The Structure of Water in PEO‐Based Segmented Block Copolymers and its Effect on Transition Temperatures

The effect of water on block copolymers that contain hydrophilic PEO flexible segments is studied. The polyether phase consisted of either PEO or mixtures of PEO and hydrophobic PTMO, monodisperse crystallisable T6T6T was used as hard segments. Water absorption as a function of relative humidity and PEO content were studied. The PEO melting temperature and crystallinity were strongly reduced when the copolymer absorbed water, while the PTMO phase remained unaffected by its presence. Freezing water was present in the PEO‐based copolymers when the PEO phase contained ≈30 vol.‐% water, its relative amount being almost independent of PEO concentration and molecular weight and the presence of hydrophobic PTMO segments.

     

Synthesis and Micellization of Star‐Shaped Poly(ethylene glycol)‐block‐Poly(ε‐caprolactone)

Summary: The relationship between the architecture of block copolymers and their micellar properties was investigated. Diblock, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymers based on poly(ethylene glycol) and poly(ε‐caprolactone) were synthesized. Micelles of star‐shaped block copolymer in an aqueous solution were then prepared by a solvent evaporation method. The critical micelle concentration and the size of the micelles were measured by the steady‐state pyrene fluorescence method and dynamic light scattering, respectively. The CMC decreased in the order di‐, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymer. The size of the micelles increased in the same order as the CMC. Theory also predicts that the formation of micelles becomes easier for 4‐arm star‐shaped block copolymers than for di‐ and 3‐arm star‐shaped block copolymers, which qualitatively agrees with the experiments.

     

Fluorene‐Based Single‐Chain Copolymers for Color‐Stable White Light‐Emitting Diodes

Fluorene‐based single‐chain copolymers with a white light emitter consisting of a blue and an orange chromophore have been synthesized and their photophysical and electroluminescent properties are investigated. The experimental results suggest that only a relatively small fraction of the orange‐emitting units incorporated into the fluorene is needed to achieve efficient white light emission by controlled incomplete energy transfer. A device from a copolymer with 0.02% DDQ content showed the highest external quantum efficiency of 2.64% with a luminance efficiency of 4.06 cd · A^?1 with CIE coordinates (0.28, 0.24). The EL emissions are extremely stable over a wide range of current densities.

     

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.     

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.

     

Synthesis and Characterization of Conducting Copolymers of (S)‐2‐Methylbutyl‐2‐(3‐thienyl)acetate with Pyrrole and Thiophene

Polymerization of methylbutyl‐2‐(3‐thienyl)acetate (MBTA) was achieved by constant current electrolysis at low temperature. Subsequently, the syntheses of block copolymers of polyMBTA were accomplished in the presence of either pyrrole or thiophene by constant potential electrolysis. Moreover, the copolymer of MBTA with thiophene was obtained with constant potential electrolysis.

The synthesis of monomer MBTA.     

Synthesis of Defined Poly(silsesquioxane)s: Fast Polycondensation of Trialkoxysilanes in a Continuous‐Flow Microreactor

The polycondensation of trialkoxysilanes to PSSQs in a microreactor setup is demonstrated. While continuous‐flow processes involving microreactors found various applications in chain growth polymerization, their influence on step‐growth polymerization is less explored, and the polycondensation of multifunctional monomers has not been studied in detail. We found significantly increased yields and a decreased polydispersity of the obtained polymers in comparison to the batch process. By variation of the residence time molecular weights could be adjusted reproducibly ranging from = 1 900 to 11 000 g · mol^?1. Thus, the microreactor setup offers for the first time the possibility to synthesize PSSQ with adjustable properties.

     

Morphology Control of Highly Sulfonated Block Copolymers by a Simple Thermal Process

Well‐defined sulfonated block copolymers were prepared by direct thermolysis with block copolymers of n‐butyl acrylate (nBA) and neopentyl styrene sulfonated (NSS), which were synthesized by Cu‐based living radical polymerization ( <1.20). A simple thermal process for 10 min at 150 °C completely deprotected the neopentyl groups in the poly(NSS) block segment to give fully sulfonated polystyrene backbone. SAXS profile of the block copolymer with 47 wt.‐% of poly(NSS) showed lamella structure, which appeared more clearly with long ranged order after sulfonation of the block copolymer.

     

Synthesis and Characterization of New Acrylate and Methacrylate Monomers with Pendant Pyridine Groups

To overcome some drawbacks of polyvinylpyridines, new monomers of acrylate and methacrylate type with pendant pyridine groups i.e., 4‐(3‐methacryloylpropyl)pyridine 1a and 4‐(3‐acryloylpropyl)pyridine 1b were successfully prepared, although it turned out to be challenging work to synthesize the acrylate monomer 1b . First polymerization studies showed that the new monomers could be polymerized easily by atom transfer radical polymerization (ATRP). The new polymers show excellent characteristics, such as very good solubility, low glass‐transition temperature, and easy quaternization.

