10.0 g of 3-arm PEG thiol was combined with 13.65 g
1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) in a flame dried 1000 mL
round-bottomed flask equipped with a stir bar. 400 mL of anhydrous
dichloromethane were added via cannula followed by 5.8 mL of
5-norbornene-2-carboxylic acid (mixture of endo and exo, Alfa Aesar). After
stirring under argon for 15 min, 17 mL of diisopropylethylamine were added to
the vessel. After 15 min of argon, the apparatus was fixed with an argon balloon
and allowed to stir overnight. The reaction mixture was diluted to a volume of
800 mL with fresh dichloromethane, then washed gently and quickly with 7 washes
of 300 mL 0.1 N hydrochloric acid. The organic layer was then washed three times
with a saturated NaHCO3 solution, once with brine, dried over
Na2SO4, and then concentrated in
vacuo to produce a clear, slightly yellow viscous liquid. (85%
functionalized) 1H NMR (400 MHz, CDCl3) δ
6.52–5.78 (m, 6H), 4.32–4.19 (m, 6H), 3.86–3.42 (m, 85H)
(Figure S1 )
1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) in a flame dried 1000 mL
round-bottomed flask equipped with a stir bar. 400 mL of anhydrous
dichloromethane were added via cannula followed by 5.8 mL of
5-norbornene-2-carboxylic acid (mixture of endo and exo, Alfa Aesar). After
stirring under argon for 15 min, 17 mL of diisopropylethylamine were added to
the vessel. After 15 min of argon, the apparatus was fixed with an argon balloon
and allowed to stir overnight. The reaction mixture was diluted to a volume of
800 mL with fresh dichloromethane, then washed gently and quickly with 7 washes
of 300 mL 0.1 N hydrochloric acid. The organic layer was then washed three times
with a saturated NaHCO3 solution, once with brine, dried over
Na2SO4, and then concentrated in
vacuo to produce a clear, slightly yellow viscous liquid. (85%
functionalized) 1H NMR (400 MHz, CDCl3) δ
6.52–5.78 (m, 6H), 4.32–4.19 (m, 6H), 3.86–3.42 (m, 85H)
(