close

Вход

Забыли?

вход по аккаунту

?

950

код для вставкиСкачать
Polymer International 45 (1998) 285È290
2-Vinylpyridine-co -N -vinyl-2-pyrrolidone
and 4-Vinylpyridine-co -N -vinyl-2pyrrolidone Copolymers: Synthesis and
Reactivity Ratios
Nicola s Gatica, Ligia Gargallo & Deodato Radic *¤
Departamento de Qu• mica-F• sica, Facultad de Qu• mica, PontiÐcia Universidad Catolica de Chile, Casilla 306, Correo 22,
Santiago, Chile
(Received 14 July 1997 ; accepted 8 October 1997)
Abstract : Copolymers containing 2-vinylpyridine (2VPy) and 4-vinylpyridine
(4VPy) with N-vinyl-2-pyrrolidone (VP) (2VPy-co-VP and 4VPy-co-VP,
respectively) were synthesized and characterized. Copolymers with di†erent compositions were obtained. The reactivity ratios were estimated by using the classical FinemannÈRoss and Kelen TuŽdos linear procedures. These parameters were
also estimated by using a computer program based on a non-linear minimization
algorithm (NLMA), starting from the values of r and r obtained by the above
1
2
linear procedures. Random copolymers with zones
containing
vinylpyridine
blocks were obtained. ( 1998 SCI.
Polym. Int. 45, 285È290 (1998)
Key words : copolymers ; N-vinyl-2-pyrrolidone ; 2-vinylpyridine ; 4-vinylpyridine ;
linear Ðtting methods ; non-linear Ðtting methods ; monomer reactivity ratios
Copolymers containing hydrophilic units are important
for compatibility in polymer blends. These copolymers
show strong interactions with one another, which give
rise to miscibility.
Increasing attention is currently being directed to the
synthesis of copolymers containing both hydrophilic
and hydrophobic segments.2 Copolymers with variable
amounts of both types of structure can be considered a
good model for cell-substrate interactions, mainly
because of the possibility of producing a chemically
homologous series of surfaces varying principally in
hydrophilicity.3 The solution behaviour should be inÑuenced by the ratio of the di†erent segments present in
the copolymer. These systems are important in a wide
variety of processes.3
Copolymerization reactions between hydrophilic and
hydrophobic monomers are rather difficult, because of
the di†erent solution behaviour of the monomers. In
INTRODUCTION
Most polymers are incompatible with one another, so
that most binary polymer blends are two-phase
systems.1 It is well known that miscibility in polymer
blends is usually the result of favourable exothermic
interactions between the components of the blend,
which can be promoted, rejecting dissimilar structures.
In order to ensure miscibility, it is necessary to match
polymer repeat units carefully, or to ensure that favourable speciÐc interactions can exist between the chains.
* To whom all correspondence should be addressed.
¤ e-mail : dradic=lascar.puc.cl
Contract/grant sponsor : Fondecyt.
Contract/grant number : Project 8970011.
Contract/grant number : Project 2960022.
Contract/grant sponsor : Catedra Presidencial en ciencias Ï95.
285
( 1998 SCI. Polymer International 0959È8103/98/$17.50
Printed in Great Britain
N. Gatica, L . Gargallo, D. Radic
286
EXPERIMENTAL
Monomer purification
Scheme 1
fact, di†erences in the monomer reactivity ratios are
observed for some of these systems depending on the
polarity of the solvent used in the copolymerization
process.2 Aggregation through hydrogen bonding,
because of the opposite nature of the comonomers,
cannot be disregarded.
Copolymers containing the N-vinyl-2-pyrrolidone
(VP) moiety are very common because of the solubility
of the parent homopolymer, poly(N-vinyl-2-pyrrolidone) (PVP),4h7 in a wide range of solvents. Copolymers of N-vinyl-2-pyrrolidone with certain functional
monomers also have general solvent compatibility, and
some of these polymers may be useful for the preparation of copolymer supports.8 Copolymers containing
2-vinylpyridine (2VPy) and/or 4-vinylpyridine (4VPy)
are frequently used in order to insert interacting basic
groups into di†erent polymer chains. The combination
of N-vinyl-2-pyrrolidone with 2-vinylpyridine or 4vinlypyridine through a copolymerization process is a
way to obtain amphiphilic copolymers which, depending on the composition, should be able to interact with
polar and non-polar systems.
