Etude des dimensions non perturbées del a polyvinyl‐2 pyridine. Observation d'une transition conformationnelle

Dondos, Par Anastasios

doi:10.1002/macp.1970.021350118

Cited by 47 publications

(6 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…This 8-temperature considerably differs from those obtained by Dondos 13 (15°C) and Arichi 14 (16.2°C). The difference may arise from differences either in purity of the solvents used or in tacticity of the samples obtained.…”

Section: (At Ii4°c In Benzene)contrasting

confidence: 85%

Preparation and Characterization of Poly(2-vinylpyridine) with Narrow Molecular Weight Distributions

Matsushita

Shimizu

Nakao

et al. 1986

Polym J

View full text Add to dashboard Cite

Anionic polymerization of 2-vinylpyridine was carried out in tetrahydrofuran at-78°C with four kinds of initiators, i.e., n-butyllithium, tritylsodium, cumylpotassium and cumylcesium. It was confirmed that the polymerizations with all these initiators proceeded on a living mechanism and the polymers obtained had riarrow molecular weight distributions. The triad isotactic contents of the polymers prepared were almost identical, independently of counter ions. The intrinsic viscosity-molecular weight relationships were determined in two good solvents and in a 8-solvent. From those relationships, it was concluded that poly(2-vinylpyridine) has almost the same chain flexibility as ordinary vinyl polymers.

show abstract

Section: (At Ii4°c In Benzene)contrasting

confidence: 85%

Preparation and Characterization of Poly(2-vinylpyridine) with Narrow Molecular Weight Distributions

Matsushita

Shimizu

Nakao

et al. 1986

Polym J

View full text Add to dashboard Cite

show abstract

“…2). In Figure 5 we show KO for PS as a function of temperature obtained from The decrease of the unperturbed dimensions at 40°C reflects an increase in flexibility of the chain, as in the transitions previously reported (4,6,13,14).…”

Section: Experimental Methods and Resultssupporting

confidence: 59%

Transition phenomena in polystyrene near the theta condition

Tsitsilianis¹,

Pierri²,

Dondos³

1983

J. Polym. Sci. B Polym. Lett. Ed.

View full text Add to dashboard Cite

In a recent paper') we have presented some preliminary results, which indicate that polystyrene exhibits a transition near its theta-conditions. In this communication we present some new results, obtained with a new polymer/solvent system. These observations corroborate our previous findings and suggest the idea that this transition must be a general phenomenon. Moreover, we show that any variation of the thetaconditions gives a corresponding variation of the transition point of the polymer.As already shown') a discontinuity in the variation of the intrinsic viscosity of polystyrene (PS) is observed at about 40 "C when the polymer is dissolved in cyclohexane. It is well known that this solvent is a theta-solvent for PS at 34°C. This transition is presented in Fig. 1 b. If now a little quantity of ethanol (precipitant of PS) is added, it will be evident that the theta-point must be observed at a higher temperature than 34 OC. As we can see in Fig. 1 a, the transition of PS is observed now at a temperature higher than in pure cyclohexane. On the contrary, if we add a little quantity of benzene (good solvent of PS) to the cyclohexane, the theta-conditions must be observed at a lower temperature than 34 "C and as we can see from Fig. 1 c the transition of PS is now observed at a temperature lower than 40°C. The above results clearly demonstrate that the PS transition is tightly related to the theta-conditions of this polymer. We must emphasize here that the observed transition phenomenon is beyond any doubt. Many of the experimental points given in this paper are the mean values of two or three independent measurements. The lowering of [ q ] above the theta-temperature is of the order of 6%.For a given polymer dissolved in a given solvent the theta-conditions can be changed, if the segment density of the polymer is changed. It is known that thetaconditions are displaced to a lower temperature as the segment density of the macromolecular coil is increased. This happens in case of star-polymers as well as in case of very low molecular weight polymers. For a star-shaped PS sample we have already shown') that the transition temperature is lower than the transition temperature of a linear PS sample, because the theta-temperature of the former sample is lower than that of the latter. In Fig. 2 the variation of [ q ] versus temperature of some PS samples in cyclohexane with very low molecular weights are given. The results show that the transition temperature becomes lower as the segment density of the sample becomes higher (transition points 38,s "C and 36°C for molecular weights 7700 and 3600, respectively). a) Part 1: cf.'). 0173-2803/84/$01 .OO

show abstract

“…This result may reflect the different molecular processes occurring in the transition between solutions of C 6 D 6 and CDC13• In CDC13, the nitrogen atom in the pyridine ring may be allowed to make intermolecular hydrogen bonding with hydrogen atoms not only of the pyridine ring but also of the chloroform. 7 On the other hand, in C 6 D 6 , there is no hydrogen bonding interaction between the polymer and solvent. The formation of the hydrogen bonding between the pyridine ring is not easy because of the steric hindrance.…”

