Looking for a Tutor Near You?

Post Learning Requirement » x
Ask a Question
x

Choose Country Code

x

Direction

x

Ask a Question

x

Hire a Tutor
Agartala

Structure Of Polymer Chain

Home > PowerPoint Slides > Structure Of Polymer Chain
Published in: Chemical
2,276 Views

Introduction To Chain Formation.

Suranjana M / Aurangabad

19 years of teaching experience

Qualification: M.Tech (IIT,Kharagpur - 2000)

Teaches: Science, Chemistry

Contact this Tutor
  1. G.S.MandaI's Maharashtra Institute of Technology Aurangabad Department of Plastic & Polymer Engineering
  2. Course Code: PPE253 Course: Physical Chemistry of Polymers Pre-requisite: Organic Chemistry, Chemistry Credits: 4 Teaching Scheme: Theory: 4 hrs/week Class Test: 20 Marks Theory Examination: 80 Marks Theory Examination (Duration): 3 hrs Course Coordinator: Ms. S.MandaI Contact: Room no : 210 Contact hours: 12.15 pm to Ipm 3.00 pm to 3.15 pm Email: suranjana26@gmail.com
  3. Unit-I ' Structure of Polymer Chain: Introduction to chain conformation, configurations, isomerism and stereochemistry. Origin and types of stereoisomerism in polymers; factors influencing stereo-regulation, Conformation of Polymer Chain.
  4. Chain conformation Conformations are different spatial arrangements of a molecule that are generated by rotation about single bonds. Introduction to chain conformation, configurations, isomerism and stereochemistry
  5. Constitution: The constitution of a macromolecule describes the type and the order of the subunits (monomers) and the resulting molecular stlucture. Example: homopolymer altemating copolymer diblock copolymer graft-copolymer Other examples: statistical copolymer, star-polymer,
  6. Conformation ' Conformation refers to order that arises from the rotation of molecules about the single bonds ' thermal fluctuation of the bond length (3%) and bond angle (3-50) are small at room temperature ' rotations around the bonds are well possible
  7. Conformation Example: Well flexible macromolecule back-folded chain
  8. polymerization Monomer various long chains (molecules of polymers} Cot-figuration collection of these long chains In different conformztizns States and properties of Polymers (pias.tics, n„100ers ar fibers) polymer chains can be flexible or rigid (sit, non flexible} and polymers could be crystalline or amorphous. Conformation: 30 spatial arrangement of—toms or grouæs that is changed under the effect of thermal nwtion, but doesn't involve breaking ofchemica/
  9. Flexibility mechanism Degree of rotation about bond conformation Flexibility 1. Ethane (CH3.CH3) There are many Inssible conformaäons far ethane. However. Interaction bet'.veen H produæs energy maximum and minimum take the anfcrmaticn with lowest energy. 4 —dips-ed sta The s',mmétryof gives 3 equivalentminha and The energy barrier {zlipsed} is equal to k' nwl-l .. 2
  10. CONFORMATIONAL ANALYSIS OF ETHANE ' Ethane is the simplest hydrocarbon that can have distinct conformations. Two, the ' staggered conformation and the eclipsed conformation, deserve special attention. ' The C-H bonds the staggered in conformation are arranged ' so that each one bisects the angle made by a pair of C-H bonds on the adjacent carbon. ' In the eclipsed conformation each C-H bond is aligned with a C-H bond on the adjacent carbon. The staggered and eclipsed conformations interconvert by rotation around the carbonDcarbon bond. Different conformations of the same molecule are sometimes called conformers or rotamers.
  11. Staggered conformation of ethane
  12. Eclipsed conformation Of ethane
  13. (a) Wedge-and-dash (a) Wedge-and-dash H H H H H H (b) Sawhorse (c) Newman projection Some commonly used representations of the staggered conformation of ethane. (b) Sawhorse (c) Newman projection Some commonly used representations of the eclipsed conformation of ethane.
