Preparation of a spirooxazine grafted PMMA and its photochromic properties

Article abstract of DOI:10.1080/00397911.2016.1178296

A novel spirooxazine (SO) compound was designed and synthesized. Macromolecular materials, called SO-g-hPMMAs (where the g means grafting and the h means partial hydrolysis), were prepared using PMMA (polymethylmethacrylate) with different degrees of hydrolysis. SO-g-5%hPMMA was prepared by reacting SO-containing active C-Br bonds with 5% partially hydrolyzed PMMA. The SO was characterized using¹H NMR and infrared. Beyond that, photochromic properties were studied in detail. We discuss the effects of hydrochloric acids and hPMMAs of different hydrolysis degrees on photochromic properties of SO-g-hPMMA. Additionally, mechanical properties of the material were studied. Results indicate that the colored ring-opening form (PMC) of SO-g-hPMMA exhibits a good performance in terms of thermal stability, in contrast to the homologous SO. Experiments additionally demonstrate that hydrochloric acid improves the PMC’s thermal stability. SO-g-9%hPMMA demonstrated a good performance of photochromic properties compared to those with different degrees of hydrolysis.

Full text of DOI:10.1080/00397911.2016.1178296

Synthetic Communications
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Preparation of a Spirooxazine Grafted PMMA and
Its Photochromic Properties
Liang Wu, Sai Zhang, Jun Gao, Peirong Qiang & Jingxin Lei
To cite this article: Liang Wu, Sai Zhang, Jun Gao, Peirong Qiang & Jingxin Lei (2016):
Preparation of a Spirooxazine Grafted PMMA and Its Photochromic Properties, Synthetic
Communications, DOI: 10.1080/00397911.2016.1178296
To link to this article: http://dx.doi.org/10.1080/00397911.2016.1178296
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Date: 18 May 2016, At: 12:47

Preparation of a Spirooxazine Grafted PMMA and its Photochromic
Properties
1
1
1
1
2
Liang Wu , Sai Zhang , Jun Gao , Peirong Qiang , Jingxin Lei
1
College of Chemical Engineering, Sichuan University, Chengdu , China
2
State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu ,
China
Corresponding to author: Jun Gao E-mail: wuliang25@yahoo.com
Abstract
A novel spirooxazine (SO) compound was designed and synthesized. Macromolecular
materials, called SO-g-hPMMAs (where the g means grafting and the h means partial
hydrolysis) were prepared using PMMA with different degrees of hydrolysis. Thus,
SO-g-5%hPMMA represents it was prepared by reacting SO containing active C-Br bonds
with 5% partially hydrolyzed PMMA. The SO was characterized using 1H-NMR and IR.
Beyond that, photochromic properties were studied in detail. We discuss the effects of
hydrochloric acids and hPMMAs of different hydrolysis degrees on photochromic properties
of SO-g-hPMMA. Additionally, mechanical properties of the material were studied. Results
indicate that the colored ring opening form (PMC) of SO-g-hPMMA exhibits a good
performance in terms of thermal stability in contrast to the homologous SO. Experiments
additionally demonstrate that hydrochloric acid improves the PMC’s thermal stability.
Especially, SO-g-9%hPMMA demonstrated a good performance of photochromic properties
compared to those with different degrees of hydrolysis.

INTRODUCTION
Photochromic compounds are materials, changing their color upon irradiation of certain
wavelength, and reverting to the original color upon irradiation of another wavelength or
applying heat. Typical classes of photochromic compounds are spiropryans, spirooxazines,
fulgides, and diaryletheneands. The spirooxazine (SO) compounds were intensively studied in
[1, 2]
the past
and are of interest due to their ability to respond with intense photochromic
reaction, fast thermal relaxation and good fatigue resistance. As shown in Fig.1, there is a
reversible reaction between uncolored ring closure structure (SO) and colored ring opening
structure (PMC). The feature is applied in various fields such as digital optical storage,
[
3–5]
color-changing textiles, optical switches
. However, a drawback of the material class was
[6]
the thermal stability, hindering the entrance in industrial applications . Previously, research
on spirooxazine was dedicated to improve the thermal stability of the PMC
Our strategy in this work is to improve the thermal resistance by introducing polymer chains
into the SO molecule in order to decrease the rate of thermal ring closure by steric effects.
[
7]
Beyond that the photochromic materials were applied as films, fibers, beads and flakes ,
opening new routes for industrial applications following this approach. In this study, PMMA
covalently grafted SO though the C-Br bonds, which were introduced into the 1- and
9
'-position of SO, with a view to preparing the functional polymer materials with
photochromic ability.
RESULTS AND DISCUSSION
Study On The Photochromic Properties Of SO
UV/Vis absorption spectra were recorded using a spectrophotometer (500W mercury lamp, 35
centimeters between lamp and samples). The SO samples were analyzed in ethanol solution
-4
(
5×10 mol/L)

