Thermal and spectral analysis of copolymers with sulphur groups
Thermal and spectral analysis of copolymers with sulphur groups
Karolina Fila 0 1
Marta Grochowicz 0 1
Beata Podkos´cielna 0 1
0 Department of Polymer Chemistry, Maria Curie-Skłodowska University , Lublin , Poland
1 & Marta Grochowicz
The paper presents the synthesis, structure and polymerization of S-phenyl 2-methylprop-2-enethioate (PSM). This compound was prepared in the reaction of thiophenol with methacryloyl chloride. The obtained PSM was purified on the chromatographic column. Chemical structure of the monomer was confirmed by spectroscopic methods (ATR-FTIR, GC-MS, 1H and 13C NMR). Next bulk polymerization of PSM with styrene (St) or methyl methacrylate (MMA) was performed. In this way, linear copolymers were obtained. The number and mass average molar mass of the obtained copolymers were determined by gel permeation chromatography (GPC). Additionally, crosslinked copolymers of the commercial monomer S,S0thiodi-4,1-phenylene bis(thiomethacrylate) (DMSPS) under the same conditions were synthesized. The influence of thiol monomers on the physico-chemical properties of the obtained copolymers was determined. Thermal properties of the synthesized materials were investigated by means of DSC and TG/DTG.
Synthesis; Thiophenol; Bulk polymerization; Average molar mass; DSC; TG/DTG
Thiols are the sulphur analogues of alcohols, but hydrogen
atom in the thiol group is more acidic than that in hydroxyl
group. These organic compounds commonly occur in
nature. Thiols and sulphides perform important biological
functions, especially in life processes. There are also
known other applications of thiols, e.g., as chain transfer
agents in the synthesis of polymers used for optical devices
In the last few years there has been a growing interest in
the methods of controlled radical polymerization that
allows the synthesis of polymers with a defined molecular
mass and a low dispersion of these mass. The molecular
mass control of polymers is an important issue because
final physical and mechanical properties of the polymer
depend on the length of its chain. In order to control the
length of the polymer chain, so-called chain transfer agents
are used in polymerization process. Thiols are well-defined
chain transfer agents in the free radical polymerization for
such ordinary monomers as styrene or methyl
methacrylate. Thiols play a significant role among the chain transfer
agents because of their efficiency in obtaining polymers of
the desired molecular mass. Two important parameters that
determine such use of thiols are weakness of the S–H bond
and high reactivity of the thiol radicals [
weakness of the S–H bond can be explained by the high
reactivity of these compounds towards chain-carrying
macroradicals, leading to high chain transfer constants,
irrespectively of the used monomer. In turn, high reactivity
of the thiol radicals is characterized by almost ideal chain
transfer behaviour of thiols, with a large decrease in the
polymer molecular mass without a substantial change in
the polymerization rate [
Henriquez et al. [
] studied the chain transfer
properties of thiophenol and several water-soluble aliphatic thiols
for the polymerization of acrylamide and
1-vinyl-2pyrrolidone in the aqueous solution at 25 C. They showed
that the addition of millimolar concentrations of thiols for
the polymerization of acrylamide reduced notably the
molecular mass of the polymer, without change in the
polymerization rate. Measurements at different pH values
indicated that the reactive factor is the protonated –SH
group. Chain transfer constants, determined from the Mayo
plots, are only slightly dependent on the thiol structure.
Aliphatic thiols and thiophenol react at similar rates. The
reaction rates of these sulphur compounds with the
electrophilic 2,2-diphenyl-1-picrylhydrazyl radical showed
higher selectivity and are not related with the chain transfer
constants measured for the acrylamide macroradicals.
