Polymer Coil Dimensions Research Articles

Photocrosslinking of polymers containing cinnamoyl groups: The change in polymer coil dimension during the reaction in solution

Intra- and intermolecular photocrosslinking reactions of poly(2-cinnamoyloxyethyl methacrylate) (PCEMA) and copoly(CEMA/MMA) in dilute solution under u.v. light irradiation at 30°C were studied by u.v. absorption, light scattering, GPC and viscosity measurements. The contraction of polymer coils proceeds due to predominant intramolecular photodimerization in very dilute solution. When the polymer concentration increases, competition between intra- and intermolecular photodimerization is observed, and the volume of polymer coils increases gradually due to the increase in molecular weight caused by the intermolecular reaction overcoming the contraction caused by the intramolecular reaction. The contribution of intramolecular crosslinking is much more important in the presence of oxygen than in its absence, showing that the shorter lifetime of the excited singlet state makes intermolecular photodimerization difficult.

Intramolecular excimer formation in macromolecules—V. Head-to-head polystyrene, block copolymers of styrene and butadiene and regular condensation polymers of α-methylstyrene

Studies of the photophysical properties of head-to-head polystyrene, block copolymers poly(butadiene- b-styrene) and polystyrenes of various sequence length of styrene chromophore and regular copolymers of α-methylstyrene indicate that interactions between phenyl chromophores located distantly upon the macromolecule are not of major significance in determination of excimer formation in styrene polymers. It is concluded that intramolecular excimer formation in polystyrenes occurs primarily as a consequence of interactions between nearest neighbour chromophores in the polymer chain. The influence of polymer coil dimensions upon intramolecular excimer formation is demonstrated. The photophysical behaviour of poly(butadiene- b-styrene) block copolymers shows the importance of intramolecular energy migration in population of potential excimer sites.

Low shear viscosity of dilute polymer solutions

AbstractA modification of a viscometer originally proposed by Zimm and Crothers in 1962 is presented, which may be used to measure ultra low shear viscosity for highly dilute polymer solutions. This may provide useful information on polymer coil dimensions and relaxation time. Use of the low shear viscosity data leads to very large values of relaxation time induced by polymer addition to a concentration of only 2 to 3 wppm. This finding is consistent with the marked viscoelastic effects exhibited by these solutions.

Molecular dimensions of polystyrene in solution near the theta point

Hydrodynamic dimensions of polymer coils in solution were investigated around the theta point for the polystyrenecyclohexane system by quasielastic light scattering. Below the theta point, the hydrodynamic radius decreases very slightly and does not exhibit the collapse of the coil near the critical solution temperature in contrast with the radius of gyration.

Evaluation of excluded-volume parameters from light-scattering results by means of graphical procedures

A description is given of a straightforward graphical procedure for evaluation of the excluded-volume parameter and the unperturbed dimensions of polymer coils from light-scattering data measured in good solvents. Its basis is the fitting of the appropriate theoretical curves for the interpenetration function z h( z) and for the expansion factor α to the experimental points by joint shifting along a suitable logarithmic axis. The condition for the correct shift is derived from the value of the extended-volume parameter, and this is determinated by the basic relation between molar mass and radius of gyration. The curve-fitting procedure is applied to certain light-scattering measurements and compared with the linearization methods most frequently used.

Drag reduction in polymer mixtures

Drag reduction was studied in dilute toluene solutions of a mixture of two polymers: polyisobutylene (of three different molecular weights) and 1,4-cis-isoprene rubber in the turbulent region at low (up to 5000) Reynolds numbers. Experiments were carried out with mixed solutions at a concentration equal to optimum concentration of polyisobutylene or higher than it. Drag reduction of the polymer mixtures depending on the ratio of the two polymers showed a positive deviation from the additive straight line at all concentrations investigated. To evaluate the degree of deviation from additivity, the excess drag reduction, was introduced which represents the difference between the actually measured drag reduction and that read from the additive straight line. The excess drag reduction showed almost no dependence on the molecular weight of polyisobutylene in the investigated range of this magnitude. Deviation from additivity depending on the ratio of the two polymers in the mixture growed higher with increasing the flow rate at a given molecular weight of polyisobutylene. The highest excess drag reduction was observed in solutions containing a larger amount of the lower molecular isoprene rubber polymer. The effect of polymer coils on drag reduction in binary polymer solutions was studied. An assumption was made that higher drag reduction in the polymer mixtures as compared to the additive was due to the change of polymer coil dimensions caused by the copresence of the macromolecules of both polymers in the solution. It was further supposed that low shear stresses at which the experiments were carried out caused sufficient orientation and deformation of isoprene rubber enlarged molecules and the contribution of the latter in increasing drag reduction of the mixture was higher.

Mechanism of action of viscosity index improvers

One reason for using polymeric additives is to obtain a product which has better viscosity-temperature characteristics than a comparable pure mineral oil. Measurements of the viscosity-temperature behaviour of motor oils with and without polymer addition show the necessity of a revision of the generally accepted concept of the mechanism of VI improvement. By addition of polymer the better viscosity-temperature characteristics of light oils, which are however of limited value for lubrication of engines, can bemaintained partially in the region of higher viscosities. So it becomes obvious how it is possible to produce multigrade oils from polymers the polymer coil dimensions of which either expand or contract with increasing temperature. Coil expansion promotes VI improvement to some extent, but in no way does this effect play a decisive part

Critical opalescence of poly-2,4-dimethylstyrene solutions in n-heptane

The critical opalescence of poly-2,4-dimethylstyrene solutions in n-heptane in the molecular weight M w range 0·5 × 10 5−2·5 × 10 5 has been investigated, using the visible light and X-ray scattering methods. The mean ranges of intermolecular forces l, the dimensions of polymer coils near the critical temperature and the molar energy of cohesion of the polymer have been determined. Compound plots of I θ −1 = f ( s/ λ) 2 are presented for the visible light and X-ray opalescence for fractions with M w = 1·08 × 10 5 and 2·5 × 10 5.

