Influence of Surface Carbon Deposition on the Bulk Crystallization of Isotactic Polypropylene

Summary: The effect of a surface‐vacuum‐evaporated ultrathin carbon layer on the bulk crystallization behavior of isotactic polypropylene (iPP) films was investigated by means of polarized optical microscopy, differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction. Results obtained from both isothermal crystallization and constant cooling experiments indicate that surface carbon deposition on an iPP film can remarkably increase the crystallization ability of it during the melt recrystallization process. Optical microscopy observations show that the melt recrystallization of iPP with a carbon coating starts about 10 °C earlier than the pure iPP during a re‐cooling process of 1 °C · min^?1. Under isothermal crystallization conditions, a much shorter induction period for nucleation is required for the carbon‐coated iPP than the non‐carbon‐coated one. The wide‐angle X‐ray diffraction and DSC analyses further demonstrate a crystallinity increment of the carbon‐coated iPP with respect to its non‐carbon‐coated counterpart. This clearly indicates that the strong influence of the interfacial interaction between the vacuum‐evaporated carbon and the iPP film on its bulk crystallization can be extended deep into the bulk material.

An OM micrograph of a hot‐pressed partially carbon‐coated (top half) iPP film.     

Synthesis of New Blue Anthracene‐based Conjugated Polymers and Their Applications in Polymer Light‐Emitting Diodes

A series of anthracene‐based conjugated copolymers containing 9,10‐bis(6‐bromonaphthalen‐2‐yl)‐2‐tert‐butylanthracene (BNA) and 2,7‐diphenyl substituted fluorene (DPPF) moieties are prepared via a palladium‐catalyzed Suzuki polymerization. All of the synthesized polymers emit blue light at around 450 nm and show good thermal and color stability. Their electroluminescence spectra remain unchanged at high driving voltage. The double‐layer polymer light‐emitting diode (PLED) fabricated with ITO/PEDOT:PSS/DPPFBNA3/CsF/Al, produces a maximum brightness of 1 650 cd · m^?2 and has a luminance efficiency of 0.39 cd · A^?1. The ITO/PEDOT:PSS/TFB/DPPFBNA3/CsF/Al multilayer PLED, incorporating a TFB layer to facilitate hole transportation, produces a maximum brightness of 5 371 cd · m^?2 and a luminance efficiency of 1.18 cd · A^?1.

     

Polyester Dendrimers Carrying NLO Chromophores: Synthesis and Optical Characterization

Summary: Four dendritic polyesters containing non‐linear optical chromophores on the periphery were synthesized and their material properties were compared for electro‐optic device applications. Thermal and optical parameters of the dendrimer materials were measured along with structural analysis. A high chromophore concentration in the dendritic polyesters produced enhancement of the optical non‐linearity. The second generation dendrimer (G1‐DAIDC) exhibited an electro‐optic coefficient of 43.4 pm · V^?1 at 1.55 µm optical communication wavelength. Aromatic ester backbones elevate the glass transition temperature of the chromophore alignment, representing good thermal stability of the optical films.

     

Synthesis of Telechelic Oligomers via Atom Transfer Radical Polymerization, 3

Summary: ATRP of butyl α‐fluoroacrylate (FABu) was carried out at 90 °C using methyl 2‐bromoisobutyrate (2‐MBiB) as initiator and the homogeneous catalyst CuBr/1,1,4,7,10,10‐hexamethyltriethylenetetramine (HMTETA). Telechelic oligomers were obtained by coupling the bromo terminated polymers in the presence of Cu⁽⁰⁾ and 2,2′‐bipyridyl ligand. The ¹H and ¹⁹F NMR, SEC and MALDI TOF analyses show that the poly(FABu) chains recombination was the main reaction (80% yield). About 20% of disproportionation reaction also occurs in the process, whereas transfer reactions can be neglected.

Compounds produced by recombination, disproportionation and transfer during the coupling reaction of poly(FABu) oligomers.     

An Easy Strategy for the Synthesis of Well‐Defined Aliphatic‐Aromatic Hyperbranched Polyesters

A one‐pot solution polymerization under mild conditions was adapted for the synthesis of well‐defined aliphatic‐aromatic polyesters with different degrees of branching. The esterification was performed at room temperature using 4,4‐bis(4′‐hydroxyphenyl)valeric acid (AB₂) and 3‐(4‐hydroxyphenyl)propionic acid (AB) as monomers. DPTS was used as a catalyst and DCC as a coupling agent. Polyesters with statistical, dendritic topology, controlled degree of branching and > 35 000 g · mol^?1 were obtained. The polymers were characterized by ¹H and ¹³C NMR, SEC, DSC, and TGA. A strong dependence of the degree of branching and the thermal properties of the polymers depending on the AB/AB₂ monomer ratio was observed.

