Showing papers in "Journal of Polymer Science Part A in 1966"

A New, General Synthetic Method for the Preparation of Linear Poly‐p‐xylylenes

Abstract: A new, general synthetic route to poly-p-xylylene and substituted poly-p-xylylenes is described. The key intermediate in the new process is di-p-xylylene [(2,2)p-cyclophane]. It has been found that di-p-xylylene is quantitatively cleaved by vacuum vapor-phase pyrolysis at 600°C. to two molecules of p-xylylene. p-Xylylene spontaneously polymerizes on condensation to form high molecular weight, linear poly-p-xylylene. The conversion of di-p-xylylene to poly-p-xylylene is quantitative. The process is adaptable to the preparation of a wide variety of substituted poly-p-xylylenes by pyrolysis of ring-substituted di-p-xylylenes and polymerization of the resultant substituted p-xylylenes. Many of these polymers are not attainable by any other route. All are linear and free of crosslinking. Evidence supporting the proposed mechanism of pyrolytic cleavage of every molecule of di-p-xylylene to two molecules of p-xylylene is presented. Tough, transparent polymeric films are obtained from the process when the polymerization of the p-xylylenes is conducted on glass or metal surfaces. Outstanding combinations of physical, electrical, and chemical properties are displayed by poly-p-xylylene, polychloro-p-xylylene, and other substituted polymers. A comparison of the relative merits of the original Szwarc route and the new di-p-xylylene route to poly-p-xylylenes is presented.

Homopolymerization of 2‐alkyl‐ and 2‐aryl‐2‐oxazolines

Abstract: 2-Aryl- and 2-alkyl-2-oxazolines have been polymerized to poly-(N-aroyl)aziridines and poly(N-acyl)aziridines, respectively, in the presence of boron trifluoride. The polymers obtained were glassy, light yellow resins with molecular weights ranging from 3500 to 7500 (35–50 oxazoline units per chain). The polymerization rates have been determined for several of these monomers. A polymerization mechanism is proposed.

Studies of thermal cyclizations of polyamic acids and tertiary amine salts

Abstract: Thermal conversion rates of the polyamic acid derived from pyromellitic dianhydride and 4,4′-diaminodiphenyl ether are presented. Formation of the imide ring proceeds by fast and slow first-order processes. Tertiary amines give ring closures faster by a factor of 10 than the free acid. The enhancement is an activation entropy rather than an activation energy effect.

Interactions of inorganic salts with poly(ethylene oxide)

Abstract: Evidence is presented for the interaction of metal salts such as potassium iodide with polyethers such as poly(ethylene oxide). This interaction is sufficiently marked that the incorporation of 10–30% of the salt in the bulk polymer markedly reduces crystallinity while retaining compatibility. Examination of electroviscous effects in methanol demonstrates that the salt–polymer adduct behaves as a typical polyelectrolyte at low salt concentrations, while the polymer in absence of salt is essentially insoluble in methanol at room temperature. Measurements of the equilibrium between salt and polymer along with a study of various molecular weight polymers strongly suggest that one salt molecule associates with about nine ethylene oxide units. It is proposed that the association is due to an ion–dipole interaction, and the anion is tentatively postulated as the species directly associating with the polymer. The association of other metal salts and other polymers are interpreted in this light. The significance of these results in interpreting salting-in phenomena is also discussed.

Heterogeneous polymer systems. IV. Mechanism of rubber particle formation in rubber‐modified vinyl polymers

Abstract: Polymerization of a solution of a rubber in a vinyl monomer consists of two stages. In the first stage (0–40 per cent conversion), in which the system is liquid, a polymeric oil-in-oil emulsion is formed, and the size of the rubber particles is established. In the second stage (40–100 per cent) this polymeric oil-in-oil emulsion hardens gradually to a solid dispersion of rubber particles in a matrix of the vinyl polymer, whereby the structure of the emulsion is retained and no significant morphological changes occur. The rubber particles are formed in the phase inversion which occurs in the first stage of polymerization. After the manuscript of this paper had been completed, a publication appeared, in which the dispersion of rubber by a phase inversion was also described. Bender's observations are in agreement with the observations presented in this paper and in the first paper in this series.) At the phase inversion point, the rubber phase is dispersed in the form of droplets in the vinyl polyme...

