Motional heterogeneity and phase separation of semi-interpenetrating networks and mixtures based on functionalised polyurethane and polymethacrylate prepolymers

Semi-interpenetrating polymer networks (SIPNs) and polymer mixtures (1:1 mass ratio) based on segmented polyester polyurethane (PU) with carboxylic groups and methacrylic copolymer (PM) with tertiary amine groups were studied by the electron spin resonance (ESR) spin label method. The concentration of functional groups varied from 0 to 0.45 mmol g⁻¹ in both prepolymers. The ESR spectra of spin labelled PM component were used to characterise the heterogeneity of segmental motion and transitions due to the additional polymer interactions imposed by complementary functional groups. The results were deduced from the temperature dependent ESR spectra. Two component spectra reflect the effect of PU chains on segmental motion of the PM component below the macroscopic glass transition temperature, T_g. The ratio of the fast and slow component was related to the complex polymer-polymer interaction or extent of miscibility. Restrictions of segmental motion of PM chains increase with functional groups concentration and above certain concentration (0.25 mmol g⁻¹) PM segments in the network assess faster motion suggesting a change in the local packing density and domain structure. An increased miscibility and disorganisation of the ordered domains are confirmed by the loss of spherulitic morphology and crystallinity at higher functional groups concentration. PU/PM mixtures reveal similar motional behaviour as SIPNs of the same composition. However, the differences in the fractional amount of fast and slow motions confirm better interpenetration and interaction of the two polymers in the SIPNs. The results of motional heterogeneity and polymer interactions were complemented with the T_gs.     

A-B-A-Triblock and multiblock copolyesters prepared from ε-caprolactone, glycolide and l-lactide by means of bismuth subsalicylate

Bismuth (III) subsalicylate, a commercial drug, was used as catalyst for 1,4-butanediol-initiated copolymerizations of ε-caprolactone (εCL) and glycolide (GL). Telechelic copolyesters having two OH-endgroups and predominantly alternating sequences were obtained. These copolyesters are amorphous with glass transition temperatures (T_gs) below −30 °C. In a second series of polymerizations, in situ chain extension with l-lactide (LLA) was performed, whereby A-B-A triblock copolymers were obtained without significant transesterification between A- and B-blocks. Finally, these A-B-A triblock copolymers were transformed into multiblock copolymers by chain extension with 1,6-hexamethylene diisocyanate. The block copolymers were characterized by ¹H and ¹³C NMR spectroscopy, by viscosity, SEC and DSC measurements.     

A glassy carbon supported bilayer lipid-like membrane of 5,5-ditetradecyl-2-(2-trimethyl-ammonioethyl)-1,3-dioxane bromide for electrochemical sensing of epinephrine

A self-assembled bilayer lipid-like membrane (BLM) supported on glassy carbon electrode (GCE) was fabricated using 5,5-ditetradecyl-2-(2-trimethyl-ammonioethyl)-1,3-dioxane bromide (DTDB) for epinephrine (EP) determination in the presence of ascorbic acid (AA). This modified electrode (DTDB/GCE) has strong membrane adsorption accumulation and electrocatalytic ability toward EP and AA. The oxidation of EP was controlled by double step adsorption accumulation process of the DTDB-BLM. The parameters of fitted Langmuir isotherm Γ_max, B_ADS, and ΔG_ADS values were determined as 1.0×10⁻¹¹ mol cm⁻², 2.04×10⁶ dm³ mol⁻¹, and −45.17 kJ mol⁻¹ for the fist step for EP concentration less than 1 mM, and 4.92×10⁻¹¹ mol cm⁻², 7.35×10⁴ dm³ mol⁻¹, and −37.1 kJ mol⁻¹ for the second step for EP concentration higher than 1 μM. The DPV peaks for EP and AA oxidations were appeared at 0.220 and 0.085 V versus SCE, respectively, allowing the determination of EP in the presence of high concentration of AA. The advantage of DTDB-BLM was demonstrated experimentally in comparison with other three BLMs, and attributed to the dioxane group as well as the suitable length of the carbon chain of DTDB molecule. The current response of the DTDB/GCE was fast and reproducible, suitable for the electrochemical sensing in flow-injection systems. A linear range of 1×10⁻⁸ to 1×10⁻⁴ M EP was preliminary obtained using a simple setup.     

