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.     

Direct synthesis of heparin-like poly(ether sulfone) polymer and its blood compatibility

In this study, heparin-like poly(ethersulfone) (HLPES) was synthesized by a combination of polycondensation and post-carboxylation methods, and was characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance hydrogen spectrum and gel permeation chromatography. Owing to the similar backbone structure, the synthesized HLPES could be directly blended with pristine PES at any ratios to prepare PES/HLPES membranes. After the introduction of HLPES, the microscopic structure of the modified PES membranes was changed, while the hydrophilicity was significantly enhanced. Bovine serum albumin and bovine serum fibrinogen adsorption, activated partial thromboplastin time, thromb time and platelet adhesion for the modified PES membranes were investigated. The results indicated that the blood compatibility of the PES/HLPES membranes was significantly improved compared with that of pristine PES membrane. For the PES/HLPES membranes, obvious decreases in platelet activation on PF-4 level, in complement activation on C3a and C5a levels, and in leukocytes activation on CD11b levels were observed compared with those for the pristine PES membrane. The improved blood compatibility of the PES/HLPES membrane might due to the existence of the hydrophilic groups (–SO₃Na, –COONa). Furthermore, the modified PES membranes showed good cytocompatibility. Hepatocytes cultured on the PES/HLPES membranes presented improved growth in terms of SEM observation, MTT assay and confocal laser scanning microscope observation compared with those on the pristine PES membrane. These results indicate that the PES/HLPES membranes present great potential in blood-contact fields such as hemodialysis and bio-artificial liver supports.     

Local chain motions in a dilute solution of phenolphthalein poly(ether sulfone)

¹³C and ¹H relaxation times were measured as a function of temperature in two magnetic fields for dilute solutions of phenolphthalein poly(ether sulfone) (PES-C) in deuterated chloroform. The spin-lattice relaxation times were interpreted in terms of segmental motion characterized by the sharp cutoff model of Jones and Stockmayer (J. S. model). The phenyl group rotation is treated as a stochastic diffusion by the J. S. model. The restricted butterfly motion of the phenyl group attached to the cardo ring in PES-C is mentioned but is not discussed in detail in this work. Correlation times for the segmental motion are in the picosecond range which indicates the high flexibility of PES-C chains. The correlation time for the phenyl group internal rotation is similar to that of the segmental motion. The temperature dependence of these motions is weak. The apparent activation energy of the motions considered is less than 10kJ/mol. The simulating results for PES are also reasonable considering the differences in structure compared with PES-C. The correlation times and the apparent activation energy obtained using the J. S. model for the main chain motion of PES-C are the same as those obtained using the damped orientational diffusion model and the conformational jump model.     

Curing kinetics of cyanated poly(ether sulfone)s of different molecular weight

Three cyanated poly(ether sulfone)s (CPESs) with number-average molecular weights of 910, 1550 and 3 240 were synthesized and their polycyclotrimerization kinetics studied by dynamic differential scanning calorimetry (DSC). The resulting apparent activation energies (E_a) are quite close and range from 87.5 to 92.0 kJ/mol. The corresponding curing reactions in relation to conversion (α) can be expressed with an autocatalytic first-order kinetics dα/dt = A (1+ Bα) (1 – α) exp (–E_a/(RT)). This kind of kinetics can be explained by a mechanism consisting of both a hydroxyl-catalyzed and an autocatalytic path. The lower pre-exponential factor (A) and contribution of autocatalytic reaction (B) for high molecular weight CPES are due to the low concentrations of catalytic species in the starting CPES and the resulting sym-triazine rings, respectively.     

Physical aging of epoxy resin blended with a medium molecular weight poly(ether sulfone)

The physical aging process of 4,4'-diaminodiphenyl sulfone (DDS) cured diglycidyl ether bisphenol-A (DGEBA) blended with a medium molecular weight (i. e., M_n = 10 600 and M_w/M_n = 2.3) poly(ether sulfone) (PES) was studied by DSC at four aging temperatures. The cured epoxy-rich phase is immiscible with the PES-rich phase, with their respective T_g values being 29°C apart. Hence, aging the network blend at a suitable temperature caused two well separated enthalpic relaxation processes due to physical aging of PES-rich and epoxy-rich phases. The experimental results indicated that the aging phenomena of the well separated phases in the network blend are similar to that of the corresponding neat polymers when the aging temperature T_a is lower than T_g by the same value.     

Conformation of phenyl rings in the helical chain polymer poly(triphenylmethyl methacrylate)

The conformation of phenyl rings in the side groups of the helical chain polymer poly(triphenylmethyl methacrylate) ( 1 ) in solution was studied by spectroscopic methods. According to the Raman spectrum the phenyl rings of 1 and triphenylmethyl methacrylate in solution have the same depolarization ratio at 1 002 cm^?1. The electronic spectra (ultraviolet and fluorescence) of 1 are similar to those of model substances, except for the “red shift” of the spectra of about 5 nm. It was concluded that the phenyl rings can rotate around the phenyl? C bond.     

