Tomohiro Hirano - Academia.edu (original) (raw)

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Papers by Tomohiro Hirano

Research paper thumbnail of De‐ tert ‐butylation of poly( N ‐ tert ‐butyl‐ N ‐ n ‐propylacrylamide): Stereochemical analysis at the triad level

Journal of Polymer Science

Research paper thumbnail of NMR Analysis of Poly(Lactic Acid) via Statistical Models

Polymers

The physical properties of poly(lactic acid) (PLA) are influenced by its stereoregularity and ste... more The physical properties of poly(lactic acid) (PLA) are influenced by its stereoregularity and stereosequence distribution, and its polymer stereochemistry can be effectively studied by NMR spectroscopy. In previously published NMR studies of PLA tacticity, the NMR data were fitted to pair-addition Bernoullian models. In this work, we prepared several PLA samples with a tin catalyst at different L,L-lactide and D,D-lactide ratios. Upon analysis of the tetrad intensities with the pair-addition Bernoullian model, we found substantial deviations between observed and calculated intensities due to the presence of transesterification and racemization during the polymerization processes. We formulated a two-state (pair-addition Bernoullian and single-addition Bernoullian) model, and it gave a better fit to the observed data. The use of the two-state model provides a quantitative measure of the extent of transesterification and racemization, and potentially yields useful information on the p...

Research paper thumbnail of Thermally induced cationic polymerization of isobutyl vinyl ether in toluene in the presence of solvate ionic liquid

Polymer Chemistry

Cationic polymerization of isobutyl vinyl ether at elevated temperatures of 60–100 °C, in which t... more Cationic polymerization of isobutyl vinyl ether at elevated temperatures of 60–100 °C, in which the propagating cations are stabilized with a solvate ionic liquid, is described.

Research paper thumbnail of Effects of Syndiotacticity on the Dynamic and Static Phase Separation Properties of Poly( N -isopropylacrylamide) in Aqueous Solution

The Journal of Physical Chemistry B, 2016

The dynamic and static phase separation behavior in aqueous poly(N-isopropylacrylamide) (PNIPAM) ... more The dynamic and static phase separation behavior in aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions is highly sensitive to the tacticity of PNIPAM. We investigated the phase separation dynamics of aqueous solutions of PNIPAM with different tacticities (atactic and syndiotactic-rich types), and found that the phase separation dynamics of syndiotactic-rich PNIPAM was much different from that of atactic-type PNIPAM. First, phase separation in syndiotactic-rich PNIPAM was faster. Second, there was a critical point (C cp) in the concentration dependence of the phase separation rate: the phase separation accelerated dramatically when the solution concentration was higher than 2.0 wt% (= C cp). Third, syndiotactic-rich PNIPAM required a higher thermal energy for phase separation compared to atactic PNIPAM. Such behavior can be explained on the basis of the high hydrophobicity of syndiotactic-rich PNIPAM in a dehydrated state and a diffusion-controlled aggregation model. The present study shows that precise control of the stereoregularity will open new channels toward the design and development of stimuli-responsive-polymer-based smart materials.

Research paper thumbnail of Initiator-fragment incorporation radical copolymerization of divinylbenzene andN-isopropylacrylamide with dimethyl 2,2?-azobisisobutyrate: Formation of soluble hyperbranched polymer nanoparticle

J Polym Sci a Polym Chem, 2004

Research paper thumbnail of Hydrogen-bond-assisted stereocontrol in the radical polymerization ofN-isopropylacrylamide with secondary alkyl phosphate: The effect of the bulkiness of the ester group

J Polym Sci a Polym Chem, 2005

The radical polymerizations of N-isopropylacrylamide (NIPAAm) were carried out in toluene at low ... more The radical polymerizations of N-isopropylacrylamide (NIPAAm) were carried out in toluene at low temperatures in the presence of phosphoric acid esters such as trimethyl phosphate, triethyl phosphate (TEP), tri-n-propyl phosphate, and tri-nbutyl phosphate (TBP). Syndiotactically rich poly(NIPAAm)s were obtained from Ϫ60 to 0°C, and TEP provided the highest syndiotacticity (racemo dyad ϭ 65%) at Ϫ40°C. On the other hand, lowering the temperature reversed the stereoselectivity of the propagation reaction so that isotactically rich poly(NIPAAm)s were obtained at Ϫ80°C. In particular, TBP exhibited the most isotactic specificity (meso dyad ϭ 57%). Job's plots for NIPAAm-TBP mixtures revealed that NIPAAm and TBP formed a 1:1 complex at 0°C and a predominantly 1:2 complex at Ϫ80°C through a hydrogen-bonding interaction. Therefore, the stereospecificity of NIPAAm polymerization should depend on the stoichiometry of the hydrogen-bond-assisted complex. Thus, the mechanism for this polymerization system was discussed.

