Self‐Healing Properties of PDMS Elastomers via Guanine and Cytosine Base Pairs

On account of the combination of base pairs interaction, DNA can realize, unlock, and repair. By introducing commercially available guanine and cytosine into poly(dimethyl siloxane) (PDMS), the self‐healing supramolecular polymer can be achieved, which will be of great interest. Herein, a kind of base pairs functionalized PDMS‐based elastomer is successfully developed and demonstrates great elasticity, tensile strength, and self‐healing abilities, such as GC‐PDMS‐10k, which can be stretched more than triple the original length and achieve 75% self‐healing efficiency. Changing the molecular weights of PDMS or the base pairs offers the desired mechanical properties. Importantly, the synthesis approach is simple enough with no external solvent.     

Acrylic‐Based Polyurethane/Silica Hybrids Prepared by Acid‐Catalyzed Sol–Gel Process: Structure and Mechanical Properties

Summary: Silica sols were first prepared based on different ratios of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) by an acid‐catalyzed sol–gel process, and then incorporated into acrylic‐based polyurethanes. The structures and morphologies of silicone‐oxo clusters were studied by ²⁹Si NMR, SAXS, and scanning electron microscopy (SEM), whereas the mechanical properties of polyurethane/silica hybrids were characterized by DMA and tensile tests. The silicone‐oxo clusters in both silica sol and polyurethane hybrids became denser and larger at a higher molar ratio of TEOS/MTES and higher silica content, and the silica‐oxo clusters of polyurethane/silica hybrids even became more compact and larger than those of silica sols, increasing the elastic modulus and tensile strength of polyurethane/silica hybrids.

Typical structure of silica sol prepared from the hydrolysis and condensation of TEOS and MTES with acid as the catalyst.     

Liquid‐Crystalline Complexes of Polyurethane Containing an Isonicotinamide Moiety with 4‐Dodecyloxybenzoic Acid

A series of supramolecular side‐chain liquid crystalline polyurethanes (SCLCPUs) was prepared by utilizing the selective hydrogen bonding interaction between polyurethane containing pyridine moieties ( 1 ) and 4‐dodecyloxybenzoic acid ( 2 ). Hydrogen bonding was confirmed by FTIR spectroscopy and supported by medium high level ab‐initio MO calculations. The components are miscible up to 0.7 mole of 2 versus the polyurethane repeat unit and the resulting complexes behave as uniform liquid‐crystalline polymers, which exhibit stable, reversible mesophases. The liquid crystalline behavior of these supramolecular polymeric complexes was established by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X‐ray diffractometry (XRD). The complexes show a highly ordered smectic phase, which does not appear for either of components 1 and 2 separately , and a nematic phase. Above the concentration limit of 0.7 mole of the acid 2 , the excess low molar mass molecules emerge to form a two phase system consisting of a polyurethane supramolecular complex and 4‐dodecyloxybenzoic acid ( 2 ). For complexes derived from polyurethane 1 and 4‐octyloxybenzoic acid ( 3 ) or 4‐butyloxybenzoic acid ( 4 ) with alkyl tails shorter than 2 , the phase separation occurs at lower molar ratios of 3 and 4 versus 1 . This means that the length of the alkyl tail in 4‐(alkoxy)benzoic acids plays an important role in the stabilization of supramolecular polyurethane complexes.     

Room Temperature Self‐Healing Methyl Phenyl Silicone Rubbers Based on the Metal–Ligand Cross‐Link: Synthesis and Characterization

Novel self‐healing silicone rubbers are prepared by a two‐step procedure: aminopropyl methyl phenyl polysiloxanes is first reacted with salicylaldehyde and then with copper acetate. The reversible nature of the metal–ligand coordination interaction between polysiloxanes with pendent Schiff‐base groups and Cu²⁺ has endowed silicone rubbers with superior self‐healing properties. As compared with other self‐healing silicone rubbers based on hydrogen bonds or Diels–Alder reaction, this cross‐linked system shows high healing power. The materials are cut into two parts and put together in a mold for 1 h at 30 °C, observing a macroscopic healing and a strength recovery up to 87.0%.

