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Shin, Yeong-Deuk,Rahman, M. Shahinur,Samal, Shashadhar,Lee, Jae-Suk WILEY-VCH Verlag 2006 Macromolecular symposia Vol.240 No.1
<P>The synthesis of new isocyanate monomers and their polymerization by anionic route is reported. Reaction of 1,6-diisocyanatohexane with aliphatic alcohols such as methanol, n-propanol and n-pentanol in 1:0.5 molar ratios was carried out in the presence of pyridine such that one &n.bond;NCO group remained unreacted. The anionic polymerization of n-alkoxycarbonylaminohexyl isocyanates was carried out using sodium napthalenide (Na-Naph) initiator in the presence of 15-crown-5 (15C5) and sodium tetraphenylborate as the additives. While polymerization of n-propyloxycarbonylaminohexyl isocyanate (PAHI) and n-pentanoxycarbonylaminohexyl isocyanate (PEAHI) was feasible that of methoxycarbonylaminohexyl isocyanate (MAHI) led to an insoluble material. The polymers were isolated in high yields with NaBPh<SUB>4</SUB> as the additive.</P>
Jang, Yun Hee,Lansac, Yves,Kim, Jae-Ki,Yoo, Hee-Soo,Chae, Chang-Geun,Choi, Cheol Ho,Samal, Shashadhar,Lee, Jae-Suk The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.45
<P>Sodium benzanilide (Na<SUP>+</SUP>BA<SUP>−</SUP>) initiators have opened a new route to living anionic polymerization of <I>n</I>-hexylisocyanate (HIC) with 100% yield and controlled molecular weight. The NaBA initiators not only provide initiation points for polymerization by attacking HIC monomers but also successfully prevent <I>back-biting</I> side reactions without any help from additives. Our hypothesis on this dual function of the NaBA initiators is that they self-assemble to form protection shields around the chain ends. Indeed, our density functional theory calculations performed under experimental conditions on the free energy of formation of (NaBA)<SUB><I>n</I></SUB> clusters of various sizes and conformations searched by Monte Carlo simulations show that the BA<SUP>−</SUP> moiety forms a stable complex with Na<SUP>+</SUP> in a fan-like circular-sector shape owing to its double binding sites (N<SUP>−</SUP>–C&z.dbd;O ↔ N&z.dbd;C–O<SUP>−</SUP>) and that the tightly-bound NaBA units spontaneously self-assemble to form small (NaBA)<SUB><I>n</I></SUB> clusters (<I>n</I> = 2 and 4). The growing end of the polymer chain [(BA)(HIC)<SUB><I>n</I></SUB><SUP>−</SUP>], which resembles BA<SUP>−</SUP>, would also assemble with <I>n</I>− 1 NaBA units to form an <I>n</I>-mer cluster. We expect that the chain end in this cluster would be more available to attack small HIC monomers coming into the cluster (leading to chain growth) rather than folding back to attack the middle of the chain (leading to cyclotrimerization to isocyanurates and depolymerization).</P> <P>Graphic Abstract</P><P>The origin of the living nature of isocyanate polymerization by sodium benzanilide (Na<SUP>+</SUP>BA<SUP>−</SUP>) initiator is understood from the relative stabilities of (NaBA)<SUB><I>n</I></SUB> clusters in THF solution. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp03596h'> </P>