Gel permeation chromatography. III. Molecular shape versus elution

Abstract: Rules were evolved to predict elution of linear, branched, and polar compounds in GPC, based on testing of 130 compounds. With these rules and in tetrahydrofuran solvent, data for all but a few compounds correlated onto a single calibration line. With small molecules, elution often changed, due to hydrogen bonding to the solvent; this occurred with alcohols, acids, and some chlorinated compounds, but not with mercaptans. Branched and linear isomers usually eluted at about the same point. One may conclude that structural elements were additive in their effect on elution volume in this study.

Sequence distribution of partially hydrolyzed poly(vinyl acetate)

Abstract: Copolymers of vinyl acetate and vinyl alcohol were studied by differential thermal analysis. The melting points of the copolymers are not a simple function of the composition, but depend on the method of preparation of the copolymers. Partial saponification of poly(vinyl acetate) with sodium hydroxide leads to high melting, ordered copolymers, while reacetylation of poly(vinyl alcohol) leads to low melting, random copolymers. Catalytic alcoholysis of PVAc yields copolymers intermediate in melting point and order. The results are treated by assuming that equal melting points indicate similar sequence length distributions of crystallizable units.

Permeation, sorption, and diffusion of water in ethyl cellulose

Abstract: The permeability of ethyl cellulose to water vapor and liquid water was measured as a function of temperature. A change of slope was found in the Arrhenius plots at about 50°C., close to the glass transition. The sorption isotherms showed essentially zero heat of mixing in agreement with other workers. The diffusion constants were measured in four ways, viz., sorption, desorption, time lag, and by dividing the permeability constants by the equilibrium solubility coefficients. The time lag method gave diffusion constants which were independent of concentration, whereas the other three methods led to diffusion constants which steadily decreased with concentration. All the methods, however, extrapolated to about the same value at zero concentration. The decreasing diffusivities are believed to be due to the clustering of water molecules in the polymer. However, no clustering appeared to take place under the conditions of the time lag measurements.

Room temperature polymerization of glycidol

Abstract: Glycidol has been shown to be easily polymerized at room temperature in the presence of triethylamine, pyridine, lithium hydroxide, potassium hydroxide, sodium hydroxide, sodium methoxide, sodium amide, and other catalysts. Its reactivity with these catalysts is vastly greater than that of propylene oxide. Evidence is presented to support the structural assignment for polyglycidol and the mechanism of polymerization.

Graft polymerization kinetics of acrylamide initiated by ceric nitrate–dextran redox systems

Abstract: The kinetics of the graft polymerization of acrylamide initiated by ceric nitrate—dextran polymeric redox systems was studied primarily at 25°C. Following an initial period of relatively fast reaction, the rate of polymerization is first-order with respect to the concentrations of monomer and dextran and independent of the ceric ion concentration. The equilibrium constant for ceric ion—dextran complexation K is 3.0 ± 1.6 l./mole, the specific rate of dissociation of the complex, kd, is 3.0 ± 1.2 × 10−4 sec.−1, and the ratio of polymerization rate constants, kp/kt, is 0.44 ± 0.15. The number-average degree of polymerization is directly proportional to the ratio of the initial concentrations of monomer and ceric ion and increases exponentially with increasing extent of conversion. The initial rapid rate of polymerization is accounted for by the high reactivity of ceric ion with cis-glycol groups on the ends of the dextran chains. The polymerization in the slower period that follows is initiated by the breakdown of coordination complexes of ceric ions with secondary alcohols on the dextran chain and terminated by redox reaction with uncomplexed ceric ions.

Mechanism of ozone attack on α-methyl glucoside and cellulosic materials

Abstract: Ozone attack on cellulose and related substances was investigated and appears to involve a twofold mechanism. One is a free-radical chain mechanism involving oxygen in the propagating step. This slow reaction is highly indiscriminate, showing very little, if any, specificity as to the site of attack and resulting in the formation of peroxide, carbonyl, carboxyl, and presumably lactone groups. In the presence of oxygen, kinetic chain lengths of over 100 were measured, but in nitrogen atmosphere the total oxidation of substrate was equivalent to the amount of ozone consumed. The second process appears to be an electrophilic attack which liberates the anomeric carbon of glycosides via an ozone-catalyzed hydrolysis of glycosidic linkages. This reaction, analogous to a nitronium or chloronium ion- or proton-catalyzed hydrolysis, is postulated since chain degradation of polysaccharides is equally severe in the presence or absence of oxygen, and occurs in buffered solutions or suspensions even in the neutral pH range, and because the main product of ozone attack on α-methyl glucoside is glucose. Brightness improvement in cellulose involves an electrophilic attack on double bonds and therefore is a direct function of the quantity of ozone used, like chain degradation. It is therefore not surprising that we have found no method of enhancing the specificity of ozone attack on the colored material relative to chain degradation. Because of the topochemical and diffusion-controlled character of the reaction on cellulose, the use of a different temperature range will cause only a trivial difference in the relative rates of attack.

