Effects of the Reaction Conditions on the Syndiospecific Polymerization of Propene Promoted by Bis(phenoxyimine) Titanium Catalysts

Summary: The propene polymerization behavior of two typical bis(phenoxyimine) titanium catalysts has been investigated by varying reaction conditions, such as the monomer concentration, the solvent, and the cocatalyst. The experimental results indicate that the stereoregularity and regioregularity of the obtained poly(propylene)s are significantly affected by the reaction conditions. Fractionation of some poly(propylene) samples indicates the formation of macromolecules of different stereoregularity in the same run, suggesting that different active complexes can be generated in situ from these bis(phenoxyimine) titanium precatalysts.

     

From CO2‐Based Multifunctional Polycarbonates With a Controlled Number of Functional Groups to Graft Polymers

Copolymerization of CO₂ and epoxides is employed to generate functional polycarbonates. The introduction of reactive double bonds at a poly(propylene carbonate) (PPC) backbone is realized by the copolymerization of aliphatic alkene epoxides with propylene oxide (PO) and carbon dioxide (CO₂). A series of copolymers with random structure and varying comonomer content (3–22%) with molecular weights in the range of 22 000–34 000 g mol^?1 is synthesized and characterized with respect to their microstructure and thermal properties. The facile transformation of the double bonds is verified by a thiol‐ene reaction, resulting in quantitative conversion of the double bonds. Polycarbonate derivatives with multiple functionalities are prepared, providing suitable moieties for further grafting.

     

Diffusion and Reaction of Methylaluminoxane (MAO) within a Silica Membrane

Summary: The self‐diffusion coefficient of MAO confined within a silica membrane is not experimentally accessible by traditional PFG NMR measurements, probably due to a susceptibility effect resulting in rather broad, unobservable resonance lines. A more indirect approach was therefore applied to probe the diffusivity of MAO within a silica membrane. MAO confined in a bulk toluene solution on one side of the membrane was free to diffuse through the membrane (saturated with toluene) and into a corresponding deuterated toluene solution on the other side of the membrane where its proton NMR signal intensity was monitored as a function of time. By introducing a relevant diffusion model, the diffusivities of both toluene and MAO were derived by model‐fitting. By refining the diffusion model, the formation of methane within the silica was explained, and its diffusivity estimated. The results suggest a significant reduction in diffusivities of both MAO and toluene within the silica as compared to the corresponding diffusivities in bulk solution.

¹H NMR spectra as a function of time within the shift region δ = 2.0–2.5 ppm (toluene) acquired during the first 40 h of the diffusion process.     

Amorphous‐Crystalline PSnPEOn Heteroarm Star Copolymers: Crystallinity and Crystallization Kinetics

Summary: The crystallization behavior and kinetics of poly(ethylene oxide) in polystyrene/poly(ethylene oxide) heteroarm star copolymers were studied by differential scanning calorimetry and optical microscopy. A comparison between star and linear amorphous‐crystalline block copolymers showed that the macromolecular architecture is an important factor affecting crystallinity. The following points were observed: the equilibrium melting point is higher in the star copolymers, the crystallinity reduces as the number of arms increases, leading to smaller and ill‐defined spherulites, and crystallization proceeds faster in linear copolymers at low supercooling.

Half crystallization times, t_1/2, calculated from the Avrami analysis of the latent heats, obtained during the isothermal crystallization experiments as a function of supercooling, ΔT, for all copolymers.     

New Regular,Amphiphilic Poly(ampholyte)s: Synthesis and Characterization

Summary: Hydrophobically substituted diallylamines bearing a hexyl, dodecyl, or octadecyl chain were synthesized and homopolymerized as hydrochlorides. Copolymerization of the diallylamines with maleic acid produces alternating copolymers. The copolymers behave as amphiphilic polyampholytes and dissolve best in the acidic or in the basic form. Only the copolymer with the hexyl chain could be dissolved in aqueous solvents and shows hydrophobic association. The copolymers with the longer alkyl chains require polar protic organic solvents. All polymers are amorphous, but show a superstructure in bulk due to their amphiphilicity.