Direct measurement of the unperturbed dimensions of polymer coils in non-ideal solvents

The Stockmayer-Fixman method (extrapolation of the ratio of intrinsic viscosity to the square root of molecular weight to zero MW) was used to determine the unperturbed dimensions of polystyrene chains in bromoform and benzyl alcohol. A similar study was made of polydimethylstyrene chains in cyclohexane and toluene. In parallel investigations the unperturbed dimensions were determined in the same solvents for the former polymer through the segmental optical anisotropy, using flow birefringence, and for the latter polymer by the Kratky-Porod method based on curves of flow angle X-ray scattering. In both cases the results were almost identical, i.e. differences in the unperturbed dimensions of the polymer chains in various solvents determined by the Stackmayer-Fixman method were substantiated by direct methods for determination of the unperturbed dimensions.

Theory of Liquid—Liquid Interface of Polymer Systems

Top of pageAbstract A theory for the interfacial tension and interface thickness of demixed polymer mixtures and polymer solutions is presented on the basis of the theory of Cahn and Hilliard, taking into account the change in the dimension of polymer coil at the interface. The following results are obtained from the theory: (1) Near critical temperature Tc in a polymer mixture with the same chain length m (a symmetrical system), interfaical tension σ increases with m in the 1/2 power of m, whereas in a polymer solution, σ decreases with m in the—1/4 power, compared at the same reduced temperature T/Tc. On the other hand, the thickness of the interface near Tc increases with increasing m, proportional to the unperturbed chain dimension, i.e., to m1/2, in a symmetrical polymer system, and to the 1/4 power in a polymer solution. (2) In high polymer systems, a first order transition from a diffuse interface to a sharp interface is predicted. The transition temperature reduced by Tc increase with increasing m. The thickness of the interface at a low temperature does not greatly depend on m and is of the order of a segment length. Keywords: Interfacial Tension; Interface Thickness; Transition; Polymer; Non-Uniform System; Mixture; Solution; Critical Phenomena

Preferential Solvation. Effect on Polymer Dimensions

Abstract In this paper we discuss the light scattering theory of preferential solvation. We also present a more recent theory predicting a preferential solvation dependence on polymer molecular weight. These theories have been confirmed by the experimental results of the present work. It was established that the polymer coil dimensions depend on the local solvent composition and not on the analytical one. The local solvent composition can be calculated, in certain cases, from the value of the preferential solvation coefficient.

Study of the concentration dependence of the viscosity of dilute polymer solutions. Compression of polymer chains

STUDY of the hydrodynamic and thermodynamic properties of polymer solutions is an important task for practical reasons and is also of considerable theoretical value. The properties of infinitely dilute polymer solutions have been studied fairly thoroughly, both theoretically and experimentally. The derived theories of viscosity, light scattering, diffusion and sedimentation, and flow birefringence at c-+0 satisfactorily fit the existing experimental material and permit determination of the molecular weight, dimensions, shape and other molecular parameters of individual polymer chains [1]. The situation is different with regard to the concentration dependence of the hydrodynamic and optical properties of polymer solutions. Theories of the dependence of these properties on the concentration of polymer solutions have been derived only for the low concentration region, or more correctly for low values of c[t/], and these fit the experimental data only qualitatively. The properties of polymer solutions are dependent to some extent on the dimensions of the polymer chains, therefore for construction of the concentration dependence of their hydrodynamic and optical properties it is necessary to take account also of the dependence of the dimensions of the polymer chain on the concentration of the solution. The dimensions of polymer coils in solution are determined not only by entropic factors, but also by the energetics of polymer-solvent and polymerpolymer interaction. In good solvents these interactions result in effective mutual repulsion of polymer chain segments. The result of this is both increase in the size of the coils in comparison with the size in an ideal solvent, and also compression of the coils as a consequence of intermolecular interaction [2-4]. One of the methods of estimating the compression of polymer coils is by study of the viscosity of dilute polymer solutions. The first a t tempt at estimating the comression of polymer coils was made in reference [5]. The present work is devoted to development of a method of estimating the compression of

A comparison between real polymer dimensions in solution and the behaviour predicted from models

The variation of polymer coil dimensions with numbers of bonds in the chain for real polymers in solution is compared with the behaviour predicted by lattice random walk models. There appears to be agreement between one form, predicted by two independent methods from models, and the real behaviour of polymers.

Calculated performance of greases in journal bearings : H. H. Horowitz and F. E. Steidler, ASLE Trans., 6 (1963) 239–248

One reason for using polymeric additives is to obtain a product which has better viscosity-temperature characteristics than a comparable pure mineral oil. Measurements of the viscosity-temperature behaviour of motor oils with and without polymer addition show the necessity of a revision of the generally accepted concept of the mechanism of VI improvement. By addition of polymer the better viscosity-temperature characteristics of light oils, which are however of limited value for lubrication of engines, can bemaintained partially in the region of higher viscosities. So it becomes obvious how it is possible to produce multigrade oils from polymers the polymer coil dimensions of which either expand or contract with increasing temperature. Coil expansion promotes VI improvement to some extent, but in no way does this effect play a decisive part