CC BY
10T. Agarwal *, K.A. Gupta **, M.G.H. Zaidi *
COMPARATIVE INVESTIGATION OF VINYL POLYMERIZATION UNDER
MICROWAVE IRRADIATION
(*Department of Chemistry, G.B.Pant University of Agriculture & Technology Pantnagar, India, ** Department of Chemistry, Hindu Post Graduate College Moradabad, M.J.P. Rohailkhand University, India)
e-mail: mgh_zaidi@yahoo.com
Microwave (MW) assisted polymerization of acrylonitrile, methyl methacrylate, N-vinyl pyrrolidone and glycidyl methacrylate was investigated and their progress has been compared with reference to MW powers ranging 25-100W. The polymerization afforded increasing monomer conversion (%C) up to 50W resulting in polymers with enhanced rheoviscosity, thermal stability and particles size ranging 4.98-100.12 nm The polymers were characterized through Uv-vis, FT-IR, 1H-NMR spectra, thermal analysis and AFM.
Key words: Microwave irradiation, Vinyl polymerization, Spectra, Microscopy and Thermal analysis
1. INTRODUCTION
Recent trends in the radiation induced processing of materials have provided a variety of rapid methods to develop polymers and related materials through green friendly alternatives at a very low cost .In this context, over past few decades, the application of microwave (MW) as a source for the synthesis of organic compounds and polymeric materials is expected to offer many advantages, including localized heating with substantial reduction of reaction time, reduction of the amount of wastes generated, energy savings, and reduction of CO2 emissions. Although many studies have been conducted on Mw assisted synthesis, there are few examples of its practical use [1-3].In current polymer science, the use of MW assisted polymer synthesis has been widely investigated and a series of reviews were appeared in recent years [1-5]. Most of such reviews highlight the successful applications of MW towards execution of controlled radical polymerizations such as free radical polymerization [6-10], co-polymerization [11], nitrox-ide mediated polymerization [12]. Most of such polymerization reactions are conducted under domestic microwave ovens [6, 13-14].
Literature survey reveals that although MW assisted polymerization of acrylonitrile has been conducted in presence of cobalt complexes as accelerator [13] and formation of polystyrene beads through free radical suspension polymerization reactions [14], no efforts are made towards investigation of MW assisted polymerization of the proposed monomers viz., acrylonitrile (AN), methyl methacrylate (MMA), N-vinyl pyrrolidone (NVP) and glycidyl methacrylate (GMA) in presence of 2, 2'-azobisisobutyronitrile (AIBN) initiator. Herein we have first time documented the comparative account of MW assisted polymerization of the various vinyl functional monomers at MW powers ranging 25-100 W. The findings
reflect MW assisted in-situ degradation of polymers formed beyond 50W [10].The present investigation furnishes a novel MW assisted green chemical approach towards understanding of the free radical polymerization of different varieties of vinyl functional monomers [1-5].
2. EXPERIMENTAL
2.1. Starting Materials. All the monomers AN and MMA (s.d.fine Chemical, India), NVP (Acros Chemicals, USA) and GMA (Merck, Germany) were received and purified through distillation. The purity of the washed monomers has been identified through measurement of their bp, density and ^max by UV-vis spectra. AN: density (g/cc), 0.81., bp (oC), 77.4., Vax (e), 245 (1.813). MMA: density (g/cc), 0.94., bp (oC), 101.5, Vax (e), 227 (1.705). NVP: density (g/cc), 1.04., bp (°C/mm Hg), 93/9.8., V« (e), 233 (1.240).GMA: density (g/cc), 1.08., bp (oC), 190; Vax (e), 230 (2.099).AIBN: mp (oC), 102104, Vax (e), 233:215(1.470). Other chemicals and solvents in AR grade were purchased from Ms Spec-trochem and Himedia chemicals India and were used without further purification.
2.2. MW Assisted Vinyl Polymerization. A series of mixtures of well defined compositions comprising monomer and AIBN were prepared under gentle vortex over 1 min in a borosilicate glass viol (10 mL) under nitrogen. The viol was subjected to MW irradiation at various powers ranging 25 to 100 W for different time intervals time in a domestic oven furnished by LG model MC 8088 NRH worth 2.45 GHz. [6, 13-14]. Due to insolubility in wide range of polar solvents, PAN was purified through repeated washings with methanol. Other polymers were purified through dissolving into chloroform followed by their re-precipitation from methanol. All the isolated polymers were dried at 50±1 oC at 200 mm.
