Anal. Chem. 1994,66, 1438-1443
Determination of End Group Functionality in Poly(methy1 methacrylate) Macromonomers by Pyrolysis Simultaneous Multidetection Gas Chromatography Hajime Ohtani, Yuan Fang L u o , ~Yasukl Nakashlma, Yasuhisa Tsukahara,* and Shin Tsuge' Department of Applied Chemistry, School of Engineering, Nagoya University, Nagoya 464-0 1, Japan
The end groups in poly(methy1 methacrylate) (PMMA) macromonomers and their radically polymerized prepolymers were determined using a pyrolysis gas chromatograph (Py-GC)equipped with a simultaneous multidetectionsystem. End groups associated with the initiator azobis(isobutyronite) (AIBN) and the chain transfer reagents such as thioglycolic acid and mercaptopropionic acid were of particular interest. Various characteristicpyrolyzates that reflectedthe end groups in the PMMAs were observed on the pyrograms. Pyrolysates that contain sulfur from the chain transfer reagent residues in the end groups were determined on the basis of the pyrograms simultaneously obtained by a sulfur-selectiveflame photometric detector and an ordinary flame ionization detector (FID). On the other hand, the cyano-group-containingend groups consisting of the AIBN residue were determined from the pyrograms simultaneously observed by FID and a nitrogen-phosphorus detector. The degree of polymerization estimated from the relative intensities of the end-group-specificpyrolyzates were comparable with those determined by size exclusion chromatography (SEC). Furthermore, the terminal ratio estimated by Py-GC proved to be in good agreement with those calculated from kinetic data.
Macromonomers have become widely used in preparation of various kinds of well-defined graft copolymers.I** The preparation of macromonomers by radical polymerization is one of the most convenient and useful techniques among many other^.^ The accurate determination of the end group functionality of macromonomers and/or prepolymers is essential for studying the copolymerization reactivity of the macromonomers.lJ However, this is not an easy task because the concentrations of the end groups in macromonomers are not always high enough to allow the utilization of conventional analytical rechniques. Recently, two instrumental methods appear to be well suited for the determination of end groups in polymers. First, high field NMR spectrometry has been extensively utilized for the determination of end groups in some polymer chains.&
' Present address: Department of Polymer Science and Engineering, South China University of Technology, Guangzhou, China. Present address: Department of Materials Science. Kyoto Institute of Technology, Kyoto 606, Japan. ( I ) Tsukahara, Y. In MacroMonomer, Macrolnitiators, Macrolniferters, Macrolnimers, Macrolnifers: Mishra. M . K., Ed.; Polym. Frontiers Corp., New York, 1993; pp 161-227. (2j Tsukahara, Y.; Tanaka, M.; Yamashita, Y . Polym. J . 1987, 19. 1121-1 125. (3) Tsukahara. Y ;Ita. K :Tsai. H-C.: Yamashita. Y .J Polym. Sci: Part.4 1989, 27, 1099-1 1 i d . (4) Bevington. J C.: Ebdon, J. R.; Huckerby, T. N. Eur. Polym. J . 1985, 2 1 , f
685--694
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I, 1994
Second, high-resolution pyrolysis gas chromatography (Py-GC) has been demonstrated to be a powerful technique for the analysis of the end groups of poly(methy1 methacrylate) (PMMA)7-9 and polystyrenelOJ1samples. In this paper, the end groups in PMMA macromonomers and their prepolymers which were synthesized radically in the presence of azobis(isobutyronitri1e) (AIBN) as an initiator and thioglycolic acid (TGA) or mercaptopropionic acid (MPA) as a chain transfer reagent are determined by Py-GC. Because one of the end groups in most of the PMMAs examined in this study should have either a sulfur atom or a cyano group, the Py-GC system used in this work is equipped with a simultaneous multidetection system. A flame ionization detector (FID) was always used in conjunction with either a sulfurselective flame photometric detector (FPD) or a nitrogenphosphorus detector (NPD). Although multidetection systems have been applied to Py-GC studies,I2-l4 they have been utilized primarily for qualitative purposes. In this work, simultaneous-multidetection systems are quantitatively applied to the analysis of end groups. The simultaneous pyrograms of PMMAs taken by FID and NPD in the presence of benzothiophene as an internal standard are used for the selective determination of the sulfur-containing chain ends. On the other hand, the simultaneous pyrograms taken by FID and NPD are interpreted in terms of the AIBN residues incorporated into the polymer chains. Finally the results observed by simultaneous multidetection Py-GC are compared with those estimated by size exclusion chromatography (SEC) and kinetic data for the polymerization.
