Increasing Comonomer Content Research Articles

Effects of molecular structure and temperature field on the crystallization behavior of poly(tetrafluoroethylene-co-perfluoroalkylvinyl ether)

Despite the wide industrial application of poly(tetrafluoroethylene-co-perfluoroalkylvinyl ether) (PFA) in semiconductor processing, its crystallization behavior has little been studied. In this work, three PFA resins with similar molecular weight but different comonomer content and distribution were synthetized. Then the non-isothermal crystallization kinetics and crystalline structures were studied by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction systematically. It is found that the incorporation of comonomers destroys the chain regularity and reduces the crystallizability of PFA thermodynamically, while the comonomer insertion improves the chain flexibility to accelerate the crystal growth dynamically. When the comonomer content of PFA is low, both the nucleation and growth rates are quite fast, which is favorable for the formation of spherulite. As the comonomer content increases or distribute uniformly in the chain, the nucleation rate declines notably and the side groups distort the crystal cell to increase the spacing of [100] plane. Moreover, two-dimensional growth mode is dominant to form bundle-like structure when crystallizing at slow cooling, where nucleation is suppressed by growth. But three-dimensional symmetrical spherulite can be activated and perfected at high cooling rate due to the initiation of substantial nucleation sites. This unique crystallization behavior is opposite to that of conventional polymers, providing a guidance for the polymerization and processing of PFA.

Crystallization Behavior of Isotactic Propene-Octene Random Copolymers

The crystallization behavior of random propene-octene isotactic copolymers (iPPC8) prepared with a homogeneous metallocene catalyst has been studied. Samples of iPPC8 with low octene content up to about 7 mol% were isothermally crystallized from the melt at various crystallization temperatures. The samples crystallize in mixtures of the α and γ forms of isotactic polypropylene (iPP). The relative amount of γ form increases with increasing crystallization temperature, and a maximum amount of γ form (fγ(max)) is achieved for each sample. The crystallization behavior of iPPC8 copolymers is compared with the crystallization from the melt of propene–ethylene, propene–butene, propene–pentene, and propene–hexene copolymers. The results show that the behavior of iPPC8 copolymers is completely different from those described in the literature for the other copolymers of iPP. In fact, the maximum amount of γ form achieved in samples of different copolymers of iPP generally increases with increasing comonomer content, while in iPPC8 copolymers the maximum amount of γ form decreases with increasing octene content. The different behaviors are discussed based on the inclusion of co-monomeric units in the crystals of α and γ forms of iPP or their exclusion from the crystals. In iPPC8 copolymers, octene units are excluded from the crystals giving only the interruption effect that shortens the length of regular propene sequences, inducing crystallization of the γ form at low octene concentrations, lower than 2 mol%. At higher octene concentration, the crystallization of the kinetically favored α form prevails.

Composition, hydrogen bonding and viscoelastic properties correlation for ethylene/α,ω-alkenol copolymers

The influence of composition of ethylene/ α,ω -alkenol ( α,ω -alkenol = 10-undecen-1-ol or 9-decen-1-ol) copolymers on comonomer distribution and dynamic rheological properties were investigated. Thermal fractionation revealed formation of multiple peaks corresponding to the presence of methylene sequences of different length in copolymers. The share of fraction with shorter methylene sequence increased with increasing comonomer content. It turned out that viscoelastic behavior of ethylene/ α,ω -alkenol copolymers was dependent on comonomer content incorporated into the polymer chain. The relaxation time of reptation increased with increasing comonomer content what confirmed that comonomer units acted as physically crosslinking agent. FT-IR investigation proved the appearance of inter- and intramolecular hydrogen bonds in ethylene copolymers with α,ω -alkenols. Higher relative content of inter- and intramolecular hydrogen bonds was observed in α,ω -alkenol with a longer hydrocarbon chain. In addition, activation energy of flow increased with increasing of the comonomer content. Moreover, incorporation of α,ω -alkenols into the polymer chain resulted in a decrease of the packing length of copolymers with increasing comonomer content, what proved that the inter- and intramolecular hydrogen bond played a significant role in viscoelastic properties. • Amount of α,ω -alkenol incorporated in copolymers affected comonomer distribution. • The content of α,ω -alkenol played a key role in rheological behavior of copolymers. • The FT-IR study showed the presence of hydrogen bonds in E/ α,ω -alkenol copolymers. • The effect of hydrogen bonding is dependent on structure of α,ω -alkenol comonomer.