Study On The Photochromic Properties Of SO In Ethanol Solution Under UV Excitation
Samples were irradiated with ultraviolet light for 30s and visible absorption spectra were
recorded subsequently. The absorbance at λmax (A) was recorded and the increased multiples
(P) of absorbance at λmax were calculated according to equation 1.
A -A
t
P
(1)
A
Where A is the absorbance at λ before irradiation and A is the absorbance at λ after
∞
max
t
max
3
0s of irradiation. The results are presented in Table 1. As can be seen, after 30s of UV/Vis
irradiation, the absorbance at λmax of SO in ethanol solution increased accompanied by a color
change from light blue to deep blue. This suggests that the thermal equilibrium reaction is
shifting toward the PMC (Fig.1).
Study On The Photochromic Properties Of SO Affected By Excitation Time
Fig.2 shows the visible absorption spectra of SO in ethanol solution at different irradiation
times. As can be seen, the absorbance of SO in ethanol solution increases with UV excitation
time, as more spirooxazine molecules are shifted from the ring closure structure (SO) towards
ring opening structure (PMC)
Study On The Thermal Fading Reaction Of SO
After 30s of UV irradiation, UV/Vis spectra were recorded at fixed intervals (15s), in order to
shed light on the fading process (Fig.3). The decreased percentages (M) of the absorbance at
λmax were calculated according to equation 2.
A -A
0
t
M
100%
(2)
A0
Where A is the absorbance at λ at 0s after irradiation and A is the absorbance at λmax at a
0
max
t
certain time interval after irradiation. Within the same period, the smaller the M value, the

slower the fading rate and the higher the thermal stability. The results are presented in Table 2.
As can be clearly seen, the absorbance (A ) of SO in ethanol solution decreases with time.
t
After 90s, the absorbance drops down by 97.90%.
Study On The PMMA Of Partial Hydrolysis (Hpmma)
The molar mass of the PMMA monomer unit is 100g/mol. As each unit contains an ester
group, the content in PMMA can be calculated according to equation 3:
m
n ≈ 1
(3)
00g / mol
Where n (mol) is the mole number of the ester group in PMMA and m (g) is the mass of
PMMA. The degree of hydrolysis was evaluated using phenolphthalein and hydrochloric acid
(c(HCl)=0.10mol/L) for back-titration. Hydrolysis degrees were calculated according to
equation 4, and results are presented in Table 3.
cNaOH VNaOH -cHCl VHCl
h
(4)
n
Study On The Photochromic Properties Of Polymer Materials Containing SO
Functional Group
Solutions of SO-g-5%hPMMA and SO-m-PMMA (the m means mixing and SO-m-PMMA
represent a mix of SO and PMMA) in dichloromethane were prepared at the concentration of
-3
1
.5×10 mol/L. Also, different SO-g-hPMMAs (the hydrolysis degrees are 5%, 9%, and 12%
-3
respectively) solutions in dichloromethane (c=3×10 mol/L) were prepared. UV irradiation
conditions: 500W mercury lamp, 35 centimeters between lamp and samples, respectively.
Study On The Photochromic Properties Of SO-G-5%Hpmma Affected By Excitation Time
-3
Fig.4 shows UV/Vis spectra of SO-g-5%hPMMA in dichloromethane solution (3×10 mol/L)
at different irradiation times. As can be seen, the absorbance of SO-g-5%hPMMA in