The abnormal light scattering behaviour of copolymers of 2VPy with VP is very well known and it has
been demonstrated that this anomalous behaviour is
due to intermolecular interactions.9 Therefore these
types of copolymers could be classiÐed as strong interacting materials. It should be interesting, therefore, to
characterize these polymers with relation to the interacting units sequence, which could inÑuence the blending behaviour signiÐcantly.
VP-2VPy (or 4VPy) copolymers are of particular
interest for studying compatibility with polymers
bearing hydrogen donor functions, because of the presence of basic units such as vinylpyridine, along the
macromolecular chain. It is of particular interest to
study possible interpolymer complex formation via
hydrogen bonding, where VP-2VPy (or 4VPy) moieties
could participate.
The aim of the present work was the synthesis, characterization and the estimation of the monomer reactivity ratios of copolymers of 2VPy with VP (2VPy-coVP) and 4VPy with VP (4VPy-co-VP) (see Scheme 1) in
order to obtain copolymers with well deÐned
hydrophilic/hydrophobic ratios. The monomer reactivity ratios were determined following the classical linear
Ðtting methods and also using procedures based on the
statistically valid error-in-variables model, following a
non-linear minimization algorithm (NLMA). In this
way it has been possible to analyse the type of interactions involved in these systems.
Commercial samples of 2-vinylpyridine, 4-vinylpyridine
and N-vinyl-2-pyrrolidone from Aldrich were distilled
under vacuum before copolymerization.
Copolymer preparation
Copolymerizations of the monomers were carried out in
bulk at 323 K under nitrogen, a,a@-axobisisobutyronitrile (AIBN) (0É1 mol%) as initiator. The monomer
feed ratio was varied in a series of copolymerizations of
both comonomers. Polymerization time was varied
from 30 min to 2 h and the conversion of monomer to
polymer was always about 10%. PuriÐcation of the
copolymers was achieved by dissolution in ethanol and
precipitation with petroleum benzin. Copolymer
samples were dried in vacuum at 298 K.
Copolymer characterization
Copolymers were characterized by 1H NMR in a
Bruker AC-200 spectrometer using tetramethylsilane
(TMS) as an internal standard and deuterated chloroform as solvent. FTIR spectra in KBr, were recorded
using a Bruker IFS 25 instrument.
Viscosity measurements in ethanol at 298 K were
carried out with a DesreuxÈBischo† dilution
viscometer10 with negligible kinetic energy corrections.
Intrinsic viscosity [g] was determined according to the
SolomonÈGotessman relationship.11
Compositions of the copolymers were determined by
UVÈvis measurements in ethanol and methanol for
2VPy-co-VP and 4VPy-co-VP copolymers, respectively,
using a calibration curve. A Perkin-Elmer Lambda 3-B
spectrophotometer was used.
RESULTS AND DISCUSSION
The solubility of 2VPy-co-VP and 4VPy-co-VP copolymers in several organic solvents and water was tested at
room temperature. The results are shown in Table 1.
The determination of the copolymer composition was
achieved by UVÈvis analysis, following the variation of
the absorption of the maximum of the corresponding
vinylpyridine with composition using a calibration
curve. Spectra were registered at 263 nm for 2VPy-coVP and 256 nm for 4VPy-co-VP, respectively. Compositions in the feed and the resulting copolymers are compiled in Table 2. Intrinsic viscosities [g] in ethanol at
298 K for unfractionated copolymers of Ðve di†erent
compositions are also summarized in Table 2 : [g]
values should be very useful in estimating qualitatively
the degree of polymerization.