Design and structure of new monomers 1a and 1b .     

Polylactones, 68

Full Paper: Using Sn(II )2‐ethylhexanoate (SnOct₂) in combination with 1,4‐butanediol, 1,1,1‐tris(hydroxymethyl)propane (THMP) or pentaerythritol as initiator systems telechelic polyesters or star‐shaped homopolyesters of ε‐caprolactone (ε‐CL) or L,L ‐lactide (L‐LA) were prepared. These homopolymers were characterized by solution viscosities, ¹H NMR and MALDI‐TOF mass spectra. Using preformed homopolymers as coinitiators star‐shaped polymers having two‐block star arms were obtained. Polymerizations of equimolar mixtures of two monomers yielded star‐shaped polymers with random copolyesters as star arms. The blockiness or randomness of the star arms was characterized by ¹³C NMR spectroscopy. Homo‐ and copolymerizations of trimethylene carbonate (TMC) were also studied, but they were plagued by intensive side reactions such as formation of cyclic oligomers, coinitiation with water and crosslinking via transesterification.

Star‐shaped polymers having two‐block star arms obtained in this study.     

Regioselective Synthesis and Structures of (+)‐Catechin‐Aldehyde Polycondensates

The polymerization of (+)‐catechin with various aldehydes has been performed in the presence of an acid catalyst to produce catechin‐aldehyde polycondensates in high yields. NMR analysis of the product showed that the polymerization regioselectively proceeded to form the polymer linked by an ethyl bridge through C‐6 and C‐8 positions of catechin A ring. Specific rotation and CD measurements of the polymer showed the change of chemical bonding and conformation at near chiral center. The direction of specific rotation was changed from dextrorotatory (+) to levorotatory (?) and a new chiral center was formed on the bridge moiety between the catechin units. Computer simulation suggests the coiled interactions in the polymer by hydrogen bonds between hydroxyl groups and pyranic oxygens.

     

What Morphologies Do We Want? – TEM Images from Dilute Diblock Copolymer Solutions

The formation of various exotic morphologies of block copolymers in dilute solutions has often been claimed on the basis of TEM imaging. Do they really exist in solutions or are they just some kinetically frozen structures arising from TEM sample preparation? It is shown that different morphologies are formed due to a competition between different time scales. More and more people are realizing that it is necessary to use cryo‐TEM to ascertain a novel morphology in polymer solutions, but not everyone is able to access a modern cryo‐TEM. Our current study serves as an alarm to those who are interested in morphologies in block copolymer solutions that it is necessary to combine different methods, such as LLS, freeze‐drying, and TEM, in their studies.

     

Novel Poly(butylene succinate)‐Based Ionomers with Sulfonated Succinate Units: Synthesis,Morphology, and the Unique Nucleation Effect on Crystallization

Summary: Poly(butylene succinate) (PBS) and PBS‐based ionomers (PBSi's) with 0.3 and 1.2 mol‐% of sodium sulfonated succinate unit were synthesized. The existence of ionic aggregates in the ionomer matrices was indicated by melt viscosity and glass transition data. It seems that the ionic aggregates have two opposing roles in crystallization: one is the induction of nucleation and the other is the interference with lamellar growth. Because of these two contrary effects, the crystallization behavior of the ionomers exhibited measurably different cooling rate‐dependencies than that of the parent PBS. The rate varied distinctly with ionic content.

Spherulitic morphologies of PBS and PBSi's measured with polarizing optical microscopy.     

Crystallization and Ring‐Banded Spherulite Morphology of Poly(ethylene oxide)‐block‐Poly(ε‐caprolactone) Diblock Copolymer

Summary: The crystallization behavior of crystalline‐crystalline diblock copolymer containing poly(ethylene oxide) (PEO) and poly(ε‐caprolactone) (PCL), in which the weight fraction of PCL is 0.815, has been studied via differential scanning calorimeter (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized optical microscopy (POM). DSC and WAXD indicated that both PEO and PCL blocks crystallize in the block copolymer. POM revealed a ring‐banded spherulite morphology for the PEO‐b‐PCL diblock copolymer.

DSC heating curve for the PEO‐b‐PCL block copolymer.     

Thermodynamic Differences Between Deuterated and Protonated Polystyrenes Evaluated Using Reversed Phase Liquid Chromatography

Summary: Deuterated compounds are generally considered to possess very similar properties to their protonated analogues. Reversed phase liquid chromatography (RPLC) was used to measure thermodynamic interactions between deuterated and protonated n‐butyl polystyrenes and a C18 stationary phase. Significant differences in enthalpies and entropies of interaction were observed for deuterated and protonated n‐butyl polystyrenes. This is very important because many techniques, such as small‐angle neutron scattering and neutron reflectivity, assume that the interaction of these molecules are identical.

Structure of n‐butyl polystyrenes.     

