefins 53 Rate behavior

    54. June 13, 2012 Polyolefins 54 Why studying kinetics is difficult the presence of different types of active sites on its surface the activity decay during the polymerization the chemical modification of the components of the catalyst during the time the influence of the procedure of contact of catalyst components on the rate of stereospecificity of the polymerization.

    55. June 13, 2012 Polyolefins 55 Free-radical vs. coordination polymerization

    56. June 13, 2012 Polyolefins 56 Polymerization kinetics

    57. June 13, 2012 Polyolefins 57 Polymerization rate equation

    58. June 13, 2012 Polyolefins 58 Termination probability

    59. June 13, 2012 Polyolefins 59 Flory distribution One type of active sites is considered. The ratio of chain termination reactions to the chain propagation reactions does not depend on the chain length. Each chain termination reaction produces one polymer chain. There are no cross-linking or other side reactions. A quasi steady-state assumption is applicable.

    60. June 13, 2012 Polyolefins 60

    61. June 13, 2012 Polyolefins 61 Particle fragmentation during polymerization reaction

    62. June 13, 2012 Polyolefins 62 Effect of operating conditions on kinetics and MWD Hydrogen effect - Polypropylene Kinetics Polymerization rate increases with increasing H2 concentration. Possible reasons: Increase in active sites number Change in oxidation states Dormant sites theory MWD Mw decreases with increasing H2 concentration. PDI relatively increases with increasing H2 concentration. (Why????)

    63. June 13, 2012 Polyolefins 63 Effect of operating conditions on kinetics and MWD Hydrogen effect - Ethylene Kinetics H2 effect is highly dependent on catalyst type. For Z-N catalyst, Rp ? H2 ? Possible reasons: Formation of stable Mt-H bond Ethylene hydrogenation MWD Mw ? with ? H2 H2 effect on PDI is highly dependant on catalyst type

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