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     

Crystallization kinetics and melting behaviour of microbial poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

Isothermal and non‐isothermal crystallization kinetics of microbial poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(3HB‐3HHx)] was investigated by differential scanning calorimetry (DSC) and ¹³C solid‐state nuclear magnetic resonance (NMR). Avrami analysis was performed to obtain the kinetic parameters of primary crystallization. The results showed that the Avrami equation was suitable for describing the isothermal and non‐isothermal crystallization processes of P(3HB‐3HHx). The equilibrium melting temperature of P(3HB‐3HHx) and its nucleation constant of crystal growth kinetics, which were obtained by using the Hoffman–Weeks equation and the Lauritzen–Hoffmann model, were, respectively, 121.8 °C and 2.87 × 10⁵ K² when using the empirical ‘universal’ values of U* = 1500 cal mol^?1. During the heating process, the melting behaviour of P(3HB‐3HHx) for both isothermal and non‐isothermal crystallization showed multiple melting peaks, which was the result of melting recrystallization. The lower melting peak resulted from the melting of crystals formed during the corresponding crystallization process, while the higher melting peak resulted from the recrystallization that took place during the heating process. Copyright © 2005 Society of Chemical Industry     

N‐Oligo(3‐hydroxybutyrate)‐functionalized polypyrroles: towards bio‐erodible conducting copolymers

New copolymer materials have been prepared by chemical grafting of oligomeric 3‐hydroxybutyric acid (OHB) onto polypyrrole (PPy) derivatives. The influence of grafting density and molecular weight of OHB brushes on the physicochemical properties of prepared copolymers was investigated. PPy substrates were prepared by FeCl₃‐driven oxidative homopolymerization of N‐(2‐carboxyethyl)pyrrole or its copolymerization with pyrrole. The grafting method employed involved controlled anionic polymerization of β‐butyrolactone on pyrrole‐tethered potassium carboxylate active sites. Obtained PPy‐g‐OHB copolymers of varying grafting density and pendant polyester chain length were characterized and the observed structure–property relationships discussed. The impact of real time exposure to phosphate‐buffered saline environment was investigated and the residue products were characterized. Cross‐correlation of spectroscopic, thermal, electrical and elemental analysis data afforded comprehensive evaluation of the structure of prepared materials and their behaviour in hydrolytic medium. Erosion and degradation pathways have been identified, indicating ways to consciously tailor the physicochemical properties of these new biomimetic materials. © 2016 Society of Chemical Industry     

Electrochemical copolymerization of pyrrole and thiophene nanofibrils using template‐synthesis method

Copolymer nanofibrils composed of pyrrole and thiophene were prepared by synthesizing the desired polymer within the pores of microporous anodic aluminum oxide (AAO) template membranes. The copolymer nanofibrils were photographed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for microstructure analyses. The results of the SEM and TEM revealed that the copolymer nanofibrils obtained had uniform and well‐aligned arrays and their diameter and length could be controlled by changing the aspect ratios of the AAO membrane. The results of cyclic voltammetry and IR spectrometry indicated that polypyrrole and polythiophene were both involved in the copolymer. The nanofibrils that were obtained were identified as copolymers rather than composites. The influence of the applied polymerization potential on the synthesis of copolymer nanofibrils was investigated. The higher potential favored the incorporation of thiophene units into the copolymer nanofibrils. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2403–2407, 2002     

Low potential electrodeposition of high‐quality and freestanding poly(3‐(6‐bromohexyl)thiophene) films

