A new thermal analytical technique for acrylic polymers

Summary An unconventional thermal analytical technique has been developed for acrylic polymers. By adding water to the polymer the melting point is depressed well below the onset temperature of cyclic thermal degradation. This addition of water depresses the melting point of polyacrylonitrile from 320°C to 185°C. The melting behavior of acrylic copolymers in the wet and dry state is explained in terms of the Eby model of a polymer crystal whereby the non-crystallizable comonomers enter the crystal lattice as defects. The melting point and heat of fusion are interpreted as a measure of the regularity and strength of the intermolecular dipolar bonding that stabilizes the lattice.     

Crystallization of 2‐methyl‐1,3‐propanediol substituted poly(ethylene terephthalate). I. Thermal behavior and isothermal crystallization

Differential scanning calorimetry (DSC) was used to evaluate the thermal behavior and isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) copolymers containing 2‐methyl‐1,3‐propanediol as a comonomer unit. The addition of comonomer reduces the melting temperature and decreases the range between the glass transition and melting point. The rate of crystallization is also decreased with the addition of this comonomer. In this case it appears that the more flexible glycol group does not significantly increase crystallization rates by promoting chain folding during crystallization, as has been suggested for some other glycol‐modified PET copolyesters. The melting behavior following isothermal crystallization was examined using a Hoffman–Weeks approach, showing very good linearity for all copolymers tested, and predicted an equilibrium melting temperature (T_m⁰) of 280.0°C for PET homopolymer, in agreement with literature values. The remaining copolymers showed a marked decrease in T_m⁰ with increasing copolymer composition. The results of this study support the claim that these comonomers are excluded from the polymer crystal during growth. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2592–2603, 2006     

Fine-tuning of thermal dissociation temperature using copolymers with hemiacetal ester moieties in the side chain: effect of comonomer on dissociation temperature

Synthesis of polymers with hemiacetal ester moieties in the side chain by radical copolymerization of 1-alkoxyethyl methacrylate with various vinyl monomers and their thermal dissociation behavior are described. Radical copolymerization of 1-alkoxyethyl methacrylates with vinyl monomers was carried out in the presence of 2,2′-azoisobutyronitrile at 60°C to afford the corresponding copolymers with hemiacetal ester moieties in the side chain. The thermal dissociation behavior of the obtained copolymers was examined by means of TG–DTA measurements to observe that the dissociation temperatures of hemiacetal ester units depended on their comonomer components. The polarity of the comonomers and the ability to form hydrogen-bonding were key forces to control their thermal dissociation behavior.     

Thermal transitions of ethylene-vinyl chloride copolymers

Differential scanning calorimetry (d.s.c.) measurements were performed on a series of ethylene-vinyl chloride (E–V) copolymers for the purpose of studying the dependence of their thermal transitions upon their microstructure. The method of preparation, via reductive dechlorination of poly(vinyl chloride) with tributyltin hydride, resulted in a series of E–V copolymers differing only in comonomer content, sequence distribution and stereoregularity of adjacent V units. Chain length distribution and branching frequencies were identical for each member of the series.Extrapolation of glass transition temperatures, T_g, measured for our E–V copolymers to pure polyethylene (PE) predicted a T_g = ?85°C ± 10°C for amorphous PE. E–V copolymers with greater than 60 mol% E units exhibited melting endotherms characterized by melting temperatures from 20°C to 128°C and degrees of crystallinity from 12 to 63%. Observed melting temperatures were plotted against the composition of the E–V copolymers and compared to Flory's equation for melting point depression of random copolymers containing one crystallizable and one non-crystallizable monomer unit. The melting point depressions observed for our E–V copolymers were in agreement with Flory's theory, if the CH₂CH₂ moiety is considered to be the crystallizable unit and theCHmoiety is assumed to prevent the CH₂CH₂ units attached on either side from being incorporated into the crystal. This implies that among all possible comonomer triad sequences only the EEE triad may crystallize. Therefore only those E–V copolymers with average lengths of consecutive E units greater than 2 exhibit crystallinity.     

