Chlorotrimethylsilane Through Hydrolysis–Condensation Reaction
Chung-Feng Jeffrey Kuo,
1Jiong-Bo Chen,
1Chung-Yang Shih,
2Chao-Yang Huang
3,41National Taiwan University of Science and Technology, Department of Materials Science & Engineering, Taipei 106, Taiwan 2Department of Materials Engineering, Kun Shan University, Tainan 710, Taiwan
3Green Energy & Environment Research Laboratories, Industrial Technology Research Institute, Hsinchu 310, Taiwan 4Department of Mechanical Engineering, National Chiao Tung University, Hsinchu 310, Taiwan
Correspondence to: C. -F. J. Kuo (E - mail: [email protected])
ABSTRACT:Silicone pressure-sensitive adhesives compositions contain a polydimethylsiloxane and a silicone resin, which can enhance the instant bonding ability and bonding strength of the adhesive. In this study, silicone resin was designed to have a low molecular weight and a highly nonpolar chemical structure. The silicone resin was applied to silicone pressure-sensitive adhesives. The molecular structure of silicone resin was characterized by FT-IR, GPC, 1H-NMR, and 29Si-NMR spectroscopic techniques. Properties such as thermal stability, solubility, hydrophobic, and transparent properties were researched and compared. When the chlorotrimethylsilane increased, it appeared that the amount of silanol groups, molecular weight and thermal stability decreased, while the hydrophobic and transparent properties increased. The silicone resin was completely soluble in toluene and xylene. It was also applied to silicone pressure-sensitive adhesives, resulting in good peel adhesion.VC 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40317.
KEYWORDS:composites; copolymers; functionalization of polymers; adhesives Received 13 July 2013; accepted 13 December 2013
DOI: 10.1002/app.40317
INTRODUCTION
Pressure-sensitive adhesives are inherently and permanently soft, sticky materials that exhibit instant adhesion or tack with minimal pressure to surfaces to which they are applied. They generally have a high cohesive strength and can often be removed from substrates without leaving any residue. The wide range of applications include tapes, labels, decals, medical products, and others.1–3 Sili-cone pressure-sensitive adhesives have traditionally been made by compounding a resinous silicone resin of M unit (monofunctional silane) and Q unit (tetrafunctional silane) with a high molecular weight polydimethylsiloxane gum at a selected resin-to-gum ratio.4 Silicone resin has a low molecular weight.5–7Basic principles for the hydrolysis and condensation of alkoxysilanes have been known.8,9In the past, silicone resin was synthesized from sodium silicate, hexamethyldisiloxane, and alcohol, while using large amounts of acid in the process. The waste liquid was difficult to be recovered, causing environmental pollution.5In the early process for the preparation of silicone resin, sodium silicate, and HMDS were used as starting materials.10Sodium silicate was acidified to silica sol, which was capped by the M units to produce silicone res-ins. Although the starting materials were inexpensive, structure control of the resin product was difficult. Gels were easily pro-duced. In addition, it was also difficult to control the M/Q molar
ratio of silicone resin synthesized by sodium silicate with a broad molecular weight distribution.6Therefore, the molar ratio of the M/Q was of the utmost importance. In this study, we synthesized silicone resin of a low molecular weight by the tetra-ethoxysilane and chlorotrimethylsilane reaction. The tetra-ethoxysilane was the source of the Q unit and the chlorotrimethylsilane was the source of the M unit. The tetra-ethoxysilane was less reactive than sodium silicate, therefore, when tetra-ethoxysilane was used as the starting material. The M/Q molar ratio of silicone resin could be controlled easily and the chlorotrimethylsilane contained a chlorine group, which produced hydrochloric acid after hydrolysis, for use as a cat-alyst.6The aim of this study was to investigate the effect of M unit content on the chemical structure, thermal stability, hydrophobic, and light transmittance property of silicone resin. Finally, the sili-cone resin was applied as a tackifier resin to silisili-cone pressure-sensitive adhesives. A discussion was made on the effect of silicone resin molecular weight on the peel strength and rolling ball tack property of silicone pressure-sensitive adhesives.