Research paper thumbnail of Hydrogen-bond-assisted syndiotactic-specific radical polymerization ofN,N-dimethylacrylamide in the presence of tartrates

J Polym Sci a Polym Chem, 2008

Research paper thumbnail of Polymerization of Vinyl Acetate Initiated with Di‐tert‐butyl Perfumarate

Macromolecular Chemistry and Physics, May 1, 2001

Research paper thumbnail of Kinetic and ESR studies on the radical polymerization of ?-n-(??-methylbenzyl) ?-ethyl itaconamates derived from racemic and (s)-?-methylbenzylamines

J Polym Sci a Polym Chem, 2000

Research paper thumbnail of Metal-free isotactic-specific radical polymerization of N-isopropylacrylamide with pyridine N-oxide derivatives: The effect of methyl substituents of pyridine N-oxide on the isotactic specificity and the proposed mechanism for the isotactic-specific radical polymerization

Polymer, Jan 21, 2008

The radical polymerizations of N-isopropylacrylamide (NIPAAm) in chloroform at low temperatures i... more The radical polymerizations of N-isopropylacrylamide (NIPAAm) in chloroform at low temperatures in the presence of pyridine N-oxide (PNO) derivatives were investigated. It was found that the methylation at meta-positions of PNO improved the isotactic specificity induced by PNO, whereas the methylation at ortho-positions prevented the induction of the isotactic specificity. NMR analysis revealed that NIPAAm and PNO derivatives formed predominantly

Research paper thumbnail of Effect of Ester Compounds on Stereospecificity in Metacrylate Polmerization with t-Butyllithium/Bis(2,6-di-t-butylphenoxy) methylaluminum

Polymer Journal, Sep 15, 1998

ABSTRACT

Research paper thumbnail of Vinyl polymerization with a binary system of p-chlorobenzenediazonium salt and sodium tetraphenylborate

Journal of Polymer Science Part a Polymer Chemistry, Dec 15, 2001

Research paper thumbnail of Kinetic and ESR studies on the radical polymerization of alpha-n-(alpha'-methylbenzyl) beta-ethyl itaconamates derived from racemic and (s)-alpha-methylbenzylamines

Research paper thumbnail of Unusual Distribution of Degree of Polymerization Observed for Heterotactic Oligomer of Allyl Methacrylate

Macromolecules, Mar 1, 2000

Research paper thumbnail of Multivariate analysis of 13C NMR spectra of methacrylate copolymers and homopolymer blends

Polymer, Jul 1, 2009

13 C NMR spectra of copolymers of methyl methacrylate and tert-butyl methacrylate with various ch... more 13 C NMR spectra of copolymers of methyl methacrylate and tert-butyl methacrylate with various chemical compositions, the homopolymers of the two methacrylates, and blends of the homopolymers with various blend ratios were subjected to principal component analysis. The first and second principal components correlated chemical composition and the randomness of comonomer sequence, respectively. Chemical composition of the copolymers was determined with high accuracy and precision by the partial least-squares regression without assignment of individual resonance peaks.

Research paper thumbnail of Dual roles of alkyl alcohols as syndiotactic-specificity inducers and accelerators in the radical polymerization ofN-isopropylacrylamide and some properties of syndiotactic poly(N-isopropylacrylamide)

J Polym Sci a Polym Chem, 2006

Research paper thumbnail of Kinetic and ESR studies on radical polymerization behavior ofN-(2-phenylethoxycarbonyl)methacrylamide

J Polym Sci a Polym Chem, 2000

Research paper thumbnail of Living ring-opening polymerization of -caprolactone with combinations of tert-butyllithium and bilky aluminium phenoxides

Research paper thumbnail of Elementary reaction analysis of the radical polymerization of ?-ethyl ?-N-(?-methylbenzyl)itaconamates carrying (RS)- and (S)-?-methylbenzylaminocarbonyl groups

J Polym Sci a Polym Chem, 2003

Research paper thumbnail of Significant effect of hydrogen-bonding interaction on syndiotactic-specificity in radical polymerization ofN-isopropylacrylamide

