Hyperbranched polymers by visible light induced self-condensing vinyl polymerization and their modifications

Article abstract of DOI:10.1021/ma401534w

Visible light induced self-condensing vinyl polymerization is explored using 2-bromoethyl methacrylate (2-BEMA) and methyl methacrylate (MMA) as inimer and comonomer, respectively, in the presence of dimanganese decacarbonyl (Mn₂(CO)₁₀

Full text of DOI:10.1021/ma401534w

Article
pubs.acs.org/Macromolecules
Hyperbranched Polymers by Visible Light Induced Self-Condensing
Vinyl Polymerization and Their Modifications
Semiha Bektas,† Mustafa Ciftci,† and Yusuf Yagci*,†,‡
†Department of Chemistry, Istanbul Technical University, Maslak, TR-34469, Istanbul, Turkey
‡Center of Excellence for Advanced Materials Research (CEAMR) and Chemistry Department, Faculty of Science, King Abdulaziz
University, PO Box 80203, Jeddah 21589, Saudi Arabia
S
* Supporting Information
ABSTRACT: Visible light induced self-condensing vinyl
polymerization is explored using 2-bromoethyl methacrylate
(2-BEMA) and methyl methacrylate (MMA) as inimer and
comonomer, respectively, in the presence of dimanganese
decacarbonyl (Mn2(CO)10) for the preparation of hyper-
branched polymers. Upon photoexcitation in the visible range,
Mn2(CO)10 undergoes irreversible decomposition leading to
the formation of initiating radicals through bromine abstraction
from 2-BEMA. Depending on the concentrations of 2-BEMA
and Mn2(CO)10 and irradiation time, hyperbranched polymers
with different branching density and cross-linked polymers were
formed. The resulting polymers possess unreacted bromide groups in the structure which allow postfunctionalization through
visible light photopolymerization and Cu(I)-catalyzed click reactions.
Scheme 1. Schematic Representation of Self-Condensing
Vinyl Polymerization (SCVP)
INTRODUCTION
■
In recent years, hyperbranched polymers have become an
attractive field of research not only due to their inherent
characteristics such as increased solubility, reduced solution
viscosity1,2 and a higher level of terminal functionality3,4 but
also relatively easier preparation methods compared to the
other dendritic polymers.5,6 Based on these properties, these
materials hold considerable future promises in different
applications particularly as drug delivery systems, bioimaging
agents, gene carriers, viscosity modifiers, and catalyst
supports.7−10
Synthesis of hyperbranched polymers can be rationalized into
three main strategies: (i) step-growth polycondensation of ABx
monomers, (ii) self-condensing vinyl polymerization (SCVP)
of AB monomers, and (iii) ring-opening polymerization of
latent ABx monomers.11−14 A stylish mode of such techniques,
transfer polymerization,16 nitroxide-mediated polymerization,17
and group-transfer and ring-opening polymerization.18,19
In a related work from this laboratory, we have recently
reported a modified version of SCVP for the synthesis of
hyperbranched and cross-linked polymers using propargyl
acrylate containing two polymerizable groups, namely acrylate
and propargyl groups, with different reactivities toward
photochemically generated free radicals.20
Photoinitiated polymerization has many advantages over
other polymerization processes including that it is fast, uses
little energy, readily occurs at room temperature, and is low
cost.21,22 The majority of industrial applications of photo-
initiated polymerizations for various techniques deal with free
SCVP, was first developed by Frec
́
het et al.15 to produce
polymers possessing both highly branched structures and
several functional groups. This approach proceeds via polymer-
ization of “inimers”, a special kind of vinyl monomer containing
a pendant group that can be converted into an initiating moiety.
Inimers are formulized as AB*, where A stands for a double
bond and B* represents an initiating group. First, the initiating
group is activated and then reacted with a double bond to form
a covalent bond and a new active side on the second carbon of
the double bond as shown in Scheme 1.
