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Free-Radical polymerization

Ashlin Deatherage polymer chem English 104 cards

Free-Radical polymerization

Cards in this deck (104)

  1. 1why are tertiary radicals the most stablethe alkyl groups act as electron donating groups to stabilize the the empty pi orbital of the radical carbon (hyper congugation)
  2. 2the most common type of radical polymerizationchain polymerization
  3. 3radicals are generated bylight or heat
  4. 4during radical polymerization, polymerization continues untilall monomers have been reacted or the chain is interupted
  5. 5couplingwhen radicals join together
  6. 6draw and describe a disproportionation reaction with free radicalstwo radicals, C-H bond on one is broken, one radical from the bond joins with the molecules radical to form a double bond, the other radical from the bond forms a new C-H bond with the other molecule, a double bind is formed and a hydrogen is transferred
  7. 7Cl and Br are not good initiators bctheir radicalization is hard to control
  8. 8name 2 good radical initiatorsperoxides and azo compounds
  9. 9draw and describe the mechanism of radical chain transfer propagationa double bond (monomer) is broken and a radical(from initiator) forms a bond with a radical (from monomer) and the other radical is left on the more hendered carbon, the cycle continues
  10. 10name the types of chain transfer terminationscombination, disproportionation,
    transfer agent, transfer to solvent, transfer to monomer, transfer to initiator, transfer to polymer
  11. 11describe radical chain transfer, combination terminiationtwo chains containing radicals combine together to form bond
  12. 12disproportionation is a type ofradical chain polymerization termination
  13. 13describe chain termination with a transfer agentthe bond between of a transfer agent is broken and the transfer agents radical forms a bond with the radical polymer chain to stop polymerization
  14. 14in chain transfer, the number of radicals isalways the same
  15. 15describe transfer to solvent terminationa proton from a solvent, like toluene is donated to the radical chain and toluene becomes radicalized
  16. 16describe transfer to monomer terminationharder to control bc of propagating monomers, the alpha hydrogen bond on a radical chain is broken, the radical forms a double bond with other radical on chain, and the double bond of the monomer forms a bond with the hydrogen and a radical. results in alpha to beta hydrogen shift
  17. 17transfer to initiatorinitiator bond is broken, and half the initiator form a bond with radical chain, and the other half becomes a radical initiator.
  18. 18transfer to polymer termination can beintramolecular or intermolecular
  19. 19intramolecular transfer to polymer terminationaka back biting, a hydrogen on a radical chain is transferred to the radical, and the radical moves.
  20. 20intermolecular transfer to polymer terminationthe radical of one polymer chain forms a bond with a hydrogen (anywhere) on another chain and the radical moves to the other chain.
  21. 21name one example to remove radicalsUse of TEMPO
  22. 22olefin is aalkene
  23. 23mono-substituted olefins =vinyl monomers
  24. 24to start with initiation, the bond of the initiatormust be weak
  25. 25two water soluble initiators areredox and persulfate initiators
  26. 26redox initiatorsinvolves a reduction-oxidation cycle to produce radicals. an example is iron (II) and hydrogen peroxide producing iron(III) and a hydroxyl radical
  27. 27persulfate initiatorpersulfate forms a sulfate radical with heat and metal cation
  28. 28the mechanism of propagation is dependent onthe relative radical stability and steric interactions
  29. 29because of steric interactions ___ placement is more common1,3- also called head to tail, versus 1,2 placement
  30. 30the rate of disappearance of a reactant is equal to-d[reactant]\dt
  31. 31rate of propagation is the same asrate of polymerization
  32. 32the rate of radicals formed by initiationis equal to twice the rate of initiators consumed, (2Kd[i]=twice the rate constant times initiator concentration)
  33. 33the two ways free-radicals can be formed arehomolytic scission (homolysis) and single-electron transfer
  34. 34homolytic scission involvesbreaking of a single bond in which the two bondng electrons go from one each onto the two atoms associated with the original bond. produces two radical species
  35. 35single electron transfer involvesTransfer of single electron to or from an ion or molecule
  36. 36homolysis can be induced byheat or light
  37. 37intramolecular chain transfer gives rise toshort chains
  38. 38intermolecular chain transfer gives rise tolong chains
  39. 39The rate of polymerization is equal tois the rate which monomer is consumed.The rate of polymerization is equal to
  40. 40the rate of initiation can be represented in two stepsthe rate of initiation can be represented in two steps
  41. 41the formation of R* from initiator proceeds much ______ than the reaction of R* w monomerslower
  42. 42the rate of initiationis controlled by the first step of initiator, the formation of radical R*the rate of initiation
  43. 43what is the eqn for the rate of propagation if M* is the concentration of total radical specieswhat is the eqn for the rate of propagation if M* is the concentration of total radical species
  44. 44describe visual paths for the rate of termination for combination and disproportionationKtc is combination, Ktd is disporportionationdescribe visual paths for the rate of termination for combination and disproportionation
  45. 45the overall rate coefficient for terminationthe overall rate coefficient for termination
  46. 46when a reaction is under steady state conditionsthe rate of radical formation equals the rate of radicals consumed, the rate of initiation = the rate of termination
  47. 47steady state total concentration of radical speciessteady state total concentration of radical species
  48. 48steady state rate of polymerizationssteady state rate of polymerizations
  49. 49initiation via thermolysis yeildsinitiation via thermolysis yeilds
  50. 50rate for formation of active centers (thermolysis)rate for formation of active centers (thermolysis)
  51. 51not all initiators react to form radicals, thereforeinitiator efficiency is measured
  52. 52initiator efficiency is equal to(the radicals that initiate a polymerization)/(radicals formed from initiator)