Studies on Ziegler‐Natta catalysts. Part V. Stereospecificity of the active center

Abstract: Experimental results on Ziegler-Natta catalysts, based on observations made with the electron microscope, and a qualitative comparison of the stereospecificity of various catalyst combinations are given. The polymerization of olefin in these experiments is performed in the gas phase on dry catalysts in the absence of solvent or excess aluminium alkyl. The crystallographic structure of the lateral faces of α-TiCl3 is established by electron microscopy and electron diffraction. The electron micrographs of α-TiCl3–AlMe3 catalysts show that the active centers, which are revealed by the dotwise formation of polymer, are located along the growth spirals, on lateral faces, and on surface defects. These regions of the surface are the only regions in which the surface titanium atoms are incompletely coordinated. The presence of chlorine vacancies and exposed titanium atoms is therefore an essential condition for the formation of active centers. However, the number of active centers is small in comparison to the number of incompletely coordinated titanium atoms, and hence it is concluded that the normally occurring α-TiCl3 sites with one vacancy do not yield active centers on reaction with aluminum alkyl. It is proposed that the reaction with aluminum alkyl on such sites leads ultimately to a bimetallic complex which fills the original vacancy on the titanium atom. That the complexation is reversible and that the deblocked alkylated site, which is of the type proposed by Cossee, is an active center is not excluded. Such a center would, however, give atactic polymer. Similar complex formation on a TiCl3 site having originally two vacancies would leave one vacancy on the titanium atom. This is believed to be the center of stereospecific polymerization. A model of this active center and a mechanism of polymer growth on it are proposed.

Correlation of cationic copolymerization parameters of cyclic ethers, formals, and esters

Abstract: Carefully determined cationic copolymerization parameters of cyclic ethers, formals, and esters are collected. Relative reactivity correlates with basicity and free energy. Further correlations of the copolymerization parameters for styrene, the effect of promoters, and the known mechanism of hydrolysis permitted a decision between the carbonium ion (including acylium ion) or the oxonium ion as the active intermediate of the propagation. Structural features which promote depropagation are identified. Equations describing these possibilities were derived and briefly discussed. Catalyst and solvent effects limited the correlation possibilities.

Copolymerization of Styrene and Methyl Methacrylate with Lithium as Initiator

Abstract: Copolymers of styrene and methyl methacrylate prepared with lithium dispersion as initiator do not contain random sequences of both monomers. Fractionation of the copolymers with acetonitrile and the NMR spectra of the insoluble fractions show that these are block copolymers which consist of a polystyrene portion and a poly(methyl methacrylate) portion. When the copolymerization is stopped at low conversion the copolymer has a high styrene content, which sometimes exceeds the value expected for radical copolymerization. This fact would indicate that styrene is preferentially polymerized at the early stages of chain propagation. When the copolymerization is carried to high conversion some crosslinked polymer is formed which contains more styrene than the soluble part of the same experiment. When a piece of metallic lithium is used as initiator, it is found that the crosslinked polymer is formed on the surface of the metal. The addition of lithium phenoxide or β-naphthoxide to the system eliminates the formation of crosslinked polymer. A possible mechanism is proposed.

Structure and physical properties of glow discharge polymers. I. Polymers from hydrocarbons

Abstract: The polymers deposited from the vapors of pentane, ethylene, butadiene, benzene, styrene, and naphthalene subjected to glow discharge have been analyzed by infrared absorption techniques. The reaction products show unsaturation, hydrogenation, and branching in the polymer chains. Aromaticity is present only in polymers from aromatic monomers.

A new series of organoboranes. VII. The preparation of poly-m-carboranylenesiloxanes

Abstract: : The following meta-carboranylene backboned polysiloxanes were obtained by ferric chloride catalyzed polymerizations: (-Si(CH3)2CB10H10CSi(CH3)2O-) from 1,7-bis(chlorodimethylsilyl)m-carborane plus bis (methoxydimethylsilyl)m-carborane; (I); (-Si(CH3)2CB10H10CSi(CH3)2OSi(CH3)2O-) from dichlorodimethylsilane (II) plus I; (-Si(CH3)2CB10H10CSi(CH3)2OSi(CH3)2OSi(CH3)2O-) from a dimer of II plus I; (Si(CH3)2CB10H10Si(CH3)2OSi(CH3)2OSi(CH3)2O-) from dilitho-m-carborane plus dichlorotetramethyldisiloxane. These compounds, and a number of substitution products thereof, were examined by X-ray diffraction and their thermal and oxidative behavior were studied by differential calorimetry.

