Polyimides, hyperbranched

Figure 5.35 Hyperbranched polyimides with 100% degree of branching.

An unusual method has been used to prepare a hyperbranched polyimide starting from two monomers a difunctional A2 and a trifunctional B3. The gel formation can be avoided with careful control of the polycondensation conditions (molar ratio, order of the monomer addition, and low concentration). The A2 and B3 monomers were respectively 6FDA and tris(4-aminophenyl)... 

Hyperbranched polyesters, 18, 32, 55-58 bulk synthesis of, 64 synthesis of, 114-118 Hyperbranched polyimides, 307-309 Hyperbranched polymers, 8-10, 348-350, 475-476, 481, 519-520 degree of branching in, 57 Hyperbranched polyphenylquinoxalines, 312-314... 

Nucleophilic displacement, PQ and PPQ synthesis by, 310-311 Nucleophilic substitution, 10, 282, 283 hyperbranched polyimides via, 308 Nucleophilic synthesis, of bisphenol-A polysulfone, 337... 

Fang, J., Kita, H., and Okamoto, K. 2000. Hyperbranched polyimide for gas separation applications. 1. Synthesis and characterization. Macromolecules, 33,4639—4646. 

Qui Qin, H.-H., Mather, P. T., Baek, J.-B., Tan, L.-S. Modification of bisphenol-A based bismalei-mide resin (BPA-BMI) with an allyl-terminated hyperbranched polyimide (AT-PAEKI). Polymer 47 (2006) 2813-2821. 

Jin Jin, F.-L., Park, S.-J. Thermal properties and toughness performance of hyperbranched-polyimide-modified epoxy resins. J. Polym. Sci. Part B Polym. Phys. 44 (2006) 3348-3356. 

Recently, the polymer science field has focused on the role of polymers as membrane materials with precise, well-ordered structures through the development of defined synthesis and analysis of polymers. Among these well-ordered polymers are the hyperbranched polymers (e.g. hyperbranched polyimides). Part of the interest in such polymers is due to the expectation that they could have different properties as compared to common linear polymers. Also, cross-linked polyimides have attracted much attention from researchers, as can be judged by a high number of publications. 

On the other hand, hyperbranched polyimides not only have the features of other hyperbranched polymers (e.g. low viscosity, good solubility) but also possess high thermal... 

Plasticization behaviour induced by condensable gases and vapours (e.g. carbon dioxide, hydrocarbons and other organic vapours) in polymer membranes is stiQ a painful problem in polymeric membrane-based gas separation applications [27,28]. Recently, novel hyperbranched polyimides were prepared from telechelic polyimides and an attempt was made to improve its gas separation performance and physical stability by obtaining plasticization-resistant materials [29-33] (see e.g. Chapters 4, 6 and 7 of this book). 

Thus, we can state that the use of hyperbranched polyimides can enhance the resistance to plasticization of polymer membranes. 

Hyperbranched polyimides can result due to the self-polycondensation reactions of AB2-, A2- and Bs-types. The preparation of hyperbranched polyimides involves chemical imidization of polyamic acid ester synthesized from AB2-monomers, which are carboxylic dianhydrides containing an ether bond and a diamine [6,19,76]. Polyamic acid in combination with a condensation agent is used because it is difficult to separate the synthesized polymer from AB2-type monomers. 

For example, it is possible to prepare hyperbranched polyimides from 3,5-dimethoxyphenol and 4-nitrophthalonitrile in the presence of diphenyl(2,3-dihydro-2-thioxo-3-benzoxazolyl) phosphonate (DBOP) as a condensation agent at room temperature. Hyperbranched polyimide was obtained through thermal or chemical imidization of the precursor (polyamic acid) (Scheme 1.3) [19]. The obtained hyperbranched polyimide had a relatively great molecular mass (A/ ) of about 190000gmor but low inhinsic viscosity of 0.30 dLg . Therefore, it had a compact configuration and the lack of entanglement of polymer chains. The polymer obtained via chemical imidization was soluble in apiotic polar solvents such as tetrahydrofuran (THF), while the polymer from thermal imidization was insoluble in any solvents. 

