Synthesis and characterization of propylene‐α‐olefin random copolymers with isotactic propylene sequence. II. Propylene–hexene‐1 random copolymers

A series of novel hexene‐1–propylene random copolymers with isotactic sequence of propylene was synthesized with a MgCl₂‐supported Cr(acac)₃ catalyst. The molecular weight distribution of copolymers and homopolymers was considerably narrower than that of typical polyolefins produced by heterogeneous Ziegler–Natta catalysts. The crystallizability of the copolymers having a propylene‐unit content of more than 50 mol % drastically decreased with decreasing propylene‐unit content, and the copolymers with a propylene content of less than 50 mol % were completely amorphous. In the present novel type of random copolymers with crystallizable and noncrystallizable units, a single glass transition was observed between pure polypropylene and polyhexene‐1, and a major component was found to govern the final morphology and the mechanical characteristics. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2949–2954, 2004     

Improvement of the impact strength of ethylene‐propylene random copolymers by nucleation

Five ethylene‐propylene random copolymers were nucleated with two soluble nucleating agents. Ethylene content changed between 1.7 and 5.3 wt %, while nucleating agent content was adjusted according to the solubility of the additive. It changed from 0 to 5000 ppm for the sorbitol (1,2,3‐tridesoxy‐4,6:5,7‐bis‐O‐[(4‐propylphenyl) methylene]‐nonitol) and from 0 to 500 ppm for the trisamide compound (1,3,5‐benzene‐trisamide) used. Crystalline structure was analyzed in detail by various methods (DSC, XRD, and SEM). Mechanical properties were characterized by tensile and instrumented impact measurements. The results showed that most properties changed moderately upon nucleation, but impact resistance increased considerably. Spherulitic structure was not detected, but instead in the presence of the soluble nucleating agents used a microcrystalline structure formed. The large increase of impact resistance could not be related directly to changes in crystalline morphology. On the other hand, local rearrangement of morphology was detected by XRD and SEM analysis including an increase of lamella thickness, crystal orientation, and the formation of shish‐kebab structures in the core of the injection molded specimens. A small increase in the γ‐phase content of PP was also observed. These changes increased crack propagation energy considerably leading to the large improvement observed in impact resistance. Although the phenomenon could be related to ethylene content, differences in molecular weight also helped to explain the changes observed. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43823.     

Isothermal crystallization of metallocene‐based propylene/α‐olefin copolymers

Isothermal crystallization and subsequent melting behavior of two propylene/hexene‐1 copolymers and two propylene/octene‐1 copolymers prepared with metallocene catalyst were investigated. It is found that γ‐modification is predominant in all copolymers. The Avrami exponent shows a weak dependency on comonomer content and comonomer type. At higher crystallization temperatures (T_c) the crystallization rate constant changes more rapidly with T_c and the crystallization half‐time substantially increases. Double melting peaks were also observed at high T_c, which is attributed to the inhomogeneous distribution of comonomer units along the polymer chains and the existence of crystals with different lamellar thicknesses. The equilibrium melting temperatures (T) of the copolymers were obtained by Hoffman–Weeks extrapolation. It was found that the T decreases with increasing comonomer content, but are independent of comonomer type, implying that comonomer units are excluded from the crystal lattice. Dilation of the crystal lattice was also observed, which depends on crystallization, comonomer content, and comonomer type. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 240–247, 2005     

Calcium dicarboxylates nucleation of β‐polypropylene

Seven dicarboxylates of calcium were synthesized. The effect of dicarboxylate on the formation of β‐form polypropylene was investigated by X‐ray diffraction. Calcium pimelate, calcium suberate, calcium phthalate, and calcium terephthalate have been found to be an effective β‐nucleator. The K_x values of the isotatic propylene samples with 0.5 wt % of the nucleators above are 0.95, 0.96, 0.93, and 0.62, respectively. Calcium succinate, calcium adipate, and calcium sebacate behave invalidly on the nucleating of the β‐phase. We conducted an investigation on the affect of particle shape, crystal form, and crystallinity upon the level of the β‐form. The X‐ray diffraction of the effective nucleators reveals a common character that their first reflection locate at the d‐spacing between 10 to 13 Å, indicating structural similarity of the nucleators with β‐polypropylene. The nucleation mechanism is explained by the cooperative effect of the nonpolar and polar part of nucleating agents in the crystallization of polypropylene. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 633–638, 2002     

