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CHEM 7010 Macromolecular Synthesis 2 nd Introduction to Polymer Synthesis: General Aspects of Polymer Structures on Po

CHEM 7010 Macromolecular Synthesis 2 nd Introduction to Polymer Synthesis: General Aspects of Polymer Structures on Polymer Properties 2011. Multidimensional Order of Structure-Property Relationships in Polymers. Microscopic *Crystallinity *Phases *Orientation. Molecular.

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CHEM 7010 Macromolecular Synthesis 2 nd Introduction to Polymer Synthesis: General Aspects of Polymer Structures on Po

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  1. CHEM 7010 Macromolecular Synthesis 2nd Introduction to Polymer Synthesis: General Aspects of Polymer Structures on Polymer Properties 2011

  2. Multidimensional Order of Structure-Property Relationships in Polymers Microscopic *Crystallinity *Phases *Orientation Molecular Microscopic Synthesis and Processing Molecular *Chemical Composition *MW/MWD *Branching and/or Cross-linking Macroscopic *Strength *Modulus *Impact Resistance Permeability Clarity Macroscopic

  3. IMPACT OF MOLECULAR WEIGHT ON MATERIAL PROPERTIES Increasing Degree of Polymerization, DP

  4. Vinyl Monomers, CH2=CH-X • XPolymer Abbreviation • H Polyethylene PE • CH3 Polypropylene PP • Cl Poly(vinyl chloride) PVC • Phenyl Polystyrene PSt • CN Polyacrylonitrile PAN • COOCH3 Poly(methyl acrylate) PMA • O-COCH3 Poly(vinyl acetate) PVAc

  5. Vinylidene Monomers, CH2=C(X)Y • XYPolymerAbbreviation • CH3CH3 Polyisobutylene PIB • ClCl Poly(vinylidene chloride) PVDC • F F Poly(vinylidene fluoride) PVDF • PhenylCH3 Poly(-methyl styrene) • CH3COOCH3 Poly(methyl methacrylate) PMMA • CNCOOR Poly(alkyl -cyanoacrylate

  6. Structural Complexity of Polymers • Homopolymers • Head to Tail vs. Head to Head Adducts e.g. a-olefins • 1,2- vs 1,4 Adducts; e.g. butadiene • Tacticity of Enchainments • Branching

  7. Tacticity • Isotactic • All asymmetric carbons have same configuration • Methylene hydrogens are meso • Polymer forms helix to minimize substituent interaction • Syndiotactic • Asymmetric carbons have alternate configuration • Methylene hydrogens are racemic • Polymer stays in planar zig-zag conformation • Heterotactic (Atactic) • Asymmetric carbons have statistical variation of configuration

  8. Structural Complexity of Polymers • Copolymers • Identity and Number of Comonomers • Ratio and Distribution of Comonomers • Statistical Alternating Gradient • Blocks Grafts

  9. Structural Complexity of Polymers • Molecular Weight • Molecular Weight Distribution, MWD • Polydispersity Index, PDI • Mn, Mw, Mz, Mv Averages • Crosslinking Density • Length of Crosslinks

  10. Structural Complexity of Polymers Time Dependent Changes • Chemical Reactions • Hydrolysis • Dehydrohalogenation • Photodegradation • Oxidation

  11. Structural Complexity of Polymers • Thermal Degradation • Processing • Aging • Crystallization • Changes in Polymorphism • Weathering-- Combination of Above • Plasticizer Loss -- Imbrittlement

  12. Microscopic Properties (Intermolecular Interactions) • Morphology • Chain entanglement –amorphous • Chain ordering--liquid crystalline • Crystallinity • Phase separations (microdomains)

  13. Types of Intermolecular Forces • Type of Force Relative Strength Low Molecular Analog Polymer • Dispersion orWeakMethane Polyethylene • Van der Waals Hexane Polypropylene • Dipole-Dipole Medium CH3Cl PVC CH3CO2CH3 PMMA Hydrogen bonding Strong H2O Cellulose CH3CONH2 Proteins ElectrostaticVery StrongCH3CO2-Na+Ionomers

  14. GLASS TRANSITION, Tg • Definition: The onset of seqmental motion of seqments with 40-50 carbons atoms • Physical Change Expansion of volume • Free volume required to allow segmental motion • Tg is an approximation • Depends upon measurement technique • Depends upon molecular weight • Polystyrene MW = 4000 Tg = 40C • = 300,000 = 100

  15. GLASS TRANSITION, Tg • Properties Affected • Specific Volume / Density • Specific Heat, Cp • Refractive Index • Modulus • Dielectric Constant • Permeability

  16. FACTORS INFLUENCING Tg • Tg is proportional to Rotational Freedom • For symmetrical polymers Tg, / Tm in K  1/2 • unsymmetical polymers  2/3 • 1. Chain flexibility • Silicone  Ether  Hydrocarbon  Cyclic HC  Aromatics

  17. FACTORS INFLUENCING Tg 2. Steric Bulk of Substituents • Tg = -120C 5C -24C -50C • Long side chains may act as plasticizers (C  6) • Tg = -55C 88C

  18. FACTORS INFLUENCING Tg • 3. Molecular Symmetry • Asymmetry increases chain stiffness. • 4. Polar Interactions increase Tg • Hydrogen bonding • 5. Molecular Weight up to Critical Limit • 6. Crosslinking • Reduces Segment Mobility

  19. FACTORS INFLUENCING Tm • 1. Chain flexibility • Silicone  Ether  Hydrocarbon  Cyclic HC  Aromatics • 2. Substituents Producing Lateral Dipoles • Hydrogen bonding • 3. Molecular Symmetry • Symmetry allows close packing

  20. FACTORS INFLUENCING Tm • 4. No Bulky Substituents to Disrupt Lattice if placement is Random • 5. Structural Regularity • monomer placement • head to tail • 1,2- vs 1,4- • 1,2- vs 1,3- vs 1,4- aromatic substitution • geometric isomers of enchainments • cis or trans -C=C-; cyclic ring • tacticity

  21. FACTORS REQUIRED TO PROMOTE CRYSTALLIZATION • Thermodynamic • 1. Symmetrical chains which allow regular close packing in crystallite • 2. Functional groups which encourage strong intermolecular attraction to stabilize ordered alignment.