Depending on inimer structure, SCVP has been successfully
adapted to a wide variety of controlled polymerization systems
including living ionic polymerization, atom transfer radical
polymerization,14 reversible addition−fragmentation chain
Received: July 22, 2013
Revised: August 14, 2013
© XXXX American Chemical Society
A
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the normalized RM value significantly differs as polymer architecture
radical systems. Many free radical photoinitiators acting at
broad wavelength range are known, and their photochemistry
has been studied in detail.23−25 Among them, the dimanganese
decacarbonyl (Mn2(CO)10)-based initiating system is partic-
ularly important due to its solubility in most of the monomers
and solvents and efficiency in generating radical species upon
photolysis at visible range. Although the dinuclear complex
itself is stable and inactive in the dark, in conjunction with
halogen containing compounds it has the ability of to generate
radicals capable of initiating free radical polymerization under
visible light. Moreover, because alkyl halides are also used as co-
initiators to generate initiating radicals, the system provides
molecular design flexibility in macromolecular synthesis.26−29
Previously, we reported that this process can be employed for
the promotion of cationic polymerization,30 mechanism
transformations involving different polymerization modes,31
and preparation of telechelic polymers.32
This study further expands metal−carbonyl assisted free
radical generation process to investigate the possibility of the
fabrication of hyperbranched polymers. Herein, we report the
synthesis and characterization of hyperbranched poly(methyl
methacrylate) (PMMA) via visible light self-condensing vinyl
copolymerization (VL-SCVP) of methyl methacrylate (MMA)
and 2-bromoethyl methacrylate (2-BEMA) using Mn2(CO)10.
moves from linear (RM = 1.00) to highly branched architectures (RM
=
0.19). This parameter thus indicates a trend of branching density of
the synthesized polymers.
General Procedure for Synthesis of Bromo Functional
Hyperbranched Poly(methyl methacrylate) (Hyperbranched
PMMA−PBEMA). A representative radical photopolymerization
procedure for MMA is as follows. Mn2(CO)10 (2.96 mg, 7.60 ×
10−6 mol), 2-BEMA (76 μL, 7.06 × 10−4 mol), and 1 mL of MMA
(9.38 × 10−3 mol) were put in a Pyrex tube and filled with dry
nitrogen prior to irradiation by a Ker-Vis blue photoreactor equipped
with six lamps (Philips TL-D 18 W) emitting light nominally at 400−
500 nm at room temperature. The light intensity was 45 mW cm−2 as
measured by a Delta Ohm model HD-9021 radiometer. At the end of
irradiation, polymer was precipitated in excess methanol and dried in
vacuum. Conversions for all samples were determined gravimetrically.
All the other polymerizations were performed under identical
experimental conditions. Depending on the conditions, lightly
branched, highly branched, or partially cross-linked polymers were
obtained. In the case of cross-linked polymer, the soluble part was
extracted by THF.
General Procedure for Azidation of Bromo Functional
Hyperbranched Poly(methyl methacrylate). Azidation of bromo
functional hyperbranched polymers was carried out as described in the
literature.35 The resulting bromo functional hyperbranched PMMA
was used as the precursor material for the “click” modification by azide
functionalization through nucleophilic substitution. The bromo
functional hyperbranched PMMA (100 mg) (content of bromo
groups determined theoretically = 8.5 × 10−5 mol) was dissolved in 3
mL of DMF and was reacted with NaN3 (11 mg, 1.7 × 10−4 mol). The
resulting solution was left to stir at room temperature for 24 h and
precipitated into 10 times excess of methanol to yield the
corresponding azido-functionalized hyperbranched PMMA.
Synthesis of Acetylene Functional Poly(ethylene glycol)
Methyl Ether. Synthesis of PEG-acetylene (PEG-a) was carried out as
described previously.36 Thus, Me-PEG (Mn ∼ 2000 g mol−1) (1 g, 0.5
mmol) was dissolved in 25 mL of CH2Cl2. 4-Pentynoic acid (0.147 g,
1.5 mmol), DMAP (0.06 g, 0.5 mmol), and DCC (0.23 g, 1.5 mmol)
in 3 mL of dichloromethane were added to the solution in that order.
The reaction mixture was stirred overnight at room temperature. It
was filtered and evaporated, and the remaining product was purified by
column chromatography over silica gel eluting first with CH2Cl2/ethyl
acetate (1:1) and then with methanol/CH2Cl2 (1:10). Finally, the
organic phase was evaporated to give PEG-a.
