The radical polymerization of N-isopropylacrylamide was carried out in toluene at low temperatures in the presence of silyl alcohols, such as triethylsilanol. Poly(N-isopropylacrylamide) with a racemo dyad content of 75% was obtained at − 80 °C with a 4:1 triethylsilanol to monomer ratio loading. NMR analysis suggests that the mechanism for syndiotactic induction, in the presence of silyl alcohols, may be similar to that observed with alkyl alcohols. In this case, a 1:2 complex formation, via hydrogen bonding interactions, leads to the induction of syndiotactic specificity. Copyright © 2012 Society of Chemical Industry
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. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Radical polymerization of N-methyl-N-(2-pyridyl)acrylamide (MPyAAm) was carried out in dichloromethane at low temperatures in the presence of trifluoroacetic acid (TFA). The m dyad contents of the polymers obtained at 0 °C increased linearly from 37 to 60% with an increase in the [TFA]0/[MPyAAm]0 ratio from 1 to 5. Nuclear magnetic resonance (NMR) analysis of MPyAAm–TFA mixtures in dichloromethane-d2 revealed that the favorable conformation in terms of the pyridyl group to the carbonyl group in MPyAAm switched from s-trans to s-cis by protonation. The results suggest that controlling the conformation of MPyAAm resulted in control of the stereospecificity in radical polymerization of the monomer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Radical polymerization of N-tert-butoxycarbonylacrylamide (NBocAAm) in toluene at low temperatures in the presence of the fluorinated alcohols, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoro-2-propanol, and nonafluoro-tert-butanol, afforded atactic, heterotactic, and syndiotactic polymers, respectively. NMR analysis revealed that the fluorinated alcohols formed hydrogen bonding-assisted complexes with NBocAAm, with different structures. The difference in the structures of the complexes was responsible for the differences in the induced stereospecificities. Based on the structures of the complexes between NBocAAm and the fluorinated alcohols, mechanisms for the three kinds of stereospecific radical polymerizations are proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010
Radical polymerization of N-methylacrylamide (NMAAm), N,N-dimethylacrylamide (DMAAm), and N-methyl-N-phenylacrylamide (MPhAAm) was investigated in toluene at low temperatures. Atactic, isotactic, and syndiotactic polymers were obtained by the polymerization of NMAAm, DMAAm, and MPhAAm, respectively, indicating that the stereospecificity of the radical polymerization of acrylamide derivatives depended on the N-substituents of the monomer used. From the viewpoint of monomer structure, the origin of the stereospecificity of radical polymerization of NMAAm derivatives is discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6534–6539, 2009
Radical polymerization of N-isopropylacrylamide (NIPAAm) in toluene at low temperatures, in the presence of fluorinated-alcohols, produced heterotactic polymer comprising an alternating sequence of meso and racemo dyads. The heterotacticity reached 70% in triads when polymerization was carried out at −40 °C using nonafluoro-tert-butanol as the added alcohol. NMR analysis revealed that formation of a 1:1 complex of NIPAAm and fluorinated-alcohol through CO···HO hydrogen bonding induces the heterotactic specificity. A mechanism for the heterotactic-specific polymerization is proposed. Examination of the phase transition behavior of aqueous solutions of heterotactic poly(NIPAAm) revealed that the hysteresis of the phase transition between the heating and cooling cycles depended on the average length of meso dyads in poly(NIPAAm). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2539–2550, 2009
Radical polymerization of N,N-dimethylacrylamide (DMAAm) was investigated in the presence of tartrates, such as diethyl L-tartrate, diisopropyl L-tartrate, and di-n-butyl L-tartrate, in toluene at low temperatures. Syndiotactic polymers were obtained in the presence of tartrates, whereas isotactic polymers were obtained in the absence of tartrates. The syndiotactic-specificity increased with increasing amount of tartrates and with decreasing polymerization temperature. NMR analysis suggested that DMAAm and tartrates formed a 1:1 complex through double hydrogen bonding. A mechanism for the syndiotactic-specific radical polymerization of DMAAm is proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1192–1203, 2009
