New phosphorus- and nitrogen-containing poly(methyl methacrylate)-based copolymer: Enhanced flame retardancy and thermal stability

Article abstract of DOI:10.1007/s10973-019-08440-0

Pure poly(methyl methacrylate) (PMMA) always exhibits high flammability and low thermal stability. To address that, a novel reactive comonomer containing phosphorus and nitrogen elements, 4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl) phenyl diethylphosphoramidate (PDM), was successfully synthesized and then introduced into PMMA matrix through emulsion copolymerization method. The structure of PDM and as-obtained poly(MMA-co-PDM) copolymers was characterized using Fourier transform infrared (FT-IR), ¹H nuclear magnetic resonance spectroscopy (¹H NMR) and ³¹P NMR. From thermal gravimetric analysis and microscale combustion calorimeter, the poly(MMA-co-PDM) copolymers exhibit significantly enhanced flame retardancy and thermal stability, such as the higher degradation temperatures, and decreased peak heat release rate (maximally by 24.1%) and total heat release (maximally by 22.1%). The glass transition temperature (T_g) values of poly(MMA-co-PDM) copolymers obtained by differential scanning calorimetry slightly decrease as the raising flexibility of polymer chain. The char residue analysis by scanning electron microscopy and FT-IR demonstrates that the incorporation of PDM can catalyze the charring of copolymers in condensed phase and form an excellent thermal stability char residue with aromatic structure, further preventing the inner substrate from further combustion. The detailed mechanism was proposed.

Full text of DOI:10.1007/s10973-019-08440-0

Journal of Thermal Analysis and Calorimetry
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New phosphorus- and nitrogen-containing poly(methyl methacrylate)-
based copolymer
Enhanced flame retardancy and thermal stability
Xingxing Shi1 Saihua Jiang1,2
Liang Xiao1
•
•
Received: 24 January 2019 / Accepted: 3 June 2019
´
´
Ó Akademiai Kiado, Budapest, Hungary 2019
Abstract
Pure poly(methyl methacrylate) (PMMA) always exhibits high flammability and low thermal stability. To address that, a
novel reactive comonomer containing phosphorus and nitrogen elements, 4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl) phenyl
diethylphosphoramidate (PDM), was successfully synthesized and then introduced into PMMA matrix through emulsion
copolymerization method. The structure of PDM and as-obtained poly(MMA-co-PDM) copolymers was characterized using
1
Fourier transform infrared (FT-IR), H nuclear magnetic resonance spectroscopy (1H NMR) and 31P NMR. From thermal
gravimetric analysis and microscale combustion calorimeter, the poly(MMA-co-PDM) copolymers exhibit significantly
enhanced flame retardancy and thermal stability, such as the higher degradation temperatures, and decreased peak heat release
rate (maximally by 24.1%) and total heat release (maximally by 22.1%). The glass transition temperature (Tg) values of
poly(MMA-co-PDM) copolymers obtained by differential scanning calorimetry slightly decrease as the raising flexibility of
polymer chain. The char residue analysis by scanning electron microscopy and FT-IR demonstrates that the incorporation of
PDM can catalyze the charring of copolymers in condensed phase and form an excellent thermal stability char residue with
aromatic structure, further preventing the inner substrate from further combustion. The detailed mechanism was proposed.
Keywords Poly(methyl methacrylate) based copolymer Á Flame retardancy Á Thermal property Á Mechanisms
Introduction
applications [1]. Consequently, improving the thermal prop-
erties and flame retardancy of PMMA has attracted increasing
attentions in recent years. Traditionally, halogenated flame
retardants are widely applied in flame retardance of PMMA in
virtue of their gas-phase quenching activity and high flame-
retardant efficiency [2–4]. Nevertheless, the utilization of
some halogenated compounds has been restrained in many
fields considering the environmental pollution. Therefore,
there is an ever-increasing trend toward the use of environ-
ment-friendly and halogen-free alternatives.
Poly(methyl methacrylate) (PMMA) has been widely used in
building construction, plastic optical fibers and optical lenses
owning to its excellent performances including good flexi-
bility, high strength, weather resistance and dimension sta-
bility. However, the poor thermal stability and high
flammability of PMMA limit its further use in many desirable
Xingxing Shi and Saihua Jiang have contributed equally to
this work.
