Rhodium(I)/Chiral Diene‐Catalyzed Enantioselective Addition of Boronic Acids to N‐Unsubstituted Isatin‐Derived Ketimines

Enantioselective addition of boronic acids to N‐unsubstituted isatin‐derived ketimines was realized using rhodium(I)/chiral diene catalysts. The reactions can be performed in the presence of catalytic amounts of a base to give adducts in high yield with high enantioselectivity. Preliminary mechanistic information including a computational model to explain the observed enantioselectivity is also provided.     

Diphenyl phosphate/4‐dimethylaminopyridine as an efficient binary organocatalyst system for controlled/living ring‐opening polymerization of L‐lactide leading to diblock and end‐functionalized poly(L‐lactide)s

The ring‐opening polymerizations (ROPs) of ε‐caprolactone (ε‐CL) and L ‐lactide (LLA) have been studied using the organocatalysts of diphenyl phosphate (DPP) and 4‐dimethylaminopyridine (DMAP). The “dual activation” property of DPP and the “bifunctional activation” property of DPP/DMAP were confirmed by the NMR measurement for ε‐CL and its chain‐end model of poly(ε‐caprolactone) and for LLA and its chain‐end model of poly(L ‐lactide) (PLLA), respectively. The molar ratio of DPP/DMAP was optimized as 1/2 for the ROP of LLA leading to the well‐defined PLLA, such as the molecular weight determined from ¹H NMR measurement of 19,200 g mol^?1 and the narrow polydispersity of 1.10. Additionally, functional initiators were utilized for producing the end‐functionalized PLLAs. The DPP‐catalyzed ROPs of ε‐CL and its analogue cyclic monomers and then the DPP/DMAP‐catalyzed ROP of LLA produced block copolymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1047–1054     

Host–guest complexation‐triggered chiroptical change of poly(phenylacetylene)s bearing binaphthocrown ether moieties on the main chain

Diacetylene monomers with respective lengths of the oxyethylene chains were cyclopolymerized with a rhodium catalyst to produce novel poly(phenylacetylene)s bearing a different cavity size of the chiral crown ether in the repeating units ( 2a – c ). In the circular dichroism spectra of the resulting polymers, characteristic Cotton effects were observed in the range from 350 to 500 nm corresponding to the absorption of the conjugated polymer backbone, indicating that the polymers possessed a helical structure with an excess single screw sense induced by the covalently bonded binaphthyl units. The host–guest complexation of 2a – c with achiral guests produced a chiroptical change based on the fluctuation in the main chain conformation. The behavior of the complexation‐induced chiroptical change was essentially dictated by the cavity size of the binaphthocrown ether units. Additionally, a chirality‐responsive helicity change was observed in the case of the complexation of 2a – c with chiral guests, which also depended on the crown ether size. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1197–1206, 2010     

Biodegradable thermoresponsive poly(amino acid)s

Reaction of poly(succinimide) with a mixture of 5-aminopentanol and 6-aminohexanol produced new thermoresponsive polymers based on biodegradable poly(amino acids)s, poly(N-substituted alpha/beta-asparagine)s, showing a clear LCST in water.     

Enantiomer‐selective polymerization of (RS)‐(phenoxymethyl)thiirane with diethylzinc/L‐amino acid

Enantiomer‐selective polymerization of (RS)‐(phenoxymethyl)thiirane (RS‐ 1 ) was carried out with ZnEt₂/L ‐α‐amino acid as an initiator system, and the effect of the initiator system on the enantiomer selectivity was examined with various amino acids. All polymerizations heterogeneously proceeded, and every initiating system was effective in producing optically active polymers. For the polymerization of RS‐ 1 with diethylzinc (ZnEt₂)/L ‐leucine (1/1), the conversion was 43.7% in 12 days, and the number‐average molecular weight of the polymer was 18,000. The enantiomer selectivity was maximum when the molar ratio of the two components in the ZnEt₂/L ‐α‐amino acid system was 1:1. When the ZnEt₂/L ‐leucine (1/1) system was used in the polymerization, the best result was obtained with an enantiomer‐selectivity value of 5.36. During the polymerization, the S enantiomer was preferentially consumed, and the isotactic‐rich polymer was enriched in the S configurational units produced. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3443–3448, 2002     

Synthesis and Mechanism of a Main‐Chain Chiral Polymer Based on Asymmetric Cyclopolymerization

A systematic study of the asymmetric cyclocopolymerization of bis(4‐vinylbenzoate)s, derived from chiral diols, with styrene has been made from the viewpoint of synthesizing the main‐chain chiral polymer. On the basis of using over 30 chiral diols as templates, we summarize the relationship between the structure of the chiral template and the chiroptical properties of the template‐free polymer. For simple chiral diols, the chirality induction efficiency increased in the order 1,2‐diol < 1,4‐diol < 1,3‐diol. Chiral diols with two chiral centers exhibited higher chirality induction efficiency than those having one chiral center only. The chirality induction efficiency for cyclic 1,2‐diols increased with the ring size in the order 5‐ < 6‐ < 7‐ < 8‐membered rings, and that for acyclic 1,2‐diols increased with the bulkiness of the substituent at the chiral center. In addition, a chirality induction mechanism has been proposed on the basis of model radical cyclization experiments and computational studies. Chirality induction could be caused by the inhibition of the formation of one racemo unit among the four stereoisomers due to the strong dependence of the stereoselectivity in intermolecular additions on the absolute configuration of the cyclized radical. The mechanism was examined using the Lewis‐acid and monomer‐concentration effects.     