EXPERIMENTAL
Materials
Tetra-ethoxysilane (TEOS) was purchased from Seedchem Company Propriety Limited, Australia. Chlorotrimethylsilane (TMCS),
(3-Aminopropyl) triethoxysilane (APTES), and Tetrabutyl titanate (TBT) were purchased from Acros organics, USA. Toluene was industrial grade and was purchased from Echo Chemical Corpora-tion Limited, Taiwan. Polydimethylsiloxane (PDMS) were purchased from Chi Giz Technology & Consultant Corporation Limited, Tai-wan. Both copper and polyvinyl fluoride (PVF) film were obtained from Forest Lai Enterprise Corporation Limited, Taiwan.
Hydrolytic Condensation Catalyzed by Acid
In the synthesis, hydrolytic condensation of a mixture of TEOS and TMCS was inhomogeneous at the beginning. The Synthesis reaction equation of silicone resins was shown in Figure 1. TEOS was the source of the tetrafunctional silane and TMCS was the source of the monofunctional silane. The trimethylsilanol and hydrochloric acid were produced by hydrolysis of TMCS. During the hydrolysis of TMCS, the trimethylsilanol not only reacted and condensed with the siloxane prepolymer, but also self-condensed to form hexame-thyldisiloxane (HMDS). The trimethylsilanol and TMCS was derived in situ from the reaction of hydrochloric acid with HMDS.11 The TMCS could continuously produce trimethylsilanol in the cycle, as seen in Figure 1(a). Next, TEOS was dripped into the sys-tem after a few minutes, and the syssys-tem turned transparent because ethanol was formed in reaction.12 The siloxane chain formation after hydrolysis of TEOS was as shown in Figure 1(b). The silicone resin with a highly cross-linking density structure was formed with trimethylsilanol condensation end-capping as shown in Figure 1(c). Synthesis of Silicone Resin
Typical process for preparation of silicone resins was as follows. An appropriate amount of deionized water was added to a
three-necked flask and the temperature was held constant at 30C. A mixture of TMCS and toluene was quickly added into the flask with vigorous agitation, and was then heated to 70C.
Appropriate amounts of TEOS were dripped (90 min) into the flask, and the temperature was raised to 70C and held for 2 hours. After cooling to room temperature, the mixtures were washed repeatedly with deionized water to neutral pH. After fil-tration and removing toluene and water by evaporation, the sili-cone resins were obtained. Detailed experimental conditions were listed in Table I.
Preparation of Silicone Pressure-Sensitive Adhesives
In a single-neck flask equipped with a stirrer, silicone resin (42 wt %), PDMS (28 wt %), APTES (1.5 wt %), TBT (0.5 wt %), and toluene (28 wt %) were proportionally added. The mixture was stirred for 20 min, and the reaction stopped. Finally, sili-cone pressure-sensitive adhesives solution was coated to copper
Figure 1.Synthesis reaction equation of silicone resins.
Table I.Components and their Quantities in the Synthesis of Silicone Resin Code M/Q molar ratioa TEOS (g) TMCS (g) Toluene (g) H2O (g) SR-A 0.6 208.3 65.4 50 82.8 SR-B 0.7 208.3 76.2 50 84.6 SR-C 0.8 208.3 87.1 50 86.4 SR-D 0.9 208.3 98.0 50 88.2
sheet with a thickness of 70 lm, cured at room temperature for 24 hours, and pasted onto the PVF film.
Characterization
Fourier Transform Infrared. Fourier transform infrared (FTIR) spectroscopy results were obtained using a FTS-1000 infrared spectrometer (Bio-Rad Digilab). The FTIR spectra were recorded in a wavenumber range of 4000–400 cm21 in trans-mission mode.
1Proton Nuclear Magnetic Resonance.1Proton Nuclear
Mag-netic Resonance (1H-NMR) spectra were recorded using deuter-ated Deuterochloroform as a solvent on a Bruker AV400 NMR. The [EtO]/[M] and [OH]/[M]ratio of silicone resins was calcu-lated according to the1H-NMR data.
