Crystallization in blends of poly(ethylene terephthalate) and poly(butylene terephthalate)

Blends composed of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) were melt-mixed in a Brabender cam mixer at different mixing speeds. The glass transition (T_g) and the crystallization behavior of the blends from glassy state were studied using DSC. It was found that although the blends had the same composition and exhibited the similar T_g, their properties of crystallization could be different; some exhibited a single crystallization peak and some exhibited multiple crystallization peaks depending upon experimental conditions. Results indicated that the behavior of crystallization from glassy state were influenced by entanglement and transesterification of chains. The crystallization time values were obtained over a wide range of crystallization temperature. From curve fitting, the crystallization time values and the temperature, at which the crystallization rate reaches the maximum, were found.     

Slow relaxations in semicrystalline poly(butylene succinate) below and above Tg

The slow molecular mobility in the amorphous part of the semi‐crystalline polymer poly(butylene succinate) (PBS) has been studied by the thermally stimulated depolarization current (TSDC) technique. Experiments were carried out in the temperature range, which includes the glassy state, the glass transformation region, and the rubber state. A broad and low intensity secondary relaxation was observed in the temperature region from ?140°C up to the glass transition region; the activation energy of the motional modes of this secondary relaxation was in the range between 35 and 55 kJ mol^?1. The glass transition temperature of PBS, provided by the TSDC technique, was T_g = ?40 °C, and the fragility index was found to be m = 43. The aging behavior of the main and of the secondary relaxations was analyzed. A strong relaxation above T_g was observed, whose molecular origin was discussed. The thermal behavior of the PBS was also characterized by differential scanning calorimetry. POLYM. ENG. SCI., 55:1873–1880, 2015. © 2014 Society of Plastics Engineers     

Phase transformations of some poly(vinyl alcohol)–NiCl2 composites

Samples of poly(vinyl alcohol)–NiCl₂ composites containing up to 30 wt% NiCl₂ were prepared by casting in order to study phase transformation–structural change relationships of these samples before and after heat treatment. Differential thermal analysis (DTA) thermograms were recorded at 10, 15, 20 and 30 °C min^?1. For untreated samples four endotherms were assigned as: rotation of hydroxyl groups in the glassy state, glass transition, structural transition in the rubber‐like state, and melting transition. Ultrasonic attenuation measurements were carried out to confirm these transitions in the glassy and rubber‐like states. In the glassy state, the effect of NiCl₂ addition is explained in terms of chain stiffness due to the creation of local crosslinked regions in amorphous parts of the polymer. Average values of activation energies for glass transition were calculated using both methods of Kissinger and Ozawa. However, addition of NiCl₂ had an opposite effect on the heating rate independent crystallization melting temperature (T_m), relative to that on T_g. The DTA thermograms of heat‐treated samples indicated that square planar NiCl₂ molecules were embedded in the polymer matrix with no local crosslinking role due to the formation of conjugated polyenes along the polymer chains by thermal treatment. Copyright © 2003 Society of Chemical Industry     

High-pressure sorption of carbon dioxide in solvent-cast poly(methyl methacrylate) and poly(ethyl methacrylate) films

Carbon dioxide sorption isotherms in poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) are reported for pressures up to 20 atm. Temperatures between 35 and 80°C were studied for PMMA and temperatures between 30 and 55°C were studied for PEMA. Typical dual mode sorption isotherms concave to the pressure axis were observed in all cases. The measured Langmuir sorption capacities of both polymers extrapolated to zero at the glass transition (T_g) consistent with the behavior of other glassy polymer/gas systems. Sorption enthalpies for CO₂ in the Henry's law mode for PMMA and PEMA are in the same range (?2 to ?4 kcal/mole) as has been reported for a variety of other glassy polymers such as poly(ethylene terephthalate), polycarbonate, and polyacrylonitrile. Some of the data suggest that postcasting treatment of the PEMA films left a small amount of residual solvent in the film. the presence of the trace residual solvent during quenching from the rubbery to the glassy state after annealing appears to cause a dilation of the Langmuir capacity and an alteration in the apparent Langmuir affinity constant of the PEMA film. These results suggest the possibility of tailoring physical properties of glassy polymers such as sorptivity, permeability, impact strength, and craze resistance by doping small amounts of selected residuals into polymers prior to quenching to the glassy state from the rubbery state.     

