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.

     

Microwave‐Assisted Synthesis and Characterization of Poly(ε‐caprolactone)/Montmorillonite Nanocomposites

Poly(ε‐caprolactone) (PCL)/montmorillonite (MMT) nanocomposites were prepared by in situ ring‐opening polymerization of ε‐caprolactone in the presence of MMT modified by hydroxyl‐group containing alkylammonium cation (Cloisite®30B) in a single mode microwave oven. For the polymerization mixtures, plateaus or exothermal peaks were observed in their temperature‐time profiles and can be attributed to the heat‐generating nature of the ring‐opening polymerization. The morphologies of the nanocomposites showed a predominantly exfoliated structure. The mechanical properties of the nanocomposites were evaluated via dynamic mechanical analysis. Compared with that of the recovered PCL matrix, the mechanical properties of the PCL/Cloisite®30B nanocomposites showed obvious improvement.

     

Novel Thermosetting Resins Based on 4‐(N‐Maleimido)phenylglycidylether, 4

Summary: A series of polymer‐clay nanocomposites were prepared by the simultaneous in situ curing of 4‐(N‐maleimido)phenylglycidylether/4,4‐diaminodiphenylmethane (MPGE/DDM) with the intercalation/exfoliation of various organo‐modified clays. The dispersion of the clays in the polymer matrix was produced by partial exfoliation and intercalation, as observed with X‐ray diffraction and transmission electronic microscopy. Clay modified with a carboxylic acid‐containing modifier showed enhancements with repesect to clay delamination in nanocomposite preparation. In comparison with the pristine resin, MPGE/DDM‐clay nanocomposites showed improved glass transition temperatures, thermal stability and flame retardance.

Preparation and characterization of polymer‐clay nanocomposites based on a new maleimide‐epoxy hybrid monomer.     

Gas‐Phase Assisted Surface Polymerization of Vinyl Monomers with Fe‐Based Initiating Systems

Summary: Gas‐phase assisted surface polymerization (GASP) of methyl methacrylate (MMA) and styrene (St) was investigated with Fe‐based radical initiating systems, FeCl₂/2,2′‐bipyridine (Bpy)/methyl α‐bromophenylacetate (MBPA), etc. GASP with these initiating systems proceeded to produce corresponding polymers on substrate surfaces. The resulting PMMA had very high PDI values, suggesting an uncontrolled reaction. In an attempt to control the GASP, polymerization with a simple initiating system, Fe(0)/MBPA, was examined on Fe(0)‐metal surfaces, resulting in significant polymerization activity to produce high‐molecular‐weight PMMA. The results of time‐course tests on GASP of MMA and St suggested that a change had taken place to produce physically controlled propagation sites on the Fe(0) powder surfaces.

GASP schemes with a simple initiating system Fe(0)/MBPA.     

Preparation of Crosslinked Poly(2‐bromoethyl methacrylate) Microspheres and Decoration of Their Surfaces with Functional Polymer Brushes

Synthesis and crosslinking copolymerization of 2‐bromoethylmethacrylate in aqueous suspension is described for preparing bromoalkyl‐functional microbeads (125–420 µm). Highly transparent microspheres with a density of accessible bromoethyl groups of 1.55 mmol · g^?1 were prepared in the suspension, stabilized with poly(N‐vinyl pyrrolidone), by using methyl methacrylate as diluting co‐monomer and ethylene glycol dimethacrylate as crosslinker. Bromoalkyl groups on the microparticles were employed as initiation sites for either surface‐initiated ATRP of glycidyl methacrylate or ring‐opening polymerization of 2‐methyl‐2‐oxazoline to generate epoxy‐ and N‐acetylethyleneimine‐functional hairy grafts, tethered to the particle surfaces with hydrolytically stable linkages.

     

Atom Transfer Radical Polymerization Using Multidentate Amine Ligands Supported on Soluble Hyperbranched Polyglycidol

Summary: Controlled polymerization of styrene in toluene was achieved by atom transfer radical polymerization (ATRP) using hyperbranched polyglycidol‐supported multidentate amine ligands/Cu^IBr catalyst systems. These catalyst systems with nanoscopic dimensions were more active than the corresponding low‐molecular‐weight ligands. The controlled/living nature of the polymerization is supported by linear first order plots (ln[M]_o/[M] versus time) and a linear increase of versus conversion as well as low polydispersity. Similar controlled polymerization of methyl methacrylate was possible in acetonitrile. Up to 97% of total copper used for polymerization could be removed from the polymer by simple precipitation in methanol and filtration.