High‐quality freestanding and conducting poly[3‐(6‐bromohexyl)thiophene] (PBHT) films with electrical conductivity of 20 S/cm were synthesized electrochemically by direct anodic oxidation of 3‐(6‐bromohexyl)thiophene (BHT) in boron trifluoride diethyl etherate (BFEE). The oxidation potential of BHT in pure BFEE was measured to be only 1.2 V versus saturated calomel electrode, SCE much lower than that determined in acetonitrile (ACN) (1.8 V vs SCE). The polymer films obtained from this media were very shiny and flexible and can be easily cut into various shapes. The structure and morphology of the polymer films were investigated by UV‐vis, infrared, ¹H‐NMR spectroscopy, thermal analysis, and scanning electron microscopy (SEM). All these results indicated that the terminal bromide did not have negative effect on the electrochemical polymerization of BHT. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Novel 2,4‐divinyl‐3‐alkylthiophene/1,3,4‐oxadiazole alternating conjugated copolymer synthesized by the Heck coupling method: Synthesis,characterization, and electronic and optical properties

A novel alternating copolymer with 3‐alkylthiophene and oxadiazole (or pyridine) units in ordered arrangement was synthesized with vinyl as a bridge for the first time. The synthesis process included four steps: bromomethylation, preparation of the ylide monomer, the formation of 2,4‐divinyl‐3‐alkylthiophene, and Heck alternating copolymerization. The Fourier transform infrared spectroscopy, ¹H‐NMR, and gel permeation chromatography measurements showed that all of the copolymers had the required structures. The weight‐average molecular weights of the copolymers were in the range 5500–15,000 with a relatively low polydispersity index of 1.4–1.7. The solubility of the copolymers in common solvents (e.g., methylene chloride, chloroform, tetrahydrofuran) was excellent. The optical properties and bandgap of the copolymers was compared with corresponding poly(3‐alkylthiophene) homopolymers. The photoluminescence quantum efficiency (QE) of the copolymers improved markedly in chloroform. The QEs of poly(2,4‐divinyl‐3‐hexylthiophene‐alt‐2,5‐diphenyl‐1,3,4‐ oxadiazole) and poly(2,4‐divinyl‐3‐octythiophene‐alt‐2,5‐diphenyl‐1,3,4‐oxadiazole) were 43.2 and 34.2%, respectively, which were about 20 and 21 times higher than those of the homopolymers, respectively. The ionization potential of the copolymers between 5.53 and 6.13 eV was appropriated to poly(3‐alkylthiophene)s. The high electron affinity of the copolymers (2.71–2.95 eV) made the electrons inject from the cathode more easily. With excellent solubility, low bandgap energy, high QE, and both electron‐transporting and hole‐transporting abilities, the proposed copolymers might be excellent polymeric materials for applications in polymer light‐emitting diodes, light‐emitting electrochemical cells, and polymer solar cells. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Nuclear magnetic resonance in solid ethylene/α-olefin copolymers: Relaxation,spin-diffusion and lamellar widths

¹H and ¹³C-n.m.r. spectra and spin-lattice relaxation behaviour (laboratory frame, T₁ (¹³C and ¹H), and rotating frame, T_1ρ (¹H)) are reported for a range of solid ethylene copolymers with α-olefins having different types and concentrations of branches. The spin-diffusion model for relaxation in semicrystalline polymers is summarised and some new theoretical results given. The ¹³C high-resolution n.m.r. spectra obtained using both cross-polarisation (c.p.) and single pulse excitation (s.p.e.) methods associate side chain resonances mainly with the mobile, short T_1ρ protons and, hence, the more disordered region of the solids, consistent with the short ¹³C T₁ components. ¹H laboratory-frame spin-lattice relaxation is single component whilst those for ¹³C and the ¹H on-resonance rotating-frame relaxation are both multiexponential processes, requiring a minimum of three components to describe them. Annealing of samples, which is known to increase the lamellar thicknesses of the crystalline region, causes large increases in the longer relaxation time components. The ¹H and ¹³C spin-lattice relaxation data for a set of annealed and quenched ethyl-branched materials having different branch contents are compared in detail with the predictions of the spin-diffusion relaxation model. The results are internally and semi-quantitatively consistent with this theory and it is concluded that for the ¹H spin-lattice relaxation the model is clearly appropriate and for ¹³C it is consistent with observations. Questions concerning the relevance of spin-diffusion for the magnetically dilute ¹³C nucleus at natural abundance are mentioned and possible alternative explanations for the relationships observed are referred to briefly.     

