Hyperbranched polyethylenes (HBPEs) with different degree of branching (DB) and similar M_n are used to investigate the effect of branch structure on their crystallization behaviors. The crystal structure, isothermal, and non-isothermal crystallization kinetics of HBPEs are studied by X-ray diffraction and differential scanning calorimetry. The isothermal crystallization process is analyzed by the Avrami equation while the non-isothermal crystallization process is analyzed through the Ozawa and Mo methods. The XRD results indicate that the crystallization ability of HBPEs is weakened with the introduction of branch structure, i.e., the crystallinity of HBPEs decreases with the increase of DB, and even tends to zero. The kinetics results of isothermal and non-isothermal crystallization verify the peculiar effects of DB on the crystallization process of HBPEs. In detail, a little of branch structure can accelerate the crystallization process of HBPEs, however a large number of branch can inhibit it. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44127.

A novel diamine monomer 1, 4,4'-(9H-fluorene-9,9-diyl)-bis(2-tert-butylaniline), was synthesized from 9-fluorenone and 2-tert-butylaniline by the condensation reaction. Then it was polymerized with several commercial aromatic dianhydrides, respectively, to produce polyimides (PIs) by the one-pot method. The number-averaged molecular weights of the resulting PIs are in the range of (4.54–8.82) × 10⁴ with polydispersity indices from 2.51 to 4.33 by gel permeation chromatography measurement. They are soluble in many organic solvents and can form transparent and tough films by solution-casting. The cut-off wavelengths of UV–vis absorption for the PI films are below 360 nm, which are much lower than that of Kapton film. The light transparency of them is above 90% in the visible light range from 400 to 760 nm. They also display relatively low dielectric constants (from 2.79 to 3.00), low water absorption rates (<1%), and high tensile strength (> 50 MPa). Their excellent solubility and transparency can be attributed to the incorporation of tert-butyl groups and fluorene units into the rigid backbones of PIs. Simultaneously, they still maintain the high thermal stability (the 5% weight loss temperature in the range from 526 to 539 °C in nitrogen) and the high glass transition temperatures (T_g > 340 °C). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 976–984

A novel aromatic diamine, 3,3′-diisopropyl-4,4′-diaminophenyl-4″-methyltoluene with a 4-methylphenyl pendant group and isopropyl side groups, was designed and synthesized in this study. Then it was polymerized with various aromatic dianhydrides including pyromellitic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride via a one-pot high temperature polycondensation procedure to produce a series of aromatic polyimides. These polyimides exhibited excellent solubility even in common organic solvents, such as chloroform and tetrahydrofuran. The flexible and tough films can be conveniently obtained by solution casting. The films were nearly colorless and exhibited high optical transparency, with the UV cutoff wavelength in the range 302–365 nm and the wavelength of 80% transparency in the range 385–461 nm. Moreover, they showed low dielectric constants (2.73–3.23 at 1 MHz) and low moisture absorption (0.13%–0.46%). Furthermore, they also possessed good thermal and thermo-oxidative stability with 10% weight loss temperatures (T_10%) in the range 489–507 °C in a nitrogen atmosphere. The glass transition temperatures of all polyimides are in the range 262–308 °C. Copyright © 2012 Society of Chemical Industry