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S. Zhang et al. / Polymer 54 (2013) 5303e5309
variety of interrelated factors, such as specific solventesolute in-
teractions, backbone flexibility (related to the high entropy of
mixing) [10,12,16], topologies (related to the free volume) [10] and
the nature of the end-groups [17].
absolute ethanol (80 mL), and light yellow needle-shaped crystals
were obtained (18.39 g, 61.3%).
2.2.2. Synthesis of 1,4 e di(S-sec propionate acid xanthate) butane
(RAFT-2)
2
Poly(vinyl acetate) (PVAc) is recognized as one of the most CO -
philic hydrocarbon materials [18,19], due to the interactions of the
methyl acetate with CO2, that is the Lewis acid-Lewis base inter-
action and a weak cooperative hydrogen bond between a proton on
1,4-butylene glycol (9.0 g, 0.10 mol) was diluted with acetone
(30 mL). At room temperature, a solution of potassium hydroxide
(11.20 g, 0.20 mol in 20 mL distilled water) was slowly added
while stirring for 2 h. After cooling in an ice-water bath, carbon
disulfide (15.2 g, 0.20 mol) was added drop-wise. The mixture
was stirred for 1 h, and then washed with potassium chloride
solution (25 g in 50 mL water). 15.0 g yellow dipotassium salt was
obtained (47%).
2
the methyl group and an oxygen of the CO [8]. However, the sol-
ubility is also limited by the molecular weight. Howdle copoly-
merized vinyl acetate with dibutyl maleate, vinyl butyrate and vinyl
pivalate, due to the increase of free volume, the solubility of the
copolymers was improved as compared to the PVAc homo-polymer
[
20e22].
Dipotassium salt (5.95 g, 0.019 mol) and dimethyl sulfoxide
(60 mL) were mixed and heated until the solid was dissolved. 2-
bromoethylpropionate (6.75 g, 0.037 mol) was added slowly at
room temperature, and stirred overnight. The reaction mixture was
extracted with ether (200 mL). The organic layer was washed with
water (3 ꢀ 20 mL), dried over magnesium sulphate, and concen-
trated. The crude product was purified by silica gel chromatography
It is well known that dendrimers and hyper-branched polymers,
such as phenyl acetylene dendrimers terminated with tert-butyl
esters [23], dendritic poly(ether imide) [24], hyper-branched pol-
y(ether ketones) [25], possesses lower viscosity, lower glass transi-
tion temperature (high flexibility and high free volume), and higher
solubility in some solvents than linear polymers. Thus the hyper-
branched structure of a polymer favours its solubility in different
solvents. Once the PVAc is designed as multi-armed structure, it
should be more soluble than that of the linear homo-polymer in
(eluent: hexane/ethyl acetate ¼ 9:1) and got a yellow viscous
1
product (55%). H NMR (400 MHz, CDCl
3
,
d
ppm): 4.53e4.64 (m, 4H,
eCH
4H, eOeCH
(d, 6H, eSeCH(CH
2
eCH
2
eOe), 4.30e4.40 (q, 2H, eSeCH(CH
eCH ), 1.86e1.95 (m, 4H, eCH eCH
)e), 1.22e1.30 (t, 6H, eOeCH
3
)e), 4.13e4.22 (q,
eOe), 1.50e1.58
eCH ).
dense CO
2
.
2
3
2
2
However, PVAc with different topologies (bi-arms, tri-arms and
tetra-arms) are not easy to synthesize, as VAc is a less activated
monomer whose polymerization still remains difficult to control
3
2
3
2.2.3. Synthesis of 1,1,1-tri(S-sec ethyl propionate O-methylene
xanthate) ethane (RAFT-3)
[
26,27]. Reversible addition-fragmentation chain transfer radical
polymerization (RAFT/MADIX) method [28e30] provides us a
useful tool to design and synthesize the oligomers (OVAcs) with
different topologies.
In this study, three xanthates (bifunctional, trifunctional and
tetrafunctional) were firstly synthesized as RAFT/MADIX agents to
control VAc polymerization, and then the PVAcs with different to-
pologies and narrow PDI were obtained by one pot reaction. The
phase behaviours were investigated, and the results indicate that
the cloud point pressure of PVAc was greatly affected by the mo-
lecular weight and topologies.