2.3. Characterization. Uv-vis spectra were recorded over Genesis 10 Thermospectronic spectrophotometer. The chemical structure was examined through FT-IR (KBr) spectra recorded through Thermo Nicolet FT-IR Spectrophotometer. 1H-NMR spectra of polymers were recorded over Brucker Av400. The morphology and average roughness of polymers was studied at room temperature over NTEGRA Prima; Atomic Force Microscope under tapping mode. The films of polymers were applied from 1.0 mg/mL solutions in chloroform on glass substrates with surface area 1 cm2. Ultra sharp Si cantilevers having force constant of 48 N/m were used. In order to have results to be comparable; the films were imaged at common XY scales ranging 10 to 2 ^m. Simultaneous TG-DTA-DTG of polymers was executed on Perkin Elmer Pyris Diamond Thermal Analyzer with sample size ranging 11.42-16.90 mg in nitrogen at 10 °C/min.
3. RESULTS AND DISCUSSION
3.1. MW Assisted Polymerization. The
present study deals with comparative investigation on the AIBN initiated polymerization reaction of four different vinyl functional monomers under MW irradiation ranging 25-100W. Effect of MW power on the progress of all such polymerization reactions has been monitored with reference to variations in the monomer conversion (% C) and rheoviscosity (nR., mPa.s) (Table 1). Polymerization reactions of AN and MMA were accomplished within 10 min yielding the respective polymers in solid phase. The optimum time required for polymerization of NVP and GMA was 20 min, respectively. Except GMA, the polymerization
nR, mPa^sx10 1.2
PAN PMMA PVP PGMA
0
25
100
50 75
MW, W
Fig. 1a: Effect of MW power on progress of polymerization
o4 tí
U >
s о U
90 -i
80 -
70 -
60 -
50 -
40 -
30 -
20 -
10 -
PAN PMMA PVP PGMA
0
25
100
50 75
MW, W
Fig. 1b. Effect of MW power on % conversion of monomer
Table 1. Reaction conditions of polymers synthesized under different MW powers
MW A Synthetic Parameters B
S.No. Polymers [M] C rp D C E n F
1 25 PAN 15.20 10 34.74 0.79
2 50 13.65 0.83
3 75 10.41 0.11
4 100 9.93 0.10
5 25 PMMA 9.40 10 76.92 1.09
6 50 73.72 1.13
7 75 61.97 1.02
8 100 60.89 1.01
9 25 PVP 9.40 20 74.04 1.09
10 50 70.19 1.11
11 75 40.38 0.98
12 100 16.35 0.62
13 25 PGMA 7.35 20 75.82 0.52
14 50 63.34 0.41
15 75 11.52 0.28
16 100 10.56 0.13
Note: A=Watt, B= AIBN concentration 0.60X10-3 mol., C= Monomer concentration x10-3mol., D=MW irradiation time (min), E=Monomer conversion (%), F=Rheoviscosity (mPas) x102.
of all the monomers was progressed with regular increase in %C and nR (mPa sx102) up to 50W. In general, with MW power, the polymerization of AN was progressed resulting in PAN with %C ranging 13.659.93 and corresponding nR ranging 0.79-0.10.Under similar conditions, polymerization of MMA afforded PMMA with relatively higher % C and nR. The longer MW irradiation time was required for the polymerization of NVP and GMA over AN and MMA. With MW power, the polymerization of NVP was progressed resulting in PVP with %C ranging 70.19-
16.35 and corresponding nR ranging 1.09-0.62.Under identical MW conditions, the polymerization of GMA was progressed resulting in PGMA with %C ranging 75.82-10.56 and corresponding nR ranging 0.52-0.13 (Fig. 1). These observations clearly indicate that the progress of polymerization reactions of the respective monomers is dependent on the monomer reactivity towards their polymerization under MW irradiation [6]. The decrease in % C and nR above 50W may be attributed to the degradation of polymers [10].
