Chemistry Reference
In-Depth Information
(b)
Contact angle.
A contact angle meter was used (Kyowa Kagaku Company). A
water drop (about 0.02 mL) was prepared by a microsyringe and brought into
contact with the surface of the sample. At 30 s after contact, the water drop was
photographed, and
h
and
x
(shown in the following equation) were measured.
The contact angle (
θ
) was calculated from the following equation:
2tan
1
h=x
θ ¼
where
x
is the radius of the contact area between the water drop and the sample
plate and
h
is the height of the water drop in contact with the sample plate.
Measurements were taken at 20
C.
(c)
Water absorption
(%). A 25
7.5 mm sample was dried for 24 h in air at
50
C, and then allowed to cool. After weighing, the sample was placed in
distilled water at room temperature for 24 h. The sample was removed from the
water, wiped lightly with a cloth and its weight measured again. The water
absorption (%) was determined by weight difference.
6.2.5.3 Material Tests and Water Absorption of the Resulting Copolymer
The plate of this copolymer, produced by a heat and press molding method, was
used to test water absorbing power. Water absorption reduced with increased
grafting (%) and decreased
M
w
of the backbone polymer dextran at a fixed grafting
(%). Perhaps, this water absorbing power depends on the water absorbing capacity
of its dextran parts.
The tensile strength of these copolymers grew with increases in grafting (%) for
each different
M
w
of backbone polymer dextran. Though a systematic effect of the
dextran
M
w
on this was not observed, it was shown that the mechanical fragility of
the dextran was reinforced by PMMA grafted on dextran. The copolymer with the
backbone polymer dextran of
M
w
61,000 (D2) had the highest tensile strength. The
relation between elongation and grafting (%) was similar to the above relation. The
copolymer with the backbone polymer dextran of
M
w
61,000 (D2) was superior to
others with regard to elongation.
The contact angle of these copolymers was lower than for PMMA, but a
systematic effect of grafting (%) and the backbone polymer dextran
M
w
was not
observed.
6.2.5.4 Characteristic Properties of Dextran-MMA Graft Copolymers
Table
6.1
shows the solubility of dextran-MMA graft copolymer with a grafting of
700 % in water, acetone and various other solvents compared with those of the
starting material dextran and the side chain PMMA. The graft copolymer was not
only insoluble in water, acetone, pyridine, tetrahydrofuran and benzene, but also in
dimethylsulfoxide, a common excellent solvent for dextran and PMMA.
