ABSTRACT: Amphiphilic diblock copolymers of polyvinyl alcohol (PVA) and polystyrene (PS), which are very difficult to prepare by common polymerization methods, have been obtained by initiation of the polymerization of styrene and vinyl acetate successively, followed by hydrolysis, using the ethanolamine-benzophenone (BP) charge-transfer complex (CTC). The effects of solvents, concentration of monomer, BP, ethanolamine, and PS prepolymer, with a reactive imino group (PS a ), on the photo-induced chargetransfer polymerization (CTP) of St and block copolymerization of VAc are discussed. The copolymer of PS-b-PVAc and the hydrolyzed product, PS-b-PVA, were characterized by FTIR, NMR, and GPC in detail. The effect of PS chain length on the crystallization of PVA was described

Junlian Huang

Xiaoyu Huang

Zaijun Lu

CiteSeerX

Synthesis and Characterization of Amphiphilic Diblock
Copolymer of Polystyrene and Polyvinyl Alcohol
Using Ethanolamine–Benzophenone as Photochemical
Binary Initiation System
ZAIJUN LU, XIAOYU HUANG, JUNLIAN HUANG
Department of Macromolecular Science, Fudan University, The Open Laboratory of Molecular Engineering of Polymer,
State Education Commission of China, Shanghai 200433, People’s Rebpulic of China
Received 4 April 1997; accepted 22 June 1997
ABSTRACT: Amphiphilic diblock copolymers of polyvinyl alcohol (PVA) and polystyrene
(PS), which are very difficult to prepare by common polymerization methods, have been
obtained by initiation of the polymerization of styrene and vinyl acetate successively,
followed by hydrolysis, using the ethanolamine–benzophenone (BP) charge-transfer
complex (CTC). The effects of solvents, concentration of monomer, BP, ethanolamine,
and PS prepolymer, with a reactive imino group (PSa), on the photo-induced charge-
transfer polymerization (CTP) of St and block copolymerization of VAc are discussed.
The copolymer of PS-b-PVAc and the hydrolyzed product, PS-b-PVA, were characterized
by FTIR, NMR, and GPC in detail. The effect of PS chain length on the crystallization
of PVA was described. q 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 109–
115, 1998
Keywords: block copolymer; polystyrene; polyvinyl alcohol; polyvinyl acetate;
charge-transfer complex
INTRODUCTION In our laboratory a novel class of amphiphilic
copolymers such as PEO-b-PMMA,6 PEO-b-PAN,7
PEO-b-PVAc, and PS-b-PVA with different molec-Diblock copolymers with hydrophilic and hydro-
phobic, crystalline, and noncrystalline immiscible ular weights were prepared, in which PEO and
PVA blocks are hydrophilic and crystalline whileblocks are of increasing interest, both theoretically
and experimentally.1–3 This is not only due to the PMMA, PS, and PVAc are hydrophobic. The self-
assembling behavior in water and some nonpolarintriguing phenomena of self-assembling of the am-
phiphilic copolymer and the unique phase structure organic solvents8 and the unique physicochemical
properties these copolymers undergo is being in-of crystalline and the noncrystalline system but also
due to important applications of such materials in vestigated. This contribution is only centered on
the preparation of the PS-b-PVAc and PS-b-PVAcoatings, adhesives, thin films, microfabrication of
electronic devices, pharmaceutical, and photo- copolymers and the kinetics of copolymerization.
graphic technologies, oil recovery, etc.
PEO-b-PS was often chosen as a typical model
copolymer for the study of self-assembling sys- EXPERIMENTAL
tems4 and phase structure relationship5 of non-
crystalline and crystalline blocks.
Materials
Ethanolamine (Shanghai Third Reagent Factory,
Correspondence to: J. Huang
China) was dried with Linde type 4 Å molecule
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 36, 109–115 (1998)
q 1998 John Wiley & Sons, Inc. CCC 0887-624X/98/010109-07 sieves followed by distillation under reduced pres-
109
8G60 97-074P/ 8g60$$074p 11-05-97 17:22:52 polcal W: Poly Chem
110 LU, HUANG, AND HUANG
sure, with the fraction at 907C/10 mmHg collected.