     

Structure and Properties of Phosphorous‐Containing Thermotropic Liquid‐Crystalline Aliphatic–Aromatic Copolyesters

A series of thermotropic liquid crystalline aliphatic–aromatic copolyesters derived from various ratios of dodecane‐1,12‐diol ( 1 ), terephthaloyl bis‐(4‐oxybenzoyl‐chloride) ( 2 ), and 2‐(6‐oxido‐6H‐dibenz〈c,e〉〈1,2〉 oxaphosphorin‐6‐yl)‐1,4‐naphthalene diol ( 3 ), has been synthesized. The chemical structures of the monomers and polymers have been confirmed by elemental analyses, and FT‐IR and ¹H NMR spectroscopy. The mesomorphic properties of polymers have been investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the content of the aliphatic unit on the phase behavior of the polymers has been examined. The polymers that contain >30 mol‐% aliphatic diol showed smectic phases while the polymers that contained <30 mol‐% aliphatic diol displayed nematic phases. The polymers revealed a reversible mesomorphic phase transition, wide mesophase temperature ranges, and high thermal stability. The degree of crystallinity increased upon increasing the content of aliphatic moieties. The char yield at high temperature increased by increasing the content of phosphorous‐containing bisphenol.

     

Carboxylic Acid Ionic Modification of Castor‐Oil‐Based Polyurethanes Bearing Amine Groups: Chemically Tunable Physical Properties and Recyclability

A family of supramolecular side‐chain ionic polyurethanes (PUs) is synthesized by a simple method using polyurethanes with tertiary amines as pendant groups, and carboxylic acids. The resulting polyurethanes contain diethyl ammonium and carboxylate moieties that are bonded by a combination of ionic and hydrogen bonds. The self‐assembling process is observed by Fourier‐transform infrared spectroscopy‐attenuated total reflection (FTIR‐ATR) and nuclear magnetic resonance (NMR) spectroscopy. The synthesized polyurethanes are characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Rheological, dielectric, and mechanical properties are investigated, and it is found that the tunability of the properties depends on the acid functionality and the chain length. Dynamic viscoelastic tests reveal a rapid and complete thermal reversibility, which opens the door to studying the recyclability of the samples.     

Modification of Oligomeric Cyanate Ester Polymer Properties with Multi‐Walled Carbon Nanotube‐Containing Particles

The properties of an oligomeric cyanate ester polymer were modified by the addition of 0.01–3 wt.‐% multi‐walled carbon nanotube (MWNT) containing particles. The dynamic mechanical behavior and thermal properties of the cyanate ester/MWNT nanocomposites were evaluated. The storage modulus, G′, of the nanocomposite with 1 wt.‐% MWNT particles was nearly 60 and 600% higher than the neat polymer at 100 and 200 °C, respectively. The glass transition temperature of the nanocomposite was also raised by 30 °C and its thermal stability in air and nitrogen was increased by 58 and 25 °C, respectively. The property improvements are attributed to reinforcement of the cyanate ester as a result of good nanotube dispersion and effective polymer‐MWNT interaction.

     

Novel Coiling Behavior in Magnet‐Polymer Composites

Magnet‐polymer (Magpol) composites have an interesting ability to undergo large strains in response to an external magnetic field. The contraction behavior of composites of silicone and micron sized iron particles induced by an external magnetic field was studied. Simply by changing boundary conditions, Magpol can exhibit shape change from axial contraction to a novel coiling mechanism due to buckling. The analytically predicted magnetic fields for buckling agreed well with the measured values. The strain versus magnetic field relationship suggested that postbuckling behavior is a stable symmetric bifurcation, which is useful for continuous actuation. The coiling mode of Magpol exhibited high actuation strain (up to 60%) and actuation stress (up to 184 kPa), thus shows good potential for use in soft actuators.