Thermal behavior of polyhydrazides and poly‐1,3,4‐oxadiazoles

Abstract: The thermal properties of a series of polyhydrazides and corresponding poly-1,3,4-oxadiazoles have been investigated using differential thermometric and thermogravimetric techniques. In addition, the conversion rates of the polyhydrazides to the corresponding oxadiazole structures have also been measured. In general, weight loss in polyhydrazides occurs in three distinct stages corresponding, respectively, to loss of adsorbed water, cyclodehydration, and decomposition of the poly-1,3,4-oxadiazole formed in situ. The polyoxadiazoles generally exhibit only a single weight loss step (below 700°C.) corresponding to decomposition and volatilization of the substrate itself. These data clearly indicate that the presence of aliphatic carbon–carbon linkages in the polymer backbone reduces the temperature at which decomposition of the polyoxadiazoles is noted. Corresponding differential thermometry patterns give additional data on phase transitions in the polymers and indicate, in general, that the poly-1,3,4-oxadiazoles formed in situ decompose before reaching their intrinsic melting points (under the specific conditions of these experiments). Comparison of the poly-1,3,4-oxadiazoles prepared under the (rapid) dynamic conditions of the differential thermometry and thermogravimetry techniques employed (30°C./min.) with isothermal rate data clearly suggests subtle structural differences in the polyoxadiazoles prepared by the two different modes. In general, ΔE‡ for the hydrazide–oxadiazole conversion amounts to about 49–53 Kcal./mole while ΔS‡ amounts to 14–17 e.u. However, both ΔE‡ and ΔS‡ for the polymer containing exclusively 1,3-phenylene linkages between incipient oxadiazole groups appear to be considerably higher (ΔE‡ = 62 Kcal./mole, ΔS‡ = 34 e.u.). This striking difference is explained in terms of the increased order resulting from the higher degree of crystallinity in the polyhydrazide.

Preparation and properties of poly(methylene terephthalates)

Abstract: A systematic study of poly(methylene terephthalates) has been made. Melting points, second-order transition temperatures, and solubility temperatures are presented for the homologous series of terephthalate polyesters of ethylene glycol through 1,10-dodecanediol, and for terephthalate copolyesters of: (1) ethylene glycol/1,3-propanediol and (2) ethylene glycol/1,4-butanediol. Fiber properties of the terephthalate polyesters and the 70/30 ethylene glycol/1,3-propanediol copolyterephthalate ester are presented. Only the first three members of the poly(methylene terephthalate) series show promise for use in textile fibers.

Oxygen diffusion limitation in autoxidation of polypropylene

Abstract: The induction period for the autoxidation of polypropylene increases with increasing sample thickness (from 1 to 75 mils) and with decreasing oxygen pressure. The rate of oxidation shows the opposite dependences. In contrast, neither the rate nor the induction period in well stirred oxidations of squalane is oxygen pressure-dependent. It is concluded that autoxidation of polypropylene is controlled by diffusion of oxygen into the sample.

New high temperature polymers. I. Wholly aromatic ordered copolyamides

Abstract: Wholly aromatic ordered copolyamides of unusually high thermal stability were prepared by the condensation of aromatic diacid chlorides with symmetrical diamines containing preformed aromatic amide units in an ordered arrangement. The preservation of order in the condensation step was assured by using interfacial or solution polymerization techniques at temperatures below 50°C. Each polymer contains units derived from aminobenzoic acids, arylene diamines, and arylene diacids. By use of para- and meta- phenylene units, eight different polymers are possible; all were prepared. Differential thermal analyses and thermogravimetric analyses showed these polymers to have melting points or decomposition temperatures in a range from 410°C. for the all-meta polymer to 555°C. for the all-para one. Substitution of the internal N-hydrogens of the diamines with methyl groups or phenyl groups leads to additional ordered copolymers. Several were prepared, but their melting points were much lower than those of the parent polymers limiting their usefulness in high temperature applications. Tough pliable films were prepared from all eight unsubstituted polymers, and crystalline fibers with tenacities of ca. 6 g./den. were prepared from three of the polymers. The properties of the fibers were retained to a high degree even when determined at temperatures up to 400°C. Fibers aged at 300°C. for extended periods of time showed remarkable retention of fiber properties.

