Some hyperbranched aromatic polyamides have been synthesized by direct polycondensation using the modified Higashi's method. Structures of the above polymers have been realized taking in proper account the analogies with amide group sequences of poly(p-phenyleneterephthalamide) (PPDT) and poly(p-benzamide) (PBA). Therefore, AB2- type monomers as well as suitable combinations of different bi- and trifunctional reactants (AA + B3) (e.g., p-phenylenediamine + trimesic acid or other trifunctional acids) have been considered. For the latter systems, network formation has been minimized. In the present paper, our results on their direct polyamidation together with some preliminary characterization data on the resultant hyperbranched aramids are given. 相似文献
In this paper, hyperbranched polyimides having the same repeating unit were synthesized by employing ideal A2+B3 polymerization, non-ideal A2+B3 polymerization and AB2 self-polymerization methods. The polymerization behavior, polymer properties were compared for three methods. Hyperbranched polyimides by ideal A2+B3 polymerization, non-ideal A2+B3 polymerization and AB2 self-polymerization methods show apparent difference in many physical properties, such as inherent viscosity, glass transition temperature, and film formation behavior etc. The hyperbranched polymers by the non-ideal A2+B3 polymerization are suitable for smooth, flexible and self-standing film preparation, which provides useful information for hyperbranched polymers toward self-standing materials. 相似文献
The kinetics of hyperbranched A2 + B3 systems is discussed theoretically with respect to the development of the 7 different structural units, the degree of branching, DB, and the monomer sequences considering the adjacent groups of a structural unit. For A2 + B3 systems, the comonomer ratio, the relative rate constants and the process conditions have an influence on the resulting structure as shown by numerical simulations. With increasing A:B ratios fA/B, the degree of branching will be increased. Also the relative reaction rate constants have a strong impact on the distribution of structural units, especially when the reaction rate constants for the pathway of the B3 monomer are changed. On the other hand, differences in the reaction rate constants for the pathway of the A2 monomer do not have any influence on the degree of branching. The simulation indicates that slow addition of either both monomers or just the B3 monomer has the strongest effect on the resulting DB. In all cases, the conversion is a critical issue to obtain high molecular weight products.
Degree of branching (DB) versus conversion of A‐functionalities (pA) for various monomer compositions. 相似文献
Summary: Hyperbranched polyesters with controlled molecular weights and properties have been prepared by an A2 + B3 approach by reacting glycerol and adipic acid without any solvents in the presence of tin catalysts. The hyperbranched polyesters have been evaluated by size exclusion chromatography (SEC) analysis and NMR spectroscopy in order to determine molecular weights and degrees of branching.
Idealized structure of the hyperbranched polyesters synthesized here from adipic acid and glycerol in the presence of tin catalysts. 相似文献
Summery: The potential of cycloaddition (CA) reactions for the synthesis of dendritic polymers is pointed out. The [4 + 2] Diels Alder cycloaddition as well as 1,3-dipolar CA reactions including “click chemistry” are addressed, and the advantages of these reactions like high selectivity, thus high tolerance towards additional functionalities, high yields and synthesis under mild reaction conditions are highlighted. New perfectly branched dendrimers as well as hyperbranched polymers have been prepared and modified using the 1,3-dipolar cycloaddition reaction of azines with alkynes. The 1,3-dipolar CA reaction of bisazine with maleimides results in hyperbranched and thus, irregular and broadly distributed polymers though with a degree of branching of 100% due to special intermediate formation. The [4 + 2] Diels Alder cycloaddition was successfully applied for the synthesis of highly branched polyphenylene structures using the AB2 + AB and the A2 + B3 approach. CA reactions are also very suitable for highly efficient polymer analogous reactions and thus, they can also be used to prepare complex polymer architectures like dendronized polymers. 相似文献
Summary: We developed a facile approach to hyperbranched polymers by applying a superelectrophilic reaction within an A2 + B3 strategy. A significant reactivity difference between the intermediate and the starting material was utilized to avoid gelation in the A2 + B3 polymerization. A number of hyperbranched poly(arylene oxindole)s were achieved in a one‐step polymerization and characterized by NMR spectroscopy and gel permeation chromatography. Moreover, further modifications at the interior and exterior of the resulting polymers were explored as well.
