Sequencing in Copolymers

Earlier work on the application of this techniqne to seqnencing studies on copolymers was fairly inconclusive [30-48]. These measurements were difficult and complex. 

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Stereosequence in homopolymers and monomer sequence in copolymers will influence the mechanical and physical properties of the polymer. 

In a combined MALDI-ToF MS, ion mobility experiment and molecular modelling study, Baker and co-workers [120] studied the sequencing in copolymers of glycidyl methacrylate and butyl methacrylate, Figure 20, with different termination groups. 

This section deals with the effect of monomeric sequences in copolymer chains upon TLC separation. A possibility of separating copolymers by the difference in their chain architectures was first demonstrated by Kamiyama et al. S9 For the preliminary TLC experiment they used copolymers composed of styrene and methyl methacrylate, for the reason that this comonomer pair is endowed with the possibility of being polymerized to three different chain architectures, namely, alternating61 , statistical, and block. 

Both the early data and the more precise values given in Table 20A differ significantly from published estimates based on monomer and polymer composition (e.g. rj r2 = 0.60 in Table 19). As all the data relate to the, in general, more consistent soluble vanadium systems, this work reinforces doubts concerning the accuracy of much of the published information. A complication is that since C2 and C4 sequences are observed in ethylene/propene copolymers inverted head to head prop-ene units must be present and this will reduce the accuracy of analyses of EP sequences. In copolymers prepared by VC /AlEtj 4% of head to head propene sequences have been reported with the catalyst VCl4/AlEt2Cl which is syndiospecific for polypropene 8% of head to head sequences was found [295]. ... 

A quantitative procedure for the characterization of the distribution of diad sequences in copolymers has been developed [14-19]. In this procedure, the relative yields of dimers Yaa, Yab and Ybb in the pyrolysate of a copolymer are experimentally determined in order to evaluate the diad concentrations [P ], [P ] and P ]. These concentrations are related to the yields Yaa, Yab and Ybb by the relations ... 

A different way to introduce silicone type sequences in copolymers is to attach acrylate end groups to a poly[oxy(dimethylsilylene)], followed by copolymerization in a vinyl type polymer. The introduction of silicone groups leads to a crosslinked material similar to that obtained with poly(ethylene glycol) dimethacrylate. The structure of a copolymer with silicone crosslinking bridges is shown below ... 

The polymerisation processes described in the previous section are the classical processes used for producing the bulk commercial polymers. Newer processes have been and are being developed with a variety of aims in mind. These involve the production of novel polymer topologies (see box) precise control over chain length and over monomer sequences in copolymers control of isomerism (see section 4.1) production of polymers with special reactive end groups, the so-called telechelic polymers, production of specially designed thermally stable polymers and liquid-crystal polymers with a variety of different structures and properties. Other developments include the production of polymers with very precisely defined molar masses, and of networks with precisely defined chain lengths... 

Plage, B. and Schulten, H.R., Sequences in Copolymers Studied by High-Mass Oligomers in Pyrolysis-Field Ionization Mass Spectrometry, Angew Makromol Chem, 184, 133 (1991). 

This assumption implies that there are no mass discrimination effects, i.e., that ion fragmentation, ionization yield, ion trasmittance, and detector response are independent of oligomer molar mass. Notably, in the case of the determination of composition and sequence in copolymers by MS techniques (Chapter 2), where one needs only to consider the relative intensity of the co-oligomers of the same length, the assumption that the relative peak intensities reflect the relative co-oligomers abundance has been proven valid. ... 

The ability of NMR spectroscopy to distinguish between dyads, triads, and higher n-ad sequences in copolymers makes it an especially powerful tool for the polymer chemist interested in the fine details of molecular structure. In this chapter, we have seen that simple expressions derived from the relative abundances of various sequence types allow characterisation of the copolymer microstructure in terms of number-average sequence lengths, without any recourse to a statistical model. A more detailed examination of copolymer... 

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