Synthesis and Characterization of Biodegradable Poly(ε‐caprolactone)‐Polyglycolide‐Poly(ethylene glycol) Monomethyl Ether Random Copolymer

Summary: Poly(ε‐caprolactone)‐polyglycolide‐poly(ethylene glycol) monomethyl ether random copolymers were synthesized from ε‐caprolactone (ε‐CL), glycolide (GA) and poly(ethylene glycol) monomethyl ether (MPEG) using stannous octoate as catalyst at 160 °C by bulk polymerization. The copolymers with different composition were synthesized by adjusting the weight ration of reaction mixture. The resultant copolymer with a weight ratio (10:15:75) of MPEG2000, GA, and CL was characterized by IR, ¹H NMR, GPC and DSC. The new biodegradable copolymer has potential for medical applications since it is combined with properties of PCL, PGA and MPEG.

     

Elaboration of Poly(ε‐caprolactone)‐g‐TiNbO5 Nanocomposites via in situ Metal Complex Initiated Intercalative Polymerization

Summary: The preparation of poly(ε‐caprolactone)‐g‐TiNbO₅ nanocomposites via in situ intercalative polymerization of ε‐caprolactone initiated by an aluminium complex is described. These nanocomposites were obtained in the presence of HTiNbO₅ mineral pre‐treated by AlMe₃, but non‐modified by tetraalkylammonium cations. These hybrid materials obtained have been characterized by Fourier transform infrared absorption spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and dynamic mechanical analysis. Layered structure delamination and homogeneous distribution of mineral lamellae in the poly(ε‐caprolactone) (PCL) is figured out and strong improvement of the mechanical properties achieved. The storage modulus of the nanocomposites is enhanced as compared to pure PCL and increases monotonously with the amount of the filler in the range 3 to 10 wt.‐%.

SEM image of the fractured surface of a PCL‐TiNbO₅ nanocomposite film.     

In Situ Preparation of a Compatibilized Poly(cis‐1,4‐butadiene)/Poly(ε‐caprolactone) Blend

The ternary Ziegler‐Natta‐type catalyst system based on neodymium versatate (NdV), diisobutylaluminium hydride (DIBAH) and ethylaluminium sesquichloride (EASC) was used for the in situ preparation of a compatibilized blend consisting of poly(cis‐1,4‐butadiene) (BR = butadiene rubber) and poly(ε‐caprolactone) (PCL). Poly(cis‐1,4‐butadiene)‐block‐poly(ε‐caprolactone) which acts as compatibilizer for the two immiscible polymers BR and PCL was obtained by a two step sequential polymerization with the preparation of a living cis‐1,4‐BR building block in the first stage and the subsequent polymerization of CL during the second stage. This preparation method resulted in a polymer blend comprising the homopolymers BR and PCL as well as the block copolymer BR‐block‐PCL. For detailed characterization the block copolymer was separated from the respective homopolymers BR and PCL by means of fractionation with the binary solvent mixture dimethylformamide/methylcyclohexane (DMF/MCH) which mixes well at elevated temperature and exhibits phase separation at ambient temperature. ¹H NMR, IR, SEC and TEM were used for characterization of the block copolymer.

TEM of BR‐block‐PCL.     

Long‐Aliphatic‐Segment Polyamides: Salt Preparation and Subsequent Anhydrous Polymerization

Long‐aliphatic‐segment polyamides were prepared based on hexamethylenediamine and α,ω‐(CH₂)_x biosynthetic diacids (x = 10, 11, 12). The pertinent monomers (salts) were isolated as solids, thoroughly characterized for the first time, and then submitted to an anhydrous melt prepolymerization technique. The obtained prepolymers exhibited in the range of 5 100–11 800 g · mol^?1, and the molecular weight was further increased by up to 55% through solid‐state finishing. The suggested overall polyamidation cycle was conducted at short melt‐reaction times, so as to avoid any thermal degradation, and was proved efficient, indicating similar reactants polymerizability independently of the methylene content.

     

Monomers for Adhesive Polymers 12 Synthesis and Free‐Radical Homo‐ and Copolymerization of 2‐Ethoxycarbonylallyl 5‐(1,2‐dithiolane‐3‐yl)‐pentanoate

The 2‐ethoxycarbonylallyl 5‐(1,2‐dithiolane‐3‐yl)‐pentanoate monomer (AODS) includes in its molecular structure C?C and S? S reactive bonds allowing it to behave as a bi‐functional monomer, possessing two groups, however, with different reactivity for use in polymer chain building. The polymerization‐specific features of this monomer are the absence of auto‐acceleration and polymer chain crosslinking. Polymerization proceeds readily through most free‐radical initiators. One exception, carboxy‐peroxides are rapidly decomposed without the production of free radicals. AODS is partially converted to a gel without the consumption of double bonds during monomer dissolution in certain organic solvents and after being mixed in solution with carboxy‐peroxides. The determined AODS‐co‐MMA copolymerization parameters are r₁ = 2.61, r₂ = 0.23 if Luperco peroxide is used as a polymerization initiator, and r₁ = 2.71, r₂ = 0.38 if AIBN is used.

