Polymer diffusion and mobility in mixtures of polystyrene and polymethylstyrenes

Tracer diffusion coefficients D* of both components were measured in mixtures of polystyrene with poly(o-methylstyrene), poly(p-methylstyrene), and a commercially available random copolymer of p- and m-methylstyrene, respectively. D* values were determined by applying the holographic grating technique where between 5 and 10% of the respective polymer component was labelled at the end group with a photoreactive dye. For molecular weights between 15 000 and 37 000 and temperatures between 175 and 200°C, the D* values differed relatively slightly when compared at equal molecular weight and equal temperature distance T–T_g from the glass transition temperature T_g. The differences were compared with those of monomeric friction coefficients obtained from dynamic mechanical experiments.     

The Influence of Fabrication Parameters on the Piezoelectric and Ferroelectric Responses of Poly(pelargonamide) Membranes

Synthesized poly(pelargonamide) membranes are shown to be a ferroelectric polymeric material based on the demonstration of the D‐E hysteresis curves of the oriented and unoriented samples. Dipole switching required a lower electric field excitation with increasing stretching ratio caused by a better orientation of the dipoles upon the uniaxial stretching of the membranes. The ferroelectric response of the samples could be greatly enhanced by uniaxial cold‐drawn. When T was >T_g , and d₃₁ was kept constant then e₃₁ increased non‐linearly with P_r for the samples within the range of the stretching ratio. However, both d₃₁ and e₃₁ increased nonlinearly with P_r for the samples within the range of the stretching ratio if T < T_g. Scanning electron microscopy photographs illustrate the stretching and poling effects on the packing of the macrofibrils of the specimens. The origin of the piezoelectric response of the poly(pelargonamide) membranes was considered to account for the effect of the dipoles reorientation under the electric field poling and was evidenced by polarized infrared spectroscopy examinations.     

Synthesis and cationic polymerization of a novel optically active vinyl ether with L-proline structure

Synthesis and cationic polymerization of a novel vinyl ether with an L -proline moiety, N-carbobenzoxy-L -proline 2-vinyloxyethyl ether (ZProVE), were carried out. ZProVE was prepared by the condensation of N-carbobenzoxy-L -proline and 2-hydroxyethyl vinyl ether. Cationic polymerization of ZProVE was carried out in dichloromethane at ?50, ?20°C, or room temperature. The number-average molecular weight (M _n) of the polymer obtained in the polymerization at ?50°C was 44900, and the [α] value of the polymer was ?36.1°, which was somewhat larger (more positive) than that of ZProVE (?46.4°). Cationic copolymerizations of ZProVE and isobutyl vinyl ether proceeded readily to afford the corresponding copolymers. Alkaline hydrolysis of poly(ZProVE) afforded poly(hydroxyethyl vinyl ether).     

Effect of structure on glass transition temperatures of poly(methacrylic ester)s with bulky side groups

The values of the vitreous transition temperature, T_g, of three poly(methacrylic ester)s having bulky side groups are correlated with structural effects. T_g has been obtained experimentally by means of differential calorimetry and by the tensiometric method suggested by Ferroni. The experimental values of T_g agree well with the calculated ones obtained by the method of Van Krevelen. The values of T_g determined by differential calorimetry are markedly affected by the heating rate and by the molecular weight of the fractions. The solubility parameters of the polymers studied have been estimated. Poly(p-tert-butylphenyl methacrylate), (BPh), exhibits higher values for the solubility parameter, the steric hindrance parameter σ and the glass transition temperature T_g than poly(p-tert-butylcyclohexyl methacrylate), (BCy), and poly(neopentyl methacrylate), (NPe). These results have been interpreted in terms of intermolecular forces and steric hindrance effects, which would be greater in BPh than in BCy and NPe.     

Transport of water vapour and gases in modified cellulose acetate matrices. Influence of the nature of the penetrant on diffusion and relaxation kinetics

Membranes developed by modification of a cellulose acetate (CA) matrix were studied by means of the flow method CA matrix is modified by poly(4-vinylpyridine) (PVP), or an interpenetrating network (IPN) agent. The obtained diffusion coefficients, permeability coefficients and relaxation kinetic parameters for oxygen, carbon dioxide and water vapour enabled us to consider not only the transport properties of the membranes but also the influence of the relaxation processes on the membrane permeability and stability. The results show that the interactions between water molecules and polar groups on the polymer chains cause the membrane material to swell. This swelling process provokes an increase in the permeation flux of ca. 20–30%. Oxygen causes a consolidation of unstable membranes of the cellulose acetate matrix modified by IPN but not of blends with PVP. The consolidation process reduces the membrane permeability by ca. 38%, while carbon dioxide has no effects on the membrane properties. Membranes based on a modified cellulose acetate matrix have higher permeability than pure CA membranes.     