POLYMER INTERNATIONAL VOL. 45, NO. 3, 1998
V inylpyridineÈvinylpyrrolidone copolymers
287
TABLE 1. Solvents and non-solvents for 2VPy-co -VP and 4VPy-co -VP copolymers
Solvent
d
(cal cmÉ3)1@2
Methanol
Ethanol
n -Propanol
n -Butanol
Acetone
Chloroform
THF
1,4-Dioxane
Toluene
Benzene
Chlorobenzene
Cyclohexane
Petroleum Benzine
Water
14·5
12·7
11·9
13·6
9·9
9·3
9·1
10·0
8·9
9·2
9·5
8·2
—
23·4
2VPy-co -VP
2VPy in copolymer (mol%)
4VPy-co -VP
4VPy in copolymer (mol%)
48·99
71·17
96·74
38·84
73·15
92·64
½
½
½
½
½/É
½
½
½/É
É
É
É
É
É
É
½
½
½
½
É
½
½
½/É
É
½/É
É
É
É
É
½
½
½
½
É
½
½
½
É
½
½/É
É
É
É
½
½
½
½/É
É
½
É
É
É
É
É
É
É
É
½
½
½/É
½/É
É
½
É
É
É
É
É
É
É
É
½
½
½/É
½/É
É
½
É
É
É
É
É
É
É
É
½, Soluble ; É, insoluble ; ½/É, partially soluble.
The structure and comonomer sequence are directly
related to the intramolecular interactions between
unlike units of the copolymer, and these interactions
inÑuence both short range and long range interactions.
For this reason, it is important to know the distribution
and the proportions of the comonomer units involved
in the copolymer. In order to characterize the copolymers, it is necessary to estimate the comonomer distribution (sequence) ; this can be performed through
knowledge of the monomer reactivity ratios (MRR).
Straight-line intersection methods12,13 for the determination of MRR arise from an approximation of the
TABLE 2. Composition in the feed (M ), copolymer
1
composition (dM ) and intrinsic viscosity [ g ] in
1
ethanol at 298 K, for 2VPy-co -VP and 4VPy-co -VP
copolymers
Copolymer
2VPy-co -VP
4VPy-co -VP
VPy (mol%)
In feed
In copolymer
20
40
50
60
80
20
40
50
60
80
48·99
79·58
71·17
88·67
96·74
38·84
69·57
73·15
84·51
92·64
ÍiË (dl gÉ1)
1·05
1·12
1·55
1·96
2·59
1·65
2·63
3·96
3·95
4·54
POLYMER INTERNATIONAL VOL. 45, NO. 3, 1998
instantaneous copolymer composition equation :
d[M ] [M ] (r [M ] ] [M ])
1 \
1 1 1
2
(1)
d[M ] [M ] (r [M ] ] [M ])
2
2 2 2
1
following a procedure which allows one to obtain a
straight line from which r and r can be estimated from
1
2
the slope and intercept. Equation (1) is applied only for
low conversions, which is the main difficulty in determining MRR. It is important to take into account that
linear methods do not consider the implicit errors in the
variables involved for the determination of MRR.
Nevertheless, this kind of method is a powerful tool, as
a Ðrst approximation, to obtain MRR. It should be of
great interest to compare MRR using both linear and
non-linear methods, such as those in this work. Nonlinear methods are nowadays most usually based on the
statistically valid error-in-variables model (EVM), or on
its modiÐcations.14h16 These methods allow us to take
properly into account all the sources of experimental
error. No groups of variables are considered to be independent and free of error, or dependent on constant
eror. Likewise, the non-linear computational method
needs, as starting values, good initial monomer reactivity ratios, although these values come from straightline intersection methods such as those of Fineman and
Ross12 or Kelen and TuŽdos,13 which could be considered as statistically invalid.14h16
Reactivity ratios were determined by the least squares
method according to Fineman and Ross12 (FR) by
plotting G against F (FR method) according to the
1
equation :
G \ Fr [ r
1
2
(2)
N. Gatica, L . Gargallo, D. Radic
288
and plotting (G/F) against F~1 (FR method), accord2
ing to :
copolymer, deÐned as :
g\
G
\ [ r F~1 ] r
2
1
F
(3)
x(y [ 1)
y
and
m\
F
a]F
(7)
a \ (F F )1@2
(8)
l h
where F and F are the lowest and highest values of F,
l
h
respectively.