dichloromethane solution increases with UV excitation time, as more spirooxazine molecules
are transforming from the ring closure structure to ring opening structure in the equilibrium
reaction (Fig.1). A comparison between Fig.2 and Fig.4 demonstrates that the grafting PMMA
reduces the light response and maximum absorbance to a low extent, underpinning the
potential of SO-g-PMMA as photochromic material.
Study On The Thermal Fading Reaction Of SO-G-5%Hpmma
-3
The fading process of SO-g-5%hPMMA in dichloromethane solution (3×10 mol/L) was
studied, and results are given in Fig.5 and Table 4. As can be seen, the absorbance (A ) of
t
SO-g-5%hPMMA in dichloromethane solution decreases with time. SO-g-5%hPMMA shows
longer fading times and a higher performance in thermal stability than SO, as the 1-position
and 9'-position of SO are replaced by PMMA polymer chains (Fig.6), intensifying the steric
hindrance and impeding the ring closure reaction of PMC in Fig.1.
Study On The Photochromic Properties Of SO-G-5%Hpmma Affected By Hydrochloric
Acids
-3
We evaluated the fading process of SO-g-5%hPMMA in dichloromethane solution (3×10
mol/L) after addition of 3mL of hydrochloric acid (c(HCl)=0.10 mol/L). The results are given
in Fig.7 and Table 5. As we can see, the absorbance (A ) of SO-g-5%hPMMA in
t
dichloromethane solution increases after addition of hydrochloric acid. Similarly the thermal
fading rate is slowed down causing higher performance in thermal stability. The obvious
-
change is possibly provoked by hydrogen bonding interactions between protonated–COO
-
groups, which were generated in hPMMA side chains, and the -O in PMC (Fig.8). This
indicates that the equilibrium reaction (Fig.1) is shifting towards PMC, leading to increased
absorbance of λmax. In other words, hydrogen bonding decreases the ring closure rate and
increases the thermal stability of PMC at the same time.

Study On The Thermal Fading Rates Of SO-G-5%Hpmma And SO-M-PMMA
UV/Vis spectra of SO-g-5%hPMMA and SO-m-PMMA solutions in dichloromethane
-3
solutions (1.5×10 mol/L) were recorded at defined intervals (10s) after 30 s of UV irradiation,
-1
yielding the kinetic decay (Fig.9) of the thermal fading process. Fading rates (k/s ) were
calculated according to equation 5.
ln (A -A ) / A
t
0
k
(5)
t
The results are presented in Table 6. As shown in Fig.9, thermal fading curves of
SO-g-5%hPMMA and SO-m-PMMA in dichloromethane solution were fitted to the
-1
first-order kinetic. The slopes of the curves represent the thermal fading rates (k/s ). In Table
6
it can be seen that the thermal fading rate of SO-g-5%hPMMA is slower than the
SO-m-PMMA counterparts. A possible explanation for the difference is the higher steric
hindrance, caused by additionally formed covalent bonds in the SO-g-5%hPMMA.
Study On The Photochromic Properties Of SO-G-Hpmma Affected By Hydrolysis Degrees
Kinetic curves (Fig.10) of various SO-g-hPMMAs in dichloromethane solution are presented
in Table 7 together with thermal fading rates. As shown in Fig.10, those curves fit very well
-1
to first-order kinetics. The slopes in Fig. 10 represent the thermal fading rates (k/s ). As can
be seen, SO-g-9%hPMMA had the slowest fading rate among the compounds. When the
hydrolysis degree is 5%, the SO groups grafted to a low degree onto the PMMA chains, and
the volume effect of PMMA dominates in the thermal stability. The fading rate of
SO-g-9%hPMMA is furthermore slower than SO-g-5%hPMMA’s, indicating that the effect
of neighboring SO groups has a high impact. Furthermore, as the degree of hydrolysis
increases to 12%, the steric hindrance to adjacent SO groups increases simultaneously,
indicating that the concomitant volume effect is responsible for the ring opening process and,