Molecular weight characteristics for styrene polymerization using PG‐triamine as a ligand.     

Polycondensations of Bisphenol‐A with Diphosgene or Triphosgene in Water‐Free Organic Solvents

Summary: Bisphenol‐A was polycondensed with diphosgene and excess pyridine in a mixture of dry dichloromethane and 1,4‐dioxane. The stoichiometry was varied to optimize the molecular weight. According to MALDI‐TOF mass spectra the fraction of cyclic polycarbonates increased with higher molecular weights. Analogous results were obtained with triphosgene. When pyridine was replaced by triethylamine, diethyl carbamoyl chloride was formed and an excess of diphosgene (plus triethylamine) yielded polycarbonates having one or two diethylcarbamate endgroups. However, the content of cycles increased again with the molecular weight and peaked for the sample with the maximum molecular weight. ¹H NMR endgroup analyses confirmed the interpretation of the MALDI‐TOF mass spectra. SEC measurement indicated high polydispersity indices (around 7) for samples rich in cycles.

     

Morphological Studies of Epoxy/Polyaniline Blends

Summary: Polyaniline‐dodecybenzenesulfonic acid (PANI‐DBSA)/epoxy resin (EP) blends were prepared by a solution‐in‐toluene process and direct mixing of PANI‐DBSA with EP. The dispersion quality of PANI‐DBSA proved to be strongly related to the final electrical properties of the cured blends. The solution processed blends showed enhanced electrical properties with small PANI‐DBSA contents (percolation threshold determined was around 2.3 wt.‐% PANI‐DBSA). The morphologies of these blends were investigated by atomic force (AFM), scanning electron (SEM) and transmission electron (TEM) microscopy. The existence of a translucent PANI‐DBSA network exists within the EP matrix. The microscopy investigations were in agreement with the results from differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA).

SEM image of the PANI‐DBSA‐rich regions (indicated by arrows) surrounded by the conductive EP/PANI‐DBSA matrix (5 wt.‐% PANI‐DBSA).     

Selective Dimerization of γ‐Branched α‐Olefins in the Presence of C2v Group‐4 Metallocene‐Based Catalysts

Summary: The oligomerization of γ‐branched α‐olefins in the presence of catalytic systems based on group‐4 metallocenes with C_2v symmetry has been investigated. The highest reactivity was obtained by using dimethylsilyl‐bis(cyclopentadienyl)zirconium‐dichloride activated by methylaluminoxane. Highly regioregular dimers were selectively obtained for hindered γ‐branched monomers, while the less hindered ones produced higher molecular weight oligomers. A molecular modeling approach was used to rationalize the experimental results. In fact, a decrease in the β‐hydrogen elimination barrier and an increase in the insertion barrier with the monomer bulkiness were calculated.

General structure of the obtained dimers.     

Donor/Spacer/Acceptor Block Copolymer Containing Poly(2,7‐carbazole) and Perylenetetracarboxydiimide Subunits

A straightforward synthesis of a conjugated rod/spacer/rod‐type block copolymer containing PCz electron‐donor and PDI electron‐acceptor blocks is described. Two chromophores are covalently connected through sebacate units as saturated spacer. The resulting donor/spacer/acceptor‐type block copolymer (PCz‐S‐PDI) can be applied to limit charge recombination between donor/acceptor interfaces and to control the scale length of nanostructure formation. PCz‐S‐PDI was used to produce a solar cell with the power conversion efficiency of 0.004%.

     

Benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐terthiophene Copolymers Containing Styryl‐Triphenylamine Side Chains: Synthesis and Photovoltaic Performance Optimization with Fullerene Acceptors

A new two‐dimensional‐conjugated polymer (PBDTT3‐TPA) containing benzodithiophene (BDT) and a side chain isolation comonomer is designed and synthesized. Interestingly, PBDTT3‐TPA is compatible with higher lowest unoccupied molecular level (LUMO) acceptors of indene‐C₆₀ bisadduct (ICBA), and polymer solar cells based on PBDTT3‐TPA/ ICBA show an open‐circuit voltage (V_OC) of ca. 0.80 V and a power conversion efficiency of 2.48% under AM1.5G illumination of at 100 mW cm^?2. Furthermore, the energy loss in the corresponding fullerene acceptor devices is discussed, and the increase in the observed V_OC is explained quantitatively by the up‐shifted LUMO energy of ICBA (0.17 eV) and the reduced saturation current (J_SO) in the blends.

