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Cooperative oxydation reactions of polymer blends. I

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Die Angewandte Makromolekulare Chemie 9 (1969) 182-185 (Nr. 115)
From the Chemical Research Institute of Non-Aqueous Solutions,
Tohoku University, Sendai, Japan
Kurzmitteilung
Cooperative Oxydation Reactions of Polymer Blends.
I. PBD PVC Systems
-
By TORUTAKAHASHI,
TAMIO
YASUKAWA,
and KENKICHI
MURAKAMI
(Eingegangenam 1. August 1969)
Many works1 have been published on the oxidative degradation of polymers,
especially of homopolymers, and mechanisms of oxidation reactions have been
discussed from various points of view. On the contrary, it seems that the
oxidative degradations of graft- and block-copolymers, as well as polymer
blends, have not been investigated sufficiently. Graft- and block-copolymers
degradate sometimes more rapidly than each homopolymer of the components
and these rapid degradations have often been ascribed t o the effects of remaining catalysts (or radiation effects) which were not removed completely
after preparation processes.
However, it is likely that the mechanism of oxidative degradations of graftand block-copolymers is somewhat different from those of homopolymers. I n
this respect, we attempted to investigate the mechanism of oxidation reactions
of polymer blends in order to avoid the ambiguities due t o the effects of remaining
catalysts.
Materials used were poly (vinyl chloride) (PVC) (NipolytSL, supplied by Chisso
Ind. Co.; M,: 5 x 103) and polybutadiene (PBD) (BR 0 1 (high cis) supplied by
Japan Synthetic Rubber Co.; M,: 3 x 105). Each homopolymer was purified by
precipitating from benzene (PBD) or tetrahydrofuran (PVC) three times and was
evacuated for one week. Polymer blends were prepared by evaporating the mixture
solutions containing given amounts of respective homopolymers with a rotary
evaporator under reduced pressure. Blend samples obtained were transparent,
suggesting that component polymers were well dispersed. Addition of radical
initiators or PVC-stabilizer t o the polymers were also carried out in similar ways.
182
Cooperative 0xy:ydCction Reactions of Polymer Blends
Samples were kept in an oxygen atmosphere a t certain temperatures and
the amounts of oxygen absorbed were measured by an apparatus described by
PENDERSON~.
The IR spectra showed that oxygen reacted with polymers to
form carbonyl, carboxyl and some other groups.
The amounts of oxygen absorbed were plotted against times in Fig. 1. It is
noteworthy that PVC-30/PBD-70 sample absorbed more than PBD homopolymer. Since PVC homopolymer absorbed oxygen only in small amounts,
we may tentatively consider that oxygen was absorbed mainly by the PBD
component in blend samples. I n Fig. 2 were replotted the amounts of oxygen
absorbed per 1 gram of PBD contained in respective blend samples. The
amounts of oxygen absorbed increased as the ratio of PVC/PBD increased. Of
course, the amount of oxygen absorbed by the PVC component becomes unnegligible when the ratio of PVC/PBDis high, but the effects of PVC seem more
remarkable than one can expect of simple superposition.
Fig. 1. The amounts of oxygen absorbed by I gram of PBD, PVC and blended samples at 130°C.
-0- PBD 100
- 0 - PBD 7O/PVC 30
-@PBD 5O/PVC 50
0- PBD 301PVC 70
--o - PBD 15/PVC 85
0 - PVC 100
(figures denote weight per cent of
components).
50
.--
-
140.
E
U
*
f
30
-
Fig. 2. The amounts of oxygen absorbed per 1 gram of PBD contained in
blended samples (replot of Fig. 1).
20
40
60
80
100
T i m e (min)
L
183
T. TAKAHASHI,
T. YASUKAWA,
and K. MURAKAMI
Both PBD and PVC were oxidized by radical chain mechanisms3A5, and
the rate of oxidation reactions (especially chain initiation reactions) was
accelerated by the addition of a radical initiator such as BPO and AIBN6.
Fig. 3 shows the effects of addition of BPO observed at 110°C. The effect of
the radical initiators was more remarkable for PBD than for PVC.
It is generally observed that PVC is unstable to heat and dehydrogenation
reactions by radical mechanism take place easily. Thus, while the rate of oxidation of PVC itself is not rapid (Fig. 1 and 3), there would be the possibility
that PVC behaves as a kind of radical source; namely, for the systems where
PVC were dispersed microscopically in the PBD phase, radicals originate from
PVC (especially Cl.) may diffuse into the PBD phase and initiate the chain
reaction of oxidation of PBD.
In order to examine the above postulation that radicals from the PVC
phase diffuse into the PBD phase and behave as initiators of oxidation reaction of PBD, we investigated the effects of lead stearate which is considered
to be effective to trap C1. and some other radicals originating from PVC and,
accordingly, stabilize PVC798. The addition of lead stearate retarded the reactions of PVC/PBD blends, as well as that of PVC homopolymer, while it
affected scarcely the oxidation of PBD homopolymer (Fig. 4). Similar results
were also obtained with dibutyl tin dithiol. These results clearly suggest that
radicals from PVC phase accelerate the oxidation reactions of PBD dispersed
in blended samples (as can be seen in Fig. 3), the oxidation of PVC is slow and
is not so accelerated by a radical initiator as that of PBD.
After all, we can consider that the mechanism of' oxidation reaction of
polymer blends where the component polymers are dispersed microscopically is
Fig. 3. The effects of addition of BPO to
PBD and PVC (observed at 1 l O O C ) .
- - PBD without BPO
- 0 - PBD with 0.5 yo BPO
- 0 - PBD with 3 Yo BPO
- A - PVC without BPO
-a- PVC with 0.5 yoBPO
- A - PVC with 3 yo BPO
0
184
10
20
30
lime(min)
40
50
60
Cooperative Oxydation Reactions of Polymer Blends
Fig. 4. The effects of addition of lead
stearate to PBD and PBD 5O/PVC 50
(observed at 130°C).
- - PBD without lead stearate
- 0 - PBD with 3 yo lead stearate
- A - PVC without lead stearate
- A - PVC with 3 yo lead stearate.
0
10
20
30
40
Time ( m i n )
fairly different from those of homopolymers ; namely, the oxidation reaction
proceeds not independently in each dispersed phase but some kind of cooperative mechanisms is unnegligible.
1
2
3
4
5
6
7
8
N. GRASSIE,Chemistry of High Polymer Degradation Processes, Intersience,
New York 1956.
H. L. PENDERSON,
Rubber Chem. Technol. 23 (1951) 18.
E. 5. ARLMAN,J. Polymer Sci. 12 (1954) 547.
D. E. WINKLER,
J. Polymer Sci. 35 (1959) 3.
R. G. BAUMANN
and S. H. MARON,
J. Polymer Sci. 22 (1956) 1; 203.
A. V. TOBOLSKY
and A. MERCURIO,J. Amer. chem. SOC.81 (1959) 5535; 5539.
A. H. FRYE
and R. W. HORST,J. Polymer Sci. 45 (1960) 1.
M. IMOTO
and T. OTSU,
J. Inst. Polytechn., Osaka City Univ., Ser. C 4 (1963)269.
185
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