Studies On Design, Synthesis And Properties Of Microporous Organic Polymers

Microporous materials possessing large specific surface areas and pores with molecular dimensions are of interest for applications in gas storage, molecular sieves, catalyst and photonic crystals et al.. Significant advances have been made most recently, particularly in the preparation of microporous pure organic polymers. Up to now, besides several limited examples of microporous polyimide networks, efforts to prepare microporous organic networks are mainly focused on several types of special polymers including poly(vinylbenzyl chloride), polyaniline, ladder-like poly(dibenzodioxane), conjugated polymer and poly(boronate). It will be strongly desirable to expand the microporosity concept to more common polymers. This dissertation is aimed to prepare novel kinds of microporous organic polymers with a rational design at the molecular level using common resins including cyanate resins, polyarylates and polyimides. Moreover, inspired by the molecular design idea of microporous polymers, several classes of high performance and functional polymers have been developed. The detail contents are listed as following:1. Tetrahedral cyanate monomer tetrakis(4-cyanatophenyl)silane (TCNS) is synthesiszed through multi-step reactions widely used in organic chemistry. It is observed that ultramicoporous structure with high surface areas (> 530m2/g) and narrow micopore size distribution (4-6 A) can be obtained by means of dilute solution polymerization method. On the contrary, no any porosity is detected for the cured product through bulk melting polymerization even under high curing temperature and long curing time, which reason is attributed to the existence of flexible intermediate segments. The finding may be an important approach to extend microporous concept (< 20 A) to general thermosetting resins in the area of polymer chemistry.2. A series of aromatic dicyanate monomers containing rigid contorted center, which is mostly used to construct microporous organic networks, have been synthesized by the reaction of phenolphthalein and its derivatives with cyanogen bromide in the presence of triethylamine. The dynamic mechanical analysis (DMA) results show that the introduction of phthalide ring (contorted center) into the polycyanurate network can effectively improve the thermal properties of the cyanate ester resin. The Tg values of the fully cured resins range from 298℃to 362℃, which are apparently higher than that of most bisphenol-based cyanate resins reported in the literatures. The thermal and thermo-oxidative properties as well as the water absorptions of the cured products are compared with those of the bisphenol-A cyanate ester (BACY), and the structure-property relationships are explained according to the chemical structures and crosslinking densities of the formed polymer networks.3. Using hydroquinone diacetate as A2 monomer and tetrakis(4-carboxyphenyl)silae as B4 monomer, the hyperbranched polyarylate precursors are successfully synthesized with high yields, during which the gelation process is efficiently suppressed by heterogeneous polycondensation method by means of the elaborate selection of reaction medium. The control of monomer ratio in the polymerization system leads to two type of precursors, i.e. mainly carboxyl-terminated hyperbranched polyarylate (CTHP) and mainly acetoxy-terminated hyperbranched polyarylate (ATHP). The precursor film, obtained by spin-coating from the mixture solution of CTHP and ATHP with equivalent amount of reactive carboxylic group and acetoxy groups, is readily thermally cured via transesterification reaction to form a crosslinked network, which exhibited excellent thermal stability, good chemical resistance, low birefringence and low dielectric constant as well as microporosity with average pore size of 11.2 A and surface area of 158 m2/g.4. Tetraphenylsilane-containing polyarylate with two pendant benzyl ester groups is synthesized successfully by direct polycondensation from a new silicon-containing aromatic diacid monomer bis[p-(benzyloxycarbonyl)phenyl]-bis(p-carbxyphenyl)siane (BBCS) with p-dihydroxybenzene in pyridine, using dimethylformamide as the activator and p-tosyl chloride as the condensing agent. Then, the benzyl ester groups are smoothly converted to carboxyl groups by catalytic hydrogenation, obtaining the polyarylate with two carboxyl groups attached on the phenylenes of tetraphenylsilane moiety. The presence of well-defined carboxyl groups and rigid tetrahedral structure of tetraphenylsilane in the polyarylate provides the feasible routes to the preparation of either hypercrosslinked covalent organic framework materials or optoelectronic materials through the reaction with chromophoric compounds.5. A series of rigid microporous and mesoporous polyimide networks is synthesized using a synthetic route that is closely related to the commercial preparations of aromatic polyimides, starting from readily available, well-defined triangular-like trisamino monomers (struts) and cheap, rigid rod-like bisanhydride monomers (linkers). Combined FTIR spectra, TGA analysis, N2 sorption analysis, atomistic simulations and SEM analysis clearly reveals that the pore structural properties such as BET surface area, pore volume and pore size in polyimide networks can be controlled by varying the size of the struts and linkers.6. Diamond-like polyimide networks are synthesized from tetrahedral monomer tetrakis(4-aminophenyl)methane (TAPM) and rigid rod-like bisanhydride monomers such as pyromellic dianhydride (PMDA) and 1,4,5,8-naphthalenetetracarboxylicdianhydride (NTDA). These polymers are substantially microporous materials and exhibit BET surface areas of up to 1400 m2/g as measured by N2 adsorption at 77K. The hydrogen storage capacities of these materials are also tested and a capacity of 3.3 wt% at 77K and 3 MPa was found for the best microporous polyimide prepared from TAPM and PMDA. The initial heats of adsorption of hydrogen molecules onto these polymers are around 5.2-7.0 kJ/mol.