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Preparation of hyperdeproteinized natural rubber was made from fresh latex and preserved highammonia latex by treatment with urea in the presence of sodium dodecyl sulfate. Concentration of urea, temperature, and time for the incubation were investigated to remove the proteins effectively. Under the best conditions, the total nitrogen content and amount of allergenic proteins for the deproteinized rubbers were 0.005 wt % and 1.0 g/ml, respectively, which were less than those of natural rubber deproteinized with proteolytic enzyme. The hyper-deproteinized natural rubber was proved through FT IR spectroscopy.

Funding information Asahi Kasei Corp.A series of poly(ester imide)s (PEsIs) were prepared using longitudinally extended structures of ester-linked tetracarboxylic dianhydrides with different numbers of aromatic rings (N Ar = 4-6). In the PEsIs obtained using p-phenylenediamine (p-PDA), a clear trend was observed: the water absorption (W A ) decreased with increasing N Ar .In contrast, no clear decrease in the T g with increasing N Ar was observed for the PEsIs obtained using 4,4 0 -oxydianiline (4,4 0 -ODA). The PEsIs obtained using a methylsubstituted tetracarboxylic dianhydride (N Ar = 5) showed more suppressed W A and higher elongation at break (ε b ) values than those of the nonsubstituted counterparts.The former result is probably closely related to the enhanced crystallinity. However, methyl substitution caused an appreciable reduction in the thermal stability. Thus, the methyl-substituted PEsIs did not meet the V-0 standard in the UL-94V test, unlike the substituent-free counterparts. The PEsI copolymer obtained using the substituent-free tetracarboxylic dianhydride (N Ar = 6) with p-PDA (75 mol%) and 4,4 0 -ODA (25 mol%) had excellent combined properties, ie, a very high T g (361 C), an ultralow coefficient of thermal expansion (2.2 ppm K −1 ), an extremely low coefficient of hygroscopic expansion (3.3 ppm/RH%), moderate film ductility (ε b max = 23%), a moderate dielectric constant (3.22), and a low tan δ (2.76 × 10 −3 ) at 10 GHz in 50% relative humidity. Thus, this PEsI is a promising novel dielectric substrate material for use in the next generation of high-performance flexible printed circuit boards. K E Y W O R D Scoefficients of hygroscopic (humidity) expansion (CHE), coefficients of thermal expansion (CTE), dissipation factors, flame retardancy, flexible printed circuit boards (FPC), poly(amic acid)s

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