EXPERIMENTAL SECTION Polymer Samples. Methyl methacrylate (MMA) was polymerized with AIBN in benzene at 60 "C for 30 min in the presence of TGA (HSCH2COOH) or MPA (HSCH2CH2COOH).15 The prepolymer was precipitated by adding each of these solutions to a large amount of petroleum ether. ~
~ ~ ~ ~ ~ _ _ _ _ _ _ _ _ _
( 5 ) Axelson, D. A.; Russell, K. E. Prog. Polym. Sci. 1985, 11, 221-282. (6) Hatada, K.; Ute, K.; Kashiyama, M. Polym. J . 1990, 22, 853-857. (7) Ohtani, H.; Ishiguro, S.;Tanaka, M.; Tsuge, S.Polym. J . 1989, 21, 41-48. (8) Ohtani, H.; Tanaka, M.; Tsuge, S. J . Anal. Appl. Pyrolysis 1989, 15, 167114. (9) Ohtani. H.: Tanaka. M.; Tsuge, S.Bull. Chem. Soc. Jpn. 1990, 63, 1 1 9 6 1200. (IO) Ohtani, H.; Ueda, S . ; Tsukahara, Y.;Watanabe, C.; Tsuge, S . J . Anal. Appl. Pyrolysis 1993, 25, 1-10, (1 I ) [to, Y . ; Ohtani, H.; Ueda, S.; Nakashima, Y.; Tsuge, S. J . Polym. Sci.: Part A 1994, 32, 383-388. (12) Sotnikov. E. E.; Torosyan, Zh. K. Zh. Anal. Khim. 1985, 40, 1887-1894. (13) Sotonikov, E. E.; Volkov, S. A. J . Chromatogr. 1986, 364, 97-104. (14) Colling, E. L.; Burda, B. H.; Kelley, P. A. J . Chromatogr. Sci. 1986,24,7-12.
0003-2700/94/0366-1438$04.50/0
0 1994 American Chemlcal Society
This reprecipitation was repeated 3 or 4 times to remove the unreacted TGA or MPA, AIBN, and MMA. Then the purified samples were freeze-dried with benzene followed by further drying in vacuum at 50 OC for 2 days. According to the mechanism of the radical polymerization which is initiated by AIBN followed by the chain transfer reactions with either TGA or MPA, most of the resulting prepolymers should be terminated by the corresponding carboxylic residues as follows: HO!CHzStCHz-F+HFH3
prepolymer-A
O'F
0
(P-1-P-3)
CH 3 HO!CHzCHzS-kCHz-{+H
EI"
monomer
prepolymer-B (P-4-P-6)
Judging from the big differences in chain-transfer constants, chain transfer reactions with AIBN, monomer, and solvent (benzene) can be regarded negligible in the polymerization in the presence of either TGA or MPA.15 However, the following polymer having the terminal AIBN residue should also be formed depending on the relative feed of AIBN: CH3 yH3 CH~++CH~-F+H CsN r-0 0 hH3
In addition, recombination of disproportionation termination reactions might yield other polymers having different combinations of terminals. Purified prepolymer-A's were converted to the corresponding macromonomers by the reaction of the end carboxylic groups with glycidyl methacrylate in xylene at 140 OC for 6 h in the presence of the small amount of hydroquinone and N,N-dimethyllaurylamine as follows:15
Similarly, macromonomer-B's (M-4 to M-6) were formed from prepolymer-B's (P-4 to P-6), respectively. These macromonomers were also purified by using the same reprecipitation procedures as were used for the prepolymers. The prepolymers and macromonomers synthesized using these conditions are listed in Table 1, together with the feed concentrations of monomer [MI, chain transfer agent [SI, and initiator [I]. The number average molecular weight (M,) estimated by SEC is also tabulated. Py-GC Conditions. The Py-GC system equipped with FPD is basically the sameas that described in the previous work.16J7 (IS) Tsukahara, Y.;Naltanishi, Y.; Yamashita, Y.; Ohtani, H.; Nakashima, Y.; Luo, Y. F.; Ando, T.; Tsugc, S.Macromolecules 1991, 24, 2493-2497.
