Tri-2-ethylhexyltrimellitate (TOTM) is one of the commercially used plasticizers for poly(vinyl chloride) (PVC). In this work, the diffusion behavior of TOTM in PVC films is investigated through ...real-time ATR-IR spectroscopy at 25, 40, and 70 °C, and the ratio changes of three CO structures of TOTM are plotted as a function of diffusion time. TOTM itself is composed of two types of CO structures: one CO structure represents a free state and the other represents an aggregated CO state formed by dipolar–dipolar interactions, as confirmed by the second derivative of FTIR and density functional theory (DFT). Furthermore, another new band related to CO groups of TOTM was observed during diffusion experiments in PVC at different temperatures, which can be assigned to dipolar–dipolar interactions between TOTM and PVC (interacting CO structure). These results show that the diffusion coefficients of TOTM in PVC increase with temperature. Conversely, the equilibrium concentrations of TOTM in PVC films decrease significantly with temperature due to rapid molecular movements and less interacting CO structures. Moreover, it is also found that free CO structures more easily interact with C–Cl groups of PVC at 25 °C, while aggregated CO structures show prior contribution at 40 °C, which is effectively confirmed by two-dimensional (2D) correlation infrared spectroscopy. At 70 °C, however, free and aggregated CO structures can reach an equilibrium much more quickly, but the content of interacting CO structures has to keep a lower level because of higher temperature.
The relationship between product structure and melt-state rheological properties is established for series of branched PP derivatives prepared by the radical-mediated grafting of tri-functional ...coagents. Peroxide-initiated, solvent-free additions of linear PP to triallyl trimesate (TAM), trimethylolpropane triacrylate (TMPTA) and triallyl phosphate (TAP) at high temperature are shown to produce bimodal molecular weight and branching distributions. Low-frequency dynamic shear viscosities as well as extensional viscosities are shown to be highly responsive to a hyper-branched chain population, whose abundance and molecular weight correlate with the kinetic chain length of the grafting process, and the propensity of a coagent to oligomerize.
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Polypropylene is transformed by simultaneous, radical-mediated chain scission and cross-linking to generate branched architectures. While macroradical fragmentation reduces the molar mass of the ...dominant chain population, cross-linking by triallyl trimesate (TAM) activation yields a minority population of hyper-branched chains that is less susceptible to molecular weight loss. This disparity in chain reactivity leads to bimodal molecular weight and branching distributions. Furthermore, a precipitation polymerization of TAM can proceed concurrently with PP branching to produce a low yield of cross-linked, TAM-rich nano-particles. The mechanisms through which unimodal composition and molecular weight distributions evolve toward a bimodal condition are discussed, along with the factors that lead to particle formation.
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Water diffusion through low density polyethylene (LDPE) film was investigated by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and two-dimensional correlation ...spectroscopy (2DCOS) over a temperature range of 25–80 °C. The 2DCOS spectra of water diffusion in LDPE at different temperatures were very similar. The broad OH stretching vibration (ν(OH)) was split into four bands assigned to three different types of water molecules, namely, bulk water, cluster water, and free water, which will be defined. It appeared that as water molecules disperse in LDPE, cluster water with moderate hydrogen bonds diffused faster than bulk water with strong hydrogen bonds. Additionally, the hydrogen bonds between water molecules may have been further weakened or even broken to form free water, possibly due to limited free volume. On the basis of a Fickian model, the diffusion coefficients could be calculated from overall, fast and slow diffusion process, respectively. The diffusion coefficients were observed to increase with temperature, possibly due to increased swelling of molecular chain, more free volume, and reduced size of the penetrants.
The radical-mediated addition of alkanethiols to the terminal unsaturation of polypropylene (PP) is used to prepare functional polyolefin derivatives without altering the molecular weight of the ...parent material. The sulfide product of thiol−ene addition, as well as the internal olefin resulting from a remarkable thiyl radical-mediated olefin migration, is characterized using a model hydrocarbon, 2,4-dimethylhept-1-ene. The yield of 3-mercaptopropyltrimethoxysilane (MPTMS) addition to atactic-PP is examined in detail, and the functionalization of high molecular weight isotactic-PP is used to produce moisture-curing resins that bind to siliceous fillers. The limited unsaturation content of PP, along with the high temperatures needed to modify the resin in its melt state, is shown to impact negatively on the reaction conversion due to the reversibility of thiyl radical attack on olefin.
Crosslinked polyethylene (XLPE) is a key material for power cables due to its superior performance as electrical insulation. It is co-extruded with a carbon black-filled semiconducting "semicon" ...polymer layer, which is significantly more conductive than XLPE. Understanding the electrical properties of the XLPE/semicon bilayer and the interface between the layers is critical due to their common use in high-voltage cables, and so XLPE/semicon bilayers were developed, examined, and compared to XLPE in isolation. These materials were examined using current-voltage and dielectric displacement-voltage (D(P)-E) loop measurements. Current-voltage measurements were meant to examine changes in leakage current while D(P)-E loops were used to examine changes in dielectric loss, in both cases due to the addition of the semicon interface. Both techniques were used to analyze the charge transport response and development of space charge polarization in the bulk polymer and across the bilayer interface as a function of polarity at 90 °C. An increase in the apparent conductivity of the XLPE was measured when layered with the semicon, attributed to the increase in charge injection at the XLPE/semicon interface. Additionally, increases in the conductivity were observed with the application of higher electric fields. The addition of the semicon layer resulted in an increase in both the dielectric constant and the dielectric loss, and greater increases in both as the field is increased. Thus, it led to an enhancement in space charge polarization. Based on the experimental measurements from high-voltage D(P)-E loop measurement, a nonlinear circuit model was developed to fit the data and provide a close match to experimental values for resistivity and capacitance. The high-field circuit model was based on forward and reverse biased resistor and diode pathways in parallel with each other and with the bulk damped capacitor, and it predicts space charge limited conduction with a semicon electrode and Poole-Frenkel conduction with a metal electrode, highlighting the importance of interfaces on XLPE insulation performance.
Crosslinkable composites of ethylene vinyl acetate copolymer (EVA)/acrylonitrile‐butadiene copolymer (NBR)/carbon black (CB) finds widespread use in industrial applications. Crosslinking and phase ...behavior and resulting mechanical properties have been reported, but a systematic investigation as a function of varying molecular architecture is still elusive. The present work combines an experimental and theoretical approach to understand the phase morphology and physical properties of crosslinked EVA/NBR/CB polymer composites. Crosslinking behavior is studied by varying the functionality content in the two polymers. A theoretical model was developed to calculate and predict the overall phase behavior of the composites as well as the preferential solubility of the peroxide in the phases. The phase morphology of the immiscible EVA/NBR polymer blend investigated clearly showed two distinct phases with the NBR phase dispersed in the continuous EVA phase and the CB particles tend to reside at the interface. The influence of varying molecular architecture and functionality of the NBR and EVA on material properties was investigated and did not significantly contribute to the crosslinking and tensile behavior of the composites. The mechanical properties were found to correlate with the degree of crosslinking and CB loading.
