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Terminally reactive liquid polymers as stationary phases for gas chromatography.

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Die Angewundte Mukromolekulare Chemie 20 ( 1971) 111-119 ( N r . 278)
From the Dunlop Forschung D-6450 Hanau, Germany
Terminally Reactive Liquid Polymers as Stationary
Phases for Gas Chromatography
By H. SCHNECKO
and 0. BIEBER
(Eingegangen am 12. Miirz 1971)
SUMMARY:
Liquid column coatings for GC are described consisting of terminally difunctional
polyenes (polybutadiene, polyisoprene, SBR etc.). Separation for non-polar and
polar classes of organic compounds is remarkable. Stability of coated columns is
good, in particular after various chain extension reactions.
ZUSAMMENFASSUNG :
Es werden flussige stationare Phasen fur die Gaschromatographie beschrieben,
die aus endstandig bifunktionellen Polyenen bestehen (Polybutadien, Polyisopren,
SBR usw.). Die Trennfiihigkeit fur polare und unpolare organische Substanzklassen
ist ausgezeichnet. Die Stabilitiit der Siiulen ist gut, besonders dadurch, da5 man auf
verschiedene Weise Kettenverliingerung durchfuhren kann.
1. Introduction
Recently, we have reported on two new column materials for gas chromatographic (GC) separation :
a ) Liquid ethylene-propylene copolymers as stationary liquid phase on solid
supports1,
b) foam-filled columns in gas-solid GC-systemsz.
Both systems afforded good separation for a broad variety of compounds. I n
continuation of this program we now applied liquid polyenes with reactive
end-groups t o coat solid support material. There has been a recent German
patent Offenlegungs t o esterify OH-containing substance (oxy propio nitrile) on
silica support. The materials described here form another versatile group of
stationary phases.
111
H. SCHNECKO
and 0. BIFBER
2. Experimental
2.1 Column Preparation
2.1.1 U n c r o s s l i n k e d Liquid P h a s e
3 g of the respective liquid polymer were dissolved in 100 ml chloroform and 27 g
of chromosorb P were added. The components were mixed in a rotatory evaporator
for 1hr. followed by slow removal of the solvent with increasing vacuum a t < 70°C.
A 2 m steel column ( a 1/4 in.) was filled with the resulting powder and heated for
3 hrs. a t 200°C with N2 as carrier gas.
2.1.2 C r o s s l i n k i n g V i a D o u b l e B o n d s
The same procedure as in 2.1.1 was applied; 60 mg (2 wt.-%) of dicumyl peroxide
(Dicup) were added. This material was cured for 5 hrs. a t 170°C under Nz in the GC
oven.
2.1.3 C h a i n e x t e n s i o n V i a E n d - G r o u p s
a ) Polybutadiene (PBd) with Br-end-groups. Here, 0.38 g (12%) of either tetra
ethylene pentamine (TEPA) or tetra methyl ethylene diamine (TMEDA) were
added to the polymer solution3 and cured for 5 hrs. a t 150°C under Nz-gas.
b) Di-isocyanate chain extension of PBd with OH-end-groups. 3 g of polymer
(R-45
M) were dissolved in 120 ml benzene, then combined with 27 g Chromosorb
P and 0.25 g tolylene diisocyanate (TDI) and treated as in section 2.1.1. Alternatively, this was done in 2 consecutive steps. First the support was coated with the
polymer, then 0.5 g (0H:NCO = 1 :2; diisocyanate end-group formation) of TDIbenzene solution was added and evaporated after the mixing.
Crosslinking efficiency was determined by extracting the column material after
it had been cured with boiling chloroform.
2.2 GC-Conditions
A Perkin-Elmer F6 chromatograph was used a t various temperatures (no temperatureprogram) with a hot-wire detector. Carrier gas was H e a t 60 ml/min. Pyrolysis
was done with an electrically heated filament a t 650 "C (Pyromatic FISCHER,
Bad
Godesberg).
3. Calculations
The factors that determine the efficency of a separating column are correlated
in the van DEEMTER-GOLAY
equation by which the height equivalent of a theoretical plate (HETP) can be calculated. For practical purposes in GC a simple
equation has been developed4 1
1000 . L
HETP
112
=-
n
(1)
Liquid Polymers jor Gas Chromatography
where L
=
length of column, and n, the number of plates is given by
n
or
=
5.54.
