High-pressure phases in polymers. I. Spherulitic growth kinetics in cis-polyisoprene

This is the first paper in a series dealing with the crystallization of high polymers at elevated pressures. Through an extension of the thin-film technique using osmium tetroxide staining, the measurement of lamellar growth kinetics at high pressures as well as the observation of micromorphological changes has proved possible. Three different morphological species of cis-polyisoprene have been detected in the pressure–temperature plane. A review is given of the conditions governing their formation and the growth kinetics of lamellar crystals are discussed in detail. Secondary nucleation theory is obeyed, the major effect of pressure being to alter the kinetics through the thermodynamic transitions. Variations in lamellar thickness with pressure may be explained simply in terms of the elevation by pressure of the equilibrium melting point.     

High-pressure phases in polymers. II. Spherulitic growth morphology in cis-polyisoprene

The morphological details of the nucleation and growth of spherulites in cis-polyisoprene at elevated pressures are discussed on the basis of transmission electron microscopy of films stained in situ by osmium tetroxide and cold-stage electron diffraction of unstained films. The crystalline structure is unchanged but growth habits are modified. Spherulites begin, as in crystallization at atmospheric pressure, with a single lamella. The formation of a spherulite proceeds primarily through “spawning” and is unaffected by the imposition of pressure. Lamellae tend to propagate as plates or hedrites at supercoolings in excess of 50–60°C (e.g., 1 kbar at 0°C) unlike at atmospheric pressure where only ribbonlike lamellae are observed. Propagation is invariably as sheafs since nucleation of lamellae which grow perpendicular to the primary lamella is suppressed. The nucleation density varies considerably with pressure, a maximum being observed in the pressure plane at constant temperature (e.g., 0.70 kbar at 0°C). It is difficult to resolve clearly the morphological details in the diffusion controlled region because of fine texture. Although much more difficult to achieve experimentally, the effects of pre-orienting the melt are similar to those occurring at atmospheric pressure.     

High-pressure phases in polymers. V. Crystallization studies of synthetic cis-polyisoprene

The effects of elevated pressure on the morphology and crystallization kinetics of cis-polyisoprenes containing 2–2.5% trans units have been determined. Lamellar growth rates of both α and β crystals are enhanced by elevated pressure. The degree of enhancement of α-crystal rates is much greater resulting in an effective suppression of β growth. Differences in lamellar growth rates between these polymers and cis-polyisoprene result from different preexponent values. Hedritic or axialitic growth, presumably due to low-molecular-weight fractions, is observed in shish-kebabs present in strained films. The high-pressure hexagonal phase cannot be grown in these polymers.     

High-pressure phases in polymers. III. The nature of the high-pressure phase in cis-polyisoprene

The morphology and growth of the disordered hexagonal phase which crystallizes in films of cis-polyisoprene at pressures in excess of 3 kbar is discussed. A two-stage growth process is proposed consisting of nucleation and crystallization followed by a pressure-enhanced thickening process. The phase is metastable and is replaced by normal spherulitic growth at long times. It transforms into lamellar sheafs with higher than usual lamellar thicknesses when pressure is lowered at constant temperature.     

Carborane polymers. IV. Polysiloxanes

Carboranes attached to silicon through straight-chain alkyl groups were prepared and characterized for thermal stability by TGA and molecular weight change on heating. The monomers for these polymers were prepared generally by platinum-catalyzed addition of a silylhydride to an alkenyl or dialkenyl carborane. Polymerization was effected by hydrolysis-condensation of chlorosilanes, ring opening of cyclosiloxanes, and condensation of alkoxy and chlorosilanes. Two types of polymer structures were prepared, one contained m-carborane in the chain backbone, the other contained o-carborane as pendant alkylcarborane groups. Both types were obtained as elastomers; however, higher proportions of carborane in the polymers reduced elasticity and finally resulted in nonelastomers. TGA of the backbone carborane siloxane polymer indicated degradation at 370°C. in nitrogen and at 235°C. in air. Chain scission, as determined by molecular weight decrease, was observed on heating in nitrogen at 350°C. TGA of the pendant carborane siloxane polymer indicated that degradation in nitrogen and in air occurred at greater than 400°C. However, chain scission, as determined by molecular weight decrease, was observed upon heating at 300°C. in nitrogen.     