Synthesis of Propargylpyrene. Synthesis of propargylpyrene was
carried out as described previously.37 To a solution of pyrene−
methanol (0.5 g, 2.15 mmol) in dry 10 mL of THF was added sodium
hydride (60 wt % dispersion in oil) (0.057 g, 2.37 mmol), and the
reaction mixture was stirred at 0 °C under nitrogen for 30 min. A
solution of propargyl bromide (0.28 g, 2.37 mmol) in toluene was
added portionwise to the solution. The mixture was kept stirring at
room temperature for 24 h, and then it was refluxed for 3 h in the dark.
The resulting mixture was cooled to room temperature and evaporated
to half of its volume. The solution was extracted with ethyl acetate, and
the organic layer was dried over anhydrous MgSO4. Evaporating ethyl
acetate afforded light yellow product. The crude product was dissolved
in toluene and was passed through a column of basic silica gel to
remove unreacted pyrene methanol. Toluene was removed by
evaporating and the residue was dried in a vacuum oven.
EXPERIMENTAL SECTION
■
Materials. Methyl methacrylate (MMA, Aldrich, 99%) and 2-
hydroxyethyl methacrylate (HEMA, 99%, Aldrich) were passed
through a column of basic alumina to remove the inhibitor. 2-
Bromoethyl methacrylate (2-BEMA) was kindly donated by Bicak
research group.33 Dimanganese decacarbonyl (Mn2(CO)10, 99%,
Aldrich) was purified by sublimation and stored in a refrigerator in
the dark. 1-Pyrenemethanol (98%, Sigma-Aldrich), sodium azide
(NaN3, 97%, Sigma-Aldrich), copper(I) bromide (Cu(I)Br, 98%,
Acros), N,N′-dicyclohexylcarbodiimide (DCC, 99%, Aldrich), 4-
(dimethylamino)pyridine (DMAP, 99%, Aldrich), 4-pentynoic acid
(98%, Alfa Aesar), poly(ethylene glycol) methyl ether (Me-PEG, Mn ∼
2000 g mol−1, Aldrich), n-hexane (95%, Aldrich), tetrahydrofuran
(THF, 99.8%, J.T. Baker), anhydrous N,N-dimethylformamide (DMF,
99.8%, Aldrich), and dichloromethane (CH2Cl2, J.T. Baker) were used
as received. N,N,N′,N″,N″-Pentamethyldiethylenetriamine (PMDETA,
99%, Aldrich), used as a ligand, was distilled before use. Methanol
(technical) was used for the precipitation of polymers without further
purification.
1
Analysis. All H NMR spectra were recorded on an Agilent NMR
System VNMRS 500 spectrometer at room temperature in CDCl3
with Si(CH3)4 as an internal standard.
FT-IR analyses were performed on a PerkinElmer FT-IR Spectrum
One B spectrometer.
In order to determine branching frequency, both apparent and
absolute molecular weights were measured from a Viscotek GPCmax
Autosampler system consisting of a pump module (GPCmax, Viscotek
Corp., Houston, TX), a combined light-scattering (Model 270 dual
detector, Viscotek Corp.), and a refractive index (RI) detector (VE
3580, Viscotek Corp.). The lightscattering detector (λ0 = 670 nm)
included two scattering angles: 7° and 90°. The RI detector was
calibrated with polystyrene standards having narrow molecular weight
distribution, and so the quoted molecular weights of the polymers are
expressed in terms of polystyrene equivalents. Two columns 7.8 × 300
mm, (LT5000L, Mixed, Medium Org and LT3000L, Mixed, Ultra-
Low Org) with a guard column 4.6 × 10 mm (Viscotek, TGuard) were
used for the chloroform eluent at 35 °C (flow rate: 1 mL min−1). Data
were analyzed using Viscotek OmniSEC Omni-01 software.
CuAAC Click Reaction of PEG−Acetylene with Azide
Functional Hyperbranched Poly(methyl methacrylate).