[GI
tdr
n=l6.[$]
2
(3)
with
total retention time in see,
breadth of peak at bottom,
b/2 = half-width-breadth.
tdr =
b
=
It is clear from these eqs. that HETP values are small for large n ; in practical
applications, good GC columns are characterized by n-values of 1000-30004.
One can also calculate the capacity ratio k (= t d r / t o with to hold-up time) ;
which is used t o characterize the load capacity of a GC column; values quoted
are often r 10).
4. Results
4.1 Seprating Power for Styrene
Table 1 lists the liquid polymers used together with n- and HETP-values for
a characteristic compound, styrene, taken from an SBR-pyrogram (Fig. 9).
Various functional polyenes with or without treatment (Nos. 1-13) are compared to some wellknown commercial column fillings used for the separation of
this class of compound (Nos. 14-16). The abbreviations are self-explanatory,
e. g. PBd-(OH)Zis a liquid polybutadiene with 2 terminal OH-groups, PI-polyisoprene etc.
Obviously, all the liquid functional polymers are efficient stationary phases
with n > 1000 and HETP < 2. In particular, Nos. 2,3,7,9,12and 13 show high
plate numbers (- 2000), i. e. some of the hydroxy-terminated polybutadienes
and nitrile rubbers (Sinclair) as well as the dibromo polybutadiene (Polymer
Corp.) after amine treatment.
With respect t o the amount of polymer required to give the highest n-value,
Fig. 1 shows a maximum between 5 - 1 0 ~ t . - 7for
~ PBd(0H)z; in general,
10 wt.-y0 were applied.
It should be added that all n-values of Table 1 will be slightly increased if
styrene is injected as a monomer; in our set-up, the pyrolysis time (10-15 see)
causes some band-broadening (- 10%). The k-value for styrene injected
comes out to 27 which can be considered as very good.
4.2. Chain Extension, Crosslinking
I n the last column of Table 1, some information on effectiveness of crosslinking as described in sections 2.1.2 and 2.1.3 is given. Peroxide crosslinking
113
Polysar
Polysar
Polysar
Perk. El.
Perk. El.
Perk. El.
R-15 M
CS-15
CN-15
ZL-452
HC-434
HycarMTBN
DBPB
DBPB
DBPB
C
K
AL
5
6
7
8
9
10
11
12
13
14
Thiokol
Thiokol
Goodrich
* For abbreviatioiis cf. Section 2.1
15
16
Sinclair
Sinclair
Sinclair
Sinclair
R-45 M
R-45 M
R-45 M
R-45 M
1
2
3
4
Sinclair
Sinclair
Sinclair
Source
1
Polyene
No.
Silicon
PE glyk.
Apiezon
PBd Brz
PBd Brz
PBd Brz
NBR(C0OH)z
PBd(CO0H)z
PBd(SH)z
PBd-(0H)z
SBR(0H)z
NBR(0H)z
PBd-(OH)Z
PBd-(0H)z
PBd-(0H)z
PBd-(OH)z
Comp .
OH-
42
42
39
45
45
45
45
numb.
3 200
3 200
2 500
3 100
3 200
3 200
3500
2 800
2 800
2800
2 800
MIl
770
1210
645
1085
2 070
1950
1740
2 050
1750
1800
1180
1960
2.7
1.66
3.1
1.84
0.97
1.02
1.15
0.97
1.14
1.02
1.11
1.7
1.18
0.99
0.95
1.60
Styrene
HETP
1700
2 005
2 110
1250
n
10% TMEDA (> 80)
10% TEPA (> 70)
(> 80)
2y0 Dicup (5)
0.2 g TDI (11)
0.5 g TDI (> 80)
crosslinking *
Wlubility, %)
Liquid Polymers #or Gas Chromatography
In
I
I
5
10
-
15
20
w t 'I. coating
Fig. 1.
Number of plates (n) for styrene as a function of surface coating with
R-45-M; 100°C.
and diisocyanate are very efficient whereas amine treatment does not decrease
solubility to a large extent; in spite of this, separation is considerably improved
for the latter system (Nos. 12, 13 vs. 11). Interestingly, isocyanate capping
(2-step reaction, cf. section 2.1.3) decreases the properties of the material: reaction with higher molar ratios of NCO : OH (No. 4) gave no improved n-values; as expected, the material was still largely soluble in chloroform.
The temperature stability of the Dicup-crosslinked material was very good :
no peaks or drifts were observed a t 280°C for 24 hrs.
