Syndiotactic- and Heterotactic-Specific Radical Polymerizations of N-n-Propyl-α-fluoroacrylamide and Phase-Transition Behaviors of Aqueous Solutions of Poly(N-n-propyl-α-fluoroacrylamide)

Radical polymerization of N-n-propyl-α-fluoroacrylamide (NNPFAAm) was investigated in several solvents at low temperatures in the presence or absence of Lewis bases, Lewis acids, alkyl alcohols, silyl alcohols, or fluorinated alcohols. Different effects of solvents and additives on stereospecificity were observed in the radical polymerizations of NNPFAAm and its hydrocarbon analogs such as N-isopropylacrylamide (NIPAAm) and N-n-propylacrylamide (NNPAAm); for instance, syndiotactic (and heterotactic) specificities were induced in radical polymerization of NNPFAAm in polar solvents (and in toluene in the presence of alkyl and silyl alcohols), whereas isotactic (and syndiotactic) specificities were induced in radical polymerizations of the hydrocarbon analogs under the corresponding conditions. In contrast, heterotactic specificity induced by fluorinated alcohols was further enhanced in radical polymerization of NNPFAAm. The effects of stereoregularity on the phase-transition behaviors of aqueous solutions of poly(NNPFAAm) were also investigated. Different tendencies in stereoregularity were observed in aqueous solutions of poly(NNPFAAm)s from those in solutions of the hydrocarbon analogs such as poly(NIPAAm) and poly(NNPAAm). The polymerization behavior of NNPFAAm and the phase-transition behavior of aqueous poly(NNPFAAm) are discussed based on possible fluorine–fluorine repulsion between the monomer and propagating chain-end, and neighboring monomeric units

De-tert-butylation of poly(N-tert-butyl-N-n-propylacrylamide) : Stereochemical analysis at the triad level

The stereochemical analysis of polymers derived from N,N-disubstituted acrylamides is usually difficult. The diad tacticity can be determined from the 1H NMR signals of the main-chain methylene groups. However, the splitting because of the configurational sequences is poor, even in 13C NMR, which does not allow determination of the tacticity at the triad level. In contrast, the stereochemical analysis of polymers derived from N-monosubstituted acrylamides is easily conducted and the triad tacticity can be determined from the 13C signals of the main-chain methine groups. Thus, stereochemical analysis of N,N-disubstituted polymers should be able to be conducted if the polymers are transformed into N-monosubstituted polymers with retention of the configurational sequence. Poly(N-tert-butyl-N-n-propylacrylamide) [poly(TBNPAAm)] was radically prepared, and de-tert-butylation was conducted by treatment with Sc(OTf)3 in a mixed solvent of CH3CN and 1,4-dioxane at 50, 80, and 110 °C. 1H NMR analysis of the resulting polymers indicated quantitative conversion after 72 h, regardless of the temperature. 13C NMR analysis of the transformed polymers confirmed that the configurational sequences were retained during the reaction. Thus, the triad stereochemical analysis of N,N-disubstituted polymers was successfully conducted by de-tert-butylation as a polymer reaction, followed by 13C NMR analysis of the transformed polymers

A Method for Producing Transgenic Cells Using a Multi-Integrase System on a Human Artificial Chromosome Vector

The production of cells capable of expressing gene(s) of interest is important for a variety of applications in biomedicine and biotechnology, including gene therapy and animal transgenesis. The ability to insert transgenes at a precise location in the genome, using site-specific recombinases such as Cre, FLP, and ΦC31, has major benefits for the efficiency of transgenesis. Recent work on integrases from ΦC31, R4, TP901-1 and Bxb1 phages demonstrated that these recombinases catalyze site-specific recombination in mammalian cells. In the present study, we examined the activities of integrases on site-specific recombination and gene expression in mammalian cells. We designed a human artificial chromosome (HAC) vector containing five recombination sites (ΦC31 attP, R4 attP, TP901-1 attP, Bxb1 attP and FRT; multi-integrase HAC vector) and de novo mammalian codon-optimized integrases. The multi-integrase HAC vector has several functions, including gene integration in a precise locus and avoiding genomic position effects; therefore, it was used as a platform to investigate integrase activities. Integrases carried out site-specific recombination at frequencies ranging from 39.3–96.8%. Additionally, we observed homogenous gene expression in 77.3–87.5% of colonies obtained using the multi-integrase HAC vector. This vector is also transferable to another cell line, and is capable of accepting genes of interest in this environment. These data suggest that integrases have high DNA recombination efficiencies in mammalian cells. The multi-integrase HAC vector enables us to produce transgene-expressing cells efficiently and create platform cell lines for gene expression

Isotactic-specific anionic polymerization of N-isopropylacrylamide with dilithium tetra-tert-butylzincate in the presence of a fluorinated alcohol or Lewis acid