Synthesis and characterization of amphiphilic block copolymers from poly(ethylene glycol)methyl ether and 4-methyl-?-caprolactone or 4-phenyl-?-caprolactone

MPEG-b-PMCL and MPEG-b-PBCL diblock copolymers were synthesized by ring-opening polymerization of 4-methyl-?-caprolactone (MCL) or 4-phenyl-?-caprolactone (BCL) using monomethoxy poly(ethylene glycol) (MPEG, M_n = 550 or 2000 g mol⁻¹) as the macroinitiator and SnOct₂ as the catalyst. These copolymers were characterized by differential scanning calorimetry (DSC), ¹H NMR, ¹³C NMR, and gel permeation chromatography. The thermal properties (T_g and T_m) of the diblock copolymers depend on the composition of polymers. When larger amount of MCL or BCL was incorporated into the macromolecular backbone there was an increase in T_g. Their micellar characteristics in the aqueous phase were investigated by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 0.5-2.9 mg L⁻¹, depending on the composition of polymers. The lengths of hydrophilic segment influence the shape of micelle. The mean hydrodynamic diameters of micelles from DLS were in the range of 70-140 nm. The drug entrapment efficiency and the drug-loading content of micelles depending on the composition of block polymers were described.     

Synthesis of biodegradable poly(trans-4-hydroxy-N-benzyloxycarbonyl-l-proline)-block-poly(ε-caprolactone) copolymers and micellar characterizations

A series of novel types of diblock poly(trans-4-hydroxy-N-benzyloxycarbonyl-l-proline)-block-poly(ε-caprolactone) (PHpr10-b-PCL) copolymers were synthesized by ring-opening polymerization from macroinitiator poly(trans-4-hydroxy-N-benzyloxycarbonyl-l-proline) (PHpr10) and ε-caprolactone (ε-CL) in the presence of organocatalyst dl-lactic acid (dl-LA). The M_n of the copolymers increased from 3370 to 19,040 g mol⁻¹ with the molar ratio (10-100) of ε-CL to PHpr10. These products were characterized by differential scanning calorimetry (DSC), ¹H NMR, and gel permeation chromatography. According to DSC, the glass-transition temperature (T_g) of the diblock copolymers depend on the molar ratio of monomer/initiator that were added. The hydrolytic degradation behavior of PHpr-b-PCLs was evaluated from weight-loss measurements and the change of M_n and M_w/M_n. With higher PCL contents resulted in a slower weight loss, while having a higher molecular weight loss percentage. Their micellar characteristics in an aqueous phase were investigated by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 1.33-4.22 mg L⁻¹. The micelles exhibited a spindly shape and showed a narrow monodisperse size distribution. The obtained micelles have a relatively high drug-loading of about 26% when the feed weight ratio of amitriptyline hydrochloride (AM) to polymer was 1/1. An increase of molecular weight and hydrophobic components in copolymers produced a higher CMC value and greater loading efficiencies were observed.     

Subaquatic oxidation of coal by water-dissolved oxygen

Subaquatic oxidation of two bituminous coals by water-dissolved oxygen was investigated using batch reactor equipped with membrane oxygen sensor. Effects of time, temperature and coal grain size were studied as basic parameters influencing the oxidation process. Obtained results showed the subaquatic coal oxidation can be considered as interaction of the first reaction order with respect to oxygen. From temperature dependence of oxidation rate, activation energies E = 72 ± 4 kJ mol⁻¹ and/or 50 ± 4 kJ mol⁻¹ were calculated. For the samples, oxygen consumption R_O2 was found to be in the range of 2 × 10⁻⁷ mol O₂ kg⁻¹ s⁻¹ to 6 × 10⁻⁷ mol O₂ kg⁻¹ s⁻¹, such values being quite comparable with R_O2 for aerial oxidation of bituminous coals.     