By plotting the g values calculated from experimental
data as a function of m, straight lines are obtained,
which extrapolated to m \ 0 and m \ 1, giving [(r /a)
2
and r (both as intercepts). This change of variables
1
used by Kelen and TuŽdos13 allows a better distribution
of the points along the gÈm axes to be obtained. Figure
1 (A and B) represents the FR and KT plots for 4VPyco-VP as an example of this kind of representation.
Similar plots are obtained for all the copolymer systems
studied with correlations R2 of up to 0É970.
Table 3 summarizes monomer compositions in the
feed (M ), the resulting composition in the copolymer
1
(dM ) and the corresponding x, y, F, G, F~1 and G/F
1
parameters obtained from eqns (4) and (5). g, m and a
values obtained from eqns (7) and (8) are also summarized in this table.
F\
x2
y
(4)
x and y are deÐned as :
M
dM
1
1
and
y\
(5)
M
dM
2
2
where M and M are the monomer molar composi1
2
tions in the feed and dM and dM correspond to the
1
2
monomer molar compositions in the copolymer.
r and r were also determined by the KelenÈTuŽdos
1
2
treatment13 (KT method), according to the equation :
x\
A
and
with a, an arbitrary constant, deÐned as :
where the transformed variables are :
G\
G
a]F
B
r
r
g\ r ] 2 m[ 2
1 a
a
(6)
where g and m are mathematical functions of mole composition ratios of monomers in the feed and in the
TABLE 3. Copolymerization data for 2VPy-co -VP and 4VPy-co -VP copolymers : composition in feed (M ),
1
resulting composition (dM ), x , y , F , G , F —1 and G /F as defined by Fineman and Ross,12 and g, n and a
1
parameters as defined by Kelen and Tudos13
G
F É1
G /F
g
m
0·065
0·114
0·405
0·288
0·539
É0·010
0·496
0·595
1·308
3·865
15·366
8·768
2·469
3·478
1·855
É0·158
4·346
1·469
4·551
7·169
É0·041
1·644
1·004
2·755
5·320
0·258
0·378
0·684
0·605
0·742
0·034
0·128
0·405
0·257
1·041
1·855
3·478
2·469
8·769
15·367
É7·168
É4·550
É1·469
É4·346
0·158
0·539
0·288
0·405
0·114
0·065
É3·865
É1·308
É0·595
É0·496
0·010
É0·997
É0·516
É0·188
É0·308
É0·008
0·258
0·395
0·316
0·622
0·742
0·250
0·667
1·000
1·500
4·000
0·635
2·286
2·724
5·456
12·587
0·098
0·194
0·367
0·412
1·271
É0·144
0·375
0·633
1·225
3·682
10·162
5·143
2·724
2·425
0·787
É1·460
1·929
1·724
2·971
2·897
É0·318
0·684
0·878
1·599
2·266
0·218
0·355
0·509
0·538
0·782
0·250
0·667
1·000
1·500
4·000
0·080
0·183
0·367
0·437
1·575
0·786
2·425
2·724
5·144
10·161
É2·895
É2·971
É1·724
É1·929
1·460
1·272
0·412
0·367
0·194
0·098
É3·682
É1·225
É0·633
É0·375
0·144
É0·801
É0·566
É0·311
É0·242
0·112
0·218
0·462
0·491
0·645
0·782
Copolymer
M
1
mol%
dM
1
mol%
x
y
2VPy-co -VPa
20
40
50
60
80
48·99
79·58
71·17
88·67
96·74
0·250
0·667
1·000
1·500
4·000
0·960
3·897
2·469
7·826
29·675
2VPy-co -VPb
20
40
50
60
80
3·26
11·33
28·83
20·42
51·01
0·250
0·667
1·000
1·500
4·000
4VPy-co -VPc
20
40
50
60
80
38·84
69·57
73·15
84·51
92·64
4VPy-co -VPd
20
40
50
60
80
7·36
15·49
26·85
30·43
61·16
a
b
c
d
F
Monomer 1 ¼ 2VPy, 2 ¼ VP, a \ 0·1874.
1 ¼ VP, 2 ¼ 2VPy, a \ 5.3385.