Styrene (St) (Shanghai First Reagent Factory)
and vinyl acetate (VAc) (Shanghai Gaoqiao
Chemical Factory) were dried by calcium hydride
and then distilled under N2 before use. All other
solvents were purified by standard methods;
Benzophenone (BP) was recrystallized twice from
ethanol.
Polymerization of St by Initiation of CTC
Photo-induced polymerization was carried out in
a 100-mL ampoule with variable conditions. A
typical polymerization procedure was described
(©CH©CH¤)n©NHCH¤CH¤OH 1 ©C©
hv
∫ VAc
O
O
CH¤CH¤OH
C®O
CH‹
(©CH©CH¤)n©NCH¤CH¤OH
(©CH©CH¤)n©N©(CH¤©CH©)m
as follows: a 100-mL ampoule 0.0061 g (1.0
1 1004 mol) of ethanolamine, 0.0182 g (1.01 1004 To a 100 mL ampoule 0.79 g PSa (4.0 1 1005mol) of BP, and 5 mL of styrene in 5 mL of benzene mol, MV n : 19,700, MV w /MV n : 1.93) and 0.0073 g of(or acetonitrile) were charged, then the ampoule BP (4.0 1 1005 mol ) in 5 mL of THF (or acetoni-
was degassed by freeze-pump-thaw three times at trile ) , and 5 mL of VAc were introduced. The
77 K. The sealed ampoule was irradiated by a 300 polymerization conditions were the same as
W high-pressure mercury lamp (Model DDZ-300 mentioned in the former paragraph. The poly-
from Shanghai Ya Ming Lamp Factory, China) merized product was precipitated with n -hex-
for 24 h at a constant 257C under N2, the cupric ane and unreacted PSa could be removed by dis-sulfate aqueous solution was used as the photofil- solution/precipitation with chloroform/metha-
ter to obtain 365 nm monochromatic light. The nol. No trace of the PVAc homopolymer was
product was precipitated by methanol and puri- found by extracting the product with methanol,
fied by dissolution/precipitation with chloroform/ because PVAc is soluble in methanol. The puri-
methanol, giving a 74.4% yield of product. The IR fied copolymer weighed 0.983 g.
spectrum (cm01) : 1601, 1493, and 1452 (benzene
ring bend vibration), 3026 (|CH of the benzene
ring); 1H-NMR (d: ppm): 6.50 and 7.04 (benzene Hydrolysis of PS-b-PVAc
ring), 1.42 ({CH2{) and 1.84
w
({CH{) , sup- The hydrolysis was carried out in benzene at 707C
with 5% sodium ethoxide benzene solution as aported the product structure.
catalyst, no acetoxy or acetyl groups were left in
the hydrolyzed product, as shown by IR and NMR
check.
1 2
HOCH¤CH¤NH¤ 1 ©C©
hv
St
HOCH¤CH¤NH¤ ©C©
O
O
∫∫
H1 transfer1
HOCH¤CH¤NH 1
HOCH¤CH¤NH©(CH¤©CH©)n
©C©
OH
∫
∫
NaOC¤Hfi
benzene
O
C®O
CH¤CH¤OH
CH‹
OH
(©CH©CH¤)n©N©(CH¤©CH©)m
CH¤CH¤OH
(©CH©CH¤)n©N©(CH¤©CH©)m
Block Copolymerization of VAc Kinetics of Copolymerization
Copolymerization kinetics was investigated withBlock copolymerization of VAc was carried out by
binary initiation system composed of the prepoly- a modified dilatometer; the method and procedure
have been reported before.9mer PS with the imine group (PSa) and BP.
8G60 97-074P/ 8g60$$074p 11-05-97 17:22:52 polcal W: Poly Chem
AMPHIPHILIC POLYSTYRENE POLYVINYL ALCOHOL DIBLOCK COPOLYMERS 111
Table I. St Homopolymerization Data in Different Solventsa
Conversion of St (%) MV n MV w/MV n
[BP]
(11003 mol/L) THF CH3CN THF CH3CN THF CH3CN
4.0 66.9 36.2 31,200 12,500 2.50 1.65
6.0 69.3 39.1 25,480 9,800 2.21 1.55
8.0 71.7 41.9 22,070 8,470 2.05 1.48
10.0 74.4 44.6 19,700 7,580 1.93 1.42
a [ethanolamine] Å [BP], [St]: 4.349 mol/L.