at the same time, impedes the ring opening reaction. As a result, the fading rate of
SO-g-12%hPMMA is faster than its SO-g-9%hPMMA counterpart.
Study The Fading Time Of SO-G-9%Hpmma Film
The fading time of SO-g-9%hPMMA film after 10s of UV irradiation was studied. The period
until the fading process had ended completely was 350s.
Study On The Mechanical Properties Of Polymer Materials Containing SO Functional
Group
Films of PMMA, SO-m-PMMA and SO-g-hPMMAs were prepared, and evaluated in terms
of tensile strength and elongation at break. The results are presented in Table 8. As we can see,
the tensile strength increases as the SO group increases and the blend film (SO-m-PMMA)
performed lower than the graft film (SO-g-5%hPMMA). Interestingly, the changing of
elongation at break exhibits no clear trend. Compared to PMMA films, those changes appear
at a low degree.
In summary, grafting SO onto the hPMMA chains, could largely improve the thermal
stability of the PMC. Besides, almost no negative influence on the mechanical properties of
PMMA could be deduced from the data.
EXPERIMENTAL
Commercially available Poly (methyl methacrylate) (PMMA) was utilized; anhydrous ethanol
was dried over MgSO for 24h, distilled at 77-78°C; anhydrous methanol was dried over
4
MgSO for 24h, and distillated at 63- 64°C; all other reagents (AR or CP) were used as
4
received. 1H-NMR spectra was recorded in CDCl on a Bruker AVANCE/400MHz NMR
3
(Switzerland). Chemical shifts are given in parts per million (ppm), using tetramethylsilane

(TMS) as internal standard. Infrared spectrums were recorded using a Nicolet 170SX infrared
spectrometer (USA). UV/Vis spectra were recorded using a Mapada UV-1800 UV-visible
spectrophotometer (Shanghai, China).
Synthesis Of The Intermediate Products
[
8]
The
intermediate
products
2,3,3-trimethyl-3H-indole
(compound
1)
,
[
9–12]
1
1
-(6-bromohexyl)-3,3-dimethyl-2-methyleneindoline
(compound
2)
,
and
[
13, 14]
-nitroso-2,7-dihydroxy naphthalene (compound 3)
were synthesized referring to
related references, and the synthetic routes were shown in Scheme 1.
Synthesis Of 1-(6-Bromohexyl)-3, 3-Dimethylspiro[Indoline-2, 3'-Naphtho[2,1-B][1,4]
[12, 15]
Oxazin]-9'-Ol (4)
To a stirred solution of 3 (1.13g, 6.0mmol) in anhydrous methanol (40mL), compound 2
1.89g, 5.88mmol) was added slowly at the reflux temperature under the nitrogen atmosphere.
(
The reaction mixture was refluxed for 12h. Then the solvent was removed under reduced
pressure and the residue was purified by column chromatography (4:1 petroleum ether: ethyl
acetate) to afford the titled compound 4 in a 22.3% yield (0.65g) as a virescent solid. 1H
NMR (400 MHz, CDCl , δ): 1.28, 1.36(s, 6H, -C(CH ) ), 1.39~1.59(m, 8H,
3
3 2
N-CH -(CH ) -CH Br), 3.23(t, J=6.3, 2H, -CH Br), 3.39(t, J=6.3, 2H, N-CH -), 6.61~7.86(m,
2
2 4
2
2
2
1
1H, Ar-H, CH=N, -OH); IR: ν = 742(υC-Br), 1072, 1244(υCspiro-O-C=), 1355(υAr-N), 1607(υC=N),
431(υO-H).
3
Synthesis Of 9'-(4-Bromobutoxy)-1-(6-Bromohexyl)-3,3- Dimethylspiro[Indoline-2,3'-
[14]
Naphtho[2,1-B][1,4]Oxazine] (5, SO)
To a stirred mixture of compound 4 (0.49, 1.0mmol) and NaOH (0.04g, 1mmol) in acetone
10mL), the solution of 1, 4-dibromobutane (0.24g, 1.1mmol) in acetone (5mL) was added
(

