CHME 498
Undergraduate Research
Final Report
New Mexico State University
Miscibility Between Poly (Ethylene Oxide) and Various Acrylate Polymers
Research Performed by Chelsea Dohrwardt
December 12th, 2016
Dohrwardt 2
ABSTRACT
The purpose of blending polymers is to generate a unique polymer with the ideal mechanical
properties for application. For instance, in lithium-ion batteries it would be ideal to create a
polymer that has the mechanical strength of a solid with ionic conductivity of a liquid. However,
blending polymers is not as simple as mixing the two together. The purpose of the research
performed this semester was to identify if poly (ethylene oxide) and various poly acrylates are
miscible. Due to error and inexperience, the results obtained were inadequate. Future endeavors
should re-examine this experimental procedure with the addition of ionic liquids.
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TABLE OF CONTENTS
1. INTRODUCTION…………………………………………………………………………….4
2. LITERATURE REVIEW…………………………………………………………………......5
i.
Phase Diagrams and Behavior………………………………………………………....5
ii.
Flory-Huggins Regular Solution Model……………………………………………….6
iii. Instrumentation for Analysis…………………………………………………………..7
3. EXPERIMENT……………………………………………………………………………….9
i.
Solution Casting………………………………………………………………………9
ii.
Analysis………………………………………………………………………………10
4. PROGRESS AND FUTURE PLANS……………………………………………………….11
i.
Progress……………………………………………………………………………....11
ii.
Results………………………………………………………………………………..12
iii.
Future Plans………………………………………………………………………….15
5. CONCLUSIONS…………………………………………………………………………….15
6. REFERENCES…………………………………………………………………………........16
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1. INTRODUCTION
The blending of polymers has been the highlight of various research experiments because of
its vast application. The challenge of blending polymers is due to the unpredictability in
miscibility and phase behavior of the polymers. However, blended polymers continue to be
examined across various industries for their application in drug delivery, membrane separation or
filtration, battery electrolytes, etc.
Research states that ideal solid-state electrolytes will have the “ionic conductivity of a liquid,
mechanical properties of a solid and convertibility into thin film structures with large surface
area” (Jeddi et al.) [6]. Poly (ethylene oxide) at high molecular weights has been widely
examined for solid-state electrolytes because it has the ability to dissolve high concentrations of
various metal salts (Gurusiddappa et al.) [5]. Although, PEO polymer chains have a high
crystallinity which reduces ionic conductivity of the polymer matrix. This has become a major
challenge when fabricating PEO-based solid-state electrolytes (Xue et al.) [13]. Accordingly,
blending of the PEO with another polymer is one method being utilized to reduce the
crystallization PEO. Poly acrylates are commonly used as co-monomers to increase plasticity of
rigid polymers (McGraw-Hill) [10]. Poly methacrylates, such as poly (methyl methacrylate)
(PMMA) or poly (butyl methacrylate) (PBMA), contain double bonds that are very reactive in
polymer processing. Studies have shown that poly (methyl methacrylate) and poly (ethylene
oxide) are miscible for various compositions and molecular weights (Marco et al) [8]. This
specific polymer blend has also been examined for enhanced ionic conductivity and nanoconfinment and research determined that the product had high mechanical strength but ionic
conductivities much lower than conventional polymer electrolytes (Jeddi et al.) [6]. Thus the
question arose, how do other poly acrylates compare to these results?
The project goal is to determine the miscibility between poly (ethylene oxide) (PEO) and
poly (butyl methacrylate) at similar weight fractions and varying compositions. The following
will identify key concepts absorbed from literature reviews, the experimental procedure
executed, the progress of the project, future plans for the project and conclusions.
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2. LITERATURE REVIEW
Prior to the execution of the project, extensive literature review was completed to obtain
more knowledge about the topic. The following sections include phase diagrams and behavior,
Flory-Huggins regular solution model, and instrumentation utilized for analysis. These sections
further explain concepts discovered in reference studies that are significant information to
understand in this research project.
i. Phase Diagrams and Behavior
When investigating the miscibility and phase behavior of polymer blends, it is important to
understand the phases of polymers and how to generate phase diagrams. All phases are displayed
below in Figure 1. The figure represents a plot of composition versus temperature.
Figure 1. Phase Diagram [image found on google search].