Section: Discussionmentioning

confidence: 99%

“…This is consistent with the result that the temperature dependence of the intrinsic viscosity of poly(2-vinylpyridine) in benzene shows a transition in the vicinity of 25°C but not in chloroform. 7 This difference may be caused by the difference in polarity of the solvents as discussed below.…”

Section: Chemical Shift and Linewidthmentioning

confidence: 99%

A Study of the Thermal Transition of Poly(2-vinylpyridine) in Solution by Carbon-13 NMR

Inoue

Konno

Nakajima

1977

Polym J

View full text Add to dashboard Cite

ABSTRACT:The variation, as a function of temperatute, of the carbon-13 spinlattice relaxation time of individual carbons of poly(2-vinylpyridine) in solution was measured and the molecular motion was analysed quantitatively. The motion of the polymer can be characterized by three contributions: namely, a segmental motion and two kinds of internal rotation of the pyridine ring. The temperature dependence of the rate of the internal rotation revealed a transitional change at about 25°C, while that of the segmental motion changed linearly. It is suggested that the internal rotation of the pyridine ring is interrupted by steric hindrance, which is probably due to a repulsive interaction between the hydrogen atoms in the pyridine ring and the methine group and by a formation of hydrogen bonding at lower temperatures. Above the transition temperature, the thermally activated motion overcomes such hindrances and the pyridine ring rotates more freely.KEY WORDS Poly(2-vinylpyridine) / 13 C-NMR / Spin-Lattice Relaxation / Molecular Motion / Internal Rotation / Transition / Recently much interest has been devoted by several investigators to transitions observed in the temperature dependence of the conformation of a macromolecular chain. It has been generally accepted that solutions of polystyrene show an anomalous temperature dependence in solution properties at about 50 and 80°c. 1 -3 A transition was observed at 80°C for both atactic and isotactic polystyrenes in several solvents in the temperature dependence of the second virial coefficient, in the mean radius of gyration, and so on. Reiss 4 ' 5 has proposed that this arises from the transition between a 31 helix and a random coil in the isotactic sequences of both polymers. On the other hand, a transition at about 50°C for isotactic and atactic polystyrenes both in solution and bulk has been reported. 1 In a previous paper, 6 this phenomenon was investigated by using carbon-13 nuclear-magneticresonance spectroscopy (NMR) and it was concluded that this transition is due to the sudden modal change in the mobility of the phenyl ring.Several properties, such as viscosity7 and optical density,8 of poly(2-vinylpyridine) in solution have also been investigated, and a transition was observed at about 25°C in several solvents in the temperature dependence of these properties. Chachaty, et al.,9 have investigated the temperature dependence of the carbon-13 spin-lattice relaxation time of backbone methine carbon of isotactic poly(2-vinylpyridine); but they found no anomaly because the temperature range of their measurement (30-80°C) was above the transition temperature (25°C), and they observed only linearity in the temperature dependence of the correlation time. The process of the transition is different according to the kind of solvents. A break point has been observed in the temperature dependence of the intrinsic viscosity of poly(2-vinylpyridine) in benzene and tetrahydrofuran solution, but no break point has been observed in chloroform. 8 In this paper we will present the r...

show abstract

Etude des dimensions non perturbées del a polyvinyl‐2 pyridine. Observation d'une transition conformationnelle

Cited by 47 publications

References 31 publications

Preparation and Characterization of Poly(2-vinylpyridine) with Narrow Molecular Weight Distributions

Preparation and Characterization of Poly(2-vinylpyridine) with Narrow Molecular Weight Distributions

Transition phenomena in polystyrene near the theta condition

A Study of the Thermal Transition of Poly(2-vinylpyridine) in Solution by Carbon-13 NMR

Contact Info

Product

Resources

About