ALBERT

Notes: The polymerization of activated fibrinogen takes place in two stages. First, the monomer units form intermediate polymers with twice the original cross-section area and about eight times the original length. The polymers have been detected under a variety of conditions between pH 6.1 and 10. The polymerization geometry is believed to be lateral dimerization with a staggered configuration, determined by a pattern of electrical charges. The negatively charged groups, though unidentified, appear to be near histidine residues, as deduced from the dependence of polymerization on pH. The positively charged groups, from this and other evidence, appear to be α-amino groups. Second, the intermediate polymers unite to form the strands of the fibrin network. This association appears to involve nonpolar groups, and the width of the final strands, unlike that of the intermediate polymer, depends markedly on the net charge as determined by the pH.

Notes: It is shown that ηsp/c for a polystyrene fraction (M̄v = 250,000) in toluene decreases approximately linearly as the concentration is lowered from 1.0 to 0.1 g./100 ml. and then increases to a maximum at 0.001 g./100 ml. as the concentration is lowered still further. This increase in ηsp/c with dilution is a new effect which we ascribe to the expansion of polymer coils as well as to the disentangling of entire polymer molecules once the concentration is lowered to where there is ample room in the solution for each polymer molecule. The new techniques employ a viscometer with a flow time of 3893 seconds for toluene, special filtering of the solutions, and prolonged agitation of the solutions after each dilution. We present data to show that ηsp/c is time dependent at concentrations below 0.1 g./100 ml.

Notes: The modification of the amorphous/crystalline ratio in polyethylene terephthalate by copolymerization with glycols or dibasic acids usually results in a lowering of the degree of crystallinity and of melting point, and impaired physical properties. A consideration of the molecular constitution of silk fibroin suggests a way of modifying the molecule to produce an increase in the amorphous content of the polymer with retention of the crystallite structure. In the silk fibroin molecule it is significant that two lengthy segments (about 170 A. long) as contrasted with the rest of the molecule carry bulky side chains which prevent their entry into the crystalline regions of the fiber. The fact that these segments are accommodated in the amorphous regions suggested by analogy that one or two linear molecules of 100-200 A. in length might be successfully incorporated in the polyester molecule with a probable improvement in such physical and chemical properties as flexibility and dyeability. The modifying component must have reactive end groups, be thermally and chemically stable under polymer-making conditions, and should have water-sensitive groupings. Polyoxyethylene glycols (Carbowaxes) of molecular weight 1000-6000 satisfy these conditions and with polyethylene terephthalate give high melting “block copolymers” that can contain as much as 30% by weight of the modifying component. The dyeability, moisture regain, and flexibility (measured by determination of the second order transition point) are all materially increased, while at the same time the tenacity and extensibility are unaltered. Since the molecular proportion of the modifying component is small (less than 2% of the repeating units are substituted), there is only a small reduction in melting point. This indicates little alternation in the crystallites, a fact confirmed by the substantially unaltered x-ray photographs. That the copolymers are not blends but are true compounds is shown by the failure to remove the modifier by continuous extraction with solvents and by the incompatibility of polyoxyethylene glycols and molten polyethylene terephthalates. Absence of fragmentation of the modifying components on entering the polymer chain is shown by its almost quantitative recovery from the alkaline hydrolyzate of the copolymer. Despite their excellent physical properties these copolymers are not technically attractive as fibers because of their instability to ultraviolet light (and to strong sunlight). Furthermore, exposure of the dyed fibers to ultraviolet light shows that the rate of fading of dye has been seriously increased by the introduction of the third component into the molecule. Polyoxyethylene glycols may also be incorporated as side chains in the copolymer molecule to give similar high-melting copolymers with improved dyeability and retention of physical properties. Copolymers of polyoxydecamethylene glycol and polyethylene terephthalate show good physical properties but no improvement in dyeability, probably because the “blocks” introduced are deficient in ether-oxygen atoms and hence lacking in hydrophilic character. It is suggested that this novel type of copolymer is probably fairly widespread in the field of proteins, and is not confined to silk fibroin. For example, some of the physical properties of collagen (and of gelatin) are best explained by assuming that certain chain segments, because of their amino-acid composition, have a strong crystallizing tendency.

Notes: The extent of branching in polystyrene is attributed to a polymer transfer step occurring during polymerization. In this process a radical abstracts a hydrogen atom from along a chain which then adds monomer at the site of the abstraction. The rate of this process should be decreased if the hydrogen is replaced by deuterium, and consequently deuterated monomers should polymerize to form polymers less branched than those from the nondeuterated monomer. Polymers of α- and β-deuterostyrene were synthesized and thier intrinsic viscosity and molecular weight by light scattering determined. In the case of the α-deuterostyrene, the polymer was also fractionated and measurements were made on the fractions. The data for the deuterated styrenes fit quite closely the same relationships as a normal styrene sample prepared simultaneously and under the same conditions, i.e., 70°C. and without catalyst. The results indicate, therefore, that branching is quite small in polystyrene prepared under such typical conditions. A check of the isotope effect on the transfer process was made utilizing S-deuterobutyl mercaptan. A value of 4.0 was obtained at 60°C. for the relative rate of transfer with butyl mercaptan to that for the deuterated mercaptan.

Notes: A viscometer for solutions of high polymers having the following features is described: (1) The lower level of the capillary viscometer is determined by an overflow into an auxiliary reservoir. (2) The solutions are prepared, insoluble gel filtered, and dilutions carried out in the auxiliary reservoir. (3) Because of the fact that the viscometer is a closed system it can be rotated through 360° within the constant temperature bath, automatically filling the upper reservoir and allowing repetitive measurements to be carried out. (4) As constructed, the viscometer can only be used for solutions of low surface tension.

Notes: Evidence is discussed for and against the existence of a common meeting point when linear plots of ηsp/C against C for polystyrene in a number of solvents are extrapolated to negative concentrations. There is rather more evidence in favor than against, and most of the contrary evidence falls into a category for which exceptional behavior might be anticipated. The ordinate of the common meeting point, unlike the limiting viscosity number, is independent of solvent and is conveniently called the true limiting viscosity number [η]T. [η]T has been identified with the intrinsic configurational character of a polymer chain. The common point of intersection has the coordinates [η]T and C2, where Cx is a negative concentration. The product of [η]T and Cx has been found to be constant over a considerable molecular weight range. This leads to an expression for [η]/[η]T in terms of Huggins' k′. [η]/[η]T represents the ratio of the hydrodynamically equivalent volume of a polymer in an actual solvent to the equivalent volume of the chain in its natural state of extension. [η]T is considered in relation to [η]θ (Flory-Fox) and [η]P (Bawan). The effect of polymer heterogeneity is discussed.