Mass spectra of copolymers which display compositional drifts or sequence constraints

Abstract

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 α-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.