In a three-necked flask, 30 mL DMSO and 2.40 g (0.020 mol) 1,1,1-
tri(hydroxymethyl) ethane were heated at 60 C until the solid was
ꢁ
dissolved. After cooling it to room temperature, potassium hydrox-
ide (5.04 g, 0.090 mol in 10 mL distilled water) was added drop-wise,
and stirred for 2 h. Under ice-water bath condition, carbon disulfide
(60 g, 0.79 mol) was added slowly within 30 min, kept stirring for
another 2 h, and got black-red solution. 2-bromoethylpropionate
(16.31 g, 0.090 mol) was dropped into the mixture solution within
1 h, and stirred overnight. The last solutionwas extracted with ether
(250 mL), washed with water (3 ꢀ 20 mL), and dried over magne-
sium sulphate. The crude product was purified by silica gel chro-
2
. Experimental section
matography (eluent: hexane/ethyl acetate ¼ 7:3), and a yellow
1
viscous product was obtained (63.5%). H NMR (400 MHz, CDCl
3
,
2
.1. Materials and methods
d
ppm): 4.49e4.64 (m, 6H, eCH
2
eOe), 4.33e4.41 (q, 3H,eSe
)e), 4.14e4.22 (q, 6H, eOeCH eCH ), 1.53e1.59 (d, 9H, eSe
)e),1.23e1.31 (t, 9H, eOeCH eCH ),1.17e1.22 (t, 9H, eCH ).
CH(CH
CH(CH
3
2
3
Vinyl acetate (VAc, Sinopharm, 97%) was freed from inhibitor by
3
2
3
3
passing through an alumina column, and was further purified by
0
distillation over calcium hydride. 2, 2 -azobis(isobutyronitrile)
(
2.2.4. Synthesis of 1,1,1,1-tetra(S-sec ethyl propionate O-methylene
xanthate) methane (RAFT-4)
The synthesis procedures for RAFT-4 were similar to RAFT-3,
except that pentaerythritol (1.36 g, 0.01 mol) reacted with KOH
AIBN, Sinopharm, 80%) and lauroyl peroxide (LPO, Sinopharm, 98%)
were re-crystallized twice from toluene. Ethyl 2-bromopropionate
99%) was obtained from Aldrich. 1, 4-di(S-sec propionate acid
(
xanthate)butane, 1, 1, 1-tri(S-sec ethyl propionate O-methylene
xanthate)ethane, 1, 1, 1, 1-tetra(S-sec ethyl propionate O-methylene
xanthate)methane were synthesized according to the literature
2
(3.39 g, 0.06 mol in 5 mL water), CS (30.40 g, 0.40 mol), 2-
bromoethylpropionate (8.20 g, 0.45 mol). The resulting product
was purified by silica gel chromatography (eluent: hexane/ethyl
1
[26]. Other reagents were obtained from Sinopharm, and used as
acetate ¼ 8:2) and yellow viscous product was obtained (62%). H
received.
NMR (400 MHz, CDCl
3
,
d
ppm): 4.60e4.85 (m, 8H, eCH
2
eOe), 4.32e
eCH ), 1.52e
)e), 1.22e1.32 (t, 12H, eOeCH eCH ).
4.40 (q, 4H,eSeCH(CH
3
)e), 4.13e4.25 (q, 8H, eOeCH
2
3
2
2
.2. Synthesis of the RAFT agents
1.62 (d, 12H, eSeCH(CH
3
2
3
.2.1. Synthesis of potassium O-ethyl dithiocarbonate
2.3. Synthesis of multi-armed OVAcs
In a 100 mL round-bottom flask fitted with a reflux condenser,
1
0.50 g (0.19 mol) of potassium hydroxide was added to ethanol
Bulk polymerization of vinyl acetate was performed in a three-
neck flask at 60 C using AIBN as initiator, and xanthates (RAFT-2,
ꢁ
(
30.10 g), and the mixture was heated under reflux for 1 h. After
cooling in an ice-bath, carbon disulfide (14.65 g, 0.19 mol) was then
slowly added to the wine-red solution, resulting in almost a solid
piece. The crystals were filtered off and washed with ether
RAFT-3, RAFT-4) as the chain transfer agents (CTA). Taking RAFT-2
for example: AIBN (0.12 g, 0.74 mmol), RAFT-2 (0.98 g,
2.21 mmol) and VAc (11.10 g, 129.10 mmol) were placed in a 50 mL
of three-neck flask. The solution was degassed by three freezing-
(
3 ꢀ 10 mL). The crude product (31.12 g) was re-crystallized from