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Synthesis of lauryl methacrylate star-like polymers via ATRP.

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ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING
Asia-Pac. J. Chem. Eng. 2009; 4: 678–682
Published online 26 June 2009 in Wiley InterScience
(www.interscience.wiley.com) DOI:10.1002/apj.317
Special Theme Research Article
Synthesis of Lauryl methacrylate star-like polymers via
ATRP
Lei Qiu,1 Yufeng Wang,1,3 Qunfang Lin,2 and Xiaodong Zhou1 *
1
State Key Laboratory of Chemical Engineering, Shangai 200237, China
School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China
3
Shanghai Zhongyuan Chemical Company Limited, Shanghai 200431, P.R. China
2
Received 14 October 2008; Revised 3 March 2009; Accepted 3 March 2009
ABSTRACT: Lauryl methacrylate (LMA) star-like polymers were synthesized by atom transfer radical polymerization
(ATRP) using the ‘arm-first’ method. Linear poly lauryl methacrylate (PLMA) precursors were firstly prepared with ethyl
α-bromoisobutyrate (EBriB) as initiator and cuprous chloride (CuCl)/N,N,N ,N ,N -pentamethyldiethylenetriamine
(PMDETA) as catalyst in cyclohexanone via ATRP, and subsequently used as macromolecule initiator(MI) to
synthesize star polymers in the presence of cross-linker ethylene glycol dimethacrylate (EGDMA). Several experimental
parameters, such as the PLMA arm length, the ratio of MI to cross-linker, the addition amount and moment of crosslinker and the reaction time for the star formation were systematically investigated. The samples were removed at regular
intervals and analyzed by gel permeation chromatography (GPC) to track Mn and Mw/Mn of star-like polymer, by
which the influence of the experimental parameters on the structures of the star-like polymers was studied. Employing
shorter arm lengths and more cross-linker could produce star-like polymers with higher molecular weight and more
arms per star.  2009 Curtin University of Technology and John Wiley & Sons, Ltd.
KEYWORDS: atom transfer radical polymerization (ATRP); star-like polymer; cross-linker; arm-first method
INTRODUCTION
Star-like polymers that contain multiple arms connecting to one central core, have recently received much
attention because of special character of smaller hydrodynamics, lower solution and melt viscosities compared
to linear polymers of the same molar mass,[1] which
facilitate coating, extrusion or other manufacturing processes.
In recent years, controlled/living free radical polymerization (CRP) techniques, including atom transfer radical polymerization (ATRP),[2] nitroxide mediated polymerization (NMP)[3] and reversible additionfragmentation chain transfer (RAFT) polymerization,[4]
as a way to synthesize star-like polymers, have
increased rapidly due to the applicability for different
monomers and their facile reaction conditions.
Star-like polymers are synthesized via CRP using
two methods: core-first[5] and arm-first.[6] The core-first
method involves reacting living chains with a multifunctional initiator and the number of arms of each star
polymer is determined by the initiating functionalities
*Correspondence to: Xiaodong Zhou, State Key Laboratory of
Chemical Engineering, Shangai 200237, China. E-mail: xdzhou@
ecust.edu.cn
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
on each initiator. However, the multifunctional initiator
must be previously synthesized, which is very difficult and expensive. The arm-first method consists of
reacting-preformed linear macromolecule initiator (MI)
with a divinyl cross-linker. It is the easiest way to synthesis star-like polymers with multiple arms and functional groups. In this procedure, the cross-linker added
at certain conversion of the monomers is a ‘one-pot’
process.[7] In contrast, the synthesis of star polymers
using the purified linear termed polymers as MIs is a
‘two-pot’ process.[8]
The polymers of higher (alkyl) methacrylate draw
significant importance in material science due to their
low glass transition temperature.[9] Linear poly lauryl
methacrylate (PLMA) is usually used as lubricating oil
additives because of the molecular structure with long
side-chain. However, few investigations are reported to
discuss about the preparation and application of PLMA
star polymers.
In this paper, we report the synthesis of multiple
arms star-like PLMA polymers via ATRP, using the
arm-first method. Using ethylene glycol dimethacrylate
(EGDMA) as cross-linker, the preformed LMA linear
polymers were used as MIs to prepare star polymers.
