NMR Sequence Analysis for Copolymers Made at High Conversions

NMR analysis of compositional heterogeneity in polysaccharides

Many copolysaccharides are compositionally heterogeneous, and the composition determined by the usual analytical or spectroscopic methods provides only an average value. For some polysaccharides, the NMR data contain copolymer sequence information, such as diad, triad, and tetrad sequence intensities. In such cases, it is possible to estimate the extent of compositional heterogeneity through NMR. Two general types of methodologies can be used: perturbed Markovian and discrete component approaches. The theoretical bases for these approaches are reviewed in this work, and three examples are shown of the application of these NMR methodologies to copolysaccharides.

Mass spectra of copolymers which display compositional drifts or sequence constraints

The spectral features appearing in mass spectra of random and block copolymers which display a drift in composition are discussed along with features appearing in mass spectra of terpolymers and tetrapolymers with sequence constraints. It is shown that previous models cannot account for these features. A new model is presented and a compact equation is derived which yields MS intensities. The prediction of the model is compared with some literature data, namely mass spectrometric data concerning a block copolymer sample containing units of alpha-methyl styrene and of methylmethacrylate which display a strong drift in composition, the molar fraction of methylmethacrylate units changing from 0.99 to 0.80 when passing from short to long macromolecular chains. The agreement between theory and experiment is good. A hyperbranched polymer obtained by condensing 4,4'-bis[p(acetoxy)phenyl] valeric acid (referred to as diphenolic acid, DPA) was then considered. The polymer turned out to be a copolymer with regular DPA units and modified DPA units (possessing a phenol group). The molar fraction of regular DPA units changes from 0.80 to 0.95 when passing from low masses to high masses. Copolymers with sequence constraints are considered, such as ABC copolymers in which AA cannot be found along the chain or ABCD copolymers in which A cannot follow A, B cannot follow B, etc. The novel method is applied to an exactly alternating copolymer with units of styrene (St) and maleic anhydride (MAH). The St-MAH sample turned out to be a complex mixture and the presence of a small amount of units of maleic acid (MAC) is detected. The abundance of MAC, estimated by the chain statistical method, is 5%. The method is applied to the copolymer obtained by reactive blending of poly(butylene terephthalate) and poly(bisphenolA carbonate). In this case, the theoretical spectra are generated and spectral features are discussed.