Zhijiao Chen,Cong Peng,Shichao Li,Zhanjun Wu,Tao sun
Phthalonitrile monomer containing oxazine ring (BPS-Ph) was synthesized using bisphenol-S, aniline, paraformaldehyde, and 4-nitrophthalonitrile via a two-step method. The differential scanning calorimetry (DSC) data of the curing process of BPS-Ph monomer indicates that the peak polymerization temperature of the cyan group is about 250°C and that confirms the promoting effect of oxazine ring on the curing reaction of phthalonitrile. The rheological data of E51/DDS containing BPS-Ph indicates that the BPS-Ph monomer also has promoting effect on the curing process. The activation energy was studied via the iso-conversional method principle. The activation energy corresponding to the E51/DDS crosslinking reaction is 75.79 and 60.54 kJ mol −1 , respectively, for pure E51/DDS and E51/DDS/BPS-Ph. Moreover, the activation energy of the crosslinking of phthalhydrazine is 74.1 kJ mol −1 which is rather lower than that in pure BPS-Ph, and that implies the synergistically catalytic effect of the oxazine ring and the amine. The addition of BPS-Ph monomer significantly improves the thermal behaviors of the thermoset. The char yield in N 2 atmosphere increased from 15.6% to 53.9% when adding 30% BPS-Ph to the E51/DDS. Moreover, the peak weight loss temperature decreased from 407 to 385°C. The phase separation size of poly-BPS-Ph in E51/DDS is about tens to hundreds nanometers according to the atomic force microscopy (AFM) phase diagram. It is indicated that incorporation of phthalonitrile monomer containing oxazine ring into epoxy/amine system is an applicable and effective way to promote the thermal behavior of the thermoset.
A novel hyperbranched polymeric ionic liquid (HBP-AMIM + PF6 − ) was explored via a thiol-ene click reaction using thiol-ended hyperbranched polyesters (THBP) and 1-allyl-3-imethylimidazolium hexafluorophosphate (AMIMPF6). The effects of HBP-AMIM + PF6 − on the curing behavior, mechanical properties and thermal stability of benzoxazine/epoxy thermosets were investigated. The gelation time and differential scanning calorimetry of non-isothermal analysis indicated that the addition of HBP-AMIM + PF6 − significantly decreased the curing temperature of benzoxazine/epoxy thermosets. Simultaneously, the addition of HBP-AMIM + PF6 − also improved the strength, toghness and thermal properties of benzoxazine-epoxy thermosets. The addition of 3 wt% HBP-AMIM + PF6 − -2 could significantly improve the mechanical and thermal performance of thermosets compared with that of cured neat benzoxazine/epoxy resin. The tensile strength, tensile toughness, flexural strength and flexural modulus, impact strength of the thermosets were improved by about 76.6%, 279.3%, 57.8%, 22.3% and 80.4%, respectively, compared with those of cured neat resin. The toughening mechanisms was attributed to the “in situ” reinforcing and toughening mechanism.
The increasing frequent occurrence of fire accidents alone with the desirable sustainable development have accelerated searching for more resilient and safer flame-retardant polymers derived from natural renewable resources. Here we have successfully designed and synthesized bio-based benzoxazine monomers ( PH-fa-[ 2 -ph, 4 -DEP] and PH-fa-[ 2 - o OHph, 4 -DEP] ) with oxazine ring substituted by diethyl phosphite (DEP) via hydrophosphonylation for the first time, thereby achieving non-flammable green thermoset materials. Specifically, PH-fa-[ 2 - o OHph, 4 -DEP] with phenolic -OH group also shows a latent catalytic feature through its in-built intramolecular hydrogen bonding. As a result, we chose this newly synthesized monomer as both latent catalyst and flame retardant for enhancing the comprehensive properties of the well-commercialized benzoxazine resin (BA-a). The peak curing temperature of BA-a thermosetting system was decreased 23.3°C and the glass transition temperature of resulting thermoset increased by 61.7% with only adding 3 mol% of PH-fa-[ 2 - o OHph, 4 -DEP] . Finally, the mechanistic insights into both advantages including low curing temperature and excellent flame retardancy have been discussed. With this work we demonstrate the possibilities for achieving bio-based non-flammable thermosets using benzoxazine chemistry, and offer molecular level insights into the functions, paving the way for new applications of green thermosetting resins for high-performance non-flammable composite materials.
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