3.2. Spectra. The starting materials display absorbance according to their respective solubility in methanol at 0.01 ppm. AIBN show X max at 215 nm. PVP display enhanced s, thus indicating maximum solubility in methanol. This was followed by PMMA, PGMA and PAN in decreasing order. A blue shift observed for all the polymers over their monomers may be ascribed to the loss of unsaturation. Such blue shift was remarkable for PAN (27 nm) followed by PGMA (9 nm), whereas PVP (6 nm) and PMMA (6 nm) rendered blue shift in the narrow range over the respective monomers. These observations indicate the highest reactivity of the AN, followed by GMA, MMA and NVP towards polymerization reaction under MW irradiation (Fig. 2).
PMMA PAN PGMA PVP
s
d «
о s
.a
о
ж
.a
<
2835.41 (VCH2 sym), 1731.76 (v C=O), 1482.86 (5 CH3 and CH2), 1444.51 (CH3 assym.), 1388.48 (CH3 sym), 1243.61 (v C-O), 1148.57 (v C-C), 1061.97 (v C-O--C sym.). PVP shows wave number (cm-1) at 3446.68 (v O-H), 2924.72 (v C-H assym.), 1657.98 (v C=O), 1462.25-1369.57 (5 C-H ,cy. def. of cyclic CH2), 1289.47-1104.38 (v C-N, 3oAmide).PGMA shows wave number (cm-1) at 3434.78 (O-H), 3069.57 (CH3), 3000.89 (asym.CH2) 2945.19 (^CH), 1729.72 (C=O),1634.78 (5 O-H)1451.46(CH3 and CH2 bend-ing),1391.62 cm-1 (asymmetric bending of CH3) and 1342.67cm-1 (symmetric bending of CH3),1264.62 (C-O-C),1149.15 (C-O-C) and 906.71-846.49 (oxirane).
200 220 240 260 280
Wavelength, nm
Fig. 2. UV -Spectra of Polymers
Fig. 3 shows comparative FT-IR spectra of polymers. PAN has revealed a broad band at 3473.64 (O-H), 2939.76 (asymmetric, CH2), 2865.02 (symmetric, CH2), 2365.06 (VCO2, atmospheric), 2244.22 (C=N), 1681.46 (5 O-H), 1454.57 (5 CH2) and 1227.08-1074.58 (C-N) due to the cyclization of ni-trile groups, it was further justified through TGA data [15]. PMMA shows wave number (cm-1) at 3440.29 (v O-H), 2997.48 (v CH3), 2951.62 (v CH2 assym),
=
oe
si о S ci
S
ci •H
4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm-1
Fig. 3. FT-IR spectra of (a): PAN, (b): PMMA, (c): PVP and (d) : PGMA
Fig. 4 shows comparative :H NMR spectra of polymers. Except PAN all the polymers shows traces of vinyl proton , probably due to incomplete polyme-
2
rization.'H NMR spectrum of PAN was obtained with DMSO solution (2.50ppm) .The characteristic chemical shift (ppm) for PAN was observed clearly at 1.301.40 (-CH3), 2.08 (-CH2-CH) and 3.13(-CH-CN) [16]. :H NMR (CDCl3; 7.30ppm) spectrum of PMMA has shown the signals at 3.60 ppm for methyl ester proton of MMA (-OCH3), -CH3 (1.02ppm) and-CHa (189)
10 987654 321 ppm
Fig. 4. 1H NMR spectra of polymers
PVP has shown chemical shift at 5 1.90 (-CH2), 3.70 (-CH), 2.70 (-CH2 (ring) adjacent to C=O), 1.30 (-CH2 (ring)), 2.70 (-CH2) and 3.19ppm (-CH2 (ring) adjacent to N) corresponded to the methylene in the ring of PVP . PGMA shows the -CH3 110 ppm, -CH2 1.90 ppm, -OCH2 (methyl ester proton of GMA) 4.27 ppm, -CH (oxirane ring) 3.24ppm and -CH2 (oxirane ring) 2.60-2.90ppm [17-18].