CuAAC click reaction of PEG-a with azide functional polymer was
performed as described previously.38 In a typical click reaction,
branched polymer (100 mg) (content of azide groups determined
theoretically = 8.5 × 10−5 mol), PEG-a (1.3 × 10−4 mol), catalyst
(CuBr, 1.3 × 10−4 mol), ligant (PMDETA, 1.3 × 10−4 mol), and 3 mL
of DMF were placed in a Schlenk tube. The reaction mixture was
degassed by three freeze−pump−thaw cycles and stirred at 25 °C for
24 h. After click reaction, the reaction mixture passed through a
column filled with neutral alumina to remove the copper salt,
The ratio between Mn,GPC‑RI and Mn,GPC‑LS (RM = Mn,GPC‑RI
/
Mn,GPC‑LS) gives qualitative information about the branching density of
the polymers since branched structures are more compact than linear
polymers for a given molecular weight.34 As can be seen in the table,
B
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Scheme 2. Visible Light Induced Synthesis of Hyperbranched Polymers
precipitated into methanol, and finally dried in a vacuum at room
temperature. Evidence for the occurrence of the “click” reaction is
1
obtained from H NMR and FTIR spectroscopy.
CuAAC Click Reaction of Propargylpyrene with Azide
Functional Hyperbranched Poly(methyl methacrylate). In a
typical click reaction, branched polymer (100 mg) (content of azide
groups determined theoretically = 8.5 × 10−5 mol), propargylpyrene
(1.3 × 10−4 mol), catalyst (CuBr, 1.3 × 10−4 mol), ligant (PMDETA,
1.3 × 10−4 mol), and 3 mL of DMF were placed in a Schlenk tube.
The reaction mixture was degassed by three freeze−pump−thaw
cycles and stirred at 45 °C for 48 h. After click reaction, the reaction
mixture passed through a column filled with neutral alumina to remove
the copper salt, precipitated into methanol, and finally dried in a
vacuum at room temperature. Evidence for the occurrence of the
1
“click” reaction is obtained from H NMR and FTIR spectroscopy.
Syntheses of Amphiphilic Star-Hyperbranched Poly(methyl
methacrylate)-b-poly(2-hydroxyethyl methacrylate) Copoly-
mers. The amphiphilic star-hyperbranched copolymers were prepared
Figure 1. Photobleaching behavior of the Mn2(CO)10 (1.3 × 10−4 M)
by photocopolymerization of bromo functional hyperbranched PMMA
macroinitiator (100 mg, 2.8 × 10−7 mol) with HEMA (0.5 mL, 3.8 ×
10−3 mol) in the presence of Mn2(CO)10 (8.3 mg, 2.1 × 10−5 mol)
under visible light irradiation. After the polymerization, the copolymer
was precipitated in n-hexane and characterized by 1H NMR and FT-IR
spectroscopy.
in CHCl3.
Table 1. Effect of BEMA Concentration on Branching
Density (RM)
a
BEMA cont soluble
BEMA
in the
polym
cont
[%]
b
c
d
e
in feed conv
polymer
Mn,GPC‑RI Mn,GPC‑LS
[mol %]
[%]
[mol %]
[g mol−1
]
[g mol−1
]
RM
RESULTS AND DISCUSSION
■
3
7.5
10
20
44
55
4.1
9.4
100
100
70
16 500
81 600
50 300
355 000
596 500
0.33
0.23
0.19
The synthesis of PMMA hyperbranched polymers having
bromo functionalities by the VL-SCVP technique was possible.
In this approach, BEMA inimer containing a vinyl function and
a bromine atom was used to generate branching points and
comonomer, MMA simply acted to form spacer units between
branching points. The overall process involving photochemical
activation by Mn2(CO)10 is outlined in Scheme 2.
12.9
113 300
a
(Co)polymerization of MMA and BEMA by irradiation (λ = 400−
500 nm) of Mn2(CO)10 (0.075 mol %) at room temperature
b
c
(irradiation time = 3 h). Determined gravimetrically. Calculated
d
e
from the 1H NMR. With refractive index detector. With light
scattering detector.
