Showing papers in "Journal of Applied Polymer Science in 1961"

Kinetic analysis of thermogravimetric data

Abstract: Thermogravimetric data are generally more extensive than are comparable isothermal aging data, and therefore afford preliminary kinetic information in greater abundance. The kinetic analysis of the thermogram, by use of either its exact equation or a more convenient approximation formula, is straightforward in cases of volatilization via simple kinetics. Application of the analytical procedure to the thermogram for the zero-order volatilization of octamethylcyclotetrasiloxane yielded an estimate of 11.65 kcal./mole as the average heat of vaporization in the temperature range of 80 to 145°C. The apparent activation energy for the first-order pyrolytic volatilization of 200-mg. samples of pulverized polytetrafluoroethylene was estimated to be 66 to 68 kcal./mole in the temperature range of 520 to 610°C.

Measurement of adhesion by a blister method

Abstract: An instrument for the measurement of the adhesion of organic coatings has been developed. It is based on the formation of a blister by injecting a liquid (generally mercury) under pressure between the coating and the substrate. The work of detachment, i.e., the energy needed to detach 1 cm.2 of coating, is determined by recording the liquid pressure as a function of the injected volume and computing the area under this curve. Extraneous factors such as deformation of the film and compressibility of the liquid are eliminated through a blank run. The design and operation of the instrument are described, an evaluation of its performance and limitations is given, and examples of its application are presented. The method should be useful for accurate measurement of adhesion of many types of surface coatings to metal and, possibly, to other substrates, as well as for studies of the various factors that influence adhesion.

Mullins effect and rubber–filler interaction†

Abstract: A previously reported theory for the Mullins softening effect has been used to interpret various new data for the behavior of filled SBR rubber under tensile load. The strength of the filler–rubber bond, the filler surface area per polymer molecule attachment, and the average filler surface separation have been determined for two fillers, HAF black and Hi Sil-233 (a silica). A styrene–butadiene type filler (Pliolite S-6) has also been investigated. The temperature dependence of the filler–rubber bond has been measured; results lead to the conclusion that the bonds to carbon black and silica are high energy bonds, probably chemical in nature. It is shown that the recovery of hardness in prestretched, filled SBR is a rate process having an activation energy of about 22 kcal./mole. It is inferred from this and from permanent set data that the recovery is the result of the chemical breaking and reforming of the rubber chain network at the higher temperatures where recovery occurs. Silica-filled rubbers are shown to possess a pseudoyield stress which gives rise to an anomalous shape for the stress–strain curve of this material when it is stretched for the first time. A prestretched, silica-filled rubber recovers its hardness when left at 115°C. for 20 hr., but the anomalous portion of the curve is replaced by more normal behavior. Possible interpretations of the observed results are given.

Polysaccharide B-1459: A new hydrocolloid polyelectrolyte produced from glucose by bacterial fermentation†

Abstract: The exocellular polysaccharide fermented from glucose in good yield by Xanthomonas campestris NRRL B-1459, has been characterized. The general aspects of chemical constitution have been established, as well as the physical properties related to practical applicability. This macromolecular polysaccharide is composed of D-mannose, D-glucose, D-glucuronic acid (as the potassium salt), and a small proportion of acetyl groups. It can be produced on an industrial scale and is stable is storage. Analytical fractionation indicates fairly sharp molecular distribution for the native polysaccharide. The polysaccharide forms homogeneous dispersions in water which show plastic rheological properties and viscosity comparable with that of high-grade plant gums. Outstanding characteristics of practical significance are the atypical insensitivity of solution viscosity to salt effects and to heat, especially when salt is present. Solutions of low concentration show a restricted viscosity decrease upon salt addition; those of higher concentrations show substantial increases. Viscosity is enhanced still further by monovalent cations at basic pH and by divalent cations at neutral or slightly basic pH. Salt moderates or eliminates any viscosity decrease due to heat and, in somewhat higher concentrations, it increases the viscosity of heated solutions. Heating or deacetylating Polysaccharide B-1459 causes no impairment of its properties, but actual improvement. The constitutional basis for these unusual properties is discussed.

