Increasing Comonomer Content Research Articles

Comparative study on the mechanical and fracture properties of acrylic bone cements prepared with monomers containing amine groups

In this work, the effect of the incorporation of comonomers containing amine groups on the mechanical and fracture properties of acrylic bone cements was studied. Cements were prepared with either diethyl amino ethyl acrylate (DEAEA), dimethyl amino ethyl methacrylate (DMAEM) or diethyl amino ethyl methacrylate (DEAEM) as comonomer in the liquid phase. It was found that strength and modulus decreased with increasing comonomer content in the bending and compressive tests. It was also observed that fracture toughness (KIC) and the critical strain energy release rate (GIC) increase with increasing comonomer concentration and are significantly higher compared to the control formulation. The mechanical and fracture properties of cements were also evaluated after soaking the specimens in Simulated Body Fluid (SBF) for 3 and 6 months. It was found that the mechanical properties of cements decreased when the samples were stored in SBF, although the impact strength increased in the first 3 months and then decreased. SEM micrographs were in agreement with the results obtained during mechanical characterization as the increase in toughness was confirmed by the appearance of ductile tearing pattern which is associated with plastic deformation.

Random copolymers of propylene with 1,5-hexadiene containing only cyclopentane units in main chain and tailoring structure and mechanical properties of the copolymers

In the presence of [Ph3C][B(C6F5)4] and Triisobutylaluminium, dimethyl pyridylamidohafnium complex exhibited remarkable catalytic activity in the copolymerization of propylene with 1,5-hexadiene, affording high molecular weight copolymers with unimodal molecular weight distributions. More noticeably, the resultant copolymers contain absolutely cyclo-group in the polymer chains without pendent vinyl groups and crosslinking. The solid state structures and properties of the homogeneous copolymers were studied by examining melting behavior, wide-angle X-ray scattering, and tensile deformation. Chain microstructures were analyzed by 13C NMR spectra, and further confirmed by the measurement of reactivity ratios of the two monomers. These copolymers display a random distribution of the comonomer, and crystallinity decreases with increasing comonomer content. The copolymers contain variable amounts of comonomeric units, showing desired physical properties ranging from thermoplastic to elastoplastomeric to elastomeric.

Responsive P(NIPAM-co-NtBAM) microgels: Flory–Rehner description of the swelling behaviour

In the present work, a systematic series of poly(N-isopropylacrylamide)(NIPAM) –poly(N-tert-butylacrylamide) (NtBAM) copolymer microgels is prepared by surfactant-free emulsion polymerisation using N,N′-methylenebis(acrylamide) (BIS) as cross-linker. The thermoresponsive behaviour of these colloids was studied in detail applying different scattering techniques. The swelling curves obtained on the basis of photon correlation spectroscopy (PCS) are analysed using the theoretical model of Flory and Rehner. The PCS measurements reveal the narrow particle size distribution of the poly(NIPAM-co-NtBAM) microgels and a decreasing hydrodynamic radius as well as a decreasing volume phase transition temperature (VPTT) with increasing comonomer content. The description of the swelling ratio α as a function of temperature by the Flory–Rehner theory for uncharged homopolymer gels was only partially satisfying and fails for higher comonomer contents. In addition, small angle neutron scattering (SANS) is used to study the internal network structure of these microgels, and the polymer network is characterised in terms of the correlation length ξ. Above the transition temperature, only interfacial scattering from the totally collapsed particles in water can be observed. Due to a certain surface roughness of the copolymer microgels, the SANS profiles beyond the VPTT were fitted using a modified Porod law.

Triple crystallization behavior of fractionated ethylene/α-olefin copolymers of different catalyst type

Non-isothermal crystallization processes in fractions of Ziegler-Natta (ZN) and single site (SS) based ethylene/1-butene and ethylene/1-hexene copolymers have been studied by differential scanning calorimetry (DSC). Fractionation of used copolymers was done according to molar mass (MM) and composition (comonomer content). It was observed in DSC scans that for fractions with high MM (larger than 10 kg/mol) in addition to the main high-temperature crystallization peak (HTCP), a very-low temperature crystallization peak (VLTCP) is present at temperatures in between 60–75 °C. Such peak is absent for the first fractions having very-low MM. The partial crystallinity and peak temperatures, obtained from VLTCP, increase with MM and level off at MM around 60–100 kg/mol. It was found that the crystallinity as related to the area of the VLTCP is catalyst type dependent, and is higher for the SS catalyst compared to the ZN. Peak temperature of VLTCP linearly decreases with increasing comonomer content at fixed MM while the partial crystallinity practically does not change with comonomer content.