These results are explained in terms of different factors that
control the reactivity of thiols with macroradicals [
In this paper, synthesis and copolymerization of the new
methacrylic derivative of thiophenol—S-phenyl
2-methylprop-2-enethioate (PSM)—are discussed. The chemical
structure of PSM was confirmed by the ATR–FTIR, GC–
MS, 1H and 13C NMR spectroscopy. Next bulk
copolymerization of PSM with styrene (St) and methyl
methacrylate (MMA) was performed. For comparison, the
copolymerization of the commercial monomer
S,S0-thiodi4,1-phenylene bis(thiomethacrylate) with St and MMA was
also carried out. Methyl methacrylate and styrene were
used as main comonomers because (especially MMA) they
are widely used in POF (polymer optical fibre technology)
]. Molecular mass control is a crucial feature in the
POFs technology since it affects significantly the quality of
the obtained materials, especially their optical properties.
So far thiols with at least one free –SH group are usually
used as chain transfer agents in the POFs technology
]. The proposed PSM monomer is a methacrylic
derivative of thiophenol with the vinyl group capable of
polymerization with MMA and St. This compound was
added as a comonomer, and its effect on the molecular
mass of the resulting copolymers was determined with the
use of GPC method. Moreover, the effects of different
chemical structure of monomers [two- (PSM) or
fourfunctional (DMSPS), aromatic (St) or aliphatic (MMA)] on
the thermal properties of the resulting copolymers were
studied by means of DSC and TG/DTG methods.
Thiophenol, methylene chloride, methyl methacrylate,
triethylamine and S,S0-thiodi-4,1-phenylene bis(thiomethacrylate)
were obtained from Sigma-Aldrich. Methacryloyl chloride
was from Fluka AG (Buchs, Switzerland).
a,a0-Azoiso-bisbutyronitrile (AIBN) was purchased from Merck (Darmstadt,
Germany). Styrene and magnesium sulphate were obtained
from POCh (Gliwice, Poland). All chemicals were used as
Synthesis of methacrylic thiophenol
In a 500-cm3 round-bottomed flask equipped with a
mechanical stirrer, a thermometer and a dropper,
thiophenol (22 mL) and methylene chloride (225 mL) were placed
with 33.4 mL of triethylamine in an ice bath and stirred for
0.5 h. Next methacryloyl chloride (23 mL) was added
dropwise for 1 h in the temperature range of 0–5 C.
Subsequently, the flask contents were stirred for 3 h at 5 C
and for 1 h at room temperature. After the reaction, the
resulting precipitate was filtered off, and magnesium
sulphate (25 g) was added to the filtrate. The obtained
methacrylic derivative of thiophenol—S-phenyl
2-methylprop-2-enethioate, in the form of colourless liquid, was
extracted with methylene chloride and purified on the
chromatographic column (chloroform/hexane 80:20) [
Figure 1 shows the scheme of the synthesis.
Copolymerization of PSM and DMSPS with styrene (St) and methyl methacrylate (MMA)
The chemical structures of all monomers used in
polymerization are presented in Fig. 2. Bulk polymerization of
methacrylic derivative of thiophenol (PSM) and
S,S0thiodi-4,1-phenylene bis(thiomethacrylate) (DMSPS) with
the commercial monomers styrene and methyl
methacrylate was carried out. Copolymerization reactions were
performed in the glass form, with different mass ratios of
monomers (1:10, 1:20) as shown in Table 1.
a,a0-Azoisobis-butyronitrile was used as an initiator (1%, w/w). The
reactions were carried out in the water bath at 60 C for 2 h
and 90 C for 12 h. Homopolymers of St and MMA were
obtained under the same conditions.
The ATR–FTIR spectra were obtained on a Bruker FTIR
spectrophotometer TENSOR 27.
The 1H and 13C NMR spectra were recorded on a Bruker
Avance 300 MSL instrument (Bruker, Germany) operating
at 300 MHz for 1H and 75 MHz for 13C resonance
frequency. Chemical shifts were referenced to deuterated
chloroform (CDCl3) which served as an internal standard.
Cross-polarization magic angle spinning (CP-MAS 13C
NMR) measurements were completed on the same
spectrometer at resonance frequency of 75.5 MHz. The
number of scans was 2048, and the spin rate was 8000 Hz.
