JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
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EFFECTS OF DIFFERENT MONOMER RATIO ON
CHARACTERISTICS OF STYRENE BUTYL
ACRYLATE COPOLYMER SYNTHESIZED BY SEMI
CONTINUOUS EMULSION COPOLYMERIZATION
1UJVALA
CHRISTIAN, Asst. Professor, Chemical Engineering Department, Shroff S.R.
Rotary Institute of Chemical Technology, Ankleshwar- Gujarat
ABSTRACT: Semi continuous emulsion copolymerization of Styrene (St) with Butyl Acrylate (BA) was carried
out in a one-liter glass reactor, in presence of Potassium Persulfate (K2S2O8) as initiator and Sodium lauryl
ether sulfate (SLES) as emulsifier. Experiments were carried out to study effects of monomer ratio. Final
conversion, viscosity, molecular weight and DSC analysis were studied. The final percentage conversion and
viscosity average molecular weight (Mv) decreased with increase in Styrene to Butyl Acrylate weight ratio.
DSC analysis of copolymer revealed only one transition temperature. There by confirming that only one type
copolymer is produced in spite of two monomers having widely varying reactivity ratios of 0.70 and 0.09
respectively.
Keywords—Emulsion, copolymer, Styrene, Butyl Acrylate.
I: INTRODUCTION:
Emulsion polymerization is one of the most
important techniques for the production of polymers,
which have found a wide range of applications in
paints, coatings, finishes and adhesives. The
economical impact of emulsion polymerization
becomes evident if one realizes that 10 to 15% of all
polymers are produced by emulsion polymerization
technique [1].
One of the most versatile families of the
commercially important emulsion polymers is
polymer derived from acrylic monomers. For last 50
years, these polymers have found interesting use as
protective and decorative coatings.
The Styrene-Butyl Acrylate system is a commercially
important base for many paints, adhesives and
coatings. It is also widely used as a component in ter
-polymerization (e.g. production of waxes). These
systems have flexibility of obtaining large number of
polymer products through the variation of copolymer
composition and polymerization process.[2]
Reacting System: Styrene- Butyl Acrylate
copolymers have received considerable attention in
the last few years due to their successful applications
in paint industries.[3] Butyl acrylate provides good
flexibility and excellent durability, as it’s elongation
is 2000% and Tg is –54 0C, but it has low tensile
strength and poor hardness. Styrene is used as the co
monomer with Butyl acrylate to improve hardness,
resistance to strain, water and alkali. It also enhance
coating reflectivity and gloss on the surface.[1]
II: Process Selection:
High solid content, semi- continuous emulsion
copolymerization is selected, to achieve an adequate
level of product properties, required for final
applications; under controlled conditions. The
reactivity ratios of styrene and butyl acrylate are 0.70
and 0.09 respectively. These create a problem of
multiple phases and glass transition temperatures;
when polymerization is carried out in a batch wise
manner, especially with high solid contents. Hence,
system of semi continuous polymerization was
selected as it has the advantage of producing co
polymer in the same ratio as that of monomer used as
explained by Arati et al.[4]
High Solid Content:
High solid content coating is one of the general
approach too low emission acrylic coatings. High
solid contents (>45-50 wt. % solid-content)
emulsions offer advantages like; Low shipping cost,
High molecular weight, good film forming properties
and high through put[5].
Advantages of Semi-Continuous Process:
Semi-Continuous process is more flexible than batch
and continuous systems and offer following
advantages:
1. Better control on heat release and/or rate of
polymerization.
2. Possibility of modifying the PSD.
3. Copolymer composition and structure
independent of reactivity ratios in order to
4. produce tailor made copolymers.[2]
III: Experimental:
Chemicals:
Styrene (St) : contained 10 - 50 ppm p-tert butylcatechol as
a inhibitor. The inhibitor was removed by extraction with
0.1N NaOH followed by water wash.
Butyl Acrylate (BA) : (without inhibitors) purity as
specified by suppliers was used.
Functional Monomer: Acrylic Acid (AA).
Continuous Phase: D.M. water was used as
continuous phase.
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Emulsifier: anionic emulsifier sodium lauryl ether
benzene as a solvent. Flow time was measured for
sulfate (SLES), Initiator: water-soluble, thermal
solution (t) and pure solvent (t0) using Ubbelohde
initiator, Potassium Persulfate (KPS).
suspended level viscometer (USLV).