Mechanical Properties and Elastic Behavior of Copolymers of Syndiotactic Polypropylene with 1-Hexene and 1-Octene

The mechanical properties of copolymers of syndiotactic polypropylene (sPP) with 1-hexene and 1-octene have been studied and correlated with the structural transformations occurring during stretching and relaxation. These copolymers crystallize in disordered modifications of form I of sPP, with crystallinity, melting, and glass-transition temperatures that decrease with increasing comonomer content. All copolymers show remarkable mechanical properties and elastic behavior, with great improvement of flexibility and ductility with respect to the sPP homopolymer already at small comonomer concentrations. For low comonomer content up to 4–5 mol %, the elastic recovery is associated to a reversible conformational phase transition between the trans-planar form III or the trans-planar mesophase and the helical form II, which gives an enthalpic contribution to the elasticity. As the comonomer content increases, the trans-planar conformation is progressively destabilized and the observed elastic properties are not associated with any conformational transformation during stretching and relaxation. In these cases, copolymers behave as conventional thermoplastic elastomers where elasticity is purely entropic and crystals only act as topological constraints of the elastomeric network. These copolymers represent an exemplary case of the possibility to combine in the same materials desired and apparently incompatible physical properties of elasticity, crystallinity, and strength by controlling the crystallization behavior, achieved by tailoring the chemical structure in the synthetic process.

The Effects of Enhancing the Crosslinking Degree in High Internal Phase Emulsion Templated Poly(dicyclopentadiene)

AbstractThe effect of enhancing the crosslinking degree in polyHIPEs made from dicyclopentadiene by additionally using a crosslinking comonomer is described. Foams of 80% porosity with 10–40 wt% comonomer content in the continuous phase are prepared and show similar porosities and morphological characteristics as foams prepared with dicyclopentadiene alone. Assessing the mechanical properties reveals that the ductility is decreasing while the stiffness of the samples is increasing with increasing comonomer content. The foams containing the crosslinking comonomer take up at least five times their mass of toluene thereby swelling to at least 30 vol%. Upon drying of the swollen specimens, their initial shape and porosity are recovered. This feature distinguishes them from polyHIPEs made from dicyclopentadiene only.

Copolymerization of Ethylene and Fluoroalkylnorbornene Using Highly Active ansa‐(Fluorenyl)(amido)titanium‐Based Catalysts

AbstractFluoroalkyl‐functionalized semi‐crystalline polyolefin is obtained by the copolymerization of ethylene and 2‐nonafluorobutyl‐5‐norbornene using ansa‐dimethylsilylene(fluorenyl)(amido)titanium complexes 1a and 1b as catalysts. The copolymerization proceeds with a moderate activity affording a copolymer with high fluorine content up to 5.7 mol% (22 wt%). The melting point decreases from 134 to 82 °C according to the increase of comonomer content. Observation of a single melting point of the copolymer obtained from complex 1b clearly shows the uniform structure of the copolymer, whereas complex 1a gives copolymer with two melting points. The number‐averaged molecular weight of the copolymer reaches over a 105 order of magnitude, which enables the formation of thin film via solvent casting process. Tensile moduli of these copolymers are greatly affected by both molecular weight of the copolymer and comonomer content, and almost comparable with that of low‐density linear polyethylene.

Frontal Ring-Opening Metathesis Copolymerization: Deviation of Front Velocity from Mixing Rules.

Frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD) shows promise for rapid, energy-efficient manufacturing of high-performance polymers and composites. Copolymerization in FROMP allows for systematic modification of materials properties while retaining the benefits of the DCPD system such as low cost of the monomer and excellent mechanical properties of the resulting polymer. While the copolymerization reactivity and copolymer properties generally exhibit monotonic dependence on monomer composition as predicted by simple, empirical mixing rules, we discovered that the frontal copolymerization behavior of DCPD with a dinorbornenyl (di-NBE) cross-linker deviates significantly from that expected relationship. As the comonomer content increases, the FROMP reaction shows a nonmonotonic increase in front velocity with intermediate compositions 40% faster than either pure component. We then studied the behavior of a series of comonomers, analyzed several factors (such as thermodynamic and kinetic properties) that might influence front velocity, and found that the nonmonotonic trend mainly results from the cross-linked structure. This copolymerization system provides a promising strategy to tune materials properties (such as glass transition temperature) and simultaneously improve the efficiency in FROMP-based materials manufacturing.

Crystallization and mechanical properties of metallocene made 1-butene-pentene and 1-butene-hexene isotactic copolymers

The structure and the mechanical properties of metallocene-made butene-pentene (iPBC5) and butene-hexene (iPBC6) isotactic copolymers are studied. The effect of the presence of pentene and hexene units on the crystallization behavior and the mechanical properties of isotactic polybutene (iPB) is analyzed. All iPBC5 copolymers crystallize from the melt in form II of iPB, which transforms into form I by aging at room temperature. On the contrary, in iPBC6 copolymers the presence of hexene units stabilizes the form II and, for hexene concentrations higher than 11 mol%, prevents the transformation of form II into form I at room temperature. Both iPBC5 and iPBC6 copolymers show mechanical behavior of highly flexible and ductile materials with enhanced ductility compared to iPB, with values of stress at yielding and of Young's modulus that decrease with increasing comonomer content. In all the iPBC5 copolymers, form II crystallized from the melt transforms into form I by stretching, whereas in iPBC6 copolymers form II is stabilized and the transformation of form II into form I by stretching is completely inhibited at high hexene concentrations.

Relationships among lamellar morphology parameters, structure and thermal behavior of isotactic propene-pentene copolymers: The role of incorporation of comonomeric units in the crystals

The correlations between the thermal behavior and the crystal morphology of isotactic propene-pentene copolymers were studied through wide-angle (WAXS) and small-angle (SAXS) X-ray diffraction. Copolymers with pentene concentration lower than 11 mol% crystallize in the α form of isotactic polypropylene (iPP) and a concomitant decrease of melting temperature and of the thickness of crystalline lamellae with increasing pentene concentration has been observed. At higher pentene concentrations the trigonal form of iPP crystallizes and a neat increase crystalline lamellar thickness and of the long period, with a slower decrease of melting temperature and crystallinity have been observed. These results have been treated in the general framework of copolymer crystallization theories, using a method proposed by Crist and correlated with the different level of inclusion of pentene co-units in the crystals of α and trigonal forms. For copolymers with pentene concentration lower than 11 mol% pentene co-units are in part incorporated in the crystals of α form. For higher pentene concentrations the decrease of melting temperature coupled with the increase of lamellae thickness with increasing comonomer content is the hallmark of the almost total inclusion of pentene co-units in the crystals of the trigonal form.

Synthesis of Metallocene Catalyzed Ethylene 1,7-Octadiene Copolymer: Effect of Copolymerization on Polymer Properties

In this article, metallocene catalyzed polyethylene homopolymer and ethylene 1,7-octadiene copolymers were synthesized and the produced polymers were characterized. The results show that these polymers were high density polyethylene. The effect of comonomer 1,7-octadiene on thermal, mechanical, and rheological properties of the polymers was investigated. The molecular weight, melting temperature (Tm), d-spacing, crystallite size, and % crystallinity (% Xc) decrease with the increase in comonomer content. Polyethylene homopolymer and copolymer exhibit cold drawing processes. The tensile stress-strain plots show multiple necks. A reduction in tensile modulus, strength, and strain at break is seen for copolymers compared to homopolymer. The effect of comonomer content on dynamic and extensional rheology of the polymers was also studied. In addition, Direct Current conductivity and dielectric property of the polymers were also reported. The results were interpreted in terms of mainly polymer type, molecular weight, and crystallinity.