Physical properties of poly(n-alkyl acrylate) copolymers. Part 2. Crystalline/non-crystalline combinations

The physical properties of n-alkyl acrylate copolymers containing one crystallizeable monomer and one non-crystallizeable or slightly crystallizeable monomer, including thermal characteristics, structure as determined by small angle X-ray scattering, and gas permeability as a function of temperature, were examined in detail and compared to the corresponding homopolymers and copolymer systems containing two crystallizeable comonomers. The current copolymers exhibit melting point depression and, for a given average side-chain length, have lower heats of fusion than the corresponding homopolymers and crystalline/crystalline copolymers. Limited SAXS experiments revealed an increase in the d-spacings, above and below the melting point, with side-chain length consistent with expectations. The crystallites predominantly exhibit end-to-end packing similar to other poly(n-alkyl acrylates) previously studied. Poly(n-alkyl acrylates) exhibit a ‘jump’ in their gas permeability at the T_m of the side-chain lengths that is mainly caused by a switch in the side-chain morphology from crystalline to amorphous upon melting. The reduced crystallinity of the crystalline/non-crystalline copolymers results in a smaller permeation jump, which in some cases were extremely broad. All jump breadths correlate with the melting endotherms for these copolymers as determined by DSC similar to that for homopolymers and crystalline/crystalline copolymers. The magnitude of the jump correlates with the heat of fusion, irrespective of the comonomer type, in all cases.     

Poly(hydroxiphenylene sulfide)s from sulfur and phenols by activation with halogens

Summary Water is known to strongly depress the melting point of polyacrylonitrile (PAN) and acrylic copolymers. A scanning calorimetric technique has been developed that utilizes this melting point depression in probing the structure of acrylic fibers. In this report the melting and crystallization of PAN and acrylonitrile-vinyl acetate copolymers is studied as a function of water content. Addition of water continually depresses the polymer melting point until a critical water level is reached where the molten polymer separates from the water and no further reduction in the melting point is observed. Both the minimum melting point and the critical amount of water required for phase separation decreases as the level of vinyl acetate comonomer is increased. The latter relationships are examined in terms of the acrylic polymer morphology and the possibility that the water molecules become associated with the nitrile group during the melting process.     

Effects of shearing and comonomer content on the crystallization behavior of poly(butylene succinate‐co‐butylene 2‐ethyl‐2‐methyl succinate)

Poly(butylene succinate‐co‐butylene 2‐ethyl‐2‐methyl succinate) (PBSEMS) random copolymers were prepared with different comonomer compositions. The effects of shearing and comonomer content on the crystallization behavior of these copolymers were investigated at 80 °C. The thermal and morphological properties of the resulting samples were also discussed. The copolymers showed a longer induction time and a slower crystallization rate with increasing comonomer content. The promoting effect of shear on the overall crystallization behavior was more notable for those copolymers containing more 2‐ethyl‐2‐methyl succinic acid (EMSA) units. The melting temperature of ‘as‐prepared’ poly(butylene succinate) (PBS) was ca. 115 °C, while that of the copolymers varied from 112 to 102 °C. Higher comonomer contents in the copolymers gave rise to lower melting temperatures and broader melting peaks. In addition, the isothermally crystallized samples showed multiple melting endothermic behavior, the extent of which depended on the comonomer content. The copolymers showed different wide‐angle X‐ray diffraction (WAXD) patterns from that of neat PBS, depending on the comonomer content and shear applied during crystallization. With increasing comonomer content, the copolymers crystallized without shearing, showing the shifting of a diffraction peak to a higher angle, while those crystallized under shear did not show any peak shift. Copyright © 2004 Society of Chemical Industry     

Poly(alkylene oxide) ionomers: 1. Copolymerization of trioxane by gas phase mixing of comonomers and initiator

Uniform copolymers of trioxane with 1,3-dioxolane and ethyl glycidate of various comonomer compositions were prepared. A special reactor was used which allowed mixing of comonomers and initiator in the gas phase above the polymerization temperature of the mixture. Polymerization was accomplished by rapidly quenching the initiated mixture to dry ice temperature, giving polymer yields in excess of 80%. The polymers were either base treated or endcapped with propionic anhydride to obtain stable materials. The copolymers of trioxane and ethyl glycidate were treated with sodium hydroxide in aqueous dioxane at 85°C to give polyoxymethylene (POM) ionomers. The polymeric sodium salts could also be exchanged to other alkali salts of POM ionomers with various alkali chlorides while the polymers were either in suspension or in film form. Treatment of the sodium salts with acetic acid gave the free POM carboxylic acids. All polymers were characterized by their inherent viscosity, infra-red spectrum and p.m.r. spectrum.     