Table 1. PMYA Propolymer and Macromonomer Samples
feed concentration
Prepolymer prepolymer-A's (S is TGA) P-1 P-2 P-3 pre olymer-Bs is MPA) P-4 P-5 P-6
(5
macromonomer-A's M-1 M-2 M-3 macromonomer-Bs M-4 M-5 M-6
4.498 4.507 4.498
0.350 0.100 0.030
0.045 0.045 0.045
7.78 2.22 0.67
2 200 5 300 14 600
4.531 0.350 0.045 4.522 0.098 0.045 4.626 0.029 0.045 Macromonomer
7.73 2.17 0.64
2 200 6 500 19 200
(from P-1) (from P-2) (from P-3)
3000 5 400 15 000
(from P-4) (from P-6) (from P-6)
3 200 6500 18 700
a [MI, [SI,and [I] are the feed concentrations of MMA, TGA or MPA, and AIBN in benzene, respectively. b Determined by size exclusion chromatography.
.
Avertical microfumacetype pyrolyzer (Yanagimoto GP1018) was directly attached to a gas chromatograph (Shimadzu, GC-7A) with a single detection system that could be operated simultaneously as FID and FPD. A relatively higher pyrolysis temperature (700 "C) was used to get higher intensities of the sulfur-containing products characteristic of the TGA or MPA chain end-residues in the PMMA samples. About 0.5 mg of the polymer sample was pyrolyzed together with ca. 0.01 mg of a solid internal standard under a flow of nitrogen carrier gas. In this work, benzothiophene was used as the internal standard because it was a stable solid material at room temperature and completely vaporized at the pyrolysis temperature to give an isolated single peak without affecting the pyrolysis of PMMA under the given Py-GC c0nditions.1~The internal standard was used to correlate the yield of MMA monomer on the FID pyrogram to those of sulfur-containing pyrolysates on the simultaneously taken FPD pyrogram. This internal standard method also improved the reproducibility of the less stable FPD. A high-resolution fused-slica capillary column (Hewlett-Packard, 50 m X 0.2 mm i.d.) coated with dimethylsilicone (Ultra 1,0.33 pm of thickness) immobilized through chemical cross-linking was used. A splitter was used to reduce the carrier gas flow rate from 40 mL min-l at the pyrolyzer to 0.7 mL min-l at the capillary column. Because the characteristic products from sulfur-containing chain ends are relatively low boiling point components, the initial column temperature was set at 0 OC by using a liquefied COz cooling unit. The column was then programmed to 250 OC at a rate of 4 OC min-1. For the analysis of the nitrogen-containing end groups in the PMMA samples, another Py-GC system was used. The same pyrolyzer was used, but in this system a gas chromato(16) Nakagawa, H.; Tsugc, S.;Murakami, K. J. AM^. Appl. Pyrolysis 1986,10, 3140. (17) Ohsawa, M.; Ohtani, H.; Tsugc, S.Fresenius' 2.AMI. Sci. 1988,329,781785.
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A
PYROLYZER CARRIER GAS
cos
CH3SH
H2S
(internal standard)
CH3SCH3
NPD FID
B
IMMA
I
SPRIT VENT
Flguro 1. Flow diagrams of P y a for simultaneous dual detection with NPD and FID.