Electropolishing of NiTi shape memory alloys in methanolic H2SO4

The electropolishing of NiTi shape memory alloys was surveyed electrochemically. Anodic polarization of NiTi up to 8 V was performed in various aqueous and methanolic H₂SO₄ solutions. The passivity could be overcome in methanolic solutions with 0.1 mol dm−3≤CH₂SO₄≤7 mol dm−3. The dissolution kinetics was studied in dependence of the polarization potential, the H₂SO₄-concentration, the water concentration and the temperature. For lower concentrations of sulfuric acids (CH₂SO₄≤0.3 mol dm−3) electropolishing conditions were not observed for potentials up to 8 V. The dissolution remained under Ohmic control. In the concentration range from 1 to 7 mol dm⁻³ a potential independent limiting current was registered depending linearly on the logarithm of concentration. The best results were obtained with a 3 mol dm⁻³ methanolic sulfuric acid at 263 K which yielded an electropolishing current of 500 A m⁻² at a potential of 8 V. Surface roughness as well as current efficiency showed an optimum under these conditions.     

Investigation of accelerated aging behaviour of high performance industrial coatings by dynamic mechanical analysis

Dynamic mechanical analysis (DMA) represents one of the most important methods for understanding mechanical behaviour of surface coatings providing a valuable link between chemistry, morphology, and performance properties. In this work, dynamic mechanical properties of several high performance industrial coatings were studied extensively. Four commercially available topcoats namely alkyd modified polyurethane (PU), economy aliphatic PU, high performance aliphatic PU and epoxy modified polysiloxane were selected based on their cure chemistries, volume solids, and overall performance. DMA was used to determine elastic modulus, glass transition temperature (T_g), crosslink density and creep behaviour of these coatings. DMA data were substantiated with mechanical and performance properties. Among the coatings, epoxy modified polysiloxane showed the highest T_g of 65.6 °C as well as crosslink density value of 2.24 × 10⁻³ mol/cc which was attributed to its superior mechanical and performance properties. In addition, topcoats were also subjected to artificial aging process in accelerated cyclic corrosion cabinet and QUV-weatherometer, respectively. The consequent changes in their physico-mechanical properties post exposure were also evaluated using DMA and correlated with other performance properties. After aging, the T_g increased substantially for all the coatings irrespective of their exposure type. For example, T_g of economy aliphatic PU increases from 38.4 °C to 52.9 °C and 51 °C after cyclic corrosion and UV-B weathering, respectively. However, crosslink densities either increased or decreased depending on the type of exposure and cure chemistries. These changes were corroborated using the Fourier transform infrared spectroscopy findings. The outcome of this study is expected to generate new insights into the behaviour of these coatings under dynamic mechanical stress and its relation with long term performance properties.     

Investigation of oil palm based Kraft and auto-catalyzed organosolv lignin susceptibility as a green wood adhesives

The aim of this study is to highlight the application and potentiality of oil palm based lignins in the synthesis of green phenolic resins. The delignification processes were conducted using Kraft and auto-catalyzed ethanol–water pulping processes. The extracted lignins were characterized using elemental analysis, Fourier transform-infrared, ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, molecular weight distribution (M_n, M_w and polydispersity), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The obtained FTIR results revealed that the Kraft lignin contained substantial amounts of guaiacyl units with smaller amounts of syringyl units. The molecular weight of Kraft lignin was 1564 g mol⁻¹ which is higher than organosolv lignin at 1231 g mol⁻¹. The activated free ring position (2.99%) of Kraft lignin was comparatively higher than that of organosolv lignin (2.06%) which was measured using Mannich reactivity analysis. Thermal analysis of Kraft lignin showed higher thermal stability compared to organosolv lignin. The structural and thermal characteristics implied that Kraft lignin had higher potential for the production of green phenolic resins when compared with organosolv lignin.     

Thermal and radio-oxidation of epoxy coatings

Degradation induced by thermal (50–110 °C) and radio-oxidation of low T_g epoxy-amine networks has been studied. It has been found that oxidation leads mainly to amide groups formation at the vicinity of tertiary amines whatever ageing conditions (thermal or radio-oxidation at 200 Gy h⁻¹). In addition, some species as acids, peracids or formates have been revealed indicating a chain scission process. Physical modifications as T_g decrease and soluble fraction increase due to chain scission process, have been correlated with chemical modifications.     

