Catalytic Synthesis and Characterization of Biodegradable ...

6.8 Experimental section
Materials and methods
Synthesis of Amphiphilic Triblock Copolymers of Acrylamide, Lactate, and Ethyleneoxide
2,2’-Azoisobutyronitrile (AIBN, Beijing Chemical Co., China) was recrystallized twice
from methanol. Monomethoxy poly(ethylene glycol) (MPEG Mw=5000 Da),
4-hydroxyl-TEMPO (TEMPOL, 97%) N,N'-Dicyclohexylcarbodiimide (DCC, 99%) and
4-dimethylaminopyridine (DMAP, 98%) were purchased from Aldrich Chemical Co. and
used as received. 4-Cyanopentnoic acid dithiobenzoate (CPAD) was prepared as described in
the literature 21. 26 4-Amino-2,2,6,6-tetramethylpiperidine (TCI, >97%) and Acryloyl chloride
(Alfa Aesar, 96%) were used without purification to prepare the
2,2,6,6-tetramethylpiperidinyl acrylamide (TAP) monomer. 27 All other reagents were used
without further purification.
1
H NMR spectra were recorded on Bruker AV 300 or Bruker AV 600 NMR spectrometer
in CDCl3. Gel permeation chromatography was performed with 0.1 M LiCl DMF eluent using
a Tosoh HLC-8220 instrument, and the molecular weight and polydispersity were calibrated
with polystyrene standards. For kinetic study, gel permeation chromatography was performed
with a Schamback SFD GmnH mGPC2000 instrument using 0.1 M LiCl DMF as the eluent at
40 o C, and the molecular weight and polydispersity were calibrated with polystyrene
standards. Dynamic light scattering (DLS) were determined by DAWN EOS 18 Angles Laser
Light Scattering Instructment (Wyatt Technology). Transmission electron microscopy (TEM
JEM-2010 electron microscope, JEOL, Japan) was also used to characterize the morphology
of the micelles. Electron paramagnetic resonance (EPR) spectra were recorded on a
JES-FA200 EPR spectrometer.
Synthesis of Macromolecular CTA: MPEG-CPAD and MPEG-b-PLA-CPAD.
Typically, MPEG5k 2.5 g (0.5 mmol), CPAD 0.28 g (1mmol) DCC 0.42 g (2 mmol) and
DMAP 0.025 g (0.2 mmol) were dissolved in 20 mL anhydrous methylene chloride. The
solution was stirred at room temperature for 48 hours. After filtration of the precipitate, the
solution was poured into 200 mL cold ethyl ether, yielding pink precipitate. The pink
precipitate was redissolved in methylene chloride and precipitated again in cold ethyl ether.
After washing with additional two times with ethyl ether, the pink product MPEG-CPAD was
finally obtained, yield 92%. The preparation of MPEG-b-PLA-CPAD was similar as
MPEG-CPAD, yield 89%. The structure of the two macromolecular CTA was verified by 1 H
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