Metathetic Selective Degradation of Polyisoprene: Low‐Molecular‐Weight Telechelic Oligomer Obtained from Both Synthetic and Natural Rubber

Summary: Degradation studies of cis‐1,4‐polyisoprene were carried out using first and second generation Grubbs catalysts to achieve end‐functionalized acetoxy oligomers in both an organic solvent and a latex phase at room temperature. Well‐defined acetoxy telechelic polyisoprene structures were obtained in a selective manner with a range of from 10 000 to 30 000, with a polydispersity index of around 2.5.

Structure produced by the metathetic depolymerization of hydroxy telechelic cis‐1,4‐polyisoprene.     

Relationship between Architecture and Adhesive Properties of Macromolecular Materials, 1

This study deals with the preparation of polyurethane‐graft‐poly(n‐butyl acrylate)s copolymers by polymerization of diphenyl‐methane‐4,4‐di‐isocyanate (MDI) with α,α′‐di‐hydroxyl‐poly(n‐butyl acrylate)s of different sizes as macromonomers. The polyaddition has been studied on the basis of kinetic measurements, and the comb‐like structure of the resulting polymer has been well‐established. Such grafted copolymers display specific adhesive properties in connection with their comb‐like architecture.

     

Pseudo‐Living Anionic Telomerization of Buta‐1,3‐diene

Low‐molecular‐weight liquid polybutadienes (1 000–2 000 g · mol^?1) consisting of 60 mol‐% poly(buta‐1,2‐diene) repeating units were synthesized via anionic telomerization. Maintaining the initiation and reaction temperature at less than 70 °C minimized chain transfer and enabled the polymerization to occur in a living fashion, which resulted in well‐controlled molecular weights and narrow polydispersity indices. MALDI‐TOF mass spectrometry confirmed that the end groups of liquid polybutadienes synthesized via anionic telomerization contained one benzyl end and one protonated end. In comparison, the end groups of liquid polybutadienes synthesized via living anionic polymerization contained one sec‐butyl or butyl end and one protonated end.

     

Influence of Addition of Organoclays on Morphologies in Nylon 6/LLDPE Blends

Summary: Polymer blend nanocomposites containing linear low density polyethylene (LLDPE), nylon 6 and organoclays were prepared by melt mixing, and their morphologies and structures were examined with a field emission scanning electron microscope (FE‐SEM) and an X‐ray diffractometer (XRD). The size of phase‐separated domains decreased considerably with increasing content of organoclay. The d‐spacing of organoclay in the nanocomposites was increased from about 18.6 to over 28 Å. This effect was highly dependent on nylon 6 contents because nylon 6 is more polar and shows higher affinity to the organoclays compared to LLDPE.

     

Lanthanide Metal‐Organic Frameworks as Ziegler–Natta Catalysts for the Selective Polymerization of Isoprene

The unprecedented ability of neodymium‐based metal organic frameworks (MOFs) as polymerisation pre‐catalysts towards isoprene is reported. Combined with methylaluminoxane (MAO) or modified MAO (MMAO), they afford mainly cis‐selective polyisoprene, up to 90.7%. Both the activity and the selectivity are tentatively ascribed to the intrinsic microstructure of the starting materials. Compared to conventional carboxylates, MOFs associated to an Al co‐catalyst are less active but the selectivity is found to be higher, and it may be modified by controlling the access to the pores, which would be favored at higher temperatures. Some residual crystalline MOF remains disseminated within the polymer matrix, as shown by X‐ray diffraction and X‐ray absorption spectroscopy studies.

     

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.

     

A Facile Method to Prepare Hydrophobic Nanoparticle Dispersions for Controlled Release

Using ethyl acrylate and methyl methacrylate as hydrophobic monomers, a series of hydrophobic nanoparticle dispersions were prepared by one‐step polymerization (i.e., soap‐free batch emulsion polymerization). To obtain stable aqueous nanoparticle dispersions, a small amount of ionic comonomer, sodium 4‐ω‐acryloyloxy‐β‐hydroalkyl sulfonate (Cops‐1) was used. The nanoparticles were characterized by TEM, Zetasizer and DSC. It was found that number average diameter ( ) values range from 144 to 202 nm at 25 °C, and the diameter distribution ( ) from 1.11 to 1.14. These results indicate that the nanoparticles show a narrow distribution of sizes. Zeta potentials of the obtained nanoparticles are in range of ?38.8 to ?29.7 mV at 25 °C. This suggests that they can be well dispersed in water. Using salicylic acid (SA) as model drug molecules, a novel swelling method was developed for loading SA into the nanoparticles in an aqueous dispersion state, and both related loading processes and controlled release behavior were investigated. It was found that the nanoparticles can sustain SA release, and compared to different types of nanoparticles, PMMA nanoparticles can retard SA release more effectively.