Changes in the morphology of cast nylon 6 through copolymerization

Correlations were made between several physical and mechanical properties and crystal morphology for copolyamides composed of caprolactam and either capryllactam or laurolactam as a minor comonomer. Incorporating a comonomer into the nylon 6 chain decreases the crystallinity and crystal size and, in addition, depresses the melting point of the polymer much more than predicted by the classical Flory theory on random copolymers. This fact, along with the change in the x-ray diffraction patterns, indicates that small amounts (up to 10 mole-%) of comonomer can enter the polymer crystals without any basic change in the α-form crystal structure. The variation of copolyamide densities with comonomer content also supports this theory. The initial moduli of the copolyamides, when tested above their glass transition temperatures, obey a linear relationship with the reciprocal of the amorphous content of the polymers. The impact strength increases dramatically with decreases in crystallinity and crystal size. Some of these materials have extremely large ultimate elongations and have glass transition temperatures below room temperature.     

Creep rupture properties of homopolymer,copolymer, and terpolymer based on poly(oxymethylene)

Polyacetal copolymers were prepared by cationic ring‐opening copolymerizations of 1,3,5‐trioxane (TOX) with 1,3‐dioxolane (DOX), and polyacetal terpolymers were prepared by terpolymerizations of TOX, DOX, and 2‐ethylhexyl glycidyl ether (EHGE). Polyacetal polymers with three different structures such as polyacetal homopolymers, polyacetal copolymers, and polyacetal terpolymers were compared in the mechanical properties and the creep characteristics, and discussed from the view point of the polymer structure. The polyacetal copolymers and the polyacetal terpolymers were determined by ¹H‐MNR measurement. About 80 mol % of DOX and EHGE amounts in feed were incorporated randomly into the each polymer. From the plots of the degree of crystallinity (X_c) versus the tensile strength, the tensile strength and crystallintiy of the polyacetal homopoymers are higher than those of the polyacetal copolymers and the polyacetal terpolymers. However, the tensile strength does not decrease linearly with a decrease in the crystallinity among the polyacetal polymers with three different structures, the polyacetal homopolymer, the polyacetal copolymers, and the polyacetal terpolymers. Creep rupture was characterized by the activation volume, υ_c, value in Zhurkov's equation, which can be estimated from the slope in the plots of load versus log (rupture time) at 80°C. The polyacetal polymers with higher molecular weight have larger values of the activation volume than those with lower molecular weight. When the activation volume values are compared among the polyacetal polymers with the same molecular weights, they increase in the following order: the polyacetal homopolymers < the polyacetal copolymers < polyacetal terpolymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Glass‐transition and melting behavior of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends

The glass‐transition temperatures and melting behaviors of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) (PET/PEN) blends were studied. Two blend systems were used for this work, with PET and PEN of different grades. It was found that T_g increases almost linearly with blend composition. Both the Gibbs–DiMarzio equation and the Fox equation fit experimental data very well, indicating copolymer‐like behavior of the blend systems. Multiple melting peaks were observed for all blend samples as well as for PET and PEN. The equilibrium melting point was obtained using the Hoffman–Weeks method. The melting points of PET and PEN were depressed as a result of the formation of miscible blends and copolymers. The Flory–Huggins theory was used to study the melting‐point depression for the blend system, and the Nishi–Wang equation was used to calculate the interaction parameter (χ₁₂). The calculated χ₁₂ is a small negative number, indicating the formation of thermodynamically stable, miscible blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 11–22, 2001     

Electrolyte‐ and pH‐responsive polyampholytes with potential as viscosity‐control agents in enhanced petroleum recovery