slowly at room temperature. The reaction was continued for two hours. Then the reaction
mixture was filtered, concentrated and further purified by column chromatography (10:1
petroleum ether: ethyl acetate) to afford the titled compound 5 in a 70.1% yield (0.44g) as a
yellow solid. 1H NMR (400 MHz, CDCl , δ): 1.28, 1.37(s, 6H, -C(CH ) ), 1.67~1.70(m, 8H,
3
3 2
N-CH2-(CH ) -CH Br), 2.05~2.08(m, 4H, 9′-OCH2-CH CH -CH Br), 3.19, 3.35(t, J=6.9, 4H,
2
4
2
2
2
2
-
CH Br), 3.56(t, J=6.6, 2H, N-CH -), 4.23~4.26(t, J=6.0, 2H, O-CH -), 6.59~7.86(m, 10H,
2 2 2
Ar-H, CH=N); IR: ν = 742(υC-Br), 1055, 1243(υCspiro-O-C=), 1370(υAr-N), 1607(υC=N).
Synthesis Of Partially Hydrolyzed PMMA (6, Hpmma)
To a stirred suspension of PMMA (1g) in 1,4-dioxane (15mL), different volumes of NaOH
aqueous solutions (0.1 mol/L) were added slowly after the PMMA was dissolved completely
at reflux temperature. The reaction mixture was continued for 12h. Then the solvent was
volatilized and the residue was dried to afford different hydrolysis degrees of compound 6
(Scheme 2).
Synthesis Of Compound 7 (SO-G-Hpmma)
To a stirred suspension of hPMMA (2g) in 1,4-dioxane (20mL), the solution of SO
(0.15mmol) in 1,4-dioxane (15mL) was added slowly after the hPMMA was dissolved
completely at 90°C. The reaction mixture was continued for 12h, and then the mixture was
kept away from light until the solvent volatilized entirely. The solid residue was washed
several times with cyclohexane to remove the unreacted SO, and the titled compound 7 was
obtained (Scheme 2).
Preparation Of SO-G-Hpmma Films
The SO-g-hPMMA (0.5g) was dissolved into 1,4-dioxane (40mL). Then we poured the
solution into the Teflon disc of 9cm in diameter. The mixture was kept away from light until

the solvent volatilized entirely to afford the film with thickness of 0.10mm. The film was cut
into rectangular film samples of 10mm×35mm, for further tests.
CONCLUSION
Novel macromolecular compounds SO-g-hPMMA were synthesized. Studies have
demonstrated that the thermal fading rates of SO-g-hPMMA were markedly slower than SO.
For instance, the absorbance at λmax of SO decreased by 97.90% after a fading time of 90s,
while the absorbance at λmax of SO-g-5%hPMMA decreased by 92.14% after a fading time of
2
70s. Addition of hydrochloric acid decreased the fading rate of SO-g-hPMMA. The slowest
-1
fading rate (0.0054 s ) and the best photochromic properties were observed for the sample
SO-g-9%hPMMA. The total fading time of the SO-g-9%hPMMA film was 6min. The
SO-g-9%hPMMA is expected to be applied in the field of photochromic polymer materials.
REFERENCES
1
. Lokshin, V.; Samat, A.; Metelitsa, A. V. Russ. Chem. Rev. 2002, 71, 893-916.
. Crano, J.C.; Guglielmetti, R. J. Organic Photochromic and Thermochromic
Compounds, Plenum Press: New York, vol.1, 85–109, 1999.
2
3
4
5
. Berkovic, G.; Krongauz, V.; Weiss, V. Chem. Rev. 2000, 100, 1741-1753.
. Little, A.F.; Christie, R.M. Coloration Technology, 2010, 126, 164-170.
. Sun, B.; He, Z. B.; Hou, Q. X.; Liu, Z. H.; Cha, R. T.; Ni, Y. H. Carbohydrate
Polymers, 2013, 95, 598-605.
6
7
. Gan, F. X. Chinese Science Bulletin. 1999, 44, 2236-2240.
. Crano, J.C.; Guglielmetti, R. J. Organic Photochromic and Thermochromic
Compounds, Plenum Press: New York, vol.2, 9-63, 1999.