Protective Colloid: Cold water-soluble, partially
From Intrinsic Viscosity, viscosity average molecular
hydrolysed, medium viscosity poly vinyl alcohol
weight (Mv) was determined by using Mark(PVA).pH Controller : Ammonia (NH 3) solution.
Houwkin’s equation:
Nitrogen (N2): Nitrogen was purged to remove oxygen[ n ] = k(Mv)a where, [n] is intrinsic viscosity, K and
from reactor which inhibits the polymerization.
a
are
constants
for
a
given
Experimental Procedure: The semi-continuous
polymer/solvent/temperature system
emulsion copolymerization was carried out using
(iii) Copolymer
Composition
By
NMRstandard recipes given as below:
Spectroscopy:
The copolymer composition was determined by
Bruker advance NMR-Spectrophotometer at 300MHz.
Table-1: Ingredients of Typical Recipe:
From the NMR measurements, quantitative analysis
Chemicals
Total Weight (g)
of final copolymer composition,can be obtained by
comparing the proton resonance of two main groups i.
H 2O
372
e. phenyl(-C6H5) and methoxy (-O-CH2).Using peak
Styrene (St)
130
areas of the phenyl ring protons (S1) and that of
Butyl Acrylate (BA)
155
methoxy group (S2) final copolymer composition is
Acrylic Acid
12
obtained by following equation:
PVA
5.0
Fraction Of Butyl Acrylate in FinalCopolymer
SLES
4.0
= (S2/2) / (S2/2) + (S1/5)
K2S2O8
8.25
(iv) Glass Transition Temperature:
The glass transition temperature of final copolymer
was obtained using
Polymerization was carried out in a one liter, four
PERKIN-ELMER 7 SERIES Thermal Analysis System,
necked glass reactor placed in a constant temperature
with heating rate of 10 0C.
bath at 76 0C. The reactor was equipped with a reflux
condenser, stainless steel anchor type stirrer;
V:Results and Discussion:
monomer-emulsion feed inlet, initiator inlet and
(i) Effect of Monomer Ratio on % conversion and
nitrogen inlet tube[5].
Molecular Weight:
Initial reactor charge was poured in the reactor and
From
the plot of conversion Vs monomer
agitation speed was measured and adjusted to 500
(Styrene/Butyl Acrylate) ratio, (Fig.1), it is observed
rpm, using stroboscope. Nitrogen purging was used
that with increase in the monomer ratio the
to remove the oxygen from the system. Liquid
conversion decreases. This is because of different
Ammonia was added as a pH controller. Pre-prepared
water solubility of the two monomers Styrene and
monomer emulsion feed was added at a constant rate
Butyl Acrylate. Water solubility of Styrene is 0.07g/L.
and initiator solution was also added at a continuous
(at300 C),while that of Butyl Acrylate is 10g/L. (at
rate; so as to complete the addition in three hours.
300C) [7]. Lower solubility of Styrene, cause large
One hour cooking time was provided after all the
desorption rate of radicals, thus with higher Styrene
reactants were added, so as to ensure to complete
concentration, conversion decrease sharply. Butyl
conversion. Samples were collected at 30-minute
Acrylate is more water-soluble which enhance the
interval, each.
homogeneous nucleation and hence higher
Experiments were performed to study six different
concentration of Butyl Acrylate leads to higher
monomer (styrene/butyl acrylate) weight ratios (i.e.
conversion. This is because the copolymer systems
30/70, 40/60, 45/55, 50/50, 60/40, 70/30) while other
using water -soluble initiator; have direct bearing on
parameters were constant.
water solubility of monomers.
Fig.1 Effect of Monomer Ratio on % Conversion
IV: Analysis and Testing:
(i) Instantaneous conversion:
Measured quantity of sample was dried at 100 0C in
a dryer for 1 hour. Dried sample was weighed and
instantaneous conversion calculated based on
polymer present in the reactor with respect to the
amount of monomer already fed to the reactor.
(ii) Viscosity:
Emulsion viscosity was measured by Brookfield
LVT model using RV5 spindle at 20 rpm.