Organometallic polymers. IV. Organometallic modifications of halogen-containing polymers

The synthesis of ferrocene-containing polymers by chemical modification of chlorinated polyethylenes, polyvinyl chloride (PVC), and other halogenated polymers, under Friedel-Crafts conditions, is described. The effect of reaction conditions on the structure and composition of the products obtained with various substrates was investigated. Soluble polymers of up to 62% ferrocene content were obtained. In most cases, substitution was accompanied by dehydrohalogenation. The ferrocene-to-vinylene ratio was higher in the reaction products of chlorinated polyethylenes than in those of PVC.     

Entangled polymers in condensed phases

We present Monte Carlo results on a model of polymers in a condensed phase, over a range of monomer densities. We imagine cutting a cube out of the system. This cube will typically have several polymer molecules running through its interior, and starting and ending on the boundary. These subchains will be mutually entangled and we present a way to assess the extent of entanglement complexity as a function of the monomer density and the number of subchains in the cube. The model is a set of k self-avoiding and mutually avoiding walks, properly embedded in the cube.     

Epitaxial growth alignment of ferroelectric smectic C phases on rubbed polymers

Several of the polymers reported for surface alignment of ferroelectric smectic C phases in the literature are tested with a ferroelectric room temperature mixture. The results for this material and the reported findings in the literature are compared to the known crystal structure of the polymers. It is found that polymers with triclinic or monoclinic crystals give good alignment and bistability for the smectic C phase. Other crystal structures or non-crystalline polymers give a poorer performance. The mechanisms for creating a highly crystalline polymer surface are discussed, and the epitaxial growth of smectic phases on the crystalline surface is shown to be in accord with experiment.     

Lactone polymers. IV. Glass transition temperatures of monomeric lactones and their polymers

Glass transition temperatures were determined for a homologous series of unsubstituted lactone monomers varying in ring size from four to sixteen atoms. Examination of these transitions as a function of ring size shows a maximum in T_g for the seven-atom ε-caproalctone ring. This behavior is interpreted on the basis of a conformational change in lactones which occurs in rings containing seven to nine atoms. The T_g values of polylactones derived from these cyclic esters were determined and correlated with T_g values of the monomers. Except for the anomolous ε-caprolactone and the strained fourmembered lactone, an apparently constant difference between monomer and polymer T_g is observed. Treatment of the polylactones as methylene copolymers permits extrapolations of the T_g values to obtain that of polyethylene. Two values suggesting the γ and β transitions of polyethylene are obtained.     

New liquid-crystalline polymers with chiral phases

Liquid-crystalline polyesters with cholesteric and probably chiral smectic C* phases were prepared using combined liquid-crystalline polymers (that is polymers with the mesogenic groups in the main chain as well as in the side groups). Copolyesters of these polymers and polymers with olefinic double bonds could be cross-linked retaining the liquid-crystalline phases. This resulted in cross-linked polymers with elastic properties.     

Diacetylene-containing polymers IV. Novel diacetylene-containing polyamides and copolyamides

New monomers, bis(3-ethynyl)dianilides, were synthesized from 3-ethynylaniline and different diacid dichlorides and were polymerized by oxidative polycoupling to give soluble high molecular weight film forming diacetylene-containing polyamides. UV-induced and thermal cross-linking of the polymer were studied. A correlation was found between the chain flexibility and the absoprtion peaks of visible spectra of cross-linked polymer films. Third order nonlinear optical susceptibility (χ⁽³⁾) of the polymer films was in the range of 10⁻¹⁰-10⁻⁹ esu.     

