Synthesis, Characterization, and Gas Permeation Properties

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Chapter5
Specific rotations ([α]D) were measured with a JASCO DIP-1000 digital polarimeter.
Thermogravimetric analyses (TGA) were conducted in air with a Shimadzu TGA–50
thermal analyzer by heating the samples (5–7 mg) from 100–700 ºC at a scanning rate
of 10 ºC min -1 . Differential scanning calorimetric (DSC) analyses were performed
using a Seiko DSC6200/EXSTAR6000 apparatus and measurements were carried out
by making use of 5–7 mg samples, under a nitrogen atmosphere, after calibration with
an indium standard. The samples were first heated from ambient temperature (25 ºC)
to 188 °C at a scanning rate of 20 ºC min -1 (first heating scan) and then immediately
quenched to -100 °C at a rate of 100 ºC min -1 . The second heating scans were run
from -100 to 188 °C at a scanning rate of 20 ºC min -1 to record stable thermograms.
The data for glass transition temperature (Tg) were obtained from the second run and
correspond to the midpoint of discontinuity in the heat flow.
Materials. Hydroxypropyl cellulose (1), 4-(dimethylamino)pyridine (Wako,
Japan), and N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride
(EDC·HCl; Eiweiss Chemical Corporation) were obtained commercially and used as
received. N-α-t-Butoxycarbonyl-L-glycine, N-α-t-butoxycarbonyl-L-alanine,
N-α-t-butoxycarbonyl-L-leucine, N-α-t-butoxycarbonyl-L-asparagine,
N-α-t-butoxycarbonyl-L-glutamine, and N-α-,N-ε-di-t-butoxycarbonyl-L-lysine were
purchased from Watanabe Chemical Ind. (Japan). Dichloromethane (CH2Cl2), used
as the reaction solvent, and distilled water, used for polymer precipitation and washing,
were purchased from Wako (Japan) and used without further purification.
The amino acid esters of hydroxypropyl cellulose (2a–f) were synthesized
according to Scheme 1. The details of the synthetic procedure and analytical data are
as follows:
N-α-t-Butoxycarbonyl-L-glycine Ester of Hydroxypropyl Cellulose (2a). A
200 mL one-necked flask was equipped with a stopper and a magnetic stirring bar.
Hydroxypropyl cellulose, 1, (1.35 g, 3.13 mmol) was added into the flask and
dissolved in CH2Cl2 (50 mL) at room temperature. 4-(Dimethylamino)pyridine (0.34
g, 2.82 mmol) was introduced followed by the addition of