In order to prepare C-PEG (PEG with carboxylic acids terminals)
for comparison, 0.01mol PEG 4000 was dissolved in 50ml toluene.
0.03 mol succinic anhydridewas added, and the mixturewas stirred
for 5 h in an oil bath at 150 ◦C. The mixture was cooled, taken up
in CH2Cl2, and the polymer was precipitated by diethyl ether. The
product was recrystallized twice from CH2Cl2/ether.