Study On Heat-resistant Polymers Containing Aryl-s-triazine Moieties

Conventional phenyl-s-triazine-based polymers are well-known for their outstanding comprehensive properties including excellent thermal stability, high strength and modulus, good flame retardance and chemical resistance, unique electronic and optical properties. However, such polymers always exhibit no melt or soften temperatures and poor solubility, and high-molecular-weight polymers are frequently prepared at high temperatures under high pressures. Therefore, it is difficult to process these polymers, which hampers their widespread application as insulting coatings, adhesives and membranes. Starting from the design in molecular structure, soluble cyano-terminated poly(phthalazinone ether)s were synthesized and thermally crosslinked to afford new phenyl-s-triazine polymers by the trimerization of cyano groups under normal pressure; new series of soluble and heat-resistant poly(aryl ether phenyl-s-triazine)s were synthesized by the nuleophilic displacement polymerization of phenyl-s-triazine-containing dihalides with 4-(4-hydroxylphenyl)(2H)-phtha-lazin-1-one monomers.The trimerization of 4-fluorobenzonitrile, 4-chlorobenzonitrile (CBN) and 4-cyanobenzoic acid (CBA) in the catalysis of ZnCl₂ or ClSO₃H under normal pressure were initially conducted as model reactions to investigate the cyclization reactivity of aromatic mono-nitriles. Two kinds of poly(pheny-s-triazine) networks were respectively prepared by the bulk polymerization of terephthalonitrile (TPH) and 4,4'-dicyanobiphenyl (DCB) under similar conditions. The cyclization conditions were optimized with respect to reaction system, time, temperature, catalyst nature and its content, and ZnCl₂ is found to be more suitable than other catalysts investigated for the trimerization of aromatic nitriles under normal pressure, and the maximum conversations of terephthalonitrile (TPH) and 4,4'-dicyanobiphenyl (DCB) were 82% and 78%, respectively. Four kinds of aromatic ether-linked dinitriles with low melting temperatures were obtained via the nucleophilic substitution of hydroquinone (HQ), resorcinol (RS), biphenol and bisphenol A with CBN. They were polymerized to afford a series of poly(pheny-s-triazine)s under the optimized conditions. The conversations (below 60%) of these polymerization reactions are much lower than those of TPH and DCB, indicating that the trimerization is favorably promoted by the activation of strong electron-withdrawing substitutents in the para-orientation. The resulting polymers were insoluble in orangnic solvents and their structure was confirmed by FTIR, elemental analysis and other measurements.Cyano-containing polymers were designed and supposed to trimerize to afford phenyl-s-triazine rings, and crank and twisted phthalazinone moieties were also incorporated into the polymer backbone to impart good solubility, with a viewing to improving the processability of the phenyl-s-triazine-based polymers. Poly(phthalazinone ether nitrile)s (PPENs) and their oligomers with N-H ends (PPEN-OL) were synthesized by the solution polycondensation of 2,6-difuorobenzonitrile with calculated 4-(4-hydroxylphenyl)(2H)-phtha-lazin-1-one (HPPZ). FT-IR, TGA, WAXD and solubility measurements demonstrated that PPENs and PPEN-OL hardly underwent any crosslinking after thermal treatment at 360℃for 6 h under normal pressure, even in the presence of TPH and ZnCl₂. To improve the cyano reactivity, cyano-terminated PPENs (PPEN-DC) were prepared by the end-capping reaction of PPEN-OL with CBN; benzonitrile terminated poly(phthalazinone ether amide)s (PPA-DC) were also prepared by the polycondensation of excess 4,4'-oxydianiline with 1,2-dihydro-2-(4-carboxyphenyl)-4-[4-(4-carboxyphenoxyl)phenyl]-phthalazinone, followed by end-capping with CBA. The polymers synthesized exhibited good solubility in NMP, DMAc and DMF, and were crosslinked to afford phenyl-s-triazine-containing polymers under the similar conditions. T_gs of crosslinked PPEN-DC, which are increased at least by 94℃upon thermal crosslinking, are higher