The relationship between glass temperature, molar cohesion, and polymer structure

Abstract: An empirical equation relating glass temperature, molar cohesion, and polymer structure has been developed from data found in the literature. A fairly extensive list of group cohesion values has been obtained from this relationship and glass temperatures which are in good agreement with reported values have been calculated. The equation is where Hc is the molar cohesion and n is an empirical number obtained from the polymer structure.

Heterogeneous polymer systems. I. Torsional modulus studies

Abstract: Torsional modulus–temperature data have been obtained on heterogeneous polymer compositions prepared by several procedures. Both the state of aggregation of the component chain molecules and their degree of compatibility are significant variables. Modulus curves similar to those for crystalline polymers can be obtained from incompatible polymers having glass temperatures sufficiently far apart. Detailed interpretations are presented for modulus curves of both individual homopolymers and bicomponent heterogeneous polymer mixtures.

Compatibility studies on polyacrylate and polymethacrylate systems

Abstract: The predicted general incompatibility of mixtures of polymers has been further confirmed. Thirty-one mixtures of homopolymer pairs showed phase separation in a common solvent. These included closely related polymers such as polyacrylates with both polymethacrylates and other polyacrylates and pairs of different polymethacrylates. Typical immiscible combinations are PMA/PEA and PEMA and PEMA/PMMA. It was also found that the presence of a common monomer constituent did not result in complete compatibility of either a homopolymer with a copolymer or a mixture of two copolymers. Apparently, none of the combinations tried were sufficiently similar to result in heats of interaction small enough to be counteracted by the small entropy change involved. Since another possibility for attaining miscibility is through polar interactions, the effects of ionic and hydrogen-bonding substituents upon polymer-polymer compatibility were considered, and selected experiments were done on a series of carboxyl-containing polymers and their sodium salts. It was concluded that hydrogen bridging occurs preferentially either intramolecularly or between polymer and solvent rather than between two different types of chains each having hydrogen-bonding ability. Thus, poly(acrylic acid) and poly(methacrylic acid) show two-phase separation in water. Although poly(sodium acrylate) and poly(sodium methacrylate) are completely miscible, mixtures of the partially neutralized acids, e.g., PAA and PNaMA mixtures, show separation. In contrast to predictions for less polar polymers, compatibility of mixtures of polymers containing high mole fractions of carboxylic acid monomers showed a pronounced dependence upon solvent. Thus, the two copolymers 45/53 EA–MAA and 47/53 MMA–MAA are incompatible in methanol or ethanol but form homogeneous solutions in DMF or DMS.

Heat of polymerization of phenyl glycidyl ether and of an epoxy resin

Abstract: A differential thermal analysis apparatus was constructed for the measurement of heats of polymerization It featured an active cell in which the reacting mixture was contained in expendable thin-walled, narrow, cylindrical brass, or aluminum cartridges The cartridges were tightly pressed into holes drilled into the body of the active cell and they, along with the solid reaction product, could be ejected therefrom at the completion of the reaction A calibration cell was provided with small electric heaters which allowed known amounts of heat to be supplied to the apparatus in calibration runs With this apparatus the mean value for three determinations of the heat of polymerization of epoxy resins, ca 22 to 26 kcal/mole, could be measured to within a standard error of 037 kcal/mole (ie, confidence limits of ±075 kcal/mole at the 95% confidence level) The heats of polymerization of phenyl glycidyl ether and of an epoxy resin were measured with ten and nine different curing agents, respectively Primary amine curing agents released about 26 kcal/mole of epoxide reacted, tertiary amines, and boron trifluoride-ether complex each released about 22 kcal/mole Mixed-type curing agents, which could react in part as tertiary amines, or boron trifluoride, and in part as primary amines could liberate intermediate amounts of heat

The glass temperatures of polyacrylonitrile and acrylonitrile–vinyl acetate copolymers

Abstract: The glass-transition temperatures Tg of various copolymers of acrylonitrile and vinyl acetate were measured by observing the linear expansion of molded discs. For vinyl acetate contents of 0 to 27 wt-.% the glass temperature is constant at 87°C. This value agrees with the results of Kolb and Izard for pure polyacrylonitrile. Fitting of the glass temperature–composition data above 27% vinyl acetate to the equation of Fox and Loshaek leads to an extrapolated value of 110°C. for completely amorphous polyacrylonitrile, which agrees with similar data of Krigbaum and Tokita. The difference between the two values can be explained in terms of the effects of crystallinity analogous to those discussed by Nielsen for ethylene–vinyl acetate copolymers. Moreover, experimental values of 92 and 103°C. were found for specially prepared samples of polyacrylonitrile. These samples were found to be less crystalline or to have a different ordering of the polymer chains as evidenced by x-ray data. It is concluded that the glass temperature of completely amorphous polyacrylonitrile can be no greater than 110°C. and that experimental values for semicrystalline polyacrylonitrile may range down to 87°C.

