摘要:
Two-dimensional correlation gel permeation chromatography (2D correlation GPC) study of the sol–gel polymerization of octyltriethoxysilane. HCl-concentration dependence Kenichi Izawa,a Toshiaki Ogasawara,b Hideki Masuda,c Hirofumi Okabayashi,*c Charmian J. O’Connord and Isao Nodae aFuji Silysia Chemical Ltd., Nakatsugawa Technical Center, 1683-1880, Nakatsugawa 509-9132, Japan. E-mail: k_izawa@fuji-silysia.co.jp; Fax: z81 573 68 7228; Tel: z81 573 68 7333 bTokai Technical Center Foundation, 710, Inokoshi 2, Meito-ku, Nagoya, 465-0021, Japan. E-mail: t_ogasawara@zttc.or.jp; Fax: z81 52 771 5164; Tel: z81 52 771 5161 cDepartment of Applied Chemistry, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, 466-8555, Japan. E-mail: fwiw4348@mb.infoweb.ne.jp; Fax: z81 52 735 5247; Tel: z81 52 735 5228 dDepartment of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand. E-mail: cj.oconnor@auckland.ac.nz; Fax: z64 9 373 7422; Tel: z64 9 373 7999 eThe Procter and Gamble Company, 8611 Beckett Road, West Chester, OH 45069, USA. E-mail: noda.i@pg.com; Fax: z1 513 634 9342; Tel: z1 513 634 8949 Received 24th August 2001, Accepted 6th December 2001 Published on the Web 7th January 2002 Two-dimensional correlation gel permeation chromatography (2D GPC) was used to elucidate intricate details of the initial ten minutes of the sol–gel transition of n-octyltriethoxysilane (OTES), catalysed by 0.5 and 2.0 M HCl?H2O.The results demonstrate that the features of 2D GPC correlation spectra directly reflect the dynamic variation of reactions or interactions present during the polymerization process.Introduction It is well known that the mechanism of acid-catalysed polymerization of silane alkoxide or alkylalkoxide is different from that of the base-catalysed reaction of silane species.1 This difference arises from various factors, which depend strongly on the concentration of water and of the silane species and on the pH of the reaction mixture. Detailed understanding of the factors influencing the polymerization process for this important class of materials should bring about further development of various applications, especially in the industrial arena. In our previous study,2 we have demonstrated that the twodimensional (2D) correlation analysis can be applied to the three time-dependent gel permeation chromatography (GPC) elution profiles, which were obtained from the reaction mixture of the n-octyltriethoxysilane (OTES)–ethanol–1 M HCl?H2O system.However, in order to obtain detailed information on the complex reaction mechanism, the 2D correlation analysis must be carried out using many time-dependent GPC profiles. In this present study, the HCl-concentration dependence of the initial ten minutes of the polymerization process for the OTES–ethanol–HCl?H2O system has been examined by the 2D GPC analysis of the twenty profiles. Background The two-dimensional (2D) correlation theory generalized by Noda et al.2,3 has been successfully utilized in IR, NIR, Raman and other spectroscopic fields.4–8 It is well established that this theory may easily be adapted to various analytical methods, such as chromatography, as well as to the more traditional spectroscopic methods.In our previous study,2,9 we have already reported the successful application of 2D correlation analysis to time-resolved GPC profiles (2D GPC). It has been demonstrated that the features depicted in a 2D GPC correlation spectrum directly reflect the details of complex dynamic variations in time-dependent elution profiles. The time-resolved GPC trace intensity I(E,t) can be expressed as a function not only of the chromatographic elution time E but also of the sampling time t for each aliquot collected during a polymerization reaction period between Tmin ~y(E,t)~ and Tmax.2,10 The dynamic GPC trace intensity, y�(E,t) of a timeresolved GPC profile is given by minƒtƒTmax (1) for T otherwise I(E,t){I(E) 0 DOI: 10.1039/b107635c PhysChemComm, 2002, 5(2), 12-16 12 where I�(E) is the reference GPC trace profile of the reaction system.The reference trace I�(E) is set to be the time-average of trace profiles over the observed period given by Tmax (2) I(E,t)dt: 1 I(E)~Tmax{Tmin �Tmin The generalized 2D correlation function2,3 for the analysis of time-resolved GPC profiles is defined as 1,E2)ziY(E1,E2)~ W(E ? (3) Y ~1(v)Y ~ 2 (v)dv: 1 p(Tmax{Tmin) 0 � The real and imaginary terms, W(v1,v2) and