Grafting vinyl monomers to starch by ceric ion. I. Acrylonitrile and acrylamide

Abstract: Studies were carried out on the grafting of acrylonitrile (AN) and acrylamide (AA) to starch by ceric ion. The variables affecting the grafting of AN and AA were investigated with granular wheat starch dispersed in aqueous N,N-dimethylformamide and ceric ammonium nitrate as catalyst. Results showed that the concentrations of monomer and catalyst are the major factors influencing the grafting of AN; thus the monomer content of the grafts can be regulated by these variables. The grafting of AA is also influenced by these variables, but to a much less degree. Increasing concentrations of monomer promote homopolymerization and increasing concentration of catalyst inhibit grafting. The extent of grafting of this monomer can best be controlled by reaction time. Under the most favorable conditions, maximum grafting efficiency (ratio of amount of grafted monomer to total amount of monomer converted to polymer) was 87% for AN and 43.8% for AA. Although the monomer content of the AN grafts was higher than that of AA grafts prepared under identical conditions, the number of branches in the grafts was almost the same; only the length of the branches was different. The AN-starch grafts have branches of higher molecular weight.

Flow rates of polymer solutions through porous disks as a function of solute. II. Thickness and structure of adsorbed polymer films

Abstract: The thickness of films of poly(methyl methacrylate) (PMMA), poly(vinyl acetate) (PVAc), and polystyrene (PS) adsorbed on Pyrex glass was studied by measuring the flow rates of polymer solutions and the corresponding pure solvents through sintered filter disks. Adsorption isotherms were in agreement with those reported by other workers and showed saturation adsorption equivalent to 2–8 condensed monolayers of monomer units. Film thicknesses were of the order of magnitude of the free coil diameters in solution and were directly proportional to the intrinsic viscosity of the polymer, except for PS in benzene where the thicknesses leveled off as molecular weight increased. It was concluded that polymers adsorb from solution in monolayers of compressed or interpenetrating coils; that below some critical molecular weight which varies with polymer and solvent, a much larger fraction of the segments lies directly in the interface; that adsorbed films may consist of a dense layer immediately adjacent to the surface and a deep layer of loops extending into the solvent; and that it is the segment—solvent interaction rather than the segment—surface interaction which dominates the conformation of the adsorbed chain.

How Ticl3 Catalysts Control the Texture of As-Polymerized Polypropylene

Abstract: Within a family of catalyst systems wherein TiCl3 was made by mixing TiCl4 and aluminum alkyl solutions, the primary particles of TiCl3 were usually thin, flat polygons with average diameters ranging from 300 to 1000 A. Even in unused catalyst these primary catalyst particles were bound together into large (∼30 μ) secondary particles. A small amount of polyolefin which formed from the aluminum alkyl reducing agent aided in cementing the particles. When propylene monomer was introduced to a slurry of secondary catalyst particles in a liquid hydrocarbon, polymer formed at the surfaces of the ultimate solid particles. The resulting polymer flakes, i.e., particles of as-polymerized polypropylene, were several times larger than the secondary catalyst particles from which they grew but they retained the same shape. The primary catalyst particles, not visibly altered by the catalytic reaction which they propagated, were distributed uniformly throughout the flake polymer. Each polymer flake consisted of many thousands of cohering roundish flakelets about a 1/2 μ in diameter. How the flakelets are agglomerated and the extent to which they are coalesced accounts for the flakes' texture. The basic morular structure of the flakes, which was manifested further by their papillary surfaces, was not altered by purification procedures which removed catalyst from the nascent polymer. Although all the flakes had the same basic small-scale structure there were significant coarse textural dissimilarities among them. Some catalysts gave rise to flakes with an open porous texture: other catalysts gave rise to flakes which were dense and compact. In the former, the flakelets were less tightly appressed, and fissures and slits were larger and more numerous than in the latter. The genetic basis for the differences in flake texture resides in the parent catalyst. Secondary catalyst particles whose constituent primary particles are held together in a dense mass produce dense flakes. Conversely, loose aggregates of primary particles produce flakes with loosely aggregated flakelets. Briefly, dissimilarities in catalyst structure carry over to the texture of the flake progeny. Such textural differences contribute importantly to properties of the flake polymer.

Ordered structures of styrene–butadiene block copolymers

Abstract: Anionically prepared block copolymers of butadiene and styrene exhibit solution properties which result from a two dimensional ordering of the polymer molecules. The most notable of these properties is the iridescent colors of toluene solutions which are dependent on concentration and abruptly change on mechanical deformation. Electron micrographs of the surface of cast films indicate that the ordered structure is retained to some degree in the solid state.