  53. 53rate of polymerization for thermolysisrate of polymerization for thermolysis
  54. 54under steady state assumption, the rate of polymerization is dependent on theconcentration of monomers and the square roots of the concentration of initiators
  55. 55the extent of the reaction is equal toone minus the fraction of monomer left unreacted (concentration of monomer at some time, divided by the initial number of monomers)
  56. 56rate constant depends ontemperature
  57. 57kinetic analysis can provide only thenumber average degree of polymerization Xn
  58. 58the number average degree of polymerization isthe number average degree of polymerization is
  59. 59the Number average degree of polymerization in the absence of chain transfer and in terms of study state assumptionthe Number average degree of polymerization in the absence of chain transfer and in terms of study state assumption
  60. 60Understudy state assumption the number average degree of polymerization is proportional to[M](1/([I]^(1/2)))
  61. 61For free radical Chain polymerization, monomer units are inactive until initiation occurs, growth then continues by sequential addition of monomer units to the reactive chainexcept for styrene
  62. 62For free radical change polymerization, monomer concentration ________ throughout the polymerization processdecreases
  63. 63For free radical chain polymerization, initiation propagation and termination all occurSimultaneously
  64. 64For free radical chain polymerization, the yield of high molecular weight polymer increases with ________extent of reaction
  65. 65For free radical chain polymerization, the process is relatively ________ to stoichiometry but ________ to reactive impuritiesinsensitive, very sensitive
  66. 66the use of a transfer agent increases theNumber of polymer chains
  67. 67The kinetic chain length isThe number of monomer units polymerized per chain initiated or per initiation event, Rp/Ri, Ri=Rt
  68. 68If no change transfer occurs the number average degree of polymerization depends onthe mode of termination
  69. 69as the concentration of initiator and efficiency increases, the kinetic chain lengthdecreases, because as you increase the # of growing chains, it increases the probability of termination
  70. 70chain transfer _____ change the rate of polymerizationdoes not
  71. 71chain transfer will ____ kinetic chain lengthdecrease, it decreases the number of monomer unites incorporated per initiation step
  72. 72Vn=(Xn)0 whentermination happens only by disproportionation
  73. 73Vn=2(Xn)0when termination happens exclusively by combination
  74. 74when rate of diffusion is low,the reaction is diffusion controlled
  75. 75as a radical propagates, it grows in size and its rate of translational diffusionlowers
  76. 76termination is diffusion __controlled
  77. 77translational diffusion isthe movement of the center of mass of the chain through space. only small chains can undergoes translational diffusion freely
  78. 78translational diffusion causes most termination to be the result ofa long and short chain radical combining
  79. 79formula for number average degree of polymerization in terms of kinetic chain lengthwhere q=Ktd/Kt
    q=1 for only disproportionation
    q=0 for only combination
    n=kinetic chain length    formula for number average degree of polymerization in terms of kinetic chain length
  80. 80kinetic chain length in terms of rate of prop. and rate of initiationv=Rp/Ri
  81. 81formula for the average lifetime of an active centerformula for the average lifetime of an active center
  82. 82whats the formula for chain transferlook at notes (32)
  83. 83chain transfer constantCt=Ktr/Kp
  84. 84rate constants aretemperature dependent
  85. 85inhibitorused to prevent highly efficient rxns. the is an induction time, at the start of the rxn when inhibitors are consumed.
  86. 86retarderused when a rxn is less efficient or yields a species that will slowly reinitiate, to reduce the rate of polymerization
  87. 87autoinhibitorsis observed in the polymerization of monomers that have easily-abstracted atoms, i.e. allylic monomers
  88. 88widely used chain transfer agentthiols
  89. 89if a monomer has a large chain transfer constant,the monomers will not polymerize well
  90. 901,2-disubstituted alkenes generally are only useful forcopolymerizations
  91. 91for disproportionation: the number average DP and weight average DP are,Xw=(1+p)/(1-p)
    Xn=1/(1-p)
    as p to 1,
    Xw/Xn to 2
  92. 92for chain and step polymerizations, the number and weight average DPare similar but depend onthe mode of termination
  93. 93for coupling: the number average DP and weight average DP are,Xn=2/(1-p)
    Xw=(2+p)/(1-p)
    as p to 1
    Xw/Xn to 1.5
  94. 94for step growth polymerizations, p=fraction of possible steps which has occured, number of reacted molecules/ initial molecules (extent of reaction)
  95. 95in chain growth polymerization, a chain can react 3 wayspropagation
    termination
    chain transfer
  96. 96the four most common methods for free radical polymerizationbulk, solution, suspension, and emulsion
  97. 97bulk polymerizationinvolves only mixing monomer and monomer-soluble initiator and can produce v high MW polymers
  98. 98for solution polymerization, the solventmust dissolve the monomer and initiator, and product.
  99. 99solution polymerizationhas a decreased [M] and therefore a decrease in rate and degree of polymerization
  100. 100suspension polymerizationused as a way to avoid heat transfer from bulk polymerization, same as bulk, except reaction medium is suspended as tiny droplets in inert medium
  101. 101emulsion polymerizationlike suspension, polymerizing a hydrophobic polymer(with hydrophilic surfactants) in water, the surfactants make the polymer form micelles
  102. 102free radical polymerization creates polymers w branched structures because ofbackbiting
  103. 103at high conversion, [M] is low (for polyethylene) and growing radical chains can terminate by abstracting a hydrogen from another growing chain, creating a radical in the middle of a growing chain, this createsLDPE, a highly branched structure, and semi-crystalline polymer
  104. 104—

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polymer chem Flashcards on Free-Radical polymerization, created by Ashlin Deatherage on 25/09/2022.
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