Increasing Comonomer Content Research Articles

Protein adsorption behaviour of ionogenic poly(HEMA) membranes: a fluorescence study.

A series of ionogenic poly(HEMA) membranes which were prepared by bulk copolymerization of 2-hydroxyethylmethacrylate (HEMA) and anionic or cationic comonomers, acrylic acid (AA), and dimethylaminoethylmethacrylate (DMAEMA), were characterized by equilibrium swelling measurements, surface free energies, and protein adsorption studies. It was found that their equilibrium water content (EWC) values are greater than 40% which increases with increasing comonomer concentration. That is why the surface free energy is approximately the same (approximately 60 erg cm-2) for all surfaces and does not depend mainly on the composition of the polymer matrix. The adsorption of two plasma proteins that have received much attention, i.e. BSA and fibrinogen, on these membranes was followed by fluorimetric measurements as a function of time. The uptake of proteins from dilute solutions appeared to be directly related to the type and density of surface charge, and also structural properties of the proteins.

Copolymerization of olefins with SiO2‐, Al2O3‐, and MgCl2‐supported metallocene catalysts activated by trialkylaluminiums

AbstractCopolymerizations of ethylene with propene, of ethylene with 1‐hexene and of propene with 1‐hexene were carried out at 40°C under atmospheric pressure with SiO2‐, Al2O3‐ and MgCl2‐supported metallocene catalysts using common alkylaluminiums as cocatalyst. From a detailed analysis of copolymers by 13C NMR, all the copolymers obtained were found to be random (r1·r2 ≤ 1). When ethylene was used as a base monomer, the polymer yield markedly increased with increasing comonomer concentration. The molecular weight of the copolymers obtained in this study were found to be much higher than those obtained with homogeneous Kaminsky‐Sinn catalysts. Whereas, the polydispersity (Mw/Mn) of the copolymer is dependent on the combination of monomers as well as on the inorganic compounds used as carrier.

Side‐chain liquid‐crystalline polymers containing siloxane spacer, 3. Thermal properties of copolymers containing different types of mesogens

AbstractCopolymerization of monomers containing the disiloxane unit in the spacer component and linear triple‐core mesogens with comonomers containing linear double‐core mesogens, or laterally attached triple‐core mesogens was carried out radically. The effect of copolymer composition and monomer structure on the mesomorphic properties of the obtained copolymers was investigated in detail. The copolymers with a comonomer content up to 50 mol‐%, exhibit an enantiotropic nematic phase, whereas the parent homopolymers containing triple‐core mesogens exhibit a smectic phase. The copolymer containing more than 50 mol‐% of the comonomer shows no mesophase. The isotropization temperature of the copolymers decreases with increasing comonomer content. However, the glass transition temperature is almost unchanged upon introduction of the comonomer unit. In case of copolymers containing laterally attached mesogens, a smectic phase was observed below the temperature range of the nematic phase. Consequently, the mesophase and the temperature range of the liquid‐crystalline state can be controlled by the introduction of the comonomer unit whose parent homopolymer does not exhibit any mesophase.

Effect of structure and composition on physico‐mechanical properties of methyl methacrylate/alkyl (meth)acrylate copolymers

AbstractThe paper describes the fabrication of cast acrylic sheets by copolymerizing a prepolymer syrup of methyl methacrylate (MMA) with varying amounts (1‐20 wt.‐%) of 2‐ethylhexyl methacrylate (EHMA), n‐hexyl methacrylate (HMA), 2‐ethylhexyl acrylate (EHA) and n‐hexyl acrylate (HA). The effect of structure of copolymer on light transmittance, density and mechanical properties was evaluated. Tensile strength and storage modulus decreased with increasing comonomer content. Strain increased significantly in the case of MMA/EHA and MMA/HA copolymer sheets having 15 and 20 wt.‐% of comonomer. Softening temperature of copolymer samples was determined using dynamic mechanical thermal analysis. Heat deflection temperature under flexural load and softening temperature decreased with increasing comonomer content in copolymer.

Structural and thermal characterization of methyl methacrylate/alkyl acrylate copolymers

Bulk polymerizations of methyl methacrylate (MMA) with n-hexyl acrylate (HA) or 2-ethyl-hexyl acrylate (EHA) were carried out using benzoyl peroxide as initiator. Polymer samples were prepared for mole fractions of HA or EHA from 0 to 1 in the initial feed. Molecular characterization of the copolymers and homopolymers was done by gel permeation chromatography and intrinsic viscosity measurements. 1H-NMR spectroscopy was used to determine copolymer compositions. Reactivity ratios were found to be r 1 (MMA) = 4.32 ± 0.02, r 2 (HA) = 0.55 ± 0.02 and r 1 (MMA) = 1.85 ± 0.01, r 2 (EHA) = 0.42 ± 0.01. Samples containing low mole fraction (i.e. < 0.102) of HA or EHA in the backbone showed multistep decompositions. In all other samples, thermal degradation proceeded in a single step. An increase in thermal stability of the copolymers was observed with increase in comonomer content.

