close

Вход

Забыли?

вход по аккаунту

?

The determination of molecular weights of polymers from critical concentrations of ternary systems polymer-polymer-solvent.

код для вставкиСкачать
Die Angewandte Makromolekulare Chemie 6 (1969) 156-160 (Nr. 65)
From the Polymer Institute, Slovak Academy of Sciences, Bratislava, CSSR
The Determination of Molecular Weights of Polymers
from Critical Concentrations of Ternary Systems
Polymer-PolymerSolvent*
By DUEANBEREK,BRANISLAV
BOHMER
and DIETERLATH
(Eingegangenam 29. Oktober 1968)
SUMMARY:
The dependence of the critical concentration of the ternary system polymerpolymer-solvent on the molecular weight can be expressed by the relation
CC
= AE-213
+ ccm
where cc is the critical concentration, the appropriate average of the molecular
weight of both polymers; A and cCmare constants for the given system.
The possibility of determining the molecular weight of one of the polymers
from the value cc and the molecular weight of the known polymer with the aid of
equation (1) is discussed.
ZUSAMMENFASSUNG :
Die Abhhgigkeit der kritischen Konzentration des ternaren Systems PolymerPolymer-Losungsmittel vom Molekulargewicht kann mittels der folgenden Gleichung ausgedriickt werden :
cC = AE-213
ccm
+
cc ist die kritische Konzentration,
der geeignete Mittelwert der Molekulargewichte der beiden Polymeren; A und ccm sind Konstanten fur das gegebene
System.
Es wird die Moglichkeit erortert, aus cc und dem Molekulargewicht des bekannten Polymeren - mit Hilfe der Gleichung (1) das Molekulargewicht des zweiten
Polymeren zu bestimmen.
The idea of assessing molecular weights of polymers from phase relationships
of ternary systems polymer-polymer-solvent is as old as the study of the
phenomenon of phase separation in the mentioned systems.
*
Presented at the Conference on Chemical Transformation of Polymers, Bratislava, 1968.
156
Determination of Molecular Weights
DOBRYand BOYER-KAWENOKI~
suggested an approximative determination
of molecular weights from phase volumes after separation of the ternary system
containing incompatible polymers. Their idea was later developed by LIPATOV~.
Simplifying assumptions proposed by the mentioned authors lead to the
conclusion that the ratio of phase volumes of separated systems would be
proportional t o the reciprocal ratio of molecular weights of the polymers in
the system. Using a standard polymer as one component, it would be easy t o
determine the molecular weight of the other macromolecular substance.
Practical utilization of this procedure and its more complicated versions
is hindered mainly by the fact that the parameters of the phase equilibrium
of the ternary systems polymer-polymer-solvent are, to a great extent, influenced by polydispersity of the macromolecular substances3. That is why it
appears to be more convenient to use the values of critical concentrations
of the systems polymer-polymer-solvent (cc) for the determination of polymer
molecular weights. Recently we founds, 5 that for numerous ternary systems
in a wide range of polymer molecular weights it can be stated
cC = AM413
+ cCm
(1)
where A and ccooare the constants for the given system and
average of the molecular weights of both polymers :
-
M=
represents the
a+= (M2 x M3)0.5, or _M =-Mm = Yz M2 + Y3 Ms
where M2 and M3 are the molecular weights of the polymers (components
2 and 3) and Yi signifies the relative weight fraction of the polymer component i defined by
where wi means the weight fraction of the polymer i in the system and w1
the weight fraction of the solvent.
By substituting in relations (1) and (2) the experimentally determined
critical concentration of an adequately selected and calibrated ternary system
we are able to calculate the value of molecular weight Mi, if Mj is known.
The dependence (1) (M = Mm ; Mi = Ii?, (viscosity average molecular
weight)) for the system polypropylene
polystyrene
toluene is shown in
Fig. 1. The respective values A and cCmare A = 6.55 x 103; cca, = 0.6 g
x d-1,and the corresponding correlation coefficient is 0.9912. It appears that
the sensitivity of the method is sufficient for normal routine molecular weight
determinations although the results are to a small extent influenced by the
polydispersity of the respective polymers. The values Mi can be substituted