     

Phase Behaviour of New Side‐Chain Liquid Crystalline Polyoxetanes

Summary: The synthesis and thermal behaviour of two new polyoxetanes with side chains having a dimer structure mesogen‐spacer‐mesogen and a long terminal alkyl group are reported. The two polymers differ in the chemical structure of the central spacer. The polyoxetanes have been obtained by cationic ring‐opening polymerisation of an appropriately substituted oxetane ring. Both polyoxetanes studied exhibit liquid crystalline properties showing a similar sequence of phases. DSC and synchrotron experiments indicate that a highly ordered phase with a probable orthorhombic packing is observed at low temperature. On heating, this phase melts into a mesophase with hexagonal order within the smectic layers, which, on further heating, is transformed into a disordered smectic mesophase.

Synchrotron X‐ray diffraction patterns of one of the poyoxetanes in a heating experiment.     

Miscibility of Carboxy‐Terminated Polystyrene/Poly[2‐(N,N‐dimethylamino)ethyl methacrylate] Blends

The miscibility/immiscibility behavior of CPS/PDMAEMA binary blends were investigated by means of DSC and optical microscopy. CPS was prepared by RAFT polymerization. CPS in a molecular weight range of 5 200–14 400 g · mol^?1 was found to be miscible with PDMAEMA as shown by the existence of a single glass transition, whereas benzyl‐terminated polystyrene with a similar molecular weight was immiscible with PDMAEMA. DSC results suggested that the carboxylic acid terminal groups effectively operated as miscibility enhancers in polystyrene/PDMAEMA blends. Moreover, it was observed that this effect depended on the molecular weight of CPS and the hydrogen bonding function of solvents.

     

Chemical Binding of Unsaturated Fluorenes to Poly(2‐chloroxylylene) Thin Films

A series of substituted fluorenes with vinyl groups as reactive sites were synthesized and characterized. Fluorene‐based polymers with vinyl groups as end chains and side chains functionalities were also prepared. In both cases, successful preparation of functionalized Parylene C films (modylayers) was achieved. The set of spectral methods used has allowed us to conclude that such functionalization is based on the chemical reaction of double bonds with xylylene radicals during deposition process. Parylene C films chemically modified with specially synthesized polyfluorenes showed PL quantum efficiency comparable with neat polyfluorenes.

     

Nuclear Magnetic Resonance Spectroscopy in Macromolecular Science

A historical overview of the role of NMR spectroscopy in macromolecular science in general and its coverage in “Macromolecular Chemistry and Physics” in particular is given. In the early days physics‐application to study molecular dynamics, partial alignment of macromolecules and phase separation prevailed, deduced from broad‐line solid‐state NMR. Only somewhat later, high‐resolution NMR in solution was established as an important tool for elucidating the chain microstructure. In the future, these two aspects are expected to merge.

Side group liquid crystalline polymers: ²H NMR has elucidated alignment and dynamics of these complex materials.     

Cover Picture: Macromol. Chem. Phys. 21/2005

Summary: In this paper, we describe the multiple morphogenesis of poly(ethyleneimine) (PEI)‐directed silicas through the facile tuning of the media in which the PEIs pre‐organize. The silica shapes and structures ranged from nanofiber‐based asters, fans, particles, plates, and/or curved films to large aggregates composed of unit nanoribbon structures and networks that contained nanospheres or particles, depending on the media compositions or media modulations coupled with the polymer concentrations and chain architectures. We found that the media modulations not only controlled the formation of the silica unit structures but also manipulated the hierarchical structures based on the unit silicas. Furthermore, methanol modulation successfully allows us to elucidate the dependence of silica deposition ability on the polymer chain architectures that cause subtle differences in their aggregates. The approach of methanol modulation to obtain shaped silicas, which involves both PEI aggregation and silica deposition at room temperature, is of particular interest to applications for the immobilization of bioactive components.

     

Stereochemical Pseudohexad 13C NMR Resonances and Regioregular Propylene/Ethylene‐1‐13C Copolymers

This paper reports the assignment of the ¹³C NMR resonances of the S_ββ and S_αγ methylenes observed in the spectra of copolymers of propylene with trace amounts of enriched ethylene‐1‐¹³C. The assignment is achieved by comparing the chemical shifts calculated by an empirical method (at the CH₂ stereochemical pseudohexad level), with the experimental spectra of regioregular copolymers with different stereochemical structure. The implications of the observed S_ββ and S_αγ resonances on the stereochemical polymerization mechanisms are also discussed.

