Sliding-graft interpenetrating polymer networks from simultaneous "Click Chemistry" and atom transfer radical polymerization

Article abstract of DOI:10.1021/ma102039n

In this work, a kind of semi-interpenetrating polymer network (s-IPN) with unique molecular structures, poly(ethylene glycol) (PEG) network with movable sliding-grafted poly(2-hydroxyethyl methacrylate) (PHEMA) (sIPN-PEG/α -CD-sg- PHEMA), were first reported. sIPN-PEG/α -CD-sg-PHEMAs were prepared by simultaneous "click chemistry" and atom transfer radical polymerization (ATRP) of a mixture of poly(ethylene glycol)-diazide/ bromobutyryloxy R-cyclodextrin inclusion complex (N3-PEGN3/( R-CD-BIBB)m), tetrakis(2-propynyloxymethyl) methane (TMOP), CuBr, pentamethyldiethylenetriamine (PMDETA), HEMA and DMF. Attributable to the controlled characters of ATRP and the quantitative yields of "click chemistry", the prepared sIPN-PEG/α -CD-sg-PHEMAs have the well-defined PEG networks, as well as uniform and tunable sliding-grafted PHEMA chains. The length of sliding-grafted PHEMA of the sIPN-PEG/α -CD-sg-PHEMA can be regulated by changing polymerization times. The molecular structures, and physical and thermal properties of the sIPN-PEG/α -CD-sg-PHEMA were studied by FTIR, 1HNMR, XPS, TGA, and DSC measurements. The sIPN-PEG/α -CD-sg-PHEMAs exhibit good physical and mechanical properties. Most important, comparing to classical semi-IPN, the diffusion of interpenetrated PHEMA from sIPN-PEG/α -CD-sg-PHEMA was largely prevented for a long time solvent immersion because the PHEMA brushes were fixed on PEG networks. The sliding-grafted PHEMA chains afford functionalities to the bulk and surface of s-IPN-PEG and could potentially be used as carriers of genes and drugs.

Full text of DOI:10.1021/ma102039n

Macromolecules 2010, 43, 9761–9770 9761
DOI: 10.1021/ma102039n
Sliding-Graft Interpenetrating Polymer Networks from Simultaneous
“Click Chemistry” and Atom Transfer Radical Polymerization
Fang Yao, LiQun Xu, Guo-Dong Fu,* and BaoPing Lin*
School of Chemistry and Chemical Engineering, Southeast University, Jiangning District,
Nanjing, Jiangsu Province, P.R. China 211189
Received September 2, 2010; Revised Manuscript Received November 6, 2010
ABSTRACT: In this work, a kind of semi-interpenetrating polymer network (s-IPN) with unique molecular
structures, poly(ethylene glycol) (PEG) network with movable sliding-grafted poly(2-hydroxyethyl metha-
crylate) (PHEMA) (s-IPN-PEG/R-CD-sg- PHEMA), were first reported. s-IPN-PEG/R-CD-sg-PHEMAs
were prepared by simultaneous “click chemistry” and atom transfer radical polymerization (ATRP) of a
mixture of poly(ethylene glycol)-diazide/bromobutyryloxy R-cyclodextrin inclusion complex (N3-PEG-
N3/(R-CD-BIBB)m), tetrakis(2-propynyloxymethyl) methane (TMOP), CuBr, pentamethyldiethylenetria-
mine (PMDETA), HEMA and DMF. Attributable to the controlled characters of ATRP and the quanti-
tative yields of “click chemistry”, the prepared s-IPN-PEG/R-CD-sg-PHEMAs have the well-defined PEG
networks, as well as uniform and tunable sliding-grafted PHEMA chains. The length of sliding-grafted
PHEMA of the s-IPN-PEG/R-CD-sg-PHEMA can be regulated by changing polymerization times. The
molecular structures, and physical and thermal properties of the s-IPN-PEG/R-CD-sg-PHEMA were studied
by FTIR, 1H NMR, XPS, TGA, and DSC measurements. The s-IPN-PEG/R-CD-sg-PHEMAs exhibit good
physical and mechanical properties. Most important, comparing to classical semi-IPN, the diffusion of
interpenetrated PHEMA from s-IPN-PEG/R-CD-sg-PHEMA was largely prevented for a long time solvent
immersion because the PHEMA brushes were fixed on PEG networks. The sliding-grafted PHEMA chains
afford functionalities to the bulk and surface of s-IPN-PEG and could potentially be used as carriers of genes
and drugs.
1. Introduction
Atom transfer radical polymerization (ATRP), a powerful tool
for preparing nearly monodispersed polymers with a controllable
molecular weight,21-24 could be used to prepare networks.25,26
However, the resulting networks exhibit poor mechanical properties.
Interestingly, ATRP not only shares a number of attractive features
with CuAAC, such as high tolerance toward a wide range of
functional groups,27 but also a same copper catalyst system.28
One-pot simultaneous reaction of ATRP and CuAAC has been
demonstrated by Haddleton’s group29 and used to prepare well-
defined block copolymers and cross-linked nanoparticles,30 as
well as well-defined semi-IPN and full-IPN.31
For classical semi-IPNs (s-IPNs), the linear polymers dispersed
in networks help improve the mechanical strength32 and elasticity
of polymers and bring special physical and chemical character-
istics, such as temperature- or PH-sensitivity33-35 and interfacial
compatibility, to polymers.36 However, the diffusion of linear
polymers from semi-IPNs for a long time immersion in solvent,
not only will reduce the physical and mechanical properties of semi-
IPNs, but also limits their applications in biomedical fields.37
Poly(ethylene glycol) (PEG) and R-cyclodextrins (R-CD) are
widely studied and used as materials for biomedical,38-42 because
PEG and R-CD are biocompatible, bioabsorbable, water-soluble,
and nontoxic. It is interesting that PEG was found to be included
in CDs and form an inclusion complex.43 On the basis of this
property, a series of slide-ring gels with a novel molecular
structure have been reported.44-46 Here, we demonstrated a
novel approach for the preparation of well-defined sliding-graft
semi-IPN of PEG and poly(2-hydroxyethyl methacrylate) (s-IPN-
PEG/R-CD-sg-PHEMAs), in which the uniform linear poly-2-
hydroxyethyl methacrylate (PHEMA) was locked on the grids of
PEG networks via simultaneous CuAAC and ATRP. The prepared
Hydrophilic interpenetrating polymer networks (HIPNs), a
polymer comprising two or more networks, which are at least
partially interlaced on a molecular scale but not covalently
bonded to each other, have attracted much attention due to their
unique properties, such as tunable responsive properties, enhanced
mechanical properties, swelling characteristic, and improved
thermal stability.1-7 Thus, HIPN could be found applications as
actuators and artificial muscles,1 as sensors,8 and in biomedical
materials.6,9-12 However, the poor mechanical properties of
classical gels restrict their applications in these fields.2 It is known
that the physical properties of the HIPN were not only dominated
by chemical composition, but also by their molecular struc-
tures.13 Efforts have been made to prepare HIPNs with unique
molecular structures, such as slide-ring gels,14-16 and nanocom-
posite hydrogels.17 However, the preparation of HIPNs with a
well-defined and novel molecular structure is still interesting to
scientists due to their unexpected properties and potential
applications.