It is known that Mn2(CO)10 in the presence of alkyl halides
undergoes an irreversible photolysis leading to the formation of
radicals. This was further confirmed by the spectral changes of
C
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Table 2. Effect of Mn2(CO)10 Concentration on Branching
a
Density (RM)
BEMA
cont. in soluble
the
polym
cont
[%]
b
c
d
e
Mn2(CO)10 conv
polym
Mn,GPC‑RI Mn,GPC‑LS
[mol %]
[%]
[mol %]
[g mol−1
]
[g mol−1
]
RM
0.038
0.075
0.150
25
44
51
8.6
9.4
100
100
100
65 400
81 600
191 000
355 000
535 000
0.34
0.23
0.20
12.3
107 100
a
(Co)polymerization of MMA (92.5% mol) and BEMA (7.5% mol) at
room temperature by visible light (λ = 400−500 nm) (irradiation time
b
c
1
= 3 h). Determined gravimetrically. Calculated from the H NMR.
d
e
With refractive index detector. With light scattering detector.
Figure 2. FT-IR spectra of bromo functional hyperbranched PMMA
(A) and star-hyperbranched PMMA-b-PHEMA copolymer (B).
Table 3. Effect of Irradiation Time on Branching Density
(RM)
a
BEMA cont in soluble
b
c
c
d
time conv
the polymer
[mol %]
polym
Mn,GPC‑RI Mn,GPC‑LS
[min]
[%]
cont [%] [g mol−1
]
[g mol−1
]
RM
60
90
25
28
32
44
8.1
8.4
8.9
9.4
100
100
100
100
8 900
9 600
16 100
27 100
39 600
355 000
0.55
0.35
0.32
0.23
120
180
12 600
81 600
a
(Co)polymerization of MMA (92.5% mol) and BEMA (7.5% mol)
by irradiation (λ = 400−500 nm) of Mn2(CO)10 (0.075% mol) at
b
c
room temperature. Determined gravimetrically. Calculated from the
d
e
1H NMR. With refractive index detector. With light scattering
detector.
the model system consisting of Mn2(CO)10 and CHCl3 (Figure
1).
The polymerizations were conducted under the same
experimental conditions using different BEMA and
Mn2(CO)10 concentrations and irradiation time. As can be
seen from Tables 1−3, although higher conversions and
branching densities were attained, high BEMA concentrations
and prolonged irradiation times resulted in the formation of
cross-linked polymers which is consisted with the proposed
mechanism. The higher concentration of inimer leads to the
gelation as this monomer possesses both initiating and
polymerization functionalities in the structure. This effect
favors radical coupling and consequently gelation.
1
Figure 3. H NMR spectra of the bromo functional hyperbranched
polymer and its star block copolymer.
tion of MMA and BEMA was performed as in literature39 by
using 2,2-azobis(isobutyronitrile) at 70 °C for 3 h yielded
poly(methyl methacrylate)-co-poly(bromoethyl methacrylate)
(PMMA-co-PBEMA) with 73% conversion. The number-
In order to confirm that polymer chains are actually initiated
by the Br-CH2 groups of BEMA and branching occurs, several
control experiments were performed. Thermal copolymeriza-
Scheme 3. Synthesis of an Amphiphilic Star-Hyperbranched PMMA-b-PHEMA Block Copolymer by Visible Light Irradiation
D
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Scheme 4. Postfunctionalization of Hyperbranched
Polymers by “Click” Chemistry Process
Figure 6. Fluorescence emission spectra of 1-pyrenemethanol (A), the
bromo functional hyperbranched polymer (B), and corresponding
pyrene-conjugated polymer (C) (λex = 345 nm).
average molecular weight value of this polymer determined by
refractive index (Mn,GPC‑RI = 99 600 g mol−1) is close to that
determined by light scattering (Mn,GPC‑LS = 106 800 g mol−1).
Subsequently, bromine functional hyperbranched polymer
was further used as macroinitiator in the visible light induced
polymerization of MMA in the presence of Mn2(CO)10. After
180 min of irradiation, a polymer with 45% conversion and
molecular weight of Mn,GPC‑RI = 84 000 g mol−1 and Mn,GPC‑LS
=
445 000 g mol−1 was obtained. The huge difference between RI
and LS measured molecular weights indicates highly branched
structure, and also BEMA units induce further chain initiation
due to the presence of bromine atoms.
Figure 4. FT-IR spectra of bromo functional hyperbranched PMMA
(A) and its azido (B) and pyrene functionalized (C) analogues.
