Studies of structures of poly-ε-caprolactam/montmorillonite nanocomposite: Part 1. Tests of compression moulded specimens

A poly-ε-caprolactam (PA6) taken as a reference and its nanocomposite (PNC) containing 1.6 wt.% of montmorillonite were examined. The specimens as discs were prepared by compression moulding at 235 °C and 70 MPa. Using the novel version of TMA, in the PA6 and PNC specimens, within the temperature range from −100 to 250 °C, a semi-crystalline structure with anisotropy of distribution of the more ordered (crystalline?) portion was found in the surface layer up to 0.5 mm thick. The amorphous regions have differed in a state of order (different transition temperatures) and related compactness. The free volume fraction in amorphous regions determined in machine direction (normal to the surface) is increased when in transverse direction is reduced; simultaneously molecular weights of polymer chains between junctions were increased by incorporation of the nanofiller.     

Comparison of results from the more informative version of TMA with other methods of polymer testing

Summary Several characteristics of the topological regions determined by the more informative version of TMA for cured rubbers based on NR/CPE and NR/ENR blends as well as PA6/cured rubber blends correlate with static and dynamic mechanical properties. These rubbers differ substantially in the structure of their network and the related topological structure because CPE does not participate in cross-links when ENR can do it. The physical interactions caused by these additives also vary, due to the different polarity that influences the formation of physical networking junctions. In blends of PA6 and cured rubber the networking junctions are assumed as being physical nature only. From these facts and the above-mentioned results it could be preliminarily concluded that the correlation depends on the formulation and related structure of the composite, and on which of the characteristics have been compared. To understand the reasons for the existence, or lack of, correlation observed, further investigations are needed.     

Influence of polymer composition on the thermal characteristics of sulfonated EPDM ionomers

Detailed thermal characterization of sulfo-EPDM ionomers was carried out. The endotherms observed via differential scanning calorimetry (DSC) and multiple inflections observed via thermal mechanical analysis (TMA) are speculated to be due to associated ionic species in the polymers. A large time dependence of the DSC endotherm was observed, suggesting substantial variations in the nature of the ionic species over this period. The influence of ionomer composition on thermal characteristics was probed with whole polymers and polymer fractions. In general, trends in the DSC and TMA data paralleled those expected on the basis of the anticipated effect of polymer sulfonation level, molecular weight, and counterion type on the strength of the physical crosslinking of these polymers. Both the DSC endotherms and the TMA inflection regions are rationalized in terms of a previously developed ionic-bond exchange model.     

Analysis of the area of material really tested by TMA

Deformation distribution within the specimen beneath the thermomechanical analysis (TMA) probe, found by using the finite element method (FEM), depends mainly on penetration depth, specimen thickness and diameter as well as on radius of the probe tip when the Poisson’s ratio influences it just slightly. For standard radius of the tip R_o=1 mm, most deformation is distributed in a material layer up to 0.5 mm thick independently on elastic modulus of a polymer at a glassy state. It is caused by the fact that maximal penetration depth for the polymers usually equals to about 0.05 mm. Because of this, the contact surface area is less than 0.17 mm² for the standard radius of the tip. This evidences that predominantly the specimen volume equal to  mm² (depth×area) is tested by the TMA at compression mode. For R_o=5 mm is tested the layer 2.5 mm thick. This makes possible to evaluate the material properties in the zone of different thickness depending on radius of the tip.     

A combination of Tedlar bag sampling and solid-phase microextraction for the analysis of trimethylamine in air: Relationship between concentration level and sample size

To extend the experimental applicability of the solid-phase microextraction (SPME) method to the analysis of trimethylamine (TMA) by the grab sampling method (i.e., Tedlar bag sampler), we investigated how experimental results are affected by the interaction between the concentration level of TMA standard and the volume size of its sample that is exposed to SPME fiber. To obtain comparative data sets for TMA analysis, all standards were analyzed as triplicate at five different concentrations (10, 20, 50, 100, and 200 ppb) each of which was prepared in four different bag sizes (1, 3, 5, and 10 L capacity). The sorptive characteristics of TMA were then evaluated in terms of recovery rate (RR) values derived by relationship between added and found quantities of TMA standard. The results of randomized block design showed that the determination of TMA is affected by the two major variables (i.e., TMA concentration level and sample size) at 95% confidence interval.     

