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High-performance low-k and low-loss circuit materials are urgently needed in the field of microelectronics due to the upcoming Fifth-Generation Mobile Communications Technology (5G Technology). Herein, a facile design strategy for non-fluorinated intrinsic low-k and low-loss polyimides is reported by fully considering the secondary relaxation behaviors of the polymer chains. A new amorphous non-fluorinated polymer (TmBPPA) with a k value of 2.23 and a loss tangent lower than 3.94 × 10−3 at 104 Hz has been designed and synthesized, which to the best of our knowledge is the lowest value amongst the non-fluorinated and non-porous polymers reported in literature. Meanwhile, TmBPPA exhibits excellent overall properties, such as excellent thermostability, good mechanical properties, low moisture absorption, and high bonding strength. As high-performance flexible circuit materials, all these characteristics are highly expected to meet the present and future demands for high density, high speed, and high frequency electronic circuit used in 5G wireless networks. [ABSTRACT FROM AUTHOR]

Janus polymerization is featured as a combination of cationic and anionic growing ends in one living polymer chain. In the copolymerization of THF and CL catalyzed by lutetium triflates and initiated by propylene oxide, three stages are identified by kinetic study including (1) fast cationic polymerization with slow anionic one, (2) fast anionic polymerization with dormant cationic one, and (3) reactivation of cationic polymerization with coupling of anionic and cationic chain ends. In this work, density functional theory (DFT) calculation is employed to investigate the reaction details of ionic polymerization and dormancy. A "tripedal crow" configuration is proposed to illustrate the unique high-coordinated ligand exchange configuration in anionic polymerization in different stages. The trigger of dormancy is determined as chain structures rather than concentration of triflate anion according to both calculation and experimental results. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) nanoparticles (NPs) based on fluorescence resonance energy transfer (FRET) were prepared by co-encapsulation of a red aggregation-induced emission (AIE) molecule, 2-(4-bromophenyl)-3-(4-(4-(diphenylamino)styryl)phenyl)fumaronitrile (TB), and a commercial NIR fluorescence dye, silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) (NIR775) with an amphiphilic polymer poly(styrene-co-maleic anhydride) (PSMA). The surface of the NPs, PSMA@TB/NIR775, was modified with poly(ethylene glycol) (PEG) to increase the in vivo biocompatibility of the NPs. The PSMA@TB/NIR775 NPs showed a strong NIR (780 nm) narrow emission and excellent two-photon absorption property. Moreover, the NPs exhibited good monodispersity, stability, and low cytotoxicity. Under the excitation of a 1040 nm femtosecond (fs) laser, the emission peaks at 680 nm of TB and 780 nm of NIR775 excited by FRET were obtained. We utilized PSMA@TB/NIR775 NPs as fluorescent contrast agents for two-photon excited NIR microscopic imaging, and good NIR imaging effect of mouse brain vasculature was obtained with the imaging depth of about 150 μm. The FRET strategy by coencapsulating AIE molecule and NIR dye will be helpful in preparing more narrow emission NIR probes for deep-tissue biological imaging. [ABSTRACT FROM AUTHOR]

A thermally triggered shape memory polymer composite was prepared by blending short carbon fiber (SCF) into a blend of poly(styrene- b-butadiene- b-styrene) triblock copolymer (SBS)/linear low density polyethylene (LLDPE) prior to curing. These composites have excellent processability compared with other thermosets. The dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) were investigated to assess the thermomechanical properties of the SCF/SBS/LLDPE composite. Scanning electron microscope (SEM) imaging of the samples was performed to show the distribution of the SCF in the composite. The study specifically focused on the effect of SCF on the shape memory behavior of the SCF/SBS/LLDPE composite. The results indicated that the large amount of SCF significantly improved the mechanical property of the polymer composites while not damaging the shape memory performance. The SCF/SBS/LLDPE composites exhibited excellent shape memory behavior when the SCF content was less than 15.0 wt%. Moreover, the shape fixity ratio and shape recovery time of the SCF/SBS/LLDPE composites increased with the SCF content. [ABSTRACT FROM AUTHOR]

In this article, we designed and synthesized a series of 5-(2,6-dimethyl-4H-pyran-4-ylidene)-1,3-diethyl-2-thioxodihydropyrimidine- 4,6(1H, 5H)-dione (PD) unit based polymers (PFTDT, CZTDT, PHTDT and THTDT) for the first time. In these polymers, fluorene, 2,7-carbazole, phenothiazine and thiophene are employed as electron-donating groups and PD as electron-withdrawing group. TGA measurements demonstrated that these polymers possess good thermal stability (all above 377 °C). Very broad absorption spectrum was also obtained from the polymer THTDT (300-850 nm). CV characterization found that these polymers owned low highest occupied molecular orbital (HOMO) energy levels (-5.39 eV for THTDT,-5.49 eV for CZTDT and-5.78 eV for PFTDT) except for PHTDT (-5.17 eV). The geometry and electronic properties of PFTDT, CZTDT, PHTDT and THTDT were investigated by means of theoretical calculation. All the above advantages demonstrate that PD based polymers could be candidates for electronic devices. [ABSTRACT FROM AUTHOR]