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Determination of the microstructure of polybutadiene by pyrolysis-gas chromatography
Awlyrlco
C/rin1lru
Aetu
303
Elscvicr Publishing C’ompuny. Amsterdam Printed in The Ncthcrlnnds
DETERMINATION POLYBUTADIENE
AND
T. SHONO
K. SHINRA
a/’ Applied Chemistry,
Department (Received
OF THE MICROSTRUCTURE OF BY PYROLYSIS-GAS CHROMATOGRAPHY
24th February
Osuku
University,
Suitu,
Osuku
565
(Jupun)
1971)
There have recently been rapid developments in the identilication of polymers by gas chromatography oftheir pyrolysis products. As well as providing a convenient means of identifying polymers, pyrolysis-gas chromatography (p.g.c.) affords the possibility of investigating their microstructure’ - 5. Recently, Takeuchi et aL6-’ investigated the sequence concentration of triad in vinylidene chloride-vinyl chloride copolymers and the distribution of the chlorine atoms in the chain of various chlorinated synthetic polymers by means of p.g.c. In this paper an attempt is made to determine quantitatively the microstructure of polybutadiene. Polybutadiene can be classified into 1,4 and 1,2 structures. The former shows cis and tram forms and the latter has different tacticities. The progress of synthetic polymer chemistry has made it possible to produce polymers that are rich in only one of these microstructures. Vacherot”, who made a structure elucidation of polyisoprene by p.g.c., found that polyisoprene produced by 3,4-addition is characterized by a hydrocarbon peak between the peaks of isoprene and dipentene which is not given by polyisoprene produced by 1,4-addition. He reported also that the peak area ratio of this hydrocarbon and dipentene is proportional to the ratio of the 1,4-type and the 3,4-type and that this provides a method for determining the ratio of the two types in the synthetic polyisoprenes. Recently, Hackathorn and Brockg have examined the d’imer pyrolysis fractions of several polyisoprenes. These larger fragments may retain certain microstructural features and provide information about polymer chain degradation . mechanisms. Perry lo did similar research on polybutadiene and studied the peak area ratio of ethylene and butadiene against the ratio of the 1,2- and the 1,4-species. TABLE ANALYSIS
I 01: MICROSTRUCTURE.5
Code
1 2 3 4 5 a By Morero
Microstructtrre’
OF STANDARD
SAMPLE!5
(“/,)
Cis-1,4-
Truns- 1,4-
1,2-
975 2.6 15.2 35.3 91.8
1.2 91.7 0 49.5 5.2
1.3 5.7 84.8 15.2 3.0
method.
’ Measured
Intrhsic viscositph
Catalyst
ltsed
1.78 1.08 1.34 1.82 1.78
Reduced nickel RJAI-VCIJ RJGTi(OR)o BuLi RJAI-Ti14
at 30’ in CS2. Anal. C/h.
Actu,
56 (1971)
303-307
304
T.
SHOWO,
K.
SHINRA
EXPERIMENTAL
M ccterials Five kinds of polybutadiene were prepared by anionic pdlymerization of butadiene. Table I shows the catalyst used and the intrinsic viscosity and microstructure of the polymer. The percentage of cis-1,4-, tram-1,4and 1,2-links was determined by the infrared spectrophotometric method of Morero’ ‘. Pyrolysis and gas chronmtography To analyze the low boiling fragments, a heated furnace-type pyrolyser PYR-1A (Shimazu)’ 2 was connected to the inlet port ofa gas chromatograph (Sh,imazu GC-2C) equipped with thermal conductivity detectors. The separation column was 4.5 m long and of 3 mm i.d., and was packed with Neosorb NP (40-60 mesh) coated with 25% hexadecane. The column temperature was 40” and the flow rate of carrier gas (helium) was maintained at 22 ml min - I. A sample size of 5 mg was used (Fig. 1).
