This work presents a new synthetic approach to aromatic and aliphatic polycarbonates by melt polycondensation of bisphenol A diacetates with alkylene-and arylenediphenyl dicarbonates. The diphenyl dicarbonates were prepared from phenyl chloroformate and the corresponding dihydroxy compounds. The process involved a precondensation step under a slow stream of dry argon with the elimination of phenyl acetate, followed by melt polycondensation at high temperature and under vacuum. The potential of this reaction is demonstrated by the successful synthesis of a series of aromatic-aromatic and aromatic-aliphatic polycarbonates having inherent viscosities from 0.19 to 0.43 dL/g. Thus low to intermediate molecular mass polymers were obtained. The 13 C-NMR spectra of the carbon of the carbonate group showed that the formed polycarbonates contain partial random sequence distribution of monomer residues in their chains. The polycarbonates were characterized by inherent viscosity, FTIR,

Herein, we report the synthesis of spherical gold nanoparticles with tunable core size (23–79 nm) in the presence of polyethylene glycol-g-polyvinyl alcohol (PEG-g-PVA) grafted copolymer as a reducing, capping, and stabilizing agent in a one-step protocol. The resulted PEG-g-PVA-capped gold nanoparticles are monodispersed with an exceptional colloidal stability against salt addition, repeated centrifugation, and extensive dialysis. The effect of various synthesis parameters and the kinetic/mechanism of the nanoparticle formation are discussed.

In order to characterize various depolymerization and imidization reactions involved during thermal and chemical imidazation of poly(amic acid) by UV-visible and fluorescence spectroscopies, several model compounds have been synthesized and characterized from 1,5-diaminonaphthalene (DAN) and phthalic anhydride. The model compounds synthesized are the derivatives of DAN such as amic acid-amine, diamic acid, amine-imide, amic acid-imide, diimide, and diisoimide. Only DAN is found to be strongly fluorescent while amic acid-amine, amine-imide, and diisoimide are very weakly fluorescent. The others have negligible fluorescence. During imidization, therefore, the fluorescence intensity can be used to quantify the amount of depolymerized DAN. Due to strong substituent effects on the UV-visible spectra, the model compounds exhibit characteristic absorption maxima and extinction coefficients. Proton NMR, IR, and differential scanning calorimetry have been used also to confirm the chémical structures and the purity of the model compounds. Chemical imidization using acetic anhydride and pyridine for polyamic acid made from DAN and a partially fluorinated dianhydride has been investigated. Deconvolution of UV-visible spectra on the basis of the model compounds provided the composition of the involved species such as diamic acid, diimide, and diisoimide. The rate constants for chemical imidization occurring in 1% solution in Nmethyl-2-pyrrolidinone indicate a fast first step in which simultaneous conversion of diamic acid to diimide and diisoimide takes place, followed by slower conversion of diisoimide to diimide in a second step.

UV−visible spectroscopy and H NMR spectroscopy were used to investigate the kinetics and the mechanisms of the chemical imidization for low molecular weight model monoamic acid and bisamic acid. Acetic anhydride and pyridine were used as the dehydrating mixture. The reaction was found to proceed by simultaneous formation of imide and isoimide through a mixed anhydride intermediate. The isomerization of isoimide to imide was found to take place only after the amic acid starting material has been completely consumed. The isomerization was very sensitive to the solvent's (NMP) exposure to humidity. In humidity-exposed NMP, the isomerization was very slow, while it occurred at a much faster rate in dry NMP. The main reason for the humidity effect on isomerization is due to the hydrogen bonding of the acetate ion (a final byproduct) by water, making the acetate ion a weak catalyst. A high concentration of the mixed anhydride was detected by H NMR during in-situ monitoring of reaction in 50/50 deuterated DMSO/deuterated toluene mixture. This result indicates that the rate-limiting step of the reaction to be the deprotonation of the mixed anhydride rather than the formation of the mixed anhydride. This result also provides the explanation for the kinetic deviation observed in the UV−visible experiment when a high concentration of amic acid was used as the starting material.

Chemical imidization of polyamic acid based on 1,5-diaminonaphthalene and a dianhydride was studied by UV−visible and FT-IR ATR techniques under various reaction conditions, such as polyamic acid concentration, solvent condition (dry vs humidity-exposed NMP), catalysts of tertiary amines with different degrees of steric crowding and base strength, and the concentration of the acetic anhydride and pyridine. With acetic anhydride and pyridine, the reaction was very similar to that of the model amic acids, with the simultaneous formation of bisimide groups and bisisoimide groups, followed by isomerization of bisisoimde groups to bisimide groups, which is very sensitive to the dryness of the solvent. The reaction with polymer films supported a similar trend. Chemical imidization seems to proceed by nucleophilic catalysis by tertiary amines, depending on the steric crowding as well as the base strength. Reducing steric crowding in the catalyst facilitates the formation of an acylammonium (or pyridinium) cation. The adjacent positive charge on the nitrogen makes the acyl group more electrophilic, making it easier for the amic acid anion to attack and form the mixed anhydride intermediate. The catalyst can further accelerate the reaction by deprotonating the mixed anhydride if the tertiary amine is not sterically crowded. The anionic mixed anhydride quickly cyclizes to give an imide group and an isoimide group. N-Methylpyrrolidine and triethylenediamine were found to make the reaction at least 50 times faster than pyridine, which is the most commonly used industrial catalyst, without changing the molecular weight and its distribution. This investigation shows that the acidity of the original amic acid and the acid produced during the reaction have a profound impact on the products and their ratio, which can be understood based on the mechanistic scheme proposed for the model amic acid. It is suggested that a careful choice of polyamic acid concentration, dehydrating agent, and catalyst may lead to greater control over the reaction and the polymer properties.