Fluorinated polymerizable phosphonium salts from PH3: Surface properties of photopolymerized films

An array of highly fluorinated polymerizable phosphonium salts (HFPPS) were synthesized from PH₃ and utilized in UV‐curable formulations. Inclusion of these salts at very low loading (0.1–1 wt %) into hexanediol diacrylate (HDDA) resulted in hydrophobic surfaces. The water repellency was achieved with short C₄F₉ fluorocarbon appendages in the monomer as opposed to the bioaccumulative C₈F₁₇ appended polymers. The physical properties of these new monomers were also characterized. The molecular architecture of the monomers had a pronounced effect on both their physical properties along with the degree of hydrophobicity imparted in the polymer. Salts utilizing the bis(trifluoromethylsulfonyl)imide anion displayed excellent compatibility with HDDA, while the chloride salts were insoluble. Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) confirmed the presence of the HFPPS at the surface of the polymer coating. For the first time this demonstrates how these salts may be used to functionalize the surface of a UV‐cured film with ionic species. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2782–2792     

Characterization of resulting network polymer precursors in stepwise crosslinking diepoxide/diamine polymerization

Our previous mechanistic discussion of network formation in chainwise crosslinking multiallyl polymerization was extended to stepwise crosslinking diepoxide/diamine polymerization, typically including bisphenol‐A diglycidyl ether (BADGE) and 4,4′‐diaminodiphenylmethane (DDM). In allyl polymerization a monomer chain transfer is an essential termination reaction, providing only oligomeric primary polymer chains. Therefore, crosslinking multiallyl polymerization could be in the category of a classical gelation theory. Thus, the gelation behavior was discussed by comparing the actual gel point with the theoretical one. Then the resulting network polymer precursors (NPPs) were characterized by size‐exclusion chromatography‐multiangle laser light scattering‐viscometry to clarify the stepwise crosslinking BADGE/DDM polymerization mechanism. Notably, the intrinsic viscosity ratio [η]_NPP/[η]_Linear tended to decrease with the progress of crosslinking and finally, it reached less than 0.2. This suggests that the structure of resulting NPP becomes dendritic at a conversion close to the gel point. These dendritic NPPs can collide with each other to form crosslinks between NPPs, eventually leading to gelation as a reflection of the high concentration of NPP. The dilution effect on gelation was marked in polar solvent; no gelation was observed at a dilution of 1/5. However, in nonpolar solvent the gelation was promoted by dilution; this is ascribed to enhanced crosslink formation between NPPs through hydrogen bonding due to abundant hydroxyl groups in the NPP generated by the polyaddition reaction. Finally, the subject of “Is cured epoxy resin inhomogeneous?” is briefly discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of sulfone containing main chain oligobenzoxazine precursors

The preparation of soluble and processable polybenzoxazine precursors capable of forming high performance networks is an important field of research with a broad spectrum of application. This study demonstrates an approach that utilizes aromatic sulfonediamine, bisphenol‐A, and formaldehyde in Mannich‐type polycondesation to prepare polybenzoxazine precursor. The structure of the oligomeric precursor (M_n = 2600) was confirmed by FTIR and ¹H NMR spectral analysis. The precursor contained both sulfone and benzoxazine ring structures in the backbone. It was shown that small amount of ring‐opened phenolic groups were also present. Thermally activated self‐curing behavior of precursor in the absence of catalyst was studied by differential scanning calorimetry. Thermal properties of the cured polymers were also investigated by thermo gravimetric analysis. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

三羟基苯甲基氨基均三嗪与双酚A型环氧树脂的固化反应研究

采用等转化率法研究了2,4,6-三(羟基苯甲基氨基)-均三嗪(MFP)与双酚A型环氧树脂(DGEBA)在等温和非等温条件下的固化反应行为,两种条件下MFP/DGEBA固化反应的表观活化能(Eα)均随转化率(α)增加呈先减后增的趋势(α=0.25 时取得最小值).由于仲胺基和酚羟基对环氧基反应的不等活性,非等温固化反应时两种反应先后发生,形成Triazine-NCH2-CH(OH)-结构后,再形成ArO-CH2-CH(OH)-结构并产生交联,前后两阶段Eα分别为69.8、86.8 kJ·mol-1.对等温固化反应,由于起始反应温度高,仲胺基和酚羟基几乎同步与环氧基发生反应,两者的相互催化作用使反应前期Eα相对较低(59.1 kJ·mol-1),固化反应速度较快,引起体系粘度迅速增大,扩散控制反应提前,从而造成反应后期Eα(89.7 kJ·mol-1)相对较大.     

Intercalated clay nanocomposites: Morphology,mechanics, and fracture behavior

Intercalated nanocomposites of modified montmorillonite clays in a glassy epoxy were prepared by crosslinking with commercially available aliphatic diamine curing agents. These materials are shown to have improved Young's modulus but corresponding reductions in ultimate strength and strain to failure. The results were consistent with most particulate‐filled systems. The macroscopic compressive behavior was unchanged, although the failure mechanisms in compression varied from the unmodified samples. The fracture toughness of these materials was investigated and improvements in toughness values of 100% over unmodified resin were demonstrated. The fracture‐surface topology was examined using scanning electron and tapping‐mode atomic force microscopies and shown to be related to the clay morphology of the system. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1137–1146, 2001     