“Click chemistry”, especially copper(I)-catalyzed azide-alkyne
cycloaddition (CuAAC), has attracted a considerable amount of
attentions for the preparation of networks due to the improved
mechanical properties, complete specificity, quantitative yields
and high functional group tolerance.18-20 Hawker et al. con-
structed well-defined PEG networks by CuAAC.18 The networks
exhibited a surprisingly improved mechanical property in com-
parison to classical photochemically cross-linked PEG networks.
*To whom correspondence should be addressed: Telephone: þ86-25-
52090625. Fax: þ86-25-52090625 E-mail: (G.-D.F.) fu7352@seu.edu.cn;
(B.L.) lbp@seu.edu.cn.
r 2010 American Chemical Society
Published on Web 11/17/2010
pubs.acs.org/Macromolecules

9762 Macromolecules, Vol. 43, No. 23, 2010
Yao et al.
s-IPN-PEG/R-CD-sg-PHEMAs exhibit good physical and me-
chanical properties. Most important, comparing with classical
semi-IPNs, the diffusion of interpenetrated PHEMAs from
s-IPN-PEG/R-CD-sg-PHEMAs was largely prevented for a long
time immersion in solvent. The sliding-grafted PHEMA chains
afford functionalities to the PEG network and could be poten-
tially used for drug or gene loading and biomedical materials with
tunable functionalities on surface.
by distillation, the residue was treated with aqueous saturated
NaHCO3 and extracted with CH2Cl2. The organic solution was
then dried over MgSO4 for 10 h and the solvent was removed by
rotary evaporation. The product was finally precipitated by
addition of a large amount of diethyl ether. About 8.9 g of
product was obtained. After that, a mixture of 8.0 g (2 mmol) of
prepared PEG and 0.65 g (10 mmol) of sodium azide in 50 mL
dry DMF was reacted at 85 °C for 24 h. The solid state was
removed by passing through an alumina column, and the
solution was concentrated by rotary evaporation. The polymer
was precipitated from DMF concentrated solution by addition
Experimental Section
diethyl ether and filtration (yield: 90%). FTIR (cm-1): ν(NdNdN)
=
2098. Elemental analysis indicated that the conversion from
poly(ethylene glycol) to N3-PEG4K-N3 is of about 96%.
1.1. Materials. The monomer 2-hydroxyethyl methacrylate
(HEMA, 97%) was purchased from Acros Organic Co. of Geel,
Belgium. The monomers were used after removal of inhibitors in
a ready-to-use disposable inhibitors-removal column. Propargyl
bromide (80%), poly(ethylene glycol) (PEG, Mn = 4000),
R-cyclodextrin (R-CD), 2-bromoisobutyryl bromide (BIBB, 98%),
and pentamethyldiethylenetriamine (PMDETA, 99%) were
purchased from Aldrich Chemical Co. and used as received.
Sodium azide (99%), CuBr (99%), methane sulfonyl chloride,
pentaerythritol and other materials were purchased from Shanghai
Chemical Reagent Plant.
2.2.2. Synthesis of Tetrakis(2-propynyloxymethyl)methane
(TPOM). Tetrakis(2-propynyloxymethyl)methane (TPOM) was
synthesized according to the method reported in the literature.31
About 2.4 g (0.017 mmol) of pentaerythritol was added into a
solution of 15 g (0.264 mmol) of KOH in 30 mL of anhy-
drous DMF. After the mixture was stirred at 5 °C for 30 min,
20 g (0.17 mmol) of propargyl bromide was slowly added over a
20 min period. The color of the solution changed to brown, and
then the reaction mixture was heated at 40 °C overnight. After
cooling, the reaction was quenched with water and extracted with
50 mL of ethyl ether thrice. The organic layers were combined,
washed with water and then with brine, and dried over Na2SO4.
Afterremoval ofthe ethylether byrotaryevaporation, the residue
was further purified by passing a silica gel column using mixed
ethyl acetate/hexanes (2/8 involume ratio) as eluent. About 3.57 g
of product was obtained (yield=79%). 1H NMR (CDCl3): 4.13
(8H, -OCHH2), 3.55 (8H, C(CH2)4), 2.43 (4H, CH). FTIR
(cm-1): ν(tCH)=3299, ν(CtC)=2120.
1.2. Characterization. The chemical structures of the synthe-
sized chemicals were characterized by 1H NMR spectroscopy on
a Bruker ARX 300 MHz spectrometer, using CDCl3 or dimethyl
sulfoxide-d6 (DMSO-d6) as the solvent in 1000 scans and a
relaxation time of 2 s. Fourier transform infrared (FTIR) spectra
were obtained from a MAGNA-IR 750 spectrometer (Nicolet
Instrument Co.). The sample was dispersed in a KBr pellet. The
tensile testing was performed on an Instron Model 5844 tensile
testing instrument at room temperature at an extension speed of
0.01 mm/sec until the failure of the sample. The hydrogels were
cut into a dumbbell shape with a length of 50 mm and width of
10 mm. The morphologies of the networks were studied by
scanning electron microscope (Hitachi X-650 SEM) at an
accelerating voltage of 5-20 kV and an object distance of about
8 mm. The absorption and transmittance spectra of the prepared
hydrogels were measured on a Hitachi U-4100 UV-vis spectro-
photometer over the 200-900 nm range with 1 nm resolution.
Deionized water was used as the background correction. The
hydrogels samples with a thickness of 0.5 cm were fixed on the
inner wall of a quartz cell. Differential scanning calorimetry
(DSC) measurement was conducted on a TA Instrument DSC
Q-10 over the temperature range from -50 to þ200 °C at a
heating rate of 10 °C/min under nitrogen environment. DSC was
calibrated with metallic indium (99.9% purity). All the prepared
PEG network samples were tested in crimped aluminum pans.