  14. Sawhorse repl'esentation t'JormaI line: 31-135ttLlEt1t in glare a: paper E roken line; qonq behind plane cf pape- Newman projection back carbon H Front carbon Heavy line; subsiüant. cam Jilt plara cf paper H • Sawhorse The representation: spatial orientation are indicated by employing heavy tapered lines for substituents coming out of the page, normal lines for substituents in the plane of the page, and dashed lines for substituents going back behind the plane of the page. this Newman projection: in representation one views the carbon-carbon bond directly end-on and represents the two carbon atoms by a circle. Lines going to the center of the circle represent substituents on the front carbon, and lines going to the edge of the circle represent substituents on the rear carbon.
  15. ' The structural feature that above figures illustrate is the spatial relationship between atoms on adjacent carbon atoms. Each H-C-C-H unit in ethane is characterized by a torsion angle or dihedral angle, which is the angle between the H-C-C plane and the C-C-H plane. ' The torsion angle is easily seen in a Newman projection of ethane as the angle between C-H bonds of adjacent carbons.
  16. Torsion Angle Torsion angle 00 Eclipsed Torsion angle 600 Gauche Isoc Torsion angle 1800 Anti Eclipsed bonds are characterized by a torsion angle of 00. When the torsion angle is approximately 600, we say that the spatial relationship is gauche; and when it is 1800 we say that it is anti. Staggered conformations have only gauche or anti relationships between bonds on adjacent atoms.
  17. Types of Strain Angle strain - expansion or compression of bond angles away from most stable o Torsional strain eclipsing of bonds on neighboring atoms Steric strain - repulsive interactions between o nonbonded atoms in close proximity RING STRAIN = combination of Angle Strain + Torsional Strain
  18. Torsional Strain Energy ' Force that opposes rotation due to the repulsion of bonding elect r O n S We do not observe perfectly free rotation There is a barrier to rotation, and some ' conformers are more stable than others ' Small energy barrier easily overcome at RT Each eclipsed H-H costs 4 kJ/mol of Torsional Energy
  19. 12 12 W;'mol eco b al 60 2.9 kcaL'n01 120 1 so Torsion angle, 240 300 Potential energy diagram for rotation about the carbon 360 — carbon bond in ethane. Two of the hydrogens are shown in red and four in green so as to indicate more clearly the bond rotation
  20. Ethane 600 eclipsed conformers 2.9 kcal/mol staggered conformers 1200 1800 2400 3000 3600 Degrees of rotation
  21. CONFORMATIONAL ANALYSIS OF BUTANE ' we consider conformations related by rotation about the bond between the middle two carbons (CH3CH2±CH2CH3). Unlike ethane, in which the staggered conformations are equivalent, two different staggered conformations occur in butane, shown in figure below. ' The methyl groups are gauche to each other in one, anti in the other. Both conformations are staggered, so are free of torsional strain, but two of the methyl hydrogens of the gauche conformation lie within 210 pm of each other. This distance is less than the sum of their van der Waals radii (240 pm), and there is a repulsive force between them. The destabilization of a molecule that results when two of its atoms are too close to each other is called van der Waals strain, or steric hindrance and contributes to the total steric strain. ' In the case of butane, van der Waals strain makes the gauche conformation approximately 3.2 kJ/moI (0.8 kcal/mol) less stable than the anti
  22. Butane 1 the bond 2 3 4 butane the C-1—C-2 bond H the C-3—C-4 bond c-1 .3 CH2CH3 c-2 CH2CH3 staggered conformation for rotation about the C-1—C-2 bond in butane eclipsed conformation for rotation about the C-1—C-2 bond in butane
  23. CH3 4.5 kcal/mol - —c-3 3.8 kcal/mol 0.9 kcal/mol 600 1200 2400 3000 4.5 kcal/mol 360' 1800 Dihedral angle Potential energy of butane as a function of the degree of rotation about the C 2 bond. Letters refer to the conformers (A-F) shown above.
  24. Potential energy, kcal/mol Potential energy, kJ/mol