Microstructure of free volume in SMA copolymers I. Free volume from Simha-Somcynsky analysis of PVT experiments

The structure of the free volume and its temperature dependence between 25 and 200 °C of copolymers of styrene with maleic anhydride, SMA (0-35 mol% MA), is studied by pressure-volume-temperature (PVT) experiments and positron annihilation lifetime spectroscopy (PALS). In this first part of the work, PVT data are reported which were analysed with the Simha-Somcynsky equation of state to estimate the volume fraction of holes, h, which constitute the excess free volume. The temperature and pressure dependence of the specific volume V, the specific occupied and free volume, V_occ=(1−h)V and V_f=hV, and the corresponding isobaric expansivities and isothermal compressibilities for both the rubbery and glassy state are estimated. We obtained the unexpected results that (i) the occupied volume changes its coefficient of thermal expansion at T_g from α_occ,g≈0.5α_g≈1×10⁻⁴ K⁻¹ below T_g to almost zero (≈0.2×10⁻⁴ K⁻¹) above T_g and (ii) the isothermal compressibility of the occupied volume at zero pressure below T_g is rather high, κ_occ≈2.5×10⁻⁴ MPa⁻¹, and decreases only slightly at T_g to about 2×10⁻⁴ MPa⁻¹ above T_g. The variation of total, occupied, and free volume parameters with the composition of the SMA copolymers is discussed.     

Ring-opening polymerization of ?-caprolactone by poly(propyleneglycol) in the presence of a monomer activator

The ring-opening polymerization of ?-caprolactone (CL) was induced by using polypropylene glycol (PPG) as an initiator in the presence of the monomer activator HCl·Et₂O to synthesize triblock copolymers composed of PPG and poly(?-caprolactone) (PCL). The degree of CL conversion and the molecular weight of PCL increased linearly with the polymerization time or with the feed ratio of CL to PPG in the presence of HCl·Et₂O in CH₂Cl₂ at 25 °C. The PCLs obtained had molecular weights close to the theoretical values calculated from the CL:PPG molar ratios and exhibited monomodal GPC curves with narrow polydispersity indexes. The apparent rate constant (k_app) for the polymerization of CL activated by HCl·Et₂O was greatly affected by the ratio of HCl·Et₂O/PPG. The activation energy for the polymerization of CL in this system was estimated to be 49.8 kJ/mol K. We successfully prepared PPG and PCL triblock copolymers using this activated monomer mechanism.     

Strain recovery of post-yield compressed semicrystalline poly(butylene terephthalate)

Cubic specimens of a semicrystalline poly(butylene terephthalate) (PBT) have been compressed up to post-yield deformation levels with a fast (3.0 × 10⁻² s⁻¹) and a slow (1.5 × 10⁻⁴ s⁻¹) strain rate at three different temperatures (25 °C, 45 °C, and 100 °C, i.e. below, close and above the glass transition temperature of the material, T_g, respectively). Differently from literature results reported for amorphous polymers, semicrystalline PBT shows that, after a post-yield deformation, recovery occurs also at temperatures higher than T_g, and that an irreversible deformation, ?_irr, is set in the material. The irreversible strain component has been evaluated as the residual deformation after a thermal treatment of 1 h at 180 °C.After unloading, isothermal strain recovery has been monitored for time periods of 1 h at various temperatures. From the obtained data, strain recovery master curves have been constructed by a time-temperature superposition scheme. The features of the recovery process for the various deformation conditions have been analysed. In particular, it appears that specimens deformed below T_g show a lower irreversible component, whereas, when deformed above T_g, they display a higher irreversible deformation and a slower recovery process. Moreover, the effect of deformation rate appears particularly marked for samples deformed above T_g.     

The effect of the interlayer anions on the electrochemical performance of layered double hydroxide electrode materials

Both high energy density and high power density are vitally required for new applications such as electric vehicles. Here we present a comparison of two well-crystallised layered double hydroxides, [Ni₄Al(OH)₁₀]OH and [Ni₄Al(OH)₁₀]NO₃, which shows that the former can maintain a better discharge capacity, 294-299 mAh g⁻¹, than the latter, 233-287 mAh g⁻¹ at a current density of 2000 mA g⁻¹ within about 300 cycles, although both electrodes deliver a similar capacity of 326 mAh g⁻¹ at 200 mA g⁻¹ initially. It is believed that both the more watery interlayer space in [Ni₄Al(OH)₁₀]OH than in [Ni₄Al(OH)₁₀]NO₃ and the morphologic changes induced by anion exchange of NO₃⁻ by OH⁻ during electrochemical cycles play key roles in their behaviour.     