Analyse du photoviellissement des materiaux polymères par évolution de la perméabilité aux gaz

The variations of diffusion constants and permeability for carbon dioxide, oxygen and nitrogen in poly(ether-block-amide)s were measured during the photooxidation of the polymer. The determination of these constants appears to be a sensitive criteria to characterize the photooxidative evolution of polymers. The decrease of the diffusion constant, observed in the course of photooxidation, is interpreted by the formation of chemical crosslinks and by the existence of physical interactions between primary hydroperoxidic photoproducts. Several treatments were developed which modify the nature of these oxidized groups; the evolution of diffusion constants is related to the modification of the interactions between these groups.     

The solid state 13C NMR studies of intermolecular hydrogen bonding formation in a blend of phenolic resin and poly(hydroxyl ether) of bisphenol A

The formation of intermolecular hydrogen bonds in blends of novolac type phenolic and poly(hydroxyl ether) of bisphenol A was investigated by studying its T_g behavior, excess volume, and solid state ¹³C NMR spectra. The T_g and parameters of solid state ¹³C NMR, such as the T_CH and spin‐lattice relaxation time in the rotating frame T^H_1ρ, indicate that the London dispersion force (entropically favored) significantly affects the intermolecular hydrogen bonding of the blend. The phenoxy chain forces opening of the intra‐association of phenolic and thus creates more free OHs. This strong entropic effect reduces the total hydrogen bonding of the system, especially when one of the polymer is the minor component. This also results in the reduction of T_g and free volume expansion, reflecting in the increase of cross‐polarization (C—H) time and molecular mobility within the phenolic/phenoxy blend.     

Effect of the catalyst-monomer ratio on the molar mass and glass transition temperature of poly(oxy-2,6-dimethoxy-1,4-phenylene)

2,6-Dimethoxyphenol was polymerized using Ag₂O-triethylamine complex as catalyst and a study made of the effect of the catalyst-monomer ratio on the yield, molar mass and polydispersity of poly(oxy-2,6-dimethoxy-1,4-phenylene). The glass transition temperatures T_g were measured with a computerized differential scanning calorimeter. The effect of the molar mass on T_g of poly(oxy-2,6-dimethoxy-1,4-phenylene) is discussed. The equation, T_g = T_{g, ∞} ? K/M, describes well the dependence of T_g on the viscosity-average molar mass M_v from 1900 to 176000 g/mol. Some poly(oxy-2,6-dimethyl-1,4-phenylene) samples were studied as reference material.     

Poly(2,6-Dimethyl-1,4-Phenylene oxide)/crosslinked polystyrene semi-interpenetrating networks: Synthesis and properties

Semi-interpenetrating networks (semi-IPN's) based on linear poly(phenylene ether)s and crosslinked polystyrene can be prepared by reactive moulding of crosslinkable polymeric mixtures. These materials show thermomechanical properties which strongly depend on both the ratio of the two polymeric matrices and the degree of crosslinking in the polystyrene network. Samples based on a 50/50 weight ratio of poly(2,6-dimethyl-1,4-phenylene oxide)/crosslinked polystyrene show glass transition temperatures (T_g) which are very dependent on the degree of crosslinking. It is therefore possible to obtain materials with desired T_g, ranging from the T_g of the corresponding linear blend to that of poly(2,6-dimethyl-1,4-phenylene oxide) alone.     

Thermally Cross‐Linkable Poly(p‐xylylene)s for Advanced Low‐Dielectric Applications

A novel series of poly(p‐xylylene) homopolymer and copolymers containing thermally cross‐linkable cyclohexenyl moiety are prepared via base‐catalyzed Gilch route to yield high‐molecular‐weight polymers. The resulting polymers are highly soluble in a wide range of organic solvents and could be solution cast into flexible and transparent films. The polymers are thermally stable up to 350 °C and the glass transition temperature (T_g) is in the range of 136 ? 250 °C. They undergo thermal cross‐linking via the cyclohexenyl moiety. The cross‐linked polymer exhibits a high T_g of 294 °C, a low coefficient of thermal expansion (CTE) of 45 ppm K^?1. A low dielectric constant of 2.5 and a very low dielectric loss tan δ of 0.0004 at 1 GHz are obtained, which are superior to conventional interconnect polymers.     

