Using Solvents to Improve the Chemical Shift Differences Between Short-Chain Branch Methines and Long-Chain Branch Methines in Polyethylene Copolymers - Polyolefin Characterization - page 160

Figure 2.
A 150 MHZ 13 C spectrum of a sample containing a mixture of a linear ethylene-hexene copolymer and a
long-chain branched HDPE. The LCB spike has a known level of 0.24 LCB per 1,000 total carbons.

or EHE triad. It is this chemical shift
separation that has been adjusted by using
various solvents in this work. It is also
important to maintain some resolution
between the LCB CH resonance and the
13 C satellite resonance of the SCB CH
resonance. The optimum placement of the

LCB methine signal is approximately 8.5
to 9 Hz down-field from the SCB CH
resonance as shown in Figure 2 for an
ethylene-hexene copolymer in biphenyl/
TCE at 150 MHz 13 C. Using chlorinated
aromatic solvents this degree of separation
requires a magnetic field in excess of

6

5

4

3

2

1

0

ODCB/TCE Biphenyl/TCE Biphenyl/Trimethyl Biphenyl 100% Naphthalene

(188 MHz) (188 MHz) benzene (188 MHz) (125 MHz)

(188 MHz)

Solvent System

Figure 3.
A bar chart comparing the LCB-SCB methine separation at 120 C for an ethylene-octene copolymer. The

optimum solvent, naphthalene, gives a separation at 125 MHz which is over 2.5X the separation observed in the
usual chlorinated solvent system at 188 MHz.

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