     

The Rapid Chain Extension of Anthracene‐Functional Polyesters by the Diels‐Alder Reaction with Bismaleimides

Summary: The chain extension of anthracene end‐capped oligoesters by reaction with bismaleimides constitutes a rapid route to high molecular weight polyesters. Polytransesterification of bis(2‐hydroxyethyl) terephthalate in the presence of a small amount of 2‐hydroxyethyl 2‐anthracenecarboxylate provides low molecular weight anthracene‐terminated macromers with anthracene end group functionality (f_AN) of 1.66–1.85. These are subject to rapid chain extension with di(4‐maleimidophenyl)methane by Diels‐Alder cycloadditions resulting in consumption of the anthracene and maleimide end groups to generate polymers with > 2.0 × 10⁴ g · mol⁻¹. Thus, generation of the polymeric structure is achieved rapidly by addition reactions rather than sluggish transesterification reactions in which a condensate must be removed from the viscous polymer melt.

Chain extension of low‐molecular weight 2‐anthracenecarboxylate terminated oligoesters.     

Synthesis and self‐assembly of polymers containing dicarboximide groups by living ring‐opening metathesis polymerization

Polymers with narrow molecular weight distributions and controlled architectures were generated by living ring‐opening metathesis polymerization of exo‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboximide. The dicarboximide units have been previously shown to exhibit biological activity, can selectively bind to the nucleic acid base adenine by hydrogen‐bonding, and are readily functionalizable. Block copolymers containing these moieties were generated, and underwent self‐assembly into nanoscale spherical aggregates, with surface localized molecular recognition motifs.

     

Modification of Polyethylene by VUV Irradiation in the Presence of Trimethylsilane and Oxygen

The photoassisted modification of LDPE by VUV irradiation in a reactive trimethylsilane/oxygen atmosphere was investigated. The modified LDPE surface was investigated by FT‐IR, XPS, contact‐angle measurements and electron microscopy. Attachment of alkylsilyl and Si–O units to LDPE was observed. Best results were obtained using an equimolar trimethylsilane/oxygen mixture. Low‐energy surfaces were obtained after a few minutes of irradiation at an intensity of 1.7 mW · cm^?2. After prolonged irradiation, the thickness of the modified polyethylene layer is approximately 700 nm. Surface modifications of this type may be of interest to obtain protective and barrier layers on polyolefins.

     

Preparation and Characterisation of Hydrophobically Modified Hydroxypropylcellulose: Side‐Chain Crystallisation

Summary: Hydroxypropylcellulose has been hydrophobically modified by reaction with different amounts of palmitoyl chloride. When the degree of substitution is sufficiently high, the side chains are able to produce lateral crystallisation, which has been analysed by DSC and diffraction experiments, using both conventional and synchrotron radiation. The melting temperatures and enthalpies depend on the degree of substitution, in such a way that it is relatively easy to get melting temperatures close to that of the human body, although a rather wide melting region is obtained.

X‐ray diffractograms of the original HPC sample and of the modified specimens.     

Branched and Functionalized Polybutadienes by a Facile Two‐Step Synthesis

Anionic polymerization was used to prepare silane‐endfunctionalized polybutadiene macromonomers with different molecular weights ranging from 9 000 to 34 000 g · mol^?1. These were polymerized by a hydrosilylation reaction in bulk to obtain branched polymers, using Karstedt's catalyst. Surprisingly, the addition of monofunctional silanes during the polymerization showed only a minimal effect concerning the degree of polymerization. Furthermore, it was possible to introduce a variety of functional silanes without increasing the overall number of reaction steps by a convenient AB₂ + A type “pseudocopolymerization” method. All branched polymers were analyzed by SEC, SEC‐MALLS, SEC‐viscosimetry. ¹H NMR spectroscopy, and DSC concerning their branching ratio. The branching parameters for the branched polymers exhibited similar characteristics as for hyperbranched polymers obtained from conventional AB₂ monomers. Detailed kinetic studies showed that the polymerization occurred very rapidly in comparison to the hydrosilylation polymerization of classical AB₂ type carbosilane monomers.