Y(E1,E2), are the synchronous and asynchronous 2D correlation intensities, respectively.The synchronous 2D correlation intensity W(v1,v2) represents the overall similarity or coincidental This journal is # The Royal Society of Chemistry 2002 Papertrends between two separate intensity variation of the GPC trace measured at different elution counts. The asynchronous 2D correlation intensity Y(E1,E2), on the other hand, can be regarded as a measure of dissimilarity or out-of-phase character of the GPC trace intensity variations. The term, Y�1(v), is the forward Fourier transform of the dynamic trace intensity variations y� (E1,t) observed at a specific elution count E1 with respect to the sampling time t. (4) Y ~y(E1,t)e{ivtdt: ~1(v)~� expressed by (5) ~y(E Y 2,t)ezivtdt: ~2 (v)~ ?{? The conjugate Fourier transform Y�1*(v) of the GPC trace intensity variation y� (E2,t) observed at elution time E2 is � 1,E2) and Y(E ?{? While the Fourier transformation of the dynamic trace y� (E,t), defined in eqn.(1), with respect to the sampling time t formally provides the synchronous and asynchronous correlation spectra, W(E1,E2) and Y(E1,E2), a simpler computational method has recently been developed to obtain W(E 1,E2) more directly.11 Further details of synchronous and asynchronous 2D GPC spectra are described elsewhere.2,9 Experimental For the reaction systems of the n-octyltriethoxysilane (OTES)– ethanol–x M HCl?H2O (1 : 1 : 0.4 weight ratio and x ~ 0.5 and 2.0) solutions, GPC measurements were carried out by using a Shimadzu high-performance liquid chromatography system equipped with a refractive index RID-10A detector.Tetrahydrofuran (THF) was used as the eluent at a flow rate of 0.6 ml min21. The system was calibrated with polystyrene standards. Aliquots (0.002 ml) were sampled from each reaction mixture at various time intervals in the initial ten minutes and were quickly diluted by 1 ml of THF chilled at 273 K. Thus, 40 samples involving the time-dependent composition were obtained. GPC was run for each THF-diluted sample. Results and discussion The GPC profiles of the 0.5 and 2.0 M HCl–catalysed OTES– ethanol systems are shown in Fig. 1. The assignments of these elution bands were made on the basis of GPC profiles of the aminopropyltriethoxysilane–ethanol and aminopropyltrihydroxysilane–ethanol systems9,10 and are listed in Table 1.The elution bands A (12.5 counts) and C (11.5 counts) Fig. 1 Time-resolved elution profiles of OTES–ethanol [A] 0.5 M HCl: (a) 60 s, (b) 180 s, (c) 300 s, (d) 420 s, (e) 600 s and [B] 2.0 M HCl: (a) 60 s, (b) 120 s, (c) 240 s, (d) 360 s, (e) 600 s systems. 13 PhysChemComm, 2002, 5(2), 12-16 Table 1 Possible correlation squares (CSqi: i ~ 1–18) in the asynchronous spectra of the 0.5 and 2.0 M HCl catalysed systems and band correlations Region System Band correlations Correlation square 0.5 M I CSq CSq CSq4 A < C A < E C < E E < F’ A < F’ II III, IV and all autopeaks I 2.0 M 123 CSq CSq CSq CSq CSq CSq CSq11 5678910 CSq CSq C < F’ A < C A < D A < E C < E F’ < F@ A < F II III, IV and all autopeaks CSq CSq CSq CSq CSq CSq12 13 14 15 16 17 18 A < F’ A < F@ C < F C < F’ C < F@ D < F’ correspond to the octyltrihydroxysilane (OTHS) and OTES monomers, respectively.The extremely weak band B may be due to mono- and di-hydrolyzed silanes (OMHS and ODHS). The bands D, E, F, F’, and F@ are assigned to polymeric components. We assume, from the GPC calibration of polystyrene-standards (MW: 580–21900), that bands D and E consist of small aggregatesquo;, and F@ are of larger aggregates.Synchronous and asynchronous 2D GPC correlation spectra were calculated from the twenty trace sets of time-resolved GPC profiles, using 2D OGAIZA software developed at Nagoya Institute of Technology. The synchronous and asynchronous spectra of the 0.5 and 2.0 M HCl-catalysed systems are shown in Fig. 2 and 3. Synchronous 2D GPC spectra. For the 0.5 M HCl-catalysed system, the synchronous spectrum (Fig. 2[A]) consists of four regions (I, II, III and IV). Region I contains three autopeaks (A(E1)<A(E2),C<CandE<E) and six cross peaks (A(E1)< C(E2), C < A, A < E, E < A, C < E and E < C). These correlation peaks evidently arise from elution bands of small aggregates. Therefore, we may regard this region as a small aggregate (SA) region.Region II comprises two autopeaks (F<F and F’<F’) and two cross peaks (F<F’ and F’<F), which derive from elution bands F