Continuous Cooling Curves Diagrams of Propene/Ethylene Random Copolymers. The Role of Ethylene Counits in Mesophase Development

A simple method to investigate polymer crystallization during fast cooling, based on in situ temperature acquisition and ex-situ structural characterization, is proposed. The approach enables one to obtain the continuous cooling curve (CCC) diagrams, widely used in metallurgy but seldom adopted for semicrystalline polymers. This method is here exploited to gain new insights on polymorphic behavior of quenched polypropylene and its copolymers with ethylene. Experimental CCC diagrams, covering a wide range of crystallization temperatures in the domains of monoclinic structure and mesophase, are obtained for the first time. The role of counits in affecting the development of the mesophase upon fast cooling is assessed: the critical cooling rate above which a predominant fraction of mesomorphic form is generated significantly decreases with increasing comonomer concentration. This is due to the remarkable hindrance of ethylene counits on the crystallization kinetics of the R-form, which indirectly favors the development of the less affected mesophase. We expect that this concept can be extended to any kind of defects that disturbs the structuring of the monoclinic phase.

Lattice sizes, crystallinities, and spacing between amorphous chains - characterization of ethene-/ɑ-olefin copolymers with various comonomers and comonomer contents measured by wide angle X-ray scattering

AbstractEthene-/ɑ-olefin copolymers having a wide range of comonomer contents with comonomers between 4 and 26 carbon atoms in length were characterized by wide angle X-ray scattering (WAXS). It was found that the crystallinities matched fairly well with the crystallinities from DSC and volumetric measurements. An increase of the crystal lattice size was found with increasing comonomer content and comonomer length. Both are attributed to the formation of defects around these short-chain branches in the crystal lattice, which widen it. Increasing the cooling time will lead to a more densely packed crystal structure, if the quenched structure is distorted, i.e. if the sample contains comonomer. A higher molar mass Mwwidens the average space between chains in the amorphous phase as well as the addition of comonomer. The latter finding is explained by the increasing number of chain ends introduced by the comonomer which increases the free volume in the sample because of the worse amorphous packing of the chain ends.

Crystallite dimensions - characterization of ethene-/ɑ-olefin Copolymers with various comonomers and comonomer Ccontents measured by small- and wide angle X-ray scattering

AbstractEthene-/ɑ-olefin copolymers having a wide range of comonomer contents and comonomers between 4 and 26 carbon atoms in length were characterized by wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS). The data was evaluated with respect to the crystallite size. The half-width of the main crystallite peaks was transformed into the crystallite size s110 and s200 using the Scherrer equation. It was found to decrease with increasing comonomer content. The crystal lamella thickness was determined from the long period and the crystallinity of the samples. The crystal lamella thickness was found to decrease with decreasing crystallinity following a 3rd order polynomial. This means that the introduction of SCBs leads to a decrease of the crystallite size. A higher Mwleads to an increase of the lamella size in comparison to lower molecular samples with the same crystallinity. The lamella thickness is limited by the average distance between two short-chain branches which is dependent on the comonomer content.

Synthesis of linear low density polyethylene with a nano-sized silica supported Cp2ZrCl2/MAO catalyst

A nano-sized silica supported Cp2ZrCl2/MAO catalyst was used to catalyze the copolymerization of ethylene/1-hexene and ethylene/1-octene to produce linear low-density polyethylene (LLDPE) in a batch reactor. Under identical reaction conditions, the nano-sized catalyst exhibited significantly higher polymerization activity, and produced copolymer with greater molecular weight and smaller polydispersity index than a corresponding micro-sized catalyst, which was ascribed to the much lower internal diffusion resistance of the nano-sized catalyst. Copolymer density decreased with the increase of polymerization temperature, probably due to the decrease of reactivity ratio r1 and ethylene solubility with increasing temperature. Polymerization activity of the nano-sized catalyst increased rapidly with increasing comonomer concentration. Ethylene/1-octene exhibited higher polymerization activity and had a stronger comonomer effect than ethylene/1-hexene.