Recently, hyperbranched polyimides were obtained by selective orderly reaction only at polymer ends using telechelic polyimides with terminal reactive groups of acetylene, vinyl and acryl [29-33],... 

Almost all hyperbranched polyimides with reported gas permeation parameters were synthesized from A2- and Bs-type monomers. The corresponding transport data are presented in Table 1.4 [20-26]. All the polymers are in a glassy state. The gas permeabilities of hyperbranched polyimides vary from 0.02 to 11 Barrer for O2 and from 0.08 to 65 Barrer for CO2 at 20-35 °C. The selectivities vary from 2.0 to 13 for a(02/N2) and from 3.4 to 70.1 for a(C02/N2). 

Table 1.4 Cas permeability coefficients (Barter) and selectivity of hyperbranched polyimides (Type III)... 

In the same manner the gas permeability in hyperbranched polyimide prepared from vinyl-terminated telechelic polyimide, 6FDA-TeMPD-PAS is reduced by UV irradiation [32], The gas permeabilities of this polymer after 120min of irradiation are as follows 50Barrer for O2 and 345Barrer for CO2 at 30 °C and latm. The selectivities are 3.5 for... 

Figures 1.3-1.5 present Robeson diagrams for different gas pairs, in various polyimide membranes. The first examination of these plots shows that the data points for Type II (cross-linked) and Type III (hyperbranched) structures can be found in the whole cloud of the data points including those of linear structures (Type 1). However, the data points for some hyperbranched and cross-linked polyimides are located near the upper bound for O2/N2 pair as shown in Figure 1.3. On the other hand, the majority of the hyperbranched polyimides tend to be located among the common Unear polyimides, as well as that of cross-linked polyimides in the diagram for CO2/N2 pair relationship as shown in Figure 1.4. Finally, the data points for aU three types of the stractures are far from upper bound for the pair CO2/CH4, as seen in Figure 1.5. Apparently, more data are required in order to discuss more specifically the relationship between gas permeation properties and the structure of hyperbranched and cross-linked polymers.

T. Suzuki, Y. Yamada, Y. Tsujita, Gas transport properties of 6FDA-TAPOB hyperbranched polyimide membrane. Polymer, 45, 7167-7171 (2004). 

Y. Yamada, J. Sakai, SUoxane-modified hyperbranched polyimide, 2006 WO 2006/082814. 

V. A. Bershtein, L. M. Egorova, P. N. Yakushev, P. Sysel, R. Hobzova, J. Kotek, P. Pissis, S. Kripotou, P. Maroulas, Hyperbranched polyimides crosslinked with ethylene glycol digly-cidyl ether Glass transition dynamies and permeability. Polymer, 47, 6765-6772 (2006). 

J. Peter, A. Khalyavina, J. Kriz, M. Bleha, Synthesis and gas transport properties of ODPA-TAP-ODA hyperbranched polyimides with various comonomer ratios, Eur. Polym. J., 45, 1716-1727 (2009). 

H. Shirokura, M. Onda, K. Imai, S. Ishimatsu, S. Kazama, K. Nagai, Gas permeabUity of hyperbranched polyimide membranes containing fluorine structure, Polym. Prep. Jpn., 57, 1610 (2008). 

Physical and Gas Transport Properties of Hyperbranched Polyimide-Silica Hybrid Membranes... 

Scheme 8.1 Preparation of hyperbranched polyimide-silica hybrid membrane...

H. Chen, J. Yin, Synthesis and characterization of hyperbranched polyimides with good orga-nosolubility and thermal properties based on a new triamine and conventional dianhydrides, J. Polym. Sci. Part A Polym. Chem., 40, 3804—3814 (2002). 

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