1 ¼ 4VPy, 2 ¼ VP, a \ 0·3537.
1 ¼ VP, 2 ¼ 4VPy, a \ 2·8264.
POLYMER INTERNATIONAL VOL. 45, NO. 3, 1998
V inylpyridineÈvinylpyrrolidone copolymers
Fig. 1. (A) FR representation of the copolymerization parameters for 4VPy-co-VP ; (B) KT representation of the copolymerization parameters for 4VPy-co-VP.
Reactivity ratios of 2VPy and 4VPy with VP were
also estimated using a computer program based on a
non-linear minimization algorithm, reactivity ratio
error in variable method (RREVM),14 starting from the
values of r and r obtained by the KT method. Figure
1
2
2 shows the 95% probability contours for r and r
1
2
starting from KT values taken from Table 4 for 2VPyco-VP and 4VPy-co-VP copolymers using the NLMA
method for the probability contour. Similar contours
are obtained for all compositions of 2VPy-co-VP and
4VPy-co-VP studied. In all cases the r and r values
1
2
obtained were generated using errors of 1% for the
monomer feed compositions and 5% for the copolymer
compositions. The comparison of these methods has
been performed for di†erent systems containing VP as
one of the comonomers with successful results.4
Table 4 collects r and r values for the copolymers
1
2
studied, determined by the FR , FR , KT and NLMA
1
2
methods. The observed di†erences among the values of
MRR obtained for the copolymers are expected, according to data reported in literature.4,5,13,17 It is interesting to note the good agreement shown in the
di†erent sets of data. In all cases the tendency is similar.
The agreement also remains when linear and non-linear
methods are compared. In all cases it is observed that
one of the monomers always has a greater tendency to
enter into the macromolecular chain.
If one of the reactivity ratios r or r is larger than
1
2
unity and the other is lower, there will be a shift in the
composition during copolymerization ; therefore the
POLYMER INTERNATIONAL VOL. 45, NO. 3, 1998
289
Fig. 2. The 95% probability contour for estimated r and r
1
2
values. (A) 2VPy-co-VP and (B) 4VPy-co-VP.
copolymer composition will be di†erent from the initial
one. This phenomenon is attributed to a larger reactivity of one of the monomers, and therefore more units
of the most reactive comonomer will be inserted in the
TABLE 4. Monomer reactivity ratios r
and r
1
2
obtained by the Fineman–Ross (FR)12 Kelen–TuŽ dos
(KT)13 and NLMA16 methods for 2VPy-co -VP and
4VPy-co -VP copolymers
Copolymer
2VPy-co -VP
Method
FR1
FR2
KT
4VPy-co -VP
NLMA
FR1
FR2
KT
RRM
2VPy or 4VPy
VP
6·34
5·56
5·56
6·34
5·45
5·45
4·28
3·19
3·60
3·60
3·18
3·33
3·33
3·93
0·54
0·33
0·33
0·54
0·31
0·31
0·28
0·34
0·47
0·47
0·34
0·39
0·39
0·52
a
b
a
b
a
b
c
d
c
d
c
d
NLMA
a
b
c
d
Monomer 1 ¼ 2VPy, monomer 2 ¼ VP.
Monomer 1 ¼ VP, monomer 2 ¼ 2VPy.
Monomer 1 ¼ 4VPy, monomer 2 ¼ VP.
Monomer 1 ¼ VP, monomer 2 ¼ 4VPy.
N. Gatica, L . Gargallo, D. Radic
290
macromolecular chain. According to the data in Table 4
it seems clear that in both copolymers the heterocyclic
comonomer is more reactive than the alicyclic comonomer. It should therefore be expected that some
tendency towards the formation of blocks containing
vinylpyridine units would be observed.