+ . -. lYYTL l
--me
5
>
Retention
Fig. 1. Pyrolysis
time
chromatogram
Retention
(min)
of 1,4-polybutadicnc
Fig. 2. Pyrolysis chromntogrnm or 1,4-polybutadicnc peak which is given only by I,4-cis-polybutadienc.
i0
((-
) and 1,2-polybutadicnc ) and 1,2-polybu~adicnc
time
_
15
(mid
(-----). (---- ); (+ ) hydrocarbon
To analyze the high-boiling pyrolysate, polybutadiene rubber was pyrolyzed previously at 4000 under nitrogen in a silica tube and an oil was collected. The separation column was 1.5 m long and of 3 mm i.d., and was packed with chromosorb W (40-60 mesh) coated with 1.5‘y0 silicone-gum SE30. The column temperature was programmed from 80° to 140° at the rate of 4” min- ’ and the flow rate of carrier gas (helium) was maintained at 50 ml min-’ at 80s (Fig. 2). To identify the characteristic hydrocarbon peak shown in Fig. 2, the Shimazu fraction collector was used. The column was 1.5 m long and of 10 mm id., and was packed with chromosorb W (60-80 mesh) coated with 20”/, silicone-gum SE30. The column temperature was maintained at 150° and the flow rate. of carrier gas (helium) was maintained at 250 ml min - I. The fractionated hydrocarbon was analyzed by n.m.r. and mass spectromctry. I
DISCUSSION
Perry’s relationship lo isnot linear for a high concentration ofthe 1,2-structure. This is believed to be due to the fact that the peak areas of ethylene and butadiene are both variables. As shown in Fig. 1, 1,4-polybutadiene and 1,2_polybutadiene can be Anal. Chim. Actn. 56 (1971) 303-307
MICROSTRUCTURE
OF
305
POLYBUTADIENE
differentiated by the butadiene peak (peak no. 6) and the characteristic peak of 1,2polybutadiene (peak no. 12). For this pyrogram, operational conditions in which the cis form and trans form were the least differentiated, were selected. The characteristic peak of 1,2-polybutadiene presumably is a methylbutene, the structure of which so far has not been identitied. Figure 2 shows that there exists a hydrocarbon peak which is given only by 1,4-cis polybutadiene. The relationship between the area of the butadiene peak (peak no. 6, Fig. 1) and the pyrolysis temperature of various polybutadiene rubbers is shown in Fig. 3. No difference in the peak areas of the butadiene peak (peak no. 6) for cis-1,4-polybutadiene and trans-1,4-polybutadiene was noticed at 700’. With a view to obtaining the relationship between peak area and total 1,4-content, the optimal pyrolysis temperature was set at 700”. Figure 4 shows the analytical results obtained by p.g.c. against the total 1,4-structure content by i.r. analysis. The peak area (mm”) of the butadiene peak (peak no. 6) and the peak height (mm) of the characteristic peak of 1,2-polybutadiene (peak no. 12) are plotted as ordinates and the content of 1,4linkage as abscissa.
400
-
200
600
700 Pyrolysis
Fig.
3. The
1.4;
(0)
relationship
800
ternperatw&
between
1
the peak area of peak 6 and pyroiysis
I
I
I
1
20
40
60
60
Total
l&structure
tcmpcruturc.
conrent
(0)
his-1.4;
(0)
frtrtts-
12.
Fig. 4. Anulytical
results
obtained
by p.g.c.
The fractionated hydrocarbon peak which is given only by the 1,4-cis form of polybutadiene was analyzed by mass spectrometry. The mass spectrum showed the parent peak at 220 which is the tetramer of butadiene. The molecular formula C1 (iH28 tits the data for the parent peak and P+ 1 peak. The pattern coefficient and retention time are in fair agreement with the authentic perhydrodimethylphenanthrene. The catalytic hydrogenation of this hydrocarbon failed in absolute ethanol with PtO, as catalyst. This means that the hydrocarbon is a saturated hydrocarbon. The n.m.r. spectrum provides conclusive confirmation for a saturated aliphatic hydrocarbon ; it shows methyl hydrogens at z= 9.1 and methylene (or methine) hydrogens at z = 7.6-9.0. Atal. Chirn.
Acta,
56 (1971) 303-307
306
T. SHQNO,
K. SHINRA
The ratio between methyl and methylene (me+hine) peak areas was 3 : 11. The polydiene ladder-type polymers are known to be prepared by polymerization of diene with complex catalysts, followed by cyclization’3 - 15.
.=s_,= C----c
---m___
-
The precursor of the final conjugated ladder-type polymer presumably contains fused cyclohexane ring. From these facts, the C16HZ8 hydrocarbon is concluded to be 1,8-dimethylperhydrophenanthrene.
0
100
cis-1.4~Structure(%)
peitk and cis-I,4 Fig. 5. The relationship bctwccn the peak urea of CIf,1-Iz8 hydrocarbon standard samples (1,2,3,5); (0) mixture of 1,4- and 1,2- forms: (a) standard siunplc (4).
content.