     

Fluorinated Styrene‐ and Carbazole‐Based Cladding Polymer Layers for EO and NLO Polymer Devices

Novel polymer cladding materials were synthesized and their potential for use in optical waveguide devices was investigated. 9‐[2‐(2,3,5,6‐Tetrafluoro‐4‐vinylphenoxy)ethyl]‐9H‐carbazole and 1‐pentafluorophenylpyrrole‐2,5‐dione were used as comonomers for preparing the acrylic cladding copolymers. These showed a low resistivity (≈2 × 10¹³ Ω · cm) at room temperature and a low optical loss (?0.6 dB · cm^?1) at a wavelength of 1.55 µm. The refractive indexes and the glass transition temperatures of the polymer cladding materials can be controlled by the composition of the copolymers. The resulting polymers are good candidates for cladding materials for practical applications in devices.

     

Investigation of Templated Mesoporous Silicate Thin Films Using High Speed,Solid‐State 1H MAS and Double Quantum NMR Spectroscopy

Two‐dimensional DQ ¹H MAS NMR has been used the investigate the local structure of a surfactant‐templated silicate thin film prepared from adding 4% polyoxyethylene(10) cetyl ether to an acidic TEOS silica sol. A close spatial contact between the surfactant and the silicate present in these materials could be demonstrated, while the high sensitivity of the NMR experiments allowed systems with limited amounts of material to be investigated. The detected inorganic‐organic interactions in these materials provide additional information into the chemical processes occurring during the self‐assembly process and the formation of meso‐structured materials.

Graphical representation of the spatial interactions observed between the silanols, oxomethylene protons of the surfactant and water within the template silicate material.     

Hydroxyl‐Functionalized Norbornene Based Co‐ and Terpolymers by Scandium Half‐Sandwich Catalyst

Copolymerization of ethylene with 5‐norbornene‐2‐methanol and terpolymerization of ethylene with norbornene and 5‐norbornene‐2‐methanol by a rare‐earth metal based catalyst, specifically the half‐sandwich bis(alkyl) scandium precursor [Sc(η⁵‐C₅Me₄SiMe₃)(η¹‐CH₂SiMe₃)₂(THF)] activated by [Ph₃C][B(C₆F₅)₄] were successfully achieved for the first time. A protocol for masking of ? OH functionality by AlⁱBu₃ to avoid catalyst poisoning was exploited. Copolymers with high molar masses and noticeable incorporation of functionalized norbornene derivative were obtained. Terpolymers with very high molar masses and with a broad range of composition were prepared with excellent yields.

     

Characterization of Carbon Monoxide Centered Triads in Poly[ethylene‐co‐(butyl acrylate)‐co‐(13C‐carbon monoxide)] by Isotopic Labeling and Two‐Dimensional NMR

Summary: Poly[ethylene‐co‐(butyl acrylate)‐co‐(carbon monoxide)] (polyEBC) samples, prepared from ¹³C‐labeled carbon monoxide, were characterized using two dimensional (2D) pulsed field gradient (PFG) 750 MHz NMR spectroscopy. To elucidate the complex mixture of structures present in this terpolymer, 2D ¹H/¹³C‐heteronuclear multiple bond correlation (HMBC) experiments were conducted by selectively exciting the enhanced peaks resulting from ¹³C‐labeling. High resolution 2D NMR combined with ¹³C‐labeling of the polymer greatly simplifies the 2D NMR spectra, selectively enhances the weak peaks from low occurrence C‐centered triad structures and aids in their resonance assignments.

     

A Facile One‐Pot Synthesis to Dextran‐Based Nanoparticles with Carboxy Functional Groups

Summary: Stabilized nanoparticles functionalized with carboxy groups were synthesized directly from dextran and acrylic acid (AA), without using any organic solvent and surfactant. The composition and morphology of these dextran‐based nanoparticles, as well as the mechanism of this one‐pot synthesis, were also investigated in this paper. This approach is anticipated to be applicable to various water‐soluble polysaccharides to fabricate nanoparticles facilely.

Facile synthesis of stabilized nanoparticles functionalized with carboxy groups from dextran and AA.     