Phosphorus-containing flame retardants, as promising
‘‘green’’ flame retardants for polymeric materials, have gained
growing attentions thanks to their nontoxicity [5, 6]. In gen-
eral, the physical incorporation of phosphorus based flame
retardants into polymers often leads to deteriorated mechan-
ical property and leaching-out phenomenon owning to the
poor compatibility [7, 8]. An alternative technique is to use
some reactive flame retardants, and several works have been
investigated to enhance the flame retardancy of PMMA with
& Saihua Jiang
meshjiang@scut.edu.cn
1
School of Mechanical and Automotive Engineering, South
China University of Technology, Wushan Road 381,
Guangzhou 510641, People’s Republic of China
2
Department of Materials Science and Engineering, University
of Pennsylvania, 3231 Walnut Street, Philadelphia,
PA 19104, USA
123

X. Shi et al.
chemical modification of the preformed homopolymers or
simple copolymerization of monomers [9]. Tian et al. [10]
synthesized a novel phosphorus-containing monomer with a-
hydroxy phosphonate PHMA and MMA via fragmentation
chain transfer polymerization, and the resultant copolymer
exhibited remarkably enhanced thermal stability and flame
retardancy. Du et al. [11] introduced a phosphorus-containing
flame-retardant DEAMP into PMMA shell to fabricate a
nanoencapsulated phase change materials (NanoPCMs), and
the incorporation of 20% DEAMP rendered the NanoPCMs
with a 39.7% decrease in peak heat release rate (PHRR) and a
18.4% decrease in total heat release (THR). Jiang et al. [12]
investigated the flame-retardant effect of a novel PMMA-
based copolymer (PMMA/DOPO-AA), and the as-fabricated
copolymer demonstrated an increased limited oxygen index
value by 4.1 and a decreased PHRR by 34.7%. In general, the
relatively low content is required for the material to achieve
sufficient flame retardancy and a good distribution is formed
due to the chemical bond between the matrix and flame
retardants, resulting in an increased durability of flame
retardance in polymer [13, 14]. However, the flame-retardant
efficiency of most single phosphorus-containing reactive
flame retardants is relatively low. According to the previous
literature, the synergic nitrogen-phosphorous flame retardant
can effectively prevent materials from thermal damage by
degrading into nonvolatile gas and forming carbonization
layers [15–17]. Nitrogen- and phosphorous-containing com-
pounds have been received more than ever attention in both
academic and industry fields.
Xuanming Chemical Industry Co., Ltd. (Changzhou, China).
Maleic anhydride (MAH), p-aminophenol and N,
N-dimethylformamide (DMF) were provided by Tianjin
Fuchen Chemical Reagent Factory (Tianjin, China). Phos-
phorus pentoxide, diethylamine (DEA), triethylamine (TEA),
tetrahydrofuran (THF), isopropyl alcohol and deionized water
were all reagent grades and purchased from Guangzhou
Qianhui Chemical Glass Instrument Co., Ltd. (Guangzhou,
China).
Synthesis of N-(4-hydroxyphenyl) maleimide
(HPM)
MAH (11 g) and DMF (50 mL) were firstly added into a
250 mL three-necked glass flask equipped with
a
mechanical stirrer and a nitrogen inlet. The mixture was
stirred under nitrogen atmosphere until MAH was dis-
solved completely in DMF. Next, p-aminophenol (10 g)
was added dropwise to the above solution and maintained
stirring at room temperature for 2 h. And the mixture of
phosphorus pentoxide (5.5 g) and sulfuric acid (2.5 g)
dissolved in DMF (50 mL) were then fed dropwise into the
solution, and the reaction mixture was heated to 80 °C and
kept at refluxing temperature for another 6 h. Then, the
product was cooled and poured into 500 mL ice water and
a yellow precipitate was obtained. The precipitate was
filtered and washed several times with deionized water.
Finally, the precipitate was recrystallized in isopropanol
alcohol and dried at 50 °C by vacuum rotary evaporation.
The synthesis route of HPM is illustrated in Scheme 1a.