3.3. Microscopy. A comparative account of the surface characteristics of polymers synthesized at 50W investigated through AFM is provided in Fig 5 (see Fig. 5). At all the XY scales, polymers rendered heterogeneous morphology consisting of their particles with size ranging 4.98-100.12 nm. With inden-ter height (nm), a characteristic increase in the particle size of all the samples was observed. Such increase in the particle size of the samples has induced a regular increase in their average roughness (Ravg, nm). PAN shows a regular increase in the particle size (nm) ranging 71.36 to 100.12 with indenter height (Z) ranging 140 to 200 nm. With indenter height ranging 100 to 120 nm, a corresponding increase in the particle size of PMMA ranging 57.55 to 66.25nm was observed. This has contributed Ravg with insignificant increase ranging 14.76 to 12.05nm.With XY scale, a general increase in the particle size of PVP was detected ranging 4.98 to 14.13nm. With indenter height, a regular increase in the Ravg of PVP was observed ranging 0.93 to 2.16nm A general increase in the particle size of PGMA was observed ranging 78.39 to 187.04 nm. With indenter height, the Ravg of PGMA was increased regularly ranging 23.68 to 61.11 nm.
3.4. Thermal Characteristics of Polymers.
The thermal characteristics of the polymers synthesized at 50W has been summarized in Table 2. PAN shows two step decompositions at 224 °C (I) and 426 °C (II). PAN shows moisture content 1.6% at 100°C. From 100°C to 224°C, % Wl of 5.3 corresponds to the loss of un-reacted monomer and initiator. A DTG at 126°C with rate of decomposition 0.06 mg/min was observed for PAN. This was supported with a DTA signal at 18.0 ^V with a weak exotherm corresponding to AH= -23.3 mJ/mg at 128°C. The decomposition of PAN corresponding to first step was started at 224°C with %WL 6.9 with formation of a brown colored polymer, insoluble in DMF. This corresponds to the formation of ladder structured polymer due to intramolecular cyclization reaction accompanied by the loss in NH3 and HCN [19]. Such decomposition process of PAN was observed up to 357°C with %WL 37.3.This decomposition of PAN in the temperature range 224-426°C was further supported with DTG (mg/min) [°C] at 0.34 [271], 0.74 [337] and 0.15 [419].
XY(^m) PAN
10
Z (nm) Ravg (nm) d (nm) PMMA
Z (nm) Ravg (nm) d (nm) PVP
Z (nm) Ravg (nm) d (nm) PGMA
Z (nm) Ravg (nm) d (nm)
200 31.33 100.12
100
12.05
57.55
25
2.16
14.13
140 61.11 187.04
140
25.70
90.19
100
12.03
100
10
0.91
4.53
250
29.39
78.39
Fig. 5. AFM picture of polymers
180
19.56
71.76
120
14.76
14.76
10
0.93
4.98
350
23.68
78.38
Table 2. Thermal characteristics of polymers synthesized at 50 W
Thermal Parameters Polymers
PAN PMMA PVP PGMA
TG
% Moisture 1.6 0.5 5.7 0.5
%Wl (oC) at DT* (First step) 6.9(224) 2.2(200) 12.8 (142) 1.9 (200)
%Wl (oC) at DT (Second step) 52.5(426) --- 28.3(375) ---
%Wl (oC) at DT (Third step) 80.5(600) 99.9 (418) 99.9 (559) 99.5 (550)
% Char (oC) 0.0 (698) 0.1(418) 0.0 (800) 0.7 (810)
DTA
Peak Temperature (oC) 349 287 489 454
Signal (^V) 146.7 6.92 71.2 32.65
AH (mJ/mg) -3490 88.6 -1.85 -2.01
DTG
Rate of decomposition (mg/min) 0.74 1.171 1.320 1.152
T ** A max 337 283 438 275
2
5
Note: *DT=Decomposition temperature: % Weight loss (oC), **Tmax= Maximum decomposition temperature (oC). **Tmax= Maximum decomposition temperature (°C).