Instruments THF is 16.1 1 1004 , and 45.0 1 1004 for acetoni-
trile. Thus, the molecular weight of the homopoly-
The IR spectra were obtained on a Magna-550 mer of PS in THF should be greater than that of
FTIR spectrometer; 1H-NMR spectra were re- the case of acetonitrile judged from formula (1)
corded by Bruker MSL-300 spectrometer with under the same conditions. The experimental re-
TMS as internal standard and CDCl3 or DMSO- sults are coincident with the theoretical estima-
d6 as solvent. The molecular weight and molecular tion. The second factor affected the photo-induced
weight distribution were derived from a Shimadzu CTP is solvent polarity. It is well known when the
LC-3A gel permeation chromatography (GPC) binary system consisting of ethanolamine and BP
with a microcomputer using a refractive index was irradiated by 365 nm light, an exciplex was
detector, and the monodistribution polystyrenes formed by mono-electron transfer from amine
were used as standard. The DSC measurement group of ethanolamine to BP, then the imino and
was performed by a Perkin–Elmer TAC 7/DX in diphenylmethanol radicals were produced by hy-
nitrogen atmosphere with the heating rate of drogen proton transfer from cation radical of
107C/min. amine to the BP anion radical. If the polar sol-
vents as THF (1: 7.58, 207C) and especially aceto-
nitrile (1: 37.5, 207C) were used, the cation and
RESULTS AND DISCUSSION anion radicals might be solvated, so the proton
transfer between them may be difficult to carry
Effect of Solvents on the CTP of St out leading to the dropping of radical concentra-
tion, and conversion of the monomer would alsoTable I shows the molecular weight and molecular
be decreased. This phenomenon is strongly depen-weight distribution data for the PS homopolymer,
dent on the solvent polarity. The stronger the po-along with conversion of St in THF and acetoni-
larity of the solvent, the lower the conversion oftrile. In all the cases, the molecular weight of PS
the monomer. Therefore, the conclusion in whichand conversion of St in THF were much higher
than that of the case in acetonitrile, under the
same conditions. In the radical polymerization the
effect of solvents could be divided into two parts:
one is the chain transfer of species to solvent; the
other is the solvent polarity. In the consideration
of the first factor the chain transfer constant Cs
was derived from the slope of the linear plot of
1/Xn vs. [S]/[M], shown in Figure 1 (conversion
of St is less than 10%) on the basis of kinetic
equation of radical polymerization of:
1/Xn Å (1/Xn )0 / CS ( [S]/[M])10 (1)
(here, Xn is the number of polymerization degree;
(1/Xn )0 is the value in the absence of the chain Figure 1. Dependence of the inverse of polymeriza-
transfer agent; [S] and [M] are the concentration tion degree of PS on the concentration ratio of solvent
vs. monomer ([ethanolamine], [BP]: 1.0 1 1002 mol/L).of solvent and monomer, respectively), the Cs for
8G60 97-074P/ 8g60$$074p 11-05-97 17:22:52 polcal W: Poly Chem
112 LU, HUANG, AND HUANG
Table II. VAc Block Copolymerization Data in Different Solventsa
PSab Conversion Conversion
Sample (11003 mol/L) of PSa (%) of VAc (%) Mn Mn /Mn
THF
A1 4.0 51.80 18.06 53,000 3.02
A2 6.0 59.16 23.57 43,100 2.85
A3 8.0 66.20 29.00 37,800 2.60
CH3CN
B1 4.0 47.04 16.06 54,700 3.04
B2 6.0 54.72 22.00 44,900 2.86
B3 8.0 61.24 27.40 39,100 2.62
a [BP] Å [PSa], [VAc]: 5.41 mol/L.
b PSa denoted the PS prepolymer with imino group, Mn: 12,500, Mw/Mn: 1.65.