As a consequence of the process, some of the bromine
groups may not be activated and remain in the branched
polymer which allows postfunctionalization through further
polymerization and a Cu(I)-catalyzed click reactions. Princi-
pally, any vinyl monomer can be polymerized by the activation
of the remaining halide groups in the presence of Mn2(CO)10
by a similar photochemical process. For our convenience, we
have selected hydroxyethyl methacrylate (HEMA) as the
second monomer, and visible light induced polymerizations
yielded amphiphilic star block copolymers possessing hydro-
phobic hyperbranched core and hydrophilic dangling chains
(Scheme 3).
Successful block copolymerization was confirmed by spectral
analyses of the precursor hyperbranched polymer and final star
block copolymer. In the FT-IR spectrum of the block
copolymer, the OH stretching band of poly(hydroxyethyl
methacrylate) (PHEMA) star arms is clearly detectable (Figure
2).
Similarly, in addition to the characteristic bands of the
PMMA core, the NMR spectrum also exhibits signals at 3.5−
4.4 ppm region corresponding to −CH2O, −OCHH2, and
−OH protons of PHEMA segments (Figure 3).
The composition of the hyperbranched PMMA−PBEMA is
1
found by H NMR data. Thus, the peak around 3.59 ppm
corresponding to the protons of methyl group of PMMA
segment and methylene protons adjacent to the bromine
moiety of PBEMA is compared to the methylene peaks of
PBEMA next to the ester functionality, which appears at 4.27
ppm. By this comparison, the ratio of PMMA to PBEMA is
calculated.
1
Figure 5. H NMR spectra of the bromo functional hyperbranched
polymer and its pyrene functionalized analogue.
E
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Figure 7. Photograph of azide-functionalized hyperbranched PMMA, propargylpyrene, and pyrene-functionalized hyperbranched PMMA dispersed
in CHCl3 which was taken when irradiated with a 366 nm UV lamp.
1
The hyperbranched polymers were modified by Huisgen type
click reactions (Scheme 4).40−44 For this purpose, bromine
groups were converted into azide functions by condensation
with NaN3 in DMF solution. In the FT-IR spectrum of the
azidated sample, the characteristic vibration band of N3 group is
observed as a sharp peak at 2106 cm−1.
Propargylpyrene and poly(ethylene glycol)−acetylene (PEG-
a) as model and hydrophilic polymer click components,
respectively, were prepared independently according to the
described literature procedures36,37 (see Experimental Section).
The model click reaction with propargylpyrene and azide-
modified hyperbrached PMMA was performed using Cu(I)
catalyst in DMF at 45 °C. The pyrene-functionalized
hyperbranched polymer was characterized by FT-IR spectra
(Figure 4), where disapperance of the azide vibration peak at
2106 cm−1 was observed.
branched polymer was characterized by FT-IR, H NMR, and
GPC measurements. In the FT-IR spectra, the disappearance of
the alkyne peak around 1965 cm−1 and azide peak around 2106
cm−1 was noted. The H NMR spectra exhibits characteristic
1
PEG protons as well as the triazole protons that appear at 8.01
ppm (see Supporting Information). Molecular weight of the
polymer is Mn,GPC‑IR = 91 000 g mol−1 and Mn,GPC‑LS = 465 000
g mol−1. The difference between RI and LS measured
molecular weight indicates that highly branched structure is
preserved after the click process.
CONCLUSION
■
In conclusion, we described a facile method for the synthesis of
well-defined soluble bromine-functional hyperbranched
PMMA. The method is based on the polymerization of AB*
methacrylic monomers, in the presence of Mn2(CO)10. Visible
light irradiation efficiently produces carbon-centered radical
without using high temperature and hard reaction conditions.
At sufficiently high concentrations of BEMA and Mn2(CO)10
gelation was observed. Both effects essentially favor radical
coupling and consequently gelation. The polymer structures as
well as branching degree and polymer compositions were
The 1H NMR spectrum of the pyrene functionalized polymer
also confirms successful click reaction. As can be seen from
Figure 5, the aromatic protons of pyrene units appear at 7.9−
8.6 ppm while triazole ring protons resonate at 7.6 ppm.
