Predicting and Measuring the Sequence Distribution of Addition Polymers - Mathematical Approaches to Polymer Sequence Analysis and Related Problems - page 220

Fig. 10.6 Results of a copolymer scission reaction simulation: the intensity variations of five mass
spectral peaks as the average number of scissions per initial molecule (S) varies from 0 to 18.
Reprinted from [ 96 ] with permission from the copyright holder Wiley 1993

called MACO was equipped with a new subroutine (ad hoc) which can simulate the
entire ozonolysis process, including the mass spectra of the partially degraded sam-
ples [ 96 ]. Figure 10.6 reports the intensity variations of five mass spectral peaks, as
the average number of scissions per initial molecule (S) varies from 0 to 18. From
the inspection of the figure, it can be seen that peaks at m

= z D 708 and 812 are

enhanced and peaks at m = z D 608 and 400 become weaker. The peak at m = z D 500

shows an initial increase, reaches a maximum at S and then decreases. The

theory predicts that the MS intensities associated with short oligomers are enhanced
with respect to MS intensities associated with long oligomers. As a matter of fact,
some of the results in the figure are in agreement with this prediction. For instance,
the intensity of the peak at m

D 10

(corresponding to the octamer St 3 BU 5 )
increases with respect to the intensity of the peak at m

= z D 708

(corresponding to
the nonamer St 3 BU 6 ). The theoretical predictions were compared with experiment
results and the agreement was good [ 96 ].
MALDI is another ion source used in MS and Fig. 10.7 reports the MALDI mass
spectrum of a copolymer [ 97 ] with units of hydroxy butyrate (HB) and valerolac-
tone (VL). It displays more than 600 MS peaks ranging from 1,500 to 4,000 Da.
The peaks are due to the chains containing crotonate starting group, and desorb
as potassium adducts as reported in Fig. 10.8 . The peaks at m/z D 1,341, 1,441,
1,541, 1,642 and 1,742 are very rich in VL units. The mass spectral intensities of
the 600 MS peaks were given as input to the MACO computer program and the
result of the calculation was plotted. Figure 10.9 (solid line) reports the composi-
tional distribution histogram, as derived from mass spectrum (the

= z D 812

histogram bars

are so close that it is actually a curve). The abscissa is c VL the molar fraction of