Radically crosslinked branched poly(N-allylethylenimine) with lithium triflate as a solid state polymer electrolyte

Branched poly(N-allylethylenimine) (BPAEI), a solid state polymer electrolyte host, was synthesized by allylation of branched poly(ethylenimine) (BPEI). Allylation was essentially complete with the 2 and 1° nitrogen atoms of BPEI being mono-allylated and di-allylated, respectively, and with little or no quaternization. BPAEI can be radically cross-linked with and without lithium trifluoromethanesulfonate (LiTf) present to form free-standing, homogeneous, minimally hygroscopic films. BPAEI has a glass transition temperature (T_g) of −65 °C, as measured by differential scanning calorimetry (DSC), which increases with the concentration of initiator upon cross-linking using V-50 (2,2-azobis(2-amidino-propane) dihydrochloride) to −15 °C at a 10:1 nitrogen to initiator molar ratio (N:initiator). BPAEI with 20:1 N:Li⁺ (molar ratio) LiTf has a T_g of −48 °C, which increases with the concentration of radical initiator upon cross-linking using V-50 to 3 °C at 10:1 N:initiator. At compositions near 60:1 N:initiator, an unusual decrease in the rate at which T_g changes with cross-linking was observed, both with and without LiTf present, indicating that some undefined morphological changes occur. The effect of this morphological change resulted in the highest Ac conductivities at 60:1 N:initiator for all LiTf concentrations studied. At 20:1 N:Li⁺ LiTf and 60:1 N:initiator, the room temperature Ac conductivity was 1×10⁻⁸ S/cm which increased to 1×10⁻⁵ S/cm at 80 °C, the highest conductivity observed in the concentration ranges studied. Infrared spectroscopy (IR) showed that the concentrations of the individual ionic species present were largely independent of either LiTf concentration or cross-linking density, suggesting that changes in ion mobility, likely resulting from morphological changes, substantially control the ionic conductivity.     

Influence of molecular weight on dynamic crossover temperature in linear polymers

Dielectric and light scattering spectra of two linear polymers, polyisoprene (PIP) and polystyrene (PS), were analyzed in broad temperature and frequency range above the glass transition temperature, T_g. The crossover temperature, T_C, was estimated using two approaches: (i) derivative analysis of relaxation times proposed by Stickel and (ii) Mode-Coupling Theory approach. Both estimates provide consistent values. T_C varies with molecular weight (MW) in both polymers, while the ratio T_C/T_g changes significantly with MW in PS only. It appears that the segmental relaxation time at T_C has value τ(T_C) ∼ 10⁻⁷ s for both polymers independent of MW and similar to the value reported for many non-polymeric glass-forming systems. No sign of the dynamic crossover has been observed in the chain relaxation around T_C of the segmental dynamics.     

Preparation, characterization and electrocatalytic properties of an iodine|lignin-modified gold electrode

Hydrolytic lignin (HL) was adsorbed from an aqueous/organic solution on bare and iodine-modified gold electrode. Subsequent electrooxidation of the lignin adsorbate generated redox-active quinone-based groups in the biopolymer structure, exhibiting high reversibility during potential cycling and fast electron transfer kinetics. The presence of the chemisorbed iodine layer on the supporting gold electrode had a pronounced effect on the electrochemical properties of the final modified electrode in terms of double-layer capacitance (C_dl) and the observed surface coverage (Γ_obs). The high electrochemical activity in connection with low C_dl made it possible to apply the Au|I_(ads)|HL electrode as a fast-responding and sensitive electrochemical sensor for NADH. When tested in the amperometric mode at a constant potential of +0.4 V vs. Ag/AgCl, the modified electrode showed a linear current-concentration response over the range of 5-120 μM with a sensitivity of 2.39 nA μM⁻¹ cm⁻² and a detection limit of 1.0 μM (S/N = 3). Kinetic studies using the rotating disk electrode revealed that the mediated oxidation of NADH on the Au|I_(ads)|HL electrode was limited by the second order reaction of the analyte molecules with o-quinone moieties with a rate constant of ca. 4.7 × 10² M⁻¹ s⁻¹ (C_NADH → 0). The modified electrode showed high resistivity against fouling and retained ca. 65% activity after storage in phosphate buffer (pH 7.4) at room temperature for 1 week.     