Nylon-6 copolymers: Copolymerization with α-amino acids

Alanine (Ala), leucine (Leu), phenylalanine (Phe) and lysine hydrochloride (Lys · HCl) were incorporated in nylon-6 by melt polycondensation. The reduced specific viscosities of the polymers decreased with increasing comonomer content, in the order Ala > Leu ≈ Phe > Lys · HCl. Glass transition temperature ( T g), cold crystallization temperature ( T ∝) and melting temperature ( T m) were measured by differential thermal analysis. T m decreased in the order Ala > Leu > Phe > Lys · HCl. T g increased slightly with increasing comonomer content. The ease of crystallization, indicated by ( T ∝ − T g), decreased in the order Ala > Leu > Phe > Lys · HCl. Heat resistance, measured by thermogravimetry, decreased in the same order. Weight loss on alkali hydrolysis increased with increasing comonomer content. The copolymer with Lys · HCl showed the largest weight loss suggesting biodegradability. Acid dyeability could be greatly improved by the incorporation of 1–2 mol% Lys · HCl.

Preparation and characterization of wholly aromatic para-linked copolyamides of poly(p-phenyleneterephthalamide)

Wholly aromatic para-linked copolyamides of poly(p-phenyleneterephthalamide) have been prepared by direct polycondensation via a phosphorylation reaction using various amounts of p-aminobenzoic acid, toluene-p-diamine or nitroterephthalic acid (NTA) as comonomer. Viscosity number, perhaps degree of polymerization as well, increased with increasing comonomer content, whereas crystallinity of copolymers decreased. In particular, a bulky nitro group decreased crystallinity and the copolymers with NTA content > 50 mol% were amorphous and similar to poly (p-pheneylenenitroterephthalamide). Melting point was not greatly changed by copolymerization. Thermal decomposition temperatures of copolymers containing NTA were lower than those of other copolymers by ca. 100 °C.

Thermal Degradation of Vinylchloride/α-Olefin Copolymers

Abstract The preliminary results obtained for the thermal degradation of vinylchloride/α-olefin copolymers are, in part, unexpected. Decrease of the initial polyene length with the increase of comonomer content is a reasonable consequence of the shorter viny chloride sequence lengths, but the constancy of these lower values in the course of further degradation indicates, that some secondary reactions of the polyenes (e.g. cyclization) must be absent here. The decrease of the HCl elimination rate in case of copolymers differs from the dependence given by the weak sites model. Formally, the rate is proportional to a netative power of conversion, the value of the exponent depending on the composition. These results indicate the necessity of further research for clearing up the unknown details of PVC degradation mechanism.

Structure‐property relationships of copolyamides. II. crystal structure of drawn copolyamide films

AbstractThe crystal structures of drawn copolyamides 6/6.6, 6/6.T, 6/6.1, 6/PXD.6, 6/MXD.6, and 6/MXD.I were examined by wide‐angle x‐ray diffraction. Copolyamide 6/6.6, which follows the inclusion model, shows only α‐characteristics at all the comonomer compositions examined (0–33.3 mol%). However, the other copolyamides, which follow either the partial‐inclusion or complete‐exclusion model, show γ‐characteristics more predominantly as the comonomer content increases. The interplanar spacing of the (200) planes, which corresponds to the hydrogen bond distance between antiparallel chains, remain constant, whereas the spacing of the (020) planes corresponding to the distance between hydrogen bonded sheets increases monotonically with increasing the comonomer content. It is also observed that both the crystal perfection index and the crystal thickness decrease as the comonomer content increases.

Thermoplastic matrix composites by aqueous electrocopolymerization onto graphite fibers

AbstractElectrocopolymerization of 3‐carboxyphenyl maleimide and styrene onto Hercules AS‐4 graphite fiber surfaces has been successfully carried out from an aqueous solution containing monomers and dilute sulfuric acid. Initiation of copolymerization of the monomers dissolved in a small amount of dimethylacetamide is achieved by constant‐current electrolysis in the cathodic chamber of a three‐compartment electrolysis cell. Polymerization is initiated at the fiber surfaces; little polymer is formed in the cell solution. Electrocopolymerization is very consistent and rapid. The amount of polymer increases predictably with increasing comonomer concentration and current density. Using a 0.4 M (1 : 1) comonomer concentration, 0.0125 M sulfuric acid solution, and a current density of 20 mA/g, more than 60 wt % of copolymer coating per unit weight of graphite fibers is obtained within thirty minutes. Thermal gravimetric analysis showed the copolymer to be very stable at elevated temperatures and has initial and final decomposition temperatures of 430 and 520°C, respectively. The glass transition temperature measurement of the copolymer coatings was carried out by differential scanning calorimetry. A single glass transition temperature was obtained of about 210°C for most samples. The glass transition temperature of the copolymers did not change significantly with changing comonomer feed composition. Functional group and compositional analysis of the copolymer was done by FTIR spectroscopy. The copolymer composition remained relatively the same for copolymers made from different styrene/3‐carboxyphenyl maleimide feed composition, confirming a strong tendency toward alternation for the system.