The influence of the experimental parameters on the
structures of the star-like polymers was also studied.
Asia-Pacific Journal of Chemical Engineering
SYNTHESIS OF LAURYL METHACRYLATE STAR-LIKE POLYMERS
EXPERIMENTAL
Materials
EGDMA (98%, Alfa Aesar) was purified by passing
through a column filled with basic alumina to remove
the inhibitor. Lauryl methacrylate (LMA) was synthesized by direct esterification from lauryl alcohol
and methacrylic acid in our laboratory. Cyclohexanone
(98%, GUOYAO Ltd. China) was dried over MgSO4 ,
filtered, and then distilled under reduced pressure. CuCl
was purified by stirring in glacial acetic acid overnight,
filtering off the solid, and washing with dry ethanol.
Pentamethyldiethylenetriamine (PMDETA) and EBriB
were purchased from Aldrich and used without further
purification.
Synthesis of PLMA-Cl MI
PLMA-Cl MI was synthesized via typical ATRP procedure. A dry three-necks-round-bottom flask with a
magnetic stir bar was charged with CuCl, PMDETA,
LMA and cyclohexanone. The volume ratio of LMA
to cyclohexanone is 1 : 1. The flask was then degassed
and back-filled with nitrogen three times. During the
final cycle, the flask was filled with nitrogen, followed
by quickly adding EBriB to the mixture and then was
placed in a thermostated oil bath at 40 ◦ C to react
until terminating. The reaction mixture was dissolved in
tetrahydrofuran (THF) and precipitated in methanol to
remove the remaining monomer and solvent after passing through an alumina column to eliminate the copper
complexes. The final product was dried in a vacuum
oven at 40 ◦ C for 2 days.
Synthesis of (PLMA)n-polyethylene
glycol-dimethacrylate(PEGDMA) star polymer
The MIs were used to synthesize (PLMA)n-PEGDMA
star polymer. Typically, a dry three-necks-round-bottom
flask with a magnetic stir bar was charged with CuCl
(40 mg, 0.404 mmol), PLMA MI (4.4 g, 0.402 mmol),
EGDMA (227.6 µl, 1.21 mmol), PMDETA (76.2 µl,
0.402 mmol) and cyclohexanone (10.7 ml). The flask
was degassed and back-filled with nitrogen three times,
and then immersed in a thermostated oil bath at 110 ◦ C.
After polymerization was conducted for various times,
the star polymer was purified in a similar way as
described for MIs.
ized with a multi-detectors gel permeation chromatography (GPC) equipped with a DAWN HELEOS static
laser scattering detector and an Optilab Rex refractive
index detector, which is produced by Wyatt Technology
Corporation. GPC was performed using THF as eluent
at a flow rate of 1 ml/min.
RESULTS AND DISCUSSION
(PLMA)n-PEGDMA star polymers were synthesized
via ATRP using arm-first method. Firstly, linear polymers were prepared with EBriB as initiator and
CuCl/PMDETA as catalyst. Then the purified linear
polymers were used as MIs to Synthesis (PLMA)nPEGDMA in the presence of the cross-linker EGDMA.
The synthesis procedure of (PLMA)n-PEGDMA star
polymers via the “arm-first” method was depicted in
Scheme1.
To investigate the influence of several reaction parameters including the PLMA arm length, the ratio of
MI/cross-linker and the additional moment of crosslinker, on the structures of the star polymers, a series of
polymers were synthesized and the results were summarized in Table 1.
Effect of amount of EGDMA on star polymer
structures
The effect of EGDMA amount on the structures of the
star polymer is shown in Fig. 1. The molecular weights
of star polymers increased with increasing the ratio
of EGDMA to PLMA and the yield of star polymer
increased too. We consider that the higher ratio of
EGDMA to PLMA affords more reaction points and
makes the arms more chances to react with divinyl
cross-linker. However, when employing the higher ratio
of EGDMA to PLMA = 7 : 1, the reaction mixture
completely gelated within 1 h, which was attributed to
the EGDMA self-polymerization (Table 1, entry S4).