Molecular mobility and physical ageing of plasticized poly(lactide)

Molecular mobility and physical ageing of amorphous plasticized polylactide (PLA) with two different contents of mesolactide are studied with the help of thermal analysis. Used plasticizers are acetyl tributyl citrate (ATBC) and triacetin (TA), two molecules with established miscibility and plasticizing efficiency. Lower plasticizer permanence of TA compared with ATBC is found. The plasticizer molecules decreased the size of the cooperativity domains at the glass transition temperature T_g and likely in the glassy state by decreasing intermacromolecular interactions and notwithstanding the mesolactide content of PLA and the chemical identity of the plasticizer. The recovery function is given and shows a significant effect of the plasticizer on the physical ageing. The supplementary free volume brought by the plasticizer enhances molecular mobility in the glassy state and increases structural relaxation at one order of magnitude. The comparison between different plasticizers reveals that the structural relaxation is however independent from the type of plasticizer and the percentage of mesolactide in PLA. POLYM. ENG. SCI., 55:858–865, 2015. © 2014 Society of Plastics Engineers     

Calorimetric study of some poly(mono-n-alkyl itaconates)

A calorimetric study of poly(mono-n-alkyl itaconates) containing 8, 10, 12 and 14 carbon atoms in the side chain was performed. No glass transition temperature (T_g) was observed in the temperature range 213-263 K, but a melting process was observed for the dodecyl and tetradecyl derivatives, which was attributed to crystalline order in the long side chains.     

Physical ageing in glassy liquid crystalline poly(p-hydroxy-benzoic acid-co-ethylene terephtalate)

Summary Glassy liquid crystalline poly(p-hydroxy-benzoic acid-co-ethylene terephthalate) is after rapid cooling from temperatures above T_g in a non-equilibrium state and exhibits physical ageing. It is shown that enthalpy and volume decrease with increasing annealing time. At the same undercooling, with respect to middle temperature of the major glass transition (T_gl), the rate of the equilibration process is significantly slower in the studied polymer than in an ordinary glassy amorphous polymer. The presence of a constraining ETP-rich phase exhibiting a 25 K higher glass temperature than T_gl may be the cause for this retarded enthalpy relaxation.     

Effects of molecular interactions on the viscoelastic and plastic behaviour of plasticized poly(vinyl chloride)

The mechanical behaviour of plasticized poly(vinyl chloride) in the glassy state was revisited in order to provide some understanding of the properties observed on the molecular scale. Nine samples were investigated, consisting either of pure poly(vinyl chloride) or of plasticized formulations including different amounts of di‐octyl phthalate or benzyl butyl phthalate in the range 5–20 wt%. Presence of the additives resulted in the depression of the glass transition temperature, T_g, and the main mechanical relaxation temperature, T_α, as determined by differential scanning calorimetry and dynamic mechanical analysis, respectively. These expected results were related to the plasticizing character of the additives on the long‐range cooperative polymer motions. In addition, a marked reduction of the secondary mechanical relaxation β was observed for additive concentrations equal to or larger than 10 wt%. This antiplasticizing effect was interpreted as the hindrance of main‐chain local polymer motions, due to poly(vinyl chloride)–additive interactions. Occurrence of such interactions was confirmed by mid‐ and near‐infrared measurements. The plastic behaviour of the materials in the glassy state was also examined. Particular attention was paid to the strain‐softening amplitude (difference between yield stress and plastic flow stress), to the percentage of non‐elastic deformation and to the mechanical energy to yield. All these quantities are strongly affected by the chain‐mobility characteristics. Copyright © 2003 Society of Chemical Industry     