Soluble polybenzimidazoles with intrinsic porosity: Synthesis, structure, properties and processability

ABSTRACTWe have explored two novel comonomers, namely, 4,16‐dicarboxyl[2.2]paracyclophane and 5,5′,6,6′‐tetraamino‐3,3,3′,3′‐tetramethyl‐1,1′‐spirobi[indane], for the synthesis of co‐polybenzimidazoles (co‐PBIs) with intrinsic porosity. Both these monomers possess twisted structures that can lead to “awkward” macromolecular shapes that cannot pack efficiently. The consequences of introducing these two monomers on the structure and properties of PBIs are reported. The random copolymers synthesized are amorphous and possess glass transition temperatures (Tgs) greater than 400 °C. Tg decreases with increasing comonomer content indicating an increase in fractional free volume. The copolymers have low surface area. TEM and BET measurements show evidence of mesopore formation. The copolymers show significant carbon dioxide adsorption. Single chain molecular dynamics simulation of 24‐mer repeat units shows intramolecular void spaces arising as a result of distorted polymer chain with reduced conformational mobility. These studies define a new synthetic strategy for “bottoms‐up” synthesis of PBIs with intrinsic porosity. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1046–1057

Effect of Random Ethylene Comonomer on Relaxation of Flow-Induced Precursors in Isotactic Polypropylene

The effect of comonomer on structure and relaxation of flow-induced precursors was investigated in a series of isotactic polypropylene and random propylene–ethylene copolymers. The polymers were subjected to flow by fiber pulling and allowed to relax above their nominal melting temperature for specific times. The type of morphology developed after cooling revealed whether flow-induced precursors were still present or the melt had fully re-equilibrated. Precursors were long-lived and, at fixed temperature, decayed significantly faster with higher ethylene content. The critical time for precursor relaxation followed an Arrhenius-type dependence with temperature. The apparent energy of activation for precursor dissolution decreased with increasing comonomer content, indicating that the rate-limiting step of the relaxation process becomes less difficult with higher ethylene fraction. This effect is attributed to ethylene counits acting as disruptors of precursor structure and is discussed in terms of quasi-cr...

Bulk copolymerization of 1,3,5-trioxane and 1,3-dioxolane in presence of phosphotungstic acid catalyst and tetrahydrofuran as retarder: crystallinity and thermal properties

In this study, cationic ring opening in situ copolymerization of 1,3,5-trioxane (TOX) and 1,3-dioxolane (DOX) occurred during bulk polymerization in the presence of phosphotungstic acid as a catalyst. In another part of the study, copolymerization occurred in the presence of retarder tetrahydrofuran (THF), and its effect on the crystallization and thermal stability of the samples was also investigated. The findings from 1HNMR spectrometry indicated that the synthesized samples of random acetal copolymer are comprised of an independent oxyethylene unit in an oxymethylene main-chain sequence. The findings from DSC indicated that crystallinity decreases with increasing comonomer content. Furthermore, the sample with retarder revealed greater crystallinity than the samples without retarder. From TGA results, it was revealed that the sample with retarder caused a larger quantity of comonomer to enter the chain and increased the thermal stability compared to the samples without retarder.

Correlation Between Physicomechanical and Swelling Properties of Weakly Basic Copolymer Hydrogels Based on (Meth)acrylate Polycations as New Smart Materials

2‐Hydroxyethyl methacrylate (HEMA) is incorporated to N,N‐dimethylaminoethyl methacrylate (DMAEMA) fabricating a series of stimuli‐responsive copolymer hydrogels by free radical copolymerization. The increasing comonomer content via adding more HEMA results in a higher network density and, therefore, a lower equilibrium swelling ratio. The uniaxial compressive testing results showed that increasing HEMA in the feed improved the mechanical strength of P(DMAEMA‐co‐HEMA) hydrogels. As HEMA increased, the elastic modulus as well as the effective crosslinked chain density increased. The work strives to provide method to tune mechanical and physical properties for weakly basic copolymer hydrogels based on (meth)acrylate polycations, which is hopefully to guide the design of hydrogels with desirable properties. image