We also noticed that the star polymers could not form
when using lower ratio of EGDMA to PLMA (1 : 1)
(Table 1, entry S1, S5, S9). In the S5 experiment, two
samples were taken out from the same reaction system
O
Br
ATRP
O
LMA
ATRP
Cl
EGDMA
Cl Cl
Cl
Cl
Cl Cl
Characterization
The absolute molecular weight and its distributions of
the PLMA, (PLMA)n-PEGDMA polymer are character 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Scheme 1.
Synthesis route of (PLMA)n-PEGDMA star
polymers.
Asia-Pac. J. Chem. Eng. 2009; 4: 678–682
DOI: 10.1002/apj
679
680
L. OIU ET AL.
Asia-Pacific Journal of Chemical Engineering
Table 1. Synthesis of (PLMA)n-PEGDMA star polymers using arm-first method.
Entrya
S1
S2
S3
S4
S51
S52
S6
S7
S8
S9
N/(X + Y)b
Arm Mn (g/mol)c
Star Mn (g/mol)c
30/1 + 0
30/3 + 0
30/5 + 0
30/7 + 0
43/1 + 0
43/1 + 0
43/3 + 0
43/1 + 2
50/3 + 0
50/1 + 0
7.74 × 103
7.74 × 103
7.74 × 103
7.74 × 103
1.09 × 104
1.09 × 104
1.09 × 104
1.09 × 104
1.27 × 104
1.27 × 104
1.13 × 104
2.52 × 105∗
4.16 × 105∗
Gelation
1.36 × 104
1.42 × 104
1.18 × 105∗
1.18 × 104
1.30 × 104
1.23 × 104
Mw/Mn of star
–
2.08
1.57
–
–
–
2.46
–
–
–
c
narm d
Time (h)
Ystare (wt%)
–
32.4
53.8
–
–
–
10.8
–
–
–
24
24
24
1
12
24
24
36
24
24
–
29.3
51.1
–
–
–
31.1
–
–
–
Experimental conditions: [PLMA]0 /[EGDMA]0 /[CuCl]0 /[PMDETA]0 = 1/(X + Y)/1/1/1,110 ◦ C in cyclohexanone.
Definitions: N = number-average DP of PLMA arm; X + Y = [EGDMA]0 /[PLMA]0 . The EGDMA was added by two-step feeding method.
X was the feeding level in the first step and Y was the feeding level in the second step.
c
Number of average molecular weight (Mn) and PDI is measured by GPC-multiple angle light scattering detection (MALLS).
∗
The GPC trace has two peaks, which is usually observed in star polymers prepared by ‘arm-first’ method. The first peak belongs to star
polymers and the second peak belongs to the residual linear polymers. Mn is the number of average molecular weight of the first peak.
d
Average number of arms in per star molecule (narm = Mn, star × armwt%/Mn, arm). In this paper, we consider narm = Mn, star/Mn, arm,
because arm wt% is big enough to ignore the effect of EGDMA in the star polymer.
e
Liner LMA polymers yield: weight percentage of reactive linear PLMA.
a
b
lack of active point system. The other is attributed to the
solvent amount (volume ratio of LMA to cyclohexanone
is 1 : 2). The increasing solvent amount not only reduces
the possibility of the gelation but also increases the
side reaction and decreases the MI and reactive radical
concentration.
Effect of arm length on star polymers
structures
Figure 1. The GPC trace of three samples (S1,S2,S3) with
different ratio of [EGDMA]/[PLMA]. The reaction conditions
were listed in Table 1. This figure is available in colour online
at www.apjChemEng.com.
in various time intervals 12 and 24 h, which denoted
S51 and S52 respectively. It was found that the Mn of
the two samples had no obvious difference.
Comparing with other monomers such as styrene or
tert-butyl acrylate, the conversion of LMA keeps in low
level (no more than 55%).[10,11] Some researchers report
the conversion of tert-butyl acrylate which is more than
90% and the star polymer can be obtain in the wild ratio
of EGDMA to monomer from 1 to 15. We consider that
there are two reasons. One is the steric hindrance of
long side-chain preventing the arms from reacting with
the divinyl cross-linker, which is more obvious in the
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Arm length is an important parameter we are interested
in. According to the reaction mechanism of arm-first
method, the reason that Mnstar increases is the arm
reacted with a divinyl cross-linker. In this case, on
the one hand, the star polymers produced by longer
arms should have larger Mn compared with that produced by shorter arms; on the other hand, the longer
arms not only have bigger steric hindrance but also
have smaller mobility, which is a kind of obstacle to
synthesize star polymer with large molecular weight.