Crystallization of the γ form in random propylene‐ethylene copolymers

Wide‐angle X‐ray scattering and differential scanning calorimetry measurements have been conducted on seven random copolymers of propylene with ethylene in order to study the γ phase formation as a function of the comonomer content. The lamellar morphology of the samples was also investigated by small‐angle X‐ray scattering. The content of the γ phase was found to go through a maximum with crystallization temperature and to increase with comonomer concentration, up to a point (ethylene ≥6.5 wt%) where the latter parameter became less influential. The multiple melting endotherms behaviour of the samples was studied by DSC and temperature‐controlled diffractometric techniques. The attribution of the DSC peaks to the different isotactic polypropylene polymorphs that form in these conditions was confirmed. The results obtained permitted us to ascertain that, in the experimental conditions chosen, some further formation of crystallites takes place during the quenching to room temperature after the crystallization isotherm. In this phase, the chains organize themselves in stacks with thin lamellae, forming a distinct population with respect to those formed on isothermal crystallization. The melting of the thinner lamellae determines a convergence of the two populations into just one, still retaining an organization in stacks, that gradually disappears until complete melting of the material. Copyright © 2004 Society of Chemical Industry     

Preparation and sorption properties of tunable polyester copolymers containing β‐cyclodextrin

Polyester copolymers were prepared with β‐cyclodextrin (β‐CD) and sebacoyl (SCl) or terephthaloyl (TCl) chloride cross linker agents using a simple, one‐pot synthesis. Variation of the mole ratios (i.e., 1 : 1, 1 : 2, 1 : 3, 1 : 6, and 1 : 9) of β‐CD to diacid chloride linker units resulted in copolymers with differing solubility and chemical stability in aqueous solution. The sorption properties of copolymers such as 1 : 6 and 1 : 9 SCl, and 1 : 9 TCl materials were investigated because of their relative insolubility and resistance to hydrolysis at pH 4.6. The monolayer sorption capacity (Q_m) of the copolymers varied according to the nature of the cross linker and the relative mole ratio of monomers. Q_m values obtained from the Sips isotherm model range from 2.7 to 5.2 mmol/g for the sorption of p‐nitrophenol at 295 K and approach the value of Q_m for a commercially available granular activated carbon sorbent. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of processing on structure of β‐nucleated poly(propylene) fibers

Fibers colored with quinacridone pigment spun at low take‐up velocities were obtained. The spun fibers, with a very high β‐form content, were drawn at room temperature and at a temperature of 120°C at different draw ratios. They were then heat stabilized at different temperatures, ranging from 140 to 150°C for different time intervals. As a result of drawing, the transition from β to mesophase, as well as that from β to α, was observed. The β to mesophase transition results from cold drawing at room temperature, while the β to α transition results from drawing at 120°C. In both cases, the significant decrease of β‐form content occurs at the low draw ratio of 2. At higher draw ratios, the β‐form content gradually decreases, and at a draw ratio of 7 the β‐form disappears altogether. As a result of heat stabilization, the β to α transformation was observed. The first change of the β‐form content was noticed at 140°C. For fibers stabilized at temperatures above 140°C, the decrease of the β‐form content is more significant and increases with the increase of the stabilization temperature. At 150°C, a rapid drop of the β‐form content occurs after only 3 min, and after a few more minutes the β‐form disappears. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1413–1418, 2004     

Influence of α′‐/α‐crystal polymorphism on properties of poly(l‐lactic acid)