GC–MS was made on a Thermo-Finnigan DSQ
spectrometer (Finnigan, USA) hyphenated with a gas
chromatograph Trace GC-Ultra equipped with a fused-silica
RTX-5 capillary column (20 m 9 0.18 mm I.D., film
thickness 0.20 lm). The conditions were as follows:
injector PTV-split 1:20, program temperature 35–320 C
with the rate 20 C min-1; MS electron ionization at
70 eV, temperature of ion volume 220 C.
Differential scanning calorimetry (DSC) curves were
obtained with the use of a DSC Netzsch 204 calorimeter
(Netzsch, Germany). All DSC measurements were taken in
the aluminium pans with a pierced lid of the sample mass
of * 5–10 mg under nitrogen atmosphere (30 mL min-1).
As the reference, an empty aluminium crucible was used.
Dynamic scans were made at a heating rate of 10 K min-1
in the temperature range 20–500 C. The decomposition
temperatures (Tonset, Toffset), final decomposition
temperature (Td), glass transition temperature (Tg) and enthalpy of
decomposition (DHd) were determined.
The TG/DTG curves were obtained with the use of a
thermal analyser STA 449 F1 Jupiter (Netzsch, Germany).
All measurements were taken in the Al2O3 crucible with
the sample mass * 7 mg under helium atmosphere
(20 mL min-1). Dynamic scans were made at the heating
rate of 10 K min-1 in the temperature range 30–800 C.
The initial decomposition temperature (IDT), loss mass
temperatures (T1), peak maximum decomposition
temperature (Tmax) and final decomposition temperature (Tf) were
The number (Mn), mass (Mw) average molar mass
(g mol-1) and the molar mass dispersity (Mw/Mn) of the
obtained copolymers were determined by the gel
permeation chromatography (GPC) performed on a Viscotek
GPCmax (Viscotek, USA) equipped with the triple detector
array TDA 305. The eluent was tetrahydrofuran (THF), the
flow rate was 1 mL min-1, the operation temperature was
set to be 35 C, and the molar mass was calibrated with the
Results and discussion
The ATR–FTIR analysis for thiophenol and its methacrylic derivative (PSM)
The methacrylic derivative of thiophenol was prepared by
the reaction of thiophenol with methacryloyl chloride. The
ATR–FTIR spectra of thiophenol and its methacrylic
derivative (PSM) are presented in Fig. 3. The spectra show
the absorption bands derived from stretching vibrations of
the aromatic groups CAr–H at the wavelengths of 3067 and
3058 cm-1, respectively. Another absorption bands present
in the spectra of thiophenol and its derivative are the
deformation vibrations of Ar–H at the wavelength of 730
and 690 cm-1.
The spectrum of the thiophenol shows also the
characteristic absorption band derived from the stretching
vibrations of thiol group at the wavelength of 2565 cm-1 which
disappears after the reaction with methacryloyl chloride.
This indicates the correct course of the modification
reaction. In the spectrum of the methacrylic derivative of
thiophenol, C–H stretching vibrations of methyl groups are
observed at 2929 and 2977 cm-1, the stretching vibrations
of the carbonyl group at 1694 cm-1 and the deformation
vibrations of –CH=CH2 group at 950 cm-1.
The NMR analysis for methacrylic derivative of thiophenol (PSM)
The chemical structure of methacrylic derivative of
thiophenol (PSM) was confirmed by 1H and 13C NMR analysis.
The detailed information about signals is presented below.
1H NMR (300 MHz, CDCl3, d, ppm): 2.05 (m, 3H);
5.75 (m, 1H); 6.35 (m, 1H); 7.40 (m, 5H).
13C NMR (75 MHz, CDCl3, d, ppm): 18.02 (–CH3);
127.61 (=CH2); 129.63 (2ArC)- 131.01 (2ArC); 135.02
(=C); 135.70 (ArC); 200.26 (C=O).
Chemical structure of PSM was also confirmed by the GC–
MS analysis. As its spectrum was not available in the
library, identification was achieved analysing molecular
and fragmentary ions. In the spectrum presented in Fig. 4,
molecular ion corresponding to the calculated molecular
weight of S-phenyl 2-methylprop-2-enethioate (m/
z = 178) is visible. Besides, a number of fragmentary ions
are also noticeable, the most important ones are identified,
and their meaning is presented in spectrum.
The analysis of the ATR–FTIR spectra of obtained copolymers
The ATR–FTIR spectra of the homopolymer of styrene
(Sthomo) and copolymer of styrene with the methacrylic
derivative of thiophenol (St-PSM) or
S,S0-thiodi-4,1-phenylene bis(thiomethacrylate) (St-DMSPS) are presented in
Fig. 5. Generally, similar absorption bands are present in
both spectra. However, for the copolymers (St-PSM and
StDMSPS) the appearance of the characteristic vibrations of
the carbonyl group (1699 and 1735 cm-1) was observed.
The presence of carbonyl groups (derived from
methacrylate unit) indicates the incorporation of the thiol monomer
into the structure of the resulting copolymers. This
confirms the planned course of copolymerization processes.
For the complete spectroscopic investigation of
copolymers, an analysis 13C CP-MAS NMR was carried out. The
spectra of styrene copolymers with PSM and DMSPS are
presented in Fig. 7a, b. Spectra have a very similar course
because the main component of studied copolymers is
styrene; only the signal at 234–235 ppm derives from the
carbonyl groups present in PSM and DMSPS comonomers
Thermal properties of copolymers
Thermal properties of the obtained copolymers were
studied by means of DSC analysis. The DSC curves of the
styrene and methyl methacrylate homopolymers and their
copolymers St-PSM, St-DMSPS, MMA–PSM and MMA–
DMSPS are presented in Figs. 8, 9, 10 and 11, respectively.
In addition, the measurement results of the DSC are given
in Tables 5 and 6.
The DSC analysis showed similarity in the thermal
behaviour of all prepared copolymers. They have a
characteristic, well-shaped calorimetric profile revealing the
presence of a single endothermic peak. The obtained data
indicate that the synthesized copolymers are characterized
by high thermal resistance. In the case of the St-PSM and
St-DMSPS copolymers, the endothermic peak at
392–417 C is associated with their total thermal
degradation. For the MMA–PSM and MMA–DMSPS
copolymers, decomposition occurs in the temperature range of
358–389 C. The enthalpy of decomposition (DHd) values
ranges from 597.8 to 884.1 J g-1 depending on the amount
C = O
Fig. 9 DSC curves of St-homo and copolymers of St-DMSPS in ratio
1:10 and 1:20
Fig. 12 TG curves of St-homo and its copolymers St-DMSPS and
StPSM in mass 1:10
Fig. 13 DTG curves of St-homo and its copolymers St-DMSPS and
St-PSM in mass 1:10
of the monomers used during copolymerization. The higher
the degree of crosslinking, the higher the thermal stability
and consequently a lower value of DHd. The enthalpy of
decomposition for copolymers of St and MMA decreases
with increasing mass fraction of the PSM and DMSPS. The
glass transition temperature (Tg) for the tested copolymers
was also determined, and it was found for all polymers.
The highest value of the Tg (121.4 C) possesses MMA–
DMSPS (1:20) copolymer, while the lowest MMA–PSM
(1:20) copolymer (72.9 C). Copolymers of styrene have a
similar Tg values ranging from 87.9 to 99.8 C. With the
increase in the amount of PSM or DMSPS in the structure
of the copolymers, the faster decrease in glass transition
temperature takes place [
Thermal stability and degradation behaviour of the
styrene copolymers were studied by means of
thermogravimetry. The TG/DTG results of thermal decomposition
process are presented in Table 7 and Figs. 12, 13. For the
St-homo and St-DMSPS copolymers, the TG curves have
almost the same course, and the initial decomposition
temperature (IDT, corresponding to the temperature of 2%
of mass loss) is about 311 and 314 C, respectively. In the
case of St-PSM, the initial decomposition temperature is
about 219 C. The final decomposition temperatures (Tf)
for the St-homo and St-PSM copolymer are about 420 C,
whereas for the St-DMSPS copolymer Tf is 620 C.