(0)
In Fig. 5 the peak area of Clc,H 213hydrocarbon is plotted as ordinate and the cis 1,4-content as abscissa. The fact that the point of sample 4 (on Fig. 5) deviates from the curve means that the microstructure of this sample differs from the other four samples. As shown in Table I, sample 4 was prepared with butyllithium as catalyst. The very low value of the CIbHZ8 peak compared with the others means that the percentage of the unit connecting four c&1,4 links (c&1,4 tetrad) is undoubtedly low. SUMMARY
Pyrolysis-*gas chromatographic studies iire presented for 1,4-cis-, 1,4-tramand 1,Spolybutadiene. 1,4_Polybutadieneand 1,2-polybutadiene can bedifferentiated by the butadiene peak in the 1,4-polybutadiene pyrogram and a characteristic peak of 1,2_polybutadiene pyrogram. We found that. there exists a hydrocarbon peak believed to be 1,8-dimethylperhydrophenanthrene, which is given only by 1,4-cispolybutadiene. RfiSUMfZ
Une Ctude est effectuCe sur la dktermination de la microstructure des polybutadi6nes (1,4-cis-, 1,4-trans- et 1,2-) par chromatographie gazeuse pyrolytique. Le Anal. Claim. Acta,
56 (1971) 303-307
MICROSTKUCTURE
OF
307
POLYBUTADIENE
p’olybutadiene-1.4 peut Ctre differencie du polybutadiene-1.2 par des pits caracteristiques des pyrogrammes obtenus. On decele un pit hydrocarbure (le dimethyl-l,Sperhydrophenanthrene) donne seulement par le cis-polybutaditne-1,4. ZUSAMMENFASSUNG
1,4-d-, 1,4-transund 1,2_Polybutadien wurden der Pyrolyse-Gaschromato1.4-Polybutadien und 1,2-Polybutadien kiinnen durch den graphie unterworfen. Butadien-Peak im 1,4-Polybutadien-Pyrogramm und einen charakteristischen Peak des 1,2-Polybutadien-Pyrogramms unterschieden werden. Es wurde ein Kohlenwasserstoff-Peak festgestellt, der 1,8-Dimethylperhydrophenanthren zugeschrieben und nur bei 1.4-cis-Polybutadien erhalten wird. REFERENCES I
2 3 4 5 6 7 8
9 IO 1I
12 13 I4
15
K. J. BoMRAUCjtt. C. E. CO<)K ANI> B. H. CLAhtWTT. A~uI/. C/lC!?l., 35 (1963) J. VAN Sct-I00’rEN ANU J. K. EVENIILJIS. Po/.vrmr. 6 (I 965) 561. L. hdICtiAJl_OV. P. ZUCJENMAIER AND H. J. CANTCIW, Po/yrmr, 9 (1968) 325. D. DEUH-SIPTAR ANI> V. Svon, J. C’/trorrru/o~~., 5 I (1970) 59. C. E. R. JONES AND G. E. J. REYNOLDS, Brir. fdyrrtcr J.. I (1969) 197.
1834.
S. Tsuoe. T. CXur.x~ro ANI> T. TAKEUCI~I, hfakronrol. Chem.. I 23 ( 1969) I23 : Mrrc~rantok~~c~ltlPs. 2 (1969) 200. 277. I-1. ITO, S. TSUCX, T. OKUMC)TO AND T. TAKEUCI.II, Makrotnof. Cfrcwr.. I38 (1970) I I I. M. VAC~ISROT, J. Gas Cfrrornatogr.. 5 (1967) 155. M. J. MAcKATttoRN ANI) M. J. BROCK, Pu/~n?rc!r Letr.. 8 (1970) 61 7. S. G. P~?RRY, J. Gas Chromatogr.. 5 (1967) 77. D. MORERO. Makronrol. Cfwnr., 61 (1963) 250. T. NAKACJAWA, K. MIYAJIMA AND T. UNO. J. Clrromutq~r. Sci., 8 (1970) 261. N. G. GAYLORI). I. KOSSLER, M. S’rot.tiA AND J. VCIIXWNAL. J. Polyrm~r Sci.. A.2 (1964) 3969. M. S’roLKA, J. V~~XIINAI. ANII I. K~SSI.ER. J. f+~/_wrrr Sci.. A.2 (1964) 3987. F. T. WALLt!NHEROER, /Inqe~. C/WI.. 76 (1964) 484.
Atrcrl. Clrittl.
