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“The Marshmallow Polymer”
Chen Group Meeting
October 21, 2013
What is it?
• Xerogel = gel dried and shrinkage allowed to
occur
• Organosilica
• Separates oil from water by absorbing oi...
Materials
• Urea
• Acetic acid
• CTAC (n-hexadecyltrimethylammonium
chloride or cetyltrimethylammonium chloride)
• Methylt...
Materials
Si
CH3
H3CO OCH3
OCH3
Si
CH3
OCH3H3CO
CH3
O
NH2NH2
CH3
O
OH
CH3 N
+
CH3
CH3
CH3 Cl
-
MTMS DMDMS
15 mL
5 mM
5 g
0...
Acid hydrolysis
• Hydrolysis of alkoxysilane (water, acid
catalyzed)
Si
CH3
H3CO OCH3
OCH3
Si
CH3
OH OH
OH
Si
CH3
OCH3H3CO...
Base condensation
• pH has increased because of reduced [H+]
• Urea acts as base (another H+ acceptor)
• CTAC prevents pha...
Caveats
• Keep septum on
• Reaction is beginning once you add the first
silane
• Don’t wait too long to add the other sila...
Gelation at 80 degrees
• Oil bath
• GC oven
• Removing byproduct alcohols and some other
things by heating
Next steps
• Molar ratio of
(MTMS+DMDMS) : water : acetic acid : urea :
CTAC
= 1.0 : 2.4 x 10 : 2.1 x 10-3 : 2.4 : 7.1 x 1...
Next steps
• Aged for 2 days in glass bottle in the base-
catalyzed condition brought about by the
hydrolysis of urea
• Wa...
Synthetic procedure p. 1
• Measure 0.8 g CTAC directly into round-
bottom flask
• Add 5 g urea beads directly into flask
•...
Synthetic procedure p. 2
• Methyltrimethoxy silane (MTMS) and
Dimethyldimethoxy silane (DMDMS) are volatile
• Use syringe ...
2013 10 21_matthew s. mac_lennan_marshmallow polymer synthesis
2013 10 21_matthew s. mac_lennan_marshmallow polymer synthesis
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2013 10 21_matthew s. mac_lennan_marshmallow polymer synthesis

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2013 10 21_matthew s. mac_lennan_marshmallow polymer synthesis

  1. 1. “The Marshmallow Polymer” Chen Group Meeting October 21, 2013
  2. 2. What is it? • Xerogel = gel dried and shrinkage allowed to occur • Organosilica • Separates oil from water by absorbing oil and not water • Two step acid-base sol/gel reaction N. Hüsing and U. Schubert, Angew. Chem., Int. Ed., 1998, 37, 23.
  3. 3. Materials • Urea • Acetic acid • CTAC (n-hexadecyltrimethylammonium chloride or cetyltrimethylammonium chloride) • Methyltrimethoxy silane (MTMS) • Dimethyldimethoxy silane (DMDMS) • Acid-Base two step sol/gel reaction
  4. 4. Materials Si CH3 H3CO OCH3 OCH3 Si CH3 OCH3H3CO CH3 O NH2NH2 CH3 O OH CH3 N + CH3 CH3 CH3 Cl - MTMS DMDMS 15 mL 5 mM 5 g 0.8 g 2 mL : 3 mL
  5. 5. Acid hydrolysis • Hydrolysis of alkoxysilane (water, acid catalyzed) Si CH3 H3CO OCH3 OCH3 Si CH3 OH OH OH Si CH3 OCH3H3CO CH3 Si CH3 OHOH CH3 H + H + CH3 OH CH3 OH
  6. 6. Base condensation • pH has increased because of reduced [H+] • Urea acts as base (another H+ acceptor) • CTAC prevents phase separation Si CH3 OH OH OH Si CH3 OHOH CH3 Si CH3 OH OH Si CH3 OH CH3 Si CH3 O OH Si CH3 OO CH3 CH3 OH H2O
  7. 7. Caveats • Keep septum on • Reaction is beginning once you add the first silane • Don’t wait too long to add the other silane • Stir very well (increasing viscosity = decreasing diffusion rate = decreasing reaction rate) • Don’t let the reaction sit for too long (1h is plenty)
  8. 8. Gelation at 80 degrees • Oil bath • GC oven • Removing byproduct alcohols and some other things by heating
  9. 9. Next steps • Molar ratio of (MTMS+DMDMS) : water : acetic acid : urea : CTAC = 1.0 : 2.4 x 10 : 2.1 x 10-3 : 2.4 : 7.1 x 10-2 • MTMS:DMDMS = 5.9 : 4.1 • Ratios of MTMS and DMDMS changes marshmallow properties
  10. 10. Next steps • Aged for 2 days in glass bottle in the base- catalyzed condition brought about by the hydrolysis of urea • Wash in 1:1 water:2-propanol • Wash twice in 2-propanol at 8h intervals • Gel washed 3 times with n-hexane and dried at RT is termed xerogel Gen Hayase et al. J. Mater. Chem., 2011, 21, 17077.
  11. 11. Synthetic procedure p. 1 • Measure 0.8 g CTAC directly into round- bottom flask • Add 5 g urea beads directly into flask • Add 5 mM CH3COOH(aq) to flask. Urea will mostly dissolve, CTAC will mostly not dissolve • Plug flask with septum • Medium stir
  12. 12. Synthetic procedure p. 2 • Methyltrimethoxy silane (MTMS) and Dimethyldimethoxy silane (DMDMS) are volatile • Use syringe needle under nitrogen to transfer silanes to reaction flask • CTAC will dissolve, solution becomes colorless and clear • Increase stirring speed as polymerization is beginning • Leave for 60 minutes (some say 30 minutes is good enough)

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