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The supramolecular crystal structure in poly(vinylidene fluoride) (PVDF) solution-cast films is studied through changing crystallization conditions in two solvents of different structures and polarities. The crystalline-state chain conformations of isothermally solution-crystallized PVDF in N, N-dimethylacetamide (DMAc), and cyclohexanone are studied through the specific FTIR absorption bands of ␣, ␤, and ␥ phase crystals. There are no changes in the FTIR spectra of cyclohexanone solution-crystallized films in the temperature range of 50 -120°C. In the case of DMAc solutioncrystallized films, low temperature crystallization mainly results in formation of trans states (␤ and ␥ phases), whereas at higher temperatures gauche states become more populated (␣ phase). This is due to the variations in solvent polarity and ability to induce a specific conformation in PVDF chains, through the changes in chain coil dimensions. This indicates that in spite of cyclohexanone solutions, the intermolecular interactions between PVDF and DMAc are temperature-sensitive and more important in stabilizing conformations of PVDF in crystalline phase than temperature dependence of PVDF chain end-to-end distance Ͻr 2 Ͼ. The high-resolution 19 F NMR spectroscopy also showed little displacement in PVDF characteristic chemical shifts probably due to changes in PVDF chain conformation resulting from temperature variations. Upon uniaxial stretching of the prepared films under certain conditions, contribution of trans state becomes more prominent, especially for the originally higher ␣ phase-containing films. Due to formation of some kink bands during film stretching and phase transformation, ␣ phase absorption bands are still present in infrared spectra. Besides, uniaxial stretching greatly enhances piezoelectric properties of the films, maybe due to formation of oriented ␤ phase crystals, which are of more uniform distribution of dipole moments.

Organic−inorganic nanocomposite protective coatings were prepared by sol−gel method using 3glycidoxypropyl-trimethoxysilane (GPTMS), tetramethoxysilane (TMOS), or tetraethoxysilane (TEOS) as silane precursors to compare the effect of two types of alkoxysilane (i.e., methoxy or ethoxy functional group) on aluminum substrate properties. In addition, the TiO 2 and AlOOH nanoparticles were derived from tetra-n-butyl titanate and aluminum butoxide, respectively, and the protective effect of these nanoparticles on the GPTMS based coatings was investigated. The formation of AlOOH and TiO 2 nanoparticles and the uniform distribution of nanoparticles in the coatings were characterized by dynamic light scattering (DLS) and different microscopic techniques. Potentiodynamic scanning (PDS) and 2000 h salt-spray testing methods were used to investigate the corrosion resistance of these hybrid sol−gel coatings. The PDS results demonstrated that the corrosion protection of hybrid coatings depends mainly on the silane content, type of the silane precursor, and type of nanoparticles. The coating protective effect improved by increasing polarization resistance (Rp) for about one decade by replacing silane precursors from TEOS to TMOS. In addition, the incorporation of TiO 2 in comparison with AlOOH nanoparticles in the GPTMS based coatings showed improving effect on polarization resistance. However, the simultaneous incorporation of TiO 2 and AlOOH nanoparticles led to high protective coatings.

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Polyetheramine (PEA)-modified epoxies with various types of PEAs were prepared and respective effects on characteristics of epoxy networks were studied. The used PEAs were polyethylene glycol diamine (PEG-amine) and polypropylene glycol diamine (PPGamine) with two different molecular weights (i.e., 200 and 400 g mol −1 ). According to mechanical tests, the structural parameters of PEAs played an important role in final properties of epoxy/amine systems. PEG 400 -amine and PPG 200 -amine had the highest and lowest effects on the properties of epoxy networks, respectively. Whereas 10 phr PEG 400 -amine increased critical stress intensity factor (K IC ) and critical strain energy release rate (G IC ) of the epoxy up to 82 and 294%, the same number of PPG 200 -amine chains caused to increase the K IC and G IC up to 11 and 34%. This discrepancy could be assigned to higher flexibility index (φ = 26.22), longer chain length (~27 atoms), and higher secondary interactions [δ = 9.69 (cal cm −3 ) 0.5 ] of PEG 400 -amine in comparison with PPG 200 -amine [with φ = 8.08,~10 atoms in chain, and δ = 8.98 (cal cm −3 ) 0.5 ]. Shear yielding as a toughening mechanism was proposed based on microscopy of the crack tips. These in-depth studies could uncover underlying structure-property relationships in a relevant class of PEA-like modifiers, shedding light on the future design of top-performing homogeneous tough polymer networks.

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In this study, a novel reactive toughener for the epoxy resin was developed and compared with traditional hydroxyl‐terminated polybutadiene (HTPB). For this purpose, the highly reactive aliphatic amine‐terminated polybutadiene (ATPB) was synthesized at ambient conditions by nucleophilic substitution amination. The characterizations of the product were provided by Fourier transform infrared and 1H NMR spectroscopy. According to the mechanical test results, incorporation of ATPB into epoxy networks can significantly toughen the epoxy matrix. The addition of 10 phr ATPB increased the critical stress intensity factor (KIC) and critical strain energy release rate (GIC) of the epoxy from 0.85 to 2.16 MPa m1/2 and from 0.38 to 3.02 kJ m−2, respectively. Furthermore, unlike HTPB, the presence of the ATPB did not deteriorate the tensile strength of the matrix. The toughening and failure mechanisms were discussed based on the epoxy network morphological characteristics. The reduction in cross‐linking density and glass transition temperature of the epoxy system upon modification with liquid rubbers was confirmed by dynamic mechanical analysis. This article opens up the possibility of utilizing reactive flexible diamines with polybutadiene backbone as effective toughening agents for thermoset polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44061.

Novel self‐healing Diels–Alder (DA) polymer and the corresponding semi‐interpenetrated polymer networks (semi‐IPNs) were synthesized and characterized. Initially, a furan‐functionalized resin (FFR) was synthesized through the ring‐opening reaction of a conventional epoxy resin [diglycidyl ether bisphenol A (DGEBA)] with furfuryl alcohol as a bio‐based compound. Subsequently, semi‐IPNs with different compositions were obtained through the blending of DGEBA, FFR, 4,4′‐diaminodiphenylmethane, and 1,1′‐(methylenedi‐1,4‐phenylene) bismaleimide in the molten state by following a predetermined time–temperature program. Fourier transform infrared and nuclear magnetic resonance analyses confirmed the successful synthesis of the materials. Thermoreversibility via retro‐DA (rDA) reaction was evidenced by differential scanning calorimetry (DSC) and sol–gel transition tests. Repeated DSC cycle was successfully performed thrice on the DA polyadduct which corroborated repeatability of the DA/rDA association/dissociation. Self‐healing and mechanical properties were preliminarily evaluated by scanning electronic microscopy and flexural testing analyses, respectively. The self‐healing efficiencies were around 80 and 95% for semi‐IPN and DA polyadduct, respectively, based on flexural strength. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48015.