The DTG curve for the St-homo polymer contains one
separate degradation step. The maximum decomposition
peak is observed in the range 300–410 C with the
maximum of the mass loss (Tmax) at 396 C and is related to its
total degradation according to the chain scission and free
radical diffusion mechanism [
]. In the case of St-PSM
and St-DMSPS, the DTG curves contain two separate
maxima related to the degradation stages. In the DTG
curve of St-PSM, the first decomposition peak between 180
and 300 C with the maximum of mass loss (Tmax1) at
236 C and the mass loss of about 10% is connected with
the decomposition of network fragments derived from PSM
monomer. The second decomposition stage takes place
between 315 and 425 C with the maximum of mass loss
(Tmax2) at 406 C. The DTG curve of St-DMSPS is of
different character which is associated with the structure of
this copolymer. Because the DMSPS monomer possesses
two methacrylate groups, the copolymer obtained with
styrene has a crosslinked network. Thus at 382 C (Tmax2)
the main decomposition of the linear fragments of the
copolymer takes place, whereas at 600 C the degradation
of the residual of crosslinked part of copolymer is
Analysing the obtained data, one can conclude that the
highest thermal resistance was found in the case of the
StPSM copolymer (about 10 C), but the earlier start of the
decomposition of these copolymers is observed. These
materials are stable up to 220 C. Generally, one can
conclude that the copolymers of styrene have a higher
thermal stability than the methyl methacrylate copolymers.
The average molecular mass (Mn, Mw) was determined for
the copolymers of St-PSM and MMA–PSM by the gel
permeation chromatography. The results of GPC analysis
are shown in Table 8. As follows from this table, the
addition of methacrylic derivative of thiophenol (PSM)
affects the molecular mass of the resulting polymers. The
PSM additive reduces the average molecular mass of the
obtained St-PSM and MMA–PSM copolymers. The largest
decrease in the molecular mass is observed for the
copolymer MMA–PSM (1:10), while the smallest is for the
copolymers of St-PSM. The Mw/Mn relationship indicative
the molar mass dispersity for the obtained polymers ranges
from 1.48 to 3.43, and it was at a relatively low level for
the polymers obtained in an alloy.
The reaction of thiophenol with methacryloyl chloride
resulted in a new sulphur monomer—S-phenyl
2-methylprop-2-enethioate (PSM). This compound was obtained in
the form of colourless liquid. A detailed spectroscopic
analysis (ATR/FTIR, GC–MS, 1H and 13C NMR) of the
resulting compound confirmed its chemical structure. The
use of PSM compound as a comonomer in the
copolymerization reaction with methyl methacrylate and styrene
allowed the synthesis of a new group of polymers. DSC
and TG/DTG measurements indicated that the obtained
copolymers possess high thermal resistance; they are
stable up to 220 C. The thermal stability of the studied
copolymers decreased with the increasing amount of PSM.
The results of DSC analysis showed an endothermic effect
in the range of 358–417 C due to the total decomposition
of PSM and DMSPS copolymers with methyl methacrylate
and styrene. The glass transition temperature of styrene
copolymers is about 90 C, whereas for MMA–DMSPS
copolymers Tg is about 115 C and about 85 C for MMA–
PSM copolymers. GPC analysis showed that PSM
comonomer influenced significantly the molecular mass of
StPSM and MMA–PSM copolymers. The average molecular
mass (Mn, Mw) of the obtained copolymers decreased with
the increasing amount of PSM comonomer. Taking into
account the chemical structure, thermal stability and
molecular mass of synthesized PSM copolymers with St
and MMA, and from the other hand the trends in POFs
technology, it can be supposed that presented in this study
PSM monomer can be used as a special additive for
polymers used in optical fibres drawing.
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