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Universal polymer analysis by 1H NMR using complementary trimethylsilyl end groups

: Päch, M.; Zehm, D.; Lange, M.; Dambowsky, I.; Weiss, J.; Laschewsky, A.


Journal of the American Chemical Society 132 (2010), No.25, pp.8757-8765
ISSN: 0002-7863
ISSN: 1520-5126
Journal Article
Fraunhofer IAP ()

New degenerative chain transfer agents, namely 4-(trimethylsilyl)benzyl 4-(trimethylsilyl)butane-dithioate, 4-(trimethylsilyl)benzyl 3-(trimethylsilyl)propyl trithiocarbonate and their 3-(trimethylsilyl)benzyl isomers, that are two-fold labeled with complementary trimethylsilyl (TMS) markers, were designed and shown to be powerful tools for universal polymer analysis by conventional 1H NMR spectroscopy. Their use in controlled free radical polymerization, here the reversible addition-fragmentation chain transfer (RAFT) method, resulted in polymers with low polydispersities up to high molar masses, as well as with defined complementary TMS end groups. Thus, routine 1H NMR spectra allowed facile determination of the molar masses of polymers of various chemical structures up to at least 105 g/mol, and simultaneously provided crucial information about the content of end groups that is typically >95% when polymerizations are correctly performed. Polymerizations were carried out in various solvents for two standard monomers, namely n-butyl acrylate and styrene, as well as for two specialty monomers, so-called inimers, namely 2-(2-chloropropionyloxy)ethyl acrylate and 2-(2-chloropropionyloxy)ethyl acrylamide. The complementary end group markers revealed marked differences in the suitability of commonly used solvents for RAFT polymerization. The results demonstrate—beyond good polymerization control—that the new RAFT agents are universal, powerful tools for facile polymer analysis by routine 1H NMR spectroscopy, of their absolute molar masses as well as of the content of end groups. This is crucial information, e.g., for the synthesis of high-quality telechelics and, in particular, of block copolymers, which is difficult to obtain by other methods. Preliminary screening experiments indicate that similar uses can be envisaged for analogous ATRP systems.