Design of Electrophoretic Non-ionic Polyurethanes and the Applications
Akinori Ohno, Mikihiro Hayashi, and Akinori Takasu
Department of Life and Applied Chemistry,
Graduate School of Engineering, Nagoya Institute of Technology,
Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan
（第一回 ポリウレタン国際技術振興財団研究助成）
Introduction
Polyurethane elastomers are ideal recycle materials,
because cross-links in these materials are formed by physicalinteractions in appropriate engineered microdomains,
crystallites, or hydrogen bonds.1 Polyurethane elastomers
are composed of alternating hard and soft segment and show
versatile mechanical properties, which fascinate polymer
chemists to apply for coating materials, too. During the past
five years, our group has focused on sulfone-containing
polymers for the investigation of the electrophoretic behavior

Figure 1. Schematic
representation of EPD.

ofinteresting
non-ionic
polymers.2
Electrophoretic deposition (EPD) is apromising and facile technique for thefabrication of inorganic or organic or Figure 2. Chemical structure ofinorganic / organic composite films3,4 onto poly(ester-sulfone) in which sulfonyl groups
electrodes. EPD is based on the controlled are marked in red.
electric-field-induced deposition of charged
particles or molecules in an orderly manner onto an electrode. The characteristics ofEPD include the capability of film formation on a complex surface shape, easy controlof thickness, and formation of a homogeneous layer. Recently, our group found that an
aliphatic poly(ester-sulfone) prepared by thiol-ene click polymerization and subsequentoxidation showed anode-selective electrophoresis under EPD conditions.2a
Anode-selective EPD coatings of bioactive glass (45S5Bioglass)2a and titanium dioxide(TiO2)2b were also demonstrated. Furthermore, these observations and the interesting
electrophoretic behavior of the sulfone-containing polyester prompted us to explore
why the poly(ester-sulfone) is deposited onto the anode,10f and what part of its

structure10d,10e is responsible for this unusual electrophoretic behavior. We now
concluded that this anode selective EPD of non-ionic polymer is the first example in theworld and discovered that sulfonyl group is essential for the EPD (Figure 2).
These research background prompted us to design electrophoretic non-ionicpolyurethane containing sulfonyl group, aiming at smart coatings equipped withpolyurethane’s features. In this magazine, we introduce synthesis of non-ionicpolyurethane containing sulfonyl group via polyaddition of methylene diphenyl
4,4’-diisocyanate (MDI) with 2,2'-thiodiethanol in the absence and presence oftriethylene glycol as the soft segment and subsequent oxone oxidation. The strength ofthe coated polyurethane was evaluated both by pencil hardness and cross-cut tests.
Synthesis of Polyurethane 1 (PU-1) via Polyaddition of MDI and2,2'-Thiodiethanol in the absence Triethylene glycol.
Polymerization conditions were surveyed, an example follows.
2,2'-Thiodiethanol 2.06 mL (20 mmol), MDI 5.01 g (20 mmol), dibutyltin dilaurate(200μL) as the polymerization catalyst , and 86 mL of toluene were added to 200 mL
round-bottomed flask with a magnetic stir bar under a nitrogen atmosphere. The mixture
was stirred at 90 °C for 5 h, then we obtained white solid polymer,
poly(MDI-alt-2,2'-thiodiethanol).
Thepolymer
wasprecipitated
from
N,N-dimethylformamide (DMF) by addition of excess acetone and dried under vacuum.
In order to convert sulfide groups to sulfones, we oxidized the parent polymer using
oxone as the oxidizing agent. The polymer (5.01 g, 13.4 mmol repeat unit) and oxone(4.08 g, 26.8 mmol) in DMF (100 mL) were added into a 200 mL round-bottom flask.
After stirring at r.t. for 12 h, the mixture was filtered, and the solvent was evaporated
under reduced pressure to give a pale-yellow solid that was then dissolved in DMF andprecipitated by addition of 90 mL of H2O/CH3OH (9/1, v/v). Obtained polymer was apale-yellow solid and named as PU1 (Scheme 1, PU-1, Mn = 1.4 × 104, Mw/Mn = 2.1).
Scheme 1. Synthesis of PU-1