Thermodynamics of polymer blends based on poly(methyl acrylate) and poly(vinyl acetate) with different molecular weights

In this work a study on thermodynamics of polymer blends, based on poly(methyl acrylate) (PMA) and poly(vinyl acetate) (PVAc), was carried out. Our foremost aim was to examine the molecular weight effect on polymer compatibility. The results confirm our hypothesis: the interaction parameter χ₁₂, varies abruptly in a very restricted molecular weight range. In this way, it can be concluded that molecular weight, as well as other parameters (i.e. lateral group hindrance, chain functionalization, composition temperature and so on), influences greatly polymer miscibility.     

Biomembrane mimetic polymer poly (2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) at the interface of polyurethane surfaces

Polyurethane (PU) is widely used to make artificial heart and blood vessel wells; however, its thrombogenicity in vivo is still in question. The biomembrane-mimetic and water-soluble polymers, poly (2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (PMB), were used to modify polyurethane (PU) surfaces for improving their hemocompatibility. The morphologies of the PMB modified PU surfaces were examined by using atomic force microscopy and the parameters of the PMB absorption kinetics were extracted from dynamic water contact angle measurements. Two-phase domains, the hard and soft segment phases, were observed on the PU surfaces under the aqueous conditions. The absorbed PMB molecules formed the isolated layers first on the hydrophobic hard segments, and subsequently networked as the PMB concentration increased. The increments of PMB concentration led to the decrement of the effective molar activation (wetting) free energy DeltaG.     

Investigations of poly(vinyl alcohol)/poly(N-vinyl-2-pyrrolidone) blends, 2. Influence of the molecular weights of the polymer components on crystallization

Blends of crystallizable poly(vinyl alcohol) (PVA) and poly-(N-vinyl-2-pyrrolidone) (PVP) of different molecular weights were prepared from aqueous solutions by evaporation and studied by Fourier-transform IR spectroscopy. When the molecular weight of one of the polymer components increases, the PVP content at which crystallinity in PVA is no longer observed decreases. The wide band representing hydroxyl stretching splits into four components at welldefined frequencies which are assigned to (1) multiple hydroxyl-hydroxyl bonding in organized PVA regions, (2) hydroxyls which are simply bonded to carboxyl, (3) hydroxyls doubly bonded to two carbonyls or to one carbonyl and one hydroxyl, and (4) simple hydrogen-hydrogen bonding in amorphous PVA regions. When the PVP content increases, the relative intensity of the bond of di-hydrogen-bonded hydroxyls remains quasi-invariant, while that of multiple hydrogen bonds in PVA decreases, and that of simple hydroxyl-carbonyl bonds increases correspondingly. It appears that the higher the molecular weight, the more effective the hindrance of PVP crystallization. An explanation of the mechanism leading to the formation of different structures in the blends is proposed on the basis of these results. It stresses the importance of the role of chain dynamics in an entangled chain network, which greatly affects the kinetics of crystallization of PVA during the drying step.     

Viscosity and light scattering measurements of poly(2-fluoro-p-phenylene-2-fluoroterephthalamide)

We report on the characterization of the conformational properties of the fully aromatic polyamides poly(2-fluoro-p-phenylene-2-fluoroterephthalamide) (FPFT) in methanesulfonic acid using dynamic and static light scattering and viscosity measurements. The results are in quantitative agreement with a model of polydisperse wormlike chains for the solution conformation of FPFT. A comparison with the results obtained for the unsubstituted polymer poly(p-phenylenterephthalamide) (PPTA) under the same experimental conditions indicates that the introduction of halogen substituents on the aromatic rings has only a weak influence on the chain flexibility.     

Synthesis and characterization of poly(ether ketone)/poly(ether sulfone) alternating and sequential copolymers by electrophilic reactions

The synthesis and NMR characterization of some poly(ether ketone)/poly(ether sulfone) (PEK/PES) alternating copolymers together with a series of sequential homopolymers containing CO, O, S and SO₂ bridging groups, all obtained by electrophilic condensation reactions using phosphorus pentoxide/methanesulfonic acid as dehydrating agent, is here reported. Properties of such polymers are compared with those of their model compounds from which it can be inferred that both proton and carbon chemical shifts are very sensitive to the electronic environment generated by the O, S, CO and SO₂ bridges. Differential scanning calorimetry indicates that our polymers are essentially amorphous irrespective of the bridging sequence. From viscosity measurements the molecular weights of these copolymers are judged to be very low.     

New polymer syntheses, 72. Telechelic and star-shaped poly(ether-sulfone)s by polycondensation of 4-fluoro-4′-trimethylsiloxy(diphenyl sulfone)

The homopolycondensation of 4-fluoro-4′-trimethylsiloxy(diphenyl sulfone) ( 2 ) in bulk and its cocondensation with 4-fluoro-4′-trimethylsiloxybenzophenone ( 1 ) yielded high-molecular-weight, amorphous (co)poly(ether-sulfone)s. The cocondensation with 4,4′-difluoro(diphenyl sulfone) ( 4 ) afforded telechelic oligomers or polymers with two fluorobenzophenone end-groups. Cocondensation with 4,4′-bis(2,4-difluorobenzoyl)[diphenyl ether] ( 5 ) gave star-shaped polymers with four branches. Cocondensation with 1,3,5-tris(trimethylsiloxy)benzene ( 6 ) yielded star-shaped poly(ether-sulfone)s with three longer than calculated star arms. Cocondensations with 2,2′,4,4′-tetrakis(trimethylsiloxy)benzophenone ( 7 ) did not result in the formation of star-shaped polymers, but yielded telechelic linear poly(ether-sulfone)s with two trimethylsiloxy end-groups. It was found that rapid cyclization of the benzophenone derivative (yielding a bis(trimethylsiloxy)xanthone) precedes the polycondensation.     