The first step decomposition TG-DTG is supported by a broad DTA corresponding to AH= -3490 mJ/mg with three consecutive DTA signals (^V) [°C] at 67.2 [270], 146.7 [349] and 69.8 [424]. Second step decomposition of PAN was started at 426°C with %WL 52.5. This was associated with a DTG (mg/min) [°C] 0.30 [591] and an exothermic signal (^V) [°C] 91.1 [583] with AH= -1760 mJ/mg. PAN was volatilized at 709 °C, leaving no char residue (Fig. 6a). PMMA shows single step decomposition at 200 oC (I) with final decomposition at 418°C. Prior to the decomposition at 200°C, a %WL of 2.2 corresponds to the loss of moisture and residual reactants. During the decomposition ranging 200 to 418°C, PMMA shows a strong and a weak DTG peaks (mg/min) [°C] at 1.171 [283] and 0.515 [349], respectively. It was further supported by a DTA signal (^V) [°C] at 6.92 [287] with AH=88.6 mJ/mg. PMMA was completely decomposed off at 418°C leaving char residue 0.1% (Fig. 6b).PVP shows two step decompositions at 375 °C (I) and 463 °C (II). A %Wl at 100°C corresponds to moisture content 5.7 associated with PVP. A steep weight loss evaluated as 22.6 % was recorded for PVP between the temperatures ranging 100 to 375°C, indicating the decomposition of low molecular mass products associated with PVP. Such steep weight loss of PVP was associated with a weak DTA signal (^V) [°C] at 1.2 [132] with AH=58.1 mJ/mg. Decomposition of PVP during temperature range 375 to 461 °C was associated with a rapid weight loss of 56.4%. The corresponding DTG was recorded at 438°C with rate of decomposition (mg/min) 1.320. This was supported with a weak DTA signal (^V) [°C] at 23.9 [412] with AH=152 mJ/mg (endotherm). The weight loss during 461 to 559°C corresponding to second step of decomposition was associated with a consecutive %WL of 15.2 and a DTG (mg/min) [°C] at 0.203 [542]. A DTA signal (^V) [°C] at 71.2 [489] with AH=-1.84 mJ/mg (exotherm). The decomposition of PVP was ended at 559°C leaving char residue 0.1% (Fig. 6c). Decomposition of PGMA was observed in a single step at 200°C (I) with %Wl 1.9. Prior to the first step decomposition, a %WL of 0.5 at 99°C may be assigned to the moisture content of PGMA. Decomposition of PGMA during the temperature ranging 200 to 400°C was associated with multiple DTG (mg/min) [°C] at 0.595 [232], 1.152 [275] and 0.159 [415], respectively. A broad DTA signal (^V) [°C] at 22.64 [338] and 32.65 [454] with associated AH=-2.01 mJ/mg (endotherm) was recorded. Decomposition of PGMA was completed at 550°C leaving char residue 0.5% (Fig. 6d).
50 150 250 350 450 550 650 Temp.Cel.
Fig. 6. TG-DTA-DTG of (a): PAN, (b): PMMA, (c): PVP and (d): PGMA
CONCLUSIONS
Polymerization of four different monomers viz., acrylonitrile, methyl methacrylate, N-vinyl pyr-rolidone and glycidyl methacrylate has been successfully conducted through AIBN initiated free radical polymerization under MW irradiation. All such polymerization reactions were compared at MW power ranging 25-100W.Formation of polymers has been ascertained through Uv-vis, FT-IR, :H-NMR spectra, AFM and simultaneous TG-DTA-DTG. Polymerization reactions conducted at 50 W has afforded respective polymers with high rheoviscosity (nR) and % conversion .At higher MW powers, the decline in the nR and % conversion of polymers may be attributed to
their degradation. The present study reveals a rapid, simple and green method towards execution of free radical vinyl polymerization providing polymers with a high % conversion, thermal stability and size down to 4.98-100.12 nm at MW powers not exceeding 50W.
Acknowledgements. The financial support granted by Department of Biotechnology India is acknowledged.
