Chemistry Reference
In-Depth Information
average molecular weight (M
W
) of 1480 kg/
mol for the arms of the star and 4760 kg/mol
for the whole star sample. The reported
whole polymer M
W
does not make sense
considering the sample was supposed to be
a three arm star with some uniarm material
present. The higher than theoretically
possible M
W
for the whole sample may
suggest the presence of some high mole-
cular weight impurities. Further, our char-
acterization of the 3-arm star sample (see
Results and Discussion Section) indicates
that the uniarm material is actually sub-
stantially lower in molecular weight than
the value supplied by the vendor.
Lightly cross-linked homogeneous ethy-
lene octene copolymer samples were frac-
tionated via a solvent non-solvent method
to produce relatively narrow fractions for
MTF. A preparative fractionation unit
(PolymerChar, Valencia, Spain) was used
to separate each whole polymer sample into
narrow fractions with the resulting M
W
's
nominally from 20 to a maximum of
200-400 Kg/mole and polydispersities
PDI's ranging from 1.3 to 1.5. For the
whole polymer samples, short chain branch
frequencies ranged from 17 to 32 short
branches per thousand backbone carbon
atoms, and short chain branching had
minimal influence on MTF elution. Long
chain branching frequencies (LCBf) of the
unfractionated materials were determined
by triple detector SEC
[4]
and ranged from
Figure 1.
SEM Image of non-functionalized Admatechs Silica.
The silica was functionalized with PS and packed into
a column by Mel Cabey of the Diazem Corporation.
was obtained directly from the LC reservoir
so as to minimize the contributions from
solvent mismatch peaks. Standard solutions
were stored in the dark at ambient
temperature when not in use. For SEC,
standards were prepared as cocktails and
the concentration of each standard in a
cocktail was 0.5 mg/mL.
A three arm star PS sample was obtained
from Polymer Source, Inc. (Dorval, Que-
bec, Canada). The star was made via
anionic polymerization followed by cou-
pling of the living anions with a trifunc-
tional coupling agent as depicted in
Figure 2. The vendor reported a weight-
Figure 2.
Reaction Scheme used by Polymer Source Inc. to synthesize the 3-arm star sample.