Inspired by the aforementioned concepts, a novel
comonomer containing phosphorus and nitrogen elements
was synthesized and copolymerized with methyl
methacrylate (MMA) to prepare poly(MMA-co-PDM)
copolymers. The structure of the comonomer and copoly-
Synthesis of 4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-
1-yl)phenyl phenyl diethylphosphoramidate
(PDM)
1
mers was confirmed by H NMR, 31P NMR and FT-IR
spectra. The thermal properties and thermal degradation
behaviors of the copolymers were investigated by differ-
ential scanning calorimetry (DSC) and thermogravimetric
analysis (TG). The flammability of poly(MMA-co-PDM)
copolymers was evaluated by microscale combustion
calorimetry (MCC). With the help of SEM and FT-IR, the
detailed mechanisms for flame retardancy enhancement
were proposed.
PDM was designed based on Scheme 1b. PDCP (21.1 g,
0.1 mol) and THF (80 mL) were firstly fed into a 250-mL
three-neck flask loaded with a reflux condenser and a
mechanical stirrer in the ice bath. Then, TEA (21.6 g,
0.21 mol) was added to the system after 30 min and HPM
(19 g, 0.1 mol) dissolved in THF (20 mL) was added
dropwise into the mixture and kept stirring for another 4 h
at 0 °C. Next, the mixture was heated to room temperature
and continually stirred for another 10 h. Finally, the pre-
cipitated triethylamine salt was removed by filtration, and
the solution was then rotary evaporated to remove the
solvent and unreacted reactants under reduced pressure to
obtain a yellow viscous liquid.
Experimental
Materials
Methyl methacrylate (MMA), sodium dodecyl benzene sul-
fonate (SDBS) and potassium persulfate were provided by
Tianjin Damao Chemical Reagent Factory (Tianjin, China).
Phenyl dichlorophosphate (PDCP) was supplied by Changzhou
Preparation of poly(MMA-co-PDM) copolymers
The poly(MMA-co-PDM) copolymers were prepared by
emulsion polymerization, and the schematic process of the
123

New phosphorus- and nitrogen-containing poly(methyl methacrylate)-based copolymer
NH2
O
(a)
OH
O
O
O
DMF
HO
O
H2N
Maleic anhydride
P-aminophenol
HO
OH
O
H+
N
80 °C
O
N-(4-hydroxyphenyl) maleimide
(b)
CI
CI
(H3CH2C)3N
O
N(CH2CH3)3
O
P
P
THF
0 °C
2N(CH2CH3)3
Triethylamine
O
CI
O
CI
Phenyl dichlorophosphate
OH
O
O
CI
CI
CI
P
(H3CH2C)3N
O
N(CH2CH3)3
N(CH2CH3)3
CI
THF
0 °C
P
O
NH(CH2CH3)3
O
N
O
O
O
N
N-(4-hydroxyphenyl) maleimide
O
O
O
O
O
P
CI
N(CH2CH3)3
P
N
O
O
CI
THF
0 °C
NH(CH2CH3)3
N
H
O
Diethylamine
O
N
N
O
O
PDM
Scheme 1 Synthesis route and structure of a HPM and b PDM
123

X. Shi et al.
O
H2
C
H
C
H
C
C
O
y
x
O
N
O
O
N
O
O
K2S2O8/SDBS
70 °C/10h
O
O
+
O
P
O
N
O
P
O
O
N
MMA
PDM
poly(MMA-co-PDM)
Scheme 2 The schematic synthesis route of poly(MMA-co-PDM) copolymers
reaction is presented in Scheme 2. Firstly, 30 mL MMA
(27.4 g) and 240 mL distilled water were poured into a
500-mL three-necked flask under nitrogen atmosphere at
room temperature and kept stirring for 30 min. Then, 1.37 g
PDM (5 mass% compare to MMA) was added into the
mixture and stirred for 1 h until it was completely dissolved.
Afterward, 10 mL SDBS solution (0.015 mol L-1) was
added into the mixture and stirred for 1 h to obtain a
homogeneous emulsion. Then, 60 mL potassium persulfate
(0.078 g) solution was fed dropwise to the above-mentioned
homogeneous emulsion; the reaction temperature was
heated to 70 °C and reflux for 10 h. The emulsion was cooled
to room temperature until the polymerization was com-
pleted. At last, the emulsion was placed in a beaker and
frozen for 12 h at - 10 °C, the product was obtained by
centrifugation with distilled water several times to remove
the unreacted emulsifier and catalysts and dried at 40 °C.