Synthesis of a novel polymeric carbohydrate via regio‐ and stereoselective cyclopolymerization of 1,2:5,6‐dianhydrohexitol

The selective cyclopolymerization of 1,2:5,6‐dianhydrohexitols corresponding to diepoxides was a new synthetic strategy for polycarbohydrates, though the polymer is a lack of the anomeric linkage which is found in the naturally occurring polysaccharides. 1,2:5,6‐Dianhydro‐3,4‐di‐O‐methyl‐D‐mannitol, L‐iditol, and D‐glucitol were polymerized using t‐BuOK and BF₃·Oet₂ to produce the polymers consisting of five‐membered rings. On the other hand, the polymers consisting of six‐membered rings were obtained by the cationic and anionic polymerizations of meso allitol and galactitol monomers, respectively.     

End‐functionalization of polystyrene by malto‐oligosaccharide generating aggregation‐tunable polymeric reverse micelle

This article describes that glucose, maltose, maltotriose, maltotetraose, maltopentaose, and maltohexaose ( a , b , c , d , e , and f , respectively) were introduced into the initiating chain‐end of polystyrene (PSt) through the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO)‐mediated radical polymerization. A series of glycoconjuaged TEMPO‐adducts, 1a–f , was synthesized and used as the initiators for the polymerization of styrene (St) for 6 h at 120 °C to afford the end‐functionalized PSt's with the acetyl saccharides, 2a–f , in the yields of 37–43%. For 2a–f obtained by the polymerizations using the [St]/[ 1 ] of 125, 250, and 500, the number‐average molecular weights determined by size exclusion chromatography (SEC), M_n,SEC's, were 4800–6300, 8800–10,600, and 18,400–25,200, respectively, which fairly agreed with the predicted values. The end‐functionalized PSt's with saccharides, 3a–f , which were obtained from the deacetylation of 2a–f using sodium methoxide in dry THF, formed the polymeric reverse micelles consisting of a saccharide‐core and a PSt‐shell in chloroform and toluene. The static laser light scattering (SLS) measurements provided the average molar mass of the aggregates in toluene, M_w,SLS's, which ranged from 7.50 × 10⁴ to 1.77 × 10⁵ for 3a , from 1.90 × 10⁵ to 4.93 × 10⁵ for 3b , from 4.41 × 10⁵ to 7.21 × 10⁵ for 3c , from 5.85 × 10⁵ to 8.51 × 10⁵ for 3d , from 7.55 × 10⁵ to 8.53 × 10⁵ for 3e , and from 8.54 × 10⁵ to 9.26 × 10⁵ for 3f . The aggregation numbers, N_agg's, which were calculated from the M_w,SLS's, were from 7 to 24 for 3a , from 20 to 37 for 3b , from 34 to 89 for 3c , from 39 to 116 for 3d , from 41 to 145 for 3e , and from 31 to 146 for 3f . It was confirmed that the aggregation property, such as the M_w,SLS or N_agg values, was strongly related to the polymerization degrees of St (DP's) or the number of the glucose residues (n's) for 3a–f . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4864–4879, 2006     

Preparation and porous control of amorphous carbons by co-defluorination of perfluorooctane and octafluorotoluene in vapor phases at 423 K

Two types of perfluorocarbon compounds, aliphatic perfluorooctane and aromatic octafluorotoluene, were co-defluorinated using sodium metal, and amorphous carbons were deposited from the vapor phase at very low temperature, 423 K. The products showed morphologies composed of fibrous, platelet, and spherical forms, which were dependent on the mixing ratio of the two. The BET surface areas also correlated well with the ratio of the starting mixtures, indicating that the surface area could be adjusted by changing the mixing ratio of these two compounds. However, when the carbonaceous product was further annealed in situ at 573 or 673 K, the porosities also modified. First the porosity decreased at 573 K, then increased greatly at 673 K, where radical interaction to shrink the pores and crystal growth of template fluoride occurred at 573 K and 673 K, respectively.     

Copolymerization of ethylene and norbornene using cyclopentadienylzirconium trichloride activated by isobutyl‐modified methylaluminoxane

The copolymerization of ethylene (E) and norbornene (NB) was investigated using the commercially available and inexpensive catalyst system, cyclopentadienylzirconium trichloride (CpZrCl₃)/isobutyl‐modified methylaluminoxane (MMAO), at a moderate polymerization temperature in toluene. For the CpZrCl₃ catalyst system activated by aluminoxane with a 40 mol % methyl group and a 60 mol % isobutyl group (MMAO), the quantities of the charged NB and the polymerization temperature significantly affected the molecular weights, polydispersities, and NB contents of the obtained copolymers and the copolymerization activities in all the experiments. As the charged NB increased and thereby the NB/E molar ratio increased, the NB content in the copolymer increased and reached a maximum value of 71 mol %. The CpZrCl₃/MMAO ([Al]/[Zr] = 1000) catalyst system with the [NB] of 2.77 mol L^?1 and ethylene of 0.70 MPa at 50 °C showed the highest activity of 1690 kg mol_Zr^?1 h^?1 and molecular weight of 21,100 g mol^?1. The ¹³C NMR analysis showed that the CpZrCl₃/MMAO catalyst system produced the E‐NB random copolymer with a number of NB homosequences such as the NN dyad and NNN triad. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7411–7418, 2008