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Odian Book 2-6, 2-14 a-e

Odian Book 2-6, 2-14 a-e. Viscosity and Molecular Weight. MW 3.4. MW 1.0. Property “X”. Viscosity. Critical MW for entanglements. Molecular Weight. “X” = tensile strength density Tg etc. How to control MW in Step Growth Polymerizations?. p = 0.990, DP = 100 p = 0.995, DP = 200.

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Odian Book 2-6, 2-14 a-e

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  1. Odian Book 2-6, 2-14 a-e

  2. Viscosity and Molecular Weight MW3.4 MW1.0 Property “X” Viscosity Critical MW for entanglements Molecular Weight “X” = tensile strength density Tg etc

  3. How to control MW in Step Growth Polymerizations? p = 0.990, DP = 100 p = 0.995, DP = 200 1 (1 – p) Xn Xn = p • Conversion • Stoichiometry

  4. Controlling MW in Step Growth Polymerizations 1 (1 – p) Xn = [M]0 [M] Xn = NA° NB° r = • Recall • And that the value of Xn at any given time equals: • We can define a stoichiometric imbalance ratio (r ≤1.0)

  5. Controlling MW in Step Growth Polymerizations NA° + NB° 2 = NA° NB° NA° r r NB° = = NA° + NA° / r 2 NA° ( 1 +1/ r) 2 = = • Total # of monomers present at the start is: • And we know that: • Substitute:

  6. Controlling MW in Step Growth Polymerizations NA° NB° rNB° r NA° = = • Since A and B groups react in a 1:1 proportion, the fraction of B groups that have reacted when the extent of reaction has reached ‘p’ is: • since: • Substitute: = pNA° = prNB°

  7. Controlling MW in Step Growth Polymerizations [ NA° (1 – p) + NB° (1 – rp) ] 2 [NA0 (1 + 1/r) ] / r [ NA° (1 – p) + NB° (1 – rp) ] 2 [M]0 [M] Xn = = 1 + r 1 + r - 2rp DP = • The total # of chains at any given time equals what? The sum of unreacted A and B groups. And since each polymer molecule has two chain ends, the total number of chains is • Recall • Substitute:

  8. How to control MW in Step Growth Polymerizations? 1 + r 1 - r DP = • As p goes to 1.0

  9. End Groups? PES 50% 25% 25%

  10. Controlled MW Poly(ether sulfone) Slight excess Controlled MW and controlled end groups

  11. Bismaleimides (BMIs) Excess diamine dianhydride polyamic acid Δcyclodehydration

  12. Controlled MW Poly(ether sulfone):“Non-functional” End groups

  13. How to control MW in Step Growth Polymerizations? NA° NB° + 2NB’° r’ = 1 + r’ 1 - r’ DP = • Stoichiometric Imbalance (r) when A-A and B-B monomers are used, with a small addition of R-B • Degree of Polymerization at p = 1.0 is Where NB’° = number of mono-functional B groups

  14. Thermosets Xn p • Xn→ ∞ • Gel point • Beginning of network formation • Need to know…ahead of time!

  15. Stages of Thermosetting Reactions % SolFraction p • Soluble • Branched system • Soluble, processible • “Gel Point” • Onset of network structure • Xn→ ∞ • We need to know when this happens… • pcrit = ? • NetworkDensification • 5% soluble fraction not uncommon for“fully cured” system

  16. Predicting the Gel Point 2 (No -N) No favg • Recallwhere N0 and N are the number of monomer molecules initially and at conversion p • Knowing that • By definition @ gel point DP → ∞ • As favg↑ ; pcrit↓ # functional groups reacted # functional groups initially p p = = 2 2 favg DP favg N0 N p = - DP = 2 favg pcrit =

  17. Gelation vs Vitrification • Gelation • Characteristic of thermosets • Significant for processing • At or beyond the gel point, system is no longer processable • Vitrification • Distinct from gelation • Transformation from a viscous liquid to a glass • Onset of vitrification shifts rate of reaction from chemical control to diffusion controlled

  18. Gelation vs Vitrification Tg Molecular Weight

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