Fullerene Substitution of Donor/Acceptor Branched Disubstituted Polyacetylenes: Significantly Accelerated Polymerization by the C60 Pendant

A novel type of soluble donor/acceptor branched disubstituted polyacetylene ( PA–C ₆₀ ) bearing C₆₀ and soft pentyl moieties in side‐chains was synthesized successfully. The product has been characterized by FTIR, ¹H NMR, ¹³C NMR, C? H COSY, UV‐vis, and fluorescence spectroscopies, confirming its branched polymeric structure comprising polyacetylene chains and covalently bound C₆₀ cages in side‐chains. Surprisingly, completely different from the conventional metathesis polymerization of acetylenes, it is found for the first time that the disubstituted monomer 4 can be polymerized within a very short reaction time (up to 1.5 min) and the molecular weight of the synthesized PA–C ₆₀ is independent of the reaction time. A plausible interpretation is proposed to understand the rapid polymerization reaction accelerated by the C₆₀ pendant. The optical properties of PA–C ₆₀ were studied by UV‐vis absorption and fluorescence spectroscopies, which indicated that the fluorescence of PA–C ₆₀ is significantly enhanced compared to monomer 4 , presumably due to its branched structure. SEM studies on the thin film morphology of PA–C ₆₀ in comparison with monomer 4 suggested the successful polymerization of monomer 4 and revealed that PA–C ₆₀ has a much smoother morphology than the aggregated morphology of monomer 4 .

     

Electroactive Polymer with Oligoanilines in the Main Chain: Synthesis,Characterization and Dielectric Properties

An electroactive polymer with well‐defined oligoanilines in the main chain has been prepared by oxidative coupling polymerization. The detailed characteristics of the polymer were systematically studied by FT‐IR, ¹H NMR, GPC and XRD. Its electrochemical behavior was explored with UV‐Vis spectra and cyclic voltammetry showing that its intrinsic electroactivity was maintained and exhibited three distinct reversible oxidative states. Its electrical conductivity is about 3.91 × 10^?4 S · cm^?1 in HCl‐doped form at room temperature. Furthermore, the polymer displays a dielectric constant of 48.4 and 13.6 at 10 and 1 MHz, respectively, mainly attributed to the improvement in delocalized charge density and electrical conductivity of the polymer by introduction of the conjugated oligoaniline segments.

     

Synthesis,Crystallization, and Enzymatic Degradation of the Biodegradable Polyester Poly(ethylene azelate)

Poly(ethylene azelate) (PEAz) was synthesized and its melting behavior was studied with DSC and Step Scan DSC. The equilibrium melting point of PEAz was found 62 °C and the heat of fusion of 100% crystalline polymer was estimated at 160 J · g^?1. Polarized light microscopy showed mixed birefringence. From isothermal crystallization DSC study, after self‐nucleation, crystallization rates were estimated. The Lauritzen–Hoffman plots showed crystallization regime I to II and II to III transition at 34 and 19 °C respectively. Non‐isothermal crystallization was studied. The activation energy was calculated applying the isoconversional method of Friedman. Chemical hydrolysis of PEAz was very slow, while enzymatic hydrolysis showed comparable rates with PCL.

     

Low‐Temperature Polymerization of Olefins in the Presence of Titanium Monoamidinate/MAO Catalyst

This paper reports the predominantly syndiotactic‐specific polymerization of propylene in the presence of titanium monoamidinate/methylaluminoxane (MAO) catalysts. The same catalysts, depending on the reaction conditions, also promote either predominantly 1,4‐cis or 1,4‐trans polymerization of 1,3‐butadiene and polymerization of styrene either to highly syndiotactic or to stereoirregular polymer. Some preliminary information about the features of propylene polyinsertion is also reported.

Expansion of the 20–24 ppm region of the ¹³C NMR spectrum of sample 2. The starred resonance at 21.75 ppm and the shoulders are not assigned.     

Blue Light Emission from a Fluorene‐Carbazole‐Fluorene Trimer Incorporated as the Side Chain into a Polynorbornene

Summary: A well defined blue electroluminescent fluorene‐carbazol‐fluorene trimer 3,6‐bis‐(9,9‐dihexyl‐9H‐fluoren‐3‐yl)‐9‐alkyl‐9H‐carbazole was synthesized using a Suzuki type cross coupling reaction as the key step. A way to attach this chromophore to a norbornene was developed and the resulting electroactive monomer was polymerised using the “3^rd generation Grubbs catalyst” (N,N‐bis(mesityl) 4,5‐dihydroimidazol‐2‐ylidene)(3‐bromo‐pyridine)₂(Cl)₂Ru?CHPh), yielding an amorphous polymer with a narrow molecular weight distribution, which was used to build a light‐emitting diode exhibiting electroluminescence peaking at 410 nm.

Incorporation of the fluorene‐carbazol‐fluorene trimer as the emissive layer in an ITO/PEDOT:PSS/emitter/Ca/Al light emitting device.