Low‐charge‐density amphoteric copolymers and terpolymers composed of AM, the cationic comonomer (3‐acrylamidopropyl)trimethyl ammonium chloride, and amino acid derived monomers (e.g., N‐acryloyl valine, N‐acryloyl alanine, and N‐acryloyl aspartate) have been prepared via free‐radical polymerization in aqueous media. These terpolymers with random charge distributions have been compared to terpolymers of like compositions containing the anionic comonomer sodium 3‐acrylamido‐3‐methylbutanoate. Terpolymer compositions determined by ¹³C‐ and ¹H‐NMR spectroscopy, terpolymer molecular weights and polydispersity indices obtained via size exclusion chromatography/multi‐angle laser light scattering, and hydrodynamic dimensions determined via dynamic light scattering have allowed a direct comparison of the fundamental parameters affecting the behavioral characteristics. The solution properties of low‐charge‐density amphoteric copolymers and terpolymers have been studied as functions of the solution pH, ionic strength, and polymer concentration. The low‐charge‐density terpolymers display excellent solubility in deionized water with no phase separation. The charge‐balanced terpolymers exhibit antipolyelectrolyte behavior at pH values greater than or equal to 6.5 ± 0.2. As the solution pH decreases, these charge‐balanced terpolymers become increasingly cationic because of the protonation of the anionic repeat units. The aqueous solution behavior (i.e., globule‐ to‐coil transition at the isoelectric point in the presence of salt and globule elongation with increasing charge asymmetry) of the terpolymers in the dilute regime correlates well with that predicted by the polyampholyte solution theories. An examination of the comonomer charge density, hydrogen‐bonding ability, and spacer group (e.g., the moiety separating the ionic group from the polymer chain) indicates that conformational restrictions of the sodium 3‐acrylamido‐3‐methylbutanoate and N‐acryloyl valine segments result in increased chain stiffness and higher solution viscosities in deionized water and brine solutions. On the other hand, the terpolymers with N‐acryloyl alanine and N‐acryloyl aspartate segments are more responsive to changes in the salt concentration. An assessment of the effects of the terpolymer structure on the viscosity under specified conditions of the ionic strength and pH from these studies should allow for rational design of optimized systems for enhanced petroleum recovery. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007.     

Remarks on copolymer sequence distributions

Distribution functions for the unit X in copolymers of the type are given. These functions have been used to calculate the expected degree of crystallinity using the Flory theory of copolymer crystallinity. The calculations indicate that differences can be expected between polymers prepared from XA and XX on the one hand and A and X on the other when the kinetics constants of the polymer-forming reactions are identical. In addition, it has been shown that the Flory results carry over to the terpolymer case with the propagation probability given in its terpolymerization form. The addition of more than one comonomer can lead to increased or decreased crystallinity with a given constant melting point, depending on whether the noncrystallizable monomers tend to alternate or “block” with one another.     

Melting and crystallization behavior of aliphatic polyketones

The basic crystallization and melting behavior of three aliphatic polyketones were studied using differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and optical microscopy. One resin was a perfectly alternating copolymer of ethylene and carbon monoxide, while the other two resins were terpolymers in which 6 mol % propylene was substituted for ethylene. Small decreases in the melting point and percent crystallinity of these materials were displayed with repeated melting. This behavior was attributed to light crosslinking as a result of condensation reactions occurring at temperatures in the melting range. WAXS showed that, after cooling to room temperature, the crystalline form in the copolymer was the α‐phase, while that in the terpolymers was the β‐phase. Optical microscopy revealed that the materials produce both negative and mixed birefringence spherulites under the conditions studied. SAXS measurements showed that the lamella thickness was largely a function of the temperature of crystallization. Attempts were made to measure the equilibrium melting temperature of these resins using several available techniques. The best value of the equilibrium melting temperature was concluded to be 278 ± 2°C for the copolymer. The results varied over a wide range for the terpolymers, but it is suggested that appropriate values are of order 252°C for the terpolymers. Crystallization kinetics studies, carried out under isothermal conditions using DSC, were evaluated using the Avrami equation. Results showed the Avrami exponent to lie in the range of 2–3. Spherulite growth rates were interpreted in terms of the secondary nucleation theory of Lauritzen and Hoffman. A transition from regime II to regime III was discovered. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2124–2142, 2002     

Synthesis, crystallization and tensile properties of poly(ethylene terephthalate-co-2,6-naphthalate)s with low naphthalate units content

A series of poly(ethylene terephthalate-co-naphthalate)s (PETN copolymers) with low naphthalate units content was synthesized. A melting point depression was observed, while the glass transition temperatures were slightly higher than that of Polyethylene terephthalate (PET). Crystallization rates of the copolymers decreased with increasing comonomer content. WAXD patterns showed that only PET crystals were formed. Co-crystallization behaviour was evaluated on the basis of the Wendling–Suter model. The tensile properties of the copolymers PETN 97/3 and PETN 94/6, Young's modulus yield stress and elongation at break was significantly improved compared to PET. WAXD showed that some crystalline precursor was generated during drawing of the specimens. DSC traces of the drawn specimens showed enhanced crystallization rates compared to that of the original amorphous specimens.     