The relative monomer reactivity in radical polymerization can be conditioned by di†erent factors such
as polarity, steric hindrance, but mainly by the stabilization by resonance of the radicals generated during the
copolymerization process. This stabilization process
increases as the electronic delocalization increases, as
would be expected in the case of comonomeric units
such as 2VPy and 4VPy. The results shown in this work
are in good agreement with the analysis discussed
above, which has also been reported for similar copolymer systems.18h20
CONCLUSIONS
According to the results obtained in this work, it is possible to analyse the type of copolymer from the particular values of the MRR. These copolymers can be
considered as random ; nevertheless, the particular
values of the MRR seem to indicate the presence of
zones with high concentrations of VPy units, which was
interpreted in terms of block formation. This copolymer
structure is of great interest, because it could be considered as an amphiphilic material due to the presence
of hydrophobic blocks of VPy together with a random
distribution of hydrophilic VP units. This kind of combination should be of interest from the solution behaviour, as well as from the compatibility, point of view. It
would be interesting to study the blending process of
hydrophobic polymeric samples through speciÐc hydrophilic units randomly distributed along the copolymer
chain.
ACKNOWLEDGEMENTS
We express our thanks to Fondecyt, project 8970011.
N.G. thanks Conicyt for a Doctoral Fellowship and
Fondecyt project 2960022 for partial Ðnancial support.
D.R. acknowledges Ðnancial support from Catedra
Presidencial en Ciencias Ï95.
REFERENCES
1 Kohl, P. R., Seifert, A. M. & Hellmann, G. P., J. Polym. Sci.,
Polym. Phys. Ed., 28 (1990) 1309.
2 Ito, K., Uchida, K., Kitano, T., Yamada, E. & Matsumoto, T.,
Polym. J., 17 (1985) 761.
3 Horbett, T. A., Schway, M. B. & Ratner, B. D., J. Colloid Interface
Sci., 104 (1985) 28.
4 Radic, D. & Gargallo, L., Macromolecules, 30 (1997) 817.
5 Radic, D., Opazo, A., Vildosola, G. & Gargallo, L., Polym. Int., 31
(1993) 175.
6 Tjsma, E. J., Chen, G., van der Does, L. & Bantjes, A., Makromol.
Chem., Rapid Commun., 11 (1990) 501
7 Timofeevskii, S. L., Baikov, B. E., Panarin, E. F. & Putov, V. D.,
Polym. Sci. Ser., 10, (1994) 36.
8 Reddy, B. S. R., Arshady, R. & George, M. H., Eur. Polym. J., 21
(1985) 511.
9 Ilida, Y., Yano, S., Aoki, K. & Ohnuma, H., J. Polym. Sci., Polym.
L ett. Ed., 14 (1976) 23.
10 Desreux, V. & Bischo†, F., Bull. Soc. Chim. Belg., 93 (1950) 59.
11 Solomon, O. F. & Gotesman, B. S., Makromol. Chem., 104 (1967)
77.
12 Fineman, M. & Ross, S. D., J. Polym. Sci., 5 (1950) 259.
13 Kelen, T. & TuŽdos, F., J. Macromol. Sci. Chem., A9 (1975) 11.
14 Dube, M., Sanayei, R. A., Penlidis, A., OÏDriscoll, K. & Reilly,
P. M., J. Polym. Sci., Polym. Chem. 29 (1991) 703, and references
cited therein.
15 McFarlane, R. C., Reilly, P. M. & OÏDriscoll, K. F., J. Polym. Sci.,
Polym. Chem. Ed., 18 (1980) 251.
16 Laurier, G. C., OÏDriscoll, K. F. & Reilly, P. M., J. Polym. Sci.,
Polym. Symp., 72 (1985), 17.
17 Bauduin, G., Boutevin, B., Belbachir, M. & Meghabar, R., Macromolecules, 28 (1995) 1759.
18 Cowie, J. M. G., Polymers : Chemistry and Physics of Modern
Materials, International Textbook Co. Ltd., London, 1973, p. 90.
19 Billmeyer, F. W., T extbook of Polymer Science, John Wiley, Singapore, 1984, p. 103.
20 Huglin, M. B. & Khairou, K. S., Eur. Polym. J., 24 (1988) 239.
POLYMER INTERNATIONAL VOL. 45, NO. 3, 1998
Документ
Категория
Без категории
Просмотров
6
Размер файла
248 Кб
Теги
950
1/--страниц
Пожаловаться на содержимое документа