Non equilibrium annealing behavior of poly(vinyl acetate)

The water absorbed by poly(vinyl acetate), PVAc, at 23°C was found in two states. The first, which can account for up to 4 weight percent, was bound to the polymer. The second was in a freezable or clustered form. The latter type of water had no effect on PVAc's glass temperature, whereas, the former kind plasticized T_g. In annealing studies, the enthalpic and dielectric response of PVAc when held at a fixed temperature increment, ΔT, below T_g, was observed to be independent of the amount of bound water. The time dependence of the shift in the dielectric relaxation spectrum and the recovery of the enthalpy towards its equilibrium value as PVAc approached its equilibrium glassy state from a lower temperature as compared to a higher temperature was initially slower. This delayed response to expansion was of the order of the polymer's average relaxation time at the lower temperature. A model was proposed to explain this asymmetric behavior based upon changes in the polymer's free volume as well as its occupied volume.     

Dielectric relaxations in poly(methyl acrylate), poly(ethyl acrylate), and poly(butyl acrylate)

A comparative study is undertaken of the dielectric relaxation spectra of poly(methyl acrylate), poly(ethyl acrylate), and poly(butyl acrylate), taking into consideration the spectra of the corresponding polymers in the series of the polymethacrylates. The three polymers, PMA, PEA, and PBA, present an α relaxation zone clearly separated from the secondary relaxations. Its shape is not altered with temperature, and it is possible to construct a master curve. With increasing length of the side chain, its distribution of relaxation times broadens and the temperature of the maximum of the relaxation decreases. A β relaxation with decreasing intensity as the length of the side chain increases is clearly perceptible in PMA and PEA, but almost not perceptible at all in PBA. In PEA this relaxation appears split into two peaks. Computer simulation of restricted motions of the side chain discard an origin similar to that of the γ relaxation in PPA or PBA for the lowest temperature component of the relaxation, and suggests the conjunction of two rotation mechanisms in this relaxation for the polyacrylates. For the experimental temperatures of our tests a γ relaxation shows up only in PBA. Its apparent activation energy, higher than in related polymers of the polymethacrylate series, suggests that the tighter packing of monomeric units in polyacrylates leads to a significant increase in the intermolecular contribution to the potential energy barrier responsible for the relaxation.     

A nonlinear regression approach to model the physical aging of poly(ether imide)

Differential scanning calorimetry (DSC) was used to measure the relaxation enthalpy of glassy amorphous poly(ether imide) (PEI) at three high isothermal aging temperatures between 190 and 200°C. A three-parameter model based on the Williams-Watts relaxation function was utilized to describe the aging process of PEI, and nonlinear regression approach was used to estimate the model parameters. The prediction according to this model was found to be more accurate in comparison with the two-parameter model based on the same Williams-Watts relaxation function. Furthermore, the peculiar aging behavior at the highest aging temperature of 200°C was explained from the molecular view point of transition from sub-T_g β-relaxation to α-relaxation near T_g.     

Phase behaviour of poly(benzophenoneimide)s having n-alkyloxymethyl side chains

A series of poly(benzophenoneimide)s (C_m-BP-PIs) having n-alkyloxymethyl side chains (−CH₂O-n-CmH_2m+1, m = 4, 6, 8) have been examined by X-ray diffraction, differential scanning calorimetry (DSC) and polarizing optical microscopy. The samples showed basically two phase transitions and both transition temperatures decreased with increasing side chain length. The first transitions were ascribed to glass transitions and the second ones were assigned to liquid crystal-to-isotropic transitions. Eicosane (n-C₂₀H₄₂) which is chemically very similar to the side chain was miscible with the side chains of C₈-BP-PI, which induced depression of the glass transition temperature. Received: 17 February 1997/Revised: 1 April 1997/Accepted: 4 April 1997     

Quantitative study of the annealing of poly(vinyl chloride) near the glass transition