Structure of the hyperbranched polymers produced using the A2 + B3 approach. 相似文献
Hyperbranched polymers, HBPs, formed via a stepwise polymerization of A2, Bg type monomers with the addition of end-capping molecules, AR, were investigated by means of recursive and kinetic models. First, gelation curves were established based on the initial compositions of reactants at various functionalities, g, of monomers Bg. According to this guide, the hyperbranched polymers without gel fraction can be obtained. The molecular structures of HBPs, such as molecular weight and the degree of branching were calculated as related to conversion. It is shown that they can be controlled by the composition of reactants. With the addition of molecules AR, the gelation can be avoided at high conversion, and the distribution of molecular weights of polymers becomes narrower. 相似文献
The new approach for synthesis of hyperbranched polymers from commercially available A2 and type monomers was extended to synthesize hyperbranched copolymers. In this work, hyperbranched copoly(sulfone-amine) was prepared by copolymerization of divinyl sulfone (A2) with 4,4′-trimethylenedipiperidine (B2) and N-ethylethylenediamine (BB’2). During the reaction, secondary-amino groups of B2 and BB’2 monomers react rapidly with vinyl groups of A2 monomers within 35 s, generating a type of intermediate containing one vinyl group and two reactive hydrogen atoms. Now the intermediates can be regarded as a new type monomer, which further polymerizes to form hyperbranched copoly(sulfone-amine). The polymerization mechanism was investigated with FTIR and LC-MSD. The degree of branching (DB) of hyperbranched copolymers increased with decreasing the ratio of 4, 4′-trimethylenedipiperidine to N-ethylethylenediamine, so DB can be controlled. When the initial mole ratio of B2 to BB′2was equal to or higher than four,r≥4, resulted copolymers were semi-crystalline, while copolymers withr3 were amorphous. 相似文献
Mathematical models of kinetically controlled random copolymerizations with intramolecular reactions have been developed for A2 + B2 and A3 + B2 type reactions, in which the B2 monomer is long and flexible enough to have a Gaussian end-to-end distance. Concentrations of different molecular species are calculated, as well as weight-average molecular weight, gel point and various network parameters. The calculations show the influence of the molecular weight and the concentration of reactants on the amount of intramolecular reaction. The results indicate that the main deviations from ideality are due to the smaller rings. 相似文献
The new approach for synthesis of hyperbranched polymers from commercially available A2 and type monomers was extended to synthesize hyperbranched copolymers. In this work, hyperbranched copoly(sulfone-amine)
was prepared by copolymerization of divinyl sulfone (A2) with 4,4′-trimethylenedipiperidine (B2) and N-ethylethylenediamine (BB’2). During the reaction, secondary-amino groups of B2 and BB’2 monomers react rapidly with vinyl groups of A2 monomers within 35 s, generating a type of intermediate containing one vinyl group and two reactive hydrogen atoms. Now the
intermediates can be regarded as a new type monomer, which further polymerizes to form hyperbranched copoly(sulfone-amine).
The polymerization mechanism was investigated with FTIR and LC-MSD. The degree of branching (DB) of hyperbranched copolymers
increased with decreasing the ratio of 4, 4′-trimethylenedipiperidine to N-ethylethylenediamine, so DB can be controlled.
When the initial mole ratio of B2 to BB′2was equal to or higher than four,r≥4, resulted copolymers were semi-crystalline, while copolymers withr3 were amorphous. 相似文献
Betulin, an abundant triterpene, can be extracted from birch bark and can be used as a renewable monomer in the synthesis of microporous polyesters. Cross‐linked networks and hyperbranched polymers are accessible by an A2 + B3 reaction, with betulin being the A2 monomer and B3 being a trifunctional acid chloride. Reaction of betulin with a diacid dichloride results in linear, soluble polyesters. The present communication proves that the polyreaction follows the classic schemes of polycondensation reactions. The resulting polymers are analyzed with regard to their micro‐porosity by gas sorption, NMR spectroscopy, and X‐ray scattering methods. The polymers feature intrinsic microporosity, having ultrasmall pores, which makes them candidates for gas separation membranes, e.g., for the separation of CO2 from N2. 相似文献