Dynamic DSC Characterization of Epoxy Resin by Means of the Avrami Equation

A phenomenological approach was used to characterize the cure processes of epoxy resins (a diglycidyl ether of bisphenol A and its modifier CTBN) from dynamic experiments by DSC. Various kinetic parameters were obtained by using a modified Avrami expression. The resulting overall activation energies for the two systems agreed very well with the published data in the whole cure temperature range. In contrast with the isothermal results and the general dynamic models, a change in the exponent and the non-linear temperature dependence of the rate constant were also observed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Influence of covalent and non-covalent modification of graphene on the mechanical,thermal and electrical properties of epoxy/graphene nanocomposites: a review

Abstract

Graphene is emerged as a highly sought after reinforcing filler for epoxy matrix in view of its superior electrical, mechanical and thermal properties. Dispersion of low concentration of graphene can significantly enhance the epoxy/graphene nanocomposites properties. Dispersion of graphene in epoxy matrix depends on processing protocols used, and interfacial interaction between epoxy matrix and graphene. Interfacial interaction between epoxy matrix and graphene can be achieved by covalent and non-covalent modification of graphene. This paper comprehensively review the influence of different processing protocols adopted for the processing of epoxy/graphene nanocomposites, and its effect on mechanical, thermal and electrical properties. In addition, covalent and non-covalent strategies adopted for modification of graphene, and its influence on mechanical, thermal and electrical properties of epoxy/graphene nanocomposites are extensively discussed. The future challenges associated with graphene reinforced epoxy nanocomposites processing have been discussed.     

Crystallization,Flame Retardancy and Mechanical Properties of Poly(Butylene Terephthalate)/Brominated Epoxy/Nano-Sb2O3 Composites Dispersed By High Energy Ball Milling

Nano-Sb2O3 particles and brominated epoxy resin (BEO) powders were dispersed in poly (butylene terephthalate) (PBT) by high energy ball milling (HEBM). Then the nanocomposites were prepared by a twin screw extruder. The influence of the nano-Sb2O3 particles on the crystallization, thermal stability, flame retardancy and mechanical properties of the PBT/BEO/nano-Sb2O3 composites were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 tests and scanning electron microscopy (SEM). The results showed that the nano-Sb2O3 particles improved the crystallizability, thermal stability and flame retardancy properties of the PBT/BEO/nano-Sb2O3 composites. When the content of nano-Sb2O3 particles was 2.0?wt%, the LOI of nano-Sb2O3/BEO/PBT composites increased from 22.0 to 27.8 and the tensile strength reached its maximum value (62.44?MPa), which indicated that the optimum value of flame retardancy and mechanical properties of PBT/BEO/nano-Sb2O3 composites were obtained.     

Morphology,toughness mechanism,and thermal properties of hyperbranched epoxy modified diglycidyl ether of bisphenol A (DGEBA) interpenetrating polymer networks

New hyperbranched poly(trimellitic anhydride‐triethylene glycol) ester epoxy (HTTE) is synthesized and used to toughen diglycidyl ether of bisphenol A (DGEBA) 4,4′‐diaminodiphenylmethane (DDM) resin system. The effects of content and generation number of HTTE on the performance of the cured systems are studied in detail. The impact strength is improved 2–7 times for HTTE/DGEBA blends compared with that of the unmodified system. Scanning electron microscopy (SEM) of fracture surface shows cavitations at center and fibrous yielding phenomenon at edge which indicated that the particle cavitations, shear yield deformation, and in situ toughness mechanism are the main toughening mechanisms. The dynamic mechanical thermal analyzer (DMA) analyses suggest that phase separation occurred as interpenetrating polymer networks (IPNs) for the HTTE/DGEBA amine systems. The IPN maintains transparency and shows higher modulus than the neat epoxy. The glass transition temperature (T_g) decreases to some extent compared with the neat epoxy. The T_g increases with increase in the generation number from first to third of HTTE and the concentrations of hard segment. The HTTE leads to a small decrease in thermal stability with the increasing content from TGA analysis. The thermal stability increases with increase in the generation number from first to third. Moreover, HTTE promotes char formation in the HTTE/DGEBA blends. The increase in thermal properties from first to third generation number is attributed to the increase in the molar mass and intramolecular hydrogen bridges, the increasing interaction of the HTTE/DGEBA IPNs, and the increasing crosslinking density due to the availability of a greater number of end hydroxyl and end epoxide functions. Copyright © 2008 John Wiley & Sons, Ltd.     

Correlation between nanohole volume and mechanical properties of amine‐cured epoxy resin blended with poly(ethylene oxide)

A set of diglycidylether of bisphenol‐A (DGEBA)/4,4′‐diaminodiphenylmethane (DDM) epoxy matrix modified with poly(ethylene oxide) (PEO), pre‐cured at two different temperatures, was examined by positron annihilation lifetime spectroscopy (PALS). The aim was to investigate the correlation between local free volume and mechanical properties. A negative deviation from the linear additivity rule of the local free volume is observed at both cure schedules. Using together the local free volume and mechanical results allows to conclude that the cure temperature makes small contribution to the flexural strength and modulus of blends but is responsible for the composition‐dependent rise of the fracture toughness. It is proposed that this behavior is a consequence of the nearest‐neighbor intrachain contacts or self‐association of the epoxy‐OH groups during cure leading to a non‐uniform space distribution of the DGEBA–PEO contacts, which causes the deflection of the crack path. Copyright © 2008 John Wiley & Sons, Ltd.