Initiation of graft polymerization on cellulose by hydroxyl radicals and by ceric salts

Abstract: Landells and Whewell have previously reported that vinyl monomers are polymerized “within viscose filaments” by hydrogen peroxide in the presence of ferrous salts and the polymers are not extractable. Such products, obtained by polymerization of acrylonitrile and styrene in viscose, have now been acetylated. Fractionation of the acetylated products has yielded graft copolymers of polyacrylonitrile and polystyrene, respectively, on cellulose triacetate. It is concluded that hydroxyl radicals initiate graft polymerization of acrylonitrile and styrene on cellulose. A similar approach, utilizing acetylation and fractionation, has been used to demonstrate that Mino and Kaizerman's method of initiation of graft polymerization with ceric salts is applicable to cellulose and results in true graft polymerization.

A quantitative study of crosslinking cotton with N‐methylol acrylamide

Abstract: Cotton was acrylamidomethylated by applying N-methylol acrylamide to it with the aid of a mild acid catalyst. When the molal ratio of N-methylol acrylamide to anhydroglucose exceeded about 0.2, the efficiency of this reaction was suddenly reduced and the variation of density with addon departed from linearity. These and other available facts indicated that only one of the three hydroxyls in cellulose, probably the one in the 6-position, was involved in the acrylamidomethyl ether formation and that cotton was about 20% accessible to this reagent. When acrylamidomethylated cotton was treated with free radical or alkaline catalysts, the double bonds became partially saturated and the mechanical properties changed in a spectacular manner. In particular, the resilience of the fabric, as measured by crease recovery, was improved. Analysis of double bond reaction at various levels of acrylamidomethyl content of the fabric indicated that free radical catalysis caused homopolymerization of the pendant double bonds, that alkaline catalysis in the presence of water resulted in Michael condensation between double bonds and the hydroxyls of cellulose, and that these two reactions competed with each other when the alkaline aftertreatment was conducted in dry state. These reactions crosslinked the fabric, and the crosslink content could be calculated from the difference of molal methylene and double bond contents. The crease recovery reached the maximum attainable value characteristic for the method of catalysis when the ratio of accessible anhydroglucose units to crosslinks was 4 to 5. When the crosslinked fabrics were hydrolyzed in acid, the crease recovery increment produced by crosslinking was eliminated after about half of the crosslinks were broken. The residual crosslinks did not contribute to crease recovery. Dry state crosslinking treatments reduced the moisture regain, increased the density, and had no effect on the x-ray pattern. In contrast to this, wet state crosslinking in-increased the moisture regain, changed the x-ray pattern, and, under certain conditions, reduced the density. These results indicate that wet state crosslinking increased the amorphous portion of cotton. Wet state crosslinking lead to higher wet than dry crease recovery whereas the opposite was true for dry state crosslinking. Although the alkaline catalyst did not degrade the fabric, alkali catalyzed crosslinking substantially reduced the tensile strength. Free radical catalysis was more favorable for tensile strength, in spite of the fact that it degraded the fabric in the absence of crosslinking agent.

Epoxide‐substituted vinyl and acrylate copolymers

Abstract: Polymers which are multifunctional in epoxide groups were synthesized by copolymerizing glycidyl methacrylate (GMA) with acrylate and vinyl monomers. The reactivity ratios at 65°C. for the monomer pair styrene (M1)–GMA (M2) are r1 = 0.34 ± 0.05 and r2 = 0.63 ± 0.01. Glycidyl methacrylate (GMA) is similar to methyl methacrylate in its copolymerization characteristics. The copolymers can be crosslinked by the same classes of materials that are useful with conventional epoxide resins based on epichlorohydrin and bisphenol A. Similar curing conditions and reactant stoichiometry can also be used. Three GMA copolymers are described: (1) a phosphated styrene/GMA (85/15) copolymer which is thermosetting and can be used as an appliance finish vehicle to yield enamels with excellent resistance properties; (2) an ethyl acrylate/GMA (97/3) elastomer which can be vulcanized with amines or diacids; and (3) a methyl methacrylate/GMA (70/30) copolymer which can be crosslinked at room temperature with amines. These polymers have good resistance to yellowing because of their aliphatic hydrocarbon backbone. The molecular weight and epoxide functionality of the polymers can be varied over wide ranges.

