Thermosetting composite matrix materials based on allyl and/or propargyl substituted cyclopentadiene, indene and fluorene

Gregory Jude Tregre


A series of all-hydrocarbon thermoset composite matrix resins was synthesized via electrophilic substitution of cyclopentadiene, indene, and fluorene ring systems with allyl and/or propargyl halides under phase transfer conditions. Reaction of cyclopentadiene with allyl chloride (ACP resin), propargyl bromide (PCP resin) or various feed ratios of allyl chloride and propargyl bromide (APCP resins) yielded mixtures of products with 2-6 substituents per cyclopentadiene ring. Reaction of indene with allyl chloride (Al resins) or propargyl bromide (PI resins) yielded mixtures of products with 2-4 substituents per indene. In both sets of resins the allyl functionality obtained a greater average degree of substitution than the analogous propargyl species. Differential scanning calorimetric (DSC) analysis of the multifunctional resins showed broad, high-energy thermal cures in all cases. The enthalpies of cure for ACP and PCP were 750 J/g and 805 J/g, respectively, with peak cure energies occurring at 310 and 248$\sp\circ$C. The enthalpy of cure for APCP resins ranged from 750 J/g to 800 J/g with higher propargyl-functional resins yielding higher enthalpies of cure. Physically mixed ACP/PCP resin systems gave peak cure temperatures and energy values comparable to APCP resins. The enthalpies of cure for Al and PI-resins were 480 J/g and 630 J/g, respectively. Peak cure temperature for Al resin was 320$\sp\circ$C, while the peak cure for PI resin occurred at 282$\sp\circ$C. Infrared spectroscopy (IR) and nuclear magnetic resonance spectroscopy (NMR) were used to evaluate mechanisms of cure in the experimental resins. The allyl functional resins cured through a combination of ene reactions and polyaddition reactions. The propargyl functional resins cured through ene reactions and polyadditions but also underwent some cyclotrimerization of the propargyl functionalities. A small amount of autoxidation was seen in all of the resins. Thermal stability and carbon yields of the cured resins were evaluated with thermogravimetric analysis (TGA). All resin systems showed good thermal stability, with less than 5% weight loss up to 400$\sp\circ$C in N$\sb2.$ The carbon yields of ACP and Al resins retained 15-20% of their initial weight at 1000$\sp\circ$C in N$\sb2.$ The carbon yields of PCP and PI resins were exceptional, retaining 75% and 68% of their initial weights, respectively, at 1000$\sp\circ$C in N$\sb2.$ The carbon yields of 5:1, 3:1 and 1:1 APCP resins (41, 55 and 66% respectively) increased with increasing propargyl functionality. The mixed ACP/PCP systems generated carbon yields of approximately 65-68%. Unidirectional glass and carbon fiber composites were fabricated and evaluated using three-point bending tests. The flexural modulus of the ACP/glass fiber composite was 42 GPa, while the flexural strength was 681 MPa. Flexural modulus values of the carbon fiber filled resin composites ranged from 165 GPa for the ACP resin composite to 115 GPa for the PCP resin composite. The flexural strengths had values of approximately 900-1100 MPa. Treatment of ACP/carbon fiber composites with boiling water or refluxing toluene had no significant effect on composite properties. Carbon-Carbon composites were fabricated from PCP, 1:1 APCP and PI resins. Preliminary evaluation gave interlaminar strength values of 1.1-1.5 MPa and carbon yields comparable to presently used systems. (Abstract shortened by UMI.)