and F’ of large aggregates. Thus, region II can be regarded as a large aggregate (LA) region. Regions III and IV include only the cross peaks which come from the correlation of elution bands F and F’ with band A, C and E (that is, the correlation between small and large aggregates). The signs of the cross peaks in Region I are all positive, reflecting the fact that the populations of the small aggregates rapidly decrease with reaction time, as a consequence of the condensation reaction, to form large aggregates. The negative sign of the cross peaks in Region III and IV implies that the condensation reaction between small aggregates brings about a rapid increase in the populations of bands F and F’.We can construct a synchronous correlation square (CSq), by connecting the two autopeaks and the two cross peaks, implying that a correlation exists between the two elution bands. In Region I, three such correlation squares, CSq1, CSq2 and CSq3, may be constructed, implying the existence of A < C, A < E and C < E correlations, respectively. In Region II, there exists a correlation square (CSq4) coming from the E < F’ correlation. Furthermore, the two correlation squares, CSq5 and CSq6, which arise from the A and C autopeaks and crossFig. 2 2D GPC correlation spectra ([A]: synchronous and [B]: asynchronous) of the 0.5 M HCl catalysed system.Fig. 3 2D GPC correlation spectra ([A]: synchronous and [B]: asynchronous) of the 2.0 M HCl catalysed system. peaks in region III and IV, are possible. Thus, there exists a correlation between small aggregates (monomers) and large aggregates. The possible correlation squares (CSqi where i ~ 1–6) and their corresponding band coordinates are listed in Table 1. For the 2.0 M HCl-catalysed system, the synchronous spectrum (Fig. 3[A]) also consists of four regions (I, II, III and IV). In Region I, a weak autopeak (D < D) and two cross peaks (D < A and A < D) newly appear, in addition to the three autopeaks and six cross peaks corresponding to those found for the 0.5 M HCl system. Therefore, a correlation square arising from the A < D correlation is additionally possible. However, since this A < D correlation peak is very weak in intensity, the contribution of components detected by this correlation to the reaction process in the initial ten minutes must be very small.For the 2.0 M HCl system, the autopeak (E < E) and the four cross peaks (A < E, E < A, C < E and E < C) are extremely strong in intensity, compared with those for the 0.5 M HCl system. Therefore, we may assume that the contribution of those correlated components (that is, those represented by the three correlation squares, CSq7, CSq9 and CSq10) to the 2.0 M HCl-catalysed reaction during the initial ten minutes is significant. In Region II, as seen in Table 1, in addition to the F’ autopeak of the 0.5 M HCl system, two positive cross peaks due to the F’ < F@ correlation and two negative cross peaks due to the F < F@ correlations further appear.The negative sign of the latter cross peaks indicates that, as the reaction time increases, component F decreases while F’ and F@ components increase. The CSq11 definitely arises from the F’ < F@ correlation, indicating that the correlation peaks representing larger aggregates are dominant in Region II. Furthermore, the correlation of bands F and F’ with bands A and D bring about five correlation squares (CSqi, i ~ 12, 14, 15, 17 and 18), in addition to the CSq13 and CSq16 corresponding to the CSq5 and CSq6 in Region II for the 0.5 M HCl system.Thus, from the well-established features of a synchronous 2D GPC spectrum, we may conclude that a high HCl concentration results in the appearance of correlation squares, which come from correlations among the LA bands and from those among SA and LA bands. Asynchronous 2D GPC spectra. The asynchronous spectrum for the 0.5 M HCl-catalysed system is shown in Fig. 2[B]. The signs of cross peaks and the band coordinates obtained from the cross peaks are listed in Table 2[A] together with the order of events. It is found that each of three elution bands (A, C and E) consists of two components AH (subscript H for the highelution component) and AL (subscript L for the low-elution component), CH and CL, EH and EL, detected by the resolution-enhancing characteristics of 2D GPC spectra.We point out that the two components AH and AL correlate separately with the other two