than 360℃, and T_d5% values (>515℃) are increased at least by 30℃upon crosslinking. The crosslinked PPA-DC exhibit no T_g up to 400℃as edvienced by DSC, and T_d5% values (>469℃) are increased at least by 10℃upon thermal crosslinking.Phthalazinone-containing bisphthalonitrile and phthalonitrile-terminated polymers were synthesized to increase the crosslinkable group content and their reactivity. The nucleophilic displacement of 4-(4-tolyl)(2H)-phthalazin-1-one with 4-nitrophthalonitrile (NPh) was investigated as a model reaction and the reaction was confirmed to proceed via a novel N-C coupling reaction. The reaction of HPPZ with NPh conducted in similar conditions as for model reaction readily afforded phthalazinone-based bisphthalonitrile (Ph-HPPZ) in high yields. The effect of temperature, time periods, reactant concentration and ratio on the yield and purity of Ph-HPPZ was also investigated and the maxium yield and purity are 96% and 98% under optimal conditions, respectively. Ph-HPPZ was polymerized to form a prepolymer (B-stage resin) in the presence of diamines or a mixture of TPH and ZnCl₂. Both monomer and its prepolymer exhibit good solubility in CHCl₃, DMSO, NMP, DMAc and DMF, and can be thermally cured to afford phenyl-s-triazine-based thermosets under normal pressure. Phthalonitrile-terminated PPENs, PPESs, PPEKs and their copolymers, were respectively synthesized via nucleophilic displacement reactions of HPPZ with activated dihalides and NPh in similar conditions. They were polymerized to B-stage resins in the presence of aromatic diamines or a mixture of TPH and ZnCl₂. The phthalonitrile-terminated polymers and B-stage resins are readily soluble in NMP, DMAc, DMF, DMSO and chloroform, and exhibit good film-forming properties. Additonally, they can be directly advanced to phenyl-s-triazine-based networks under normal pressure. The addition of TPH increases the phenyl-s-triazine content in the produced networks. The networks exhibit no detectable T_g up to 400℃and show excellent thermal stability (N₂: T_d5%>509℃, C_y>73%; Air: T_d5%>505℃).To improve the organosolubility of conventional poly(aryl ether phenyl-s-triazine)s (PAEPs), three kinds of new PAEPs were prepared by the nuleophilic displacement polymerization of 2,4-bi(4-fiuorophenyl)-6-phenyl-1,3,5-triazine (BFPT) with RS, 4,4'-dihydroxydiphenyl sulfone and HPPZ, respectively. The obtained polymers were readily soluble in NMP and DMAc at room temperature, and exhibited high thermal stabilities and oxidative stabilities (T_gs>243℃; N₂:T_d5%>536℃; Air: T_d5%>529℃). Similarly, a new series of copoly(aryl ether phenyl-s-triazine)s were synthesized via the polycondensation of BFPT with various ratios of HQ and RS. A good agreement of T_g values (ranging from 241～248℃) of the copolymers with values predicted by Fox equation was also observed and they exhibit excellent thermal stability (N₂: T_d5%>575℃; Air: T_d5%>541℃). Four kinds of poly(aryl ether phenyl-s-triazine)s containing alkyl-, aryl- and chloro-substituted phthalazinone moieties (PPEPs) were prepared through solution polycondensation of BFPT with substituted phthalazinones. The T_gs of resulting polymers are ranging from 255-265℃. A new series of copoly(phthalazinone ether sulfone phenyl-s-triazine) were prepared starting from HPPZ, BFPT and DCS in similar procedures. The copolymers exhibit better solubility in NMP, DMAc, DMF and Py than the polymers described above. Their T_gs (271～300℃) increase with an increase in sulfone content in the polymer main chain, while the crystallinity and overall thermal stability appear to decrease. All films of the polymers synthesized possess good mechanical properties in the ambinent temperatures. The apparent activation energy (E_a) of the produced polymers was detemined under N₂ flow in dynamic heating conditions and the decomposition mechanism was also proposed. The E_a values of the obtained polymers are much higher than that of the commercial available poly(aryl ether)s, suggesting their superior thermal stability due to the incorporation of phenyl-s-triazine rings.