Physical aging of poly(ether sulfone) from enthalpy relaxation measurements

Enthalpy relaxation due to physical aging of hydroxyl-terminated poly(ether sulfone)s (PES) with various molecular weights was studied by DSC at three aging temperatures between T_g ? 45°C and T_g ? 10°C. The experimental results revealed that both the average enthalpy relaxation time 〈τ〉 and limiting enthalpy relaxation ΔH_∞ decrease slightly with increasing molecular weight for PESs aged at the same temperature intervals T_g ? T_a (where T_a < T_g). This behavior is not quite consistent with the enthalpy relaxation process of polystyrene. Agrawal reported that the relaxation spectra for polystyrenes with different molecular weights could be superimposed when T_g ? T_a was the same. The experimental results of the present work suggest that the motion of segments is affected by intermolecular hydrogen bonding through the ? OH groups of the PES chain ends.     

Glass transition temperatures in blends of poly(N-vinyl-2-pyrrolidone) with a copolymer of bisphenol A and epichlorohydrin or with poly(vinyl butyral)

Blends of poly(vinyl butyral) (PVB) and of a copolymer of bisphenol A and epichlorohydrin (Phenoxy) with poly(N-vinyl-2-pyrrolidone) (PVP) were prepared by solution casting. The glass transition temperatures T_g for different compositions of the blends were measured by differential scanning calorimetry (DSC). The T_g behaviour of PVB/PVP blends suggests the existence of a single phase for blends containing less than 50 wt.-% PVP, and of two phases in blends containing more than 50 wt.-% PVP. Phenoxy/PVP blends showed to be miscible over the entire composition range. It was found that the Gordon-Taylor equation predicts adequately the T_g-composition dependence with a K parameter equal to 0,5 and 1,25 for PVB/PVP and Phenoxy/PVP blends, respectively.     

Threshold Temperature Sensors with Tunable Properties

Thermochromic polymer/dye blends based on small amounts (0.6–2.3 wt.‐%) of chromogenic sensor dyes and glassy amorphous polymers were prepared. Subjecting melt‐processed, quenched blends to temperatures above T_g leads to permanent and pronounced changes of their absorption and fluorescence spectra as a result of phase separation and assembly of dye aggregates. The influence of dye structure and polymer T_g on the aggregation kinetics of these blends was investigated. It is shown that increasing the length of the dye's rigid core leads to slower aggregation rates due to limited mobility in the polymer. The threshold of the color change can be tailored by adjusting the polymer T_g, as was shown by the systematic investigation of blends based on poly(alkyl methacrylate) copolymers of varying composition.

     

Caprolactam‐Laurolactam Copolymers: Fast Activated Anionic Synthesis,Thermal Properties and Structural Investigations

Anionic poly(caprolactam‐co‐laurolactam) has been isothermally synthesized at 155°C by hexamethylene dicarbamoylcaprolactam as fast activation agent and two Na lactamates (from the mixed monomers or neat caprolactam, respectively) as initiators. The specific roles of both the chosen initiator and the laurolactam content in the feed have been investigated in terms of high polymer yield, structural defects of the polymer chains due to side reactions, T_g and T_m values, degree of crystallinity, molecular and superlattice order of the copolyamides. Namely, structural and thermal peculiarities of the latter have been brought into evidence on as‐polymerized samples as well as on high polymers after the deoligomerization process. Interesting differences among the various materials have been found and some possible explanations of the above behavior are given.     

Ester-carbonate interchange reaction in the solid state: synthesis of poly(ester-carbonate)

Poly(ethylene terephthalate-co-bisphenol A carbonate) was synthesized by ester-carbonate interchange reaction in the solid state. The polymerization reaction was carried out by heating two chemically distinct oligomers, namely, poly(aryl carbonate) and poly(ethylene terephthalate) in the temperature range of 180–230°C, during which period both chain extension as well as interchange reactions occurred. A copolymer of η_inh = 0.84 dL/g was obtained. With the progress of the interchange reaction the T_g of the copolymer slowly increases and reaches a maximum value of 102°C. The oligomer mixture, which exhibits initially two distinct T_m's, shows a single T_m at the end of the reaction. Formation of copoly(aryl ester-carbonate)s by an ester-carbonate interchange reaction was also found in the solid state at temperatures below 230°C. High molecular weight poly(aryl ester-carbonate)s with a T_g = 163°C and η_inh = 0.52 dL/g were prepared from the corresponding low molecular weight oligomers of poly(aryl ester) and poly(aryl carbonate)s.     