graph (Hewlett-Packard, Model-5890 A) equipped with a parallel detection system for FID and NPD was employed. Chromatography was performed on a high resolution fusedsilica capillary column (Hewlett-Packard, 50 m X 0.2 mm i.d.) coated with immobilized dimethylsilicone (PONA, 0.50 pm of thickness). Figure 1 shows the flow diagram of this Py-GC system; the outlet of the capillary column was divided into two comparable lines through a dual outlet splitter (SGE, VSOS) connected to the NPD-FID simultaneous detection system. About 0.5 mg of the polymer sample was pyrolyzed at 460 O C under a flow of helium carrier The 60 mL min-* carrier gas flow rate at the pyrolyzer was reduced to 1.0 mL min-l at the separation column by a splitter. The column temperature was programmed from 40 to 250 OC at a rate of 4 OC min-l. Identification of the peaks on pyrograms was mostly carried out using a gas chromatograph/mass spectrometer (GC/MS) system (Shimdazu QP-1000) to which the pyrolyzer was also attached. SEC Measurements. SEC measurements were carried out with a high-performance liquid chromatograph (Japan Spectroscopic Co. Ltd. HPLC-system equipped with 880-PU pump, 860420 column oven, 830-RI refractive index detector and 807-IT integrator) which was operated with Showdex K-80M and K803 columns connected in series. All SEC experiments were performed at 40 OC using chloroform as the mobile phase. M , and the degree of polymerization (P,)were calculated with the calibration curve generated using PMMA standards (Polymer Laboratories Ltd.).
RESULTS AND DISCUSSION Typical programs of the prepolymers prepared in the presence of TGA or MPA as a chain transfer reagent are illustrated in Figures 2 and 3, respectively, where benzothiophene was used as a common internal standard for FPD and FID. PMMA has a tendency to depolymerize mostly into the MMA monomer at elevated temperatures; therefore, the MMA monomer is the main pyrolyzate (more than 70% of the total peak intensities except for the internal standard) on the pyrograms observed by FID. However, the sulfurcontaining products characteristic of the TGA or MPA chainend residues are difficult to detect via FID, because even the outstanding peaks observed at retention time up to 10 min are 1440
Ana!WalChemlstry, Vol. 66,No. 9, May 1, 1994
I
b
I
10
20
3b
20
I 50 min
Flguro 2. Simultaneously observed programs of PMMA prepolymer (P-1) prepared in the presence of TQA at 700 O C : (A) by F W (B) by FID, benzothlophene internal standard.
A
cos
(internal standard)
L
IMMA
B
II
/I I
I
0
I
10
I 20
I 30
I 40
I 50 m i n
Flguro 3. Simultaneously observed programs of PMMA prepolymer (P-4) prepared in the presence of MPA at 700 O C : (A) by FPD; (B) by FID, benrothlophene internal standard.
mostly assigned to hydrocarbons by GC/MS. On the other hand, only sulfur-containing products formed from the end group moiety of the TGA or MPA residues along with the internal standard were detected on the pyrograms observed by FPD. The main component of the MMA monomer is not observed at all because it contains no sulfur atoms. Therefore, in order toquantitate the yields of sulfur-containingcompounds on the FPD pyrogram relative to the MMA-related products on the FID pyrogram, benzothiophene was used as the correlating internal stanadard because the peak due to this compound was observed by both FPD and FID. The pyrograms observed by FID for the prepolymers synthesized in the presence of TGA and MPA were almost identical. However, when comparing the corresponding pyrograms detected by FPD, a fairly strong peak due to CHsCHzSH was characteristic of the prepolymers P-4 to P-6
A
0
E! 6 400
O
500
600
700
PY-TEMP(0C)
Flgure 4. Relationships between pyrolysis temperature and peak intenskies of characteristic pyrolyzates (HIS. COS, CH3SH, CH3CHr SH, CHaSCH3, and CS2)relative to total peak intensltles In pyrograms of prepolymers detected by FPD: (A) P-1; (B) P-4.