Polymers can either exhibit a lower critical solution temperature (LCST), meaning it
undergoes a phase separation when heated, or an upper critical solution temperature (UCST)
where it undergoes the phase separation upon cooling. The area between the two curves indicate
a single-phase or miscible region. The outermost curve is called the bimodal curve which
represents the initiation of phase separation or un-mixing. “The phase separation takes place
when a single-phase system suffers a change of either composition, temperature or pressure”
(Anderson, Bistra) [2]. The meta-stable regions represent the state of apparent equilibrium that is
capable of changing to a more stable state (Anderson, Bistra) [2]. Transitioning from the singlephase to the meta-stable region indicates slow nucleation followed by growth of phase domains,
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resembling crystallization (Anderson, Bistra) [2]. The spinodal curve represents another point of
un-mixing until finally, the phase separated region is achieved. Transitions from the single-phase
to the spinodal region happen via spinodal decomposition (Anderson, Bistra) [2].
The phase behavior can also be determined thermodynamically:
By definition, the complete miscibility of the mixture is:
∆𝐺𝑚 = ∆𝐻𝑚 − 𝑇∆𝑆𝑚 < 0
Where ∆𝐺𝑚 is the Gibb’s free energy of mixing, ∆𝐻𝑚 is the enthalpy of mixing, ∆𝑆𝑚 is the
entropy of mixing, and T is the temperature (Anderson, Bistra) [2].
The entropic term (𝑇∆𝑆𝑚 ) remains positive due to the increase in entropy upon mixing
therefore, to be miscible the enthalpic term must be less than the entropic term.
∆𝐻𝑚 < 𝑇∆𝑆𝑚
In terms of binary composition at fixed temperatures and pressures the criteria becomes:
(
𝜕 2 ∆𝐺𝑚
) >0
𝜕𝜙 2 𝑝,𝑇
For phase separation at the spinodal curve:
𝜕 2 ∆𝐺𝑚
(
) =0
𝜕𝜙 2 𝑝,𝑇
ii. Flory-Huggins Regular Solution Model
The thermodynamics of binary polymer solutions were first investigated by Paul Flory and
Maurice Huggins in the early 1940s. Their work lead to the development of a mathematical
model known as the Flory-Huggins regular solution model and is defined below:
ΔG𝑚 = 𝑅𝑇[𝑛1 ln(𝜙1 ) + 𝑛2 ln(𝜙2 ) + 𝑛1 ϕ2 𝜒12
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The Gibbs free energy of mixing is dependent on the number of moles, n1 and n2, the volume
fractions, 𝜙1 and 𝜙2 , and the polymer-solvent interaction parameter, 𝜒12 also known as the
Flory-Huggins interaction parameter (Ruzette et al.) [11].
The model makes three major assumptions:
1. It is incompressible and exhibits no volume change during mixing
2. The entropy of mixing is only dependent on the combinatorial entropy
3. The enthalpy of mixing is caused by interactions of different segments after the
dissolution of interactions of the same type of segments.
The Flory-Huggins interaction parameter is used to describe the heat of mixing and is defined as:
𝜒12 =
𝑧∆𝜖
=
𝑘𝑇
𝑧 [𝜖 𝐴𝐵 −
𝜖 𝐴𝐴 + 𝜖 𝐵𝐵
]
2
𝑘𝑇
Where ∆𝜖 represents the excess exchange interaction energy, z is the lattice coordination, 𝜖 𝑖𝑗 is
the nearest-neighbor van der Waals interaction energy between segments i and j and k is the
Boltzmann constant (Ruzette et al.) [11].
iii. Instrumentation for Analysis
Literature review assisted in the selection of the proper instrumentation for this project.
Furthermore, investigation was performed to understand the operation of each tool. The
instruments discussed in this section can determine the miscibility of polymer blends.
Cloud Point Analyzers utilize built in cooling systems and optics to detect the temperature
at which a phase separation initially occurs; defined as the cloud point [1]. They are commonly
used in the petroleum industry. They utilize several analysis techniques determined by the
Analytical Society for Testing Materials (ASTM) such as ASTM D2500, D7346, etc. They are
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convenient because they can include automated samplers to test multiple samples automatically.
Below are two figures that display types of cloud point analyzers.
Figure 2. CPP 5G from A Roper Company [1].
Differential Scanning Calorimetry (DSC) is a technique used to study the thermal
transitions of polymers between phases. A thermogram is generated, which plots the heat flow as
a function of temperature. A DSC contains two pans, one contains the polymer blend and the
other remains the reference. The heat rate is set and remains constant as it is applied to each pan
simultaneously. The difference in heat outputs between the reference (empty) pan and the pan
with polymer are plotted on the thermogram. Phase changes can be recognized by the peaks on a
thermogram as shown in Figures 4 and 5 below. [3]
Figure 3. DSC Operation [3].
Figure 4. Crystallization
peak on a thermogram [3].
Figure 5. Glass
transition on a
thermogram [3].