Even more convincing evidence for pyrene incorporation was
obtained from fluorescence measurements. Peaks correspond-
ing to the emission from propargyl pyrene at 350 and 400 nm
appear as a weak broad band for the pyrene functionalized
PMMA. Moreover, the polymer exhibits structureless excimer
emission centered at 480 nm, indicating strong interaction of
pyrene groups present in the hyperbranched structure also in
the excited state (Figure 6).
Pyrene incorporation can also be verified by the visual
observation of the fluorescence properties of propargylpyrene
and hyperbranched polymer in CHCl3 before and after click
reaction when irradiated with a 366 nm UV lamp (Figure 7).
The click reactions with PEG-a and azide-modified
hyperbrached PMMA was carried out under similar exper-
imental conditions. The resulting PEG-a functionalized hyper-
1
investigated by H NMR and GPC LS/IR measurements.
Such polymers obtained by photochemical means may be
used in numerous applications such as biomedical and drug
delivery systems. In the described synthetic methodology,
bromine functionalities provide possibility to use hyper-
branched PMMA as a macroinitiator in the polymerization of
HEMA and MMA and as a starting material in “click chemistry”
reactions. The amphiphilic characters of hyperbranched
polymer can be adjusted by incorporating polymeric segments
of hydroxylic monomers. For the synthesis of functional
materials by simple coupling and polymerization reactions, the
bromine end groups of hyperbranched polymer can be a perfect
starting point.
F
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(27) Koumura, K.; Satoh, K.; Kamigaito, M. Macromolecules 2008, 41
(20), 7359−7367.
ASSOCIATED CONTENT
■
S
* Supporting Information
(28) Koumura, K.; Satoh, K.; Kamigaito, M. Macromolecules 2009, 42
(7), 2497−2504.
1H NMR and FT-IR spectra of star-hyperbranched PMMA-b-
PEG copolymer. This material is available free of charge via the
Internet at http://pubs.acs.org.
(29) Asandei, A. D.; Adebolu, O. I.; Simpson, C. P. J. Am. Chem. Soc.
2012, 134 (14), 6080−6083.
(30) Yagci, Y.; Hepuzer, Y. Macromolecules 1999, 32 (19), 6367−
6370.
AUTHOR INFORMATION
Corresponding Author
*E-mail yusuf@itu.edu.tr; Fax +90-212-2856386; Tel +90-212-
2853241 (Y.Y.).
■
(31) Kahveci, M. U.; Acik, G.; Yagci, Y. Macromol. Rapid Commun.
2012, 33 (4), 309−313.
(32) Iskin, B.; Yilmaz, G.; Yagci, Y. Macromol. Chem. Phys. 2013, 214
(1), 94−98.
Notes
(33) Gunes, D.; Karagoz, B.; Bicak, N. Des. Monomers Polym. 2009,
12 (5), 445−454.
The authors declare no competing financial interest.
(34) Bally, F.; Ismailova, E.; Brochon, C.; Serra, C. A.; Hadziioannou,
G. Macromolecules 2011, 44 (18), 7124−7131.
(35) Tsarevsky, N. V.; Sumerlin, B. S.; Matyjaszewski, K. Macro-
molecules 2005, 38 (9), 3558−3561.
ACKNOWLEDGMENTS
■
The authors are thankful for Istanbul Technical University
Research Fund and TUBITAK (The Scientific and Technical
Research Council of Turkey) Project no. 113Z234. M.C. thanks
TUBITAK for the financial support by means of a graduate
program.
(36) Amici, J.; Kahveci, M. U.; Allia, P.; Tiberto, P.; Yagci, Y.;
Sangermano, M. . J. Mater. Sci. 2012, 47 (1), 412.
(37) Gacal, B. N.; Koz, B.; Gacal, B.; Kiskan, B.; Erdogan, M.; Yagci,
Y. J. Polym. Sci., Part A: Polym. Chem. 2009, 47 (5), 1317−1326.
(38) Ates, S.; Durmaz, Y. Y.; Torun, L.; Yagci, Y. J. Macromol. Sci.,
Part A: Pure Appl. Chem. 2010, 47 (8), 809−815.
(39) Zheng, J.; Goh, S. H.; Lee, S. Y. Polym. Bull. 1997, 39 (1), 79−
84.
(40) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed.
2001, 40 (11), 2004−2021.
(41) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B.
