Accelerating Simulated Annealing of Glassy Materials with Data Assimilation

The ultra-long relaxation time of glass transition makes it difficult to construct atomic models of amorphous materials by conventional methods. We propose a novel method for building such atomic models using data assimilation method by simulated annealing with an accurately computed interatomic potential augmented by penalty from experimental data. The advantage of this method is that not only can it reproduce experimental data as the structure refinement methods like reverse Monte Carlo but also obtain the reasonable structure in terms of interatomic potential energy. In addition, thanks to the interatomic potential, we do not need high $Q$ range diffraction data, which is necessary to take into account the short-range order. Persistent homology analysis shows that the amorphous ice obtained by the new method is indeed more ordered at intermediate range

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

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 2:1 complex through a hydrogen bonding interaction. Furthermore, the induction of the isotactic-specificity was attributed to the conformationally-limited propagating radicals. Based on these findings, the mechanism of the isotactic-specific radical polymerization was discussed

Hydrogen-bond-assisted syndiotactic-specific radical polymerization of N-isopropylacrylamide : The solvent effect on the stereospecificity

Radical polymerizations of N-isopropylacrylamide (NIPAAm) in several solvents at low temperatures in the absence or presence of hexamethylphosphoramide (HMPA) or 3-methyl-3-pentanol (3Me3PenOH) were examined. The isotacticities of the poly(NIPAAm)s obtained in the absence of HMPA and 3Me3PenOH at lower temperatures slightly increased as the polarities of the solvents used increased. The addition of HMPA significantly induced the syndiotactic-specificity even in polar solvents such as tetrahydrofuran and acetone, although the use of the solvents having proton-donating ability, such as chloroform, prevented the induction of the syndiotactic-specificity, even if their polarities are low. In the presence of 3Me3PenOH, a good correlation between the polarities of the solvents used and the syndiotacticities of the obtained poly(NIPAAm)s was observed, and poly(NIPAAm) with r = 73% was obtained using the toluene/methylcyclohexane mixed solvent

Direct synthesis of syndiotactic-rich poly(N-isopropylacrylamide) via radical polymerization of hydrogen-bond-complexed monomer

Radical polymerization of N-isopropylacrylamide (NIPAAm) in toluene was investigated in the presence of hexamethylphosphoramide (HMPA). We succeeded in directly preparing syndiotactic-rich poly(NIPAAm), the syndiotacticity of which (r = 70%) is the highest among those of radically-prepared poly(NIPAAm)s so far reported, by lowering polymerization temperature to –60°C in the presence of a twofold amount of HMPA. The NMR analysis revealed that the induced syndiotactic-specificity was ascribed to 1:1 complex formation between NIPAAm and HMPA. Furthermore, thermodynamic analysis described that the induced syndiotactic-specificity was enthalpically achieved

HYDROGEN-BONDING INTERACTION IN DBI POLYMERIZATION

We have reported that intramolecular chain-transfer reaction takes place in radical polymerization of itaconates at high temperatures and/or at low monomer concentrations. In this paper, radical polymerizations of di-n-butyl itaconate (DBI) were carried out in toluene at 60°C in the presence of amide compounds. The 13C NMR spectra of the obtained poly(DBI)s indicated that the intramolecular chain-transfer reaction was suppressed as compared with in the absence of amide compounds. The NMR analysis of DBI and N-ethylacetamide demonstrated both 1:1 complex and 1:2 complex were formed at 60°C through a hydrogen-bonding interaction. The ESR analysis of radical polymerization of diisopropyl itconate (DiPI) was conducted in addition to the NMR analysis of the obtained poly(DiPI). It was suggested that the suppression of the intramolecular chain-transfer reaction with the hydrogen-bonding interaction was achieved by controlling the conformation of the side chain at the penultimate monomeric unit of the propagating radical with an isotactic stereosequence

Effect of polymerization conditions on the syndiotactic-specificity in radical polymerization of N-isopropylacrylamide and fractionation of the obtained polymer according to the stereoregularity

Radical polymerization of N-isopropylacrylamide (NIPAAm) was examined in the presence of hexamethylphosphoramide (HMPA). The addition of an excess amount of HMPA induced syndiotactic-specificity that gradually enhanced as the feed monomer was consumed. The syndiotacticity of the obtained poly(NIPAAm)s was improved by increasing the [HMPA]0/[NIPAAm]0 ratio to 5 and prolonging the polymerization time to 96h (racemo = 72%). It was also revealed that more stereoregulated poly(NIPAAm) could be fractionated by reprecipitating the resulting polymers from hexane-THF mixture. This result suggested that more stereoregulated poly(NIPAAm) showed a lower solubility than less stereoregulated poly(NIPAAm)s. Furthermore, unusual hysteresis was observed in transmittance analysis of an aqueous solution of the fractionated syndiotactic poly(NIPAAm)

Remarkable effect of hydrogen-bonding interaction on stereospecificity in the radical polymerization of N-vinylacetamide

Radical polymerization of N-vinylacetamide (NVA) in toluene at low temperatures was investigated. It was found that the addition of Lewis bases or alcohol compounds significantly influenced stereospecificity in NVA polymerization. For example, syndiotacticity increased from 25% to 34% by adding tri-n-butyl phosphate at –40°C. Mono-alcohol compounds increased heterotacticity and heterotactic poly(NVA) with mr triad content of 58% was obtained at –40°C in the presence of 1,1,1,3,3,3-hexafluoro-2-propanol. Furthermore, isotactic poly(NVA) with mm triad = 49% was obtained at –60°C in the presence of diethyl L-tartrate. The NMR analysis demonstrated that complex formation between NVA monomer and the added agents, through hydrogen-bonding interaction, played an important role to induce the stereospecificity

Hydrogen-bond-assisted stereocontrol in the radical polymerization of N-isopropylacrylamide with bidentate Lewis base

Radical polymerization of N-isopropylacrylamide (NIPAAm) in toluene was investigated in the presence of bidentate Lewis base such as diphosphonates. Isotacticity of the obtained poly(NIPAAm)s slightly increased at –80°C, whereas syndiotactic-rich poly(NIPAAm)s were obtained at –40 to 0°C. This result corresponded to the results observed in the presence of primary alkyl phosphates. NMR analysis revealed that NIPAAm monomer and tetraisopropyl methylenebisphosphonate formed mono-binding hydrogen-bond-assisted complex at 0°C, but a chelate complex at –80°C. Thus, it was concluded that the stereospecificity in NIPAAm polymerization strongly depended on the complexation mode of the added bidentate Lewis base