Effect of Index on Curing Kinetics & Viscoelastic Properties of PU gels Lifeng Wu TRFA 2006 Annual Meeting September 11, 2006 HUNTSMAN POLYURETHANES

Polyurethanes  Gel: a colloidal system consisting of a liquid which is dispersed in a solid polymeric matrix resulting in a soft, gelly, material.  Applications:  Adhesives  Energy absorbers, dampers Gel

Polyurethanes PU Gels  Hydrogel  Poly(ethylene oxide) network swelled with water  Plasticizer gel  PU network plasticized with phthalates  Polyol gel:  PU network with excess multifunctional polyol  Monol gel * :  Polyol mixture of diol and monol crosslinked with multifunctional isocyanates * US and US (Huntsman patents)

Polyurethanes Polyol Gel  Materials:  Rubinate  1209: prepolymer based on MDI (NCO% = 21.5)  Jeffol G31-55: polyether triol (OH v = 55)  Jeffcat TD-33A: tertiary amine catalyst OH HO + NCO OCN OH NCO H O OCN H O Cat.  Index:  r  [NCO] 0 /[OH] 0  r = 0.5 – 1.0  Conversion:  p  ([NCO] 0 – [NCO])/[NCO] 0

Polyurethanes Rheology  Rheology: study of the flow and deformation of matter. AR 2000 Rheometer G’: storage modulus G”: loss modulus  : phase angle = tan -1 (G”/G’)  G” G’ liquid solid

Polyurethanes Curing Rheology (r = 0.5, 0.6) Gel Point: G’ = G”

Polyurethanes Curing Rheology (r = 0.7, 0.8)  Similar behavior to r = 0.6.

Polyurethanes Curing Rheology (r = 0.9, 1.0)  G” shows 2 nd stage growth. High crosslink density

Polyurethanes Curing kinetics  Molecular weight * : M w (r,p)  Crosslink density * :  (r,p) * Macosko and Miller, 1976 Gel Point

Polyurethanes Viscosity at Initial Stage  Viscosity  0 = G”/  (  = 1 rad/s)

Polyurethanes Initial Growth of Molecular Weight   0 ~ M w for unentangled polymers   0 ~ M w 3.4 for entangled polymers  0 ~ M w 2 Entanglement

Polyurethanes Crosslink Density – 

Polyurethanes Viscoelastic Properties (r = 0.5,0.6) G’ ≈ G” ~  0.5 (critical gel) G’ ~  0 (low  ),G” ~  0.5

Polyurethanes Viscoelastic Properties (r = 0.7,0.8) G’ ~  0, G” ~  0.5

Polyurethanes Viscoelastic Properties (r = 0.9,1.0) G’ ~  0, G” ~  0 – 0.5

Polyurethanes Plateau Modulus – G 0

Polyurethanes Curing Rheology at High Indices

Polyurethanes Relaxation Behavior During Curing G” ~  0.5 G” ~  0

Polyurethanes Mechanism: Dangling Chains NCO H O OCN H O NCO H O OH NCO H O OCN H O G” ~  0.5 G” ~  0  Before transition:  After transition:  50%  > 0.6 mol/L  dangling chains < 25%

Polyurethanes Conclusion  Before gel point:  Initial  and M w growth is nearly independent of index:  log(  ) ~ t  After gel point:  index r   crosslink density    #dangling chain   G’(  ), G”(  ) :  r = 0.5: G’ ≈ G” ~  0.5 (critical gel)  r = 0.6 – 0.8: G’ ~  0, G” ~  0.5  r = 0.9, 1.0: G’ ~  0, G” ~  0 – 0.5 (2 nd stage growth)

Polyurethanes Effect of Conversion on M w and   Macosko and Miller, 1976  MwMw