     

Polystyrene/Montmorillonite Nanocomposites Prepared by In Situ Intercalative Polymerization: Influence of the Surfactant Type

Summary: Na‐montmorillonite (MMT) with a cation exchange capacity (CEC) of 90 meq/100 g was converted to MMT‐CTAB and MMT‐CPC by the intercalation of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC), respectively. The intercalation of CPC onto the basal space of the montmorillonite expanded the basal space from 12.19 to 21.47 Å, whereas in the case of CTAB, the spacing was only expanded to 19.35 Å. The MMT‐CPC and MMT‐CTAB forms were subsequently used as hosts for the preparation of polystyrene nanocomposites via intercalative free‐radical polymerization of styrene. Different structures were obtained by varying the preparation conditions; the exfoliated and intercalated nanocomposites were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), and differential scanning calorimeter (DSC). The produced nanocomposites exhibited improved thermal stability in comparison with that of pure polystyrene above 400 °C especially in the case of the nanocomposites based on the MMT‐CPC, in which intercalation exists. A glass transition temperature (T_g) could not be detected for the prepared nanocomposites using DSC; this was assumed to result from the restricted molecular motion of the polymer chains.

XRD pattern of PS nanocomposites prepared by intercalative polymerization.     

Synthesis and Properties of Syndiotactic Poly(propylene)/Carbon Nanofiber and Nanotube Composites Prepared by in situ Polymerization with Metallocene/MAO Catalysts

Summary: The preparation of syndiotactic poly(propylene) (sPP) nanocomposites with multi‐walled carbon nanotubes (MWNTs), carbon nanofibers (CNFs), and carbon black (CB) as fillers was accomplished by the in situ polymerization of propylene with a metallocene/methylalumoxane (MAO) catalyst. Different pre‐treatments were applied to achieve a homogeneous dispersion of the fillers in the matrix. The resulting nanocomposites were investigated with respect to their properties, which were then compared to those of the pure polymer and among each other. The thermal stability of the nanocomposites was slightly enhanced compared to the pure polymer. In addition, the yield strength of the nanocomposites could be slightly raised in comparison to the neat sPP. The most significant influence of the nanofillers was detected on the crystallization behavior. The crystallization temperature was increased with rising filler content in all cases. Moreover, the half‐time of crystallization was significantly reduced in the nanocomposites. The rate constant of crystallization was also greatly enhanced for all nanocomposites as compared to the neat sPP. The nanofillers acted, therefore, as nucleating agents. This effect was most pronounced in the case of MWNTs as fillers.

Influence of the type of filler on the degradation temperature (temperature of maximum weight loss).     

Poly(propylene glycol)‐Grafted Multi‐Walled Carbon Nanotube Polyurethane

Summary: Poly(propylene glycol)‐grafted MWNT polyurethane was synthesized based on the hydroxyl functionalized MWNTs through a two‐step reaction. The grafted MWNTs can improve the rheological behavior of the polyol/MWNT dispersion, and have a better reinforcing effect on the mechanical properties of polyurethane and lower hysteresis compared to the raw carbon nanotubes. A comparison for energy dissipation in PU/carbon nanotube and exfoliated PU/organoclay nanocomposites was given. The energy dissipated in the grafted MWNT composite system is lower.

Dispersion stability of carbon nanotubes in polyether polyol after 40 min centrifugation (A: MWNT, B: MWNT‐OH, C: MWNT‐graft‐PU).     