Viscous flow of molten polyethylene resins

Abstract: A screw extruder and capillary dies of different length radius ratios were used to measure melt flow and end effects for three commercial polyethylene resins, two of low density and one of high density. The apparent melt viscosities of the low density resins decreased faster with increasing shear and temperature than that of the high density resin. Zero shear activation energies for viscous flow were 11.6 and 12.7 kcal./mole for the low density resins and 7.0 for the high density resin. Apparent activation energies at fixed shear stresses were independent of shear stress while apparent activation energies at fixed shear rates decreased with increasing shear rate. End effects and recoverable shear strain were smallest for the high density resin. The differences between the melt flow characteristics of the two types of polyethylene are tentatively correlated with structure.

Diisocyanate-linked polymers. III. Relationships between the composition and ultimate tensile properties of some polyurethane elastomers†‡

Abstract: The ultimate tensile properties (tensile strength and elongation at rupture) of various series of polyurethane elastomers which apparently do not crystallize were studied. Elastomers which contained 0–20% isodecyl pelargonate were prepared from polyoxypropylene glycol 2025 (PPG), dipropylene glycol (DPG), trimethylolpropane (TMP), and toluene 2,4-diisocyanate (TDI); the ratios of ingredients were varied so that all clastomers had approximately the same number of chains per unit volume v and tho same concentration of urethane groups [U]. Unplasticized elastomers were also prepared that were similar except that they were linked by hexamethylene 1,6-diisocyanate, TDI, m-phenylene diisocyanate, and naphthalene 1,5-diisocyanate. Over a wide temperature range, the ultimate proper- ties of elastomers in both series were identical at equal values of T − Tg,. Series of elastomers were also preparcd from TMP, TDI, triethylme glycol, and two polyester diols: a 50/50 and an 80/20 copolymer of e-caprolactone and methyl e-caprolactone. In these series, v was held constant and [U] was varied. Within each series, the ultimate properties were identical at equal values of T − Tg, although the ultimate properties depended on the nature of the polyester diol and were different from those of similar elastomers prepared from PPG. To study the effect of the crosslinker type and the concentration, elastomers having a constant [U] were prepared from PPG, DPG, TUI, and six crosslinkers, three being trihydroxy and three being tetrahydroxy materials. At a given temperature, the tensile strength and ultimate elongation appeared to be inde- pendent of the crosslinker type and proportional to ve½ and 1/ve, respectively, the proportionality constants being temperature-dependent. On these elastomers, equilibrium swelling ratios in benzene and rough values of the per cent sol were also measured and certain relations among these and the mechanical properties were observed.

Solution properties of water‐soluble polymers. I. Control of aggregation of sodium carboxymethylcellulose (CMC) by choice of solvent and/or electrolyte

Abstract: Previous investigations on the solution properties of sodium carboxymethylcellulose (CMC) have led to the conclusion that crystalline cellulose regions, remaining after processing act as binding or crosslinking sites for the establishment of a fraction comprised of swollen gels or aggregates in solution. The present paper deals with recent work which has led to a broader characterization of the degree of aggregation of CMC and its control in solution. Stages of disaggregation are defined for CMC when added to a solvent, ranging from a polymer particle unaffected by solvent through various degrees of swelling to a state of complete dispersion. Examples are given of these various disaggregation stages which were attained and controlled by varying the solvation power and/or ionic strength of the solvent. Degrees of disaggregation were characterized by broad variations in rheological behavior. Viscosity differences of several hundredfold as well as other physical changes in the solutions were found. The results are interpreted to mean that the numerous binding centers which cause CMC aggregation have a wide distribution of strengths. The addition of CMC to a good solvent causes the weaker binding forces to be destroyed and the stronger to remain intact, imparting rheological properties commensurate with the resulting degree of aggregation. The use of a poorer solvent or the addition of a simple electrolyte causes fewer binding centers to be destroyed, and a corresponding change in dispersion properties. Little, if any, re-formation of broken binding centers has been detected. Known and proposed forces involved in the dispersion of macromolecules into solvent are discussed and applied to observations from the present work.