components XH and XL, respectively. That is, the component AH correlates with the CL (and EL) components and band F’, while the AL component relates with the CH (and EH) components and band F. It is very interesting to compare the intensity of the AH<CL (or EL or F’) correlation with that of the AL<CH (or EH or F) correlation. The intensity of the AH<CL cross peak is slightly stronger than that of the AH < CH cross peak. The AH < EL cross peak is extremely strong in intensity, compared with the AL<EH cross peak. Thus, the strength of the band correlation evidently depends on the species of elution bands.In particular, we note that the component AH strongly correlates with bands F’, F@ and F-, while the AL component strongly relates only with band F. The existence of elution band F- was confirmed, as a consequence of resolution-enhancement, in the asynchronous spectra (Fig. 3[A] and [B], Table 2). In order to explain these correlation behaviors, we suggest that there exists a marked difference in reactivity between the AH and AL PhysChemComm, 2002, 5(2), 12-16 14Table 2 Synchronous and asynchronous correlations for [A] the 0.5MHCl?H2O-catalysed system and for [B] the 2.0MHCl?H2O-catalysed system– band correlations, intensities, signs and order of events Correlationa 0.5 AH < AL(m), CL(m) AH < F-(s) AL < CH(m), EH(m) AL < EL(s) AL < F(s) CH < EL(s) CH < F-(s) CL < F(s) EH < F-(s) EL < F(s), F’(s) 2.0 F < F@(s) F’ < F-(s) AL < CL(w), EL(s), F(w) AL < D(w) AL < F’(s), F@(s) H < EL(w) L < D(w), EH(w) L < EL(m) L < F(w) L < F’(m) L < F@(s) CCCCCCD < F’(w) EH < EL(m) EH < F’(w), F@(w) EL < F(m) EL < F’ (s) EL < F@(s), F-(s) F < F’(w) F < F@(m) F’ < F@(s) abECount number of elution peaks: AH(12.59), AL(12.53), CH(11.65), CL(11.49), EH(10.04), EL(10.88), F(10.67), F’(10.36), F@(10.24), F-(10.09).s: strong, m: medium, w: weak in intensity. cEx A Ey: the event of Ex occurs before that of Ey. components.We conclude that the AH component is higher in reactivity than the AL component, bringing about the strong correlation of AH component with bands F’, F@ and F- The result indicates that the higher elution components easily condense with each other to form larger aggregates. For the two components of bands C and E, similar correlation behaviors are found. In particular, we find that the CH < EL correlation is much stronger than the CL < EH correlation, and that the CH component strongly correlates with band F-, while the CL component with band F. Similarly, the EH component is strongly connected with bands F’ and F@, while the EL component connects only with band F. Thus, it is evident that the H-components of bands C and E is more reactive, compared with the L-component.The resolutionenhancing characteristics of an asynchronous correlation spectrum provides ample evidence that the larger aggregates which furnish the bands F’, F@ and F- are produced in the polymerization process, even during the initial ten minutes. The asynchronous spectrum for the 2.0 M HCl-catalysed system is shown in Fig. 3[B]. The signs of the cross peaks and the band coordinates obtained from the cross peaks are listed in Table 2[B], together with the order of events. Splitting of the elution bands, which was found in the asynchronous spectrum of the 0.5 M HCl-catalysed system, also appears in the asynchronous spectrum for the 2.0MHCl system. The very weak cross peak with a positive sign at coordinate (E 2 ~ 11.54) and that with a negative sign at coordinate (11.53, 11.45) correspond well to the CL < CH and CH < CL correlation peaks in the asynchronous spectrum for the 0.5 M HCl system, respectively. Since these two cross peaks evidently arise from the correlation between the L- and H-components, the elution bands at E1 ~ 11.45 and 11.53 counts are ascribed to the L- and H-components of the band C, respectively.Similarly, the relatively strong cross peak with a positive signz z F’ A F@ at coordinate (10.92, 11.07) and that with a negative sign at coordinate (11.07, 10.92) arise from the EL<EH and EH<EL correlations respectively. Thus, the two elution bands at E1 ~ 10.92 and 11.07 counts are assigned to the L- and H-components of the band E respectively.The correlations of the L- and H-components with other bands are summarized in Table 2[B]. We should note that the correlations of the L-component with other bands are dominant. For the correlation of CL with other bands, the CL<F’ correlation is very strong, although the CL<D (or E) and CL < F correlations are intermediate in intensity. The CL-component also correlates weakly with high molecular weight bands. However, the correlations of the EL-component with the bands F, F’ and higher molecular weight bands (F@ or F-) are extremely intense. 