TRACTION OF COPPER AND ZINC IONS WITH POLYMETHACRYLIC ACID (PMA)
TRACTION OF COPPER AND ZINC IONS WITH POLYMETHACRYLIC ACID (PMA)
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Date
1974-04
Authors
EMMANUEL, GBADEBO KOLAWOLE
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Abstract
The interaction between polymethacrylic acid
(PMA) and divalent metal ions has been studied at
25 oC and. varying conditions of ionic strength, polymer
concentration, cation concentration and degree of
ionization by different experimental techniques.
The experimental techniques used were conductance
measurements, viscometric t i t r a t i o n , spectrophotometric
t i t r a t i o n , dialysis equilibrium, potentiometric t i t r a -
tion and light scattering.
Data from different experimental methods reveal
that both copper and zinc interact quite strongly with
preionized PMA to form complexes. Copper has been
found to he a stronger hinder than zinc.
Copper ions bind PMA to form complexes involving
four, two and one carboxylate groups per copper ion
while zinc forms complexes involving two and one carhoxylate
groups per zinc ion.
FMA molecules exist in t i g h t l y coiled state when
unneutralized or at low degrees of ionization (0.1>α).
The ionized molecules undergo a configurations! trans
i t i o n in the range 0.1 < α <0.27. The t r a n s i t i o n
is completed at a = 0.27. Maximum chain extension
has been achieved at 70% n e u t r a l i z a t i o n . The uncoiling
of the polymer molecule has been attributed to strong
e l e c t r o s t a t i c repulsive forces between the charged
carboxylate groups along the polymer backbone. The
uncoiling of the compact PMA molecules is a single-step
process.
It has been established that some experimental
techniques used were more sensitive than others. With
conductance measurements, spectrophotometry and potentiometric
t i t r a t i o n s it is quite possible to detect
almost all types of complex species present in M2+ -PMA
systems with their corresponding co-ordination numbers,
while viscometric t i t r a t i o n s and d i a l y s i s equilibrium
will only detect the most stable complex formed and
the corresponding co-ordination number.
The r e s u l t s presented in chapter 4 for spectrophotometries
t i t r a t i o n s show that Cu2+-FMA complexes are
charge-transfer complexes.
In chapter 5, equations were derived for M2+ PMA
systems to enable the author t o c a l c u l a t e the s t a b i l i ty
c o n s t a n t s and the c o - o r d i n a t i o n numbers of complexes
formed. These e q u a t i o n s were t e s t e d g r a p h i c a l l y and
t h e r e was s a t i s f a c t o r y agreement between t h e o r y and
e x p e r i m e n t . It was found t h a t , on t h e a v e r a g e , each
c a t i o n formed complexes i n v o l v i n g two c a r b o x y l a t e groups
per metal ion and t h a t t h e mode of b i n d i n g could be
e i t h e r i n t r a m o l e c u l a r l y or i n t r a m o l e c u l a r l y depending
on the i o n i c s t r e n g t h and d e g r e e of i o n i z a t i o n ( a ).
I t has been shown c o n v i n c i n g l y in c h a p t e r 6 t h at
t h e acid d i s s o c i a t i o n c o n s t a n t Ka is not a c o n s t a n t but
a function of a. Potentiometric behaviour of PMA in
t h e absence and in the presence of d i v a l e n t c a t i o ns
has been d i s c u s s e d in l i g h t of double l a y e r e f f e ct
and a l s o in l i g h t of t h e e m p i r i c a l e q u a t i o n s developed
for calculating [coo-]bound and [M2+]bound.
Light s c a t t e r i n g s t u d i e s confirm t h a t at low
d e g r e e s of i o n i z a t i o n a dimer is formed in t h e p r e s e n ce
of Cu2 + and Zn2 + ions because the molecular weight is
a p p r o x i m a t e l y doubled. This s u g g e s t s t h a t the most
l i k e l y mode of b i n d i n g is i n t e r m o l e c u l a r l y . Light
s c a t t e r i n g s t u d i e s a l s o confirm t h a t p a r t i a l ly
i o n i z e d PMA m o l e c u l e s e x i s t in random c o i l s.
Finally in chapter 8, the results obtained from
different chapters are compared and the interpretation
and deductions made are found to corroborate. Cumulative
constants 3 have been calculated for the various
complex species in the reaction mixture.
Description
Dissertation
presented to
The Ahmadu Bello University
for the degree of
DOCTOR OF PHILOSOPHY
in the
Faculty of Science
BY
EMMANUEL GBADEBO KOLAWOLE
Department of Chemistry
Ahmadu B e l l o U n i v e r s i ty
Z a r i a .
A p r i l , 1974
Keywords
COPPER,, POLYMETHACRYLIC,, ACID (PMA),, ZINC IONS