High-pressure XeNMR study of supercritical xenon interacting with polymers

High-pressure ¹²⁹XeNMR experiments have been performed by using a newly designed probe. ¹²⁹XeNMR spectrum for the mixture of Xe and a polymer, either bisphenol-A polycarbonate or polytetrafluoroethylene, consists of two lines in a pressure range of 0.3–10 MPa. ¹²⁹XeNMR chemical shift (δ) for the free Xe is mainly governed by the Xe–Xe interactions. δ for Xe confined in the micropore of polymers is strongly affected by the Xe-wall interactions. It is found that δ of the confined Xe is mainly determined by a sort of ‘virtual pressure' and is not influenced by a drastic change of the free Xe density in the critical region.     

The nature of multiple melting transitions in cis-polyisoprene

The multiple melting transitions previously reported for cis-polyisoprene have been related to different morphological species observed in thin films using transmission electron microscopy. Two distinct types of spherulitic lamellar crystal have been identified which have characteristic growth rates, lamellar thicknesses, and fold planes. In addition to the α-lamellar crystals, which grow in prestrained films with the a axis perpendicular to the stretch direction, a second type of lamellar crystal was identified with the b axis perpendicular to the stretch direction: β-lamellae. From an analysis of the kinetics of growth and the variation of lamellar thicknesses with crystallization temperature, values of the side and surface free energies of the two types of lamellar crystal have been calculated.     

Characterisation of stationary phases in subcritical fluid chromatography with the solvation parameter model IV. Aromatic stationary phases

The purpose of the present work was to systematically study the chromatographic behaviour of different aromatic stationary phases in a subcritical fluid mobile phase. We attempted to assess the chemical origin of the differences in retention characteristics between the different columns. Various types of aromatic stationary phases, all commercially available, were investigated. The effect of the nature of the aromatic bonding on interactions between solute and stationary phases and between solute and carbon dioxide-methanol mobile phase was studied by the use of a linear solvation energy relationship (LSER): the solvation parameter model. This study was performed to provide a greater knowledge of the properties of these phases in subcritical fluid chromatography, and to allow a more rapid and efficient choice of aromatic stationary phase in regard of the chemical nature of the solutes to be separated. Charge transfer interactions naturally contribute to the retention on all these stationary phases but are completed by various other types of interactions, depending on the nature of the aromatic group. The solvation vectors were used to compare the different phase properties. In particular, the similarities in the chromatographic behaviour of porous graphitic carbon (PGC), polystyrene-divinylbenzene (PS-DVB) and aromatic-bonded silica stationary phases are evidenced.     

Liquid crystalline polymers as stationary phases. IV. Chemical bonding and immobilization of the polymer on silica characterization by solid-state nuclear magnetic resonance spectroscopy

Chemical bonding reaction and immobilization through low energy radiation (heating) have been investigated to fix a side-chain liquid crystalline polymer (SC-LCP) on silica particles in order to use the resulting modified silica in normal-phase HPLC. Highly stable chromatographic stationary phases are observed under excellent polymer solvent flow conditions (THF) for both methods and better column efficiencies are also exhibited towards PAHs' separation compared to the classical coated stationary phase. The characterization of these new stationary phases and the rationale for improved column stability have been investigated by solid state 13C and 29Si CP/MAS NMR spectroscopy. It is clearly shown that the chemical bonding is achieved by the classical hydrosilylation reaction between PHMS chains and vinyl modified silica. The bonded polymer is likely a copolymer than a homopolymer. The immobilization of the SC-LCP by heating results in the breaking of Si-O-Si bonds of the polysiloxane chain after the attack of the silica surface silanols. Applications to fullerenes and carotenes separation of these bonded stationary phases are compared to the separation power of a classical monomeric C18 stationary phase in NP-HPLC as n-hexane-toluene or methyl-tertiobutyl ether-methanol mixtures.     