Other copolymers with various amounts of PDM were
obtained by the same procedure. The poly(MMA-co-PDM)
copolymer with 0 mass%, 5 mass%, 10 mass%, 15 mass%
PDM (the mass ratio of PDM to MMA) is abbreviated to MP,
MP5, MP10, MP15, respectively.
temperature to 700 °C at a heating rate of 20 °C min-1
under N2 atmosphere.
DSC was carried out on a DSC 204F1 Phoenix (Netzsch,
Germany) under nitrogen flow from 30 to 200 °C at a
heating and cooling rate of 10 °C min-1 to investigate the
thermal properties of all the samples.
MCC tests were carried out on a Govmak MCC-1
microscale combustion calorimeter. About 6–8 mg of
powdery sample was heated from 25 to 650 °C at a heating
rate of 1 °C s-1 under nitrogen. Then, the pyrolysis prod-
ucts were mixed with oxygen (20 mL min-1) prior to
entering a 900 °C combustion furnace, and the combustion
heat of the pyrolysis products was measured by oxygen
consumption principle.
SEM images were obtained with a scanning electron
microscope FEI Quanta FEG 250 at an accelerating voltage
of 10.0 kV.
Results and discussion
Synthesis and structure characterization
Measurements and characterization
The chemical structure of HPM and PDM was character-
1
ized by H NMR, 31P NMR and FT-IR. Figure 1a shows
FT-IR spectrum was recorded in transmittance mode using
VERTEX 33 (Bruker, Germany) in a spectrometer in a
range of 4000–400 cm-1 with a range resolution of
the FT-IR spectrum of HPM and PDM. The most signifi-
cant absorptions of HPM can be observed at 3484 cm-1
and 1701 cm-1 corresponding to –OH and C=O vibration,
respectively [18–20]. The absorption peaks at 1597 cm-1
and 1520 cm-1 are attributed to the aromatic vibration of
benzene, and the peak at 831 cm-1 corresponds to di-
substitution vibration of benzene [21, 22]. And, the
absorption at 1415 cm-1 and 690 cm-1 is assigned to C–
N–C stretching vibration and C=C vibration of maleimide
ring, respectively [23, 24]. These above results reveal that
4 cm-1
.
1H NMR and 31P NMR spectra were registered with a
Bruker AV400 NMR spectrometer (400 MHz) operating in
the Fourier transform mode using deuterated chloroform
(CDCl3) as solvent for PDM.
TG was conducted on a TGA STA449 F3 IR thermal
gravimetric analyzer (Netzsch, Germany) from room
123

New phosphorus- and nitrogen-containing poly(methyl methacrylate)-based copolymer
(a)
(b)
a
c
b
a
N
P
O
O
HPM
c
O
O
N
–OH
O
C–N–C
C = O
–C6H4
Ar
PDM
C–H
CDCl3
b
TMS
P–O
P = O
1500
8
7
6
5
4
ppm
3
2
1
0
4000
3500
3000
2500
2000
1000
500
Wavenumber/cm–1
(d)
(c)
MP15
MP
–C = C–
P–O
–C6H4–
20
10
0
– 10
– 20
– 30
4000
3500
3000
2500
2000
1500
1000
500
ppm
Wavenumber/cm–1
1
Fig. 1 a FT-IR spectra of HPM and PDM, b H NMR spectra of PDM, c 31P NMR spectra of PDM and d FT-IR spectra of MP and MP15
the precursor HPM is fabricated successfully as Sche-
me 1a. As shown in Fig. 1a, the emerged absorption of
PDM monomer at 2975 cm-1 is assigned to C–H anti-
symmetric stretching of –CH3, and the new bands at
1269 cm-1 and 1039 cm-1 correspond to P=O vibration
and P-O stretching vibration, respectively [15]. Besides,
the absorption of -OH is significantly reduced for the rea-
son of the chemical reaction between HPM and PDCP.
