Xiaolin Tang

Polyoxometalate cured epoxy resins with photochromic properties

Novel photochromic thermosetting materials were facilely prepared by polyoxometalate, Keggin-type H3PW12O40, cured epoxy networks with ethylene oxide blocks. The dual functions of polyoxometalate as both hardener and photochromophore were studied by differential scanning calorimetry, infrared spectroscopy, ultraviolet–visible spectroscopy (UV–vis), and generalized two-dimensional correlation analysis. Polyoxometalate initiates the cationic polymerization of epoxy resin through dissolving in either polyethylene oxide epoxy or organic solvents. When subjected to UV irradiation, the transparent thermosetting materials with ethylene oxide blocks change from colorless to blue, and could be bleached in air at various temperatures to recover its initial state. From the UV–vis measurements, all the resultant thermosetting materials demonstrated similar photochromic behavior after ultraviolet irradiation showing characteristic d–d transition band and intervalence charge transfer band. The 2D correlation analysis of the photochromic spectra clearly revealed the sequence of electron movements in the framework of PW12 anion.

Studies on the Phase Separation of Poly(Ether Imide)‐Modified Cyanate Ester Resin

Abstract A high temperature thermosetting bisphenol‐A dicyanate (BADCy) was blended with a novel thermoplastic poly(ether imide) (PEI) at various composition. The phase separation behavior during isothermal curing was studied by differential scanning calorimeter (DSC), time‐resolved light scattering (TRLS), scanning electron microscopy (SEM), and rheological measurements. The results suggested that the phase structure changed from separated phase, via co‐continuous phase, to phase inversion with the increase of the PEI content. The curing conversion of BADCy was slightly affected by the composition in the blend and the curing rate was decreased with the increase of PEI content. The co‐continuous phase morphology was attributed to a spinodal decomposition. The initial concentration of PEI had an effect on the rheological behavior during phase separation. It was found by tensile test that the blend with 15 wt.% PEI had higher tensile strength and elongation at break than that without PEI.

STUDIES ON PHASE SEPARATION OF POLYESTERIMIDE-MODIFIED EPOXY RESINS. I. SYNTHESES AND PROPERTIES OF ORGANO-SOLUBLE POLYESTERIMIDES

ABSTRACT A series of polyesterimides based on aromatic bis(trimellitate) dian-hydride in main chain were prepared by polycondensation of t-butyl-p-phenylenebis(trimellitate) dianhydride (BPBDA) and phenylene bis(trimellitate) dianhydride (PBDA) with benzidine and its derivates. The results show that the incorporation of noncoplanar structure led by introducing alkyl substituents on dianhydride and benzidine can improve the solubility of polyesterimides in organic solvents. It also displays that the introducing substituents lead to a decrease in glass transition temperature and influence the β relaxation of PEsI. By comparing the chemical structure and the dynamical mechanic date, we suggest that the β relaxation correspond to the motion involving the imide ring and phenylene groups of the diamine.

Fabrication of a superhydrophilic epoxy resin surface via polymerization-induced viscoelastic phase separation

Surface roughness and porosity play important roles in the wetting behavior of materials. In this study, we introduced a novel method to tune the wettability of epoxy resin surfaces. A micro–nano hierarchical structure on polyethylene glycol (PEG) modified epoxy system was fabricated by polymerization-induced viscoelastic phase separation. By manipulating the curing procedure and concentration and molecular weight of PEG, surfaces with different topography and porosity were obtained. The phase evolution was monitored by time-resolved light scattering (TRLS) and the morphologies of the surfaces were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Static water contact angle was also measured. With increasing the content of PEG in the blends, the effect of viscoelasticity on phase separation was strengthened, which resulted in an increase of porosity and a more hydrophilic epoxy resin surface. Higher molecular weight PEG exerted an impact on the viscoelastic behavior of phase separation, which rendered a rougher epoxy surface. With the aid of higher viscoelasticity on phase separation of the PEG modified epoxy system, surfaces with a micro–nano structure exhibited superhydrophilicity.

Effect of Attapulgite Nanorods and Calcium Sulfate Microwhiskers on the Reaction-Induced Phase Separation of Epoxy/PES Blends

The influence of two kinds of mesoscale inorganic rod fillers, nanoscale attapulgite and micron-sized CaSO4 whisker, on the reaction-induced phase separation of epoxy/aromatic amine/poly- (ether sulfone) (PES) blends has been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and time resolved light scattering (TRLS). By varying the PES concentration and curing temperature, we found that the incorporation of attapulgite and CaSO4 had dramatic impact on the phase separation process and the final phase morphology of blends. In blends at higher content than critical concentration, the process of phase separation was retarded by the incorporation of nanoscale fillers but accelerated by that of the micron-sized fillers, mainly due to the enhanced viscoelastic effect and the preferential wettable effect, respectively. Meanwhile both mesoscale fillers could change the cocontinuous phase structure of blends with lower PES content than critical concentration into PES-rich dispersed structure due to the surface affinity of fillers to epoxy matrix.

Water absorption and corrosion protection of esterified novolac resin cured epoxy resins applicable for microelectronics packing

In the present work, to study the effects of side group on water absorption, a series of novolac epoxy resins was cured with esterified a phenol novolac resin and phenol novolac resins separately. Thus, the hydroxyl group of phenol novolac resin was replaced by CH/sub 3/COO- group, C/sub 3/H/sub 7/COO/spl rho/oup and C/sub 6/H/sub 5/CH/sub 2/COO- group, and the cured resins were named as EP, EPA, EPB and EPP, respectively. FTIR showed that there were no hydroxyl groups but ester functional groups in the cured resins cured. with the esterified phenol novolac resins. The influence of the side groups on the water absorption behavior of the cured epoxy resins was investigated using gravimetric method, DSC, and corrosion test.