Molecular and thermal studies of carbon fiber precursor polymers with low thermal‐oxidative stabilization characteristics

In this investigation, terpolymers, copolymers, and homopolymer of acrylonitrile with dimethylaminopropyl acrylamide (DMAPA), itaconic acid (IA) viz., poly(acrylonitrile‐ran‐3‐dimethylaminopropyl acrylamide‐ran‐itaconic acid) [P(AN‐DMAPP‐IA)], poly(acrylonitrile‐co‐3, dimethylaminopropyl acrylamide) [P(AN‐DMAPP)] were synthesized with varying amounts of comonomers using solution polymerization process. The chemical structure, composition, bonding network were determined employing infrared, 1H and, 13‐carbon nuclear magnetic resonance spectroscopic techniques. Molecular characteristics of as‐synthesized polymers such as different kinds of average molecular weights, molecular weight distribution were estimated applying solution viscometry and size exclusion chromatography. The influence of comonomers (DMPAA, IA) on the thermal stabilization characteristics of acrylonitrile terpolymers in comparison with copolymers and homopolymers of acrylonitrile were studied using differential scanning calorimetry (DSC), hyphenated thermal techniques (thermal gravimetry coupled with differential thermal analyzer).The DSC curves of P(AN‐DMAPP‐IA) exhibit a distinct broader bimodal peaks with thermal exotherm initiating at as low as 165 °C, and followed by two peaks with temperature difference of 42 °C, releasing the evolved heat at a release rate of 0.7–0.11 J g^?1s^?1over 10 min as compared to 1.2, 7.5 J g^?1s^?1 in 4.5, 2 min as observed in P(AN‐DMAPP), polyacrylonitrile, respectively. The thermal stability of P(AN‐DMAPP‐IA) and P(AN‐DMAPP), as evidenced by TGA‐DTA was found to be higher than PAN homopolymers. Specific heat capacity measurements confirmed the DSC results. Bulk densities of P(AN‐DMAPP‐IA) were in the range 0.31–0.35 g/cc. These results confirm the low‐temperature stabilization characteristics and suitability of P(AN‐DMAPP‐IA) as low cost carbon fiber precursor polymers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46381.     

Mechanical enhancement of amine‐functionalized TiO2 reinforced polyimine composites

Polyimine vitrimers are known for their malleability, which endows these materials with properties such as self‐healing, recycling, and reshaping. To enhance the mechanical properties of the polyimine vitrimers, composites were fabricated by incorporating amine‐functionalized TiO₂ microspheres (amTiO₂MS) into polyimine matrix. The pure polyimine matrix and polyimine composites hybridized with TiO₂ microspheres (TiO₂MS) without surface modification were also obtained and examined as the controls in characterization. X‐ray powder diffraction, scanning electron microscopy, and energy dispersive X‐ray spectroscopy were employed to demonstrate the presence and distribution of amTiO₂MS and TiO₂MS in the polyimine matrices. The investigation of mechanical properties of the amTiO₂MS enhanced polyimine composites and control samples indicated that incorporation of amTiO₂MS and TiO₂MS exhibited different characteristic distribution, which strongly affected the performance of the composites. The optimal filling concentration of amTiO₂MS was found to be 3%, with which the microspheres were uniformly distributed in the polyimine matrix. The self‐healing behavior of the polyimine‐amTiO₂‐X was also studied. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46446.     

Curing behavior and properties of benzoxazine‐co‐self‐promoted phthalonitrile polymers

A new high‐performance copolymer was successfully obtained via concerted catalysis polymerization of mono‐functional benzoxazine (P‐a) and self‐promoted 4‐aminophenoxy phthalonitrile (4‐APN) monomers. The FTIR and DSC curves of the P‐a/4‐APN in different blend ratios suggested that the monomer blends can be completely cured without the addition of curing additive. The P‐a/4‐APN copolymers were cured at relatively lower curing temperatures and time. The TGA curves revealed that the P‐a/4‐APN copolymers have good thermal stability in terms of T₅, T₁₀, and char yield. A gradual increase in the glass transition temperature (T_g) values and decline were seen in the storage modulus as the loading of 4‐APN was increased from 10 to 30 wt % in the copolymer. The SEM analyses showed that copolymer's fracture surface is dendritic, showing the stress has been dispersed to a certain extent. The study revealed that the poly(P‐a/4‐APN) copolymer have much better thermal stabilities than the poly(P‐a), and the prepared copolymer can be used as a high‐performance thermosetting resin. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46578.     

High‐performance thermosets with tailored properties derived from methacrylated eugenol and epoxy‐based vinyl ester

A renewable chemical, eugenol, is methacrylated to produce methacrylated eugenol (ME) employing the Steglich esterification reaction without any solvent. The resulting ME is used as a low‐viscosity co‐monomer to replace styrene in a commercial epoxy‐based vinyl ester resin (VE). The volatility and viscosity of ME and styrene are compared. The effect of ME loading and temperature on the viscosity of the VE–ME resin is investigated. Moreover, the thermomechanical properties, curing extent and thermal stability of the fully cured VE–ME thermosets are systematically examined. The results indicate that ME is a monomer with low volatility and low viscosity, and therefore the incorporation of ME monomer in VE resins allows significant reduction of viscosity. Moreover, the viscosity of the VE–ME resin can be tailored by adjusting the ME loadings and processing temperature to meet commercial liquid molding technology requirements. The glass transition temperatures of VE–ME thermosets range from 139 to 199 °C. In addition, more than 95% of the monomer is incorporated and fixed in the crosslinked network structure of VE–ME thermosets. Overall, the developed ME monomer exhibits promising potential for replacing styrene as an effective low‐viscosity co‐monomer. The VE–ME resins show great advantages for use in polymer matrices for high‐performance fiber‐reinforced composites. This work is of great significance to the vinyl ester industry by providing detailed experimental support. © 2018 Society of Chemical Industry     