- 18.17 ppm is caused by some impurity. These results
further confirm that PDM has been successfully
synthesized.
The poly(MMA-co-PDM) copolymers were prepared by
emulsion polymerization, and the FT-IR spectra of MP and
MP15 copolymers are illustrated in Fig. 1d. The absorption
bands of pure MP around 2997 cm-1, 2952 cm-1 (asym-
metric) and 2841 cm-1 (symmetric) are assigned to C–H
stretching vibrations. The peaks appeared at 1485 cm-1
and 1438 cm-1 correspond to the bending vibration bands
of the methyl (–CH3) group, while the peaks around
1387 cm-1 are attributed to the deformation mode of the
methylene (–CH2–) group. In addition, the stretching
vibrations and bending vibrations of the carbonyl (C=O)
group appear at 1728 cm-1 and 753 cm-1, respectively
[25, 26]. It can be seen that some new characteristic peaks
arise after the reaction between MMA and PDM. For PM15
copolymers, the aromatic vibrations of benzene appear at
1
Figure 1b, c presents the H and 31P NMR spectra of
1
PDM, respectively. The H NMR spectrum of PDM dis-
plays some characteristic peaks: the peak at 1.07 ppm
corresponds to the protons of –CH3; the peak at 3.24 ppm
corresponds to the protons of –CH2–; the peaks at
7.15–7.40 ppm are attributed to the protons of aromatic
ring; and the strong peak at 6.83 ppm is attributed to the –
CH=CH– protons of maleimide ring. The peak at 7.26 ppm
is attributed to CDCl3. The 31P NMR spectra of PDM show
a strong single peak at 0.58 ppm, and the weak peak at
123

X. Shi et al.
1592 cm-1 and 1512 cm-1. Besides, the new bands at
1039 cm-1 correspond to P–O stretching vibration and the
emerged sharp peaks at 690 cm-1 is assigned to the C=C
vibration of maleimide ring. These results indicate the
successful copolymerization between MMA and PDM.
while the poly(MMA-co-PDM) copolymers begin to
degrade at a higher temperature compared to pure MP,
which is mainly caused by the presence of maleimide ring
structure in PDM molecular. In detail, the T0.1 and T0.5
values of MP15 sample increase gradually from 316.6 to
370.6 °C and from 371.5 to 401.8 °C, respectively, as
PDM content rises to 15 mass%. It can be clearly found
that the introduction of PDM can enhance the decompo-
sition temperature of pure MP. Furthermore, pure MP has
no carbon residue at 500 °C, while the corresponding char
residue of copolymers at 500 °C rises from 0.7 mass% for
MP5 to 2.6 mass% for MP15. Even if it goes up to 600 °C,
there is still 2.4 mass% char left in the MP15 sample. The
char yields of poly(MMA-co-PDM) samples are increased
slightly with the increasing PDM content. The char formed
in the condensed phase can inhibit the transfer of oxygen,
heat and flammable gaseous products [27, 28]. As a result,
the copolymers containing PDM can notably enhance the
thermal stability and char residue.
Thermal properties analysis
The thermal properties of the poly(MMA-co-PDM)
copolymers were analyzed by DSC, and the second heating
segments curves are presented in Fig. 2. The glass transi-
tion temperature (Tg), one of important thermal parameters,
can be used to characterize polymers and other amorphous
or semicrystalline materials, and the Tg data of the samples
are represented in Table 1. In general, the Tg values of the
poly(MMA-co-PDM) copolymers are shifted to a lower
temperature with the loading of PDM, indicating that the
incorporation of PDM can plasticize the neat MP. In detail,
the Tg values of MP5, MP10 and MP15 copolymers
decrease by 1.4 °C, 9.6 °C and 5.9 °C compared with MP.
The main reason is that the increased free volume in the
molecules caused by the relatively higher molecular mass
of PMD leads to the raising flexibility of polymer chain,
resulting in the decreased Tg values of poly(MMA-co-
PDM) copolymers.
Flame retardancy
To evaluate flammability properties of the copolymers, all
samples were characterized by microscale combustion
calorimeter (MCC). Figure 4 elaborates the HRR curves of
poly(MMA-co-PDM) copolymers versus temperatures, and
the relevant PHRR and THR values are listed in Table 1.