Dialkyl vinylphosphonates such as dimethyl vinylphosphonate (DMVP) and diethyl vinylphosphonate were quantitatively polymerized with dicumyl peroxide (DCPO) at 130°C in bulk. The polymerization of DMVP with DCPO was kinetically studied in bulk by fourier transform near-infrared spectroscopy (FTNIR) and electron spin resonance (ESR) spectroscopy. The initial polymerization rate (Rp) was given by Rp = k[DCPO]0.5[DMVP]1.0 at 110°C, being the same as that of the conventional radical polymerization involving bimolecular termination. The overall activation energy of the polymerization was estimated to be 26.2 kcal/mol. The polymerization system involved ESR-observable propagating polymer radicals under the practical polymerization conditions. ESR-determined rate constants of propagation (kp) and termination (kt) were kp = 19 L/mol s and kt = 5.8 × 103 L/mol s at 110°C, respectively. The molecular weight of the resultant poly(DMVP)s was low (Mn = 3.4 − 3.5 × 103), because of the high chain transfer constant (Cm = 3.9 × 10−2 at 110°C) to the monomer. DMVP (M1) showed a considerably high reactivity in the radical copolymerization with trimethoxyvinylsilane (TMVS) (M2) at 110°C in bulk, giving an inorganic component-containing functional copolymer with potential flame-retardant properties; r1 = 1.6 and r2 = 0. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
The radical polymerizations of N-alkylacrylamides, such as N-methyl-(NMAAm), N-n-propyl-(NNPAAm), N-benzyl-(NBnAAm), and N-(1-phenylethyl)acrylamides (NPhEAAm), at low temperatures were investigated in the absence or presence of hexamethylphosphoramide (HMPA) and 3-methyl-3-pentanol (3Me3PenOH), which induced the syndiotactic specificities in the radical polymerization of N-isopropylacrylamide (NIPAAm). In the absence of the syndiotactic-specificity inducers, the syndiotacticities of the obtained polymers gradually increased as the bulkiness of the N-substituents increased. Both HMPA and 3Me3PenOH induced the syndiotactic specificities in the NNPAAm polymerizations as well as in the NIPAAm polymerizations. The addition of 3Me3PenOH into the polymerizations of NMAAm significantly induced the syndiotactic specificities, whereas the tacticities of the obtained polymers were hardly affected by adding HMPA. In the polymerizations of bulkier monomers, such as NBnAAm and NPhEAAm, HMPA worked as the syndiotactic specificity inducer at higher temperatures, whereas 3Me3PenOH hardly influenced the stereospecificity, regardless of the temperatures. The phase-transition behaviors of the aqueous solutions of poly(NNPAAm)s were also investigated. It appeared that the poly (NNPAAm) with racemo dyad content of 70% exhibited unusual large hysteresis between the heating and cooling processes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4575–4583, 2008
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-n-butyl phosphate (TBP). Syndiotactically rich poly(NIPAAm)s were obtained from −60 to 0 °C, and TEP provided the highest syndiotacticity (racemo dyad = 65%) at −40 °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 −80 °C. In particular, TBP exhibited the most isotactic specificity (meso dyad = 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 −80 °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. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 50–62, 2005
The radical polymerization of N-isopropylacrylamide (NIPAAm) in toluene at low temperatures was investigated in the presence of triisopropyl phosphate (TiPP). The addition of TiPP induced a syndiotactic specificity that was enhanced by the polymerization temperature being lowered, whereas atactic polymers were obtained in the absence of TiPP, regardless of the temperature. Syndiotactic-rich poly(NIPAAm) with a racemo dyad content of 65% was obtained at −60 °C with a fourfold amount of TiPP, but almost atactic poly(NIPAAm)s were obtained by the temperature being lowered to −80 °C. This result contrasted with the result in the presence of primary alkyl phosphates, such as tri-n-propyl phosphate: the stereospecificity varied from syndiotactic to isotactic as the polymerization temperature was lowered. NMR analysis at −80 °C revealed that TiPP predominantly formed a 1:1 complex with NIPAAm, although primary alkyl phosphates preferentially formed a 1:2 complex with NIPAAm. Thus, it was concluded that a slight increase in the bulkiness of the added phosphates influenced the stoichiometry of the NIPAAm–phosphate complex at lower temperatures, and consequently a drastic change in the effect on the stereospecificity of NIPAAm polymerization was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3899–3908, 2005
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 article, 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 itaconate (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. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4895–4905, 2004
![Poly[oxy(1-oxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25300/25248-42-4.png)
![Poly[oxy(1-oxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25300/25248-42-4_b.png)