Poly(vinyl chloride) displays a normal DSC of DTA curve for the glass transition when quenched from above its T_g. However if cooled slowly or annealed near the glass transition temperature, a peak appears on the DSC or DTA curve at the T_g. In this paper quantitative studies of the time and temperature effects on the production of this endothermal peak during the annealing of PVC homopolymer and an acetate copolymer are presented. The phenomenon conforms to the Williams, Landell, and Ferry equation for the relaxation of polymer chains, the rate of the peak formation becoming negligible at more than 50°C below T_g. The energy difference between the quenched and annealed forms is small. For a PVC homopolymer annealed 2 hr at 68°C, which is T_g ?10°C, the difference is 0.25 cal/g. For a 13% acetate copolymer of PVC similarly annealed, the difference is 0.36 cal/g. The measured rates of the process give a calculated activation energy of 13–14 kcal/mole for PVC homopolymer and copolymer. This appearance of a peak on the T_g curve for a polymer when annealed near the glass temperature appears to be a general phenomenon.     

The glass transition temperature of poly(phenylene sulfide) with various crystallinities

The glass transition temperature (T_g) of poly(phenylene sulfide) (PPS) with various crystalline fractions has been studied using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The DSC measurements show that T_g can be observed from the heating curves for the PPS sample with very low crystallinity, and no T_g is observed when the crystallinity is over 8%. DMA indicates that crystallinity has an important effect on molecular chain segment motion of PPS. When the crystallinity, X_c, of PPS is over 38%, there is only one chain segment motion, which mainly results from the crystalline chain vibration; while three different chain segment motions occur for PPS samples with lower crystallinity (X_c < 26%), which are amorphous chain segment motion, crystalline chain segment motion and constrained amorphous chain segment motion. T_g of PPS is mainly caused by the amorphous chain segment motion which is independent of the crystallinity, while the relaxation temperature corresponding to crystalline chain motion shifts to lower temperature as the crystallinity increases. The reduction of the relaxation temperature can be attributed to the disorder‐order transition of amorphous chains for PPS with lower crystallinity. © 2012 Society of Chemical Industry     

Phase behavior of poly (pyromellitimide)s having flexible (n-alkyloxy)methyl side chains

Summary Phase behavior of poly(pyromellitimide)s having (n-alkyloxy)methyl side chains (-CH₂OC_mH_2m+1, m=4, 6, 8) has been studied by wide angle X-ray scattering, differential scanning calorimetry and ¹³C solid-state NMR. While there are no observable transitions in the polymers bearing short side chain(m=4, 6), there is one transition in the polymer bearing the longest side chain(m=8), which is assigned to mesophase-mesophase transition. All the samples show layered mesophase at room temperature, in which the side chains are amorphous but the main chains form two-dimensional crystals in each layer. In the polymer bearing the longest side chain(m=8), it shows another layered mesophase at high temperature. In the high temperature mesophase, the main chains do not form two-dimensional crystals in each layer; only the lateral packing of the main chains remains undisrupted. Received: 7 July 2000/Accepted: 22 September 2000     

The effects of thermal history on the density and mechanical properties of poly(methyl methacrylate)

The purpose of this work was to show that physical aging effects in poly(methyl methacrylate) (PMMA) could be correlated with the nonequilibrium state of the glassy polymer, as measured by dilatometry. Specimens were annealed at a series of temperatures within the glass transition region (90, 95 and 100°C) and quenched or slowly cooled to the test temperature (40 or 60°C). Volume recovery was monitored throughout the experiment by accurate dilatometry, and low strain tensile creep compliance measurements were made simultaneously on specimens subjected to identical thermal treatments. At both test temperatures, creep behavior and volume recovery showed a similar dependence on annealing temperature and time. However, the specific volume alone was not sufficient to characterize the aging behavior of glassy PMMA: it was also necessary to define the path by which the state of the glass was reached. This memory effect, which has a direct parallel in volume recovery, is attributed to the presence of a distribution of retardation times, and accounts for, the seemingly paradoxical observation that the creep compliance can initially increase on aging at a temperature below T_g if the specimen has previously been stored for a long period at a lower temperature.     