     

In vitro Degradation of Poly[(L‐lactide)‐co‐(trimethylene carbonate)] Copolymers and a Composite with Poly[(L‐lactide)‐co‐glycolide] Fibers as Cardiovascular Stent Material

TMC/LLA copolymers with several TMC/LLA ratios are synthesized and a composite is obtained by reinforcing with short PLGA fibers. In vitro degradation is studied at 37 °C in pH = 7.4 buffer and compared with a PLLA homopolymer. The degradation of the copolymers appears slower than that of PLLA, showing that TMC units are more resistant to hydrolysis than LLA. Compositional changes indicate a preferential degradation of LLA units as compared to TMC ones. Morphological changes with crystallization of degradation by‐products are observed. The composite degrades much faster than the neat copolymer and PLLA because the faster degradation of PLGA fibers speeds up the degradation of the matrix. The composite appears promising for the fabrication of totally bioresorbable stents.

     

Near Infrared Reflection Spectroscopy: A Versatile Tool for Rapid Characterization of Olefin Copolymers and High‐Throughput Experiments

Near infrared (NIR) spectroscopy was developed as a rapid analytical method for the determination of the composition of olefin copolymers obtained in high‐throughput screening. NIR spectra of ethene/propene and ethene/1‐hexene copolymers, also characterized by means of ¹³C NMR spectroscopy, were recorded and used to design multivariate calibration models. Different methods for the preprocessing of the spectra, including the linearization by non‐linear transformations, were compared. Optimal methods and error estimates were established using crossvalidation. This technique is of particular interest for the rapid on‐line analysis of high‐throughput experiments in the field of polymer and catalyst design employing methods from combinatorial chemistry.

Predicted versus true value of the propene incorporation and standard deviation for ethene/propene copolymers.     

Synthesis of Block Copolymers containing Chain‐Controlled Aramid and Fluoroethylene Segments

Summary: Novel block copolymers containing aromatic polyamide (aramid) and fluoroethylene segments were synthesized by a two‐step solution polycondensation. This synthetic method could control the chain‐length of aramid segments and these copolymers could have high structural regularity. The number‐average molecular weight ( ) of one of these polymers is over 2.0 × 10⁴. Incorporating fluoroethylene segments improves the solubility of the resulting polymer compared with conventional aramids.

The synthesis of the fluoroethylene‐aramid block copolymers.     

Chiral N,N′‐Dioxide–Yttrium Triflate Complexes‐Catalyzed Asymmetric Aldol Cyclization of α‐Keto Esters with α‐Isothiocyanato Imide

A highly effective aldol cyclization of α‐isothiocyanato imide to both β,γ‐unsaturated α‐keto esters and aryl‐substituted α‐keto esters has been developed. A chiral N,N′‐dioxide–yttrium triflate complex was used as the catalyst. A series of cyclic thiocarbamates bearing chiral quaternary stereocenters was synthesized in good to high yields, excellent diastereo‐ (up to 25:1 dr) and enantioselectivities (up to 99 % ee). In addition, the reaction could be carried out on a gram‐scale, and other functionalized derivatives are also conveniently transformed. Interestingly, a discrepancy of diastereoselection was observed between the reactions of β,γ‐unsaturated α‐keto esters and aryl‐substituted α‐keto esters. Moreover, a substrate dependency of non‐linear effects was observed in this reaction. On the basis of the experimental results and the absolute configuration of the products, possible catalytic models have been proposed to explain the origin of the asymmetric process.

     

1,8‐Naphthalimides as Blue Emitting Fluorophores for Polymer Materials

The copolymerization of 1,8‐naphthalimide derivatives (as fluorophore) with acrylonitrile has been investigated. The photophysical characteristics of monomeric and polymeric fluorophores in N,N‐dimethylformamide solution have been determined and discussed. During copolymerization, no changes in the chromophoric systems of the fluorophore occur. The influence of the studied monomeric 1,8‐naphthalimide fluorophores upon the structurally bleached polyacrylonitrile has been determined. Infrared absorption characteristics of the polymerizable 4‐alkoxy‐ and 4‐allyloxy‐N‐substituted‐1,8‐naphthalimides have been measured and discussed. The effect of the substituents upon the vibration frequencies of the carbonyl and allylic groups has been established.

Blue fluorescent polyacrylonitrile copolymers with 1,8‐naphthalimides side‐group.     