     

Synthesis and Thermal Characterization of Perfluorocyclobutyl (PFCB) Polymers Containing Crown Ether Vertebrae

Summary: The synthesis and polymerization of novel 18‐crown‐6 and 24‐crown‐8 bis aryl trifluorovinyl ethers is described. Thermally induced polymerization yields linear crown ether fluoropolymers with hexafluorocyclobutyl linkages. The polymers exhibit T_g's above 120 °C and show good thermal stability with no appreciable weight loss below 350 °C. Incorporation of crown ether macrocycles into the polymer is expected to increase cationic uptake of an otherwise electroneutral fluoropolymer.

     

Relationship Between Architecture and Adhesion in Polyurethane‐Based Copolymers, 2

Summary: This study describes the chain extension, with polycaprolactone diols, of polyurethane‐graft‐poly(butyl acrylate)s which were first prepared by the step growth polymerization of a mixture of diphenylmethane‐4,4′‐diisocyanate (MDI) and α,α′‐dihydroxyl‐poly(butyl acrylate)s. The success of the chain extension reaction was studied and confirmed by ¹H NMR, SEC and DSC analysis. The incorporation of polycaprolactone sequences in the polyurethane chains modified their specific adhesive properties, bringing cohesion to the material, as demonstrated by tack measurements.

PUR‐graft‐PBA extended with PCL.     

Photoactive Azobenzene Polymers Containing Carbazole Chromophores

Summary: Polymeric systems containing side‐chain photoactive chromophores were prepared by free‐radical copolymerization of N‐vinylcarbazole with 4‐methacryloyloxyazobenzene and 4‐methacryloyloxy‐4′‐cyanoazobenzene. The resulting materials were characterized by size exclusion chromatography, TGA and DSC thermal analysis, FT‐IR, ¹H NMR, UV‐vis, and fluorescence spectroscopy and photoisomerization experiments. In all cases, the copolymer composition was almost independent of the feed composition, in agreement with the strong tendency of the investigated monomers to alternating copolymerization. Spectroscopic and thermal data clearly highlighted the occurrence of charge‐transfer electronic interactions between electron‐rich carbazole rings and electron‐poor azobenzene chromophores. These interactions facilitate the trans‐cis photoisomerization of azobenzene side‐chains.

Aromatic proton NMR spectra of different poly(MCA‐co‐NVK) samples.     

Electron Spin Resonance Spin Trapping Technique: Application to the Cleavage Process of Photoinitiators

The cleavage of different photoinitiators (PIs) of polymerization is investigated by the ESR spin trapping using two different spin traps (STs): 5,5′‐dimethyl‐1‐pyrroline N‐oxide (DMPO) and phenyl N‐tert‐butyl nitrone (PBN). The hyperfine splitting constants for the different adducts are measured and provide a new set of data. These results show a difference of selectivity between the two (STs) and outline their complementarities.

     

Macromol. Chem. Phys. 21/2009

Alternating copolymers of maleimides containing pyrenyl and alkynylpyrenyl moieties with isobutene (IB) were synthesized as a new class of heat‐resistant and fluorescent polymers. N‐(1‐Pyrenyl)maleimide (1) and N‐[4‐(1‐pyrenylethynyl)phenyl]maleimide (2) were copolymerized with IB in the presence and absence of N‐methylmaleimide (3) . The obtained maleimide/IB copolymers showed excellent thermal stability and high glass transition temperatures, and were soluble in common organic solvents. The copolymers including the alkynylpyrenyl fluorophore emitted strong fluorescence with a high quantum efficiency (Φ = 0.83) even in the presence of air and upon heating. Solid‐state fluorescence in transparent films was also investigated.

     

Photoinduced Polymerization of Thiophene Using Iodonium Salt

Summary: Thiophene was polymerized by means of UV irradiation using diphenyliodonium hexafluorophosphate as a photoinitiator. An initiation mechanism involving electron transfer from photochemically generated onium radical cations to thiophene was proposed. N‐Ethoxy‐2‐methylpyridinium hexafluorophosphate and triphenylsulfonium hexafluorophosphate were also found to be effective in facilitating the polymerization of thiophene. Polymerization is accompanied with the film formation on the surface of the reaction tube. The photochemically obtained polymers were characterized by FT‐IR, DSC, and SEM analyses and compared with those obtained by oxidative and electrochemical means. Electrical conductivities of the samples were measured by four‐probe technique.

Photograph of the polymerization mixture containing thiophene and iodonium salt in CH₂Cl₂ before (a), after 5 min of irradiation (b), and dried film (c).     