Acta.
56 (1971)
303-307
C/rin1lru
Aetu
303
Elscvicr Publishing C’ompuny. Amsterdam Printed in The Ncthcrlnnds
DETERMINATION POLYBUTADIENE
AND
T. SHONO
K. SHINRA
a/’ Applied Chemistry,
Department (Received
OF THE MICROSTRUCTURE OF BY PYROLYSIS-GAS CHROMATOGRAPHY
24th February
Osuku
University,
Suitu,
Osuku
565
(Jupun)
1971)
There have recently been rapid developments in the identilication of polymers by gas chromatography oftheir pyrolysis products. As well as providing a convenient means of identifying polymers, pyrolysis-gas chromatography (p.g.c.) affords the possibility of investigating their microstructure’ - 5. Recently, Takeuchi et aL6-’ investigated the sequence concentration of triad in vinylidene chloride-vinyl chloride copolymers and the distribution of the chlorine atoms in the chain of various chlorinated synthetic polymers by means of p.g.c. In this paper an attempt is made to determine quantitatively the microstructure of polybutadiene. Polybutadiene can be classified into 1,4 and 1,2 structures. The former shows cis and tram forms and the latter has different tacticities. The progress of synthetic polymer chemistry has made it possible to produce polymers that are rich in only one of these microstructures. Vacherot”, who made a structure elucidation of polyisoprene by p.g.c., found that polyisoprene produced by 3,4-addition is characterized by a hydrocarbon peak between the peaks of isoprene and dipentene which is not given by polyisoprene produced by 1,4-addition. He reported also that the peak area ratio of this hydrocarbon and dipentene is proportional to the ratio of the 1,4-type and the 3,4-type and that this provides a method for determining the ratio of the two types in the synthetic polyisoprenes. Recently, Hackathorn and Brockg have examined the d’imer pyrolysis fractions of several polyisoprenes. These larger fragments may retain certain microstructural features and provide information about polymer chain degradation . mechanisms. Perry lo did similar research on polybutadiene and studied the peak area ratio of ethylene and butadiene against the ratio of the 1,2- and the 1,4-species. TABLE ANALYSIS
I 01: MICROSTRUCTURE.5
Code
1 2 3 4 5 a By Morero
Microstructtrre’
OF STANDARD
SAMPLE!5
(“/,)
Cis-1,4-
Truns- 1,4-
1,2-
975 2.6 15.2 35.3 91.8
1.2 91.7 0 49.5 5.2
1.3 5.7 84.8 15.2 3.0
method.
’ Measured
Intrhsic viscositph
Catalyst
ltsed
1.78 1.08 1.34 1.82 1.78
Reduced nickel RJAI-VCIJ RJGTi(OR)o BuLi RJAI-Ti14
at 30’ in CS2. Anal. C/h.
Actu,
56 (1971)
303-307
304
T.
SHOWO,
K.
SHINRA
EXPERIMENTAL
M ccterials Five kinds of polybutadiene were prepared by anionic pdlymerization of butadiene. Table I shows the catalyst used and the intrinsic viscosity and microstructure of the polymer. The percentage of cis-1,4-, tram-1,4and 1,2-links was determined by the infrared spectrophotometric method of Morero’ ‘. Pyrolysis and gas chronmtography To analyze the low boiling fragments, a heated furnace-type pyrolyser PYR-1A (Shimazu)’ 2 was connected to the inlet port ofa gas chromatograph (Sh,imazu GC-2C) equipped with thermal conductivity detectors. The separation column was 4.5 m long and of 3 mm i.d., and was packed with Neosorb NP (40-60 mesh) coated with 25% hexadecane. The column temperature was 40” and the flow rate of carrier gas (helium) was maintained at 22 ml min - I. A sample size of 5 mg was used (Fig. 1).
