The liquid‐crystalline properties of three cellulose esters, phenylacetoxy cellulose (PAC), 4‐methoxyphenylacetoxy cellulose (4MPAC), and p‐tolylacetoxy cellulose (TAC) and two cellulose silyl ethers, trimethyl silyl cellulose (TMSC) and t‐butyldimethylsilyl cellulose (TBDMSC), are reported. Hot‐stage polarized light microscopy provided evidence regarding the formation of thermotropic mesophases in the PAC, 4MPAC, TAC, and TMSC in bulk form upon heating. The concomitant DSC data showed further evidence of the thermotropic nature of these materials. PAC, 4MPAC, TAC, and TMSC formed lyotropic mesophases at 44, 48, 50, and 27 wt%, respectively in CH2Cl2. The presence of fingerprint patterns in wholly anisotropic solutions in conjunction with optical rotation measurements confirmed the cholesteric nature of these liquid crystalline solutions. TBDMSC formed neither a lyotropic nor a thermotropic liquid‐crystalline phase due to the low degree of substitution (DS 0.68) of this derivative. The hydroxyl substituents of PAC, 4MPAC, TAC, and TMSC may be readily removed under mild conditions to regenerate cellulose.

SYNOPSISThe influence of a potassium carbonate ( K2C03) additive on the base catalyzed hydrolysis of polyimide ( Kaptont) film in aqueous potassium hydroxide (KOH) was determined experimentally. The etch rate is significantly greater for KOH/K2C03 solutions compared with solutions composed of KOH only. The experimental order of the reaction with respect to the KOH concentration was found to be 1.5. In addition, the rate was found to increase linearly with respect to the KzC03 concentration at a fixed KOH concentration. Visual observations of a thinner gel layer on the surface of the film, combined with increased solubility of the etch by-products in KOH/K2C03 relative to KOH, help to explain the difference in etch rate. It appears the ability of K2C03 to enhance the solubility of the hydrolyzed polyimide (polyamic acid salt) results in faster etch rates. I NTRODUCTIO NPolyimide film is used extensively as a dielectric insulating layer in flex circuitry and microelectronics applications because of its good chemical, mechanical, and electrical properties.'-3 In particular, Kapton polyimide film is the workhorse of the electronics industry. Kapton is prepared via the polycondensation of pyromellitic dianhydride (PMDA) and oxydianiline ( ODA) in N,N-dimethylacetamide ( DMAc) , forming the corresponding polyamic acid.The polymer solution is chemically imidized using the appropriate chemicals, followed by a heat treatment to remove solvent and conversion chemicals and to also complete the imidi~ation.~ Kapton HN contains a slip additive, phosphate of calcium, but Kapton H does not.5Patterning the dielectric is an important step in microelectronics processing as it can provide increased design and product flexibility. These patterns may be formed by mechanical means or chem- ically using plasmas or wet etchants. Polyimide can be etched using aqueous base at elevated temperatures.6-s The effect of alcohol type and concentration on etch rate, when alcohol/water/KOH solutions are used to etch Kapton, have been described by Kreuz and hawk in^.^^'^ An increase in the etch rate was found for solutions containing about 80 wt % alcohol and 20 wt % water compared with pure water systems at similar KOH concentrations. Although isopropanol and n -propano1 were found to increase the etch rates above that of ethanol at 0.1 M KOH, the ability of ethanol/water mixtures to dissolve higher KOH concentrations (e.g., 1.OM) results in higher overall etch rates. One proposed explanation was plasticization of the Kapton by the alcohol, allowing faster penetration of the hydroxide anion into the Subsequent work by Stern l1 showed that the rate of alcohol permeation through Kapton is orders of magnitude lower than that of water, indicating the concentration of alcohol in the Kapton would be too low to plasticize the film. Another postulation is that the attacking hydroxide anion is less solvated at high alcohol concentrations and thus reacts with the polyimide more readily.gv10The kinetics of the base catalyzed hydrolysis of Kapton H over a ra...

SynopsisSeveral cellulose derivatives were synthesized and characterized by IR and 'H-NMR spectroscopy. T h e positions of substitution in these derivatives were confirmed using solid state I3C-NMR spectroscopy techniques.

Acetoacetoxypropyl cellulose, formed by the acetoacetylation of hydroxypropyl cellulose using a diketene/acetone adduct at elevated temperature, forms both thermotropic and lyotropic liquid‐crystalline phases. DSC and hot‐stage polarized light microscopy confirmed the thermotropic nature of the bulk polymer. Thin layers showed green reflection colors at room temperature. The wavelength λ0 of selective reflection was measured spectrophotometrically. The crystalline structure of the polymer was investigated using x‐ray diffraction. A lyotropic mesophase formed in acetic acid at ≥ 40 wt% polymer. The value of λ0 for the lyotropic cholesteric mesophase was determined by optical rotatory dispersion (ORD) and circular dichroism (CD) of a thin layer of a wholly anisotropic solution.