Jun-Hwan Ahn

Synthesis of well-defined block copolymers of n-hexyl isocyanate with isoprene by living anionic polymerization

n-Hexyl isocyanate (HIC) was polymerized at different reaction temperatures and times, using alkali metal naphthalenide, via anionic polymerization in THF. To prevent the formation of trimers, the polymerization of HIC was also performed utilizing sodium tetraphenylborate (NaBPh4) as a common ion salt. As the reaction temperature decreases, yield of the polymer increases due to stabilization of the active amidate anion at low temperature. In the absence of the additive, a quantitative yield was obtained at −98 °C. However, after most of the monomer was polymerized, further reaction led to trimerization. This was prevented in the presence of NaBPh4 effectively and the living polymerization was performed successfully at −98 °C. The reaction rate retarded with increasing concentration of NaBPh4, the optimum concentration of NaBPh4 was 10 times the concentration of the initiator for the living polymerization of HIC. The living system led to the polymers of molecular weight (MW) as high as 50,000 g/mol. The observed MW was well in agreement with the calculated one. At the higher reaction temperature, −78 °C, the quantitative yield was obtained at 2 min of the reaction time, however the living character was not observed at longer reaction time. The study indicated that the amidate anion was stabilized using NaBPh4 having bulky contact ion pair. The block copolymer of HIC with isoprene, poly(HIC-b-isoprene-b-HIC), was synthesized with help of the living character of polyisoprene and NaBPh4. The morphology and composition of the block copolymers were investigated using TEM and 1H NMR, respectively.

Anionic polymerization of isocyanates with optical functionalities

Abstract Polyisocyanates of 2-[4-(4-nitrophenylazo)-N-ethylphenyl amino]ethoxy carbonyl amino hexyl isocyanate, DR1NCO, and (s)-(−)-2-methyl-1-butyloxy carbonyl amino hexyl isocyanate, MBI, were synthesized by anionic polymerization using sodium naphthalenide as an initiator in THF at −98°C. In the polymerization reaction, crown ether (15C5) and octyl isocyanate (Oct-NCO) were used to suppress side reactions such as backbiting or chain transfer reaction. In the homopolymerization of DR1NCO, the polymers with high yield (∼94%) were obtained due to suppression of backbiting by 15C5. In the random copolymerization of DR1NCO with MBI, the chain transfer reaction was suppressed due to the low reactivity of anionic chain end induced by octyl isocyanate. The random copolymers showed the optical activity in CD and ORD measurements, and specific rotations increased with increasing the component of MBI.

Anionic Polymerization of Chiral Isocyanate and Influence of the Initiator on Changes in the Optical Activity

A chiral polyisocyanate, poly[6-{1-[(S)-(–)-2-methylbutyl]oxycarbonylamino}hexyl isocyanate], was synthesized using sodium diphenylmethanide and sodium naphthalenide as unidirectional and bidirectional initiators, respectively, via anionic polymerization in THF at –98°C. NaBPh4 as a common ion salt was used to produce the polymer in quantitative yield and with narrow molecular-weight distribution. The polymer showed different optical activity depending on the nature of the initiator.

Anionic Polymerization of Isocyanates with Optically Active Properties

Abstract Random copolymers, an optically functionalized isocyanate containing disperse red 1 (DR1NCO) with a chiral isocyanate containing (s)-(-)-2-methylbutanol (MBI), were prepared by anionic polymerization in THF at -98°C with Na-Naph as a two-directional initiator. As the contents of MBI in the copolymer increased, the optical rotation of the polymer was also increased. To study about the optical activity change with initiator systems, homo polymer of MBI was synthesized with one-directional and two-directional initiator. The difference of optical activity in both systems was investigated using Circular Dichroism (CD) spectroscopy and optical rotation.