The thermal stability of the prepared PEG network, were carried
out on a thermogravimetric analyzer (SDT-Q600, TA In-
structments) at a temperature ranging from 50 to 700 °C at
heating rate of 10 °C/min under nitrogen atmosphere. XPS
measurements were carried out on a Kratos AXIS HSi spectro-
meter (Kratos Analytical Ltd., Manchester, England) with a
monochromatized Al KR X-ray source (1486.6 eV photons).
The X-ray source was run at a reduced power of 150 W (15 kV
and 10 mA). The samples were mounted on the standard sample
studs by means of double-sided adhesive tapes. The core-level
spectra were obtained at the photoelectron takeoff angle (with
respect to the sample surface) of 90°. The pressure in the analysis
chamber was maintained at 10-8 Torr or lower during sample
measurements.
2.2.3. Synthesis of the Macroinitiator Bromobutyryloxy R-
Cyclodextrin (R-CD-BIBB). A 250 mL round-bottom three-
necked flask with a magnetic stirring bar was charged with
6.48 g (6.67ꢀ10-3 mol) of R-CD and kept under nitrogen before
the addition of 120 mL of dry pyridine. The reaction mixture
was cooled to 0 °C under stirring, a solution of 1.0 mL (8ꢀ10-3
mol) of 2-bromoisobutyryl bromide (BIBB) in 40 mL of CHCl3
was slowly added within 30 min. Then, the reaction mixture was
further stirred at room temperature for 24 h. The reaction
mixtures were washed with ice water several times to remove
the salt, and the organic layers were dried over anhydrous mag-
nesium sulfate, filtered, and concentrated under reduced pres-
sure. The obtained white solid was washed with ice water again
until PH value reaches 7.0, then dried under vacuum at 50 °C to
1
give R-CD-BIBB as a white solid. H NMR (DMSO-d6): 4.88
(6H,-CH(O-)2,3.35-3.9 (42H, -OH; dCHO-,-CH2O-), 1.84
(6H, -CH3). FTIR (cm-1): ν(CdO)=1738, ν(O-H)=3369.
2.2.4. Preparation of Inclusion Complex N3-PEG4K-N3/(R-
CD-BIBB)m. About 2.0 g (0.5 mmol) of poly(ethylene glycol)
diazide were dissolved in 100 mL water. Then 400 mL of
aqueous R-CD-BIBB solution 1.145 g (1 mmol) or 1.72 g (1.5
mmol) was added at room temperature. The mixture was
ultrasonically agitated for 30 min and then allowed to stand
overnight. The white precipitate was collected by centrifugation,
washed with ice water, then dried under vacuum at 70 °C to give
R-CD-BIBB and N3-PEG4K-N3 inclusion complex (N3-PEG4KN3/
(R-CD-BIBB)m, m=1.1 or 2.3). FTIR (cm-1): ν(CdO) =1738,
ν
(O-H)=3413.
2.2.5. Preparation of s-IPN-PEG/R-CD-sg-PHEMAs from
2.2. Chemical Synthesis. 2.2.1. Synthesis of Poly(ethylene
glycol)-Diazide (N3-PEG4K-N3). Poly(ethylene glycol) diazide
was prepared from PEG according to the method reported in the
literature.47 About 10 g (2.5 mmol) of PEG (Mn=4000 g/mol)
was dissolved in 50 mL dry of pyridine. The solution was cooled
to 0 °C, and 0.98 g (12.5 mmol) of methanesulfonyl chloride in
10 mL of dry dichloromethane was dropwise added over 20 min.
After 1 h, the reaction mixture was allowed to rise to room
temperature and stirred for another 12 h. Removal of the solvent
Simultaneous CuAAC and ATRP. A typical procedure for
preparation of s-IPN-PEG/R-CD-sg-PHEMAs via simulta-
neous ATRP of HEMA and “click chemistry” of inclusion
complex N3-PEG4K-N3/(R-CD-BIBB)m with tetrakis(2-propy-
nyloxymethyl)methane was briefly described as follows. 2.64 mL
(22 mmol) of HEMA, 29 mg (0.2 mmol) of CuBr, 0.52 g (0.1 mmol)
of inclusion complex N3-PEG4K-N3/(R-CD-BIBB)1.1, 14.4 mg
(0.05 mmol) of tetrakis(2-propynyloxymethyl)methane and 1.5 mL
of DMF were introduced into a small vial. After 20 min of argon

Article
Macromolecules, Vol. 43, No. 23, 2010 9763
Scheme 1. Process of the Preparation of Poly(ethylene glycol) (PEG, Mn=4000 g/mol) Network with Movable Sliding-Graft Poly(2-hydroxyethyl
methacrylate) (PHEMA) (s-IPN-PEG/r-CD-sg-PHEMA) via Simultaneous ATRP and “Click Chemistry” (CuAAC)
degassing, PMDETA [42 uL (0.2 mmol)] was added to the flask
with a syringe under ultrasonic agitation (the ratio of reagents
[N3-PEG4K-N3/(R-CD-BIBB)1.1]:[TOPM]:[CuBr]:[PMDETA]:-
[HEMA]=0.5:0.25:1:1:110). The gelation of reaction occurs in
2 min. The mixture was kept at 60 °C for a predetermined period
of time to obtain the uniform solid semi-IPN. A uniform s-IPN
was obtained upon removal from the vial. The prepared s-IPN-
PEG/R-CD-sg-PHEMA was transferred to an EDTA (5%) solu-
tion to remove the copper ions and DMF. Finally, the s-IPN-
PEG/R-CD-sg-PHEMA was immersed into a large volume of
pure deionized water to allow the maximum water absorption.
2.2.6. Preparation of Pristine PEG Network from CuAAC.
About 0.1 g (0.025 mmol) of poly(ethylene glycol) diazide (N3-
PEG4K-N3), 3.6 mg (0.0125 mmol) of tetrakis(2-propynyloxy-
methyl)methane, 8.7 mg (0.05 mmol) of PMDETA, and 1 mL of
DMF were introduced into a small vial. After the mixture turned
clear, the vial was degassed with argon for 20 min, and 7.2 mg
(0.05 mmol) of CuBr was quickly added under ultrasonic agitation.
The gelation point was reached in 1 min, and the reaction was
allowed to continue to a predetermined period of time at 60 °C. A
uniform PEG network was obtained upon removal from the
vial. The prepared network was transferred to an EDTA (5%)
solution to remove the copper ions and DMF. Finally, the PEG
network was immersed into a large volume of pure deionized
water to allow the maximum water absorption.
