Macromolecular Chemistry and Physics

Dwindling fossil resources, surging energy demand and global warming stimulate growing demand for renewable polymer products with low carbon footprint. Going well beyond the limited scope of natural polymers, biomass conversion in biorefineries and chemical carbon dioxide fixation are teamed up with highly effective tailoring, processing and recycling of polymers. “Green monomers” from biorefineries, and “renewable oil”, gained from plastics' and bio wastes, render synthetic polymers renewable without impairing their property profiles and recycling. In context of biofuel production, limitations of the green economy concepts are clearly visible. Dreams and reality of “green polymers” are highlighted. Regardless of their new greenish touch, highly versatile and cost‐effective polymers play an essential role in sustainable development.

Thermally and photochemically initiated thiol–ene click reactions using thiol‐ and allyl‐ end functionalized linear polystyrenes with various enes (allyl bromide, methyl acrylate, and methyl methacrylate) and thiol (3‐mercaptopropionic acid) have been investigated. Allyl‐ and thiol‐end‐capped polystyrenes with controlled molecular weight and low polydispersity were prepared by atom transfer radical polymerization (ATRP) of styrene using functional initiator and end group modification approaches, respectively. Thiol–ene reactions can be initiated by both cleavage type photoinitiators such as (2,4,6‐trimethylbenzoyl)diphenylphosphine oxide (TMDPO) and 2,2‐dimethoxy‐2‐phenyl acetophenone (DMPA) and H‐abstraction type photoinitiators such as benzophenone (BP), thioxanthone (TX), camphorquinone (CQ), and classical thermal initiator, 2,2′‐azobis(isobutyronitrile) (AIBN) at 80 °C. The kinetics of the reactions was monitored online with a real time ATR‐FTIR monitoring system and the conversions were determined by ¹H NMR spectroscopy. A comparison of click efficiencies of the studied initiator systems was performed. Compare to the thermal initiators and H‐abstraction type photoinitiators, cleavage type photoinitiators were found to induce thiol–ene click reactions with higher efficiency.

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Aliphatic homopolyesters and copolyesters based on 1,3‐propanediol and containing terephthalic acid as aromatic compounds and sebacic acid as aliphatic compound were synthesized by condensation in bulk. Intrinsic viscosity and weight‐average molecular weight were measured. Melting temperatures were studied by differential scanning calorimetry. For all polyesters the biodegradability was tested. Test media were inoculated with either municipal compost eluates or decanted sewage sludge. Criteria measured were visible changes, weight loss, and scanning electron microscopy indicating the visible changes of the surface. Compositions of copolyesters were characterized by ¹³C NMR spectroscopy. As a major result it is concluded that biodegradability depends substantially on the sequential structure of the polymer.

With unique physicochemical properties, multiwalled carbon nanotubes (MWCNTs) have enabled major achievement in polymer composites as reinforcing fillers. Nevertheless, high conductivity of raw MWCNTs (R‐MWCNTs) limits their wider applications in certain fields, which require outstanding thermal conductivity, mechanical, and insulation properties simultaneously. In this article, silica (SiO₂) coated MWCNTs core–shell hybrids (SiO₂@MWCNTs) and organically modified montmorillonite (O‐MMT) are employed to modify epoxy (EP) simultaneously. The epoxy‐clay system is cured by using anhydride curing agent. The impact strength and flexural strength of final nanocomposites are greatly improved. Meanwhile, the final composites remain in high electrical insulation. Compared to mixed acid treated MWCNTs (C‐MWCNTs) (0.5 wt%)/EP nanocomposites, the volume resistivity of the O‐MMT(4 wt%)/SiO₂@MWCNTs(0.5 wt%)/EP nanocomposites increases more than six orders of magnitude. Synergistic toughening effect occurs when using core–shell SiO₂@MWCNTs and MMT bifillers. The electrical insulation is attributed to the suppressed electron transport effect by SiO₂layer on the CNTs surface, and the blocked conductive CNTs network by the buried 2D structural O‐MMT. The SiO₂@MWCNTs core–shell hybrids also benefit to decrease the dielectric constant and dielectric loss of CNTs/EP composites. This work provides guidance to using CNTs as reinforcement fillers to toughen the polymers for electric insulating applications.

Summary: Biodegradable triblock copolymers based on 1,3‐trimethylene carbonate (TMC) and different lactides (i.e. D,L‐lactide(DLLA), L‐lactide (LLA), D‐lactide (DLA)) designated as poly(DLLA‐TMC‐DLLA), poly(LLA‐TMC‐LLA) and poly(DLA‐TMC‐DLA) were prepared and their mechanical and thermal properties were compared with those of high molecular weight poly(TMC) and poly(TMC‐co‐DLLA) statistical copolymers. Triblock copolymers containing crystallizable LLA or DLA segments perform as thermoplastic elastomers (TPEs) when the poly(lactide) blocks are long enough to crystallize. In blends of poly(LLA‐TMC‐LLA) and poly(DLA‐TMC‐DLA) triblock copolymers, stereo‐complex formation between the enantiomeric poly(lactide) segments occurs as demonstrated by differential scanning calorimetry and light microscopy. These blends have good tensile properties and excellent resistance to creep under static and dynamic loading conditions.