Fracture Behaviour of Styrene/Butadiene Block Copolymers having Different Molecular Architecture

The crack toughness behaviour of styrene/butadiene block copolymers of triblock and star architectures was investigated using instrumented Charpy impact testing. In order to evaluate adequately the toughness behaviour of the investigated materials, different concepts of elastic‐plastic mechanics (J‐integral and crack‐tip opening displacement, CTOD concepts) were used. Although the lamellar block copolymers showed a remarkably enhanced ductility in the tensile test than the neat block copolymer having hexagonal PB cylinders in PS matrix, no pronounced difference in crack toughness was found. This behaviour implies that the tensile strain cannot be regarded as the only parameter defining the toughness value. A brittle/tough transition was observed in a lamellar star block copolymer on blending with a linear thermoplastic elastomeric SBS triblock copolymer.

SEM micrograph showing the details of the stable crack propagation region in a binary block copolymer blend.     

Atom Transfer Radical Block Copolymerization of 2‐(N,N‐Dimethylamino)ethyl Methacrylate and 2‐Hydroxyethyl Methacrylate

Block copolymerization of 2‐(N,N‐dimethylamino)ethyl methacrylate (DMAEMA) with 2‐hydroxyethyl methacrylate (HEMA) via atom transfer radical polymerization (ATRP) was studied in methanol using a macroinitiator method and a “one‐pot” sequential addition method. The polymerization sequence of the two monomers strongly affected the block copolymer formation. When DMAEMA was used as the first monomer, both methods produced block copolymer samples containing significant amounts of DMAEMA homopolymer chains, because of the elimination of active halogen chain‐ends during the preparation of polyDMAEMA. Well‐controlled block copolymers with various block lengths were obtained via the macroinitiator method when polyHEMA was used as macroinitiator to initiate the polymerization of DMAEMA. The sequential addition method, in which HEMA was polymerized first with 90% conversion and DMAEMA was subsequently added, also yielded controlled block copolymers when the polymerization was carried out at room temperature with the DMAEMA conversion below 60%. Increasing the temperature to 60 °C promoted the copolymerization rate but the reaction suffered from gel formation. The addition of water to the system accelerated the polymerization rate, but led to the loss of the system livingness.

Gel permeation chromatograms of poly(HEMA‐b‐DMAEMA). The samples were prepared in methanol at room temperature with different block molecular weights using the macroinitiator method.     

Segmented Block Copolymers with Monodisperse Hard Segments: The Influence of H‐Bonding on Various Properties

The properties of segmented‐copolymer‐based H‐bonding and non‐H‐bonding crystallisable segments and poly(tetramethylene oxide) segments were studied. The crystallisable segments were monodisperse in length and the non‐hydrogen‐bonding segments were made of tetraamidepiperazineterephthalamide (TPTPT). The polymers were characterised by DSC, FT‐IR, SAXS and DMTA. The mechanical properties were studied by tensile, compression set and tensile set measurements. The TPTPT segmented copolymers displayed low glass transition temperatures (T_g, ?70 °C), good low‐temperature properties, moderate moduli (G′ ≈ 10–33 MPa) and high melting temperatures (185–220 °C). However, as compared to H‐bonded segments, both the modulus and the yield stress were relatively low.

     

Poly[ethylene‐co‐(vinyl alcohol)]‐graft‐Poly(ε‐caprolactone) by Reactive Extrusion, 2 – Parameter Analysis

EVOH‐g‐PCL were prepared by a solvent‐free reactive extrusion process using a co‐rotating twin screw extruder. Kinetic simulations were made of selected reaction conditions at 185 °C. Changes in the screw rotation rate resulted in evolution of the residence time distribution and slightly changed the monomer conversion. An increase of the [OH]₀/[Cl]₀ ratio made the reactive system more viscous and decreased the overall pumping capacities of the extruder. Increase of the mean residence time, combined with a positive kinetic effect of [OH]₀ increase, leaded to an important increase in conversion. For all the conducted experiments, equivalent distribution dispersions and good agreements between calculated conversion and those measured were obtained. An increase in temperature from 185 to 200 °C resulted in total conversion.

     

Zinc‐Catalyzed Stereo‐ and Regioselective 1,4‐Hydrative Fluorination of 3‐En‐1‐ynamides with Selectfluor

Zinc‐catalyzed 1,4‐oxofluorinations of 3‐en‐1‐ynamides with Selectfluor in acetonitrile/water proceeded with high regio‐ and stereoselectivity, giving E‐configured γ‐fluoro‐α,β‐unsaturated amides efficiently. Our control experiments indicate that kinetically unstable C‐bound zinc dienolates are chemically reactive to undergo S_E2′‐electrophilic fluorinations whereas the detectable O‐bound dienolates preferably undergo protodemetalation reactions instead.