Studies on the γ‐irradiation of natural rubber latex. The effects of organic halogen compounds on crosslinking by γ‐irradiation

Abstract: As the accelerating effect of water in the crosslinking reaction of rubber in natural latex by gamma irradiation was assumed to stem from the decomposition of water into radicals by gamma irradiation, more effective reagents were sought among the organic halides which have greater G values for radical formation by gamma irradiation and, simultaneously, an affinity for rubber greater than that of water. l,2-Dichloroethane, chloroform, carbon tetrachloride, and benzene (for comparison) were tested, and these compounds, except for benzene, were found to accelerate the reaction in proportion to their G values for radical formation. Benzene was found to have no effect, in concentrations between 1 and 5 phr. The optimum dosage was decreased to 2.1 x l0/ sup 6/, l.0 x l0/sup 6/, and 7.6 x l0/sup 5/ r by the addition of 1, 3, and 5 phr of carbon tetrachloride, respectively, and was assumed to have decreased to l.l7 x 10/sup 7/, 9.0 x l0/sup 6/, and 7.6 x 10/sup 6/ r with 1, 3, and 5 phr of l,2- dichloroethane, and to 8.6 x 10/sup 6/, 6.2 x 10/sup 6/, and 5.2 x 10/sup 6/ r spectively. The physical properties of the films obtained at the optimum dosagesmore » under these accelerating condiitions were equal to those of the latex irradiated up to ihe optimum dosage with no addition of halide. No side reactions occurred during the halide-accelerated crosslinking that were sufficiently extensive to influenee the infrared spectra. (auth)« less

Studies on the γ‐irradiation of natural rubber latex

Abstract: Vulcanized latex was obtained by the γ-irradiation of natural rubber latex. The optimum cure was attained with ca. 2 × 107 r, in the case of 40% latex. Owing to the acceleration action of the water present, rubber in latex crosslinked more easily than it did in previously dried latex film, but no appreciable difference was found between the crosslinking in latices of various water contents. The protein in the latex deteriorated under γ-irradiation, but the properties of the latex were not damaged. The maximum tensile strength of the film obtained by drying this irradiated latex was larger than that of solid rubber irradiated in air; this may correspond to the fact that the irradiation, even when carried out in air, brought about no side reactions such as oxidation, etc., of rubber in latex. The aging behavior of the irradiated film was quite superior, the tensile strength being greater after aging than before.

Determination of intrinsic viscosity from one-point measurements

Abstract: A method is described by means of which reliable intrinsic viscosities, [η], can be obtained for a polymer–solvent system from viscosities determined at only one concentration. The method involves, first, the preparation for one sample of the polymer of an ηsp/C and ln ηr/C vs. C plot. The ratio of the slopes of these two curves yields then a parameter γ which is independent of molecular weight, and which allows single point [η] determinations on samples of the polymer at any other molecular weight, whether homogeneous or not. Results are presented to show that the method described yields [η]'s in good agreement with those obtained in the usual manner from multipoint viscosity measurements.

Influence of the initiator on the grafting of polyvinyl polymers

Abstract: The dependence of grafting on the type of initiator has been examined in the case of three polymer–monomer systems: polystyrene–methyl methacrylate, polymethyl methacrylate–vinyl acetate, and polyethyl α-chloroacrylate–vinyl acetate. The different initiators used in these experiments were benzoyl peroxide (Bz2O2), azobisisobutyronitrile (AIBN), di-tert-butyl peroxide (DTBP), and tert-butyl hydroperoxide (TBHP). In each case the graft copolymers were separated from the homopolymers by fractional precipitation or by extraction. In the case of the system polystyrene–methyl methacrylate, an appreciable degree of grafting as well as formation of graft copolymer occur in the presence of Bz2O2; in contrast, the grafting is low with DTBP and doubtful with AIBN. For the other two systems no noticeable differences occurred as function of the initiator. In the case of polyethyl α-chloroacrylate the amount of graft copolymer is exceptionally high owing to the sensitivity of this polymer to a radical attack; this sensitivity results in the partial insolubility of the graft copolymers in the presence of TBHP and DTBP, but not in the presence of AIBN.