Chemical composition distribution study in ethylene/1‐hexene copolymerization to produce LLDPE material using MgCl2‐TiCl4‐based Ziegler‐Natta catalysts

AbstractThe characteristic features of LLDPE polymerization with ZN catalyst are the time drift effect during polymerization and the bending effect when trying to decrease density of the copolymer by adding more comonomer to the polymerization. The time drift in LLDPE polymerization is revealed by a constant decrease of comonomer incorporation during polymerization time. The bending is revealed by difficulties in lowering the density of LLDPE material below the density of 920 kg/m3. With increasing comonomer content during polymerization, the density does not decrease, but the soluble fraction increases. To try to observe if these phenomena are connected, two types of catalysts, SiO2 supported and precipitated MgCl2 ZN catalysts, were studied. A short time (10 min) and an extended time (60 min) copolymerization test series where the polymerizations were performed in the presence of a gradually increasing comonomer amount. Both catalysts show a strong bending when density is presented as a function of 1‐hexene both in 10‐ and 60‐min polymerization, indicating no connection between time drift and bending. The density, melting point, and crystallinity results all indicate that both catalysts are making similar copolymer material with identical chemical composition distribution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Study of Very Low Temperature Crystallization Process in Ethylene/α‐Olefin Copolymers

AbstractSummary: The crystallization behavior of Ziegler‐Natta (ZN) and single site (SS) based ethylene/1‐butene and ethylene/1‐hexene copolymers and SS copolymer fractionated by composition and molar mass (MM) has been studied by differential scanning calorimetry. It was observed that in addition to the high temperature crystallization peak (HTCP), and for ZN copolymers in addition also to low temperature crystallization peak (LTCP), a very‐low temperature crystallization peak (VLTCP) is present at temperatures in between 60–75 °C. Peak temperature of VLTCP, TVLTCP, decreases with increasing comonomer content (Ccomon) at fixed MM. If Ccomon is kept approximately constant, TVLTCP increases with increasing MM. It turns out that TVLTCP does not depend on the type of catalyst used. The degree of crystallinity calculated from the VLTCP is independent of the chemical nature of the comonomers present, but slightly changes with Ccomon. It also steeply increases with MM and levels off at MM around 50 kg/mol. It was found that the crystallinity as related to the area of the VLTCP is catalyst type dependent, and is higher for the SS catalyst used compared to the ZN catalyst.

Ethylene Homo‐ and Copolymerization Using a Bis‐IndZrCl2 Metallocene Catalyst: Structural Composition Distribution of the Copolymer

AbstractA bis‐IndZrCl2 catalyst was synthesized and used for ethylene homo‐ and copolymerization. The activity of the catalyst increases with increasing Al/Zr ratio; optimum activity was reached at 60 °C. $\overline M _{\rm v}$ of the polymer decreased as the polymerization temperature increased; increasing reaction pressure increased both $\overline M _{\rm v}$ and catalyst activity. The copolymerization of ethylene with different α‐olefins was studied using the same catalyst system. The results indicate that under identical conditions there was a general decrease in the rate of polymerization as compared to the homopolymerization. The CCD and the lamellar thickness were investigated using DSC. The heterogeneity of the CCD increased with increasing comonomer content and molar mass.magnified image

Influence of phenoxy-terminated short-chain pendant groups on gas transport properties of cross-linked poly(ethylene oxide) copolymers

Gas transport properties of rubbery cross-linked poly(ethylene oxide) films containing short phenoxy-terminated pendant chains are reported. Poly(ethylene glycol) diacrylate (PEGDA) was UV-polymerized with poly(ethylene glycol) phenyl ether acrylate co-monomers of two different ethylene oxide repeat unit lengths: n = 2 (DEGPEA) and n = 4 (PEGPEA). Although fractional free volume increased with increasing co-monomer concentration, gas permeability did not rise accordingly. For instance, while FFV increased from 0.120 to 0.135 in both series of copolymers, CO 2 permeability went from 110 to 35 barrer (DEGPEA) or to 100 barrer (PEGPEA). At the same time, glass transition temperature increased from −37 to −12 °C (DEGPEA) or to −28 °C (PEGPEA). The observed decrease in chain mobility with phenoxy-terminated co-monomer content indicated by increasing glass–rubber transition temperature apparently had a stronger influence on gas transport properties than the increase in fractional free volume.