[N3-PEG4K-N3/(R-CD-BIBB)1.1]:[TOPM]:[CuBr]:[PMDETA]=
0.5:0.25:1:1:1). The gelation of reaction occurs in 90 s. The
mixtures were kept at 60 °C for a predetermined time to obtain a
solid uniform gel. The PEG network was transferred to an
EDTA (5%) solution to remove the copper ions and DMF.
Finally, the PEG network was immersed into a large volume of
pure deionized water to allow the water absorption.
2.2.8. Preparation of s-IPN-PEG/PHEMA via Simultaneous
CuAAC and ATRP. Typical s-IPN of PEG/PHEMA was pre-
pared via simultaneous ATRP of HEMA and “click chemistry”
of N3-PEG4K-N3 with TPOM was briefly described as follows.
2.64 mL (22 mmol) of HEMA, 29 mg (0.2 mmol) of CuBr, 0.4 g
(0.1 mmol) of N3-PEG4K-N3, 14.4 mg (0.05 mmol) of tetrakis(2-
propynyloxymethyl)methane, 29.4 uL (0.2 mmol) of ethyl R-
bromobutyrate (EBB), and 1.5 mL of DMF were introduced
into a small vial. After 20 min of argon degass, 42 μL (0.2 mmol)
of PMDETA was added to the flask with a syringe under ultra-
sonic agitation (the ratio of reagents [N3-PEG4K-N3]:[TOPM]:-
[EBB]:[CuBr]:[PMDETA]:[HEMA] = 0.5:0.25:1:1:1:110). The
gelation of s-IPN occurred in 2 min. The mixture was kept at
60 °C for a predetermined time to obtain the uniform solid s-IPN.
The copper catalyst and DMF in the s-IPN were also removed in
5% EDTA solution, and maximum water absorption was
achieved by immersing the s-IPN in deionized water.
2.2.9. Swelling Ratio. Swelling behavior of the prepared PEG
networks was studied by a gravimetric method. Dry films were
immersed in distilled water at 25 °C, and the swollen weight was
measured for each sample at a given time after excess surface
water was blotted carefully with moistened filter paper. The
value was recorded until the weights do not increase further. The
swelling ratio (SR) of PEG networks were determined gravime-
trically using following relation:
2.2.7. Preparation of Slide-Ring PEG/(R-CD-BIBB)m Net-
work from CuAAC. A typical procedure for preparation of
slide-ring PEG/R-CD network via “click chemistry” as follows.
A 29 mg (0.2 mmol) sample of CuBr, 0.52 g (0.1 mmol) of inclu-
sion complex N3-PEG4K-N3/(R-CD-BIBB)1.1,14.4mg(0.05mmol)
of tetrakis(2-propynyloxymethyl)methane, and 1.5 mL of DMF
were introduced into a small vial. After 20 min of argon
degass, 42 uL (0.2 mmol) of PMDETA was added to the flask
with a syringe under ultrasonic agitation (The ratio of reagents
SR ¼ ½ðmt - m0Þ=m0ꢁꢀ100%

9764 Macromolecules, Vol. 43, No. 23, 2010
Yao et al.
Here mt is the mass of the swollen hydrogels at time t and m0 is
the mass of the dry gel. Each value was the average value from
five measurements.
2.2.10. Water Extraction. The prepared semi-IPN were initi-
ally dried at 50 °C in vacuum more than 24 h until sample weight
reached a constant value, and the weight was recorded as W0.
Then the dried semi-IPN sample was immersed in water for
predetermined time to allow linear PHEMA diffuse into water.
Afterward, sample was collected out of water and dried at 50 °C
in vacuum until sample weight reached a constant value, and the
weight was recorded again as Wt, where t is immersion time.
Weight percent=W0/Wt. Each value was the average value from
five measurements.
3. Results and Discussions
3.1. Synthesis of Sliding-Graft Semi-IPN of PEG and
PHEMA (s-IPN-PEG/r-CD-sg-PHEMAs) via Simultaneous
ATRP and CuAAC. Scheme 1 shows the preparation of the
sliding-graft semi-IPN of PEG and PHEMA (s-IPN-PEG/R-
CD-sg-PHEMA) from simultaneous CuAAC and ATRP.
s-IPN-PEG/R-CD-sg-PHEMA was prepared from the one-
pot simultaneous reactions of (1) “click chemistry” (CuAAC)
of the poly(ethylene glycol) diazide (Mn = 4000 g/mol, N3-
PEG4K-N3) and R-CD-BIBB inclusion complex initiators
(N3-PEG4K-N3/(R-CD-BIBB)m) and tetrakis(2-propynylox-
ymethyl)methane (TPOM) to generate the network with
1,2,3-triazole linkages and (2) ATRP of 2-hydroxyethyl met-
haycrylate (HEMA) using N3-PEG4K-N3/(R-CD-BIBB)m as
initiator, copper(I) bromide as catalyst and pentamethyl-
diethylenetriamine (PMDETA) as ligand. Here N3-PEG4K
-
N3/(R-CD-BIBB)m not only serves as reaction agents for
“click chemistry”, but also acts as the initiators for ATRP of
HEMA.
Figure 1. Photographs (a) of the pristine PEG hydrogel from “click
chemistry” (CuAAC), (b) of slide-ring PEG/(R-CD-BIBB)1.1 hydrogel
from “click chemistry” (CuAAC), and (c) of the s-IPN-PEG/R-CD1.1
-
First, the ATRP initiator of R-CD-BIBB was synthesized.
The successful preparation of R-CD-BIBB was confirmed by
FTIR with characteristic absorption peak of ester group at
1738 cm-1. Calculating from 1H NMR results of R-CD-BIBB
with the integral areas of peak at 1.84 ppm (CH3) and peak at
4.88 ppm((-O)2CH-), each R-CD-BIBB has about of 1.12
initiating sites. Then, R-CD-BIBB were threaded onto poly-
(ethylene glycol)-diazide (N3-PEG4K-N3) chains to prepare
N3-PEG4K-N3/(R-CD-BIBB)m. The formation of inclusion
complex was studied by FTIR characterization. The R-CD-
sg-PHEMA51 hydrogel via simultaneous “click chemistry” (CuAAC)
and ATRP (in Table 1), respectively.