29Silicone Nuclear Magnetic Resonance (29Si-NMR).29Silicone
Nuclear Magnetic Resonance (29Si-NMR) spectra were obtained on a Bruker AV600 NMR spectrometer. The relative ratio of siloxane for silicone resins was calculated according to the29 Si-NMR data.
Thermogarvimetric Analysis. Thermal analyses of the silicone resin were performed with thermogravimetric analysis (TGA; TGA 1, Perkin-Elmer). The sample size was about 5 mg. The samples were heated at 20C/min from 30C to 600C under a dry nitrogen flow at 20 mL/min.
Gel Permeation Chromatography. The molecular weight and its distribution of silicone resin were determined by Perkin-Elmer series 200 gel permeation chromatography (GPC) system, using THF as an eluent and polystyrene as the standard. Ultraviolet–Visible. The Ultraviolet–visible (UV-vis) spectra were recorded on a Jasco V-530 Ultraviolet–visible spectrometer and scanned between 350 and 650 nm. The silicone resin solu-tion was concentrated for 60 wt % at different wavelengths of 400, 500, and 600 nm, respectively, in order to study their transmittance properties.
Contact Angle Analysis. The contact angles (C.A.) were meas-ured with deionized water on a film of silicone resin at room temperature. The water was poured as a drop by a syringe. Contact angles were measured by image analyzer software, and images were acquired by a camera. The sessile drop method was
used. All measured contact angles were the averages of three measurements.
Softening Point (S.P.). The softening point (S.P.) of silicone resin was checked using a S.P. tester at a speed of 5C/min.
Peel Strength Analysis. The peel strength was measured at a peel rate of 254 mm/min at room temperature using a tensile testing machine (HT9501, Hung Ta Instrument) in accordance with ASTM D1876 (ASTM International Standards). All meas-ured peel strength were the averages of five measurements. Rolling Ball Tack Analysis. The rolling ball tack tester, meeting the standards of the pressure sensitive adhesive tape PSTC-6, was used for testing the tack of pressure-sensitive adhesives. Measure the distance from the point where the ball initially contacts the adhesive to where the ball stops. The average of the stopping distance measurements was reported in millimeters.
RESULTS AND DISCUSSION 29Si-NMR Analyses
In Figure 2, the sharp signals at 12 ppm belonged to M unit. The signals ascribed to siloxane units Q3and Q4, which denoted
the unit structure Si(OSi)n(RO)4-n(n 5 1–4, R 5 Et), at 2100 to
2105 and 2105 to 2112 ppm, respectively.13,14The relative ratio of siloxane unit for silicone resin was summarized in Table II. The content of M unit increased and those of the Q unit decreased. This suggests that M unit was always in the end group
Figure 2.29Si-NMR spectrum of silicone resin.
Table II.29Si-NMR Analytical Data of Silicone Resin
Code M/Q molar ratioa Ratio of siloxane unit (%) M unit Q unitb SR-A 0.66 39.84 60.16 SR-B 0.80 44.44 55.56 SR-C 0.90 47.39 52.61 SR-D 1.04 51.02 48.98
aCalculated from29Si-NMR spectra. bQ 5 Q31Q4.
of each chain, and limits the crosslink of Q unit. Additionally, the molar ratio of the silicone resins found by 29Si-NMR was close to that calculated from the ratio of the starting materials. For example, the molar ratio of SR-A calculated from the ratio of the starting materials was 0.60 and the molar ratio found by
29Si-NMR was 0.66; the calculated unit ratio of SR-B was 0.80
and the molar ratio found by 29Si-NMR was 0.90. Therefore, it was easy to produce silicone resins of different molar ratios by changing the composition of the feed.