4.3 Separation for Various Substances
Figs. 2-5 show a selection of isothermal chromatograms made with column
filling No. 2 of Table 1. I n all cases sharp and narrow peaks are observed.
Water and acetic acid are not included because some tailing is observed and
solid columns (e. g. foam fillingsz) are to be preferred.
As a rule, non-polar substances are separated according to their boiling
points (Fig. 2); isomer separation in case of olefins (Fig. 4) is satisfactory;
c-hexane and benzene with a bp-difference of 0.7"C are separated (Fig. 5 ) a t
this relatively high column temperature of 150 "C.
For polar compounds electronic requirements and polar interaction may be
dominant (cf. Fig. 6, methyl cellosolve bp 125 "C - dioxane bp 101 "C, or butane
diol bp 235 "C - benzyl alcohol bp 205 "C).
115
H. SCHNECKO
and 0. BIEBER
Fig. 2.
Gas chromatogram of
c6-c16hydrocarbons a t
200°C.
0
min.
Fig. 3.
20
15
10
5
0
Gas chromatogram of Ketones a t 100°C;
1 acetone
5 3-heptanone
2 pentanone
6 2-octanone
3 2-butanone
7 acetophenone.
4 2.4-dimethyl-3-pentanone.
The material can also be used t o detect pyrolysis products of polymers, cf.
Fig. 7-9. SRB-pyrogram (Fig. 9) is unmatched by any other column.
116
Fig. 4.
Gas chromatogram of olefins a t 75 "C ;
4 3-heptene
1 2 -methyl-2 - butene
5 2.4.4.-trimethyl-2-pentene
2 4-methyl-1-pentene
6 2-ethyl-1-hexene.
3 2-hexene
Q
Fig. 5.
Gas chromatogram of aromates and cycloaliphatics at 150°C;
1 c-hexane
5 o-xylene
6 trans-decalin
2 benzene
7 cis-decalin.
3 toluene
4 m-xylene
P
I
min 15
Fig. 6.
I
10
k
b
Gas chromatogram of ethers and alcohols at 150OC;
1 ether
5 i-amyl ether
6 1.4-butanediol
2 methyl cellosolve
7 benzyl alcohol.
3 dioxane
4 butyl acetate
117
H. SCHNECKO
and 0. BIEBER
Fig. 7.
Pyrolysis gas chromatogram of nylon 6 a t 100°C.
Fig. 8.
Pyrolysis gas chromatogram of nylon 6,6 a t 100°C.
min
Fig. 9.
118
20
15
10
5
Pyrolysis gas chromatogram of Buna 150 (SBR) at 100°C.
0
Liquid Polymers for Gas Chromatography
5 . Conclusions
The liquid polyenes form interesting stationary phases for GC. Good results
are obtained in the separation of a variety of different substances. Fixation by
reaction with the double bonds of the polymer backbone or with the end-groups
does improve the efficiency to a certain extent. In this sence, the effect and the
importance of the end-groups is not quite clear. Presently, corresponding liquid
polyisoprenes are synthesized with and without OH-functionality. Likewise,
the effect of mol. wt. with respect to separating properties will be checked. I n
case of the urethane formation, chain extension appears to be advantageous
whereas prepolymer formation (NCO: OH = 2) is not successful. However, it
could also be possible that the reaction with the diisocyante is not possible
once the polymer is adsorbed a t the surface of the support. It might be speculated that the polar OH-end-groups interact with the solid surface so that
they are not fully available for condensation reactions. Support from IRspectra (OH-shift etc.) cannot be obtained and more detailed investig.ations
using refined techniques would be required to clarify this point.
Although the low volatility of the polyenes does in itself foster stability a
particular advantage of the new column material can be seen in the fact that
the coating can be insolubilized on the support by peroxide crosslinking or
urethane formation, thus providing a stable, non-bleeding phase with improved
separation power.
1
2
3
4
0. BIEBER,G. DEGLER
and H. SCHNECKO,
J. Chromatogr. Sci. 10 (1969) 591.
0. BIEBERand H. SCIINECKO,
Chromatographia 4 (1971) 109.
F.P. 1 488 811 and DOS. 1 908 576, Sept. 18. 1969. Polymer Corp., Inv.: D. C.
EDWAXDS
and P. N. LEWIS.
R. KAISER,
,,Chromatographie in der Gasphase", Vol. 1, Bibliograph. Inst.itut,
Mannheim 1960, p. 50.
DOS. 1 902 226, July 23. 1970, Inv.: I. HALASZ.
119
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