4448
Z. Zhang et al. / Polymer 54 (2013) 4446e4454
Table 1
(Chem-Supply, LR grade) was distilled from CaH2 prior to use.
Deuterated chloroform (CDCl3) þ 1% v/v tetramethylsilane (TMS) (D,
99.8%) was purchased from Cambridge Isotope Laboratories. Argon
(UHP) was purchased from BOC, Australia. Copper TEM grids
(300 mesh) were purchased from ProSciTech Pty Ltd.
Characterisation of 4, 6, and 21 armed fluorinated star polymers.
PDIc
Tg (ꢁC)
PFPA monomer
contente (mol%)
Ef (GPa)
d
Star
Mwb (kDa)
polymersa
4S1
4S2
4S3
4S4
6S1
6S2
6S3
6S4
21S1
21S2
21S3
21S4
21S5
76.8
58.7
39.6
90.5
60.9
296.8
88.6
88.5
66.5
225.0
61.6
1.05
1.13
1.08
1.05
1.23
1.26
1.08
1.08
1.07
1.15
1.20
1.22
1.11
69.5
49.7
44.5
20.8
57.3
52.3
41.0
26.7
94.5
74.1
55.4
53.5
21.8
25.8
35.0
42.0
58.6
30.0
33.0
41.0
54.5
4.4
20.5
32.5
33.0
57.2
4.86
4.15
3.88
3.54
4.40
4.25
3.90
3.62
5.07
4.63
4.34
4.26
3.50
2.2. Measurements
Gel permeation chromatography (GPC) was performed on a
Shimadzu liquid chromatography system fitted with a Wyatt DAWN
HELEOS LS detector (
¼ 633 nm) and Shimadzu SPD-20A UVeVis detector, using three
identical Polymer Laboratories PLgel columns (5 m, MIXED-C) and
l
¼ 658 nm), Shimadzu RID-10 refractometer
(l
m
DMF with 0.05 M LiBr (70 ꢁC, 1 mL/min) as the mobile phase. ASTRA
software (Wyatt Technology Corp.) was used to process the data
using either known dn/dc values or based upon 100% mass recovery
of the polymer where the dn/dc value was unknown. 1H and 13C NMR
spectroscopic analysis was performed on a Varian Unity Plus 400
spectrometer operating at 400 and 100 MHz, respectively. Deuter-
ated chloroform (CDCl3) with 1% TMS was used as solvent and in-
ternal reference, respectively. Differential scanning calorimetry
(DSC) was performed on 2920 Modulated DSC (TA Instruments). TA
Universal Analysis 2000 was used to process the data for determi-
nation of Tg. Each sample was heated and cooled at a rate of 10 ꢁC/
min and this was repeated twice. The Tg values were recorded on the
second heating run. Contact angle measurements were conducted
on Data Physics OCA 20 Tensiometer. Measurements were recorded
by OCA software, using a sessile drop profile. Atomic force micro-
scopy (AFM) was performed on Asylum Research MFP-3D AFM. Non-
242.5
196.5
a
4S, 6S, and 21S represent 4, 6, and 21 armed star polymers, respectively.
Weight-average molecular weight of star polymers determined by GPC-MALLS
b
and based upon the assumption of 100% mass recovery.
c
Polydispersity index determined by GPC.
d
Glass transition temperature determined by DSC.
e
Mol% based upon 1H NMR spectroscopic analysis.
f
Young’s modulus determined by AFM on planar films.
