O k l u h 74004 synopsis A method described for the determination of molecular weight and long-chain branching distributions of polymers requires no prior knowledge of the functional relation b e tween branching frequency and molecular weight. It is based on preparative fractionation and viscometric and gel-permeation chromatographic measurements on both fractions and whole polymer. The technique is applied to several polybutadienes and but+ diene-styrene copolymers differing widely in method of synthesis and pattern of longchain branching. 657
SynopsisPoly(pheny1ene sulfide) (PPS) has been characterized using a novel high temperature gel permeation chromatograph (GPC). Samples were injected in slurry form a t ambient temperature, and redissolved by an in-line precolumn heater at 250°C. A viscometer consisting of a capillary tube with inlet and outlet taps connected to a sensitive differential pressure transducer was used as sole detector, with deflections converted to concentration using the column calibration. Columns and viscometer were operated a t 210°C. Universal calibration was carried out using intrinsic viscosityimolecular weight relations for polystyrene and PPS, determined by light scattering. Satisfactory operation was confirmed by agreement between inirinsic viscosity calculated from GPC with independently measured values, and comparisons with melt flow data. Samples of PPS tested were found to be of relatively narrow distribution, with M J M , typically less than two.
Intrinsic Viscosity of Linear Polyethylene in a -Solvent 3109 * wave length. This is compatible with the explanation of the abnormally short wave length of the fourmembered propiolactone in terms of bond angle strain advanced by Closson and Hang.10 According to their interpretation, reduction of the internal angles leads to an increase in the s-character in the -bond of the carbonyl group, which in turn leads to the shortening of both theand -bonds and thus raises the *-1ß ß1.This explanation is also compatible with the high energy of the -* * transition observed in cyclobutanone in comparison with the other members of the series. However, this theory fails to explain the lowest -> * transition energy in cyclopentanone. Also, compounds I and III would be expected to differ significantly, in the degree of strain, yet their n * transition energies are experimentally indistinguishable. At the same time, compound IV should be less strained than either I or III and does show a lower n -* transition energy, which is in qualitative agreement with the strain theory.In spite of the preliminary and tentative nature of the correlations presented in this work, they point to the importance of considering excitation energies in the discussion of C13 chemical shifts. sample of bicyclooctanone and the Hooker ChemicalCo. for a generous gift of hexachlorocyclopentadiene.
Butadiene‐styrene block copolymers form micelles in selective solvents. Micelles of several BS diblock and BSB triblock polymers varying in composition and block length were investigated in n‐hexane, n‐heptane, and n‐decane using light scattering and sedimentation velocity, thus permitting characterization of both the micellar weight and abundance of micellar material. Depending upon polymer structure, solvent, concentration and temperature, solutions can be molecular, wholly micellar or a discrete mixture of both. The dominant structural variable is the length or molecular weight (Ms) of the polystyrene block. For Ms < 10, 000, solutions tend to be molecular; for Ms > 20, 000, they are essentially all micellar, with mixtures occurring at intermediate Ms. At any given Ms, increasing length of the polybutadiene block tends to solubilize the polymer. The mean number of molecules per micelle (n) depends upon whether the micelles are formed by direct dispersion of the polymer in the solvent at ambient temperature or whether they are formed from a true solution upon cooling. In the first instance, n rises rapidly with Ms; in the second, it is nearly independent of Ms. Blending of micellar solutions results in complex behavior with rearrangements to new micelles governed primarily by the thermal history of the solutions.
For a system of equivalent bonds undergoing random bond scission it is reasonable to assume that the rate of bond breaking (hence the rate of creation of new molecules) reported in the literature and data presented here demonstrate that the number of molecules created is not proportional to the time of thermal treatment hence they seem to belie this reasonable hypothesis. Other authors have adduced the presence of some non‐equivalent bonds in order to account for the observed cruvature and still retain the hypothesis. Implicit in these arguments is the assumption of a steady‐state concentration of reactive fragments. Our analysis explores the consequences of abandoning the steady‐state assumption and shows that a quantitative explanation of the observed degradation behavior may be had by this means wihile still retaining the hypothesis of a constant probability of a bond being broken per unit time.
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