     

Novel Polymerizable Sulfur‐Containing Benzophenones as Free‐Radical Photoinitiators for Photopolymerization

Summary: Three novel polymerizable sulfur‐containing benzophenone photoinitiators, MAATPBP, CMAATPBP and BMAATPBP, were synthesized. These novel photoinitiators possess strongly red‐shifted maximum UV absorption and very weak fluorescence emission. The photopolymerization of two monomers with different functionality, bifunctional HDDA and trifunctional TMPTA, initiated by these three polymerizable photoinitiators, was studied by photo‐DSC using the unsaturated tertiary amine DMAEMA as the coinitiator. The results show that all the polymerizable photoinitiators were highly efficient and different photoinitiators exhibited different behaviors towards different monomers: BMAATPBP was the most efficient for HDDA; MAATPBP was the most efficient for TMPTA. They could also efficiently initiate the photopolymerization without the coinitiator because of photolysis at the C S bond.

Structures of the polymerizable sulfur‐containing photoinitiators synthesized.     

Novel Soluble N‐Phenyl‐Carbazole‐Containing PPVs for Light‐Emitting Devices: Synthesis,Electrochemical, Optical,and Electroluminescent Properties

Summary: Novel PPV derivatives (PCA8‐PV and PCA8‐MEHPV) containing N‐phenyl‐carbazole units on the backbone were successfully synthesized by the Wittig polycondensation of 3,6‐bisformyl‐N‐(4‐octyloxy‐phenyl)carbazole with the corresponding tributyl phosphonium salts in good yields. The newly formed and dominant trans vinylene double bonds were confirmed by FT‐IR and NMR spectroscopy. The polymers (with of 6 289 for PCA8‐PV and 7 387 for PCA8‐MEHPV) were soluble in common organic solvents and displayed high thermal stability (T_gs are 110.7 °C for PCA8‐PV and 92.2 °C for PCA8‐MEHPV, respectively) because of the incorporation of the N‐phenyl‐carbazole units. Cyclic voltammetry investigations (onsets: 0.8 V for PCA8‐PV and 0.7 V for PCA8‐MEHPV) suggested that the polymers possess enhanced hole injection/transport properties, which can be also attributed to the N‐phenyl‐carbazole units on the backbone. Both the single‐layer and the double‐layer light‐emitting diodes (LEDs) that used the polymers as the active layer emitted a greenish‐blue or bluish‐green light (the maximum emissions located 494 nm for PCA8‐PV and 507 nm for PCA8‐MEHPV, respectively). Compared with those of the single‐layer devices, the emission efficiencies of the double‐layer devices, in which an electron‐transporting layer (Alq₃) was added, were enhanced by a factor of 10, implying that the better hole‐electron balance is achieved because of the incorporation of the electron‐transporting layer.

The N‐phenyl‐carbazole‐containing polymers synthesized.     

Accurate Elemental Analysis of Metal‐Containing Polymer Latexes Using ICP‐Optical Emission Spectrometry

The use of ICP‐OES to determine the metal content of metal‐complex‐containing colloidal dispersions is explored. Colloidal dispersions containing a defined amount of metal complex were produced by miniemulsion polymerization. It was found that simple ICP‐OES measurements yielded apparent metal concentrations significantly below the expected value. To examine the behavior of the colloidal dispersions in the ICP spectrometer, a systematic study on measurement conditions was performed. It was found that the addition of a surfactant to both colloidal dispersions and standards led to measured metal contents close to the theoretical value. Most reliable results were obtained using SDS in concentrations above the cmc.