“Click” Synthesis of a Bipolar Dendrimer as a Host Material for Electrophosphorescent Devices

A new solution‐processable bipolar dendrimer with carbazole units as hole‐transporting units and oxadiazole units as electron‐transporting units was efficiently synthesized based on a convergent approach by alternation of a Cu‐catalyzed azide/alkyne cycloaddition reaction and Williamson ether synthesis. The orthogonal chemistry completely avoided protection and activation of the focal points in the process of dendrimer synthesis. The dendrimer showed a wide bandgap and good thermal stability. Electrophosphorescent devices with the configuration ITO/PEDOT:PSS/bipolar dendrimer:Ir(ppy)₃/TPBI/LiF/Al were fabricated. The devices showed a maximum current efficiency of 16.8 cd · A^?1, a maximum power efficiency of 4.22 lm · W^?1 and an external quantum efficiency of 5.7%.

     

Measurement of Transfer Coefficients to Monomer for n‐Butyl Methacrylate by Molecular Weight Distributions from Emulsion Polymerization

The average kinetic coefficient for chain transfer to monomer 〈k_tr,M〉 in the free‐radical polymerization of n‐butyl methacrylate (BMA) has been determined by the analysis of molecular weight distributions obtained by seeded emulsion polymerization under conditions such that chain transfer to monomer is the dominant chain‐stopping event. Measurements between 40 and 70 °C gave data fitting an Arrhenius‐type relationship with exponential factor E_A = 30 900 ± 4 500 J · mol^?1 and pre‐exponential factor log A = 3.45 ± 0.15. The value for E_A is comparable with published data for chain transfer to monomer from methyl methacrylate (MMA) and n‐butyl acrylate (BA). The A value, however, is 1–3 orders of magnitude smaller, suggesting that there is more hindrance for chain transfer to monomer for BMA than for either MMA or BA.

     

Control of the radical polymerization by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl and its sodium salt

The control of the radical polymerization of styrene by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl is reported here in bulk at 90 °C, 120 °C and in miniemulsion. Similarly, the control by its sodium complex is reported in bulk at 90 °C.

M _n vs. conversion for 3 , 3Na , and TEMPO.     

Optical Proof of Mesophase Transitions between Smectic and Nematic Phase of the Side‐Group Polyacrylate PAC6

The liquid‐crystalline side‐group polyacrylate PAC6 forms two mesophases in thin layers within the temperature range between 90 and 100 °C. The structures developing by self‐organization can be made clearly visible by Schlieren‐optical methods. If a low lateral temperature gradient is maintained in the temperature range mentioned above one can simultaneously and abreast observe four phases in PAC6 layers. Both new phases occur between the smectic and the nematic phase. Layer surface deformations arise during this phase transition. They were analyzed with a microscope interferometer. The PAC6 melt shows a considerable change of surface tension in this temperature range.

Schlieren‐optical image of a PAC6 layer with two mesophases.     

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.     

Double‐Gyroid Morphology of a Polystyrene‐block‐Poly(ferrocenylethylmethylsilane) Diblock Copolymer: A Route to Ordered Bicontinuous Nanoscale Architectures

A polystyrene‐block‐poly(ferrocenylethylmethylsilane) diblock copolymer, displaying a double‐gyroid morphology when self‐assembled in the solid state, has been prepared with a PFEMS volume fraction ?_PFEMS = 0.39 and a total molecular weight of 64 000 Da by sequential living anionic polymerisation. A block copolymer with a metal‐containing block with iron and silicon in the main chain was selected due to its plasma etch resistance compared to the organic block. Self‐assembly of the diblock copolymer in the bulk showed a stable, double‐gyroid morphology as characterised by TEM. SAXS confirmed that the structure belonged to the Ia d space group.

     

4‐Alkylphenoxymethyl‐Substituted Polystyrenes for Liquid Crystal Alignment Layers

We synthesized a phenoxymethyl‐substituted polystyrene (PHP) and a series of 4‐alkylphenoxymethyl‐substituted polystyrenes, where the alkyl group is ? (CH₂)_nH (n = 1, 2, 4, 6, and 8), using polymer analogous reactions, in order to study the effect of the phenoxymethyl and 4‐alkylphenoxymethyl side groups on the liquid crystal (LC) alignment properties. The LC cell fabricated with the rubbed PHP film exhibited homogeneous planar and perpendicular LC alignment with respect to the rubbing direction. On the contrary, the LC cells made from the 4‐alkylphenoxymethyl‐substituted polystyrenes showed homeotropic LC alignment behaviors even at a very high rubbing density of 250, regardless of the length of the alkyl groups. Previously, n‐alkylsulfonylmethyl‐substituted polystyrenes with alkyl groups having more than 8 carbons (n > 8) showed homeotropic LC alignment behavior. Therefore, the additional phenoxy group in the side chain was found to improve the homeotropic LC aligning ability of the polystyrene derivatives.