Preparation and properties of polyester–urethane block copolymers

Abstract: Polyester–urethane block copolymers were prepared by the block polyaddition reaction of diisocyanate with two kinds of linear polyesters, one of which was polyethylene terephthalate. The melting points of polyester–urethane block copolymers containing more than 30% polyethylene terephthalate are independent of the total molar fraction of the two polyester components, so that the melting point–composition curves are step-shaped. The relation between the second-order transition point of the block copolymer and its composition, on the other hand, is the same as that for a random copolymer. It is observed that some polyester–urethane block copolymers containing 15–50% of polyethylene terephthalate have elastic properties. For example, the 15/85 polyethylene terephthalate/polyethylene adipate–tetramethylene diisocyanate block copolymer has a tensile strength of 240 kg./cm.2 and an elongation of 700%. It may be supposed that these elastic properties are due to the structure of the block copolymer chains: the flexible polymer chains in the amorphous region may be joined to the crystallites of polyethylene terephthalate, so that a type of network structure similar to crosslinking is formed.

Use of the HLB system in selecting emulsifiers for emulsion polymerization

Abstract: In the present work a wide variety of nonionic emulsifiers and anionic/nonionic blends of emulsifiers were evaluated in the emulsion polymerization of vinyl acetate and styrene. It was found that the emulsion stability and other polymer emulsion properties are often dependent upon a certain property of the emulsifier known as the HLB value. It has been shown elsewhere that the HLB value can be correlated with a fundamental physical property of the system oil–water–emulsifier, namely, the spreading coefficient of the internal phase liquid on the surface of a 1% solution of the emulsifier in the external phase. In the emulsion polymerization of styrene, good emulsion stability coupled with adequate conversion rate was obtained in an emulsifier HLB range of 13 to 16. For certain emulsifier blends it was found that emulsion viscosity and emulsion particle size were strongly dependent on the HLB of the emulsifier. Similar comments apply to vinyl acetate polymerization, except that the most stable emulsions were obtained with emulsifiers in an HLB range from 14.5 to 17.5. These observations on preferred HLB range apply only to nonionic emulsifiers and anionic/nonionic emulsifier blends, which were the emulsifier types screened in the present investigation. For both styrene and vinyl acetate the most generally satisfactory emulsion properties were obtained in the present work by the use of an anionic/nonionic emulsifier blend (G-3300/G-3920).

The retardation of drop breakup in high‐velocity airstreams by polymeric modifiers

Abstract: Investigations are being conducted on the factors involved in the breakup of Newtonian and non-Newtonian (viscoelastic) liquids in high velocity airstreams. Viscoelastic solutions are formed by the addition of small amounts of polymeric modifiers to the test liquid. The mechanism of breakup is shown to be significantly different between the thickened and unthickened solutions. It was found that Newtonian liquid drops are broken into very fine particles by a breakup mechanism which begins with a stripping of the liquid from the surface of the drop. On the other hand, drops of non-Newtonian liquids break up by formation of ligaments rather than by surface stripping and are broken into much larger particles. An increase in viscosity by a factor of 25 in the Newtonian liquids showed no significant change in the breakup mechanism.

A comparison of the thermal gradient and elution methods of polymer fractionation

