1. “The Marshmallow Polymer”
Chen Group Meeting
October 21, 2013

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. 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. 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. 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. 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

9. 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)

10. Gelation at 80 degrees
• Oil bath
• GC oven
• Removing byproduct alcohols and some other
things by heating

11. 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

12. 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.

13. 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

14. 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)