  25. ' Figure in slide no 22 illustrates the potential energy relationships among the various conformations of butane. The staggered conformations are more stable than the eclipsed. 'At any instant, almost all the molecules exist in staggered conformations, and more are present in the anti conformation than in the gauche. ' The point of maximum potential energy lies some 25 kJ/moI (6.1 kcal/mol) above the anti conformation. The total strain in this structure is approximately equally divided between the torsional strain associated with three pairs of eclipsed bonds (12 kJ/moI; 2.9 kcal/mol) and the van der Waals strain between the methyl groups.
  26. ' Arithmetically, the total strain energy (Es) of an alkane or cycloalkane can be considered as Es—E band stretching -f- E torsional + angle bending van der Waals where ' Ebond stretching is the strain that results when C-C and C-H bond distances are distorted from their ideal values of 153 pm and 111 pm, respectively. ' Eangle bending is the strain that results from the expansion or contraction of bond angles from the normal values of 109.50 for sp3 hybridized carbon. ' Etorsional is the strain that results from deviation of torsion angles from their stable staggered relationship. ' Evan der Waals is the strain that results from "nonbonded interactions."
  27. The bonds that are axial in one chair conformer are equatorial in the other chair conformer. The bonds that are equatorial in one chair conformer are axial in the other chair conformer. push this carbon up flagpole hydrogens boat conformer Of cyclohexane 5 Cyclohexane pull this carbon down ring-flip 6 CH cR2 6 4 Newman projection of the boat conformer 5 ball-and-stick model of the boat conformer of cyclohexane The boat conformer of cyclohexane and the Newman projection of the boat conformer
  28. 12.1 kcal chair half-chair 8 kcal boat half-chair twist-boat twist-boat 5.3 kcal Diagram showing the con- formers of cyclohexane (and their relative energies) as one chair conformer interconverts to the other chair conformer. chair
  29. Assignment I (submission 31st January, 2018) ' Of the three conformations of propane shown, which one is the most stable? Which one is the least stable? Why? (a) (c) Sight down the C-2±C-3 bond, and draw Newman projection formulae for the (a) Most stable conformation of 2,2-dimethyIbutane (b) Two most stable conformations of 2-methylbutane (c) Two most stable conformations of 2,3-dimethyIbutane
  30. End to End Distance, Adapted from Fig. 14.6, Callister 7e.
  31. Configuration describes the spatial position of atoms within the molecule: The geometrical in arrangement polymers arising from the order of atoms determined by chemical bonds. The regularity and symmetry of the side-groups can affect strongly the properties of polymers. Side groups are atoms or molecules with free bonds, called free-radicals, like H, O, methyl, etc. • The configuration of a polymer cannot be altered unless chemical bonds are broken and reformed. asymmetric C-atom all substituents are different
  32. ' Configurational isomers - separable isomers that do not readily interconvert chiral centers - absolute stereochemistry sp3 carbons (or nitrogens, or ...) chiral-handed (left or right) enantiomers (enantio = opposite) non-identical (non-superimposable) mirror image R = recto (right-handed) S = sinestro (left-handed) behind plane forward of the plane
  33. Priority Rules at the chiral center: 1. 2. 3. atomic number priority 4, largest atomic number first if atoms same, go to next atom c O C—C is C--C, C O is ...........C) isotopes higher atomic mass view with lowest priority group away 1 3 1 2 2 s 3
  34. ' Configurational isomers separable isomers that do not readily interconvert. Most would require "breaking" and "making" of bonds. ' a. cis-trans (olefins) ' b. chiral centers - absolute stereochemistry Configurational isomers c c.H5 trans E (entgegen) (opposite) cis and trans olefins Note: no acetylenes H3C c.H5 NH CIS Z (zusammen) (together) Rules: 1. largest atomic number first SO > 7N > 6C 2. if same, go to second atonm 3 . most substituted c •c
  35. Molecular Structures Covalent chain configurations and strength: Linear Cross-Linked Branched Network Direction of increasing strength Adapted from Fig. 14.7, Callister 7e.