FT-IR Analyses
The infrared spectra of the SR-A and SR-B were shown in Fig-ure 3. The broad peak at 3100–3500 cm21was attributed to O-H stretching vibration of Si-OO-H. The sharp peak at 2963 and 2902cm21 was because of the symmetric -CH3and asymmetric
C-H hydrocarbon portion of the spectra. The strong peak at 1086 cm21 belongs to Si-O-Si groups. The peak at 1170 cm21 belonged to the -Si-OEt. Moreover, the bands centered at 1170 cm21 correspond to the ethoxy groups of TEOS, and permit the evaluation of the degree of hydrolysis and condensation of TEOS molecules. Peaks at 1000–1100 cm21suggested the pres-ence of Si-O-Si. The characteristic absorption of M unit were 2963, 756, 842, and 1254 cm21. Additionally, the appearance of the wide peak at 3100–3500 cm21 expressed an indication of hydrolysis of the ethoxy group of the TEOS, as well as the peak
at 1086 cm21and an indication of condensation of the hydroxyl groups of the TEOS and TMCS (Table III).
1H-NMR Analyses
A1H-NMR spectrum with the assignment of the chemical shift for the silicone resin (SR-B) was shown in Figure 4. The ratio of [EtO]/[M] and [OH]/[M] for silicone resin was summarized in Table IV. The peak centered at 0.2 ppm was the resonance of the methyl protons in the M unit, and the peak centered at 3.80 and 1.20 ppm were the resonances of the methylene protons and methyl protons of the ethoxy groups, respectively.5 Hydroxyl protons appeared as a broad peak at 1.7–3 ppm depending on their concentration. The content of M unit increased with the [EtO]/[M] and [OH]/[M] ratio decreased.20 The reduced [OH]/[M] ratio indicated that the end-cap was nearly complete.21
GPC Analyses
A GPC curve of silicone resin was shown in Figure 5. Table V shows the variation of molecular weight for the silicone resin synthesized in the solvent of toluene as a relative amount of M unit. The content of the M unit increased, and the molecular weight of silicone resin decreased from 7713 to 1967 g/mol. It was interesting to indicate the change in the molecular weight distribution after the condensation reaction. The resin SR-D had a monomodal and narrow molecular weight distribution. Contrarily, the resin after condensation reaction (SRA, SR-B, and SR-C) showed a very broad distribution in the GPC chro-matogram. This meant that the average molecular weight depends on the content of M units that came from the TMCS, which limited the growth of the resin molecule and decreased the amount of silanol groups. TMCS acted as chain-stoppers during the polymerization process: once attached to the chain,
Table III.Assignments of Peaks Detected in FT-IR Spectrum of Silicone Resin
Wave number (cm21)
Active
bond Mode Reference
3100–3500 -OH Stretching mode 15
2963 -CH3 Symmetric stretching
mode
16
2902 -C-H Symmetric mode 16
1254 -Si-CH3 Stretching bending mode
16
1170 -Si-OC Asymmetric mode 17
1086 -Si-O-Si- Stretching mode 18
842 -CH3 Stretching bending mode 19
756 -Si-CH3 Asymmetric mode 6
Figure 4.1H-NMR spectrum of silicone resin (SR-B).
Table IV.1H-NMR Analytical Data of Silicone Resin
Code [EtO]/[M] ratio [OH]/[M] ratio SR-A 0.053 0.030 SR-B 0.048 0.022 SR-C 0.045 0.014 SR-D 0.043 0.008
the chain could no longer grow on that particular side.22Lower molecular weight of silicone resin contained relatively great amounts of M unit functional end-groups with the molecular weight distribution range narrowed as the amount of M unit increased. This meant that TMCS could effectively inhibit self-condensation of TEOS, and resulted in homogeneity of the molecule segments of silicone resin. After removal of solvents, the silicone resin was obtained to be either transparent colorless viscous resins or white solids. The S.P. and molecular weight were also decreased as the content of M unit increased. Whereas a significant decreased in the molecular weight could be seen, the profound change in the structure was reflected in the S.P.5 Solubility and Transmittance Analyses
The solubility and hydrophobic properties of silicone resin was shown in Table VI. Solubility was evaluated as the volume of solvent to dissolve silicone resin of 6 g and solvent of 4 g. The silicone resin was very soluble, especially in the benzene solvent. Although solubility tended to decrease slightly as the molecular weight increased, all the samples were insoluble in methanol and ethanol, but were soluble in toluene and xylene. As far as
Table V.Molecular Weight of Silicone Resin
Code Mw(g/mole) Mn(g/mole) Mw/Mn Appearances S.P. (C)
SR-A 7713 2618 2.9 Transparent solid; melt while heating 180–190
SR-B 5358 2324 2.3 Transparent solid; melt while heating 140–150
SR-C 3997 2045 1.9 Transparent solid; melt while heating 130–140
SR-D 1967 1428 1.3 Transparent; semisolid 90–80
Figure 6.UV-vis spectrum of silicone resin.