+ . -. lYYTL l
--me
5
>
Retention
Fig. 1. Pyrolysis
time
chromatogram
Retention
(min)
of 1,4-polybutadicnc
Fig. 2. Pyrolysis chromntogrnm or 1,4-polybutadicnc peak which is given only by I,4-cis-polybutadienc.
i0
((-
) and 1,2-polybutadicnc ) and 1,2-polybu~adicnc
time
_
15
(mid
(-----). (---- ); (+ ) hydrocarbon
To analyze the high-boiling pyrolysate, polybutadiene rubber was pyrolyzed previously at 4000 under nitrogen in a silica tube and an oil was collected. The separation column was 1.5 m long and of 3 mm i.d., and was packed with chromosorb W (40-60 mesh) coated with 1.5‘y0 silicone-gum SE30. The column temperature was programmed from 80° to 140° at the rate of 4” min- ’ and the flow rate of carrier gas (helium) was maintained at 50 ml min-’ at 80s (Fig. 2). To identify the characteristic hydrocarbon peak shown in Fig. 2, the Shimazu fraction collector was used. The column was 1.5 m long and of 10 mm id., and was packed with chromosorb W (60-80 mesh) coated with 20”/, silicone-gum SE30. The column temperature was maintained at 150° and the flow rate. of carrier gas (helium) was maintained at 250 ml min - I. The fractionated hydrocarbon was analyzed by n.m.r. and mass spectromctry. I
DISCUSSION
Perry’s relationship lo isnot linear for a high concentration ofthe 1,2-structure. This is believed to be due to the fact that the peak areas of ethylene and butadiene are both variables. As shown in Fig. 1, 1,4-polybutadiene and 1,2_polybutadiene can be Anal. Chim. Actn. 56 (1971) 303-307
MICROSTRUCTURE
OF
305
POLYBUTADIENE
differentiated by the butadiene peak (peak no. 6) and the characteristic peak of 1,2polybutadiene (peak no. 12). For this pyrogram, operational conditions in which the cis form and trans form were the least differentiated, were selected. The characteristic peak of 1,2-polybutadiene presumably is a methylbutene, the structure of which so far has not been identitied. Figure 2 shows that there exists a hydrocarbon peak which is given only by 1,4-cis polybutadiene. The relationship between the area of the butadiene peak (peak no. 6, Fig. 1) and the pyrolysis temperature of various polybutadiene rubbers is shown in Fig. 3. No difference in the peak areas of the butadiene peak (peak no. 6) for cis-1,4-polybutadiene and trans-1,4-polybutadiene was noticed at 700’. With a view to obtaining the relationship between peak area and total 1,4-content, the optimal pyrolysis temperature was set at 700”. Figure 4 shows the analytical results obtained by p.g.c. against the total 1,4-structure content by i.r. analysis. The peak area (mm”) of the butadiene peak (peak no. 6) and the peak height (mm) of the characteristic peak of 1,2-polybutadiene (peak no. 12) are plotted as ordinates and the content of 1,4linkage as abscissa.
400
-
200
600
700 Pyrolysis
Fig.
3. The
1.4;
(0)
relationship
800
ternperatw&
between
1
the peak area of peak 6 and pyroiysis
I
I
I
1
20
40
60
60
Total
l&structure
tcmpcruturc.
conrent
(0)
his-1.4;
(0)
frtrtts-
12.
Fig. 4. Anulytical
results
obtained
by p.g.c.
The fractionated hydrocarbon peak which is given only by the 1,4-cis form of polybutadiene was analyzed by mass spectrometry. The mass spectrum showed the parent peak at 220 which is the tetramer of butadiene. The molecular formula C1 (iH28 tits the data for the parent peak and P+ 1 peak. The pattern coefficient and retention time are in fair agreement with the authentic perhydrodimethylphenanthrene. The catalytic hydrogenation of this hydrocarbon failed in absolute ethanol with PtO, as catalyst. This means that the hydrocarbon is a saturated hydrocarbon. The n.m.r. spectrum provides conclusive confirmation for a saturated aliphatic hydrocarbon ; it shows methyl hydrogens at z= 9.1 and methylene (or methine) hydrogens at z = 7.6-9.0. Atal. Chirn.
Acta,
56 (1971) 303-307
306
T. SHQNO,
K. SHINRA
The ratio between methyl and methylene (me+hine) peak areas was 3 : 11. The polydiene ladder-type polymers are known to be prepared by polymerization of diene with complex catalysts, followed by cyclization’3 - 15.
.=s_,= C----c
---m___
-
The precursor of the final conjugated ladder-type polymer presumably contains fused cyclohexane ring. From these facts, the C16HZ8 hydrocarbon is concluded to be 1,8-dimethylperhydrophenanthrene.
0
100
cis-1.4~Structure(%)
peitk and cis-I,4 Fig. 5. The relationship bctwccn the peak urea of CIf,1-Iz8 hydrocarbon standard samples (1,2,3,5); (0) mixture of 1,4- and 1,2- forms: (a) standard siunplc (4).
content.