Intrinsic Viscosity: Emulsion was precipitated
in acetone and air dried. Solution of polymer with
various concentrations were prepared by using
R10 (St/BA=30/70)
R14(St/BA=40/60)
R7 (St/BA=45/55)
R18 (St/BA=50/50)
R20 (St/BA=60/40)
100
R22 (St/BA=70/30)
% Conversion
80
60
40
20
0
0
50
100
150
200
250
300
time (min.)
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The viscosity average molecular weight decreases
with increase in Styrene/Butyl Acrylate ratio (Fig.2);
mainly due to poor solubility of styrene. Higher
concentration of styrene drastically increases number
of micelle (reaction centers) creation there by
reducing average molecular weight of copolymer.
Fig.2 Effect of Monomer Ratio on Mv
formed is in the same ratio of monomer added and
there are no multiple alloys unlike batch
polymerization.(In case of batch polymerization the
composition of polymers changes with time because
of difference in reactivity ratios)[6].
Fig.4DSC Curve:
Table-2: Results of NMR and DSCAnalysis
St/BA weight ratio 45/55 gave the best conversion
profile with low overall viscosity.
(ii) Final Copolymer Composition By H NMR –
SPECTROSOPY:
The 1H NMR spectrum for final copolymer product
(St/BA=45/45) is given in Fig.3. Results of NMR
analysis are given in Table-2, indicate that the final
copolymer composition ratio is almost same as the feed
composition ratio. Thus composition-controlled
copolymers are obtained with use of semi continuous
polymerization irrespective of reactivity ratio.
Sr.
Monomer
No.
(St/BA)
ratio
(St/BA)
(wt/wt)
(wt/wt)
30/70
45/55
45/55
60/40
31.8/68.2
50.9/49.1
50.9/49.1
58.93/41.06
1
Fig:3 NMR Spectrum:
(ii) Glass Transition Temperature (Tg):
DSC curve
for final copolymer product
(St/BA=45/45) is given in Fig.4. From the DSC
analysis of the final copolymer samples; it was
observed that the range for glass transition
temperature (Tg) was 35.25 0C to 45.340C as for
different monomer weight ratio, as given in Table-2.
There was only one glass transition temperature in all
the cases there by confirming that the copolymer
1
2
3
4
NMR
Results
Glass
Transition
Temp.
(0C)
37.1
36.26
46.18
35.35
VI: CONCLUSION:
From the present study on laboratory synthesis of
Styrene/Butyl Acrylate emulsion copolymerization,
with continuous separate mode of addition of initiator
for a fixed time-interval of four hours; it is observed
that, monomer weight ratio is one of the important
process parameter for this polymerization process.
Higher conversion and viscosity average molecular
weight were obtained at high Butyl Acrylate to Styrene
weight ratio in monomer emulsion feed. The viscosity
of final product was about 1 poise and glass transition
temperature (Tg) was 35.250C to 45.340C as for
different monomer weight ratio. NMR analysis indicate
that the final copolymer composition ratio is almost
same as the feed composition ratio. Thus compositioncontrolled copolymers were obtained with use of semi
continuous polymerization irrespective of reactivity
ratio.
REFRENCES
[1] Kirk & Othmer D F, Encyclopedia of Chemical
Technology, 4th edn (John Wileyand Sons, New
York),[1998].
[2]Lovell Peter A & El Asser Mohamed S, Emulsion
Polymerization and Emulsion Polymers (John Wiley
and Sons, New York), [1997].
[3] Odian George, Principles of Polymerization, 2nd
edn (John Wiley and Sons, New York), [1970].
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[4] Chandel Arti M, Kinetics of Styrenated Acrylics,
M.E.Thesis, Faculty of Technology & Engineering,
M S University, Baroda, 2001.
[5] Madan R N & Dikshit R C, “Different Mode of
Addition of Monomers for Styrene/Butyl acrylate
Copolymer System”, Indian Journal of Chemical
Technology, September, Vol.12, [2003].
[6] Christian Ujvala, Emulsion Copolymerization of
Styrene/Butyl acrylate, M.E.Thesis, Faculty of
Technology & Engineering, M S University, Baroda,
2003.
[7] Djkhabha S and Guillot J, European Polymer
Journal, [1989].
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