Figure 7.Contact angle of silicone resin film.
Table VI.Solubility and Transmittance Properties
Code
Solubility propertiesa Transmittance properties
Methanol Ethanol Toluene Xylene 600 nm 500 nm 400 nm
SR-A – – 1 1 83.3 % 73.2% 48.8%
SR-B – – 1 1 87.3% 83.2% 71.8%
SR-C – – 11 11 90.4% 84.9% 68.7%
SR-D – – 11 11 93.2% 91.9% 87.6%
a11, easily soluble, 1, soluble, –, insoluble.
the transmittance of resin solution was concerned, it increased in the order of SR-D > SR-C > SR-B > SR-A within the visible light range, as shown in Figure 6. The data in the three wave-length regions (400, 500, and 600 nm) were presented in Table VI. As seen, the transmittance of the resin solution was almost greater than 80%, but the others were between 68% and 80%. Contact angle measurements had traditionally provided a simple but powerful method for studying the wetting properties of surfaces, particularly their degree of hydrophobicity or hydro-philicity. The sphericity of a water drop on the resin surface was characterized by the contact angle (h). According to the photograph of the contact angles, as shown in Figure 7, it was clear that the sphericity of the water droplet was increasing. It was observed that h increased from 96 to 111 with an increased amount of M unit from 39.84 % to 51.02 %. This indicated that an increase in the hydrophobicity was because of the attachment of -Si-(CH3)3 groups by end-capping surface
-OH groups from siloxane prepolymer. Moreover, the amount of non-polar CH3group increased and the siloxane prepolymer
became highly hydrophobic.23 The highest contact angle was 111, suggesting that with a higher contact angle, the sphericity
of the water drop on the hydrophobic surfaces was greater.
After observing the strong 12 ppm signal from the M unit on the silicone resin and the similar intensity of Q unit in 29 Si-NMR, obvious hydrophobicity of SR-D was indicated in 29 Si-NMR. The decrease in the hydrophobicity of SR-A was observed in29Si-NMR, as indicated by the decrease in the intensity of M unit signal and the increase in the amount of Q unit.
TGA Analyses
To investigate the influence of the M unit content on the thermal performance of silicone resin, the TGA curves of the four silicone resins were measured in an inert atmosphere. The results were presented in Figure 8. Values of T5 and T10, the temperature of
the maximum rate of decomposition (MRD), and the ceramic yield at 500C were calculated from the TGA curves. These were listed in Table VII. Each curve was divided into three regions. Region 1 (30–250C) corresponded to the desorption of
physi-cally adsorbed water or perhaps residual solvent. Region 2 (250– 550C) was related primarily to the removal of organics (principal weight loss) accompanied by polymerization and structural relax-ation. The transition from a polymeric material to an inorganic material occurred at 550–600C. For all the samples over 45% M unit content, the weight loss in Region 1 was very small because
-Figure 9.Rolling ball tack and peel strength of silicone pressure-sensitive adhesives.