Composition, thermal properties, and biodegradability of a new biodegradable aliphatic/aromatic copolyester

AbstractA series of new aliphatic/aromatic copolyesters [poly(hexylene terephthalate‐co‐hexylene adipate) (PHTA)] were synthesized on the bases of 1,6‐hexanediol, adipic acid, and dimethyl terephthalate and characterized by gel permeation chromatography, 1H‐NMR, wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and compost testing. 1H‐NMR results show that the compositions of the copolyesters were in accordance with the feed molar ratios. The WAXD patterns indicated that the crystal structures of the PHTA copolyesters were determined by the dominant crystal units, and the copolyesters became less crystallizable, even amorphous, with increasing comonomer content. The DSC curves showed that the glass‐transition temperatures (Tg′s) of the PHTA copolyesters decreased linearly, and both the melting temperature (Tm) and heat of fusion decreased first and then increased with increasing hexylene adipate unit content. Under compost conditions, PHTA copolyesters with less than 60 mol % aromatic units were biodegradable. Particularly, compared with the copolyester poly(butylene terephthalate‐co‐butylene adipate), the PHTA copolyester with the same aliphatic/aromatic composition possessed a lower Tg and Tm and better biodegradability. Additionally, the biodegradability of the copolyesters could be predicted by the number‐average sequence length of aromatic units, Tg, and the temperature difference between Tm and the temperature at which biodegradation took place. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Behaviour of the very-low-temperature crystallization peak of linear low-density polyethylene

The crystallization behaviour of Ziegler–Natta (ZN) and single-site catalyst based ethylene–1-butene and ethylene–1hexene copolymers with different comonomer content were studied by differential scanning calorimetry. In addition to a hightemperature crystallization peak, and for ZN copolymers in addition to a low-temperature crystallization peak, quite often a verylow-temperature crystallization peak (VLTCP) was observed at temperatures in between approximately 330 and 345 K. It was found that the VLTCP temperature decreased with increasing comonomer content and did not depend on the type of catalyst used. The fractional degree of crystallinity calculated from the VLTCP was independent of the chemical nature and content of the comonomers present as well as of the polydispersity of molar mass within the used range of magnitudes. However, crystallinity as related to the area of the VLTCP was strongly catalyst type dependent and was higher for the single-site catalyst used compared to the ZN catalyst used.

Influence of chemical structure of short chain pendant groups on gas transport properties of cross-linked poly(ethylene oxide) copolymers

Three series of amorphous cross-linked poly(ethylene oxide) (XLPEO) rubbers were prepared by photopolymerization of prepolymer solutions containing poly(ethylene glycol) diacrylate (PEGDA) cross-linker and one of three structurally similar short chain acrylate co-monomers: 2-hydroxyethyl acrylate (2-HEA), ethylene glycol methyl ether acrylate (EGMEA) and 2-ethoxyethyl acrylate (2-EEA). Copolymerization with the mono-functional acrylates led to the insertion of short side branches along the network backbone, terminated by either hydroxy, methoxy or ethoxy functional groups. Permeability measurements for the copolymers (35 °C) are presented for CO 2, H 2, CH 4, O 2 and N 2; corresponding solubility and diffusivity data are presented for CO 2 and CH 4. The side branches significantly influenced the thermal and gas transport properties of the polymers: methoxy and ethoxy terminated side-branches modestly increased fractional free volume and gas permeability. This effect was more pronounced by the introduction of ethoxy-terminated 2-EEA, while the presence of hydroxy terminated 2-HEA side-branches reduced free volume, resulting in a strong decrease in gas permeability with increasing co-monomer content. In each case, gas diffusivity correlated with polymer fractional free volume, while gas solubility was a function of both free volume characteristics and the corresponding concentration and accessibility of polar groups within the networks. The resulting selectivity ratios reflected variations in penetrant affinity and size discrimination as a function of copolymer composition. This study highlights the significant changes in various XLPEO properties that can be achieved by making small changes to its network structure.

Comonomer Length Influence on the Structure and Mechanical Response of Metallocenic Polypropylenic Materials

AbstractThe structure and properties have been comprehensively studied for metallocene copolymers of propylene‐1‐hexene (CiPH) and propylene‐1‐octadecene (CiPOD). The comonomer content constitutes the most important factor affecting both structure and properties in these CiPH and CiPOD copolymers, although the length of the comonomer is also very important. Thus, a considerable decrease in crystallinity and an easier obtainment of mesomorphic‐like ordered entities are observed in the two kinds of copolymers as comonomer content increases. The variations in crystalline structure significantly influence the viscoelastic and mechanical behaviors of these CiPH and CiPOD copolymers. Consequently, the location and intensity of the different relaxation mechanisms as well as stiffness parameters (storage, Young's moduli, and microhardness) and deformation mechanism are strongly dependent upon composition.magnified image