  36. Polymers — Molecular Shape Configurations — to change must break bonds ' Stereoisomerism —c—c D or mirror plane —c—c 36
  37. cis/trans Isomerism CH3\ C=C —C 1-12 cis cis-isoprene (natural rubber) bulky groups on same side of chain C 1-13 \ c=c —C 1-12 trans trans-isoprene (gutta percha) bulky groups on opposite sides of chain 37
  38. Assignment Il (submission 31st January, 2018) ' What is the difference between configuration and conformation (use examples)? Which configurational isomers are important for polymers? Which ones are likely to form crystalline structures?
  39. Extra Reading on Conformation and Configuration http://sIidepIayer.com/sIide/8459490/ http://ocw.polytechnic.edu.na/courses/materials-science-and- engineering/3-091sc-introduction-to-soIid-state-chemistry-faII- 2010/organic-materiaIs/28-poIymers-structure-composition/ https://www.youtube.com/watch?v=yWwxFmyZNfg http://sIidepIayer.com/sIide/4395311/ http://www.open.edu/openlearn/science-maths- technology/science/chemistry/introduction-polymers/content- section-2.3.3#fig002-004
  40. About NR and Gutta Percha Gutta Percha and Natural rubber (Refer Goodman1974thermopropertiesGP.pdf) ' https://books.googIe.co.in/books?id=OX4cQus2gz8C&pg=PA659&Ipg=PA 659&dq=why+gutta+percha+is+more+crystaIIine&source=bI&ots=66tJvIe sjBpeHYAhWJv18KHVCGBaMQ6AEIVDAF#v=onepage&q=why%20gutta%2 Opercha%20is%20more%20crystaIIine&f=faIse
  41. Stereoisomers Compounds with atoms connected in the same order o but which differ in three-dimensional orientation, are stereolsomers The terms "cis" and 'trans" should be used to specify stereoisomeric ring structures Constitutional isomers (different connections between atoms) Stereoisomers (same connections but different three- dimensional geometry} ThamnTl CH3 CH3 and and H3C CH3
  42. Tacticity: ' The orderliness of the succession of configurationally repeating units in the main chain of a polymer molecule (important for crystallization). ' if the radicals are linked in the same order, the configuration is called isotatic ' in a stereoisomer in a syndiotactic configuration, the radical groups are at alternative sides in the chain ' in the atactic configuration, the radical groups are positioned at random
  43. Tacticity Tacticity — stereoregularity of chain isotactic — all R groups on same side of chain syndiotactic — groups alternate Sides H H C H H H C H H H H H H C H H atactic — groups random H C H C H H H H C H H H H H H 43
  44. Styrene monomer Isotactic PS (highly crystalline) Syndiotactic PS (semi-crystalline) Atactic PS (amorphous)
  45. Stereochemistry of repeating units Chiral centers Br—CLCl CH3 Cl CH3 Mirror Figure 2.2 Two optical isomers of the same compound as mirror images (11b Chemically identical but they rotated plane-polarized light in opposite directions.
  46. Tacticity in polymers Polymerization of monosubstituted ethylene CH2=C —CH Pseudochiral center
  47. ? —? ? ? ? ? ? —lc— —?—? ? —?—?— ? ? ? 3) ? ? R ? ? R ? ? ? ? ? ? ? ? R ? ? ? R ? ? ? ? ? ? ? ? ? ? R ? ? R R ? ? ? ? ? ? ? ? ? ? R ? ? isotactic syndiotactic atactic
  48. Figure 2.3 Isotoctic Syndiotoctic Aloctit Three different configurations of a monosubstituted polyethylene,
  49. 5 5 5 5 ? ? 5 5 5 5 5 ? ? 14 ? 14 ? ? 1-1 ? 5 ? ? 5 5 ??????-?????
  50. Figure 2.4 Isotactic and syndiotactic structures of poly(vinyl chloride). Allyn and Bacon Molecular Model Set for Organic Chemistry.
  51. 2.4.3 Substitutional isomerism Synthesis of diene type polymers —c H c I H I II 2 H H c H c H H c I 1*2-addition H I H I 'H 1 ,4-addition 1,2 addition polymerization isoprene
  52. Extra Reading on Stereoisomerism http://www.open.edu/openlearn/science-maths- technology/science/chemistry/introduction-polymers/content- section-2.3.4
  53. Thank You

Need a Tutor or Coaching Class?

Post an enquiry and get instant responses from qualified and experienced tutors.

Post Requirement

Related PPTs

Upload PPTs

If you have your own PowerPoint Presentations which you think can benefit others, please upload on LearnPick. For each approved PPT you will get 50 Credit Points and 50 Activity Score which will increase your profile visibility.

Upload Now