S2, S6 and S8 were reacted in the same mole ratio of
[PLMA]0 /[EGDMA]0 . The experiment conditions and
GPC traces were shown in Table 1 and Fig. 2 respectively. The star polymers with shortest arms (n = 30)
had larger Mn and narrow molecular weight distribution
(MWD) (Table 1, entry S2). In contrast, star polymers
formed from the longer arms (n = 43) had a much
smaller molecular weight and broader polydispersity
(PDI) (Table 1, entry S6). However, star polymers could
not be successfully obtained from the longest arms
(n = 50), in which the molecular weight of product did
not change obviously as compared with that of the arms
(Table 1, entry S8). During the reaction process, the
star polymers were obtained via two approaches. One
Asia-Pac. J. Chem. Eng. 2009; 4: 678–682
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
SYNTHESIS OF LAURYL METHACRYLATE STAR-LIKE POLYMERS
Figure 2. Comparison of the GPC results of three independent samples(S2,S6,S8) with same ratio of [EGDMA]/[PLMA]
and different arm length. This figure is available in colour
online at www.apjChemEng.com.
is star–star reaction and the other is star–arm reaction.
Both approaches increase the molecular weight of the
star polymers, but star–star reactions broaden MWD
of the final product. Because of big steric hindrance
resulting from long side-chain of LMA, the star–star
reaction in this system is difficult to occur. Star–arm
reaction is the primary approach to increase the degree
of polymerization, which is consistent to the relatively
narrow MWD. Star polymers formed from the shortest arm had the largest Mn (4.16 × 105 g/mol) and the
most arms per star molecule (narm = 53.8). For longer
arms, it is difficult to get into the center of star polymer
and react with the cross-linker due to the bigger steric
hindrance and the smaller mobility. At the same time,
the subsequent arms must diffuse through the existing
star polymers to reach the reactive center. This barrier
becomes more pronounced and prevents the subsequent
arms from the star polymers when using longer arms.
So the star polymers formed from shortest arms had
larger Mn and narrow MWD. When the length of the
arms reaches to a relatively high level, the cross-linking
reaction cannot go on.
Effect of addition moment of cross-linker on
star polymers’ structures
We also investigated the reaction activity of star polymers using two-step feeding of EGDMA and the GPC
traces shown in Fig. 3. In the cases of S6 and S7, both
the ratio of EGDMA to PLMA is 3 : 1, but EGDMA
of S7 is added in two batches. In the initial stage of
the reaction, EGDMA was added according to the ratio
of EGDMA: PLMA = 1 : 1. The residual EGDMA was
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Figure 3.
Comparison of the GPC results of two
independent samples(S6,S7) with the same ratio of
[EGDMA]/[PLMA]and different method [EGDMA] added.
This figure is available in colour online at www.apjChemEng.
com.
added into after 24 h. As seen in Table 1, the Mn of
S7 did not increase and was almost similar with the
Mn of arm, while the Mn of S6 in which EGDMA was
added by one-step feeding reached to 1.18 × 105 g/mol.
It implies that both the ratio of EGDMA: PLMA = 1 : 1
and 2 : 1 cannot initiate the cross-linking reaction and
the reaction activity of the active points cannot hold for
a long time.
CONCLUSIONS
(PLMA)n-PEGDMA star polymers were synthesized
via ATRP using the ‘arm-first’ method. The star polymers formed from shortest arms had larger molecular
weight and narrow MWD. When the length of the
arms reaches to a relatively high level, the cross-linking
reaction cannot go on. The molecular weights and the
yield of star polymers increase with increasing ratio
of EGDMA to PLMA. The lower ratio of EGDMA to
PLMA (2 : 1) cannot initiate the cross-linking reaction,
but the excess high ratio of EGDMA to PLMA (7 : 1)
results in the gelation. During the polymerization procedure, the reaction activity of EGDMA’s active points
cannot hold for a long time.
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L. OIU ET AL.
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Asia-Pacific Journal of Chemical Engineering
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Asia-Pac. J. Chem. Eng. 2009; 4: 678–682
DOI: 10.1002/apj
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