Poly(l ‐lactic acid) (PLLA) is a biodegradable and biocompatible thermoplastic polyester produced from renewable sources, widely used for biomedical devices, in food packaging and in agriculture. It is a semicrystalline polymer, and as such its properties are strongly affected by the developed semicrystalline morphology. As a function of the crystallization temperature, PLLA can form different crystal modifications, namely α′‐crystals below about 120 °C and α‐crystals at higher temperatures. The α′ modification is therefore of special importance as it may be the preferred polymorph developing at processing‐relevant conditions. It is a metastable modification which typically transforms into the more stable α‐crystals on annealing at elevated temperature. The structure, kinetics of formation and thermodynamics of α′‐ and α‐crystals of PLLA are reviewed in this contribution, together with the effect of α′‐/α‐crystal polymorphism on the properties of PLLA. © 2018 Society of Chemical Industry     

β‐Polypropylene/wood flour composites: Effects of specific β‐nucleation and coupling agent on mechanical behavior

Polypropylene/wood flour composites were prepared by melt compounding. To improve their mechanical performance, the matrix polypropylene was modified with a specific nucleation agent based on an amide of dicarboxylic acid, which promotes crystallization predominantly in the β‐phase. The resulting material was used as a matrix for composites containing 10%, 20%, and 30% of wood flour. Uniform dispersion of the filler and improved interfacial adhesion was ensured by compatibilization with a small amount of maleic anhydride‐grafted polypropylene. A beneficial effect of application of the nucleation agent together with a compatibilizer on the resulting mechanical behavior was shown. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 506–511, 2007     

Dielectric properties of copolymers based on cyano monomers and methyl α‐acetoxyacrylate

With the aim of developing dielectric polymers containing CN groups with strong dipole moment, alternating and statistical copolymers of the cyano monomers vinylidene cyanide (VCN), acrylonitrile and methacrylonitrile with methyl α‐acetoxyacrylate (MAA) were synthesized and characterized. The copolymer's composition and microstructure were analysed by NMR spectroscopy, SEC and elemental analysis. The reactivity ratios calculated from the Q–e Alfrey–Price parameters for these copolymers indicated the alternating and statistical structures confirmed by NMR analysis. The copolymers have glass transition temperatures T_g in the range 83–146 °C and are stable up to 230 °C. The thermal stability of the copolymers depends on the nature of the cyano monomers. Their molecular dynamics were investigated by dielectric relaxation spectroscopy. We revealed a weak relaxation β at sub‐T_g temperature for poly(VCN‐co‐MAA) usually originating from molecular motions that are restricted to the scale of a few bond lengths. Strong α‐relaxation processes occurred above T_g for these copolymers. This primary relaxation was associated with cooperative movements of the polar groups (CN) at the time of mobility of the principal chains. The activation energy of the α‐relaxation process was also calculated. The values of the dielectric increment Δε for these copolymers were determined by Cole–Cole plots and indicated that the copolymers exhibit interesting dielectric properties compared with similar cyano materials. The polarity–permittivity relationship was also established. © 2012 Society of Chemical Industry     

Cationic copolymers of α,β‐poly‐(N‐2‐hydroxyethyl)‐DL‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy): synthesis and characterization

In the present study the derivatization of two water‐soluble synthetic polymers, α,β‐poly(N‐2‐hydroxyethyl)‐DL ‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy), with glycidyltrimethylammonium chloride (GTA) is described. This reaction permits the introduction of positive charges in the macromolecular chains of PHEA and PAHy in order to make easier the electrostatic interaction with DNA. Different parameters affect the reaction of derivatization, such as GTA concentration and reaction time. PHEA reacts partially and slowly with GTA; on the contrary the reaction of PAHy with GTA is more rapid and extensive. The derivatization of PHEA and PAHy with GTA is a convenient method to introduce positive groups in their chains and it permits the preparation of interpolyelectrolyte complexes with DNA. © 2000 Society of Chemical Industry     

