Predicting and Measuring the Sequence Distribution of Addition Polymers - Mathematical Approaches to Polymer Sequence Analysis and Related Problems - page 216

has a larger number of degrees of freedom (four). It uses an asymmetric function,
namely an exponentially modified gaussian, and therefore, the average P -matrix el-
ements and unperturbed P -matrix elements are different, contrary to ( 10.44 ).
A wide variety copolymerization reactions can be modeled; for instance, the
copolymerization of styrene and ethyl methacrylate using three different polymer-
ization techniques, the copolymerization of styrene and butyl acrylate in batch mode
(i.e., when the reaction vessel is not opened during the reaction), free-radically poly-
merized vinyl chloride-vinylidene chloride copolymers and isobutylene/isoprene
copolymers obtained by cationic copolymerization at different

is the
monomer-to-polymer conversion). It can be applied also to homopolymers. For in-
stance in the anionic copolymerization of poly(methyl-alfa chloroacrylate), tacticity
is treated as a copolymer problem, with meso (m) and racemic (r) configurations as
comonomers.

values (

10.22 Sequence Measurement

The measurement of the sequence distribution of addition polymers can be per-
formed using pryolysis-gas chromatography (Py-GC), liquid chromatography, wet
chemistry methods, radiolabeling and spectroscopy [ 80 ]. Three popular spectro-
scopic techniques are FTIR, NMR and MS. The first technique (FTIR) is very
important for assessing copolymer composition. It often happens that two bands
are detected in the FTIR spectrum, due to A and B units, respectively. The compo-
sition is obtained by measuring the areas under the two bands and taking the ratio
[ 81 ]. Nevertheless, FTIR is less suited than NMR and MS for copolymer sequenc-
ing, since the signals in the FTIR spectrum are due to short sequences, shorter than
the sequences “seen” by NMR and MS. For this reason, it will not be discussed.

10.23 Nuclear Magnetic Resonance

Coleman and Fox published a famous paper on Journal of Polymer Science , dealing
with stationary sequences and NMR [ 82 ]. The paper is peculiar. A series of theorems
are proven in a manner similar to math handbooks, starting with some definitions,
two statements (the hypothesis and the thesis) and the formal proof. After these
pioneering studies, many experiments were conducted which showed that
copolymer sequencing by NMR is feasible. Frank Bovey analysed a number of
copolymers by NMR. He also noted that the natural abundance of fluorine iso-
topes is very attractive and he worked on repeat units which possess one, two,
three, four fluorine atoms. In the late 1970s, the field was fully mature and Randall
summarized the know-how and the entire methodology in a topic [ 83 ]. It has an
initial chapter that deals with NMR spectra and spectral assignments, followed by
a chapter on number-average sequence lengths in vinyl homopolymers (tacticity,