the conversion of St in THF was much higher than We think that the reluctant effect of the sol-
vents on this system might be attributed to thethat in acetonitrile could also be derived from the
discussion of solvent polarity. entanglement of PSa prepolymer in solvent, and
a part of the imine groups was enveloped, which
lead to the lower efficiency of photochemical reac-
Effect of Solvent on Copolymerization tion between the imine group and BP, and lower
conversion of VAc.Table II lists the data of the copolymer of PS-
b-PVAc produced by photo-induced initiation of It is well known that both THF and acetonitrile
are good solvents for PSa, from which it wasbinary system consisting of PSa and BP of the
polymerization of VAc. In this case, THF and ace- judged that the situation of entanglement of PSa
and envelopment of the imine groups are verytonitrile were also used as solvents. It was re-
vealed that no sharp difference between them in similar with each other for them, so the photo-
chemical reaction environment between PSa andmolecular weight, molecular weight distribution
of the copolymer, and conversion of VAc could be BP and polymerization rate are also very similar
with each other in THF and acetonitrile. This ex-found. This means that the solvents did not exert
a great influence on this polymerization system. planation can be confirmed by kinetics investiga-
tion.We also could derive the chain transfer constants
in THF and acetonitrile for this system from Fig- Figures 3, 4, and 5 showed the relationship of
the polymerization rate (Rp ) with concentrationure 2, the Cs is 7.1 1 1004 for THF and 9.2 1 1004
for acetonitrile, in which the difference between of the monomer, ethanolamine (or PSa), and BP.
For the system of ethanolamine and BP, the nor-them was in the experimental error range.
Figure 2. Dependence of the inverse of polymeriza-
tion degree of PVAc on the concentration ratio of solvent Figure 3. Relationship between Rp with concentra-
tion of ethanolamine and PSa-12,500 ([BP]: 8.0 1 1003vs. monomer ([PSa], [BP]: 6.0 1 1003 mol/L, MV n of
PSa: 12,500, MV w /MV n : 1.65). mol/L, [St] , [VAc]: 5.41 mol/L).
8G60 97-074P/ 8g60$$074p 11-05-97 17:22:52 polcal W: Poly Chem
AMPHIPHILIC POLYSTYRENE POLYVINYL ALCOHOL DIBLOCK COPOLYMERS 113
Figure 5. Relationship between Rp with concentra-
Figure 4. Relationship between Rp with concentra- tion of St and VAc ([ethanolamine], [PSa], [BP]: 8.0
tion of BP ([ethanolamine], [PSa]: 8.0 1 1003 mol/L, 1 1003 mol/L).
[St] , [VAc]: 5.41 mol/L).
[BP]0.46[PSa]0.34[VAc]0.54 for acetonitrile. There is
nearly no difference for both cases in the experimen-mal kinetic relationship was obtained for THF,
the Rp} [BP]0.52[ethanolamine]0.49[St]0.98, but the tal error range, although the greater deviation from
the normal kinetic equation for both of them wasdeviation for acetonitrile, Rp} [BP]0.49[ethano-
lamine]0.45[St]0.82 was found due to the strong sol- found. Therefore, it could be concluded that the
small effect of solvent on the copolymerization ofvation of acetonitrile. In the system containing
PSa with a molecular weight 12,500, however, the VAc is attributed to the similar situation of entan-
glement of PSa and similar envelopment of iminokinetic relationship for both cases is rather identi-
cal, the Rp} [BP]0.49 [PSa]0.37[VAc]0.60 for THF and groups in both THF and acetonitrile.
Figure 6. IR spectra of PS-b-PVAc and PS-b-PVA.
8G60 97-074P/ 8g60$$074p 11-05-97 17:22:52 polcal W: Poly Chem
114 LU, HUANG, AND HUANG
Figure 7. 1H-NMR spectra of PS-b-PVAc and PS-b-PVA.
Figure 8. GPC measurement of PS prepolymer (A)
and PS-b-PVAc (B). Figure 9. DSC measurement of PS-b-PVA.