     

Supramolecular Branching and Crosslinking of Terpyridine‐Modified Copolymers: Complexation and Decomplexation Studies in Diluted Solution

A series of poly(methyl methacrylate) copolymers with terpyridine units in the side chains was obtained by free radical polymerization. The free terpyridine units were complexed by iron(II ) and zinc(II ) ions, and the complexation behavior was studied in detail, utilizing UV‐vis and viscosity titration experiments. Complexation of the polymer chains could be observed, which resulted in characteristic UV‐vis absorption bands and an increase in the solution viscosity. Addition of a strong competitive ligand (hydroxyethyl ethylenediaminetriacetic acid, HEEDTA) resulted in an efficient decomplexation.

UV‐vis spectra and photos of uncomplexed copolymer 2b before and after complexation with iron(II ) ions (in chloroform) and after decomplexation with HEEDTA.     

Modification of Polyacrylonitrile Particles and Grafted Films with Oxazolines

Summary: Oxazoline functionalities were introduced onto the surface of polyacrylonitrile particles and polyacrylonitrile‐grafted films by the catalyzed reaction of a substituted aminoalcohol with the nitrile groups. The resulting oxazoline group was reacted with methyl triflate to use the resulting oxazolinium salt as initiator for the ring opening grafting of 2‐ethyl‐2‐oxazoline. The products were characterized with Fourier transform infrared spectroscopy (FTIR), elemental analysis, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The modification of polyacrylonitrile with the substituted aminoalcohol achieves high conversions. Conversely, the amount of grafted 2‐ethyl‐2‐oxazoline is low. The results show that controlled levels of 2‐oxazolines or polyoxazolines can be incorporated onto the surface of polyacrylonitrile.

Reaction of a nitrile group to form an oxazoline functionality.     

Thickening Processes of Lamellar Crystal Monolayers of a Low‐Molecular‐Weight PEO Fraction on a Solid Surface

Using hot‐stage atomic force microscopy, the thickening processes of monolayer crystals of PEO ( = 5 000 g · mol^?1 and = 1.008) from one‐folded (FC1) to extended‐chain (EC) lamellae are experimentally monitored at three temperatures: 50, 52, and 58 °C. At 50 °C some small areas in large FC1 crystals spontaneously thicken into EC crystals. At 52 °C the spontaneously thickened area further expands so as to inductively thicken the entire FC1 lamella into EC lamella. At 58 °C EC crystals first force the adjacent FC1 crystals to melt and then absorb the melted molecules to grow laterally into large EC lamellae till all FC1 lamellae vanish. The three thickening steps express the main thickening process of lamellar crystals from a metastable state to another metastable (or equilibrium) state. The possible mechanisms are discussed in the text.

     

Synchrotron X‐ray and DSC Studies of the Phase Behaviour of Poly(diethylene glycol p,p′‐bibenzoate)

Time‐resolved synchrotron X‐ray and DSC experiments were applied to investigate the phase behaviour of poly(diethylene glycol p,p′‐bibenzoate), PDEB. The DSC results are indicative of the formation of a smectic mesophase, previously identified as a SmCA type, which can be easily quenched down to room temperature. However, the synchrotron results show that the SmCA phase undergoes some kind of ordering or transformation at temperatures below 110 °C. Moreover, the annealing of PDEB at temperatures above T_g for sufficiently long times leads to the formation of a highly ordered structure, although very thin crystals and low crystallinities are obtained.

Scattering profiles corresponding to sample PDEB85 in a melting experiment.     

Synthesis of Laser‐Alignable Liquid Crystalline Conducting Polymers

Summary: The synthetic routes to three series of liquid crystal conducting polymers (based on pyrrole, thiophene, and aniline monomers) are reported and the optimum conditions for polymer preparation are described. These polymers show increased conductivity when laser‐aligned, the greatest effect being shown by the N‐substituted pyrrole‐based system. Information on their liquid crystal and spectroscopic properties and other characteristics are also included.

Structure of the monomers M1, M2, and M3.     

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 Characterization of Polymer Brushes on Micromechanical Cantilevers

Summary: A technique to cover microelectromechanical systems (MEMS), such as micromechanical cantilever (MC) sensors, with a covalently bound brush layer has been developed. The polymer layer was grown using a “grafting‐from” synthesis of polymer brushes under mild conditions, by surface‐initiated atom transfer radical polymerization. Atomic force microscopy (AFM) and ellipsometry have revealed a uniform thickness of about 12 nm from which a grafting density of polymer brushes of 0.19 chains · nm^?2 was estimated. The coating with polymer brushes can be realized on a selected surface. It was shown that a single‐sided brush layer swells reversibly in toluene, resulting in a bending of the micromechanical cantilever.

Schematic representation of the PMMA brush synthesis on the MC surface, by surface‐initiated ATRP.