Abstract: The elution method is essentially a single-stage process, whereas the thermal gradient method is a multistage process which depends upon a thermal gradient to bring about reprecipitation of polymer in the fractions. As a test of the effectiveness of the thermal gradient, comparisons have been made of fractionation by these two column methods on high molecular weight polystyrene samples. It was found that the thermal gradient method definitely provides superior resolution and reproducibility, as expected. However, the degree of fractionation obtained by the elution method was surprising, accounting for at least 80% of the sample under the usual conditions and giving complete fractionation with certain modifications of conditions. These results indicate the difference in performance of the two methods is less than expected from an elementary consideration of the operation of the columns, and fractionation by the elution method, as conducted here, exceeds that expected for a single-stage extraction process. Although the reasons for the observed behavior are not clear, the following conclusions have been reached about certain factors which influence fractionation. Alternative methods of controlling the concentration of polymer in the fractions give almost equivalent results but enhanced resolution of the high molecular weight portion of the sample is obtained with extended solvent gradients. The inhibitor, tert-butyl catechol, which it was necessary to add to the solvents to limit degradation of the very high molecular weight sample, plays a specific role in the fractionation due to a reaction with the polystyrene which alters the fractionation behavior without affecting the molecular weight. Also, trace amounts of chemical heterogeneity in the polymers, presumably hydroxyl groups, have a marked adverse effect on fractionation by the elution method and probably account for molecular weight reversals observed in some fractionations by the thermal gradient method. It is suggested that adsorption on the surface of the beads is responsiblp for the adverse effect of chemical heterogeneity on the fractionation and that possibly an adsorption which increases with molecular weight contributes to fractionation by the elution and thermal gradient methods.

Structural characterization of vulcanizates. Part II. Use of triphenylphosphine to determine the structures of sulfur linkages in unaccelerated natural rubber–sulfur vulcanizate networks

Abstract: Treatment of unaccelerated natural rubber–sulfur vulcanizate networks with triphenylphosphine in benzene at 80°C. effects the removal of part of the combined sulfur, the proportion removed decreasing with increasing cure time. This partial desulfurization of the network is attributed, on the basis of the mode of interaction of simple organic di- and polysulfides with triphenylphosphine, to the conversion of polysulfide linkages in the network into either mono- or disulfide groups. Knowledge of the amount of sulfur removed by the reagent, and of the chemical degree of crosslinking and combined sulfur content of the untreated networks permits the following semiquantitative conclusions to be reached concerning the structures of the sulfur linkages in the networks: (1) long polysulfidic crosslinks (S11 to S12) are initially formed, which on continued cure progressively decrease in length to a limiting value of S2 to S4; and (2) a very high proportion to the combined sulfur (ca. 77% for short cure times, increasing to ca. 95% on extended cure) is present in cyclic monosulfide groups situated along the polyisoprene chains.

The mechanism of post cure of viton A Fluorocarbon elastomer

Abstract: The necessity for oven post-curing Viton A vulcanizates is explained in the following way: The formation of crosslinks is accompanied by the elimination of HF from the polymer. In the subsequent reaction of HF with the magnesium oxide present as acid acceptor water is formed which acts to inhibit the full development of cure unless it is removed from the vicinity of the polymer by post-curing in an open system. Measurement of the rate of elimination of water from the polymer serves as a method of following the development of crosslinking during cure. Approximately two moles of water, derived from four moles of hydrogen fluoride, are associated with the use of one mole of diamine curing agent. This ratio is confirmed by independent estimates of the relationship of crosslinking density to curing agent level based on measurements of swollen compression moduli.

Diazonium derivatives of cellulose as initiators of graft polymerization

Abstract: Cellulose p-aminophenacyl ether (I) has been prepared from cotton and the partial p-aminophenacyl ester of carboxymethyl cellulose (III) has also been prepared. Derivatives (I) and (III) have been diazotized and then used to initiate polymerization of acrylonitrile. In the presence of ferrous sulfate the polymerization proceeds to formation of a graft copolymer and no polyacrylonitrile homopolymer was detected. Attempts to graft styrene and vinyl acetate on the same derivatives were not successful. Thermal degradation of the diazonium derivatives leads to insolubilization, probably due to crosslinking by combination of free radicals. Attempts to prepare cellulose p-aminobenzoate by reaction of cellulose derivatives with p-aminobenzoyl chloride (IV) in the presence of a basic catalyst led to polymerization of (IV) and to the formation of a supposed cellulose–poly-p-benzamide graft copolymer.