CuAAC with a the same reaction condition as that for the
preparation of s-IPN-PEG/R-CD-sg-PHEMAs albeit in the
absence of HEMA. Figure 1 shows the optical images (a) of
the pristine PEG network from CuAAC, (b) of slide-ring
PEG/(R-CD-BIBB)1.1 from CuAAC, and (c) of the s-IPN-
PEG/R-CD1.1-sg-PHEMA51 via simultaneous CuAAC and
ATRP (in Table 1), respectively.
BIBB shows an extremely strong absorption band at 3369 cm-1
,
which is attributable to the symmetric and asymmetric O-H
Since CuAAC and ATRP share a same catalyst system, the
concentration of Cu(I) catalyst plays an important role in the
gelation effect. Previous work31 shows, the increase in the
amount of Cu(I) catalyst can reduce the gelation time. In this
study, N3-PEG4K-N3/(R-CD-BIBB)1.1 inclusion complex was
used for the preparation of s-IPN-PEG/R-CD1.1-sg-PHEMAs.
By increasing the concentration of CuBr from 25%
to 200% (relative to the mole concentration of azido and
alkynyl groups), the respective gelation time decreased from
stretching mode. The shift of broad O-H band to 3413 cm-1
,
due to the noncovalent interaction between O-H of R-CD and
the N3-PEG4K-N3 macromolecules, reveals that the N3-
PEG4K-N3 and R-CD-BIBB inclusion complex is formed
by host and guest interaction.48 The number of R-CD-BIBB
in inclusion complex can be readily tuned by changing the
R-CD-BIBB and N3-PEG4K-N3 feed ratio. The number of
R-CD-BIBB in each N3-PEG4K-N3/(R-CD-BIBB)m inclusion
complex can be calculated from 1H NMR results, using the
integral areas of peak at 4.88 ppm ((-O)2CH-), assigned to
character protons of R-CD-BIBB, and peak in the range of
3.2-4.0 ppm ((-OCH2CH2-) attributable to N3-PEG4K-N3
protons. Here, N3-PEG4K-N3/(R-CD-BIBB)m inclusion com-
plexes, having average 1.1 of R-CD-BIBB (N3-PEG4K-N3/
about 30 min to 20 s. In this study, s-IPN-PEG/R-CD1.1
-
sg-PHEMAs were prepared with an [N3-PEG-N3/(R-CD-
BIBB)1.1]:[TPOM]:[HEMA]:[CuBr]:[PMDETA] molar ratio
of 0.5:0.25:110:1:1. The gelation was reached in 2 min. The
disappearance of FTIR absorption band at 2080 cm-1 assig-
ned to azide group and at 2120 cm-1 assigned to alkynyl
group, as well as the appearance of the strong broad absorption
band at 3360 cm-1 attributed to the hydroxyl group of
PHEMA, suggested that the s-IPN-PEG/R-CD-sg-PHEMAs
was prepared. The successful preparation of s-IPN-PEG/
R-CD-sg-PHEMAs was also confirmed by X-ray photoelec-
tron spectroscopy (XPS). Figure 2 shows the XPS C 1s core-
level spectra (a) of the pristine PEG network, (b) of slide-
ring PEG/(R-CD-BIBB)1.1 network, and (c) of sliding-graft
(R-CD-BIBB)1.1, m=1.1) and 2.3 of R-CD-BIBB (N3-PEG4K
-
N3/(R-CD-BIBB)2.3, m = 2.3) on each N3-PEG4K-N3, were
prepared.
Sliding-graft semi-IPN of PEG and PHEMA (s-IPN-
PEG/R-CD-sg-PHEMA) was prepared via simultaneous
CuAAC and ATRP from a reaction mixture of N3-PEG4K-N3/
(R-CD-BIBB)m, TPOM, CuBr, PMDETA, HEMA and DMF.
Slide-ring PEG/(R-CD-BIBB)m networks were prepared via

Article
Macromolecules, Vol. 43, No. 23, 2010 9765
Scheme 2. Theoretical Molecular Structures (a) of Pristine PEG Net-
work from “Click Chemistry” (CuAAC), (b) of Slide-Ring PEG/(r-
CD-BIBB)m from “Click Chemistry” (CuAAC) and (c) of s-IPN-PEG/
r-CD-sg-PHEMA via Simultaneous “Click Chemistry” (CuAAC) and
ATRP
s-IPN-PEG/R-CD-sg-PHEMAs (s-IPN-PEG/R-CD1.1-sg-
PHEMA23 in Table 1), respectively. For pristine PEG net-
work from CuAAC, it has only one peak component at
286.2 eV, which is attributable to C-O and C-N=species.49 The
C 1s core-level spectrum of slide-ring PEG/(R-CD-BIBB)1.1
network can be curve-fitted into four peak components with
bonding energy (BEs) at about 284.6 eV, 286.2 eV, 287.6 and
288.4 eV, attributable to C-H/C-C, C-O/C-Br, O-C-O,
and O-CdO species, respectively. Since a-CD-BIBB is
water-soluble, unthreaded a-CD-BIBB on gel surface would
be removed by long time water immersion. Thus, the pre-
sence of peak components at 287.6 and 288.4 eV, associated
with the a-CD and bromide-capped ester group of a-CD-
BIBB, reveals that slide-ring PEG/(a-CD-BIBB)m network
has been successfully prepared. In Figure 2c, the increase in
intensity of C-H/C-C and O-CdO species is consistent
with the appearance of the poly(2-hydroxyethyl methacrylate)
(PHEMA) brushes in s-IPN-PEG/R-CDm-sg-PHEMAs.
Scheme 2 shows the possible molecular structures (a) of the
pristine PEG network, (b) of slide-ring PEG/(R-CD-BIBB)m
network, and (c) of sliding graft sliding graft s-IPN-PEG/
R-CDm-sg-PHEMAs, respectively. XPS results consist with
the molecular structures of the corresponding networks.
The gel fraction of the s-IPN-PEG/R-CDm-sg-PHEMAs is
one of the main concerns. The data in Table 1 show that gel
fraction of pristine PEG network, slide-ring PEG/(a-CD-
BIBB)m and sliding graft s-IPN-PEG/R-CDm-sg-PHEMA.
The gel fraction was obtained from the expression: Gel frac-
tion=Massdried-gel/Masspolymer-precursors. The gel fraction of

9766 Macromolecules, Vol. 43, No. 23, 2010
Yao et al.