8G60 97-074P/ 8g60$$074p 11-05-97 17:22:52 polcal W: Poly Chem
AMPHIPHILIC POLYSTYRENE POLYVINYL ALCOHOL DIBLOCK COPOLYMERS 115
Table III. PS-b-PVA diblock copolymer DSC data
Mn (11004) Compositiona
Tg1 Tg2 Tm Hm
Sample PS PS-b-PVA PS PVA (7C) (7C) (7C) (kJ/mol) Hm /Hm0b
A1 1.25 3.37 19.97 80.03 83.3 101.9 224.3 2.70 0.39
A2 1.25 2.86 24.73 75.27 83.5 101.7 221.8 2.47 0.36
A3 1.25 2.59 28.30 71.70 83.5 101.4 218.9 2.31 0.33
B1 1.97 3.70 32.51 67.49 83.8 102.1 219.3 2.15 0.31
B2 1.97 3.30 38.53 61.47 83.6 101.8 216.8 2.00 0.29
B3 1.97 3.10 42.45 57.55 83.6 101.6 213.1 1.79 0.26
a mol %: from the NMR data.
b Hm0 Å 6.86 kJ/mol11.
Characterization of PS-b-PVAc and PS-b-PVA line melting temperature Tm appeared compared
with the Tm 2287C for homopolymer PVA shown in
The purified PS-b-PVAc and PS-b-PVA with a Figure 9. It was found that the variation of copoly-
well-defined structure were characterized by mer composition did not exert great influences on
FTIR, 1H-NMR, and GPC in detail. Figure 6 de- the Tgs of PS and the noncrystalline part of PVA,
picts their IR spectra, both of the peaks at 1601, but the Tm of PVA was changed with the increase
1486, 1448, and 3026 cm01 in (a), and 1574, 1443 of molecular weight of PS shown in Table III. This
cm01 in (b) attributed to the benzene ring of the may be caused by the drop of packing density or
PS segment were found, the peak at 1730 cm01 crystayllinity (Hm /Hmo) (Hm is the melt enthalpy of
for the carbonyl group in (a) and disappearance the PVA block of PS-b-PVA, Hmo is the melt en-
of this peak and appearance of a new peak at 3394 thalpy of pure PVA) of the PVA chain due to the
cm01 for the hydroxyl group of in (b) confirmed insertion of the PS chain. The higher the molecular
the existence of PS-b-PVAc and PS-b-PVA. The weight of PS, the lower the crystallinity of PVA.
same conclusion could also be derived from the
measurement of 1H-NMR shown in Figure 7. All Financial support of this project by the Natural Science
the resonance signals that are corresponding with Foundation of China and State Education Committee
of China is gratefully acknowledged.the structure of PS-b-PVAc and PS-b-PVA ap-
peared, such as 7.04–6.5 (benzene ring), 1.83
w
({CH{ connected with the benzene ring), and REFERENCES AND NOTES
1. P. Linse and M. Malmsten, Macromolecules, 25,
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w
({CH2{ ) for PS segment, 4.87 5434 (1992).
2. J. R. Quintana, M. Villacampa, and I. A. Katime,w
({CH{) , 2.00 (CH3CO{) , and 1.82 ppm Macromolecules, 26, 601 (1993).
({CH2{) for the PVAc block, 4.64 ({OH), 3.84 3. D. Nguyen, C. E. Williams, and A. Eisenberg, Mac-
romolecules, 27, 5090 (1994).w
({CH{) , and 1.44 ppm ({CH2{) for the 4. Y. Wang, C. M. Kausch, M. Chun, R. P. Quirk, and
W. L. Mattice, Macromolecules, 28, 904 (1995).PVA block. All the acetyl group at 2.00 ppm in
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Polym. Sci., Part C, 4, 507 (1963).after hydrolysis and the hydroxyl group at 4.64
6. J. L. Huang and X. Y. Huang, J.M.S.-Pure Appl.ppm appeared. Figure 8 shows the GPC measure- Chem., A34, 685 (1997).
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8G60 97-074P/ 8g60$$074p 11-05-97 17:22:52 polcal W: Poly Chem


Synthesis and characterization of amphiphilic diblock copolymer of polystyrene and polyvinyl alcohol using ethanolaminebenzophenone as photochemical binary initiation system.

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Synthesis and characterization of amphiphilic diblock copolymer of polystyrene and polyvinyl alcohol using ethanolaminebenzophenone as photochemical binary initiation system.

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