(0)
In Fig. 5 the peak area of Clc,H 213hydrocarbon is plotted as ordinate and the cis 1,4-content as abscissa. The fact that the point of sample 4 (on Fig. 5) deviates from the curve means that the microstructure of this sample differs from the other four samples. As shown in Table I, sample 4 was prepared with butyllithium as catalyst. The very low value of the CIbHZ8 peak compared with the others means that the percentage of the unit connecting four c&1,4 links (c&1,4 tetrad) is undoubtedly low. SUMMARY
Pyrolysis-*gas chromatographic studies iire presented for 1,4-cis-, 1,4-tramand 1,Spolybutadiene. 1,4_Polybutadieneand 1,2-polybutadiene can bedifferentiated by the butadiene peak in the 1,4-polybutadiene pyrogram and a characteristic peak of 1,2_polybutadiene pyrogram. We found that. there exists a hydrocarbon peak believed to be 1,8-dimethylperhydrophenanthrene, which is given only by 1,4-cispolybutadiene. RfiSUMfZ
Une Ctude est effectuCe sur la dktermination de la microstructure des polybutadi6nes (1,4-cis-, 1,4-trans- et 1,2-) par chromatographie gazeuse pyrolytique. Le Anal. Claim. Acta,
56 (1971) 303-307
MICROSTKUCTURE
OF
307
POLYBUTADIENE
p’olybutadiene-1.4 peut Ctre differencie du polybutadiene-1.2 par des pits caracteristiques des pyrogrammes obtenus. On decele un pit hydrocarbure (le dimethyl-l,Sperhydrophenanthrene) donne seulement par le cis-polybutaditne-1,4. ZUSAMMENFASSUNG
1,4-d-, 1,4-transund 1,2_Polybutadien wurden der Pyrolyse-Gaschromato1.4-Polybutadien und 1,2-Polybutadien kiinnen durch den graphie unterworfen. Butadien-Peak im 1,4-Polybutadien-Pyrogramm und einen charakteristischen Peak des 1,2-Polybutadien-Pyrogramms unterschieden werden. Es wurde ein Kohlenwasserstoff-Peak festgestellt, der 1,8-Dimethylperhydrophenanthren zugeschrieben und nur bei 1.4-cis-Polybutadien erhalten wird. REFERENCES I
2 3 4 5 6 7 8
9 IO 1I
12 13 I4
15
K. J. BoMRAUCjtt. C. E. CO<)K ANI> B. H. CLAhtWTT. A~uI/. C/lC!?l., 35 (1963) J. VAN Sct-I00’rEN ANU J. K. EVENIILJIS. Po/.vrmr. 6 (I 965) 561. L. hdICtiAJl_OV. P. ZUCJENMAIER AND H. J. CANTCIW, Po/yrmr, 9 (1968) 325. D. DEUH-SIPTAR ANI> V. Svon, J. C’/trorrru/o~~., 5 I (1970) 59. C. E. R. JONES AND G. E. J. REYNOLDS, Brir. fdyrrtcr J.. I (1969) 197.
1834.
S. Tsuoe. T. CXur.x~ro ANI> T. TAKEUCI~I, hfakronrol. Chem.. I 23 ( 1969) I23 : Mrrc~rantok~~c~ltlPs. 2 (1969) 200. 277. I-1. ITO, S. TSUCX, T. OKUMC)TO AND T. TAKEUCI.II, Makrotnof. Cfrcwr.. I38 (1970) I I I. M. VAC~ISROT, J. Gas Cfrrornatogr.. 5 (1967) 155. M. J. MAcKATttoRN ANI) M. J. BROCK, Pu/~n?rc!r Letr.. 8 (1970) 61 7. S. G. P~?RRY, J. Gas Chromatogr.. 5 (1967) 77. D. MORERO. Makronrol. Cfwnr., 61 (1963) 250. T. NAKACJAWA, K. MIYAJIMA AND T. UNO. J. Clrromutq~r. Sci., 8 (1970) 261. N. G. GAYLORI). I. KOSSLER, M. S’rot.tiA AND J. VCIIXWNAL. J. Polyrm~r Sci.. A.2 (1964) 3969. M. S’roLKA, J. V~~XIINAI. ANII I. K~SSI.ER. J. f+~/_wrrr Sci.. A.2 (1964) 3987. F. T. WALLt!NHEROER, /Inqe~. C/WI.. 76 (1964) 484.
Atrcrl. Clrittl.
Acta.
56 (1971)
303-307