Chemistry Reference
In-Depth Information
Table 6.10
Typical recipes for preparation of butadiene-styrene rubbers by emulsion polymerization
“Hot” process
“Cold” process
Material
Parts
Purpose
Parts
Purpose
Butadiene
75
Comonomer
72
Comonomer
Styrene
25
Comonomer
28
Comonomer
Water
180
Carrier
180
Carrier
Fatty acid soap
5.0
Emulsifier
4.5
Emulsifier
n
-Dodecyl mercaptan
0.5
Chain transferring agent
-
-
t
-Dodecyl mercaptan
-
-
0.2
Chain transferring agent
Potassium persulfate
0.3
Initiator
-
-
Auxiliary surfactant
-
-
0.3
Stabilizer
Potassium chloride
-
-
0.3
Stabilizer
p
-Menthane hydroperoxide
-
-
0.06
Initiator system
Ferrous sulfate
-
-
0.01
Ethylenediamine tetraacetic acid sodium salt
-
-
0.05
Sodiumformaldehyde sulfoxylate
0.05
a
From ref. [
127
] and other patent literature
during the 1930s was followed by a particularly strong impetus in the United States during World
War II. This led to a development of GR-S rubber in the United States and Buna-S rubber in
Germany. After World War II further refinements were introduced into the preparatory procedures
and “cold” rubber was developed. Industrially, the copolymer is prepared by emulsion copolymeriza-
tion of butadiene and styrene at low temperatures in a continuous process. A typical product is a
random distribution copolymer, with the butadiene content ranging from 70 to 75%. The diene
monomer placement is roughly 18%
cis-
1,4; 65%
trans-
1,4; and 17% 1,2.
M
n
of these copolymers
is about 100,000.
A “redox” initiator is used in the cold process, but not in the “hot” one. Also, the “hot” process is
carried out at about 50
C for 12 h to approximately 72% conversion. The “cold” process is also
carried for 12 h, but at about 5
C to a 60% conversion. The two recipes for preparation of GR-S
rubbers are shown in Table
6.10
for comparison of the “hot” and “cold” processes.
In both polymerizations, the unreacted monomer has to be removed. In the “hot” one the reaction
is often quenched by addition of hydroquinone, and in the “cold” one by addition of
N
,
N
-diethyldithiocarbamate. After the monomers are steam stripped in both processes, an antioxidant
like
-phenyl-2-naphthylamine is added. The latex is usually coagulated by addition of a sodium
chloride-sulfuric acid solution. The “cold” process yields polymers with less branching than the
“hot” one, slightly higher
N
ratios.
During the middle 1960s a series of butadiene-styrene and isoprene-styrene
trans
to
cis
block-copolymer-
elastomers
were developed. These materials possess typical rubber-like properties at ambient
temperatures, but act like thermoplastic resins at elevated ones. The copolymers vary from diblock
structures of styrene and butadiene
m
n