  22. FACTORS REQUIRED TO PROMOTE CRYSTALLIZATION • Kinetic • 1. Sufficient mobility to allow chain disentanglement and ultimate alignment • Optimum range for mobility • Tm -10 Tg + 30 • at Tm segmental motion too high • at Tg viscosity too high • 2. Concentration of nuclei • concentration of nucleating agents • thermal history of sample

  23. Macroscopic Properties (Physical Behavior) • Tensile and/or Compressive Strength • Elasticity • Toughness • Thermal Stability • Flammability and Flame Resistance • Degradability • Solvent Resistance • Permeability • Ductility (Melt Flow)

  24. Step Polymerization (Polycondensation) After many repetitions: Polyethyleneterephthalate (PET)

  25. Step Polymerization Two Routes: A-A + B-B; or A-B 1 on 39 1 on 40 2 on 39 2 on 40 • Either way, need: • high conversion • stoichiometric amount

  26. Step vs. Chain Polymerization Step Polymerization • 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 hardly changes. • All molecular species are present throughout. • Usually (but not always) polymer repeat unit has fewer atoms than had the monomer.

  27. Step vs. Chain, cont. Chain Polymerization • Growth occurs only by addition of monomer to active chain end. • Monomer is present throughout, but its concentration decreases. • High polymer forms immediately. • MW and yield depend on mechanism details. • Chain growth is usually very rapid (seconds to microseconds). • Only monomer and polymer are present during reaction. • Usually (but not always) polymer repeat unit has the same atoms as had the monomer.

  28. Step Polymerization Concepts Comparison of Step and Chain Polymerization 1. Step: any 2 molecules in the system can react with each other Chain: chain growth occurs on end of growing polymer 2. Step: loss of monomer at early stage (dimers, tetramers, etc.) Chain: monomer concentration decreases steadily 3. Step: broad molecular weight distribution in late stages Chain: narrower distribution; just polymer and monomer

  29. Step Polymerization Basis for Kinetics (2-1a): 3 on 40 4 on 40 5 on 40 6 on 40

  30. Step Polymerization Basis for Kinetics: 1on 41 2 on 41

  31. Step Polymerization Basis for Kinetics (2-1b): NOTE: Assume equal reactivity of functional groups table 2.1on 42 Thus, assumption looks ok

  32. Step Polymerization Kinetics (2.2) Example: diacid + diol Mechanism (acid catalyzed): 2 on 44 1 on 45 2 on 45

  33. Chain Polymerization Concepts General Mechanism Initiation Propagation

  34. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1 3-1a. Comparison of Chain and Step Polymerizations Step: a. Monomer gone fast, get dimer, trimer, etc. b. MW increases with time c. No high mw until end Chain: a. Rapid high mw b. Snapshot: monomer, high poly, growing chains c. MW does not change with time

  35. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1 3-1b-1. General Considerations of Polymerizability Thermodynamics (Chain t-fer)

  36. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1 3-1b-2. Effects of Substituents on C=C monomers for Ionic Polymerization A. Initiation opportunities: 2 types of bond cleavage/resonance B. Radical, Anionic, Cationic: Depends on: i. Inductance ii. Resonance

  37. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1 3-1b-2. Effects of Substituents on C=C monomers for Ionic Polymerization C. Donating Groups Good for cationic • Inductance • Resonance • e.g. Polym of vinyl ether Example of resonance stabilization of cation by Delocalization of of positive charge. If oxygen not there, no stabilization

  38. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1 3-1b-2. Effects of Substituents on C=C monomers for Ionic Polymerization C. Donating Groups • ii. Resonance • e.g. Polym of Styrene

  39. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1 3-1b-2. Effects of Substituents on C=C monomers for Ionic Polymerization D. Withdrawing Groups i. inductance Good for anionic ii. resonance

  40. Chain Polymerization Concepts: Nature of Chain Polymerization; 3-1 3-1b-2. Effects of Substituents on C=C monomers for radical polymerization A. Radicals not affected by charge, but can have resonance stabilization B. Also stabilized by primary<secondary<tertiary Draw your own pic

  41. Chain Polymerization Concepts: Structural Arrangement of Monomer Units; 3-2 3-1a. Possible Modes of Propagation • A. Two possible points of attachment • i. On carbon 1: ii. On carbon 2:

  42. Chain Polymerization Concepts: Structural Arrangement of Monomer Units; 3-2 3-1a. Possible Modes of Propagation B. If attachment is regular, get head-to-tail (H-T) C. If attachment is irregular, get head-to-head (H-H) [and T-T]

  43. Chain Polymerization Concepts: Structural Arrangement of Monomer Units; 3-2 3-1a. Possible Modes of Propagation Usually only 1-2% H-H. How do we know? A. Chemical Methods B. NMR Methods (we’ll check this out in the Spectroscopy section)

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