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Figure 6. DSC used for analysis in Genesis B, Room 104.
3. EXPERIMENT
i. Solution Casting
1. Prepare polymer blends
a. Polymers utilized are displayed below in Table I.
Table I. Experimental Polymers
Material
Mw (g/mol)
Monomer
M0 (g/mol)
Weight
Fraction
𝑀
(𝑛𝑤 = 𝑀𝑤 )
Glass
Transition
Temperature
(Tg) (°C)
0
Poly (butyl
methacrylate)
Poly (ethyl
methacrylate)
Poly (methyl
methacrylate)
Poly (ethylene
oxide)
337000
142.2
2369.90
20
340000
114.14
2978.80
65
120000
100.121
1198.55
105
100000
44.05
2270.15
-66
Data retrieved from Sigma Aldrich [12].
b. A total of 500mg were prepared for each blend.
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c. Weigh out each polymer sample for the varying weight compositions from 100
wt% PBMA to 10 wt%, in increments of 10 wt% (i.e. 100wt%, 90wt%, etc.).
2. Add 5 mL of toluene to polymer blends while continuing to stir until completely
polymers are completely dissolved.
Figure 7. Mixed polymer blend in Toluene.
3. Cast 1 mL samples of polymer/toluene blends onto a glass dish/slide.
Figure 8. Experimental Set-up and casted samples.
4. Let casted samples sit under fume hood to evaporate toluene at room temperature for 1
to 7 days.
5. Evaporate excess solvent by placing casted samples in a vacuum oven for 2 to 4 days at
45C.
6. Perform full vacuum set at 70C for 24 hours.
7. Analyze results.
ii. Analysis
The phase behavior was analyzed both under a microscope and using a DSC instrument.
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Prepare samples for DSC:
1. Weigh Tzero pan with lid and record.
a. Tzero pan: T 160202
b. Tzero lid: T 151126
2. Weigh out a polymer sample size between 5-10mg.
3. Fit polymer sample into pan, replace lid, and press closed.
Figure 9. Pressed DSC pan
4. Adjust DSC run mechanism.
a. Heat/cool/heat method
b. Ramp 5C/min to -80C
c. Ramp 10C/min to 80C
5. Save new run for each sample.
6. Analyze thermogram.
4. PROGRESS AND FUTURE PLANS
i.
Progress
The work accomplished this semester lead to the development and approval of an
experimental safety plan (ESP). The ESP includes the solution casting procedure and analysis
using a microscope, DSC and micro-rheology. Materials were ordered and ten samples were
prepared for blends of poly (ethylene oxide) and poly (butyl methacrylate) for various weight
compositions. Few results were generated from analysis under a microscope and DSC and are
discussed in the following section.
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ii. Results
The ten prepared, casted samples can be seen in Figure 8. The image was taken after three
days of evaporation at room temperature. A white crystalline powder appeared in several of the
samples with increasing PEO weight compositions (PEO > 90 wt%). Of the ten blended samples
prepared, three were analyzed under a microscope. The following figure displays the results:
PBMA60/PEO40, 100X
PBMA70/PEO30, 100X
PBMA80/PEO20, 100X
Figure 10. Microscope images of PBMA/PEO blends.
Figure 10 above represents PBMA/PEO blends of three different samples: PBMA at 60
wt%/PEO at 40 wt%, PBMA at 70 wt%/PEO at 30 wt%, and PBMA at 80 wt%/PEO at 20 wt%,
respectively. No heat or cooling was applied to the slide during analysis. Crystals can be seen in
each sample above, however the greatest crystallization appears in the PBMA60/PEO40 blend.
Following the visualization under a microscope, samples with PBMA weight compositions of
60 or greater were analyzed using DSC. The thermogram results are displayed below in Figures 11
through 15. Estimated glass transition temperatures from the DSC results are displayed in Table II.
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Figure 11. DSC of PBMA at 100 wt%.
Figure 12. DSC of PBMA at 90 wt%, PEO at 10 wt%.
Figure 13. DSC of PBMA at 80 wt%, PEO at 20 wt%.
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Figure 14. DSC of PBMA at 70 wt%, PEO at 30 wt%.
Figure 15. DSC of PBMA at 60 wt%, PEO at 40%.
Table II. Estimated Tg and Tm from thermograms
PBMA
Glass Transition
Melting
Composition
Temperature (Tg)
Temperature (Tm)
(wt %)
(°C)
(°C)
100%
20
90%
20
65
80%
27
61
70%
30
66
60%
30
68
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iii. Future Plans
Much was achieved in the duration of this project, but future research can be done. For
instance, research would include the completion of poly (ethyl methacrylate)/poly (ethylene
oxide) sample blends for comparison. The addition of ionic liquids such as Lithium Perchlorate
would also be investigated to identify ionic conductivity in comparison to PEO/PMMA blends.
