Chemistry Reference
In-Depth Information
Methine Carbons
H
3
C
CH
3
SCB
LCB
CH
3
CH
3
Figure 1.
Structure illustrating SCB and LCB methine carbons in an ethylene-octene (EO) copolymer.
Experimental Part
750 MHz. Prior to data acquisition, the
observed pulse widths are verified for both
the
13
Cand
1
H channels. Typical acquisition
parameters for the Varian Inova 500 and
600 MHz and Varian Unity Plus 750 MHz
NMR spectrometers are 64 K data file,
3.3 sec repetition rate and a 90
Sample Preparation
A total of 0.45 g of polymer is weighed
into a 10 mm o.d. NMR tube. The solvent is
added to the NMR tube. The tube is capped
and placed in a heating block. The nominal
temperature of the heating block is 150
8
C.
The hot sample is frequently mixed using a
vortex mixer or a Buchi oven with rotating
sample holder. The solvents used in this
study are marginal polyethylene solvents;
therefore preparation of a homogeneous
sample is tedious. A significant amount of
time and mixing is required to achieve
solutions of sufficient homogeneity.
8
pulse width.
Data Processing
Chemical shift assignments are based on
previously determined values of 30.0 ppm
for the backbone methylene signal.
[2,3]
All
data processing is done using NUTS (NMR
Utility Transform Software) available from
Acorn NMR.
[4]
The data files were pro-
cessed with a weak Gaussian apodization
function by setting LB
¼
0.7 Hz and GF
¼
0.10. This effectively changed the lineshape
from Lorentzian to Gaussian without sig-
nificant resolution enhancement except at
the peak base.
Sample Description
The total polymer weighed is a mixture of
a linear low density ethylene-hexene or
ethylene-octene copolymers and a long-
chain branched homopolymer containing a
known amount of branching. The various
solvents used in this study are summarized
in Table 1.
Results and Discussion
The primary feature of interest when
quantifying LCB in these copolymers is
the separation between the LCB CH and
the CH of the SCB associated with the EOE
Data Acquisition
Nalorac high temperature 10 mm Z-spec
probes were used at both 600 MHz and
Table 1.
Solvent compositions used in this study.
Name
Composition
TCE/ODCB
50/50 by weight 1,1,2,2-tetrachloroethane (TCE-d
2
) and o-dichlorobenzene (ODCB).
Biphenyl
90/10 wt/wt biphenyl/biphenyl-d
10
Mesitylene
90/10 wt/wt 1,3,5 trimethyl benzene and 1,3,5 trimethyl benzene-d
12
Biphenyl/TCE
3.6/1 wt/wt biphenyl/TCE-d
2
Naphthalene
90/10 wt/wt naphthalene/naphthalene-d
8