     

Mechanical and Thermal Properties of Networks Prepared from Reactive Poly(urethane‐imide)s and Blocked Polyurethane Prepolymer

Reactive poly(urethane‐imide)s with varying functionality were prepared using 4,8‐diphenyl‐1,5‐diazabicyclo(3.3.0)octane‐2,3,6,7‐tetracarboxylic dianhydride, 4,8‐(di‐p‐phenylol)‐1,5‐diazabicyclo(3.3.0)octane‐2,3,6,7‐tetracarboxylic dianhydride and N‐methylaniline blocked polyurethane prepolymer ( 1 ). The resulting polymers with reactive phenylol groups, pendent in the dianhydride, were treated with 1 to give poly(urethane‐imide) networks. The cast films were characterized by FT‐IR, TG, static and dynamic mechanical analyses. Thermal stability of the polymers was found to be higher than that of the conventional polyurethane. Higher cross‐linking leads to lower damping and improved strength.     

State of Order of the Crosslinker in Main‐Chain Liquid Crystalline Elastomers

Rigid anisotropic crosslinkers have been shown to decrease the nematic order and the transition temperatures of main‐chain liquid crystalline elastomers (MCLCEs). In order to look into this phenomenon, the state of order of an anisotropic crosslinker in an MCLCE was investigated separately from that of the matrix. For this purpose, multifunctional perylene derivatives were synthesized and used as a crosslinker and as a reference mesogen probe. Their states of order were measured by their dichroism, and were compared to that of the MCLCE matrix. A systematically lower degree of order was observed for the crosslinker in comparison to the matrix, both when attached to and dissolved in the network.

     

Macromolecular Crystal Engineering Based on Segmented Polymers: Influence of Heteroatoms on the Thermal Properties and Crystallization of m,n‐Polyurethanes Derived from Long‐Chain,Heteroatom‐Containing,Monodisperse α,ω‐Diols

Long‐chain heteroatom‐containing telechelic diols with 29–32 atoms in the backbone were synthesized by a one‐step, free‐radical telomerization of 10‐undecene‐1‐ol with commercially available α,ω‐dithiols. The oxygen and sulfur atoms caused a decrease in the melting point and enthalpy of the diols, compared to the corresponding purely aliphatic diols. The heteroatom‐containing α,ω‐diols HO? (CH₂)₁₁? S? (CH₂)₂? X? (CH₂)₂? S? (CH₂)₁₁? OH, where X = CH₂, O, or O? (CH₂)₂? O, were reacted in the melt with 1,6‐diisocyanatohexane O?C?N? (CH₂)₆? N?C?O, producing a series of polyurethanes containing an increasing amount of heteroatoms. Characterization by differential scanning calorimetry, infra‐red spectroscopy, thermogravimetric analysis, and wide angle x‐ray scattering of the m,n‐polyurethane series showed that, like the telechelic diols they were synthesized from, the heteroatoms caused a decrease in the melting point and enthalpy. However, they did not affect either the decomposition temperature or the crystal structure/packing.

Typical decomposition behavior of all the heteroatom‐containing m,6‐polyurethane.     

Synthesis and Gas‐Transport Properties of Novel Copolymers Based on Tricyclononenes Containing One and Three Me3Si‐Groups

In this work the authors report the preparation of new addition copolymers based on 3‐trimethylsilyltricyclononene‐7 (TCNSi1) and 3,3,4‐tris(trimethylsilyl)tricyclononene‐7 (TCNSi3). A number of high molecular weight copolymers are synthesized with the content of TCNSi3 units from 5 up to 20 mol% in the presence of catalyst Pd(OAc)₂/[Ph₃C]⁺[B(C₆F₅)₄]⁻ with the yields of 50%–80%. The obtained copolymers are amorphous. They possess large free volume elements (R ₃/R ₄) based on positron annihilating lifetime spectroscopy analysis and Brunauer–Emmett–Teller surface area up to 640 m² g⁻¹. Permeability coefficients of the obtained copolymers are determined for a wide range of gases He, H₂, O₂, N₂, CO₂, CH₄, C₂H₆, C₃H₈, n‐ C₄H₁₀. The correlation between the content of TCNSi3 units and gas permeation parameters of the resulting copolymers is explored. It is found that the introduction of TCNSi3 moieties results in the rise in gas permeability of the corresponding copolymers. Moreover, increase in TCNSi3 content in the copolymer leads to an increase of gas permeability.