The polymerization of N-isopropylacrylamide (NIPAAm) with dilithium tetra-tert-butylzincate (TBZL) has been investigated in toluene at low temperatures in the presence of alkyl and fluorinated alcohols. Of the alcohols examined, 1,1,1,3,3,3-hexafluoro-2-propanol induced isotactic specificity and accelerated the polymerization process, affording the corresponding poly(NIPAAm)s in relatively high yields with meso (m) diad contents of 82%. It is worthy of note that the introduction of a fluorinated alcohol, which is typically used as an inhibitor in conventional anionic polymerization processes, enabled control over the stereospecificity and rate of the anionic polymerization of NIPAAm when TBZL was used as an initiator. Yttrium trifluoromethanesulfonate also induced isotactic specificity in the NIPAAm polymerization process in methanol and gave poly(NIPAAm) in high yield with an m diad content of 88%

Syndiotactic- and heterotactic-specific radical polymerization of N-n-propylmethacrylamide complexed with alkali metal ions

We investigated the radical polymerization of N-n-propylmethacrylamide (NNPMAAm) in the presence of alkali metal bis(trifluoromethanesulfonyl)imides (MNTf2), in particular LiNTf2. The addition of MNTf2 led to a significant improvement in the yield and molecular weight of the resulting poly(NNPMAAm)s. Furthermore, the solvent employed influenced stereospecificity in the presence of LiNTf2. The stoichiometry of the NNPMAAm–Li+ complex appeared to be critical to determining the stereospecificity in the NNPMAAm polymerization. The 1:1-complexed monomer in protic polar solvents provided syndiotactic-rich polymers, whereas the 2:1-complexed monomer in aprotic solvents gave heterotactic-rich polymers. Stereochemical analyses revealed that m-addition by an r-ended radical was the key step in the induction of heterotactic specificity in the aprotic solvents. Spectroscopic analyses suggested that the Li+ cation played a dual role in the polymerization process, with Li+ stabilizing the propagating radical species and also activating the incoming monomer. Kinetic studies with the aid of electron spin resonance spectroscopy revealed that the addition of LiNTf2 caused a significant increase in the kp value and a decrease in the kt value. The stereoregularity of poly(NNPMAAm)s was found to influence the phase transition behavior of their aqueous solutions. In a series of syndiotactic-rich polymers, the phase-transition temperature decreased gradually with increase in rr triad content. Furthermore, heterotactic-rich poly(NNPMAAm) exhibited high hysteresis, which increased in magnitude with increasing mr triad content

Dual role for alkali metal cations in enhancing the low-temperature radical polymerization of N,N-dimethylacrylamide

The radical polymerization of N,N-dimethylacrylamide (DMAAm) has been investigated in the presence of several alkali metal salts, including lithium bis(trifluoromethanesulfonyl)imide (LiNTf2). The addition of an alkali metal salt led to a significant increase in the yield and molecular weight of the resulting polymer. NMR analysis of mixtures of DMAAm and LiNTf2 suggested that DMAAm was being activated by the coordination of Li+ to its C=O group. Electron spin resonance analysis of the DMAAm polymerization in the presence of LiNTf2 suggested that the propagating radical was being stabilized by Li+ through a single-electron lithium bond, because a signal for the propagating radical of the acrylamide derivatives was observed for the first time in solution when LiNTf2 was added. Based on these results, we have proposed a mechanism for this polymerization, where the propagation steps occur between a lithium ion-stabilized propagating radical and a lithium ion-activated incoming monomer. Furthermore, polymers with a wide range of stereoregularities, such as isotactic, syndiotactic and heterotactic systems, were successfully prepared using this method by carefully selecting the appropriate combination of solvent and alkali metal salt

NMR Analysis of Poly(Lactic Acid) via Statistical Models

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 polymerization mechanism

Multivariate analysis of NMR spectra

In this paper, we report multivariate analyses, such as principal component analysis (PCA) and partial least-squares (PLS) regression, of NMR spectra of poly(N-isopropylacrylamide)s [poly(NIPAAm)s]. PCA successfully interpreted the assignments of NMR spectra of poly(NIPAAm)s in terms of stereostructures for the methine carbons at triad levels and for the methylene protons at tetrad levels. Furthermore, triad tacticity was successfully predicted by PLS regression of 1H NMR spectra of the methine and methylene groups, although the low resolution of the signals of the methine protons confines determination of tacticities by conventional methods to the diad levels. Consequently, it is assumed that chemometric approaches are useful for assigning NMR spectra in terms of stereostructures and for predicting tacticity distributions

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

Radical polymerization of isobutyl vinyl ether (IBVE) was attempted with the aid of the interaction between the corresponding propagating radical and lithium cation (Li+). LiN(SO2CF3)2 (LiNTf2) and ester compounds, such as methyl methacrylate (MMA) and vinyl acetate (VAc), were added as a Li+ source and dissolving agent for LiNTf2, respectively. Homopolymers of cationically polymerizable IBVE were obtained despite the presence of radically polymerizable monomers such as MMA and VAc. Contrary to our expectation, the polymerization proceeded via not a radical mechanism but a cationic mechanism. However, this cationic polymerization was found to be unusual. In particular, the polymer yield increased with the polymerization temperature; successful polymerization was observed at 100 °C, whereas no polymerization occurred at lower temperatures such as at 0 °C. The behavior of the present system was therefore defined as “thermally induced cationic polymerization”. The mechanism of thermally induced cationic polymerization is still not clear, but it is assumed that the propagating cation is markedly stabilized through its interaction with the solvate ionic liquid formed between LiNTf2 and the Lewis base