corresponding to the chain end MPA-residue (HOCOCH2CHzS-) in the prepolymer-B's. Figure 4 shows the relationship between pyrolysis temperature and sum of the relative intensities of major low boiling point sulfur-containing products such as HIS, COS, CHBH, CHsCH2SH, CH3SCH3, and CS;! in the pyrograms of P-1 and P-4 detected by FPD. The relative peak intensities of the characteristic low boiling point products increase as the pyrolysis temperature is increased, and the sum of these peaks accounts for 98% of the total peak intensities in the FPD pyrograms at 700 OC. This fact suggests that the sulfurcontaining end groups in the PMMAs are almost quantitatively accounted for by the lower boiling point pyrolyzates at 700 OC. Because the FPD-FID detection system provides simultaneously measured pyrograms, it is possible to correlate relative response factors for the two detectors. The concentration of the sulfur-containing chain ends (HOCOCH2S- or HOCOCH$H2S-) is then calculated using the corrected relative yield of the sum of the characteristic peaks that appeared during the first 12 min on the FPD pyrogram. This peak area sum is referenced against the area of the MMA monomer peak in the FID pyrogram. The MMA monomer peak accounts for the main chain degradation of PMMA. Sulfur-related quantitation is achieved via the following system. First, the yield of the characteristic sulfur-containing pyrolyzates (RI,) relative to the internal standard is calculated using the following equation:
where Ii and Istd represent the peak intensities of the characteristic sulfur-containing pyrolyzates up to 12 min and the internal standard, respectively. The square root relationship is used because the FPD response is known to be linearly related to the square of the amount of sulfur atoms
c,
L
J
ro
20
30
40
50
I
1
60 min
Flgure 5. Simultaneously observed pyrograms of PMMA prepolymer (P-8) at 460 OC: (A) by NPD (B) by FID. Peak assignmentsare listed in Tables 2 and 3.
in the sulfur compound.18 In this case, the FPD response is regarded to be independent of the structure of either the original polymer or the pyrolyzates and dependent only the sulfur content of the polymer. Second, the relative molar yield of the MMA monomer (RIMMA)against the internal standard is estimated from the corresponding peak intensities on the FID pyrogram after making a correction for the molar sensitivity of the FID using the effective carbon number (n)for both of MMA (n = 3.65) and the internal standard (n = 8)19 as follows:
where I'MMAand I i t d represent the corresponding peak intensities on the FID pyrogram. Third, eqs 1 and 2 are combined in eq 3 and the new parameter RA, is defined. In this way it is possible to express the molar ratio of sulfur-containing chain ends against MMA units in the PMMA as follows. = ",/RIMMA (3) On the other hand, the amounts of cyanoisopropyl end groups due to the initiator AIBN are estimated from the pyrograms simultaneously observed with FID and NPD. Figure 5 shows typical pyrograms of a prepolymer (P-6) at 460 OC. In the NPD pyrograms the peaks are predominantly due to nitrogen compounds which reflect the ABIN residues incorporated into the terminals of the polymer. The main peaks on the FID pyrograms are due to the MMA related products which reflect the backbone of the polymer. When these end groups are analyzed, the sample is pyrolyzed at 460 OC for two First, peak intensities of the characteristic fragments reflecting the nitrogen-containingend groups decreased at higher temperatures. Second, at the lower temperatures there is significant peak broadening and poorer reproducibility of the resulting pyrograms. Tables 2 and 3 summarize the characteristic pyrolyzates that were observed on the pyrograms and identified by GC/ MS. They are the MMA backbone-related products (peaks RAs
(18) Maruyama, M.;Kakemoto, M. J . Chromorogr.Sci. 1978, 16, 1-7. (19) Jorgcnsen, A. D.; Picel, K. C.; Stamoudis, V. C. Anal. Chem. 1990,62,683689.