PNVCL‐PEGMA nanohydrogels with tailored transition temperature for controlled delivery of 5‐fluorouracil

ABSTRACTSensitive nanohydrogels were prepared via surfactant free emulsion copolymerization of N‐vinylcaprolactam and poly(ethylene glycol) methyl ether methacrylate, and either N‐vinylpyrrolidone (VP) or 2‐methacryloyloxybenzoic acid (2MBA) to adjust the transition temperature (Ttr). The crosslinker ethylene glycol dimethacrylate was used for the polymer network construction. The resulting nanohydrogel sizes are between 120 and 300 nm. ρ‐Parameter, obtained from light scattering studies, suggests that core‐sell nanogels of flexible chains were obtained. Ttr increases with increasing comonomer content (VP or 2MBA) and decreases with decreasing pH for 2MBA containing nanohydrogels. Nanohydrogels containing 15.5% of 2MBA exhibit Ttr close to 38 °C. Nanogels are able to control the release of the loaded antineoplastic drug 5‐fluorouracil. For the prepared T/pH‐sensitive nanogels, the release is slower at pH 7.4 and 37 °C than at tumor conditions: pH 6 and 40 °C. Mathematical models were applied to evaluate the kinetics of drug release; Peppas model fitted best indicating a Fickian diffusion trough a sphere. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2662–2672

Crystallization behavior and mechanical properties of copolymers of isotactic poly(1-butene) with 1-octene from metallocene catalysts

The crystallization behavior and the mechanical properties of random isotactic butene–octene copolymers (iPBC8) prepared with a metallocene catalyst are presented. Samples with low octene concentrations, up to nearly 6 mol%, crystallize from the melt in form II. In these samples octene units stabilize the tetragonal form II, decelerating or even preventing the transformation of form II into the trigonal form I. Octene concentrations higher than 7 mol% prevent crystallization of the samples from the melt and the obtained amorphous samples crystallize by aging at room temperature in mixtures of form II and form I'. The sample with the highest octene concentration of 11.5 mol% crystallizes surprisingly from the amorphous phase directly in the pure form I'. In these samples, form I' crystallized from the amorphous phase transforms into form II by stretching. Form II transforms back into form I' upon releasing the tension. Therefore, in samples where form I' is favored in powder samples, form II is favored in stretched fibers. The transformation of form I into form II by stretching and the back transformation of form II into form I after releasing the tension is unusual for isotactic polybutene (iPB) and rather unexpected. The presence of octene comonomer units also affects the mechanical behavior of iPB and produces increase of flexibility and ductility with increasing comonomer content, and samples with octene concentration higher than 6–7 mol% show unexpected remarkable elastomeric properties. The formation of crystals of form II or form I' during aging allows development of elastomeric properties and enhancement of mechanical strength. The elastic properties are associated to the reversible crystal–crystal phase transition between form II and form I occurring during stretching and when the tension is removed.

Interplay between a Strong Memory Effect of Crystallization and Liquid–Liquid Phase Separation in Melts of Broadly Distributed Ethylene–1-Alkene Copolymers

Narrow metallocene-made random ethylene copolymers display a strong memory effect of crystallization above their equilibrium melting point akin to the melt memory effect observed in model ethylene–1-butene copolymers. The onset temperature for self-nucleation or surviving self-seeds displays a bell shape with increasing comonomer content with a maximum at ∼2 mol % branches. Self-seeds do not survive at temperatures above the equilibrium melting point for homopolymers and copolymers either with very low branching or with a branching content >4.5 mol %. The self-seeds are associated with clusters of ethylene sequences that remain in the melt in close proximity and accelerate a subsequent crystallization, as observed by higher crystallization peak temperatures and higher nucleation density. Contrasting this behavior, commercial ethylene–1-alkene copolymers with a broad, bimodal comonomer distribution display an inversion of the crystallization rate in a range of melt temperatures where narrow copolymers show...