Phase equilibria in SBR/polybutadiene elastomer blends: Application of Flory–Huggins theory

Blends of anionically-polymerized polybutadiene (BR) and styrene–butadiene copolymer (SBR) must be treated as mixtures of terpolymers and tetrapolymers, due to the presence of three different BR isomers: cis-1,4, trans-1,4, and vinyl-1,2. Moreover, in the absence of specific interactions or chemical reactions that strongly influence miscibility, structural characteristics of the component polymers, such as BR isomer content, SBR styrene content, monomer sequence distribution, molecular weight, and molecular weight distribution, are expected to have an increased role in determining the blend miscibility characteristics. Small angle neutron scattering (SANS) studies of SBR/BR blends have resulted in the computation of the monomer–monomer segmental interaction energetics via a Flory–Huggins treatment. This allows quantitative prediction of miscibility behavior as a function of polymer structure. We have used the Flory–Huggins chi parameters, describing the styrene/cis-1,4, styrene/trans-1,4, and cis-1,4/trans-1,4 segmental interactions, to identify certain blend combinations expected to exhibit phase transitions in an experimentally accessible temperature range. The appropriate polymers were synthesized, solution blended, and the blends analyzed via optical microscopy and thermal analysis. Our results show that the blend behavior, observed experimentally, is consistent with the calculated cloud point curves. © 1994 John Wiley & Sons, Inc.     

Phase behavior of poly(ε-caprolactone)/ poly (vinylidene fluoride) blends

The miscibility of blends of poly (ε-caprolactone) (PCL)/poly(vinylidene fluoride) (PVDF) was studied by measuring the cloud point, melting point depression and crystallization kinetics. Lower critical solution temperature (LCST) behavior was observed at PCL-rich compositions, whilst it was not observed at high compositions of PVDF. However it is possible that an LCST could exist below the melting point of PVDF. From analysis of the melting point depression, the Flory interaction parameter x₁₂, was calculated from the Nishi-Wang equation and the value was found to be-1.5. The crystallization rate of PCL increased with increasing amount of PVDF in the blend. The spinodal curve for PCL/PVDF blends was simulated by using the lattice-fluid theory.     

Multicolor emission and thin film transistor properties of 1,8-diethynylcarbazole-based conjugated copolymers

1,8-Carbazole-based conjugated copolymers are synthesized by the Sonogashira polycondensation between the 1,8-diethynylcarbazole derivative and dibromo comonomers. The resulting polymers are fully characterized by GPC, and ¹H NMR and IR spectroscopies, and their high thermal stability with the 5% decomposition temperature exceeding 350 °C by thermogravimetric analyses. The optical properties of the carbazole polymers reveal that the comonomer structures significantly affect the absorption and emission spectra. For example, a bathochromic shift of the spectra is achieved when electron-accepting comonomers are selected, finally leading to the production of additive primaries. The mixtures of three carbazole polymers with red, green, and blue emission colors provide a white light emission both in solutions and in thin solid films. In addition, the thin film transistor properties of the carbazole polymers are investigated. The 1,8-carbazole-based polymers display an intermediate mobility between the 2,7-carbazole and 3,6-carbazole-based counter polymers. All these results suggest the potential application possibilities of the 1,8-carbazole-based conjugated polymers in optoelectronic devices.     

Fourier transform ir studies of the degradation of polyacrylonitrile copolymers—I: Introduction and comparative rates of the degradation of three copolymers below 200°c and under reduced pressure

Polyacrylonitrile (PAN) and copolymers of PAN containing comonomers of vinyl acetate (VAc), methacrylic acid (MAA), acrylamide (AM) and other acrylics are important precursors to the formation of carbon fibers. Fourier transform IR spectroscopy has proved to be an excellent technique with which to study the degradation of these polymers in the initial stages where cyclization of the polymer chain takes place. In this communication we present comparative rate studies of the degradation of three PAN copolymers containing approx. 4 wt% of VAc, MAA and AM respectively. The rate of degradation is observed to be markedly dependent upon the chemical structure of the comonomer.     

Extreme thermal behaviors of polytetrafluoroethylene and random tetrafluoroethylene fluorinated copolymers

By differential scanning calorimetry (DSC), the thermal behavior of polytetrafluoroethylene (PTFE) and random fluorinated copolymers of tetrafluoroethylene-containing hexafluoropropylene (FEP copolymers) or perfluoroalkylvinylether (PFA copolymers) as comonomers was investigated. Rapid-melt crystallization was employed to provide new data about the problem of inclusion/exclusion of co-units from the homopolymer crystal lattice. Equilibrium melting points were determined and tested in light of random copolymer predictions. Both nonequilibrium and equilibrium behaviors seem to point to the inclusion of  CF₃ side groups and the exclusion of larger ones. Finally, a new value of the equilibrium melting point of PTFE is given, in good agreement with those present in the literature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 919–925, 1999