Autonomic self‐healing of poly(vinyl butyral)

The self‐healing behavior of poly(vinyl butyral) (PVB) is evaluated below the glass transition temperature T_g. It is found that PVB shows autonomic self‐healing even at room temperature, although T_g is around at 76°C. Furthermore, a large amount of water is found to be adsorbed on the surface of the film. This is attributed to the surface localization of hydroxyl group in PVB, which is confirmed by X‐ray photoelectron spectroscopy. Since the surface is plasticized by water, the scar applied by a razor blade is healed even in the glassy state of the bulk. Moreover, the healing efficiency is enhanced at high humidity condition, owing to the pronounced plasticizing effect by water. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42008.     

Shape memory behavior of poly(methyl methacrylate)-graft-poly(ethylene glycol) copolymers

This paper describes a shape memory behavior of graft copolymers poly(methyl methacrylate)-graft-poly(ethylene glycol) (PMMA-g-PEG). In shape memory test, the sample was deformed from its original shape to a temporary shape above glass transition temperature (T_g), cooled below T_g to fix the temporary shape, and subsequently heated above T_g for spontaneous recovery to the original shape. By grafting PEG onto PMMA backbone, shape memory ability was drastically enhanced than PMMA homopolymer. The shape recovery ratio was decreased with the increase in the shape deformation temperature. With considering a good miscibility of backbone and side chain in PMMA-g-PEG, this shape memory ability may be related to a physically cross-linked network structure by chain entanglement of the comb-like graft copolymer. Stress relaxation measurements were investigated in order to confirm the effect of the graft chains on the shape memory behavior.     

Compatibility of polyacrylates and polymethacrylates with poly(vinyl chloride): 2. Measurement of interaction parameters

Interactions of various solvents with poly(vinyl chloride) and a series of polyacrylates and polymethacrylates have been studied by inverse gas chromatography. Values of the interaction parameters χ₁₂ have been calculated and show the importance of specific interactions between the polymers and the solvents. Low values of χ₁₂ indicating a strong interaction were found for the polyacrylates and polymethacrylates with a proton donating solvent, chloroform, and for the poly(vinyl chloride) with some proton accepting solvents, especially butan-2-one. Interactions of solvents, with mixtures of poly(vinyl chloride) with some compatible polyacrylates and polymethacrylates, have also been studied. From this, and using the values of χ₁₂ found above, values of the polymer-polymer interaction parameters χ₂₃ have been calculated. Low values of χ₂₃, indicating a strong interaction were found, especially for polymethacrylates and polyacrylates with shorter ester side chains. Lower values were obtained for polymethacrylates than polyacrylates again indicating greater interactions. These results fit in well with the results of a previous paper where we found that the polymers with longer ester side chains were not compatible with PVC or phase separated on heating, and that fewer acrylates than methacrylates are compatible with PVC.     

Morphology and physical properties of poly(butylene terephthalate)

Liquid nitrogen-quenched PBT samples produce much larger spherulites of an optic axis orientation different from the of the air-cooled samples. Optical and scanning electron microscopy show that glass fibers in the glass-reinforced PBT sample nucleate the growth of well-defined spherulites along the glass fiber axis. Fracture studies at temperatures below and above the T_g indicate, respectively, brittle and ductile interspherulite boundary fracture. From dynamic mechanical studies, three transitions designated by α (flow transition), β (T_g), and γ (secondary relaxation) are observed. The magnitudes of the β and γ transitions are larger for the more amorphous quenched sample than the air-cooled sample, suggesting their amorphous phase origin. Addition of glass fibers raises the dynamic modulus and flow temperature, but suppresses the γ transition without significantly affecting the melting and glass transition temperatures.