Highly filled graphite polybenzoxazine composites for an application as bipolar plates in fuel cells

Highly filled graphite polybenzoxazine composites as bipolar plate material for polymer electrolyte membrane fuel cell (PEMFC) are developed. At the maximum graphite content of 80 wt % (68 vol %), storage modulus was increased from 5.9 GPa of the neat polybenzoxazine matrix to 23 GPa in the composite. Glass transition temperatures (T_g) of the composites were ranging from 176°C to 195°C and the values substantially increased with increasing the graphite contents. Thermal conductivity as high as 10.2 W/mK and electrical conductivity of 245 S cm^?1 were obtained in the graphite filled polybenzoxazine at its maximum graphite loading. The obtained properties of the graphite filled polybenzoxazine composites exhibit most values exceed the United States department of energy requirements for PEMFC applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3909–3918, 2013     

Synthesis and properties of cross‐linked polymers from epoxidized rubber seed oil and triethylenetetramine

A series of epoxidized oils were prepared from rubber seed, soybean, jatropha, palm, and coconut oils. The epoxy content varied from 0.03 to 7.4 wt %, in accordance with the degree of unsaturation of the oils (lowest for coconut, highest for rubber seed oil). Bulk polymerization/curing of the epoxidized oils with triethylenetetramine (in the absence of a catalyst) was carried out in a batch setup (1 : 1 molar ratio of epoxide to primary amine groups, 100°C, 100 rpm, 30 min) followed by casting of the mixture in a steel mold (180°C, 200 bar, 21 h) and this resulted in cross‐linked resins. The effect of relevant pressing conditions such as time, temperature, pressure, and molar ratio of the epoxide and primary amine groups was investigated and modeled using multivariable nonlinear regression. Good agreement between experimental data and model were obtained. The rubber seed oil‐derived polymer has a T_g of 11.1°C, a tensile strength of 1.72 MPa, and strain at break of 182%. These values are slightly higher than for commercial epoxidized soybean oil (T_g of 6.9°C, tensile strength of 1.11 MPa, and strain at break of 145.7%). However, the comparison highlights the potential for these novel resins to be used at industrial/commercial level. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42591.     

Mechanical and thermal properties of biphenyldiol formaldehyde resin/gallic acid epoxy composites enhanced by graphene oxide

In this study, the gallic acid‐based epoxy resin (GA‐ER) and alkali‐catalysed biphenyl‐4,4′‐diol formaldehyde resin (BPFR) are synthesized. Glass fibre‐reinforced GA‐ER/BPFR composites are prepared. Graphene oxide (GO) is used to improve the mechanical and thermal properties of GA‐ER/BPFR composites. Dynamic mechanical properties and thermal, mechanical, and electrical properties of the composites with different GO content are characterized. The results demonstrate that GO can enhance the mechanical and thermal properties of the composites. The glass transition temperature, T_g, of the BPFR/GA‐ER/GO composites is 20.7°C higher than the pure resin system, and the 5% weight loss temperature, T_d5, is enhanced approximately 56.6°C. When the BPFR: GA‐ER mass ratio is at 4 : 6 and GO content is 1.0–1.2 wt %, the tensile and impact strengths of composites are 60.97 MPa and 32.08 kJ/m² higher than the pure resin composites, respectively. BPFR/GA‐ER composites have better mechanical properties, and can replace common BPA epoxy resins in the fabrication of composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42637.     

Improvement of epoxy thermosets using a thiol‐ene based polyester hyperbranched polymer as modifier

The anionic curing initiated by 1‐methyl imidazole of diglycidyl ether of bisphenol A with a hyperbranched polymer (HBP) containing long aliphatic chains in the structure were studied. The hydroxyl groups present as chain ends in the HBP structure played an important role in the curing kinetics, as demonstrated by differential scanning calorimetry, Fourier transform infrared spectroscopy and rheological studies. Properties such as shrinkage on curing and thermomechanical characteristics were also investigated. The structure of the HBP, which contains long aliphatic chains and reactive hydroxyl groups as chain ends, flexibilizes the network significantly, improving the impact resistance without notably affecting either the glass transition temperature or the microhardness of the modified thermosets. Copyright © 2012 Society of Chemical Industry     

Curing of mixtures of epoxy resins and 4‐methyl‐1,3‐dioxolan‐2‐one with several initiators

Diglycidyl ether of bisphenol A or 3,4‐epoxycyclohexylmethyl 3,4‐epoxycyclohexane carboxylate were mixed with different proportions of 4‐methyl‐1,3‐dioxolan‐2‐one and cured using lanthanide triflates as initiators. In order to compare the materials obtained, conventional initiators such as boron trifluoride complexes and N,N‐dimethylaminopyridine were also tested. The curing process was followed by differential scanning calorimetry (DSC) and Fourier transform IR in attenuated total reflectance mode. This technique proved that the carbonate accelerates the curing process because it helps to form the active initiating species, although it was not chemically incorporated into the network and remained entrapped in the material. The DSC kinetic study was also reported. © 2006 Wiley Periodicals Inc. J Appl Polym Sci 102: 2086–2093, 2006     

Cure kinetics of the cardanyl acrylate–styrene system using isothermal differential scanning calorimetry

The curing kinetics of styrene (30 wt %) and cardanyl acrylate (70 wt %), which was synthesized from cardanol and acryloyl chloride, was investigated by differential scanning calorimetry under isothermal condition. The method allows determination of the most suitable kinetic model and corresponding parameters. All kinetic parameters including the reaction order, activation energy E_a and kinetic rate constant were evaluated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2034–2039, 2002