to a flask under argon. The mixture was cooled to ꢂ18 ꢁC and 2-
bromo-2-methylpropanoyl bromide (7.00 mL, 56.6 mmol,
9 equiv.) dissolved in anhydrous dioxane (50 mL) was added
dropwise over a period of 1 h. The resulting mixture was stirred at
room temperature for 20 h and then diluted with chloroform
(400 mL) and stirred for another 30 min. The organic solution was
washed with
2
M
HCl (2
ꢃ
200 mL), saturated NaHCO3
porous thin films were prepared by depositing 20 mL of a polymer
(2 ꢃ 200 mL), aqueous 5 wt% NaHCO3 (2 ꢃ 200 mL), dried (MgSO4),
filtered, and concentrated in vacuo to afford a dark orange oil. The
product that crystallised upon cooling at 0 ꢁC was recrystallised
from hot ethanol, cooled at 0 ꢁC and filtered off to afford initiator 2
as a colourless crystalline solid, 5.45 g (76%). 1H NMR (CDCl3,
400 MHz): dH 1.93 (s, 36H, 12CH3), 3.60 (s, 4H, CH2OCH2), 4.29 (s,
12H, 6CH2O) ppm. 13C NMR (CDCl3, 100 MHz): dC 30.7 (12CH3), 44.3
(2C(CH2)4), 55.5 (6CBr), 63.2 (6CH2O), 69.1 (2CH2O), 170.9 (6C]O)
ppm.
solution on a clean microscope glass slide and allowing the solvent
to evaporate at room temperature. The Young’s modulus (E) of the
thin films was measured in force mode using pyramid shaped silicon
cantilevers (Model AC240Ts, 70 (50e90) kHz, 2 (0.5e4.4) N/m;
AC200Ts, 115 (75e175) kHz, 9.7 (4.0e22.3) N/m; AC160TS, 300
(200e400) kHz, 42 (12e103) N/m, Asylum Research). The Hertzian
contact mechanics model [46e48] was applied on approach curves
to obtain E. HC films were imaged by scanning electron microscopy
(SEM) using a FEI Quanta 200 ESEM FEG. Samples were coated with
gold using a Dynavac Mini sputter coater prior to imaging. Image-
ProÒ software was employed to analyse SEM images of HC films and
2D Fast Fourier Transform (FFT) images.
2.5. Synthesis of b-CD-Br21 multifunctional initiator 3
This compound was prepared according to the procedure
described by Li and Xiao [49]. 1H NMR (CDCl3, 400 MHz): dH 1.87 (m,
2.3. Synthesis of tetra-functional initiator 1
Pentaerythritol (2.00 g, 14.7 mmol, 1 equiv.), TEA (12.3 mL,
88.2 mmol, 6 equiv.) and anhydrous dioxane (100 mL) were added to
a flask under argon. The mixture was cooled to ꢂ18 ꢁC and 2-bromo-
2-methylpropanoyl bromide (10.9 mL, 88.2 mmol, 6 equiv.) dis-
solved in anhydrous THF (20 mL) was added dropwise over a period
of 1 h. The resulting mixture was stirred at room temperature for
12 h and then diluted with dichloromethane (400 mL) and stirred for
another 30 min. The organic solution was washed with 2 M HCl
(2 ꢃ 250 mL), saturated NaHCO3 (2 ꢃ 250 mL), dried (MgSO4),
filtered, and concentrated in vacuo to afford a yellow solid. The solid
was recrystallised from hot ethanol, cooled at 0 ꢁC and filtered to
afford initiator 1 as a colourless crystalline solid, 8.82 g (79%). 1H
NMR (CDCl3, 400 MHz): dH 1.94 (s, 24H, 8CH3), 4.33 (s, 8H, 4CH2)
ppm. 13C NMR (CDCl3, 100 MHz): dC 30.6 (8CH3), 43.6 (C(CH2)4), 55.2
(4CBr), 62.9 (4CH2O), 170.9 (4C]O) ppm.
2.4. Synthesis of hexa-functional initiator 2
Dipentaerythritol (1.60 g, 6.28 mmol, 1 equiv.), TEA (8.00 mL,
56.6 mmol, 9 equiv.) and anhydrous dioxane (100 mL) were added
Fig. 1. The relationship between PFPA content and glass transition temperature (Tg) of
the fluorinated star polymers.