Epoxy Resin Containing Octamaleimidophenyl Polyhedral Oligomeric Silsesquioxane

Summary: Octamaleimidophenyl polyhedral oligomeric silsesquioxane (OmipPOSS) was synthesized via the imidization reaction between octaaminophenyl polyhedral oligomeric silsesquioxane (OapPOSS) and maleic anhydride, and it was characterized by means of Fourier transform infrared (FTIR) and NMR spectroscopies. OmipPOSS was further employed to prepare epoxy hybrids. The thermosetting hybrids containing OmipPOSS up to 10 wt.‐% were obtained via in situ polymerization of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐diaminodiphenylmethane (DDM) in the presence of OmipPOSS. High‐resolution transmission electronic microscopy (TEM) indicates that the nanometer‐scaled dispersion of POSS molecules was obtained, suggesting that the nanocomposites were successfully prepared. The results of DSC showed that the glass transition temperatures (T_g's) of the POSS‐containing nanocomposites are dependent on the content of POSS in the nanocomposites. When the contents of POSS are less than 5 wt.‐%, the nanocomposites displayed the enhanced glass transition temperatures (T_g's) in comparison with control epoxy. Thermogravimetric analysis (TGA) showed that all the nanocomposites containing POSS displayed improved char yield, suggesting the flame retardance of the materials is improved.

     

A Simple Water‐Based Synthesis of Au Nanoparticle/PDMS Composites for Water Purification and Targeted Drug Release

AuNP/PDMS nanocomposites have been synthesized in the form of gels, foams, and films with distinctive structure and morphology. A simple in situ process in aqueous medium for the formation of such composite materials is described. The nanoparticles are held firmly within the PDMS while still being chemically accessible to substances soluble in PDMS. We demonstrate the utility of this property for water purification applications such as removing aromatic solvents and sulfur‐containing contaminants from water. The contaminants can be freed from the composite with a simple thermal treatment, allowing the material to be reused. We also demonstrate chemically selective uptake and release of a fluorescent dye by the nanocomposite as a drug delivery model system.

     

Ni‐Catalyzed Polymerization of Poly(3‐alkoxythiophene)s

The Ni‐catalyzed polymerization of P3AOTs was studied and compared with the controlled chain‐growth polymerization of P3ATs. By varying the ratio of the initial monomer concentration to the initiator concentration, no linear dependence of the molar mass was observed, revealing that the polymerization does not proceed via a controlled mechanism. This was also confirmed by analyzing the end‐groups of the polymer with MALDI‐TOF mass spectrometry. To acquire more information on the polymerization mechanism, the formation of the actual monomer and the polymerization reaction were studied into more detail. These experiments proved that the polymerization proceeds via a chain‐growth mechanism, although not in a controlled way.

     

Nanocomposites of Hairy‐Rod Macromolecules: Concepts,Constructs, and Materials

The rational construction of nanocomposites based on so‐called hairy‐rod macromolecules (HRM) is the objective of this review covering 15 years of extensive research at the Max Planck Institute for Polymer Research. HRM are described as shape‐persistent objects, which are processed into ultrathin films by the Langmuir–Blodgett protocol. Transfer of monolayers initially formed on the water surface to solid substrates is understood as a two‐dimensional analogue of an extrusion process giving rise to molecular orientation phenomena. The scope of HRM concerning chemical composition and molecular architecture is reviewed, and examples of how to obtain complex constructs having device functions are given. Recent work on hairy‐rod polyelectrolytes based on poly(p‐phenylene sulfonates)s is summarized as well, and their ability to form hierarchical superstructures in aqueous solution is presented.

Assembly process of multilayers of hairy‐rod macromolecules by the LB technique.     

Negatively Birefringent Polymer Films

Polymer films exhibiting large negative birefringence, suitable for compensating residual positive birefringence of liquid crystal displays, have been achieved for syndiotactic polystyrene. Procedures involving axial stretching at different draw ratios of unoriented films, followed by different crystallization routes, have been compared. The control of the polymer polymorphic behavior, i.e., of the formation of crystalline and co‐crystalline (with low‐molecular‐mass guest molecules) phases, allows to control the negative birefringence up to Δn = n_? ? n_|| = 0.17.

     

Synthesis and Dielectric Study of New Liquid‐crystalline Polysiloxanes Presenting a Thioether Spacer

Three new cyanobiphenyl polysiloxanes presenting long thioether spacers have been carried out. This type of spacer leads to very stable liquid‐crystalline polymers at room temperature and remove the crystallinity phenomenon. Dielectric analysis results show that the thioether spacer brings much more molecular flexibility to the system.

Example of an “interdigitated” structure observed by X‐ray analysis.