Figure 3. Swelling ratio in deionized water of (a) pristine PEG hydrogel
from “click chemistry” (CuAAC), (b) of slide-ring PEG/(R-CD-
BIBB)1.1 hydrogel from “click chemistry” (CuAAC), and (c) of
s-IPN-PEG/R-CD1.1-sg-PHEMA23 via simultaneous “click chemistry”
(CuAAC) and ATRP (in Table 1) as a function of time.
increases the conversion of ATRP, but the PEG gel fraction
can not be improved further.
3.2. Swelling and Transmittance Performance. Figure 3
shows the degree of swelling ratio (SR) of (a) pristine PEG
network, (b) of slide-ring PEG/(R-CD-BIBB)1.1, and (c) of
s-IPN-PEG/R-CD1.1-sg-PHEMA23 as a function of time. As
shown, all samples can reach swelling degree of 80% in 500 min.
Pristine PEG network from CuAAC exhibit a swelling
degree of about 1570%, which is much higher than that
(820%) of slide-ring PEG/(R-CD-BIBB)1.1 and that (520%)
of s-IPN-PEG/R-CD1.1-sg-PHEMA23. The increase in the num-
ber of R-CD-BIBB thread on PEG chain50 and the length of
PHEMA also leads to the reduction of swelling degree of
hydrogels. The data in Table 1 show, the slide-ring PEG/
Figure 2. X-ray photoelectron spectroscopy (XPS) C 1s core-level
spectra (a) of the pristine PEG networks, (b) of slide-ring PEG/(R-CD-
BIBB)1.1 network, and (c) of s-IPN-PEG/R-CD-sg-PHEMAs (s-IPN-
PEG/R-CD1.1-sg-PHEMA23) network in Table 1, respectively.
(R-CD-BIBB)
hydrogel has a swelling degree of about
2.3
660%, which is much low than that of slide-ring PEG/(R-
CD-BIBB)1.1 hydrogel. The swelling degree of s-IPN-PEG/
R-CD1.1-sg-PHEMA51 is about of 320%, which is lower than
that (370%) of s-IPN-PEG/R-CD1.1-sg-PHEMA35 and that
(520%) of s-IPN-PEG/R-CD1.1-sg-PHEMA23. This could be
accounted for the facts as follows: (1) the networks from
“click chemistry” are well-defined and the maximum SR of
PEG network are dominated by the size of network lattice,
that is the chain length of PEG. Since the networks are made
from PEG4K, thus the theoretic free volume of hydrogels are
same; (2) the inclusion of the R-CD-BIBB and the sliding-
grafted R-CD-sg-PHEMA chains would reduce the free
volume of the PEG network lattices; (3) moreover, the inter-
action of the R-CD-BIBB and entanglement of the sliding-
grafted R-CD-sg-PHEMA chains restrict the full stretching
of the network lattices and resulting in a lower degree of
swelling; (4)The decrease in the swelling degree of s-IPN-
PEG/R-CD-sg-PHEMA with a high PHEMA composition
could also be accounted for the fact that PHEMA is a
relatively more hydrophobic than PEG. Figure 4 shows the
scanning electron microscopy (SEM) cross-sectional images
of the freeze-dried samples (a) of the pristine PEG network,
(b) of slide-ring PEG/(R-CD-BIBB)1.1 and (c) of s-IPN-PEG/
R-CD1.1-sg-PHEMA51 networks. As shown in Figure 4a, the
pristine PEG network is highly porous with pore sizes
slide-ring PEG/(R-CD-BIBB)1.1 network was about 90%,
which was slightly lower than that (94%) of pristine PEG
network, while is higher than that (84%) of slide-ring
PEG/(R-CD-BIBB)2.3 networks. The gel fraction decreases
with increase in the number of R-CD-BIBB in N3-PEG4K
-
N3/(R-CD-BIBB)m. This could be accounted for the facts
that the inclusion of the R-CD-BIBB enhances the rigid of
the PEG chain and reduces the molar free volume of polymer
chains, which reduced the efficiency of “click chemistry”.
The length of PHEMA brushes of s-IPN-PEG/R-CDm-sg-
PHEMAs can be calculated from the conversion of HEMA
monomers. The conversion of HEMA was calculated from
the expression of [Massdried-gel of s-IPN-PEG/R-CDm-sg-PHEMA
-
Massdried sliding-ring PEG/(R-CD-BIBB)m gel]/MassHEMA. The data
in Table 1 indicate that, at a reaction time of 6 h, the
conversion of HEMA is of about 0.23, that is, the theoretical
length of PHEMA on R-CD-BIBB is about of 23. The length
of PHEMA brushes can be regulated by polymerization
time. Table 1 also shows, with the polymerization time
increase from 6 to 12 and 24 h, the conversion of HEMA
enhanced from 23% to 35% and 51%, respectively. Corre-
spondingly, the length of PHEMA brushes on R-CD-BIBB
increases from 23 to 35 and 51 repeat units. In fact, the rate of
“click chemistry” was very fast. In the process of simulta-
neous “click chemistry”(CuAAC) and ATRP, about 90%
of Click conversion can be achieved in 5 min.29 Thus, in the
first few minutes, “click chemistry” was the predominant
reaction. With process of reactions and completion of the
Click reaction, ATRP of HEMA became dominated reaction.
At this stage, the polymerization may be considered as the
ATRP of HEMA in a PEG-based network. Previous works31
indicated that after 30 min, extending reaction time just
ranging from 40 to 120 μm. While s-IPN-PEG/R-CD1.1
-
sg-PHEMA51 has a homogeneous and dense morphology.
The morphologies reveal the sliding-grafted R-CDm-sg-
PHEMAs chains take up the space volume between the lat-
tices of PEG networks, thus leading to a low swelling degree
in s-IPN-PEG/R-CD-sg-PHEMAs. The SEM results are
consistent with the swelling ratio, that is, the more porous
the structure, the higher the degree of swelling.

Article
Macromolecules, Vol. 43, No. 23, 2010 9767
Figure 5. UV-visible transmittance spectra (a) of the pristine PEG
hydrogel, (b) of slide-ring PEG/(R-CD-BIBB)1.1, and (c) of s-IPN-
PEG/R-CD1.1-sg-PHEMA51 hydrogels.