Compatibilité de polymères porteurs de groupements amides tertiaires avec le poly(difluoro-1,1 éthylène). Etude par enthalpimétrie différentielle

The miscibility of poly(1,1-difluoroethylene) ( 1 ) with poly(N-vinyl-2-pyrrolidone) poly(N-methyl-N-vinylacetamide) and poly(N,N-dimethylacrylamide), containing tert-amido groups, was investigated by differential scanning calorimetry. Amorphous homogeneous blends were obtained whenever the weight fractions of polymer 1 is less than 0,7. The dependence of the single glass transition temperature (T_g) versus composition may be readily analyzed either through the Gordon-Taylor equation (high values of the k parameter, suggesting strong specific interactions between the homopolymers) or by means of the Couchman relation (no adjustable parameter). The broadening of the glass transition range and the variation of the increment of specific heat at T_g for the blends are discussed.     

Gas permeation through a side-chain liquid-crystalline polysiloxane-based membrane

A membrane was prepared by sandwiching the side-chain liquid-crystalline polysiloxane (LCP) 3 between two porous poly(propylene) (Celgard) films. Permeation properties for H₂, O₂, N₂, CH₄ and CO₂ through the side-chain LCP-based membrane was measured using a gaschromatographic method at several different temperatures corresponding to the different states of the side-chain LCP. The gas permeation behaviour depends strongly on the different states of the side-chain LCP. The plots of permeability versus reciprocal temperature show an abrupt change of the slope in the vicinity of the glass transition temperature (T_g) of the side-chain LCP for all five gases. The activation energy for permeation obtained at these different states exhibits different values. The value obtained in the liquid-crystalline state is the highest. Separation factors (P_O2/P_N2) and (P_CO2/P_CH4) exhibit an unusual behaviour when the temperature changes across T_g. They increase abruptly when the temperature increases and the phase changes from the glassy state to the liquid-crystalline state of the side-chain LCP. The fact that both permeability and selectivity increases with increasing temperature above the glass transition is attributed to the supermolecular arrangement of the liquid-crystalline state of the side-chain LCP.     

Dielectric properties of poly[bis(trifluoroethoxy)phosphazene] and poly[bis(m-methylphenoxy)phosphazene]

Dielectric properties of poly[bis(trifluoroethoxy)phosphazene] (PFEP) and poly[bis(m-methylphenoxy)phosphazene] (PmMPP) were studied in a temperature range from ?195 to 120°C and at several frequencies between 0,1 and 100 kHz. In PFEP, two relaxations, an α relaxation above the glass transition temperature (T_g) and a β relaxation below T_g, which are related to a glass-rubber transition and a local molecular motion of short segments, respectively, were observed. However, PmMPP shows no β relaxation. From the above dielectric results, it was concluded that side groups play an important role in molecular motion of the polyphosphazenes. In PmMPP a γ′ relaxation was found below T_g by immersing the polymers into water. The γ′ relaxation is related to the molecular motin of absorbed water.     

Ethylene‐co‐Norbornene Copolymers Grafted Carbon Nanotube Composites by In Situ Polymerization

Vinyl functionalized multiwalled carbon nanotubes (MWCNT‐vinyl) are synthesized and used as monomers to prepare poly(ethylene‐co‐norbornene)‐grafted carbon nanotube composites by in situ polymerization with [Ti(η⁵‐C₅Me₅)(N?C^tBu₂)Cl₂] activated with methylalumoxane (MAO). The glass transition temperatures (T_g) of grafted MWCNT composites are more than 30 °C higher than those of copolymers. This difference is rationalized by the immobilization of the copolymer chain to the MWCNT surface by a covalent bond. The Young's modulus is shown to increase by more than 200% compared to poly(ethylene‐co‐norbornene) by incorporating 3.4 wt% functionalized MWCNT.     

Miscibility and interpolymer complexation of poly(1-vinyl-imidazole) with hydroxyl- and carboxyl-containing polymers

The miscibility of poly(1-vinylimidazole) (PVI) with some hydroxyl- and carboxyl-containing polymers was studied. Each of the binary blends or complexes of PVI with poly(p-vinylphenol) (PVPh), poly(2-hydroxypropyl methacrylate) (PHPMA) and poly(acrylic acid) (PAA) showed a single glass transition temperature (T_g), indicating miscibility. However, PVI is immiscible with poly(styrene-co-allyl alcohol) (SAA) and poly(hydroxyether of bisphenol-A) (Phenoxy) as shown by the appearance of two T_g's in each of the blends. Based on the frequency shifts of the hydroxyl band of the hydroxyl-containing polymers, the intensities of hydrogen bonding interactions between PVI and hydroxyl-containing polymers are in the order PVPh > PHPMA > SAA and Phenoxy. PVI interacts with PAA via ionic interaction.