     

Four‐Electron Electrocyclic Ring‐Opening/Intermolecular [4+2] Cycloadditions of α‐Hydroxycyclobutenones: Stereoselective Synthesis of Multiple Substituted δ‐Lactams

A four‐electron electrocyclic ring‐opening/intermolecular [4+2] cycloaddition of α‐hydroxycyclobutenones is reported. The reaction represents the first example for the intermolecular cycloaddition of the extensively studied enol‐ketene intermediate, and provides a new synthetic route to multiply substituted δ‐lactams in high stereoselectivity.

     

Simulation of Nylon 6 Polymerization in an Industrial Two‐Step VK Tubular Reactor

A commonly used nylon 6 two‐step VK tubular reactor is simulated in this work. To verify the reliability of the model, careful comparison with results obtained on different continuous plants is made. The effect of various conditions and parameters, e.g. feed composition, temperature, pressure, etc. on the product properties such as caprolactam conversion, degree of polymerization (DP), dimer, integral heat and their distribution index is studied. It is observed that the caprolactam conversion and DP of the product may be affected by various conditions in the first stage and the temperature profile at the top of the second stage, but they finally reach the equilibrium values if the residence time is long enough. The most effective way to increase DP of the product is to increase the vacuum at the top of the second stage.

CPL conversion and DP profile for pressure of tube 2: 0.032, 0.037, 0.042 mPa; other parameters as given for example A of Table 5 .     

Grafting of Hindered Amine Stabilizer in Poly(propylene) Films under γ‐Irradiation

Summary: In this paper, the grafting of a hindered amine stabilizer (HAS) is studied in isotactic poly(propylene) (PP) films under γ‐irradiation. The HAS used has a definite structure that combines a hindered amine functionality and a UV‐absorbing unit (benzylidene malonate ester group) detectable at 308 nm in the UV spectrum of PP film and 314 nm in chloroform. The stabilizer is added to the polymer at various concentration ratios: 0.1, 0.2, and 0.3 wt.‐%. The percentage of HAS grafting in the PP film at various additive concentrations is determined as a function of γ‐radiation dose in the range of 0–100 kGy by direct spectroscopic measurements through the absorption band of the stabilizer in the UV spectra of the PP film. The percentage of free HAS extracted with chloroform from the PP film versus the radiation dose is determined by UV spectroscopy for all the additive concentrations used. This study reveals that only 80% of the HAS is grafted on the 100 kGy irradiated PP matrix independent of the additive concentration used. However, the percentage of HAS grafted on PP films displays an exponential dependence on γ‐radiation dose. These results are consistent with the data obtained on the free HAS content. γ‐Irradiation grafting of HAS in the PP is accompanied by the oxidative degradation of the polymer substrate that is evaluated by increasing the carbonyl index and reducing significantly the oxidation induction time of the PP films.

The percentage of hindered amine stabilizer grafted to the PP film as a function of γ‐radiation dose.     

Colloidal Crystalline Arrays of β‐Polymorphic Poly(vinylidene fluoride)

Stable layers of nearly monodisperse spheres of β‐polymorphic poly(vinylidene fluoride) with iridescent properties are prepared. The colloidal crystalline arrays (CCAs) were characterized by optical microscopy, differential scanning calorimetry (DSC), and FT‐IR spectroscopy. FT‐IR spectroscopic and wide‐angle X‐ray scattering (WAXS) studies revealed a β‐polymorphic PVF₂ structure, the DSC study showed that the level of crystallinity in the CCA was much higher than that in the melt‐crystallized sample, and UV‐visible spectroscopy showed extinction peaks at 323 and 510 nm in the CCAs. The β‐polymorphic PVF₂ structure, along with the optical extinction properties of these CCAs, raises the prospect of their application in optical filters and/or piezoelectric sensors.

Optical micrograph of PVF₂ CCA films cast on glass substrates.     

Defined Comonomer Re‐Feeding During the Metallocene‐Catalyzed Copolymerization of 10‐Undecene‐1‐olate with Propene through FTIR In‐Line Monitoring

The consumption of 10‐undecene‐1‐olate (UOA) during its continuous re‐feeding in the metallocene‐catalyzed copolymerization with propene was investigated by ATR‐FTIR spectroscopy in‐line monitoring through evaluation of the integral absorbances of the characteristic IR bands. For the quantitative determination of the comonomer concentration during the copolymerization reaction with and without continuous re‐feeding of UOA, multiple calibration functions based on the chemometric partial least squares method were applied. For the first time, a direct correlation between the consumption of an olefin and the addition of a polar comonomer during a metallocene‐catalyzed copolymerization was demonstrated. By means of this technique, a relatively constant molar stoichiometric ratio of the comonomer and propene over the whole polymerization time was achieved, which is very important in obtaining copolymers with defined random structure and, thus, from the point of view of reaction engineering, constant product quality.