As illustrated in Fig. 4, both PHRR and THR values of the
copolymers are shifted to lower values with the addition of
PDM. For example, the THR and PHRR of pure MP are
28.0 kJ g-1 and 379.0 W g-1, respectively, while the
incorporation of 15.0 mass% PDM leads to a 22.1%
maximum decrease in THR (21.8 kJ g-1) and a 24.1%
maximum decrease in PHRR (287.5 W g-1). In addition,
the poly(MMA-co-PDM) copolymers reach the peak of the
heat release rate at a higher temperature compared with
neat MP. These results confirm that the flame retardancy of
MP is enhanced remarkably with the raised PDM feed. The
improvement of flame retardancy in MCC test is closely
related to the enhanced thermal decomposition temperature
and the increased char yield in TG test.
In order to study the thermal stability of poly(MMA-co-
PDM) copolymers, TG test of all samples was employed.
The TG curves of all samples under N2 atmosphere are
illustrated in Fig. 3, and the corresponding data are sum-
marized in Table 1. T0.1 corresponding to the temperature
at 10% mass loss is defined as the onset degradation tem-
peratures, while T0.5 corresponding to the temperature at
50% mass loss is used as the measure of half degradation
temperatures. And the solid char yields at 500 °C and
600 °C are obtained from TG curves. The mass loss pro-
cess of pure MP mainly occurs in the range of 160–430 °C,
Flame-retardant mechanism analysis
To explore the specific mechanism of char formation on the
enhanced flame retardancy of poly(MMA-co-PDM)
copolymers, the char residue of all samples was obtained
by heating all samples with the same mass in a muffle
furnace at 500 °C for 15 min. Figure 5a elaborates the
optical photographs of the char residue for poly(MMA-co-
PDM) copolymers, and the char structure was studied by
SEM at different magnification. As shown in Fig. 5a, pure
MP has been completely decomposed at 500 °C and almost
MP
MP5
MP10
MP15
40
60
80
100
120
140
160
180
200
Temperature/°C
Fig. 2 DSC curves of poly(MMA-co-PDM) copolymers
123

New phosphorus- and nitrogen-containing poly(methyl methacrylate)-based copolymer
Table 1 Composition, flame retardancy and thermal properties of MMA/PDM copolymers
Samples
PDM content/
mass%
Tg/°C
T0.1/°C
T0.5/°C
Char at
500 °C/mass%
Char at
600°C/mass%
PHRR/W g-1
THR/KJ g-1
MP
0
124.7
123.3
115.1
118.8
316.6
366.6
370.5
370.6
371.5
393.1
401.2
401.8
0
0
379.0
349.1
316.7
287.4
28.0
23.8
21.0
21.8
MP5
MP10
MP15
5.0
0.7
2.0
2.6
0.7
1.7
2.4
10.0
15.0
(9 5000). The dense char layer can hinder the release of
flammable gases and inhibit the heat and mass transfer in
the burning area, preventing the internal substrate from
further combustion. Furthermore, the presence of a bubble-
like structure especially in Fig. 5b, d can intuitively
demonstrate that the gas product volatilized during the
pyrolysis process is inhibited by the formed char residue.
These results illustrate that the catalytic charring effect of
PDM is favorable for the improvement of flame retardancy
in MP matrix.
100
80
MP
MP5
MP10
MP15
60
10
8
6
4
2
0
40
20
0
In order to further evaluate the thermal degradation
process of the samples, FT-IR spectra of the char residue
obtained at different temperatures for MP and MP15
copolymers are explained in Fig. 6. FT-IR spectra of pure
MP reveals absorption bands t (cm-1): 2997 cm-1 and
2952 cm-1 (C–H asymmetric stretching); 2841 cm-1 (C–
H symmetric stretching); 1485 cm-1 and 1438 cm-1
(–CH3 bending vibration); 1728 cm-1 and 753 cm-1
(C=O); and 1387 cm-1 (–CH2–) [29, 30]. The relative
intensity of these characteristic peaks of MP decreases
sharply as the increased temperature, suggesting that the
main decomposition of MP occurs at this stage. However,
the main peaks can still be detected at 380 °C for neat MP.