Analytical Chemistry, Vol. 66, No. 9, M y 1, 1994
1441
even on the FID pyrogram. Likewise the AIBN-related peaks (B-K) are also normalized using peak D on the corresponding pyrogram by NPD. Thus, if the NPD response to characteristic products B-K is independent of their structure and dependent solely on their C N content, the molar ratio of cyanoisopropyl end groups can be calculated using the following equation:
Table 2. Asslgnment of Peaks Reflectlng Chaln End AIBN Resldue In the Pyrogram of PMMA
peak code
mol wt
B
67
structure CH3-C
I
CN
C
69
CH3
I
K
24
CH3-CH
I
CN
D
123
CH3
(4)
CH3
I
C H ~ - :-CH~-
I
C=CH,
I
In this equation RAN is the mole ratio of cyanoisopropyl end groups to backbone MMA units; Z’i and Z’D are the intensities of peak i and D, respectively, on the FID pyrogram; ni and 7 . 2 are the effective carbon numbers (FID) for the pyrolyzate i and D, respectively, and mi is the number of MMA units in pyrolyzate i as shown in Table 3; Z”D are the peak intensities of peaks i and D, respectively, on the NPD pyrograms. In this calculation higher oligomers are taken into account as well as the MMA monomer, because considerable quantities of dimeric and trimeric fragments are formed at 460 OC. Provided that the prepolymer sample consists entirely of molecules in which one terminal is either an AIBN or one of the chain transfer reagent (TGA or MPA) residues, the average degree of polymerization (P,)for the prepolymers can be calculated using eq 5
CN
E
125
CH3-
C= CH
I
NC
F
136
G
155
CH,
I
169
I
C-CH
I I
&N
&OOCH~
CH3 CH,
I I
CN
169
I
I
CH,--C-C-CH,
I
CH3
CH3 CH3 CH3-
H
I
COOCH3
t t
COOCH,
CH,
I I
CH3-C-CHZ-CH CN
J
167
CH3 I CH3-C-CH2-7
I
K
183
CH3
I I
COOCH,
P, = l/(RA,
fiH2 I
CN
COOCH3
CH3
CH3
I
CH,-C-CH,-C-CH,
I
I
I
1-24)1° and the AIBN-related ones (peaks B-K) which are also observed in the NPD pyrograms. AIBN-related peak D was used to normalize the MMA backbone related peaks because it was observed as a moderately strong, isolated peak
+ RAN)
(5) Moreover, because the basic patterns on the programs for a prepolymer and the corresponding macromonomers are almost identical, P, for the macromonomers can be estimated in a manner similar to that used for the prepolymers. Table 4 summarizes RA, and RAN values and the P, of the PMMA samples estimated by both Py-GC and SEC. The fairly good agreement between the results obtained for the prepolymers by Py-GC and by SEC suggests that the following two conclusions are justified. First, the assumptions implicit in the calculation of P, are quite reasonable; Second, Py-GC can be used to make rapid and sensitive estimations of the P,, values for PMMA prepolymers. On the other hand, P,,values
Table 3. Assignment of Maln Chaln MMA Related Peaks In the Pyrogram of PMMAB
peak no.
mol wt
structure
effective carbon number
Monomeric Fragment (m* = 1) 88 102 100 116 114
1
2 3 425 6-8
14 15 16,18 17,19-21 22,23
142 140 156 158 158 186 200 214
24
300
10,12, 13 11
CHaCHzCOOCH3 CH&H(CH3)COOCH3 CHFC(CH~)COOCH~[MMA monomer] C6HlZOZ C6HlOOZ
2.75 3.75 3.65 4.75 4.65 6.65 6.55 7.65 7.75 7.75 6.4 7.4 8.4
Trimeric Fragment (mb = 3) 0
CH~C(CH~)(COOCH~)CHZC(CH~)(COOCH~)CH=C(CH~)COOCH~
*
11.25
For molor sensitivity correction of FID response.sJ8 Number of MMA unit and the related structure in the fragment. -
1442
AnalyticalChemistry, Vol. 66,No. 9,May 1, 1994
(n)O
Table 4. Edlmatd Number Average Dagrw of Polymerlzatton of PMMA Samples degree of polymerization, P,,
sample code
RAS"x1og RAd x log by Py-GC' by SEC
prepolymera
P-1
46.0 f 2.8 13.6 f 0.6 5.03 f 0.17 36.1 f 2.5 11.6 f 0.7 3.53 f 0.19
2.91 f 0.13 2.52 f 0.10 1.89 f 0.06 2.16 f 0.20 1.76 f 0.10 2.26 f 0.18
20 62 144 26 27 173
21 52 145 21 28 191
*
27 72 202 35 88 280
28 53 148 31 64 186
P-2 P-3 P-4 P-5 P-6 macromonomer M-1 33.8 f 0.1 2.86 f 0.08 M-2 11.1 f 0.9 2.72 f 0.10 M-3 2.79 f 0.06 2.17 f 0.21 1.95 f 0.05 M-4 26.6 f 0.3 9.62 f 0.22 1.80 f 0.01 M-5 2.05 f 0.12 1.52 0.04 M-6
a Molar ratio of sulfur-containing chain end against MMA unita in PMMAE estimated by FPD and FID. b Molar ratio of CNcontaining chain end against MMA units in PMMAs estimated by NPD and FID. e P . 1/(R& + RAN).