The behavior of polyisobutylene during melt shear

Abstract: Studies were made of the apparent melt viscosity and chain rupture of polyisobutylene melts during high mechanical shear at various temperatures, and for varied times of shearing action. A biconical rheometer was constructed and used for this study. It was observed that the torque developed in such a rheometer by the action of shear on molten polymer shows peculiarities. The initial high torque, or the apparent melt viscosity which may be derived from it, drops rapidly to a pseudo steady state value in about one or two minutes. An interval of shear cessation permits considerable return of the system to the original high value of the apparent melt viscosity, especially if the cessation interval is long (e.g., 10 min. at 45°C.). During the pseudosteadystate period there is a small and continuous drop in the already reduced torque or the apparent melt viscosity. Study of the chain rupture rate, made by examination of dilute solution viscosities, and the viscosity-average molecular weights determined from them, showed the rate of chain degradation to decrease as the temperature during the shearing operation is raised. The chain rupture rate decreases steadily as shearing is continued, and increases with increase of shear rate at a given temperature and time of shear application. The behavior of the apparent melt viscosity, decreasing sharply to a pseudosteady-state value shortly after intense shear begins, is presently pictured as due to two mechanisms, one chemical, the other mechanical, acting simultaneously. One process is considered to be the rapid breakdown of the chainlike molecules to smaller fragments forming mainly free radicals or ion pairs at their ends. These reactive ends begin immediately to recombine at a rate which increases with the rise in their concentration until the pseudoequilibrium state is reached. The second process is considered to arise from both chain disentanglement and the preferential migration of holes in the liquid away from the center of gravity of the chains to form regions of low viscosity which may be termed fault lines or regions.

Isobutylene copolymers of vinylbenzyl chloride and isopropenylbenzyl chloride

Abstract: The styrene derivatives vinylbenzyl chloride and isopropenylbenzyl chloride were prepared and copolymerized with isobutylene and propylene in order to produce polymers with reactive halogens. Vinylbenzyl chloride and isobutylene have relative reactivities such that the copolymer is much richer in isobutylene than the starting mixture, while with isopropenylbenzyl chloride and isobutylene the difference in reactivities is less and is in the opposite direction. Copolymers containing small amounts of the reactive benzylic chlorine were vulcanized, either with amines or with a conventional butyl rubber cure. Permselective membranes were prepared from copolymers rich in benzylic chlorine.

Polymerization of acrylonitrile by use of potassium alkoxides

Abstract: The heterogeneous anionic polymerization of acrylonitrile in petroleum ether by potassium alcoholic alkoxide solutions at low temperature was studied. Alkoxides of the more electropositive metal were more active catalysts, ROK > RONa. Increasing amount of alcohol in the polymerization mixture up to a limit, had an activating effect. Yield of polymer increased with catalyst concentration. The mechanism of the polymerization consists of initiation by direct interaction of alkoxide anion with monomer, with no cocatalyst; this is substantiated by the presence of alkoxyl groups in the polymers and by the existence of steric effects of bulkyl alkoxide groups. Termination is by proton abstraction from alcohol. In accordance with this, the degree of polymerization was found to be independent of catalyst concentration, directly proportional to monomer, and inversely to alcohol concentrations, according to the equation, DP = kp[M]/kt[ROH]. Plot of DP versus monomer and the reciprocal of the alcohol concentrations gave values for kp/kt of about 35. All polymerizations showed an induction period with the following regularities. It increased with increasing concentration of alcohol and with lowering of temperature, and decreased with increasing catalyst and monomer concentrations and was smaller with the more active potassium catalysts. Induction periods seem to originate from the competing side-reaction of cyanoethylation, the initiation step of the polymerization being identical with the first step (RO− addition) in the cyanoethylation reaction. Cyanoethylation products were isolated from polymerization mixtures.

The infrared identification of short-chain branches in polyolefins

Abstract: A series of polymers have been prepared that contain ethyl, n-propyl, n-butyl, n-pentyl, and n-hexyl branches. We have determined the rocking vibrations of the branches and have shown that branches in solid polymers have their rocking vibrations at frequencies comparable with those shown by liquid hydrocarbons. The ethyl branches in seven different polymers have infrared absorption bands in the 785–760 cm. −1 (12.74–13.18 μ) region. The terminal n-propyl group absorbs at 740 cm.−1 (13.51 μ) and the n-propyl branch at 735 cm.−1 (13.61 μ). The n-butyl, n-pentyl, and n-hexyl branches in polymers have their infrared absorption at 724 cm.−1 (13.81 μ), 723 cm.−1 (13.83 μ) and 722 cm.−1 (13.85 μ), respectively. The above data have been used to identify ethyl, n-propyl, and n-butyl branches in polymers produced by the cationic polymerization of propylene and l-butene.