Figure 6. Thermogravimetric analysis (TGA) curves (a) of pristine PEG
network, (b) of slide-ring PEG/(R-CD-BIBB)1.1, and (c) of s-IPN-PEG/
R-CD1.1-sg-PHEMA51 networks.
hydrogels is lower less than 1%. At the wavelength of 400 nm,
the transmittance of s-IPN-PEG/R-CD1.1-sg-PHEMA51 hydro-
gel is about 4.9%, which is lower than that (15.2%) of slide-
ring PEG/(R-CD-BIBB)1.1 and that (21.6%) of pristine PEG
hydrogels. The good UV-resistance of s-IPN-PEG/R-CD-sg-
PHEMAs may attribute to the UV absorption of PEG and
PHEMA polymers,51 as well as the reflection at interfaces and
scattering due to the phase separation. In the visible region, the
transmittance of hydrogels increases with the increase in the
wavelength. The pristine PEG hydrogel and slide-ring PEG/
(R-CD-BIBB)1.1 exhibit a high transparence. At the wave-
length of 800 nm, the transmittance of the slide-ring PEG/(R-
CD-BIBB)1.1 hydrogel is about of 71%, which is very close to
that (75%) of pristine PEG hydrogel. The presence of sliding-
grafted R-CD-sg-PHEMA in s-IPN-PEG/R-CD-sg-PHEMA
hydrogel largely reduces the transparence. For the s-IPN-
PEG/R-CD1.1-sg-PHEMA51 hydrogel, the transmittance is
less than 35% at 800 nm. The low transmittance of s-IPN-
PEG/R-CD-sg-PHEMA could be attributable to the phase
separation between the PEG network and sliding-grafted R-CD-
sg-PHEMA chains.
3.3. Thermal and Mechanical Properties. The thermal
stability is very important for materials aiming for biomedi-
cal applications. Here the thermal properties of s-IPN-PEG/
R-CD-sg-PHEMA were studied by TGA and DSC. Figure 6
shows the thermalgravimetric analysis (TGA) curves of dried
pristine PEG network, slide-ring PEG/(R-CD-BIBB)1.1 and
s-IPN-PEG/R-CD1.1-sg-PHEMA51 networks. It shows three
different decomposition temperatures (Td) at about 337, 359,
and 237 °C for pristine PEG network, slide-ring PEG/
(R-CD-BIBB)1.1 and s-IPN-PEG/R-CD1.1-sg-PHEMA51
networks, respectively. The slide-ring PEG/(R-CD-BIBB)1.1
Figure 4. Scanning electron microscopy (SEM) cross-sectional views of
the freeze-dried samples (a) of the pristine PEG network, (b) of slide-
ring PEG/(R-CD-BIBB)1.1 and (c) of s-IPN-PEG/R-CD1.1-sg-PHEMA51
networks.
One of the possible plausible applications of s-IPN is used
as soft contact lenses. The optic property of s-IPN-PEG/R-
CD-sg-PHEMA is another concern. Figure 5 shows the
transmittance (a) of the pristine PEG hydrogel, (b) of slide-
ring PEG/(R-CD-BIBB)1.1 and (c) of s-IPN-PEG/R-CD1.1
-
sg-PHEMA51 hydrogels. The pristine PEG hydrogel has a
higher transmittance than those of slide-ring PEG/(R-CD-
BIBB)1.1 and s-IPN-PEG/R-CD1.1-sg-PHEMA51 hydrogels.
The slide-ring PEG/(R-CD-BIBB)1.1 hydrogel and s-IPN-PEG/
R-CD1.1-sg-PHEMA51 hydrogel exhibit a high UV resistance.
In the range of 200 to 300 nm, the transmittance of slide-ring
PEG/(R-CD-BIBB)1.1 and s-IPN-PEG/R-CD1.1-sg-PHEMA51

9768 Macromolecules, Vol. 43, No. 23, 2010
Yao et al.
Figure 8. Weight loss of s-IPN-PEG/R-CD1.1-sg-PHEMA35 and s-IPN-
PEG/PHEMA networks as a function of water immersion time.
to pristine PEG hydrogel, the little decrease in the tensile
stress of sliding-ring PEG/(R-CD-BIBB)m hydrogels could
be attributed to their relatively lower gel fraction (Table 1). A
higher gel yield means a fewer defragments, leading to a
higher tensile stress. The s-IPN-PEG/R-CD1.1-sg-PHEMA23
hydrogel has a tensile stress of about 980 kPa, which is much
higher that of pristine PEG hydrogel. The increase in tensile
stress of s-IPN-PEG/R-CD-sg-PHEMA may attribute to the
entanglement, as well as the friction between the sliding-
grafted PHEMA chains. The data in Table 1 also show that
the longer the sliding-grafted PHEMA chains, the higher the
tensile stress of s-IPN-PEG/R-CD-sg-PHEMA gels. It is
obvious that the extension in the sliding-grafted PHEMA
would enhance the entanglement. The maximum extension
to break (MEB) of slide-ring PEG/(R-CD-BIBB)m and s-IPN-
PEG/R-CD-sg-PHEMA hydrogels is lower than that of
pristine PEG hydrogel. The data in Table 1 also reveals,
the increase in the number of R-CD threaded onto PEG and
the length of sliding-grafted PHEMA decreases the MEB. The
PEG network form “click chemistry” is well-defined and the
mesh size of networks is decided by the size of PEG. It is
obvious, the bigger the mesh size, the larger space volume in the
network lattices and thus a higher MEB. The introduction of
the R-CD onto PEG lattice, as well as the sliding-grafted
PHEMA chains would largely reduce the space volume among
the lattice of PEG network, and thus leading to a low MEB.
3.4. Water Extraction. Hydrophilic semi-IPN is a good
candidate for biomaterials.54,55 However, the interpenetrat-
ing linear polymers, especially those with a relatively lower
molecular weight would diffuse out from the semi-IPN. The
diffusion of linear polymers from semi-IPN for a long time
immersion in an aqueous solution, will not only reduce
the physical and mechanical properties of semi-IPNs, but
also limits their applications in biomedical fields.37 To study
the antiwater-extraction property of s-IPN-PEG/R-CD-sg-
PHEMA hydrogel, a classical semi-IPN of PEG and PHE-
MA (s-IPN-PEG/PHEMA)was prepared under a same reac-
tion condition as that of s-IPN-PEG/R-CD1.1-sg-PHEMA35,
except using ethyl 2-bromobutyrate and N3-PEG-N3 instead of
N3-PEG-N3/(a-CD-BIBB)m inclusion complex. Figure 8
shows the weight loss of s-IPN-PEG/R-CD1.1-sg-PHEMA35
and s-IPN-PEG/PHEMA hydrogels as a function of water
immersion time. After 20 h water immersion, the weight of
s-IPN-PEG/R-CD1.1-sg-PHEMA35 hydrogel was almost
stable, while for s-IPN-PEG/PHEMA, the weight decreases
to 96%. The weight loss of s-IPN-PEG/PHEMA could be
attributed to the diffusion of the linear PHEMA from the
s-IPN. Since the PHEMAs were fixed onto the network
lattices, the diffusion of the PHEMAs from s-IPN-PEG/
R-CD-sg-PHEMA hydrogels was largely prevented. The
prolongation of the water extraction of s-IPN-PEG/PHEMA
would cause a further weight loss due to the diffusion of
PHEMA. However, after 48 h, the weigh loss was not as
Figure 7. Differential scanning calorimetry (DSC) curves of dried (a) pri-
stine PEG network, (b) slide-ring PEG/(R-CD-BIBB)1.1, and (c) s-IPN-
PEG/R-CD1.1-sg-PHEMA51 networks.