estimated by Py-GC of a given macromonomer tend to be larger than those for the corresponding prepolymer although those estimated by SEC are almost the same. Moreover, the prepolymers give higher RA, values than the corresponding macromonomers even though RAN values are almost comparable between the prepolymers and the corresponding macromonomers. These facts suggest that formation of the characteristic sulfur-containing pyrolyzates might be depressed to some extent for the macromonomers. In general, it is very difficult to determine RAN by using other analytical techniques whereas R& can be estimated using lH N M R via the unsaturated proton signals in the macromonomers or by the titration of the end carboxylicgroups in the ~repo1ymers.l~In contrast, because Py-GC can provide individual RAs and RANvalues, the terminal ratios between AIBN and thechain transfer residues can directly be estimated. For the radical polymerization of vinyl monomers in the presence of a chain transfer agent, Pn of the polymer is approximately related to the kinetic data as follows:15
where P,,o is the Pnof PMMA polymerized without any chain transfer reagents and equal to (ktRp/k2[Ml2)-l; R, is the polymerization rate, C, is the chain-transfer constant to the chain transfer reagent, and k, and kt are the rate constants for the propagation and termination reactions, respectively; [MI and [SI are the feed concentration of the monomer and
Table 5. Eathated AIBN/(TGA or MPA) Termlnal Ratlo In Propolymers relative AIBN/(TGA or sam le R,xl(ra MPA) fractions (% / % ) cde (mol L-ls-l) by Py-GCb from kinetic datac
P-1 P-2 P-3 P-4 P-5 P-6
3.77 3.08 3.67 3.05 2.64 3.14
6/94 16/84 27/73 6/94 13/87 39/61
4/96 8/92 25/75 3/97 8/92 28/72
a Polymerization rate. Calculated fromRAN/R& in Table 4 after being normalized by RAN + R& = 100. Calculated from P,k& kP2[Ml2using P,,by SEC in Table 4, R in this table, [MI in Tab e 1,and k, = 5.15 X 102 and kt = 2.55 2107.
P
the chain transfer reagent, respectively. Thus, provided that these polymer molecules have either one AIBN or one chain transfer reagent residue, the fraction having AIBN residue shouldbeconsistentwith Pn/Pn,oor PnktRp/k,Z[MI2calculated from the polymerization data. The terminal ratios estimated by Py-GC for the prepolymers are listed inTable 5 together with those calculated from the polymerization data using k, = 5.15 X lo2 and kt = 2.55 X lo7 (L mol-' s-'),15 the R, values in Table 5 , [MI from Table 1, and Pndetermined by SEC (Table 4). These results suggest that Py-GC can be used to directly estimate the terminal ratios. In summary, these results demonstrate that pyrolysis simultaneous multidetection GC is a new and effective technique for the chain end analysis of PMMA macromonomers and their prepolymers synthesized via radical polymerization. In this method, minute amounts of heteroatomcontaining end groups in PMMAs are determined using the ratios between heteroatom-containing fragments and backbone MMA related products, which are simultaneously detected by the heteroatom-selective detector and by FID, respectively. An appropriate internal standard is used to correlate the simultaneously observed pyrograms. Furthermore, this technique might be generally applicable for the characterization of heteroatom-containing end groups in various polymeric materials.
ACKNOWLEDGMENT We thank Professor Yuya Yamashita, Department of Applied Chemistry, Tokyo Denki University, for helpful discussions. This research was financially supported by the Tokuyama Science Foundation, for which the authors are very grateful. Recelved for review August 24, 1993. Accepted February 9, 1994." *Abstract published in Advance ACS Abstructs, March 15, 1994.
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