Miscibility,crystallization kinetics,and mechanical properties of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)(PHBV)/poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate)(P3/4HB) blends

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)(PHBV)/poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) blend films were prepared by solvent‐cast method. The nonisothermal crystallization results showed that PHBV and P3/4HB are miscible due to a single glass transition temperature (T_g), which is dependent on blend composition. The isothermal crystallization results demonstrate that the crystallization rate of PHBV becomes slower after adding amorphous P3/4HB with 19.2 mol% 4HB, which could be proved through depression of equilibrium melt point ($T_m^o$ ) from 183.7°C to 177.6°C. For pure PHBV and PHBV/P3/4HB (80/20) blend, the maximum crystallization rate appeared at 88°C and 84°C, respectively. FTIR analysis showed that PHBV/P3/4HB blend films would maintain the helical structure, similar to pure PHBV. Meanwhile, with increasing P3/4HB content, the inter‐ and intra‐interactions of PHBV and P3/4HB decrease gradually. Besides, a lower elastic modulus and a higher elongation at break were obtained, which show that the addition of P3/4HB would make the brittle PHBV to ductile materials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Study on copolymerization of ethylene/1‐hexene catalyzed by a novel polystyrene‐supported metallocene catalyst

Ethylene/1‐hexene copolymerization was carried out with polystyrene‐supported metallocene catalyst. It was found that the kinetic of the copolymerization was strongly influenced by the steric hindrance of carrier. The influences of 1‐hexene concentration in the feed on catalyst productivity and comonomer reactivity were investigated. The microstructure of resultant copolymer was analyzed by ¹³C NMR. It was found that the different carriers have slight effect on the composite of copolymer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1574–1577, 2006     

Copolymerization kinetics of acrylonitrile with amino ethyl‐2‐methyl propenoate in H2O/DMSO mixture

Amino ethyl‐2‐methyl propenoate (AEMP) was used successfully to copolymerize with acrylonitrile (AN). This was achieved by using azobisisobutyronitrile as the initiator. Kinetics of copolymerization of AN with AEMP was investigated in H₂O/dimethylsulfoxide (DMSO) mixture between 50 and 70 °C under N₂ atmosphere. The rate of copolymerization was measured. The kinetic equation of copolymerization system was obtained and the overall activation energy for the copolymerization system was determined. Values of monomer apparent reactivity ratios were calculated using Kelen–Tudos method. It has been found that the apparent reactivity ratios in aqueous suspension polymerization system are similar to those in solution polymerization system at polymerization conversion less than 25%. At conversion beyond 45%, the changes of monomer apparent reactivity ratios become less prominent. In water‐rich reaction medium (H₂O/DMSO > 70/30), monomer apparent reactivity ratios are approximately equivalent to those in aqueous suspension polymerization system. In DMSO‐rich reaction medium (DMSO/H₂O > 70/30), apparent reactivity ratios are similar to those in solution polymerization system. With an increase of polarity of solvent, values of apparent reaction ratios both decrease. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2095–2100, 2006     

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     

Characterization of conducting poly(3‐methylthiophene) films prepared under sono‐electrochemical conditions

