Polymerisation spinning method

A review of the application of ESR to the study of free radical polymerisation is given by Yamada and co-workers [146]. A survey of the application ESR spectroscopy spin label/probe methods in heterogeneous polymer systems is provided by Veksli and co-workers [147]. Spin probe methods allow the study of the MD of the polymer, its free volume, phase separation and phase morphology. 

It was reasoned that the polymer must consist of a, a -coupled pyrrole units, with fi coupling less important, because of the fact that oc-substituted pyrroles do not polymerise whereas -substituted species do, and on the basis of magic angle spinning 13C nmr and IR techniques. The method of labelling the monomer ring positions is also shown in Scheme 3.9. 

Polymers with more than one type of repeating unit are referred to as copolymers, and they are important in that they have properties different from either homopolymer. One example of a copolymer is polyethylene-vinylacetate which is widely used as a hot melt adhesive. Another is acrylic fibre where a small amount of comonomer added to acrylonitrile makes it easier to spin and to dye. In both these examples the monomers are mixed together and then polymerised by a free radical process the resulting copolymer has a random arrangement of the two units along the chain. Using more specific methods of polymerisation it is possible to prepare block and graft copolymers. 

ESR has been useful in studying the influence of dissolved gases on polymer mobility [801]. Stable nitroxyl radicals, such as 2,2,6,6-tetramethylpipe-ridin-l-oxyl (TEMPO) are widely employed as spectroscopic probes for observing binding sites and molecular motion of macromolecules [802]. ESR spectra of the TEMPO free radical in PC film at various temperature and in solution were reported [795]. The TEMPO spin probe method was also used to study diisooctylphthalate (DIOP) plasticiser diffusion in suspension polymerised PVC particles [803]. Similarly, the compatibility Umit of PVAc and di-nonylphthalate (DNP) was studied by means of 2,2-di-n-nonyl-5,5-dimethyl-3-oxazolidinyloxy spin probe ESR measurements and DSC [804] DNP is an effective plasticiser for PVAc for concentrations not exceeding 17 wt.%. According to ESR evidence BBP in PVC forms radicals more easily than DOP [805]. 

AU of these methods produce randomly labelled polymers with the labels on in-chain segments. End-labelled i>olymers are generally prepared by anionic polymerisations. The living chain end is terminated with a suitably functionalised spin label, usually an acid chloride [11]. A different method was used to prepare end labelled poly(n-butyl isocyanate) [12]. Here the spin label 2,2,5,5- tet-ramethyl-l-pyrrolidinyloxy-3-carboxamide was used as an initiator in competition with cyanide ion (Scheme 5). This produced a spin concentration of one label per three polymer chains. 

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