Structure-Dynamic Relationship of Side-Chain Liquid Crystal Polymer with Rigid Backbone

To understand better the antagonistic behaviour of the backbone in comparison with the mesogenisity of the pendant side groups in side-chain liquid crystal polymers series of measurements using mechanical spectroscopy as well as DSC were carried out on two disubstituted polynorbornene derivatives. In order to clarify the specific arrangement of chains, the influence of thermal history on the smectic phase stabilisation were studied. By quenching samples from different temperatures, it was possible to obtain the systems which were either in the glassy liquid-crystalline (LC) state or in the glassy isotropic amorphous state. The samples prepared in such ways were used to study the influence of the LC structure on the mobility of chains in amorphous regions. The quality model of the supermolecular structure of the LC polymers is proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

New benzimidazole-2-yl-substituted polybenzimidazoles: Synthesis, properties, and hydrodynamic characteristics

The synthesis of novel benzimidazole-2-yl-substited polybenzimidazoles and initial compounds has been described. The polymers are studied by FTIR spectroscopy, TGA, and TMA. The hydrodynamic properties of macromolecules are investigated by translational diffusion and viscometry in 96% H₂SO₄; the molecular characteristics of the polymers are determined. Positive temperature dependences for intrinsic viscosities of the polymers are obtained. The polymers under study possess high hydrolytic stability with respect to sulfuric acid solutions up to 150°C and high thermal stability in the bulk. The TGA data correlate with the chemical structure of the polymers. The new polybenzimidazoles may be used as materials for the production of medium-temperature proton-conducting membranes.     

Mechanical properties of anion exchange membranes by combination of tensile stress–strain tests and dynamic mechanical analysis

The thermomechanical properties of anion exchange polymers based on polysulfone (PSU) quaternized with trimethylamine (TMA) or 1,4‐diazabicyclo[2.2.2]octane (DABCO) and containing hydroxide or chloride anions by tensile stress–strain tests and dynamic mechanical analysis (DMA) have been determined. The reported mechanical properties included the Young's modulus, tensile strength, and elongation at break from tensile tests and the storage and loss modulus and glass transition temperature from DMA. The anion exchange membranes behaved as stiff polymers with Young's modulus in the order of 1 GPa, relatively with high strength (about 30 MPa) and low elongation at break (around 10%) was observed. Tensile tests were also made with membranes exchanged with hydrogen‐carbonate and carbonate anions to control the absence of important carbonation of the OH form. The glass transition temperatures were of the order of 150 °C (PSU‐TMA) or 200 °C (PSU‐DABCO) for the hydroxide form, confirmed by differential scanning calorimetry; they increase further by about 50 K, when hydroxide ions are replaced by chloride. This result and the increase of the storage modulus could be interpreted by the higher hydration of hydroxide ions and the plasticizing effect of water, which reduced the Van der Waals interactions between the macromolecular chains. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1180–1187     

Thermomechanical study of low-density polyethylene, polyamide 6 and its blends

By using thermomechanical analysis (TMA) multiple relaxation transitions in the amorphous part of semi-crystalline polymers and their blends can be found. These result from differences in the interaction energies between segments of macromolecules, and as a result, in molecular mobility. TMA shows essential changes in the structure of low-density polyethylene (LDPE) resulting from the grafting of a maleic anhydride (LDPE-g-MAH) onto this semi-crystalline polymer. The grafting process did not suppress the ability of polyethylene to crystallize. Essential changes were found in molecular weight distribution and relaxation transitions of the ternary blends LDPE/PA6 (polyamide 6, PA6)/LDPE-g-MAH studied. For a concentration of PA6 up to 30 wt.%, a single relaxation transition is visible, which testifies that the components are miscible in the amorphous region. For blends with 40 and 50 wt.% of PA6, this structure was transformed and two relaxation transitions are visible. From the results obtained in this study it is concluded that the introduction 5 wt.% of grafted polyethylene is sufficient to produce a PA6/LDPE blend only for PA6 concentration up to 30 wt.% which is homogenous on “molecular” level. The transformation of the structure of the ternary polymer blend was explained by the interaction of the components during the melt mixing and changes in the structure of its amorphous regions.     

Formation of Octameric Methylaluminoxanes by Hydrolysis of Trimethylaluminum and the Mechanisms of Catalyst Activation in Single‐Site α‐Olefin Polymerization Catalysis

Hydrolysis of trimethylaluminum (TMA) leads to the formation of methylaluminoxanes (MAO) of general formula (MeAlO)_n(AlMe₃)_m. The thermodynamically favored pathway of MAO formation is followed up to n=8, showing the major impact of associated TMA on the structural characteristics of the MAOs. The MAOs bind up to five TMA molecules, thereby inducing transition from cages into rings and sheets. Zirconocene catalyst activation studies using model MAO co‐catalysts show the decisive role of the associated TMA in forming the catalytically active sites. Catalyst activation can take place either by Lewis‐acidic abstraction of an alkyl or halide ligand from the precatalyst or by reaction of the precatalyst with an MAO‐derived AlMe₂⁺ cation. Thermodynamics suggest that activation through AlMe₂⁺ transfer is the dominant mechanism because sites that are able to release AlMe₂⁺ are more abundant than Lewis‐acidic sites. The model catalyst system is demonstrated to polymerize ethene.