Polymeric amphiphiles with hydrophilic main chain spacers: Studies in monolayers and Langmuir-Blodgett multilayers

A methacrylic lipid was polymerized to form an amphiphilic homopolymer and random copolymers with various levels of acrylic acid comonomers. The behavior of these polymeric lipids was investigated in monolayers at the air-water interface and in Langmuir-Blodgett multilayers on polymer foil supports. The acrylic acid acts as a hydrophilic spacer along the polymer backbone, and improves the ability of the polymer to self-organize into highly ordered monolayers and ultimately LB multilayers. It is shown that the quality and stability of the multilayers increase substantially with the increase in comonomer content.

Structural Distribution of Linear Low-Density Polyethylenes

Molecular and crystalline structures of linear low-density polyethylenes (LLDPE) were investigated by a series of characterization techniques. Molecular structural characteristics were elucidated by temperature-rising elution fractionation (TREF) and solvent-gradient elution fractionation (SGEF). A bird’s eye view and a contour map of LLDPE obtained by a combination of TREF and size exclusion chromatography exhibited a broad and multimodal chemical composition distribution (CCD), in contrast to a sharp and single CCD of conventional high-pressure low-density polyethylene (HP-LDPE). Short chain branching (SCB) was found to decrease with increase of molecular weight by SGEF technique. Thermal analysis of cross-fractions proved that a characteristic broad endothermic curve of LLDPE is attributable to its broad and multimodal CCD. Then, using DSC results, an indicative index (DI) which expresses the degree of the distribution of lamellar crystal thickness is proposed. DI was found to be sensitive both to CCD and to a kind of SCB. The crystallinity and melting temperature of cross-fractions having comparable molecular weights decrease with increasing comonomer content in the order of octene-1≍4-methyl-pentene-1>hexene-1>butene-1. From a statistical approach to the relationship between crystallinity and degree of SCB, the probability of exclusion of a bulky branching such as isobutyl from a crystalline lattice is considered to be twice as large as than that of ethyl branching.

Effect of comonomer content and annealing on morphological changes in acrylic copolymers and fibers

AbstractA better understanding of internal microstructure is necessary to understand various properties of acrylic fibers, such as dyeability, mechanical properties, and comfort. In the present paper, the application of x‐ray methods for the investigation of fiber microstructural parameters, namely, crystallinity and crystallite size, is demonstrated. Effect of comonomer incorporation on acrylic copolymer microstructure is assessed in the present work. Influence of annealing aftertreatment on the changes in structure is investigated using the evidence presented by x‐ray and DSC studies. Introduction of small amounts of a comonomer (methyl acrylate, MA) results in diminishing crystallinity. Annealing of acrylic copolymers causes the onset of an intramolecular cyclization, as well as an increase in segmental mobility; both these factors lead to an increase in crystallinity and crystallite size. With increasing comonomer content, the exothermic peak in the thermogram is found to shift toward higher temperatures. Some evidence is presented that shows the effect of spinning process variables on acrylic fiber microstructure. The results and findings of the present work have been interpreted in terms of a two‐phase structure for acrylic fibers.

DSC studies of linear low density polyethylene. Insights into the disrupting effect of different comonomers and the minimum fold chain length of the polyethylene lamallae

AbstractThis paper reports a DSC examination of a series of linear low density polyethylenes (LLDPE) prepared variously with propylene, 1‐butene or 4‐methyl‐1‐pentene comonomers. The enthalpy of fusion of the crystalline regions of the LLDPE decreases progressively with increasing comonomer content and is effectively independent of the comonomer type. Disruption of polymer crystallinity is thus determined principally by the number and distribution of the chain irregularities. A sequence length of n = 14 was calculated as the critical chain dimension below which polyethylene segments cannot be readily packed into a stable crystal lattice.

The Effects of Fluorescent Substances on the Photofading of Colours.

