Catalytic Synthesis and Characterization of Biodegradable ...

Synthesis of MPEG-b-PLA-b-PTAm.
Synthesis of Amphiphilic Triblock Copolymers of Acrylamide, Lactate, and Ethyleneoxide
0.56 g MPEG-b-PLA-CPAD (0.04 mmol), 0.50 g (2.4 mmol) TAP monomer and 3.3 mg
AIBN (0.02 mmol) ware dissolved in 6mL 1,4-dioxane/methanol (9:1, v/v). The mixture was
deaerated by applying three times freeze-pump-thaw cycle. Afterwards, the tube was
immerged in 90 o C oil bath and stirred for 8 hours. After cooling to room temperature, the
mixture was precipitate in cold ethyl ether. The pale pink precipitate was collected and
washed twice with ethyl ether. The product was obtained after vacuum drying for 24 h with a
yield of 79% (0.84 g). An additional oxidation procedure was also needed to gain the final
product MPEG-b-PLA-b-PTAm in good yield. (Mn=32300, PDI=1.42 by GPC)
Micelles preparation and characterization.
The preparation procedures for the MPEG-b-PTAm and MPEG-b-PLA-b-PTAm micelles
are the same. Typically, 50 mg of the block copolymer was firstly dissolved in 5 mL of THF
and then added dropwise into 10 mL deionized water. The mixture was then transferred into a
dialysis bag (molecular weight cut-off = 3500 Da) and dialyzed against deionized water for
24h. Afterwards, the micelles solution was diluted to 50 mL with deioinized water. The final
concentrations of the micelles were 1.0 mg mL -1 . The structure of the micelles was
characterized by DLS and TEM.
EPR study.
To evaluate the stability of the nitroxyl radicals containing micelles in the reducing
environment, EPR study of the micelles in PBS buffering solution containing ascorbic acid at
high concentration was conducted. 0.5 mL of the prepared micelle solution (1.0 mg.mL -1 )
was mixed vigorously with 0.5 mL of PBS solution (pH 7.4, 0.2 M containing 10.0 mM
ascorbic acid). The mixture was then transferred into capillary tube immediately for EPR
measurement over time. The final concentrations of the micelle and the ascorbic acid were
0.5 mg.mL -1 and 5.0 mM, respectively. The same assay was performed toward TEMPOL at
concentration of 0.5 mg mL -1 in the same buffer as the control.
Cytotoxicity assay.
The cytotoxicity of the block copolymers were assessed using MTT method. Polymer
samples were dispersed in DMEM medium (Dulbecco's Modified Eagle Medium)
supplemented with 10% fetal calf serum (Gibco) in a humidified incubator at 37 and 5%
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