networks undergoes thermal decomposition at 359 °C, which
is higher than that (337 °C) of pristine PEG network. The
PEG/R-CD inclusion complex exhibits a high thermal stabi-
lity than both PEG and R-CD chemicals.52 Thus, the increase
in thermal stability suggests that the slide-ring PEG/(R-CD-
BIBB)m have been successfully prepared. The weight loss of
s-IPN-PEG/R-CD-sg-PHEMA commences at 237 °C, which
is much lower than that of pristine PEG network and slide-ring
PEG/(R-CD-BIBB)m. The presence of the easily decomposable
composition (sliding-grafted R-CD-sg-PHEMA) reduces the
thermal stability of the s-IPN-PEG/R-CD-sg-PHEMA networks.
Figure 7 shows the differential scanning calorimetry (DSC)
curves (a) of pristine PEG network, (b) of slide-ring PEG/
(R-CD-BIBB)1.1 and (c) of s-IPN-PEG/R-CD1.1-sg-PHEMA51
networks, respectively. The melting transition temperature
(Tm) of slide-ring PEG/(R-CD-BIBB)1.1 network is of about
50.9 °C, which is lower than that (53.1 °C) of pristine PEG
network. The threaded R-CD onto the lattice of PEG net-
work both destroys the ordered molecular structure and
decreases the mobility of PEG. Thus, the decrease in Tm also
suggests that the slide-ring PEG/(R-CD-BIBB)m networks
have been successfully prepared. There were two transitions
in the DSC curves of s-IPN-PEG/R-CD-sg-PHEMA. The
first weak endothermic peak appeared at around 35 °C is
associated with the melting temperature (Tm) of the PEG
network. The second endothermic peak at around 104 °C
is attributable to the glass transition temperature (Tg) of
PHEMA. The decrease in the Tm of PEG network in s-IPN-
PEG/R-CD-sg-PHEMA can be accounted that the appear-
ance of sliding-graft R-CD-sg-PHEMA largely reduced the
crystallinity of PEG networks. The decrease of the crystal-
linity of PEG networks in s-IPN-PEG/R-CD-sg-PHEMA
was also revealed by the reduction of melting enthalpy. The
melting enthalpy of a 100% crystalline PEG (MW=4000) is
51.5 cal/g (214.6 J/g).53 The melting enthalpy of the pristine
PEG networks from CuAAC is about of 22.1 J/g (crystal-
linity=10.3%), which is higher than 15.2 J/g (crystal-
linity=7.1%) of slide-ring PEG/(R-CD-BIBB)1.1 network
and higher than 0.34 J/g (crystallinity=0.16%) of s-IPN-
PEG/R-CD1.1-sg-PHEMA51 network.
All prepared hydrogels exhibit a good mechanical prop-
erty, in comparison to the classic hydrogels.32 In comparison

Article
Macromolecules, Vol. 43, No. 23, 2010 9769
glycol) (PEG) network with movable sliding-graft poly(2-hydro-
xyethyl methacrylate) (PHEMA) brush (s-IPN-PEG/R-CD-sg-
PHEMA), were successfully prepared by simultaneous “click
chemistry” and atom transfer radical polymerization (ATRP).
The number of the sliding-graft PHEMA can be regulated by
threading different amount of R-CD-BIBB to N3-PEG-N3. The
chain length of sliding-graft PHEMA can be tunable by changing
the ATRP polymerization time. The s-IPN-PEG/R-CD-sg-
PHEMAs exhibit a good physical and mechanical property. The
s-IPN-PEG/R-CD-sg-PHEMAs hydrogels with various mechan-
ical strengths were prepared by changing the molecular structure,
such as the number and the chain length of sliding-graft polymer.
Most important, the s-IPN-PEG/R-CD-sg-PHEMA hydrogels
exhibit a strong antiwater-extraction. The diffusion of linear
penetrating polymers from the networks under long time solvent
immersion was largely prevented in s-IPN-PEG/R-CD-sg-
PHEMA hydrogels, because the interpenetrating polymers were
fixed on the network lattices. Furthermore, the sliding-graft
polymers can afford the s-IPN-PEG/R-CD-sg-PHEMAs more
functionalities, which extended their applications in biomedical
fields. In summary, simultaneous “click chemistry” and ATRP is
a powerful method to prepare semi-IPN with well-defined and
designed molecular structures.
Figure 9. XPS C 1s core-level spectra of (a) of the surface of s-IPN-
PEG/PHEMA, (b) of the cross-section of s-IPN-PEG/PHEMA, (c) of
the surface of s-IPN-PEG/R-CD1.1-sg-PHEMA35, and (d) of the cross-
section of s-IPN-PEG/R-CD1.1-sg-PHEMA35 networks after 20 h water
immersion, respectively.
Acknowledgment. This work was supported by National
Natural Science Foundation of China under the Grant 20804009
and 21074022, and the Key Project of Chinese Ministry of
Education Grant 108062. This work was also supported by the
Program for New Century Excellent Talents in University of Grant
NCET-08-0117.
remarkable as the starting few hours, and maintained around
of 6% after 72 h. The sol-gel fraction of s-IPN-PEG/R-CD-
sg-PHEMA and s-IPN-PEG/PHEMA hydrogels can also be
calculated from the data of SR and gel fraction of corre-
sponding networks. The data in Table 1 shows the sol-gel
fraction of s-IPN-PEG/R-CD-sg-PHEMA also maintained
stable after water extraction, while the sol-gel fraction of the
s-IPN-PEG/PHEMA changed from 2.7:6.3:91.0 ([PEG/R-
CD]:[PHEMA]:[H2O]) to 2.8:5.9:91.3.
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