A fluorescent whitening agent of a pyrazoline type (FJ was found to accelerate the fading of Methyl Violet (MV) on irradiation at 366 nm in a film of polyacrylonitrile, while MV quenched the fading of F. In copolymers of acrylonitrile with vinyl acetate or acrylamide, the fading rates of F and MV as well as the acceleration of the fading of MV by F decreased with increasing comonomer content. The accelerated fading of MV by Fw was also observed in a commercial acrylic fibre, Vonnel W, on irradiation at 330 nm, while F had little effect on the decay of MV in this fibre in visible light. The fastness on polymers of MV exposed to a xenon lamp was in the following order: polyacrylonitrile&lt;gelatin&lt;cellulose acetate&lt;acrylonitrile‐vinyl acetate copolymer.

Preparation of amide and amine groups containing copolymers of methyl methacrylate and their performance in solid polymer composites

AbstractMethyl methacrylate (MMA) was copolymerized with acrylamide, N‐methylacrylamide, N,N‐dimethylacrylamide, 1‐vinyl‐2‐pyrrolidone, 4‐vinylpyridine, and 2‐dimethylaminomethyl methacrylate in 1,4‐dioxane solution at 65°C, using AIBN as initiator, to yield copolymers with comonomer contents between about 5 and 50 mole‐%. The monomer reactivity ratios were evaluated. The copolymerizations are in general non‐azeotropic and non‐ideal. The amine group containing comonomers are preferentially incorporated in relation to MMA, but MMA is preferentially incorporated in relation to the amide group containing comonomers. The average molecular weights of the copolymers, with the exception of the N,N‐dimethylacrylamide copolymer, decrease with increasing comonomer concentration, especially in the case of the amine group containing comonomers. The increasing content of amide and amine group containing monomeric units in the copolymers influences the adsorption of the polymers on an iron oxide red pigment, the dispersion stability, as well as the adhesion of the polymer coatings on steel plates and their corrosion protection.

Carbon-13 NMR investigation of vinyl-chloride/ vinyl-acetate copolymers

Copolymers of vinyl chloride with vinyl acetate have been studied by Carbon 13 NMR specroscopy to determine the influence of the copolymerization on the tacticity of PVC sequences. Diad and triad resonances have been assigned in terms of constitutional as well as of configurational sequences. The syntacticity of the PVC sequences appears to decrease with increasing comonomer content. This decrease might be caused by a steric hindrance which would favour a more atactic addition.

POLY (ETHYLENE TEREPHTHALATE) COPOLYMERS WITH HALOGENATED TEREPHTHALIC ACIDS

Poly (ethylene terephthalate) copolymers were prepared by substitution up to 40 mol% of diacid comonomers: 2, 5-dichloroterephthalic acid (TCl2) and 2, 5-dibromoterephthalic acid (TBr2). ηsp/C of the copolymers does not depend on the comonomer content. Melting point depression shows that copolymers with TCl2 and TBr2 are non-isomorphous. Glass transition temperature shows a minimum at 30mol% copolymer. The crystallization rate followed by the change of density decreases with increasing comonomer content. Solubility increases by the copolymerization. The resistance to alkali-hydrolysis increases a little for 10mol% copolymer and decreases for more halogen-containing copolymers. Flame-retardancy was estimated by heating the copolymers for 1h at 350°C in air. Weight loss of halogen atoms in the copolymers increases, and residue except halogen atoms in the copolymers decreases with increasing comonomer content. These variations with increasing comonomer content were more pronounced for copolymers with TBr2 than for those with TCl2.

Order—disorder transitions in polytetrafluoroethylene

The phase diagram of polytetrafluoroethylene is enlarged by differential scanning calorimetry to include the concentration of hexafluoropropylene comonomer units. The two transitions near 292 and 303 K in the homopolymer move to lower temperatures and apparently become one at small concentrations. Analysis of the data yields 295 K for the temperature and 13.2 J/g for the heat of transition of an infinitely large homopolymer crystal. The heat of transition associated with the formation of a crystal defect is 0.021 eV. The qualitative features of the transition can be accounted for by a mean-field model which involves two order parameters corresponding to planar units and helix reversals. This model yields two transitions which move closer together and to lower temperatures with increasing comonomer concentration. Decreasing lamella thickness will have a qualitatively similar effect.

NYLON 66 COPOLYMERS WITH CHLORINATED TEREPHTHALIC ACID

Nylon 66 copolymers were prepared by substitution up to 40 mol% of diacid comonomers: 2, 5-dichloroterephthalic acid (TCl2) and 2, 3, 5, 6-tetrachloroterephthalic acid (TCl4). The thermal properties measured by DTA were compared with those of previously reported nylon 66 copolymers with terephthalic acid (T) and isophthalic acid (I).ηsp/C decreases with increasing comonomer content. Melting point depression shows that copolymers with TCl2 and TCl4 are non-isomorphous. Glass transition temperature (Tg) increases in the order of copolymers with TCl4 TCl4>TCl2>I. Solubility increases by the copolymerization. Flame-retardancy estimated by TG and self-ignition test increases with increasing chlorine content of copolymers.