Etude de phases quaternaires Winsor IV. Diagrammes de phases et propriétés electriques

A comparative study of phase diagram features and electrical properties of Winsor IV phases (so-called microemulsions) led to define two types of quaternary systems involving water, a hydrocarbon, and an ionic surfactant/alcohol combination defined byk, the surfactant/alcohol mass ratio. Systems of the first type exhibit a Winsor IV domain consisting of two disjointed areas corresponding to water-in-oil (w/o) and oil-in-water (o/w) monophasic fluid transparent isotropic media. The w/o and o/w areas are separated by a composition zone over which exist viscous turbid long-range organized structures related to the o/w w/o phase inversion mechanism. In that case, over the w/o area, the low frequency electrical conductivity and permittivity undergo non-monotonous changes as the composition varies. From conductivity maxima and minima, it is possible to define in the general case two lines ₁ and ₂ separating three adjacent sub-areas to which can be assigned compositions representing pre-micellar entities, inverted swollen spherical micelles and micelles clusters. For systems of the second type, the w/o and o/w sub-areas merge so as to form a unique monophasic area, which implies that the w/o o/w phase inversion occurs through a progressive diffuse mechanism. In that case the conductivity exhibits much higher values than in the preceding situation, and its variations with composition allow to define two linesC _d andC _m partitioning the Winsor IV domain into three adjacent areas. AboveC _d , that is for low and medium water contents, the conductivity variations with water content follow equations derived from the Percolation and Effective Medium theories, which indicates that the w/o swollen spherical micelles are submitted to attractive interactions. Below C_m, i. e. in the water rich region, the conductivity decrease with water content results from the progressive dilution of the external aqueous phase of the o/w Winsor IV media. BetweenC _d andC _m , the Winsor IV media exhibit an anomalous conductive behaviour which suggests that they are neither w/o nor o/w systems. This region can be considered as the diffuse phase inversion zone over which the systems are in a hybrid state that could be depicted tentatively as resulting from the formation of equilibrium bicontinuous structures.

     

Oriented polymers from solution. IV. Polyethylene/polypropylene blend films

Work on the surface-growth method of producing blend films from mixed solutions of two polymers has exposed a random fluctuation in both growth rate and composition of the blend film with time of deposition. The effects are explained by heterogeneous separation of the two polymer components in the solution induced by the stirring action of the rotor of the Couette apparatus used. The solution is thus converted to a colloidal sol which on cooling forms a gel which exhibits syneresis at room temperature. The sol-to-gel transition is thermally reversible.     

Surface modification of polymers. IV. UV initiated degradation of polymers with stabilizers grafted onto the surface

Polypropylene (PP), Polyethylene (PE), and polystyrene (PS) films were grafted with glycidylmethacrylate in thin surface layers. To the oxiran groups thus grafted onto the surface three UV stabilizers were attached, 4-amino-2,2,6,6-tetramethylpiperidine (AP), 2,4-dihydroxybenzophenone (DHBP), and phenyl 4-aminosalicylate (PAS). The amount of stabilizer grafted onto the surface varied between 25 and 40 nmol/cm² depending on the polymer substrate. The samples were exposed to UV radiation in air, and the degradation and oxidation of the polymers were studied with IR, UV, and ESCA spectroscopy and by stress–strain measurements. PP grafted with AP exhibited a near 20-fold increase in lifetime compared with the unprotected PP, AP did not stabilize the PE or PS samples. DHBP was an efficient stabilizer of PE, the oxidation rate of the grafted sample being 1/2 to 1/3 of the ungrafted. A similar effect was observed when DHBP was grafted onto PP and PS. PAS underwent a rearrangement reaction when irradiated with UV light, and had only a slight stabilizing effect.     

High performance polymers and composites. IV. Copolymers containing benzoxazole units

Several new copolymers have been synthesized. Initial polycondensation of mixtures of aryl and arylalkyl carboxylic acids containing aromatic hydroxyl and amine substituents led to random copolyamides. Thermal cyclization of these prepolymers (inherent viscosities of about 0.2 dL/g) gave copolybenzoxazoles with inherent viscosities of about 1.4 dL/g. Thermal stability as measured by TGA was similar for the 1:1 copolymers and the homopolymers containing hydrocinnamic units; i.e., catastrophic decomposition occurred at 450°C. Copolymers with lower ratios of the hydrocinnamic units displayed greatly improved thermal stability while maintaining good molecular weight.