J Polym Sci a Polym Chem, 2004

Research paper thumbnail of De‐ tert ‐butylation of poly( N ‐ tert ‐butyl‐ N ‐ n ‐propylacrylamide): Stereochemical analysis at the triad level

Journal of Polymer Science

Research paper thumbnail of NMR Analysis of Poly(Lactic Acid) via Statistical Models

Polymers

The physical properties of poly(lactic acid) (PLA) are influenced by its stereoregularity and ste... more The physical properties of poly(lactic acid) (PLA) are influenced by its stereoregularity and stereosequence distribution, and its polymer stereochemistry can be effectively studied by NMR spectroscopy. In previously published NMR studies of PLA tacticity, the NMR data were fitted to pair-addition Bernoullian models. In this work, we prepared several PLA samples with a tin catalyst at different L,L-lactide and D,D-lactide ratios. Upon analysis of the tetrad intensities with the pair-addition Bernoullian model, we found substantial deviations between observed and calculated intensities due to the presence of transesterification and racemization during the polymerization processes. We formulated a two-state (pair-addition Bernoullian and single-addition Bernoullian) model, and it gave a better fit to the observed data. The use of the two-state model provides a quantitative measure of the extent of transesterification and racemization, and potentially yields useful information on the p...

Research paper thumbnail of Thermally induced cationic polymerization of isobutyl vinyl ether in toluene in the presence of solvate ionic liquid

Polymer Chemistry

Cationic polymerization of isobutyl vinyl ether at elevated temperatures of 60–100 °C, in which t... more Cationic polymerization of isobutyl vinyl ether at elevated temperatures of 60–100 °C, in which the propagating cations are stabilized with a solvate ionic liquid, is described.

Research paper thumbnail of Effects of Syndiotacticity on the Dynamic and Static Phase Separation Properties of Poly( N -isopropylacrylamide) in Aqueous Solution

The Journal of Physical Chemistry B, 2016

The dynamic and static phase separation behavior in aqueous poly(N-isopropylacrylamide) (PNIPAM) ... more The dynamic and static phase separation behavior in aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions is highly sensitive to the tacticity of PNIPAM. We investigated the phase separation dynamics of aqueous solutions of PNIPAM with different tacticities (atactic and syndiotactic-rich types), and found that the phase separation dynamics of syndiotactic-rich PNIPAM was much different from that of atactic-type PNIPAM. First, phase separation in syndiotactic-rich PNIPAM was faster. Second, there was a critical point (C cp) in the concentration dependence of the phase separation rate: the phase separation accelerated dramatically when the solution concentration was higher than 2.0 wt% (= C cp). Third, syndiotactic-rich PNIPAM required a higher thermal energy for phase separation compared to atactic PNIPAM. Such behavior can be explained on the basis of the high hydrophobicity of syndiotactic-rich PNIPAM in a dehydrated state and a diffusion-controlled aggregation model. The present study shows that precise control of the stereoregularity will open new channels toward the design and development of stimuli-responsive-polymer-based smart materials.

Research paper thumbnail of Initiator-fragment incorporation radical copolymerization of divinylbenzene andN-isopropylacrylamide with dimethyl 2,2?-azobisisobutyrate: Formation of soluble hyperbranched polymer nanoparticle

J Polym Sci a Polym Chem, 2004

Research paper thumbnail of Hydrogen-bond-assisted stereocontrol in the radical polymerization ofN-isopropylacrylamide with secondary alkyl phosphate: The effect of the bulkiness of the ester group

J Polym Sci a Polym Chem, 2005

The radical polymerizations of N-isopropylacrylamide (NIPAAm) were carried out in toluene at low ... more The radical polymerizations of N-isopropylacrylamide (NIPAAm) were carried out in toluene at low temperatures in the presence of phosphoric acid esters such as trimethyl phosphate, triethyl phosphate (TEP), tri-n-propyl phosphate, and tri-nbutyl phosphate (TBP). Syndiotactically rich poly(NIPAAm)s were obtained from Ϫ60 to 0°C, and TEP provided the highest syndiotacticity (racemo dyad ϭ 65%) at Ϫ40°C. On the other hand, lowering the temperature reversed the stereoselectivity of the propagation reaction so that isotactically rich poly(NIPAAm)s were obtained at Ϫ80°C. In particular, TBP exhibited the most isotactic specificity (meso dyad ϭ 57%). Job's plots for NIPAAm-TBP mixtures revealed that NIPAAm and TBP formed a 1:1 complex at 0°C and a predominantly 1:2 complex at Ϫ80°C through a hydrogen-bonding interaction. Therefore, the stereospecificity of NIPAAm polymerization should depend on the stoichiometry of the hydrogen-bond-assisted complex. Thus, the mechanism for this polymerization system was discussed.

