摘要:

AbstractThe dynamic mechanical behavior of carbon black filled polymers of styrene and butyl methacrylate was examined at low strain amplitude and frequency in order to minimize destruction of the composite structure and elucidate the basis of yield and plasticization observed in steady shear. For specific filled systems, bothG′ andG″ became independent of frequency and temperature at low frequencies, consistent with a yield phenomenon and the formation of a carbon black network. On the other hand, although the high molecular weight polystyrene showed plasticization effects at higher shear rates in steady shear rheology, such, plasticization effects were never observed in dynamic mechanical analysts. Yield behavior was observed most readily for the low molecular weight polystyrene. Limiting moduli for filled polystyrenes were independent of temperature, whereas, for polybutyl methacrylate, were sensitive to temperature. It is suggested that an independent network of carbon black is strongest in the low molecular weight polystyrene and weakest in poly (butyl methacryla

ISSN:0032-3888    

DOI:10.1002/pen.760281402

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA series of amine terminated polypropylene oxide based thermoplastic polyureas with hard segment contents of 30%, 50%, and 70 percent were synthesized via solution polymerization and reaction injection molding (RIM). Amine terminated polypropylene oxide (PPO‐NH2) of Mn= 2000 was used as the soft segment and 4,4′‐diphenylme‐thanediisocyanate (MDI) extended with diethyltoluenediamine (DETDA) as the hard segment. These polyureas are linear, amorphous, and phase separated. Polymers were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), dynamic mechanical spectroscopy (DMS), small angle X‐ray scattering (SAXS), and tensile testing. RIM polyureas had significantly lower molecular weights than solution polymerized polyureas, but their mechanical properties did not suffer, RIM polyureas have poorer phase separation than solution polyureas as evidenced by DSC, DMS, and SAXS, especially at high hard segment levels. SAXS shows phase separation levels of up to 100 percent for low hard segment polyureas and down to 10 percent for high hard segment RIM polyurea. DSC found no evidence of a hard segment glass transition, and the evidence from DMS was inconclusive. In addition to polymer characterization, demolding behavior was studied. The 30 percent hard segment was always tough and elastomeric, while the 70 percent hard segment was always very brittle. The 50 percent hard segment showed the greatest variation in properties, ranging from very brittle to very though as mold temperature and in‐mold time were increased. Demold brittleness is explained by the presence of low molecular weight DETDA/MDI oligomers on demolding, which continue to rea

ISSN:0032-3888    

DOI:10.1002/pen.760281403

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractUnder different experimental conditions, various liquid polyurethanes (PU) were synthesized from castor oil and isophorone diisocyanate varying NCO/OH ratio. These polyurethanes were then subsequently interpenetrated with n‐butyl acrylate (nBA) monomer and ethylene glycol di‐methacrylate as crosslinker by radical polymerization using benzoyl peroxide as an initiator. This leads to the formation of novel PU/PnBA interpenetrating polymer networks (IPNs) by transfer molding. These IPNs were characterized by their resistance to chemical reagents, thermal behavior (TGA), mechanical properties, namely; tensile strength, Young's modulus, elongation at break (%) and hardness (Shore A). The morphology of the IPNs was studied by Scanning Electron Microscopy. The dielectric behavior was computed in terms of electrical conductivities, dielectric constant (ε′), loss tangent (tan δ) and dielectric lo

ISSN:0032-3888    

DOI:10.1002/pen.760281404

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe relationships, between chemical structures of various aromatic polyimides and their thermal expansion coefficients, were investigated and the properties of low thermal expansion polyimides were elucidated. Such low values were observed for polyimides obtained from pyromellitic dianhydride or 3,3′,4,4′‐biphenyltetracarboxyIic dianhydride and aromatic diamines, which included only benzene or pyridine rings fused at para‐positions without a flexible linkage. It was proposed that these low thermal expansion coefficients were related to the linearity of their polymer molecular skeletons. In particular, PIQ‐L100 (Hitachi Chemical Co. Ltd) is one such low thermal expansion polyimide and, it has excellent mechanical properties, thermal stability, and low absorbed moistur

ISSN:0032-3888    

DOI:10.1002/pen.760281405

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractPolymer complex of poly (4‐vinylpyrldine) and malonic acid was investigated as a new type of electron beam (EB) resist for dry development, as malonic acid was decomposed by EB irradiation. It was found that the polymer complex could be developed with O2plasma etching and that the positive resist patterns with high resolution could be obtained. The mechanism for this lithography process was studied by means of IR and ESCA spectr

ISSN:0032-3888    

DOI:10.1002/pen.760281406

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe thermodynamic phase behavior of two polymer‐liquid crystal blends was investigated in both the solid and molten states. One of the blends (p‐hexyloxybenzoic acid and poly[ethylene glycol]) contains a semi‐crystalline polymer. The second example (p‐pentyloxycinnamic acid and bisphenol‐Apolycarbonate) contains a high‐impact‐resistant amorphous thermoplastic. Whereas, the former system is almost completely immiscible at ambient temperature, yet advantageous for applications in the microelectronics industry, the latter blend exhibits partial (concentration‐dependent) miscibility. Our multi‐technique assessment of miscibility/phase separation includes high‐resolution carbon‐13 solid state NMR spectroscopy, differential scanning calorimetry (DSC), and group‐contribution thermodynamics (Universal Quasi‐Chemical Functional‐Group Activity Coefficient formalism including a Free Volume correction for the small molecule activity, UNIFAC‐FV). Approximate temperature‐composition (equilibrium) phase diagrams are constructed for both blends in light of the resul

ISSN:0032-3888    

DOI:10.1002/pen.760281407

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThis paper presents some modeling work on the behavior of wire bonds during a typical transfer molding operation. In order to fill up the small recesses in a production size mold, transfer pressures as high as 1.000 psi are commonly required. The large driving pressure is potentially harmful to the fragile wire bonds. Lit the worst case scenario, the highly viscous melt front may cause enough shearing action to lift off the wire bonds completely. More often, however, wire sweeping is reported as one of the major causes of shorts in devices where long interconnect wires are looped between bond pads. Several interdependent factors govern the extent of wire sweep in a mold cavity of arbitrary geometry. The dimensions of the cavity, for instance, dictate the velocity of the melt front profile with the corresponding flow stresses and shear rates. The location of the chip to be encapsulated similarly influences the plastic filing pattern. So does the configuration of the particular chip design (e.g. planar vs recessed lead frames). Naturally, the severity of the problem is also controlled by the nature of the wires used during the bonding. For example, wire sweep may be controlled to a certain degree by tailoring the wire modulus to offer resiliency and spring‐ back after the melt front has swept across, but prior to curing. Furthermore, a low drag coefficient would also be obtained if some measure of control on the shape of the wire (e.g. circular vs rectangular cross‐section) or the pro‐ file exposed (e.g. angle of orientation of the wires with respect to the flow) is ex

ISSN:0032-3888    

DOI:10.1002/pen.760281408

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760281401

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY