Styrene-divinyl benzene IR Spectroscopy

Pendent vinyl groups in styrene-divinylbenzene copolymers have been analysed by IR and Raman spectroscopy [73-84] and by wet chemical methods [83, 85] after extents of reaction varying from before gelation to after nearly complete conversion of monomers. Periysamy and Ford [86] report a new analytical approach to the problem. Copolymers of styrene with methane- C-labelled p-divinylbenzene were analysed by liquid-state and solid-state cross-polarisation magic angle spinning (CP-MAS) i C-NMR methods. 

The residual vinyl groups of all labelled samples were analysed quantitatively from peak areas in the NMR spectra by two methods. First, the area of the 137 ppm vinyl peak was compared with the area of all of the aromatic carbon signals in the spectrum due to styrene and divinylbenzene carbons in natural abundance. Second, the area of the 137 ppm peak was compared with the area of all of the aliphatic carbon signals in the spectrum, which includes signals from polymerised labelled carbons of the DVB and from all other aliphatic carbons at natural abundance. It was assumed that all carbon atoms in the sample are equally detectable in each NMR spectrum (Table 9.6). All of the labelled polystyrene networks were also analysed by bromination of residual vinyl groups. 

The C-NMR and bromination methods were also applied to several commercial crosslinked polystyrenes prepared with unlabelled divinylbenzene, which usnally consists of a 2 1 metalpara mixture of isomers and contains also meta and para ethylvinylbenzene. NMR results for 20-80% crosslinked macroporous polymers are in Table 9.6. 

Periyasamy and Ford [86] concluded that all common styrene-DVB copolymers, even those containing as little as 1 % DVB, contain imreacted DVB vinyl groups. No method is available yet for accurate, quantitative analysis of the residual vinyl groups because wet chemical methods do not detect vinyl groups in the most hindered parts of the highly crosslinked, heterogeneous networks. IR and C-NMR analyses may contain systematic errors in peak area determinations. 

DVB (wt%) Polymerisation temperature (°C) CP-MAS Direct polarisation Bromine addition  

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