8
9
1
1
1
. Hugo, I.; Lance, F. J. Org. Chem. 1968, 33, 4283-4285.
. Colin, P. M.; Louise, D.; Sean P. G. Tetrahedron Letters. 2007, 48, 657-661.
0. Ren, N.; Toyokazu, H.; Yasuo, A. Dyes and Pigments. 2002, 52, 95-100.
,
1. Wurthne, F. Synthesis. 1999 12, 2103-2113.
2. Vitali, I. T.; Renat, K.; Thomas, H. R.; Jens H.; Armin, B. Tetrahedron Letters. 2000,
4
1, 2351-2355.
1
1
3. Toung, A. S.; Young, M. P.; Myung, S. C. Dyes and Pigments. 2007, 75, 279-282.
4. Zhang, C. R. Design, Synthesis and Property of Bifunctional Photochromic
Spirooxazine Molecule. Ph.D. Thesis, Technical Institute of Physics and Chemistry,
Beijing, China, 2007.
1
5. Heizn, D.; Yinmian, M.; Giogic, C. Synthesis. 1995, 3, 294-298.
11 / 31

Table 1. Photochromic changes of the solution before and after irradiation
Irradiation
Color
A
P
Before irradiation
After irradiation
Light blue
Deep blue
0.0334
2.2625
——
67.74
12 / 31

Table 2. Absorbance changes in the fading process of SO in ethanol solution
Fading times,
0
15
30
45
60
75
90
s
At
2.2625 1.6308 1.2138 0.7367 0.3161 0.1534 0.0475
44.20 46.35 67.44 86.03 93.22 97.90
M,%
0
13 / 31

Table 3. Hydrolysis degrees of hPMMA determined by titrimetry
VNaOH, mL
0
0
3
5
10
15
Hydrolysis degrees of PMMA(h), %
3.0
5.0
8.9
12.0
14 / 31

Table 4. Absorbance changes in the fading process of SO-g-5%hPMMA in
dichloromethane solution
Fading times, s
0
1.8961
0
60
120
180
240
270
At
1.0746
43.32
0.8619
54.54
0.4207
77.81
0.2545
86.58
0.149
92.14
M,%
15 / 31

Table 5. Absorbance changes in the fading process of SO-g-5%hPMMA in
dichloromethane solution added 3mL of hydrochloric acids
Fading
times, s
At
0
60
120
180
240
300
350
2.1493 1.7747
17.43
1.3393
37.69
1.0746
50.00
0.8619
59.90
0.5295
75.36
0.2545
88.16
M,%
0
16 / 31

-1
Table 6. Thermal fading rates(k/s ) of SO-g-hPMMA, SO-m-hPMMA in
dichloromethane solution
Compounds
SO-g-5%hPMMA
0.0097
SO-m-PMMA
0.02479
Thermal fading
-1
rates(k/s )
17 / 31

-1
Table 7. Thermal fading rates(k/s ) of SO grafting hPMMA marked by different
hydrolysis degrees in dichloromethane solution
Compounds
SO-g-5%hPMMA SO-g-9%hPMMA
0.00877 0.0054
SO-g-12%hPMMA
0.00948
Thermal fading
-1
rates(k/s )
18 / 31

Table 8. Tensile strength and elongation at break of different PMMA films containing
SO functional group
Films
PMMA SO-m- SO-g-5% SO-g-9% SO-g-12% SO-g-15%
PMMA hPMMA hPMMA hPMMA
hPMMA
17.21
Tensile strength, 14.98
MPa
15.17
16.97
17.07
17.67
Elongation at
break, %
14.54
14.99
16.54
15.86
15.33
14.42
Tensile speed: 100mm/min; Temperature: 23.5 °C; Humidity: 29.5%
19 / 31

Scheme 1. Synthetic route for SO
20 / 31

Scheme 2. Synthetic route for SO-g-hPMMA
21 / 31

Figure 1. Photochromic reaction of spiroxazine
22 / 31

Figure 2. Visible absorption spectra of SO under irradiation of 500W mercury lamp
at different times in ethanol solution
23 / 31

Figure 3. Visible absorption spectra of SO in ethanol solution during fading reaction
24 / 31

Figure 4. Visible absorption spectra of SO-g-5%hPMMA under irradiation of 500W
mercury lamp at different times in dichloromethane solution
25 / 31

Figure 5. Visible absorption spectra of SO-g-5%hPMMA in dichloromethane
solution during fading reaction
26 / 31

Figure 6. Open-loop structure of SO-g-hPMMA
27 / 31

Figure 7. Visible absorption spectra of SO-g-5%hPMMA in dichloromethane
solution added 3mL of hydrochloric acids during fading reaction
28 / 31

Figure 8. Hydrogen bonding interactions between hydrochloric acids and ring
opening form of SO-g-hPMMA
29 / 31