1~11.45, We find that the elution bands (at least seven bands) in the region E2 ~ 9.0–12.0 correlate with band A. In these correlation bands, the elution count of band A is E1 ~ 12.49 min and closely corresponds to that (12.53) of the ALcomponent for the 0.5 M HCl system.Therefore, we may regard the elution peaks in the region E1 ~ 12.49, E2 ~ 9.0– 12.0 as the correlation peaks of the AL-component with other bands. The elution peaks in the region E1 ~ 12.59 and E2 ~ 9.0–12.0, arising from the correlation of the component A with other bands, may be superimposed with the lower contour levels for the correlation peaks of AL and other bands. We may assume even in this elution region that the correlations of the AL-component with other bands are dominant. The existence of the intense correlations, AL<EL and AL< F@ (or F-), as well as the strong AL < F cross peaks, reflects that the condensation reaction of OTHS molecules to form the EL-component and higher molecular weight bands (F@ and F-) rapidly occurs.Furthermore, we should note that the correlation among bands F, F’, F@ and F- in the region of 15 PhysChemComm, 2002, 5(2), 12-16 Signb Synchronous (W) z z AH A AL, CL 22 2 F- A A 2 zz z AL A EL z z z CH A EL 2 F A CLH F, F’ A E L L A CL, EL, F D A A CH A EL CL A EL 22 2 F’, F @A A 2 zz z CL A D, EH zz z CL A F z 2 2 F- A CH 22 2 F- A E 2 z z z F A F@ z z F’ A Fz z A z L F’ A C H 22 2 F@ A CL 2 EH A EL F’, F@ A E H AL A CH, EH L F A A LL z z D A F’ z2 z z z EL A F 22 2 F@, F- A EL 22 2 F@ A FL F’ A E F’ A F Asynchronous (Y) zzz Order of eventsc Helution counts around 10–11 min is more intense for the 2.0 M HCl system even during the initial ten minutes.When we compare the intensity of the CH < EL correlation between the asynchronous spectrum for the 2.0 M HCl system and that for the 0.5 M HCl system (Table 2[A] and [B]), we notice that the CH < EL correlation peak for the 2.0 M HCl system is weak while that for the 0.5MHCl system is strong. Such a difference in correlation intensity between the two different HClconcentration systems is also found for the CL < F and EL < F (or F’) correlations. We should attribute these correlative behaviors to the consequence of the polymerization reactions promoted by a high HCl-concentration. The reason why the L-components correlate predominantly with other bands may be explained as follows. At high HCl concentration, the consumption of most of the reactive H-components brings about high populations of the L-components remaining unreacted and makes these L-components more reactive. Conclusion The polymerization process promoted by high HCl concentration is directly reflected in the synchronous spectrum. In particular, resolution-enhancing characteristics of the asynchronous correlation have provided the significant result that the elution bands arising from small aggregates consist of a reactive H-component and a less-reactive L-component. Thus, the 2D GPC correlation technique can be successfully utilized to follow details of the HCl-concentration dependence of the polymerization process. References 1 H. Einaga, in Inorganic Synthesis in Solution as a Reaction Field, Baifukan, Tokyo, 2000, p 169. 2 K. Izawa, T. Ogasawara, H. Masuda, H. Okabayashi and I. Noda, PhysChemComm, 2001, 12. 3 I. Noda, Appl. Spectrosc., 1993, 47, 1329. 4 I. Noda, A. E. Dowrey, C. Marcott, G. M. Story and Y. Ozaki, Appl. Spectrosc., 2000, 54, 236A. 5 I. Noda, Appl. Spectrosc., 1990, 44, 550. 6 N. L. Sefara, N. P. Magtoto and H. H. Richardson, Appl. Spectrosc., 1997, 51, 536. 7 I. Noda, Y. Liu, Y. Ozaki and M. Czarnecki, J. Phys. Chem., 1995, 99, 3068. 8 Y. Ren, M. Shimoyama, T. Ninomiya, K. Matsukawa, H. Inoue, I. Noda and Y. Ozaki, J. Phys. Chem., B, 1999, 103, 6475. 9 K. Izawa, T. Ogasawara, H. Masuda, H. Okabayashi and I. Noda, Macromolecules, 2001, in press. 10 T. Ogasawara, A. Nara, H. Okabayashi, E. Nishio and C. J. O’Connor, Colloid Polym. Sci., 2000, 278, 1070. 11 I. Noda, Appl. Spectrosc., 2000, 54, 994. PhysChemComm, 2002, 5(2), 12-16 16
ISSN:1460-2733
DOI:10.1039/b107635c
出版商:RSC
年代:2002
数据来源: RSC