Permanent deformation (after 2 h recovery) of compression‐molded poly(TMC) and solvent‐cast poly(LLA‐TMC‐LLA) and poly(ST‐TMC‐ST) films.

Glycidol (2‐epoxy‐1‐propanol) was polymerized under the action of Lewis acids (BF₃OEt_2,, SnCl₄) and protonic acids (CF₃COOH, CF₃SO₃H). Polymers with number‐average molecular weights (M̄_n) varying from 2500 to 6000 g/mol were obtained. The structure of obtained polymers was characterized by ¹³C and ²⁹Si NMR spectroscopy, and the amount of 1‐3 units, 1‐4 units and chain branches was determined. The structure of the polymers was related to the polymerization mechanism, especially to the contribution of activated monomer mechanism in chain growth.

Nanoscale thin films of PVDF containing the β‐crystalline phase were directly prepared by heat‐controlled spin coating without the influence of external stimuli either in the form of additives or post‐treatments. Sample preparation was carried out at different temperatures, ranging from 10 to 70 °C. At elevated temperatures (40, 50, 60 and 70 °C), PVDF was crystallized into the β‐phase, while at near‐ambient conditions (20 and 30 °C) it was crystallized into the α‐phase. Some samples exhibited a phase‐segregated morphology, with varying particle sizes depending on the preparation temperature. The ferroelectric nature of a typical sample, prepared at 40 °C, was visualized by piezoresponse imaging studies.

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We present a comprehensive investigation on the formation of gold nanoparticles in spherical polyelectrolyte brushes. These colloidal carrier particles consist of a solid polystyrene core onto which long cationic polyelectrolyte chains are grafted. Immersed in water these polyelectrolyte chains can be used to enrich AuCl ions. The metal ions thus confined in the polyelectrolyte layer can be reduced to gold nanoparticles of approximately 1 nm diameter. Cryogenic transmission electron microscopy shows that the Au particles are located near the surface and exhibit a narrow size distribution. Measurements by dynamic light scattering demonstrate that the polyelectrolyte chains are located near the surface of the core particles. This is explained by a crosslinking of the cationic polyelectrolyte chains by the nanoparticles that carry a negative charge. If the Au nanoparticles are removed, the spherical polyelectrolyte brushes re‐expand. High‐resolution electron microscopy together with wide‐angle X‐ray scattering measurements demonstrates that the Au nanoparticles are amorphous. We demonstrate that these Au nanoparticles exhibit catalytic activity for hydrogenation reactions that is slightly below the one of Pt and Pd nanoparticles.

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Previous assignment of the signals in the spectra of carboxymethylcellulose, based on an incremental calculation and hence on low‐molar‐mass model substances, made determination of the partial degree of substitution fundamentally impossible because overlapping of the relevant signals was predicted. However, the methods of acid and enzymatic hydrolysis employed generate the monomer or a mixture of polymers, oligomers and monomers and hence a large number of end groups, which also influence the nuclear magnetic resonance (NMR) spectra. By using ultrasound, it was possible to degrade the molar mass (lower limit of molar mass approx. 100000 g/mol), without oligomers being generated and cleavage of side groups occuring. The viscosity of 10 wt.‐% polymer solutions was so low that the partial degree of substitution could be determined quantitatively for the first time. An additional ¹³C NMR spectroscopic examination of the acid hydrolysate enabled the composition of the eight monomers of sodium carboxymethylcellulose (NaCMC) to be determined in a degree of substitution (DS) range of 0,8–3,0. Knowledge of the monomer compositions is then used to reassign the signals of the polymer spectra, which are then evaluated. Comparison with titrimetric methods (polyelectrolyte titration and ASTM method) showed some wide discrepancies with the absolute method (NMR) in the case of samples with a DS greater than 1. The results of the ¹³C NMR spectroscopic examination of the acid hydrolysate were also used to determine the relative rate constants of the etherification reaction (k₂:k₃:k₆ = 3,0:1,0:2,1), and these were then compared with published data.

Novel bridged dinuclear diimine nickel and palladium complexes catalyzed the vinyl addition polymerization of norbornene at a single active site with high activity. The latter exhibited higher activity than the former. Smaller substituents around the imido group in the ligand were more favorable for increasing the activity than bulkier ones. The polynorbornenes were all noncrystalline but had short‐range order and their glass transition temperature, T_g, ranged from 270 to 400 °C. Furthermore, the random copolymerization of norbornene and styrene was catalyzed by the bridged dinuclear diimine nickel complex with MAO (methylaluminoxane). Gel permeation chromatography (GPC), FTIR and ¹H NMR spectroscopies, wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC) indicated that the copolymers are “true” copolymers. The reactivity ratios were r_styrene = 0.281, r_norbornene = 18.7. The packing density, thermostability and the glass transition temperatures of copolymers are increased relative to polystyrene. The solubility and processability of the copolymers are improved relative to polynorbornene.

The structures of bridged dinuclear diimine nickel and palladium complexes.