Stable isotopes and nuclear magnetic resonance

NMR methods can be applied to give quantitative determination of initiator-derived and other end groups and provide a wealth of information on the polymerization process. They provide a chemical probe of the detailed initiation mechanism and a greater understanding of polymer properties. The main advantage of NMR methods over alternative techniques for initiator residue detection is that NMR signals (in particular nC NMR) are extremely sensitive to the structural environment of the initiator residue. This means that functionality formed by tail addition, head addition, transfer to initiator or primary radical termination, and various initiator-derived byproducts can be distinguished. 

Selective labeling of the initiator allows substantial enhancement of the signals of the initiator residues relative to the signals due to the backbone. Various stable isotopes have been employed in this context (including D, F, l5N and 3IP), however, most work has involved the use of 1JC-labcling (Table 3.13). The method has been reviewed.536 58 l 58 The power of the technique is illustrated by the fact that one experiment allows the determination of  

The use of l3C-labeled initiators in assessing the kinetics and efficiency of initiation2 14,32 60,84 requires that the polymer end groups, residual initiator, and various initiator-derived byproducts should each give rise to discrete signals in the NMR spectrum. So far this method has been demonstrated for homo- and copolymerizations of S and MMA prepared with AIBN-a-L C3 AIBMc-a-13C or HlKi-carbonyl- C/BVQ-rmg- C (1 1) as initiator. 

Solomon, D.H. Moad, G. Makromol Chem.. Macromol. Symp. 1987, 10/11, 109. 

Solomon, D.H. In Comprehensive Polymer Science Eastmond, G.C.  

Solomon, D.H. Cadoli, P. Moad, G. Pure Appi Chem. 1985, 57, 985. 

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