Poly(3‐methlthiophene) films were prepared under “silent” and “sono‐electrochemical” potentiostatic (SEP) conditions. A three‐electrode one‐compartment sono‐cell was used with a working platinum disc electrode. The sono‐electrochemically formed polymer films were deposited with different working electrode‐to‐horn distances. The composition, electrochemical, spectroscopic, and morphological characteristics of the resulting polymer films were determined. Elemental analysis, FTIR‐spectra, and X‐ray photoelectron spectroscopy (XPS) data proved that the polymer films prepared under SEP conditions have predominant α‐α′‐couplings between the 3MT units, and the aromatic ring integrity is maintained in the film. Scanning electron microscopy showed that those films are more compact and less porous compared to the films prepared under silent conditions. The use of sono‐irradiation during electropolymerization enhanced the diffusion of the monomer units towards the electrode surface and resulted in relatively less doped polymers with less conductivity. Electrochemical impedance spectroscopy (EIS) data for films prepared under silent and SEP conditions were collected in a monomer‐free solution. The results show that the impedance of SEP films is relatively higher than those prepared under silent conditions, and a combination of charge transfer kinetics with diffusion‐controlled conduction mechanism within the films. The diffusion was found to be a function of the porosity of the film. Conductivity measurements are in good agreement with EIS, elemental analysis, and XPS data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2416–2425, 2006     

Shape‐memory behaviors of biodegradable poly(L‐lactide‐co‐ϵ‐caprolactone) copolymers

A series of biodegradable poly(L ‐lactide‐co‐?‐caprolactone) (PCLA) copolymers with different chemical compositions are synthesized and characterized. The mechanical properties and shape‐memory behaviors of PCLA copolymers are studied. The mechanical properties are significantly affected by the copolymer compositions. With the ?‐caprolactone (?‐CL) content increasing, the tensile strength of copolymers decreases linearly and the elongation at break increases gradually. By means of adjusting the compositions, the copolymers exhibit excellent shape‐memory effects with shape‐recovery and shape‐retention rate exceeding 95%. The effects of composition, deformation strain, and the stretching conditions on the recovery stress are also investigated systematically. A maximum recovery stress around 6.2 MPa can be obtained at stretching at T_g ? 15°C to 200% deformation strain for the PCLA70 copolymer. The degradation results show that the copolymers with higher ?‐CL content have faster degradation rates and shape‐recovery rates, meanwhile, the recovery stress can maintain a relative high value after 30 days in vitro degradation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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     

Synthesis of well‐defined polystyrene by radical polymerization using 1,1,2,2‐tetraphenyl‐1,2‐ethanediol/feCl3/PPh3 initiation system

Well‐defined polystyrenes with an α‐hydrogen atom and an ω‐chlorine atom end groups and narrow polydispersity (M_n = 2500–4200, M_w/M_n = 1.29–1.48) have been synthesized by a free radical polymerization process using a 1,1,2,2‐tetraphenyl‐1,2‐ethanediol (TPED)/FeCl₃/PPh₃ initiation system. The end groups were monitored by ¹H nuclear magnetic resonance spectroscopy. When the polymerization of styrenes in bulk carried out at 120°C and the ratio of [St]₀ : [TPED]₀ : [FeCl₃]₀ : [PPh₃]₀ was 200 : 1 : 4 : 12, the polymerization exhibited some living/controlled radical polymerization characteristics. The polymerization mechanism was proposed proceeding via a reverse atom transfer radical polymerization (ATRP). Because the polymers obtained were end‐functionalized by chlorine atoms, they were used as macroinitiators to proceed chain extension polymerization in the presence of CuCl/2,2′‐bipyridine catalyst system via a conventional ATRP process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1607–1613, 2000     

Zur Synthese und Funktionalisierung neuer Poly[(silylen)‐2,5‐thiophene]

Treatment of 2,5‐dilithiothiophene with (dimethylamino) methylsilylbis(triflates) gave poly[(dimethylamino‐silylene)‐2,5‐thiophene] 4 in high yield. The amino–silyl bond was cleaved selectively by triflic acid leading to triflate substituted poly[(silylene)‐2,5‐thiophene] 5 . Conversions of this polymers with nucleophiles gave other functionalized derivatives 6 – 9 . Hydrosilylation reaction between silicon–vinyl and silicon–hydrogen derivatives results in polymer networks which may serve as interesting preceramic materials. The structures of the polymers were proven by NMR spectroscopy (²⁹Si, ¹³C, ¹H).