The FT-IR spectrum of MP15 (Fig. 6b) is similar to that
of MP. Some new characteristic peaks of PDM emerge:
450
500
550
600
650
700
100
200
300
400
500
600
700
Temperature/°C
Fig. 3 TG curves of poly(MMA-co-PDM) copolymers under N2
atmosphere
no residue is left, while the char yields of poly(MMA-co-
PDM) copolymers are obviously increased as the PDM
content rises, consistent with the previous TG data. And it
can be clearly observed that a compact and integrate char is
formed for MP5, MP10 and MP15 samples. With the
increased PDM loading, the char structure becomes much
rough and dense and a relatively uniform char is observed
for MP15 copolymers by SEM at high magnification
(a)
(b)
500
30
MP
MP
MP5
MP5
400
300
200
100
0
25
MP10
MP15
MP10
MP15
20
15
10
5
0
100
200
300
400
500
600
100
200
300
400
500
600
Temperature/°C
Temperature/°C
Fig. 4 Heat release rate of poly(MMA-co-PDM) copolymers
123

X. Shi et al.
1592 cm-1 and 1512 cm-1 (aromatic vibrations);
1039 cm-1 (P–O stretching) and 690 cm-1 (C=C vibration
of maleimide ring). However, the degradation patterns of
MP15 are a little different from that of MP. The relative
intensity of MP15 is decreased sharply as the temperature
rises to 190 °C, and the basic peaks are all maintained.
However, the peak values of MP15 at above 310 °C are
much weaker compared with MP because of the initial
thermal degradation of PDM units. That is consistent with
the TG results: the mass loss of the copolymer is shifted to
a higher temperature. In addition, the intensity of the peak
has a little increase at 380 °C, especially the maximum
intensity of P-O stretching vibration at 1039 cm-1, owing
to the formation of polyphosphate during the degradation
of PDM. When the temperature reaches 430 °C, almost all
characteristic peaks disappear, indicating that MP15
copolymers have been completely decomposed. And there
is almost one strong peak around 1630 cm-1 left above
430 °C, indicating that the aromatic structure is stably
existed in the char residue. The excellent thermal stability
of the formed char contributes to the flame-retardant
enhancement for MP15 copolymers.
Conclusions
Fig. 5 a Optical photographs of the char residue for poly(MMA-co-
PDM) copolymers. b–d SEM images of char residues for MP5, MP10
and MP15 at low magnification (9 100), respectively; e–g SEM
images of char residues for MP5, MP10 and MP15 at high
magnification (9 5000), respectively
In this work, a novel reactive flame retardant containing
phosphorus and nitrogen elements was successfully
synthesized and incorporated into PMMA matrix through
emulsion polymerization. The as-fabricated poly(MMA-
(a)
(b)
σC = C
600 °C
νC–H
480 °C
430 °C
νC–O
νC = O
380 °C
350 °C
310 °C
νP–O
380 °C
350 °C
310 °C
190 °C
190 °C
RT
1039
1640
RT
2952
2997
1194 1148
1728
4000 3500 3000 2500 2000 1500 1000
Wavenumber/cm–1
500
4000 3500 3000 2500 2000 1500 1000
Wavenumber/cm–1
500
Fig. 6 FT-IR spectra of a MP and b MP15 copolymers obtained at different temperatures
123

New phosphorus- and nitrogen-containing poly(methyl methacrylate)-based copolymer
´
9. Gerard C, Fontaine G, Bourbigot S. New trends in reaction and
co-PDM) copolymers exhibit significantly enhanced
flame retardancy and thermal stability, such as the higher
degradation temperature, decreased PHRR by 24.1% and
THR by 22.1%. The compact and dense char layer
formed by the catalytic charring effect of PDM in con-
densed phase can inhibit the diffusion of flammable gas
products into the flame zone and prevent the inner of
copolymers from further combustion. In addition, the
aromatic structure is stably existed in the char residue
and the excellent thermal stability of the formed char
contributes to the flame-retardant enhancement for MP15
copolymers. This work not only endows a promising
reactive monomer for PMMA with excellent combined
properties of thermal stability and flame retardancy, but
also stimulates more efforts for creating effective flame
retardants for polymers.
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