Rod‐Length Dependent Aggregation in a Series of Oligo(p‐benzamide)‐Block‐Poly(ethylene glycol) Rod‐Coil Copolymers

Summary: The synthesis of a series of rod‐coil diblock copolymers with flexible poly(ethylene oxide) chains ( = 5 000 g · mol⁻¹) and rod blocks consisting of monodisperse oligo(p‐benzamide)s is described. The formation of defined supramolecular aggregates in solution as well as the solid state has been analyzed. The length of the oligo(p‐benzamide)s has been systematically varied from n = 1 to 7 units. The influence of n on aggregation in chloroform and aqueous solution was investigated by GPC as well as UV‐vis spectroscopy. A critical aggregation length was found for chloroform (n = 5) and water (n = 4), below which no aggregation is observed under otherwise identical experimental conditions. Aggregation of the polymers in chloroform solution can be chemically reversed by the addition of PCl₅, resulting in conversion of the aromatic amides into imidoyl chlorides. Such amide‐protected block copolymers show no aggregation in NMR and GPC experiments. Imidoyl chloride formation was shown to be reversible, i.e., addition of water regenerated the oligo(p‐benzamide) blocks.

Conversion of aramide block copolymer into molecularly dissolved form using PCl₅.     

Allyl End‐Functionalized Poly(ethylene oxide)‐block‐poly(methylidene malonate 2.1.2) Block Copolymers: Synthesis,Characterization, and Chemical Modification

Summary: Poly(ethylene oxide)‐block‐poly(methylidene malonate 2.1.2) block copolymer (PEO‐b‐PMM 2.1.2) bearing an allyl moiety at the poly(ethylene oxide) chain end was synthesized by sequential anionic polymerization of ethylene oxide (EO) and methylidene malonate 2.1.2 (MM 2.1.2). This allyl functional group was subsequently modified by reaction with thiol‐bearing functional groups to generate carboxyl and amino functionalized biodegradable block copolymers. These end‐group reactions, performed in good yields both in organic media and in aqueous micellar solutions, lead to functionalized PEO‐b‐PMM 2.1.2 copolymers which are of interest for cell targeting purposes.

Synthetic route to α‐allyl functionalized PEO‐b‐PMM 2.1.2 copolymers.     

Dynamics of Dense Suspensions of Star‐Like Micelles with Responsive Fixed Cores

Summary: PBMA‐PCEMA block copolymer micelles, consisting of poly(2‐cinnamoyloxyethyl methacrylate) (PCEMA) cross‐linked core and poly(butyl methacrylate) (PBMA) hairs (shell), are used as model responsive soft colloids, where the core swelling can be tuned by changing solvent quality. Our extensive dynamic light scattering study, complemented by viscosity and small angle neutron scattering (SANS) measurements, demonstrates the richness of dynamics of such dense micellar suspensions and in particular the strong influence of solvent‐mediated core swelling on the concentration dependence of the self‐diffusion. Brownian dynamics (BD) simulations using appropriate effective core‐core interactions support these findings. Such novel micelles offer new possibilities for controlling the interactions and macroscopic properties of colloidal suspensions.

The self‐diffusion coefficient D for core‐shell particles, as calculated from the Brownian dynamics simulations.     

The Effect of PEG Crystallization on the Morphology of PEG/Peptide Block Copolymers Containing Amyloid β‐Peptide Fragments

Ordered nanostructures are observed in the melt and solid state for a series of three peptide/PEG conjugates containing fragments of amyloid β‐peptides. These are conjugated to PEG with = 3 300 g · mol^?1 and a melting temperature T_m = 45–50 °C. The morphology at room temperature is examined by AFM and POM. This shows spherulite formation for the weakly fibrillizing KLVFF‐PEG sample but fibril formation for FFKLVFF‐PEG. The fibrillization tendency of the latter is enhanced by multiple phenylalanine residues. Simultaneous SAXS and WAXS was used to investigate the morphology as a function of temperature. The secondary structure is probed by FTIR.

     

Pyrene Containing Polymers for the Non‐Covalent Functionalization of Carbon Nanotubes

Pyrene containing diblock copolymers based on poly(methyl methacrylate) were synthesized and investigated regarding their adsorption on carbon nanotubes (CNT). The pyrene units were introduced using a reactive ester monomer for the build up of the second block which later on was reacted polymer‐analogously with amine functionalized pyrene derivatives. As we started from the same reactive ester intermediate, full block length identity is given. We varied the length of the anchor block to find an optimal block length and used pyren‐1‐yl‐methylamine as well as 4‐pyren‐1‐yl‐butylamine as anchor units. For both anchor units a maximal adsorption was found for 13 and 20 anchor units, respectively. The absolute adsorption was best for the 4‐pyren‐1‐yl‐butylamine anchor units as the longer spacer enhances the mobility of the anchor unit. The dispersion diagram of CNTs and diblock copolymer in terms of dispersion stability was investigated and a stable dispersion of 2.5 mg · ml^?1 CNTs in THF was found.