Research paper thumbnail of Hydrogen-bond-assisted syndiotactic-specific radical polymerization ofN,N-dimethylacrylamide in the presence of tartrates

J Polym Sci a Polym Chem, 2008

Research paper thumbnail of Polymerization of Vinyl Acetate Initiated with Di‐tert‐butyl Perfumarate

Macromolecular Chemistry and Physics, May 1, 2001

Research paper thumbnail of Kinetic and ESR studies on the radical polymerization of ?-n-(??-methylbenzyl) ?-ethyl itaconamates derived from racemic and (s)-?-methylbenzylamines

J Polym Sci a Polym Chem, 2000

Research paper thumbnail of Metal-free isotactic-specific radical polymerization of N-isopropylacrylamide with pyridine N-oxide derivatives: The effect of methyl substituents of pyridine N-oxide on the isotactic specificity and the proposed mechanism for the isotactic-specific radical polymerization

Polymer, Jan 21, 2008

The radical polymerizations of N-isopropylacrylamide (NIPAAm) in chloroform at low temperatures i... more The radical polymerizations of N-isopropylacrylamide (NIPAAm) in chloroform at low temperatures in the presence of pyridine N-oxide (PNO) derivatives were investigated. It was found that the methylation at meta-positions of PNO improved the isotactic specificity induced by PNO, whereas the methylation at ortho-positions prevented the induction of the isotactic specificity. NMR analysis revealed that NIPAAm and PNO derivatives formed predominantly

Research paper thumbnail of Effect of Ester Compounds on Stereospecificity in Metacrylate Polmerization with t-Butyllithium/Bis(2,6-di-t-butylphenoxy) methylaluminum

Polymer Journal, Sep 15, 1998

ABSTRACT

Research paper thumbnail of Vinyl polymerization with a binary system of p-chlorobenzenediazonium salt and sodium tetraphenylborate

Journal of Polymer Science Part a Polymer Chemistry, Dec 15, 2001

Research paper thumbnail of Kinetic and ESR studies on the radical polymerization of alpha-n-(alpha'-methylbenzyl) beta-ethyl itaconamates derived from racemic and (s)-alpha-methylbenzylamines

Research paper thumbnail of Unusual Distribution of Degree of Polymerization Observed for Heterotactic Oligomer of Allyl Methacrylate

Macromolecules, Mar 1, 2000

Research paper thumbnail of Multivariate analysis of 13C NMR spectra of methacrylate copolymers and homopolymer blends

Polymer, Jul 1, 2009

13 C NMR spectra of copolymers of methyl methacrylate and tert-butyl methacrylate with various ch... more 13 C NMR spectra of copolymers of methyl methacrylate and tert-butyl methacrylate with various chemical compositions, the homopolymers of the two methacrylates, and blends of the homopolymers with various blend ratios were subjected to principal component analysis. The first and second principal components correlated chemical composition and the randomness of comonomer sequence, respectively. Chemical composition of the copolymers was determined with high accuracy and precision by the partial least-squares regression without assignment of individual resonance peaks.

Research paper thumbnail of Dual roles of alkyl alcohols as syndiotactic-specificity inducers and accelerators in the radical polymerization ofN-isopropylacrylamide and some properties of syndiotactic poly(N-isopropylacrylamide)

J Polym Sci a Polym Chem, 2006

Research paper thumbnail of Kinetic and ESR studies on radical polymerization behavior ofN-(2-phenylethoxycarbonyl)methacrylamide

J Polym Sci a Polym Chem, 2000

Research paper thumbnail of Living ring-opening polymerization of -caprolactone with combinations of tert-butyllithium and bilky aluminium phenoxides

Research paper thumbnail of Elementary reaction analysis of the radical polymerization of ?-ethyl ?-N-(?-methylbenzyl)itaconamates carrying (RS)- and (S)-?-methylbenzylaminocarbonyl groups

J Polym Sci a Polym Chem, 2003

Research paper thumbnail of Significant effect of hydrogen-bonding interaction on syndiotactic-specificity in radical polymerization ofN-isopropylacrylamide

J Polym Sci a Polym Chem, 2004