Preparation and sorption studies of β‐cyclodextrin/epichlorohydrin copolymers

β‐Cyclodextrin (β‐CD) copolymer materials were synthesized by reacting different mole ratios (1 : 15, 1 : 25 and 1 : 35) of β‐CD with epichlorohydrin (EP). The products were characterized using N₂ porosimetry, Fourier Transform Infrared spectroscopy, ¹³C CP‐MAS NMR spectroscopy, thermogravimetry analysis, elemental (C and H) analysis, and scanning electron microscopy. The sorption properties in aqueous solution were studied using p‐nitrophenol (PNP) with UV–Vis spectrophotometry. Sorption isotherms were obtained at pH 4.6 and three temperatures (22, 35, and 45°C) and at pH 10.3 at 22°C. The isotherms were analyzed using the BET isotherm model and the sorption parameters provided estimates of the surface area, sorption capacity, and isosteric heats of sorption for each polymeric material. The estimated surface areas are as follows: 58.2, 52.1, and 90.1 m²/g at pH 4.6. At pH 10.3, the estimated surface areas are 44.2, 40.5, and 58.5 m²/g, respectively. The removal efficiency of PNP by the polymeric materials ranged between 4.5 and 58% for the conditions investigated whereas the isosteric heats ranged between ?24.5 and ?13.6 kJ/mol. Removal efficiencies were concluded to strongly depend on the sorption conditions such as pH, temperature, and the relative amounts of sorbent and dye in aqueous solution. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of poly(propylene carbonate) on the crystallization and melting behavior of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate)

The crystallization and melting behavior of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate) (PHBV) and a 30/70 (w/w) PHBV/poly(propylene carbonate) (PPC) blend was investigated with differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR). The transesterification reaction between PHBV and PPC was detected in the melt‐blending process. The interaction between the two macromolecules was confirmed by means of FTIR analysis. During the crystallization process from the melt, the crystallization temperature of the PHBV/PPC blend decreased about 8°C, the melting temperature was depressed by 4°C, and the degree of crystallinity of PHBV in the blend decreased about 9.4%; this was calculated through a comparison of the DSC heating traces for the blend and pure PHBV. These results indicated that imperfect crystals of PHBV formed, crystallization was inhibited, and the crystallization ability of PHBV was weakened in the blend. The equilibrium melting temperatures of PHBV and the 30/70 PHBV/PPC blend isothermally crystallized were 187.1 and 179°C, respectively. The isothermal crystallization kinetics were also studied. The fold surface free energy of the developing crystals of PHBV isothermally crystallized from the melt decreased; however, a depression in the relative degree of crystallization, a reduction of the linear growth rate of the spherulites, and decreases in the equilibrium melting temperature and crystallization capability of PHBV were detected with the addition of PPC. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2514–2521, 2004     

Control and development of crystallinity and morphology in poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate)/poly(propylene carbonate) blends

Two different methodologies (reactive blending and mechanical blending) for preparing blends of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate) (PHBV) and poly(propylene carbonate) (PPC) were used. The miscibility, chemical structure, thermal behavior, crystallinity, morphology, and mechanical properties of the blends were investigated with Fourier transform infrared spectroscopy, differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy, and tensile tests. A certain extent of hydrogen‐bonding interactions between PHBV and PPC took place in the blends. The graft copolymerization was confirmed in the reactive system. The incorporation of PPC hampered the crystallization process of PHBV and evidently altered the morphology, and the effect was enhanced in the reactive blend. The mechanical properties of PHBV could be changed by 1–2 orders of magnitude by blending modification. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1427–1436, 2005     

Comparative study on the crystallization behavior of β‐isotactic polypropylene nucleated with different β‐nucleation agents —effects of thermal conditions

In this study, the crystallization behavior of the β‐isotactic polypropylene (β‐iPP) samples nucleated by a rare earth based β‐nucleating agent (β‐NA) WBG‐II and a metal salts compound β‐NA NAB83 (denoted as WPP and NPP, respectively) under different cooling conditions were comparatively investigated. The thermal conditions such as the cooling rate, isothermal crystallization temperature, isothermal crystallization time, and the subsequent cooling to room temperature. The results of WAXD, SEM, and nonisothermal crystallization reveal that under the same processing conditions, the crystallite size of NPP is smaller, which arrange more compactly as compared with WPP. Meanwhile, NPP has shorter crystallization rate and higher β‐nucleation selectivity, but WPP can crystallization at wider temperature range. The results of isothermal crystallization showed that NPP has higher selectivity and higher β‐nucleation efficiency, which favors the formation of high proportion of β‐phase at the isothermal crystallization temperature of 110–130°C with and without subsequent cooling; WPP has lower selectivity, which can only induce high content of β‐phase under isothermal crystallization without subsequent cooling to 25°C. In tuning the crystallization behavior and the properties of β‐PP, the joint influence of the efficiency and selectivity of the β‐NA, and the thermal conditions should be taken into consideration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40115.     