Table VII.Effect of M Unit Content on Thermal Behavior of Silicone Resin
Code T5a(C) T10b(C) T15c(C) MRDd(%=C) Residual weight (%)
SR-A 418.7 470.3 539.6 20.07 87.6
SR-B 396.7 433.7 462.3 20.21 76.9
SR-C 317.3 354.3 383.0 20.25 66.6
SR-D 278.0 296.7 309.3 20.39 38.6
CH3groups were hydrophobic and can prevent the adsorption of
water.20Clearly, the values of T5, T15, and T10for the four silicone
resins generally increased with the decreased M unit content as the moieties of the organic groups in the silicone resins decreased at the same time. The residual weight at 500C increased with the decreased M unit content. Meanwhile, the values of MRD decreased with the decreased M unit content. This indicated that the thermal decomposition rate of the silicone resin slowed down with the reduction of the size of the organic group moiety. In fact, as discussed above, some silanols could exist quite stably in silicone resins even when more severe experimental conditions were adopted. Therefore, in addition to the degradation reaction of silicone resin taking place in the TGA test at elevated tempera-tures, a cross-linking reaction also occurred at the same time. With the decrease in M unit content, there was a decrease in the amount of the end-capping groups attached to the surface of the silicone resin, thus causing more unterminated silanols to stay in the system. Under increased temperatures, these active silanols reacted and condense with each other, which leaded to the cross-linking of the silicone resins. The crosscross-linking density of the resins was highly dependent on the amount of residual silanols. As reported previously, the thermal stability of polysiloxane increased with the increase in the crosslinking density.24–27 There-fore, with the increase in the amount of Q (SiO4/2) segment, an
improvement in the thermal stability of silicone resins was obtained. When the M unit content was larger than 50%, SR-D showed a greater total weight loss than did SR-A, B, and C. This implied that the silicone resin with the M units contained -Si-CH3bond in the end group of each chain, and decreased the
crosslinking density. It was well known that the dissociation energy of Si-C bond (326.4 kJ/mol) was lower than that of the Si-O bond (460.5 kJ/mol).18The weight loss of SR-D was shown
apparently in Region 2 because of the high content of -CH3
groups. In the present study, when the M unit content decreased from 51.02% to 39.84%, the MRD values increased from 20.39 (%/C) to 20.07 (%/C), together with an increase in the
residual weight at 500C from 38.6% to 87.6%. Silicone Pressure-Sensitive Adhesives Analyses
The rolling ball tack and peel strength of silicone pressure-sensitive adhesives according to the type of silicone resin was shown in Figure 9. The rolling ball tack depended on the Mw
of silicone resin. The low Mw silicone resin, such as SR-D, has
better tack property. Similar results were found in previous research.1 In the region of silicone resin weight, the average molecular weight was less than ca. 2000, thus the peel strength was poor. At a low molecular weight, silicone resin showed cohesive failure upon the peel test. The cohesive failure was defined as the inability of an adhesive to resist internal separa-tion. Because of cohesive failure, the adhesive sticks on both surfaces (copper and PVF film), but could not hold them together.28 As the Mw approaches 3900, the peel strength rose
sharply and appears to pass through a maximum. The peel strength increased with the molecular weight of silicone resin up to an optimum Mwof 3997 of SR-C.
This phenomenon was attributed to the combined effects of wettability and peel strength of silicone resin at the opti-mum molecular weight, and was ascribed to the maxiopti-mum
cohesive and adhesive strength during the peeling action. At the optimum silicone resin molecular weight, the adhesive layer could not easily be ruptured, hence showing maximum peel strength. Thus, at the optimum molecular weight of 3997 (g/mol), the optimum combination of cohesive and adhesive strength was achieved, and further contributes to the highest peel strength in this study. For silicone resin molecular weights > 5500 (g/mol), the silicone pressure-sensitive adhesives did not completely wet the test panel interface (PVF film). Probably because of the effect of entan-glement, the entangled PDMS chain with silicone resin did not flow effectively to produce poor wettability on the test panel interface.
CONCLUSIONS
Silicone resins were synthesized through hydrolytic condensation of TEOS and TMCS. The content of M unit was increased, while the amount of silanol groups, molecular weight, and thermal sta-bility decreased. The hydrophobic and transparent properties increased the silicone resin. The resin was completely soluble in solvents, such as toluene and xylene. Finally, the silicone resin was applied as a silicone resin to silicone pressure-sensitive adhesives. The silicone pressure-sensitive adhesives formulated various sili-cone resin, and the rolling ball tack and peel strength were meas-ured. The peel strength increased with the molecular weight of silicone resin up to an optimum Mwof 3997 (g/mol) of SR-C.
The silicone pressure-sensitive adhesives prepared from as-synthesized silicone resin have good tack and peel adhesion.
ACKNOWLEDGMENTS
The research was supported by the Bureau of Energy, Ministry of Economic Affairs of the Republic of China under the grant No. 102-E0608.
REFERENCES
1. Kong, W. k.; Ju, T. J.; Park, J. H.; Joo, S. R.; Yoon, H. G.; Lee, J. W. Int. J. Adhes. Adhes. 2012, 38, 38.
2. Fujita, M.; Kajiyama, M.; Takemura, A.; Ono, H.; Mizumachi, H. J. Appl. Polym. Sci. 1998, 70, 771.
3. Williams, J. A.; Kauzlarich, J. J. Int. J. Adhes. Adhes. 2008, 28, 192.
4. Lin, S. B. J. Appl. Polym. Sci. 1994, 54, 2135.
5. Huang, W.; Huang, Y.; Yu, Y. J. Appl. Polym. Sci. 1998, 70, 1753.
6. Sun, F.; Hu, Y.; Du, H. G. J. Appl. Polym. Sci. 2012, 125, 3532.
7. Mikrut, M.; Noordermeer, J. W. M.; Verbeek, G. J. Appl. Polym. Sci. 2009, 114, 1357.
8. Wang, C.; Lii, K. J. Solid State Chem. 2003, 172, 194. 9. Huang, S.; Shan, Y. J. Solid State Chem. 2000, 152, 229. 10. He, M.; Zhang, Q.; Guo, J. Adv. Mater. Res. 2011, 306–307,
1773.
11. Bains, R. S.; Kendrick, D. A.; Parsonage, J. R. Polym. Int. 1993, 31, 87.
12. Lentz, C. W. Inorg. Chem. 1964, 3, 574.
13. Gunji, T.; Hayashi, Y.; Komatsubara, A.; Arimitsua, K.; Abea, Y. Appl. Organometal. Chem. 2012, 26, 32.
14. Abe, Y.; Gunji, T. Prog. Polym. Sci. 2004, 29, 149.
15. Yang, Z.; Han, S.; Zhang, R.; Feng, S.; Zhang, C.; Zhang, S. Polym. Degrad. Stab. 2011, 96, 2145.
16. Montejo, M.; Partal Ure~na, F.; Marquez, F.; Ignatyev, I. S.; Lopez Gonzalez, J. J. Spectrochim. Acta A 2005, 62, 293.
17. Elvira, M. R.; Mazo, M. A.; Tamayo, A.; Rubio, F.; Rubio, J.; Oteo, J. L. J. Chem. Chem. Eng. 2013, 7, 120.
18. Xu, X.; Wu, C.; Zhang, B.; Dong, H. J. Appl. Polym. Sci. 2013, 128, 4189.
19. Mahadik, D. B.; Venkateswara Rao, A.; Parvathy Rao, A.; Wagh, P. B.; Ingale, S. V.; Gupta, S. C. J. Colloid Interface Sci. 2011, 356, 298.
20. Mah, S. K.; Chung, I. J. J. Non Cryst. Solids 1995, 183, 252.
21. Sudo, Y. J. Chromatogr. A 1997, 757, 21.
22. Knoester, H. Macromol. Theory Simul. 2009, 18, 61.
23. Li, J.; Cao, J.; Yang, M.; Yin, W.; Yao, Y.; He, X. J. Non Cryst. Solids 2013, 362, 216.
24. Redondo, S. U. A.; Radovanovic, E.; Torriani, I. L.; Yoshida, I. V. P. Polymer 2001, 42, 1319.
25. Jose, N. M.; Prado, L. A. S. A.; Yoshida, I. V. P. J. Polym. Sci. B Polym. Phys. 2004, 42, 4281.
26. Jose, N. M.; Prado, L. A. S. A.; Schiavon, M. A.; Redondo, S. U. A.; Yoshida, I. V. P. J. Polym. Sci. B Polym. Phys. 2007, 45, 299. 27. Prado, L. A. S. A.; Sforc¸a, M. L.; de Oliveira, A. G.; Yoshida,
I. V. P. Eur. Polym. J. 2008, 44, 3080.