Synthesis of polyurethane 2 (PU-2) via Polyaddition of MDI and 2,2'-Thiodiethanol
in the presence of Triethylene glycol.
Triethylene glycol 1.39 mL (10 mmol), MDI 5.01 g (20 mmol), dibutyltin
dilaurate (200μL), and 86 mL of toluene were added to 200 mL round-bottomed flaskwith a magnetic stir bar under a nitrogen atmosphere. The mixture was stirred at r.t. for
3 h, then we added 2,2'-thiodiethanol 1.03 mL (10 mmol) and stirred them for 21 h. The
polymer was precipitated from DMF by addition of diethyl ether and dried undervacuum. To convert sulfide groups in the polymer backbone to sulfones, we oxidized
thepolymerbyoxone
similartoPU-1.
The
parentpolymer,poly(MDI-alt-2,2'-thiodiethanol)-co-poly(MDI-alt-triethylene glycol) (6.43 g, 9.57mmol repeat unit) and oxone (2.91 g, 19.14 mmol) in DMF (70 mL) were added into a
100 mL round-bottom flask. After stirring at r.t. for 12 h, the mixture was filtered, andthe solvent was evaporated under reduced pressure to give a pale-yellow solid that wasthen dissolved in DMF and precipitated by addition of 90 mL of H2O/CH3OH (9/1, v/v).
Obtained polymer was a pale-yellow solid and named PU2 (Scheme 2, PU-2, Mn = 1.2
× 104, Mw/Mn = 1.7)
Scheme 2. Synthesis of PU-2

Electrophoretic Deposition of PU-1 and PU -2.
PU-1and PU-2 formed colloidal suspensions in mixed solvents of DMF andethanol and could be deposited onto a stainless-steel anode by EPD. The results aresummarized in Table 1.
Table 1. Result of EPD

The distance between the electrodes was 6.5 mm and the deposition time was 90 s at a voltage of 200 V.

As shown in Table 1, we succeeded in anode-selective EPD of non-ionicpolyurethane and an expected amount of deposition was confirmed in comparison withprevious work.2 It seems that coating of PU-2 formed more smooth and uniform surface
than PU-1.
Pencil Hardness Test.
We first evaluated coating hardness by pencil hardness test (JIS K5600-5-4). Asshown in Figure 3, we scratch coating by apencil known hardness. Coatig of PU-1 wasdameged by a pencil hardness of 2B, on theother hand, coating of PU-2 by pencil
hardness of 2H. We confirmed that strenghthof EPD coating was improved by introducing
triethylene glycol as the soft segment.

Figure 3. Image of pencil hardness test.

Cross Cut Test.
We also investigated resistance of peeling from metal substrate by cross cut test
(JIS K5600-5-6). It is a qualitative method for evaluation of the peeling strength, inwhich after cutting cross on coating, we put an adhesive tape on the coating film,subsequently peel the tape as shown in Figure 4. As a result of this test, PU-1 waseasily peeled and classified in 4 and, on the other hand, PU-2 was classified in 1 (seeFigures 5 and 6). We confirmed that EPD coating become stronger by introducing
triethylene glycol as the soft segment.

Figure 4. Image of cross-cut test.
PU-1

Figure 5. Evaluation of cross-cut test.

PU-2

Figure 6. Results of cross-cut test [PU-1(left) and PU-2 (right)].

Conclusion
We successfully synthesize non-ionic polyurethane and we could observe theanode selective EPD. The strength of the polyurethane-based coating film wasimproved by adding triethylene glycol as the ternary monomer. These fundamental
results should provide new guideline for smart coating using polyurethane elastomers.
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