+
+
157
D. BEREK,
B. BOHMER
and D. LATH
I
I
I
I
0
5
10
15
I
- -21
I
20
'Ym'3 7c4
Fig. 1. The dependence of the critical concentration of the ternary systems polypropylene-polystyrene-toluene (atactic polymers) on weight average
molecular weights of polymers. The values Mw/Mn = R for systems
marked by numbers are aa follows :
Point
1:
2:
3:
4:
5:
Rpp 1.41,
1.41,
1.41,
1.41,
1.37,
RPS 2.67;
2.11;
1.80;
1.67;
1.61 ;
6:
,
7:
8:
9:
10:
Rpp 1.41,
3.65,
3.41,
3.65,
2.85,
RPS 1.44;
1.61;
2.27;
2.27;
1.46.
by number or weight etc. averages of the molecular weights of polymers
using different values of A and cCm for any kind of molecular weight average.
When applying the proposed simple method of determination of values of
critical concentration5 we proceed from molar volumes of polymers (Vi): from
equation (3), resulting from SCOTT'Sconsiderations6
we can calculate the ratio of the theoretical critical volume fractions (vie) of
polymers in the system.
The optically determined limiting miscible concentration of ternary systems
containing the polymers in the theoretical critical representation can be considered in good approximation with the proper critical concentration of the
systems.
168
Determination of Molecular Weights
I n our case one of the Vi values is unknown. Therefore, we must first
estimate the molecular weight of the polymer examined and then - based on
the obtained results - carry out one or more re-determinations. Under such
conditions the accuracy of the determined molecular weight will be better
than & 15% depending on the molecular weight range and calibration accuracy.
For purposes of more approximate but speedy molecular weight determinations, however, the determination of limiting miscible concentrations of
ternary systems containing equal weight portions of both polymers (Yi = 0.5)
is sufficient. Such procedure is particularly suitable for polydisperse polymers,
where values of limiting miscible concentrations are often less changing with
relative concentration of the polymers in the system335. For in equation (1)
it then seems to be better to use the geometric mean value
a
(a+).
The proposed method of the polymer molecular weight determination is
unpretentious with respect to time, experimental equipment and sample
consumption (0.1g). It could be applied particularly in routine series analyses
preferably in the range of lower molecular weights (104- 3 . 104) and for
the determination of molecular weights of copolymers. (In this case, increased
attention is to be given to the selection of the solvent and reference polymer
because of the influence of chemical composition of the copolymer on critical
concentration of the ternary system.) The method can also be of use for direct
analysis of polymer mixtures, production of which is a t present steadily
growing.
Experimental
Experimental data on purification, on fractionation, and on viscosity molecular
weight determination of polymers as well aa on determination of limiting miscible
concentrations have been described395. The values of
were calculated from
the relation [q] = K-a calibrated by light scattering (polypropylenepoints 5,107,
polystyrene points 1, 2, 3, 4, 5, 6, 7, lo*), those of P,, were calculated from fractionation data (polypropylenepoints 1, 2,3, 4, 5, 6, 7, 8, 9,polystyrene points 8,9).
The other values of H, were determined osmometrically (static osmometers with
Ultracella “allerfeinst” membranes Sartorius Membranfilter, Gottingen) in toluene
at 30°C.
zw
1
2
3
4
A. DOBRY
and F. BOYER-KAWENOKI,
J. Polymer Sci. 2 (1947)90.
S.M.LIPATOV,
Kolloid-J. 22 (1960)639.
D.BEREK,D. LATHand V. ~ ~ U R ~ O VJ.I Polymer
~ ,
Sci. C 16 (1967)659.
F.BURKHARDT,
H. MAJERand W. KUHN,Helv. chim. Acta 43 (1960)1192.
159
D. BEREK,B. BOHMER
and D. LATH
5
6
7
8
D. BEREK,B. BOHMER
and D. LATH,Plaste und Kautschuk 14 (1967) 556.
R. L. Scow, J. chem. Physics 17 (1949) 279.
8. FLORI~N,
Polymer Institute SAV, unpublished results.
M. I ~ R A Tand
A W. H. STOCKMAYER,
Fortschr. Hochpolymeren-Forsch.3
(1963) 196.
160
Документ
Категория
Без категории
Просмотров
1
Размер файла
206 Кб
Теги
polymer, molecular, ternary, concentrations, critical, weight, solvents, determination, system
1/--страниц
Пожаловаться на содержимое документа