The heterogeneous modified-polypropene-supported Ziegler catalyst/MMAO system for producing ultrahigh molecular weight polyethene and poly(ethene-co-hex-1-ene) with a homogeneous comonomer distribution

A heterogeneous modified-polypropene-supported Ziegler catalyst (modified-PP-supported catalyst) combined with modified methylaluminoxane (MMAO) was successfully used for the production of ethene/hex-1-ene copolymers with a homogeneous distribution of hex-1-ene. The modified-PP-supported catalyst/MMAO also gave polyethene and ethene/hex-1-ene copolymers with ultrahigh molecular weight (M_w > 2×10⁶). The MMAO concentration and hex-1-ene content in the feed were found to affect the activity, comonomer content in the resulting copolymer, and melting temperature, while no influence on the molecular weight and comonomer distribution was detected.     

Synthesis of amphiphilic block copolymers by polymer analogous modification of poly(2-chloroethyl vinyl ether)-block-poly(isobutyl vinyl ether)

Amphiphilic block copolymers were prepared starting from poly(2-chloroethyl vinyl ether)-block-poly(isobutyl vinyl ether) (PCEVE-b-PIBVE) via polymer analogous reaction. The chlorine function in the hydrophobic poly(2-chloroethyl vinyl ether) segment was substituted by polar groups to achieve block copolymers containing a hydrophilic poly(vinyl ether) segment. This procedure allows the synthesis of tailor made amphiphilic block copolymers.     

Modification of poly(ether urethane)elastomers by incorporation of poly(isobutylene)glycol. Relation between polymer properties and thrombogenicity

Non-polar hydrophobic poly(isobutylene)glycol (PIBG) was substituted for poly(tetramethylene ether)glycol (PTMEG) in poly(ether urethanes) based on 4,4'-methylenebis-(phenylisocyanate) (MDI) and 1,4-butanediol (BD) as chain extender. Two series of polyurethanes differing in their soft segment length, polymer composition, and hard segment content were studied by dynamic mechanical analysis (DMA) and static, as well as dynamic, contact angle measurements. The thrombogenicity of these polymers was characterized by studying the adhesion and activation of platelets using ELISA for GMP 140 and fluorescence microscopy. It was found by DMA that in PIBG-containing polyurethanes (PUE) exist soft domains containing hard segments, strictly separated hard segment domains, and hard segments partially mixed with soft segments. Contact angle measurements revealed that 25% PIBG or even less, are sufficient for a remarkable enrichment of these non-polar soft segments on the polymer surface. The platelet adhesion/activation on these materials was demonstrated to increase with the rise in hard segment content, as well as with an enhancement of the PIBG content. However, comparison of PIBG-containing PUE with medical applied polypropylene and pellethane expressed that PUE with PIBG content equal or less 25% have excellent haemocompatibility.     

Hydrophobic water-soluble polymers, 1. Dilute solution properties of poly(1-vinyl-2-piperidone) and poly(N-vinylcaprolactam)

Poly(vinyllactams) form a class of non-ionic water-soluble polymers from which only poly-(1-vinyl-2-pyrrolidone) (PVP) is well known and has been investigated extensively. The homologues poly(1-vinyl-2-piperidone) ( 1 , poly[1-(2-oxo-1-piperidyl)ethylene]) and poly(N-vinylcaprolactam) ( 2 , poly[1-(2-oxoperhydroazepin-1-yl)ethylene]) which are still soluble in water at room temperature have not yet been studied in aqueous solution. In this work the synthesis of these two polymers by radical polymerization in solution and the investigation of the dilute aqueous solution properties of these polymers by static and dynamic light scattering measurements are presented. Special attention is paid to the influence of the increasing hydrophobicity of these polymers on coil dimensions and structures in aqueous solution.     

Photoinitiated degradation of poly(diacetylene)s in solution by random chain scission

Poly(diacetylene)s dissolved in common organic solvents undergo random chain scission, if irradiated by UV-light. The pure polymers and their solutions are, however, stable, if they are photoirradiated within the main-absorption band of the polymer backbone. The usual triplet sensitizers, especially in the presence of oxygen, and radical donors such as 2,2′-azoisobutyronitrile (AIBN) enhance the rate of photodegradation. Suitable dyes are able to sensitize the chain-scission in the visible regions as well. Random chain scission occurs also in the dark, but only at temperatures above room temperature and is enhanced by the addition of radical-donors, e.g. AIBN. A mechanism of chain scission, induced by the attack of a radical to a multiple bond of the polyconjugated backbone of the polymer is proposed.