Along with the investigation of new materials, it would also be interesting to implement the use
of theoretical models to predict phase behavior during analysis.
5. CONCLUSIONS
In conclusion, the thermograms display one glass transition and one melting temperature,
insinuating that the polymer blend is miscible. However, the melting temperature appears to be
very similar to the melting temperature of poly (ethylene oxide) (Tm= 66°C). Consequently, it is
too difficult to determine by DSC if miscibility occurred. Similarly, the results achieved via
microscope cannot be used to determine miscibility either. This is because, the polymers could
not be visualized at a magnification greater than 100X and no heating or cooling was applied to
help visualize phase transitions. Therefore, without the analysis by a third instrument such as
FTIR or NMR, the results appear inconclusive.
There were many opportunities for error while executing this experiment that could have
occurred leading to inconclusive results. First of all, there was a lack of experience performing
the solution casting procedure. The polymer solution may have been casted earlier than it should
have been leading to an immiscible polymer. Secondly, the vacuum step of the procedure was
not completed. Thirdly, there was inexperience running the DSC. Meaning, the method of the
DSC may have not been adequate.
Ultimately, the purpose of this research project was to determine the miscibility of poly
(ethylene oxide) and poly (butyl methacrylate) at varying weight compositions. The results
discovered were inconclusive and the goal was not achieved. Future work should include a
second attempt at this procedure to verify results.
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REFERENCES
[1]
Analytical Instruments for Lab and Process Applications. PAC L.P. A Roper Company,
n.d. Web. 27 Sept. 2016.
[2]
Andersen, Bistra. Investigations on Environmental Stress Cracking Resistance of
LDPE/EVA Blends. Diss. Halle (Saale), U, Diss, 2004. PDF.
[3]
"Differential Scanning Calorimetry." Polymer Science Learning Center, 2016. Web. 27
Sept. 2016.
[4]
"Flory-Huggins Lattice Theory of Polymer Solutions, Part 1." Polymer Properties
Database. Polymerdatabase.com, 2015. Web. 28 Sept. 2016.
[5]
Gurusiddapppa, J., W. Madhuri, R. Padma Suvarna, and K. Priya Dasan. "Electrical
Properties of PEO-Based Electrolytes." International Journal of Innovative Research in
Science, Engineering and Technology November 2015 4.11 (2015): 11447-1454.
Ijirset.com. Web. 28 Nov. 2016.
[6]
Jeddi, Kazem, Nader Taheri Qazvini, Seyed Hassan Jafari, and Hossein Ali Khonakdar.
“Enhanced Ionic Conductivity in PEO/PMMA Glassy Miscible Blends: Role of NanoConfinement of Minority Component Chains”. Journal of Polymer Science: Part B
Polymer Physics. 48, 2065-2071.
[7]
Kuo, Shiao Wei, and Feng Chih Chang. "Miscibility and Hydrogen Bonding in Blends of
Poly (vinylphenol-co-methyl Methacrylate) with Poly (ethylene Oxide)." Macromolecules
34 (2001): 4089-097. American Chemical Society.
[8]
Marco, C., J.G. Fatou, M.A. Gomez, Hajime Tanaka, and A.E. Tonelli. "Molecular Weight
Effect on the Miscibility of Poly (ethylene Oxide) and Isotactic Poly (methyl Methacrylate)
in Their Blends." Macromolecules 23 (1990): 2183-188. American Chemical Society.
[9]
Paul C. Painter and Michael M. Coleman. “Essentials of Polymer Science and
Engineering”. Destech Publications, Inc. 2009.
[10] "Polyacrylate." McGraw-Hill Dictionary of Scientific & Technical Terms, 6E. 2003. The
McGraw-Hill Companies, Inc. 21 Sept. 2016.
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[11] Ruzette, Anne-Valerie G., and Anne M. Mayes. "A Simple Free Energy Model for Weakly
Interacting Polymer Blends." Macromolecules 34 (2001): 1894-907. American Chemical
Society.
[12] Sigma-Aldrich. Sigma-Aldrich Co. LLC., n.d. Web. 27 Sept. 2016.
[13] Xue, Zhigang, Dan He, and Xiaolin Xie. "Poly (ethylene Oxide)-based Electrolytes for
Lithium-ion Batteries." Journal of Materials Chemistry A 3.38 (2015): 19218-9253. Web.
28 Nov. 2016.