No abstract

ABSTRACT:Two series of soluble and light-colored poly(ether imide)s (III and IV) were synthesized from 2,2-bis [4-(3,4-dicarboxyphenoxyl)phenyl]hexafluoropropane dianhydride (I) and various fluorinated and non-fluorinated aromatic diamines (II a{g and II 0 a{g ) by a conventional two-step procedure that included a ring-opening polyaddition to give poly(amic acid)s, followed by chemical cyclodehydration to poly(ether imide)s. The III series were lighter-colored and higher optical transparency as compared with the non-fluorinated IV series. On comparing the IV series with the common lightly-colored aromatic polyimides (V series) based on 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), the IV series revealed less colored than the V series. This indicated that both the III and IV series were lightly-colored poly(ether imide)s. These polymer films showed the cutoff wavelength in the range of 364-371 nm. The III series showed good solubility in all testing solvents at a concentration of 5-10 wt/v % and most of IV series was soluble. These polymers exhibited glass-transition temperatures in the range of 194-264 C, and the 10% weight-loss temperatures were higher than 492 C under either nitrogen or air atmosphere. The III series also showed lower dielectric constants of 3.01-3.65 at 1 MHz and lower moisture absorption of 0.09-0.44 wt % than IV series.

A series of poly(ether imide)s (PEIs), III a-k , with light color and good physical properties were prepared from 1,4-bis(3,4-dicarboxypheoxy)-2,5-di-tert-butylbenzene dianhydride (I) with various aromatic diamines (II a-k ) via a conventional two-stage procedure that included a ring-opening polyaddition to yield poly(amic acid)s (PAA), followed by thermal imidization to the PEI. The intermediate PAA had inherent viscosities in the range of 1.00 -1.53 dL g Ϫ1 . Most of the PEIs showed excellent solubility in chlorinated solvents such as dichloromethane, chloroform, and m-cresol, but did not easily dissolve in dimethyl sulfoxide and amide-type polar solvents. The III series had tensile strengths of 96 -116 MPa, an elongation at break of 7-8%, and initial moduli of 2.0 -2.5 GPa. The glass-transition temperatures (T g ) and softening temperatures (T s 's) of the III series were recorded between 232 and 285°C and 216 -279°C, respectively. The decomposition temperatures for 10% weight loss all occurred above 511°C in nitrogen and 487°C in air. The III series showed low dielectric constants (2.71-3.54 at 1 MHz), low moisture absorption (0.18 -0.66 wt %), and was light-colored with a cutoff wavelength below 380 nm and a low yellow index (b * ) values of 7.3-14.8.

SummaryThe thio-additions of glycals were efficiently promoted by a stoichiometric amount of trimethylsilyl bromide (TMSBr) to produce S-2-deoxyglycosides under solvent-free conditions in good to excellent yields. In addition, with triphenylphosphine oxide as an additive, the TMSBr-mediated direct glycosylations of glycals with a large range of alcohols were highly α-selective.

A highly regio‐ and stereoselective glycosylation of a boronic acid‐containing thioglucoside and unprotected methyl glycosides is described. A boronic acid moiety was installed at the ortho‐position of the 2‐O‐benzyl group of a thioglucosyl donor. This provides transient partial protection for the unprotected glycosyl acceptor upon condensation and concomitantly prearranged the acceptor with respect to the donor for the ensuing intramolecular glycosylation.