Dilute solution studies of polymers in these laboratories have recently been extended to studies of some stereoregular polymers in solution. This paper reports results of an investigation of viscosity-molecular weight relations for an isotactic polybutene-1. ExperimentalThe polybutene-1 was furnished by the Sun Oil Co. The material was soluble in pentane at room temperature. The x-ray pattern, using the powder technique, clearly indicated that the polymer is crystalline. FractionalionFractionation was carried out by the fractional precipitation method from 1.5% solution in cyclohexanone at 115°C. A 3:l (volume) mixture of cyclohexanol-glycol was used as the nonsolven t. Melting Point DeterminationMelting points of several of the fractions were determined with a Bausch and Lomb microscope equipped with a Kofler micromelting apparatus. The crystals were prepared by heating slowly to 165°C. on the hot stage, followed by slow cooling over a period of several hours. The spherulites thus formed were viewed through crossed prisms and the temperature was raised slowly until the field disappeared. This temperature was taken as the melting point of the polymer. Fraction 8 melted at 121.4"C. while fractions 5,6, and 7 melted at 127°C. Viscosity and Light ScatteringIntrinsic viscosities were determined in decalin a t 115°C. and in heptane at 35 and at 60°C. An Ubbelohde dilution viscometer was used. Flow times for the reagent-grade solvents exceeded 100 sec. in all cases.Refractive index increments (dnldc) were determined with a BricePhoenix differential refractometer. For polybutenel in heptane at 60°C.) dn/dc was found to be 0.115 ~m.~g.-lfor X = 5460 A. and 0.120 cm.3g.-lfor X = 4360A.
Three high molecular weight samples of poly(isobuty1 methacrylate) designated as 937, SW63/0082, an3 SW62/0298 were obtained from Edgewood Arsenal, Maryland. Sample 937 has been fractionated a n l described1Ia) earlier. Initial investigations have shown that the solution viscosities were shear dependent. The three samples were subjected to centrifugation at constant velocity for various times. The intrinsic viscosity and molecular weight (Rw) dropped slightly for sample 937, but dropped drastically for the other two samples.The number average molecular weight (mn) remained constant for each sample under these conditions. In this presentation we have also shown the necessity for taking measurements a t low angles during light scattering measurements in order to obtain the correct molecular weight (&) for these bigh molecular weight species. ZUSAMMENFASSUNG:Drei Proben von Polyisobutylmethacrylat mit bohem Molekulargewicht, 937 1n *), SW 63/0082 und SW62/0298, Edgewood Arsenal, Maryland, wurden verschiedene Zeiten hindurch bei konstanter Geschwindigkeit zentrifugiert. Erste Untersuchungen zeigten, daI3 die Losungsviskositfiten von der Scherkraft abhangig sind. Die Viskositatszahl und das Molekulargewicht (mw) der Probe 937 fielen leicht ab, ein starker Abfall jedoch wurde bei den beiden anderen Proben festgestellt. Das Durchschnittsmolekulargewicht (Ha) blieb unter diesen Bedingungen bei allen drei Proben konstant. Bei dieser Untersuchung haben wir auch gezeigt, dal3 es notwendig ist, Lichtstreuungsmessungen bei kleinen Winkeln zu machen, um bei diesen hohen Molekulargewichten einen genauen Wert des Molekulargewichts (P,) zu erhalten.
Polyalkyl methacrylate polymers were prepared by the emulsion technique and fractionated. The intrinsic viscosity molecular weight relations were established in several ideal solvents. Light scattering determinations were run on polyalkyl methacrylates in an ideal and a nonideal solvent. The results of this experiment have proven that neither size nor shape of the solvent molecules has an effect on the dimensions of the unperturbed polymer. Also, it was shown that the unperturbed polymer dimensions are not altered by the choice of mixed or single theta solvents. It was found that the degree of chain extension increases as the size of the pendant groups (methyl, ethyl, and n‐butyl) increases.
Conventional procedures for the determination of intrinsic viscosity require measurement of specific viscosity at several concentrations followed by extrapolation to infinite dilution. When less precision is required, calculation of the intrinsic viscosity from a single measurement is an attractive Hart' rearranged the equation of Schulz and Blaschke4 in the form:where N is the reciprocal of k in the SchulzBlaschke equation. Hart used a graphical relation between N and specific viscosity in estimating [ q ] from a single measured viscosity.In determining the intrinsic viscosities of stereoregular polybutene-1 samples in Decalin it was found that, intrinsic viscosities could be estimated
Previous dilute solution work in these has involved use of the techniques of light scattering and viscosity. Recently some experimental information has been obtained on the polydispersity of some of the methacrylate polymer samples by additional measurements of number-average molecular weights.Stabin-Immerguts osmometers were used with duPont gel cellophane No. 300 membranes. Membrane pretreatment included immersion in a series of liquids, the last one being the solvent (toluene) in vr-hich measurements were to be made. A static method was used, equilibrium osmotic pressures usually being reached in 48 to 72 hr. Corrections were made for membrane asymmetry. The osmometers were maintained in a thermostat at 25 f 0.005°C.Over the concentration range studied the plots are satisfactorily linear. Number-average molecular weights are shown in Table I.From this table it is observed that Afw/Mn values for the fractions are in the range 1.5 t o 2, while the value for an unfractionated poly(n-docosyl methacrylate) is 10. The osmotic measnrements on fractions of poly(n-lauryl methacrylate) and poly(2-ethylbutyl methacrylate) in conjunction with previous light-scattering studies on the same ~amples,~,3 indicated that M J M , ratios were surprisingly high. Therefore, some of the poly(2-ethylbutyl methacrylate) fractions were re-examined by light scattering in methyl ethyl ketone a t 25°C. Since only dissymmetry measurements had been made earlier,' measurements were carried out at a series of angles between 32 and 135" for 4 or 5 concentrations of each fraction. Table I compares molecular weights obtained in the two cases. If there was any degradation of the samples during storage, it must have been small. It is of interest to obtain the relation between intrinsic viscosity and viscosity-average molecular weight once M , and M, are known. An exponential distribution was assmned.6 Using the viscosity data obtained earlier for poly(2-ethylbutyl methacrylate) in methyl ethyl ketone a t 25"C., the viscosity-niolecular weight relations are: Figure 1 shows the plots of T / C vs. c.[q] = 3.72 X 10-6M,P.77
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.