     

Enhanced Mechanical Properties of PET‐Based Thermoplastic Elastomers: Brittle–Ductile Transition via Micro Cross‐linking Technology

A novel micro cross‐linking technology is proposed to enhance the mechanical properties of poly(ethylene terephthalate) (PET)‐based thermoplasctic elastomers (TPEEs) whose molecular weights are difficultly increased via traditional synthetic technologies. It is found that the brittle fractures of TPEEs, usually observed in polymers with low molecular weights, can be converted into ductile form with the introduction of a certain fraction of 1,2,3,4‐butane tetracarboxylic acid as a cross‐linking agent. Unlike the traditional cross‐linking technologies, which usually cause the elastomers to suffer the deficiencies of extremely high stiffness, inherent weakness, and the inability to be efficiently reused, TPEEs still maintain their elastomeric characteristics well with the incorporation of micro cross‐linking structure and are endowed with a well‐defined microphase‐separated structure, excellent tensile properties, and the abilities to be melt‐processed and reused. This work offers a new guideline to improve the mechanical properties for polymers with relatively low molecular weights.     

Synthesis of Functional Sugar‐Based Polyurethanes

Three new polyurethanes (PUs) with multiple pendant allyl groups were synthesized from L ‐arabinitol as versatile materials for the preparation of tailor‐made PUs with varying degrees of functionalization. Their allyl functional groups can take part in thiol‐ene reactions to obtain greatly diverse materials. Thus, six new highly functional PUs were prepared by click chemistry to give polymers with NHBoc [NH‐CO‐OC(CH₃)₃], amino, carboxylic, and 1,2‐dihydroxyethyl side groups. The thermal stability of the novel PUs was investigated by thermogravimetric analysis and differential scanning calorimetry. This strategy provides a simple and versatile platform for the design of new materials whose functionality can be easily modified to anchor diverse biologically active molecules.     

Dielectric Relaxation of Side‐Chain Liquid Crystalline Ionomers Containing Alkaline Metal Ions

Summary: Two sets of side‐chain, liquid‐crystalline ionomers based on copolymers of butyl acrylate and 4‐{[6‐(acryloyloxy)hexyl]oxy}benzoic acid containing 2.5–20 mol‐% of lithium or rubidium ions were studied. As the content of ions of alkali metals increases, segmental mobility markedly decreases. As compared with rubidium‐containing ionomers, ionomers containing lithium ions are characterized by a far more efficient decrease in their dielectric relaxation times because ionic radius of lithium ions is lower than that of rubidium ions.

     

Metal‐Free Ring‐Opening Alternating Copolymerization of Epoxides and Cyclic Anhydrides Mediated by a Ternary Phosphazene Base and Carboxylic Acids

Organocatalytic, metal‐free ring‐opening alternating copolymerization (ROAP) of epoxides and cyclic anhydrides to produce polyesters with well‐defined alternating structure remains a challenge despite several organocatalysts having been reported. Herein, the ROAP of cyclohexene oxide (CHO) with phthalic anhydride (PA) using a series of carboxylic acids as initiator in the presence of an organic cyclic trimetric phosphazene base (CTPB) as catalyst is reported. The molar ratio of CTPB to carboxylic acid is proven to be crucial to obtain polyester with well‐defined alternating structure without formation of polyether homopolymer. The effects of carboxylic acid, temperature and feed molar ratio on monomer conversions and resultant molecular weights of poly(PA‐alt‐CHO) are systematically investigated. This work enriches the opinion of initiator for the ROAP of epoxides and cyclic anhydrides.