A study of the synthesis and characterization of ethylene/dicyclopentadiene copolymers using a metallocene catalyst

Copolymers of ethylene/dicyclopentadiene were produced using a Me 2Si(Ind) 2ZrCl 2/methylaluminoxane catalyst system. The melting and crystallization points of the freshly prepared copolymers steadily decreased with increasing comonomer concentration. This was attributed to increased comonomer concentration in the polymer. When the comonomer incorporation, as measured by 13C NMR, is plotted against the comonomer concentration in the reactor, a plateau appears at concentrations higher than 0.12 mol/L. At concentrations greater than 0.12 mol/L time dependant crosslinking begins to be observed in the copolymers after exposure to air for several months. This crosslinking is also apparent in the thermosetting behavior of the copolymers when they are allowed sufficient time to crosslink. Copolymers with lower comonomer concentrations possess melting enthalpies even after several weeks, suggesting that there is a threshold concentration of 0.12 mol/L for the crosslinking process. Tensile tests of thermoplastic samples showed that incorporation of ca. 5 mol% of comonomer into the polyethylene main chain results in a semi-elastomeric material which possesses high strain recovery and whose strain hardening is similar to that observed for the homopolymer.

Thermal oxidation of metallocene ethylene-1-olefin copolymer films during one year oven aging

Metallocene ethylene homopolymer, ethylene-1-hexene and ethylene-1-octadecene copolymer films were characterized and analysed during their aging in a forced draft oven at 60 °C and compared to commercial polymers (HDPE and LDPE). Each polymer is essentially different in its structure, and the variables used in the present study are comonomer size and content in the main linear backbone polymer. The polymers were characterized initially using GPC, DSC, FTIR, and tensile tests. Later, at different time intervals, samples were removed from the oven and characterized using FTIR and GPC in order to detect changes in chemical structure, size, and molecular weight distribution due to thermo-oxidative aging. At the end of aging, films were subjected to tensile tests to quantify the effect of time on their useful life. As a qualitative reference parameter, the carbonyl index, the ratio of the infrared absorbance of the CO stretching band at 1715 cm −1 and the absorbance of a reference band at 718 cm −1, was determined. Kinetic thermo-oxidation is related to comonomer size and content in the main backbone polymer. As comonomer size decreases or comonomer content increases, degradation rate increases. The scission factor ( S) and carbonyl index (CI) graphs of each material show a slope increase which is related to the autocatalytic rate of oxidation.

Effect of crystallization temperature and propylene sequence length on the crystalline structure of propylene-ethylene random copolymers

Crystallization behavior and resultant crystalline structure of a series of temperature-rising elution-fractionated specimen of a Ziegler-Natta catalyst-synthesized propylene-ethylene random copolymer were studied by DSC, WAXD and AFM. The experimental results indicate that both crystallization temperature and propylene sequence length exhibit great influence on the crystallization behavior and crystalline structure of the copolymer. It was found that the ethylene co-monomers acting as point defects inserted into the polypropylene chains play an important role in the formation of γ-iPP. As the co-monomer content increases, the crystallizable sequence length of iPP decreases, which produces an appropriate condition for its γ crystallization. At the same time, the existence of chain defects leads to a lower crystallinity of the copolymer and imperfection of the resultant crystals. For each individual sample with certain propylene sequence length or ethylene content, the increment of γ-iPP crystal content with increasing crystallization temperature demonstrates that higher crystallization temperature is in favor of the γ-iPP crystallization. Pure γ-iPP crystals have been got in samples with propylene sequence length lower than 21 under suitable crystallization conditions.

Propylene Copolymers with Odd Carbon Number Olefins

AbstractPreliminary investigation on propylene copolymers with odd carbon number olefin are reviewed. Additional experimental data presents propylene copolymers with 1‐heptene and 1‐nonene having higher impact strength and lower tensile strength values than copolymers of propylene and 1‐pentene.Thermoanalysis shows that the melting temperatures of the different copolymers decreases with increasing comonomer content. Slight changes were observed between the different propylene/1‐heptene copolymer melting and propylene/1‐pentene while the 1‐nonene copolymers show broadening of the melting curves as the comonomer content increases. It was highlighted that the source of novelty for these polymers is the comonomer type and content.