REFERENCES
1. Kempe K., Becer C.R., Schubert U.S. // Macromole-cules,2011. V. 44. N 15. P. 5825.
2. Sinnwell S., Ritter H. // Australian Journal of Chemistry. 2007. V. 60. N 10. P. 729.
3. Wiesbrock F., Hoogenboom R., Schubert U.S. // Macro-molecular Rapid Communication. 2004. V. 25. P. 1739.
4. Ebner C., Bodner T., Stelzer F., Wiesbrock F. // Macro-molecular Rapid Communication.2011. V. 32. N 3. 254
5. Bardts M., Gonsior N., Ritter H . // Macromolecular Chemistry and Physics. 2008. V. 209. N 1. P. 25.
6. Porto A.F. , Sadicoff B.L., Amorim M.CV., Mattos M.CS. // Polymer Testing.2002. V. 21. N (2). P. 145.
7. Heiner S., Michael L, Norbert N., Michel P., Andreas G. // Macromolecular Rapid Communication. 2006. V. 27. N 2. P. 156
8. Oberti T.G., Schiavoni M.M., Cortizo M.S. // Radiation. Physics and Chemistry. 2008. V. 77. N 5. P. 597.
9. Erdmenger T., Becer C.R., Hoogenboom R., Schubert U.S. // Australian Journal of Chemistry. 2009. V. 62. N 1. P. 58.
10. Singh V., Tiwari A., Kumari P., Sharma A.K.. // Journal of Applied Polymer Science. 2007. V. 104. N 6. P. 3702
11. Heiner S., Andreas G. // Macromolecular Rapid Communication. 2007. V. 28. N 4. P. 504.
12. Li J., Zhu X., Zhu J., Cheng Z. // Radiation Physics and Chemistry. 2006. V. 75. N 2. P. 253.
13. Biswal T., Samal R., Sahoo P.K. // Journal of Applied Polymer Science. 2010. V. 117. N 3. P. 1837.
14. Sen I., Dadush E., Penumadu D. // Journal of Cellular Plastics. 2011. V. 47. N 1. P. 65.
15. Han N., Zhang X.X.,Wang X.C. // Iranian Polymer Journal .2010. V. 19. N 4. P. 243.
16. Kim J.S., Jeon H.J., Lee K.M., Im1 J.N., Youk J.H. // Fibers and Polymers. 2010. V. 11. N 2. P. 153.
17. Brar A.S., Kumar R. // Journal of Applied Polymer Science. 2002. V. 84. P. 50.
18. Hayek A., Xu Y., Okada T., Barlow S., Zhu X., Hyuk J., Seth M., Marder R., Yang S. // Journal of Materials Chemistry. 2008. S1-S5.
19. Tager A. // Physical Chemistry of Polymers. 2nd Edition. M.: Mir. 1978. P. 72.
УДК 661.72.886
С.М. Романова, А.М. Мухетдинова, С.В. Фридланд
МОДИФИЦИРОВАНИЕ АЗОТНОКИСЛЫХ ЭФИРОВ ЦЕЛЛЮЛОЗЫ НЕСИММЕТРИЧНЫМ
ДИМЕТИЛГИДРАЗИНОМ И ЕГО ГИДРАЗИДАМИ
(Казанский государственный технологический университет, Инженерный химико-технологический институт) e-mail: romksenya@yandex.ru, almi_almi@mail.ru, fridland@kstu.ru
Изучено взаимодействие нитрата целлюлозы с несимметричным диметилгидра-зином и гидразидами карбоновых кислот. В результате физико-химических исследований были установлены наиболее вероятные пути протекания реакций.
Ключевые слова: нитрат целлюлозы, несимметричный диметилгидразин, гидразиды карбоно-вых кислот, замещение нитратных групп, омыление нитратных групп
ВВЕДЕНИЕ
В связи с конверсией пороховых производств и уничтожением некондиционных взрывчатых веществ в последние годы большое внимание уделялось утилизации нитратов целлюлозы (НЦ) путем химической модификации. Работа в целом направлена на то, чтобы разработать способ переработки нитратов целлюлозы, срок хранения
которых истек и не соответствует требованиям ГОСТ, в продукты хозяйственного назначения (основу для нитролаков, нитроэмалей, этролов и др.).
Благодаря наличию в нитратах целлюлозы реакционноспособных -0К02 групп существует возможность нуклеофильного замещения их иными фрагментами, что позволяет целенаправленно изменять комплекс эксплуатационных свойств: повышать устойчивость к химическим реагентам,