Influence of γ‐ray irradiation on structure and properties of PAN precursor fibers

To improve the oxidative efficiency of polyacrylonitrile (PAN) precursors, modification of PAN precursors was employed by gamma ray irradiation. Effects of irradiation on the structure and properties of PAN precursors were investigated. The results showed that cyclized structure in the precursors was formed after γ‐ray irradiation. Meanwhile, irradiation could reduce the heat evolved, relax the exothermic behavior, decrease the mechanical properties and enhance the density of PAN fibers. It is supposed that the modification of γ‐ray irradiation could remarkably accelerate the stabilization process of PAN precursors and reduce the production cost of resulting carbon fibers. POLYM. ENG. SCI., 56:1313–1318, 2016. © 2016 Society of Plastics Engineers     

The effect of specific β‐nucleation on morphology and mechanical behavior of isotactic polypropylene

The commercial grade of isotactic polypropylene was modified by a specific β‐nucleating agent in a broad concentration range. The supermolecular structure of the specimens prepared by injection molding was characterized by X‐ray scattering and correlated with mechanical behavior. It was found that at a critical nucleant concentration of 0.03 wt % the content of the β‐modification virtually reaches a saturation level. With further addition of the nucleant, the β‐phase content increases only slightly. The long period passes through a distinct maximum at the same nucleant concentration. This singularity in structure remarkably correlates with a minimum of the yield stress and maxima of strain at break and fracture toughness. Such general behavior is also reflected in the correlation between the β‐phase concentration and fracture toughness profiles along the injection‐molded bars. It is suggested that in the critically nucleated material an optimum thickness of the amorphous interlayer with connecting chains between the β‐crystallites is established, rendering the material the highest possible ductility and toughness. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1174–1184, 2002     

Correlation of chemical composition and microstructure with properties of poly(ɛ‐caprolactone‐co‐p‐dioxanone) random copolymers

With the aim to develop novel biodegradable materials with good flexibility and fast degradation rate, random copolymers of ?‐caprolactone (CL) and p‐dioxanone (PDO) with a full range of compositions were synthesized in bulk using stannous octoate as the ring‐opening catalyst. The chemical composition and number average sequence lengths of CL and PDO units determined by ¹H‐NMR were used to correlate with various properties of the copolymers. Although both CL and PDO are crystalline components, only one crystalline phase could be present for each copolymer. The low limit of average block length for the copolymers that could crystallize is 3.22 for L_CL and 3.43 for L_PDO, respectively. The crystallinity and crystalline morphology of the copolymers are dependent on the crystalline component as well as its number average sequence length. Irrespective of composition, all the copolymers have good solubility in chloroform with glass transition temperature much below room temperature, implying good flexibility of the materials. The incorporation of PDO component could significantly increase the water wettability of the copolymer surfaces and thereby accelerate the degradation rate of the materials. In conclusion, flexible biodegradable polymers with adjustable degradation and crystalline properties were acquired by random copolymerization of CL and PDO, which are expected to use in tissue engineering and drug delivery fields. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2978–2986, 2013     

Tensile properties of microbial β‐glucan films

β‐glucan films with different plasticizer concentrations (glycerol and water) were deformed in tension and various mechanical characteristics (modulus of elasticity, yield stress, strength, and strain at rupture point) were evaluated. The influence of both plasticizers was of additive nature describable by the total plasticizer content. The influence is reflected by an exponential decrease of either modulus of elasticity or yield stress with increasing total plasticizer content. The film strength decreased linearly with plasticizer concentration, whereas the decline in strain at the rupture point followed a power function. It was also found that the stress parameters can be expressed via modulus of elasticity: the strength as linear function of the square root of the elasticity modulus and the yield stress as a linear function of the latter parameter. On the basis of such relations a quadratic function between strength and yield stress was proposed. This relation well describes the character of the deformation curves that were obtained at different deformation conditions. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers