THERMALLY STABLE POLYMERS BASED ON 1,3,4-OXADIAZOLE RINGS

In the present work, new thermally stable polymers containing 1,3,4-oxadiazole units have been synthesized through Huisgen reaction of the aromatic bis-tetrazole compounds with the aromatic/aliphatic bis-acid chlorides in pyridine as solvent. The obtained polymers are insoluble or slightly soluble in polar aprotic solvents such as DMSO and DMF. Thermal analyses of the polymers using DSC and TGA techniques showed that the polymers had improved thermal stabilities. The model reaction was also investigated and the resulting bis-1,3,4-oxadiazole compounds were characterized by conventional spectroscopic methods.

THERMALLY STABLE POLYMERS CONTAINING 1,3,4-OXADIAZOLE UNITS OBTAINED FROM HUISGEN REACTION

Thermally stable polymers containing 1,3,4-oxadiazole units have been synthesized through Huisgen reaction of the aromatic/aliphatic bis-tetrazole compounds with the aromatic/aliphatic bis-acid chlorides in pyridine as solvent.The obtained polymers are insoluble or slightly soluble even in polar aprotic solvents such as DMSO and DMF.Relatively high inherent viscosity values（0.61-1.33 dL/g,in 0.125%H_2SO_4 at 25℃） were observed for these compounds.Thermal analyses of the polymers using DSC and TGA techniques showed that the polymers have improved thermal stabilities.The glass transition temperature has not been observed in the fully aromatic polymers,but the polymers obtained from 5-[6-（1H-tetrazol -5-yl）hexyl]-lH-tetrazole（Ⅳ） showed very clear T_g.A model reaction was also investigated and the resulting bis-1,3,4-oxadiazole compound was characterized by conventional spectroscopy methods.

SYNTHESIS AND CHARACTERIZATION OF POLY[(METHYLSILYLENE ETHYNYLENEPHENYLENEETHYNYLENE)-CO-(DIMETHYLSILYLENE ETHYNYLENEPHENYLENEETHYNYLENE)]S

A series of poly[（methylsilylene ethynylenephenyleneethynylene）-co-（dimethylsilylene ethynylenephenyleneethynylene）]s were synthesized by the incorporation of various ratios of methylsilylene to dimethylsilylene units into the polymer chain backbone. The resultant copolymers were soluble in a variety of common organic solvents at room temperature. The copolymers were characterized by FT-IR, ^1H-NMR, GPC, rheological analysis, differential scanning calorimetry （DSC） and thermogravimetric analysis （TGA）. The results showed that the copolymers exhibited good processability and cured at low temperatures like 200℃. The curing reactions involved in hydrosilylation of Si-H and alkyne groups and the polymerization of alkynes. Td5 （5% weight loss） of the cured copolymers ranged from 629℃ to 686℃, and the decomposition residues of cured copolymers at 1000℃ ranged from 88.1% to 90.9% under nitrogen. Thermal stability of the copolymers increased with the introduction of methylsilylene traits into polymer chains. The cured copolymers were sintered at 1450℃, and the results of X-ray diffraction analysis showed that β-SIC was formed in the sintered products.

SYNTHESIS AND CHARACTERIZATION OF OPTICALLY ACTIVE POLYAMIDES BASED ON 2-(1,3-ISOINDOLINEDIONE-2-YL)GLUTARIC ACID BY DIRECT POLYCONDENSATION

Five new optically active polyamides （PAs） 6a-6e were prepared by direct polycondensation reaction of 2-（1,3- isoindolinedione-2-yl）-glutaric acid 4 as a new chiral diacid with various aromatic diamines 5a-Se in a medium consisting of triphenyl phosphite （TPP）, calcium chloride, pyridine （Py） and N-methyl-2-pyrrolidone （NMP）. The polycondensation reaction produced a series of polyamids 6a-6e in quantitative yields with inherent viscosities of 0.26-0.39 dL/g. The resulting polymers were fully characterized by means of ^1H-NMR, FT-1R spectroscopy, elemental analysis, inherent viscosity and specific rotation. Thermal properties of these polymers were investigated using thermal gravimetric analysis （TGA） and differential thermal gravimetry （DTG）. Phthalimide rings as a bulky pendent group in the polymer chains disturb the interchain and intrachain interactions and make these PAs readily soluble in polar, aprotic solvents such as N,N-dimethyl acetamide （DMAc）, N,N-dimethyl formamide （DMF）, dimethyl sulfoxide （DMSO）, N-methyl-2-pyrrolidone （NMP） and sulfuric acid.

WHOLLY AROMATIC CHIRAL POLYAMIDES BEARING PENDANT PHTHALIMIDO AND L-ISOLEUCINE MOITIES

A potential biodegradable and optically active bulky chiral aromatic amide-imidic diacid monomer,（2S,3S）-5-（3- methyl-2-phthalimidylpentanoylarnino）isophthalic acid（7）,containing a rigid phthalimide and flexible L-isoleucine pendant group was synthesized in three steps.New aromatic polyamides including pendant phthalimido groups and flexible side spacers have been synthesized by direct polycondensation reaction of equimolar amounts of different aromatic diamines with an optically active diacid 7,using N-methyl-2-pyrrolidone（NMP） as a solvent and triphenyl phosphite/CaCl_2/pyridine as a condensing agent.These polyamides were characterized by FTIR,~1H-NMR spectroscopy,specific rotation, thermogravimetric and elemental analysis.The resulting polymers have inherent viscosities in the range of 0.21-0.45 dL/g. Amino acid existence in this backbone results in optically active polymers.Due to introduction of bulky and flexible groups in these polyamides,they show improved solubility in polar aprotic solvents such as NMP and dimethylacetamide and also good thermal stability（10%weight loss temperatures in excess of 330℃,and char yields at 600℃in nitrogen higher than 62%）.