Photo-Crosslinked Poly(ε-caprolactone fumarate) Networks: Roles of Crystallinity and Crosslinking Density in Determining Mechanical Properties

We present a material design strategy of combining crystallinity and crosslinking to control the mechanical properties of polymeric biomaterials. Three polycaprolactone fumarates (PCLF530, PCLF1250, and PCLF2000) synthesized from the precursor polycaprolactone (PCL) diols with nominal molecular weights of 530, 1250, and 2000 g mol⁻¹, respectively, were employed to fabricate polymer networks via photo-crosslinking process. Five different amounts of photo-crosslinking initiator were applied during fabrication in order to understand the role of photoinitiator in modulating the crosslinking characteristics and physical properties of PCLF networks. Thermal properties such as glass transition temperature (T_g), melting temperature (T_m), and degradation temperature (T_d) of photo-crosslinked PCLFs were examined and correlated with their rheological and mechanical properties.     

Microstructure of free volume in SMA copolymers II. Local free volume from PALS

The structure of the free volume and its temperature dependence between, at maximum 133 and 503 K of copolymers of styrene with maleic-anhydride, SMA (0-35 mol% MA), is studied by pressure-volume-temperature (PVT) experiments and positron annihilation lifetime spectroscopy (PALS). In this second part of the work, PALS data are reported from which the temperature dependence of the mean size and size distribution of local free volumes (subnanometer size holes) is analysed. The mean hole volume, ν_h, varies in PS between 80 Å³ (133 K) and 212 Å³ (503 K) and shows a systematic decrease with increasing MA content for a given temperature above T_g. The specific number of holes, N_h′, estimated from a comparison of PVT and PALS results, increases slightly with MA content from N_h′=(0.60±0.02)×10²¹ g⁻¹ to N_h′=(0.70±0.02)×10²¹ g⁻¹ which corresponds to N_h(T_g)=N_h′/V_g=0.62-0.82 nm⁻³ (V_g is the material's specific volume at T_g) and 1/N_h(T_g)=1.6-1.2 nm³ for the volume which contains one hole. The analysed size distributions of the holes above T_g follow the compressibility of the free volume as it is predicted by the theory of thermal volume fluctuation. We also comment on the connection between the hole size as measured by PALS and the size of a cluster of randomly distributed unoccupied cells as defined by the Simha-Somcynsky theory.     

Novel triol-crosslinked polyurethanes and their thermorheological characterization as shape-memory materials

A new family of crosslinked polyurethanes was synthesized and characterized as shape-memory polymers. Three-arm network junctions are provided by 1,1,1-trimethylol propane with an isocyanate group on each arm. Three diisocyanates are used: 4,4′-methylene bis(phenyl isocyanate), toluene diisocyanate, and 4,4′-dibenzyl diisocyanate. They are linked together by macrodiol soft segments formed from either polytetrahydrofuran with molar mass of 650, 1000 or 2000 g mol⁻¹ or polycaprolactone glycol with molar mass of 830 or 1250 g mol⁻¹. Thermorheological response of each polymer was characterized by tensile creep tests through the glass transition of the soft segments, to obtain the linear viscoelastic retardation spectrum, limiting compliances and time-temperature shift factor. These were used to predict significant features of shape-memory performance. With a decrease in soft segment chain length, the temperature of maximum shape recovery rate increased and the width of the recovery window decreased, consistent with loss of soft segment chain mobility remote from the crosslinks. Tensile modulus in the switched condition (above T_g) was 8-16 MPa, increasing with crosslink density and hard-segment rigidity. The results confirmed the potential of these polyurethanes as a new family of tunable shape-memory materials.