Effect of Solvent Type on High‐Temperature Thermal Gradient Interaction Chromatography of Polyethylene and Ethylene–1‐Octene Copolymers

The effects of the solvent type and operation conditions on the high‐temperature thermal gradient interaction chromatography (HT‐TGIC) of ethylene homopolymers, ethylene–1‐octene copolymers, and their blends are investigated. While the HT‐TGIC profiles of single polymers measured with 1,2,4‐trichlorobenzene (TCB) and chloronaphthalene (CN) are similar, they are always narrower when o‐dichlorobenzene (ODCB) is used, particularly for samples with lower 1‐octene fractions. Significant differences between the experimental and the calculated profiles of binary blends are observed with all three solvents, but better peak separation is seen when the ODCB is used. Having higher fractions of a 1‐octene‐poor component in the blend causes a more significant distortion of the shape expected for the peak from the component with the higher 1‐octene fraction. The effect of the molecular weight on HT‐TGIC profiles is also studied using samples with the same comonomer content and different molecular weights. Samples with low molecular weight have broader distributions and significant lower‐temperature tails, particularly when TCB is used. Chain crystallization after adsorption effects may also play a minor role for low‐comonomer samples. Finally, HT‐TGIC profiles are compared with their equivalent crystallization elution fractionation (CEF) profiles. The HT‐TGIC curves are broader than the equivalent CEF profiles, but these differences decrease as the comonomer content increases. image

Study on the crystallization of poly(butylene azelate-co-butylene succinate) copolymers

Poly(butylene azelate-co-butylene succinate) samples with different azelate/succinate ratios were synthesized and characterized. Calorimetric data indicate a semicrystalline character for all copolyesters studied and a melting point depression that could be interpreted on the basis of complete exclusion of comonomers from well organized lamellae. Crystallization first occurred through the succinate rich segments, which resulted in a peculiar behavior of copolymers having an intermediate composition. In this case, crystallization of azelate segments was paradoxically enhanced when samples were quenched. Equilibrium melting temperatures significantly decreased with increasing comonomer content compared to those of the corresponding homopolymers. Incorporation of comonomers had a distinct effect on the secondary nucleation constant depending on the composition as deduced from Lauritzen and Hoffman analysis. Thus, azelate units clearly increased the nucleation constant of copolymers rich on succinate units, whereas the incorporation of succinate units had a lower influence on the constant of copolyesters having high azelate content.

Catalytic performance of ZnO nanoparticle in formation of LLDPE/ZnO nanocomposites

ZnO nanoparticle was used for preparing supported catalyst, which was applied in copolymerization of ethylene and 1-octene to obtain LLDPE/ZnO nanocomposite. There were two different impregnation methods (in situ and ex situ) in preparing the nano-ZnO supported catalyst. The investigation to compare both methods was conducted by employing various 1-octene initial concentrations in copolymerization. It was found that a heterogeneous catalytic system comprised a supported catalyst, prepared by in situ impregnation, provided higher catalytic activities and 1-octene incorporations compared to those of ex situ impregnation under similar condition perhaps due to closer similarity to a homogeneous system. For the ex situ impregnation, it was found that when zirconocene was directly impregnated onto the support, the catalytic activity decreased. This was due to zirconocene close vicinity to the supports and even deep into the support structure proved by XPS and TGA measurements. Therefore, it was more inaccessible to monomer attack and reducing the catalytic activity. The separate study on each catalytic system relating to the comonomer effect was also conducted by applying initial comonomer concentrations varied between 0 and 18 mmol. The increase in catalytic activity with increasing comonomer concentration can be considered as a positive comonomer effect, and the opposite was true for a negative comonomer effect. It was found that both positive and negative comonomer effects occurred in in situ impregnation and ex situ impregnation systems with Zn/(Al + Zr) support, whereas only positive comonomer effect was found in an ex situ impregnation system with Zn/Al support. This suggested that the comonomer effect was varied according to the nature of each system. The polymer properties, such as relative crystallinity and thermal properties were also investigated and found to alter with 1-octene concentration.