Angew. Chem., Int. Ed. 2002, 41 (14), 2596−2599.
(42) Tasdelen, M. A.; Yagci, Y. Angew. Chem., Int. Ed. 2013, 52 (23),
5930−5938.
REFERENCES
■
(1) Hawker, C. J.; Frechet, J. M. J. J. Chem. Soc., Perkin Trans. 1 1992,
0 (19), 2459−2469.
(2) Wooley, K. L.; Frechet, J. M. J.; Hawker, C. J. Polymer 1994, 35
́
(21), 4489−4495.
(3) Sunder, A.; Mulhaupt, R.; Frey, H. Macromolecules 1999, 33 (2),
̈
309−314.
(4) Sunder, A.; Mulhaupt, R.; Haag, R.; Frey, H. Adv. Mater. 2000, 12
̈
(3), 235−239.
(43) Tasdelen, M. A.; Yilmaz, G.; Iskin, B.; Yagci, Y. Macromolecules
2012, 45 (1), 56−61.
(44) Tasdelen, M. A.; Yagci, Y. Tetrahedron Lett. 2010, 51 (52),
6945−6947.
(5) Voit, B. J. Polym. Sci., Part A: Polym. Chem. 2000, 38 (14), 2505−
2525.
(6) Voit, B. I.; Lederer, A. Chem. Rev. 2009, 109 (11), 5924−5973.
(7) Gao, C.; Yan, D. Prog. Polym. Sci. 2004, 29 (3), 183−275.
(8) Sendijarevic, I.; McHugh, A. J. Macromolecules 2000, 33, 590−
596.
(9) Kim, Y. H. J. Polym. Sci., Part A: Polym. Chem. 1998, 36 (11),
1685−1698.
(10) Romagnoli, B.; Hayes, W. J. Mater. Chem. 2002, 12 (4), 767−
799.
(11) Inoue, K. Prog. Polym. Sci. 2000, 25 (4), 453−571.
(12) Yates, C. R.; Hayes, W. Eur. Polym. J. 2004, 40 (7), 1257−1281.
(13) Jikei, M.; Kakimoto, M.-a. Prog. Polym. Sci. 2001, 26 (8), 1233−
1285.
(14) Gaynor, S. G.; Edelman, S.; Matyjaszewski, K. Macromolecules
1996, 29 (3), 1079−1081.
(15) Frechet, J. M. J.; Henmi, M.; Gitsov, I.; Aoshima, S.; Leduc, M.
R.; Grubbs, R. B. Science 1995, 269 (5227), 1080−1083.
(16) Wang, Z.; He, J.; Tao, Y.; Yang, L.; Jiang, H.; Yang, Y.
Macromolecules 2003, 36 (20), 7446−7452.
(17) Hawker, C. J.; Frechet, J. M. J.; Grubbs, R. B.; Dao, J. J. Am.
Chem. Soc. 1995, 117 (43), 10763−10764.
(18) Sunder, A.; Hanselmann, R.; Frey, H.; Mulhaupt, R.
̈
Macromolecules 1999, 32 (13), 4240−4246.
(19) Liu, J.; Huang, W.; Zhou, Y.; Yan, D. Macromolecules 2009, 42
(13), 4394−4399.
(20) Ciftci, M.; Kahveci, M. U.; Yagci, Y.; Allonas, X.; Ley, C.; Tar, H.
Chem. Commun. 2012, 48 (82), 10252−10254.
(21) Yagci, Y. Macromol. Symp. 2006, 240 (1), 93−101.
(22) Fouassier, J.-P. Photoinitiation, Photopolymerization, and Photo-
curing: Fundamentals and Applications; Hanser: Munich, 1995.
(23) Bamford, C. H.; Mullik, S. U. J. Chem. Soc., Faraday Trans. 1
1973, 69, 1127−1142.
(24) Bamford, C. H.; Paprotny, J. Polymer 1972, 13 (5), 208−217.
(25) Tasdelen, M. A.; Yagci, Y. Aust. J. Chem. 2011, 64 (8), 982−991.
(26) Koumura, K.; Satoh, K.; Kamigaito, M. J. Polym. Sci., Part A:
Polym. Chem. 2009, 47 (5), 1343−1353.
G
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