Mechanistic study on the thermal decomposition of polybenzoxazines: Effects of aliphatic amines

The thermal degradation of a series of polybenzoxazines based on bisphenol A and various aliphatic amines has been studied. Using the hyphenated techniques of thermogravimetric analysis-Fourier transform infrared spectroscopy (TGA-FTIR), and gas chromatography-mass spectrometry (GC-MS), the mechanisms of thermal decomposition have been proposed. It is also proposed that the Mannich base in polybenzoxazines plays a significant role in the thermal degradation of polybenzoxazines. The contribution of hydrogen bonding to the degradation mechanism of the Mannich base has been examined. The proposed mechanisms have also been supported through the thermal degradation study of benzoxazine model dimers. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1935–1946, 1998     

Dynamic mechanical and thermal characterization of high-performance polybenzoxazines

Two polybenzoxazines are cured in an autoclave from the polyfunctional benzoxazine monomers, 8,8′-bis(3,4-dihydro-3-phenyl-2H-1,3-benzoxazine) and 6,6′-bis(2,3-dihydro-3-phenyl-4H-1,3-benzoxazinyl) ketone. The density and tensile properties of these polybenzoxazines are measured at room temperature. Dynamic mechanical tests are performed to determine the T_g, crosslink density, and the activation enthalpy of the glass-transition process for these two polybenzoxazines. The effect of postcure temperature on the T_g of the polymers is investigated and discussed in terms of crosslink density. Fourier transform infrared (FTIR) spectroscopy is also applied for the molecular characterization of the curing systems. Thermal properties of these polybenzoxazines are studied in terms of isothermal aging and decomposition temperature via thermogravimetric analysis. These two polybenzoxazines show mechanical and thermal properties similar to or better than bismaleimides and some polyimides. They also show very high char yield after being carbonized in a nitrogen atmosphere. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3257–3268, 1999     

Improved thermal and mechanical properties of polybenzoxazines based on alkyl‐substituted aromatic amines

The thermal and mechanical properties of polybenzoxazine thermoset networks containing varying amounts of phenolic Mannich bridges, arylamine Mannich bridges, and methylene bridges have been investigated. In materials based on m‐toluidine and 3,5‐xylidine, the onset of thermal degradation is delayed until around 350 °C with no significant effect on the final char yield. The first of the three weight‐loss events usually seen in aromatic amine‐based polybenzoxazines is absent in these two materials. Materials with additional amounts of arylamine Mannich bridges and methylene bridges show improved mechanical properties, including higher crosslink densities and rubbery plateau moduli. Correlations between the observed mechanical properties and network structures are established. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3289–3301, 2000     

Synthesis and analysis of thermal characteristics of polybenzoxazine based on phenol and 3‐Amino phenyl boronic acid

In this work, 3‐amino phenyl boronic acid (AB) was used as an aniline derivative in the preparation of polybenzoxazine based on phenol. In order to investigate the effect of boronic acid on thermal characteristics, polybenzoxazines based on pure aniline and 50% aniline and AB mixture were also prepared and analyzed. Significant improvements in thermal characteristics, increase in thermal stability and char yield, was recorded for the polymers based on AB or its mixture. This behavior was associated with crosslinked structures generated by condensation reactions of B? OH groups. Morphologic and thermal characteristics of polybenzoxazines samples were investigated by NMR, FTIR, DSC, TGA, and direct pyrolysis mass spectrometry (DP‐MS) techniques. Application of DP‐MS technique also supplied additional information on crosslinked structures produced by boronic acid units. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1711–1716     

A novel polymeric stabilizing system for modified lyocell solutions

A novel polymeric stabilizer consisting of iminodiacetic acid sodium salt (ISDB) and benzyl amine (BSDB) covalently bound to a styrene/divinyl benzene copolymer were studied. Calorimetric, spectroscopic, rheological, and high performance liquid chromatography analysis revealed distinctive improvements of the thermal stability of modified Lyocell solutions compared to the unstabilized solution and to that with conventional NaOH/propyl gallate stabilizer. Segregation processes of the system cellulose/N‐methylmorpholine‐N‐oxide and autocatalytic reactions caused by carboxyl group‐containing additives are suppressed by ISDB/BSDB. Concerning to surface‐active additives, enhanced thermal stability is only received for a weakly reactive charcoal. In the case of nanoscaled carbon black modifier, autocatalytic reactions indicated by isoperibolic measures are prevented by the new polymeric stabilizer system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1702–1713, 2006     

Cocuring behaviors of benzoxazine and maleimide derivatives and the thermal properties of the cured products

The cocuring behaviors of 3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine (P‐ABz) and various N‐phenylmaleimide compounds were studied with DSC, FTIR, and TGA‐GC/MS. The presence of benzoxazine compound promoted the polymerization of maleimide groups. In contrast, 4‐hydroxyphenylmaleimide (MI‐OH) and 4‐maleimidobenzoic acid (MI‐COOH), which possess acidic moieties, showed an acid‐catalytic effect on the polymerization of benzoxazine groups. The cocuring composition of P‐ABz/MI‐COOH showed low polymerization temperatures, high glass transition temperature above 220 °C, and comparable thermal stability to conventional polybenzoxazines. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1890–1899, 2006     

Thermal stability of polybenzoxazines with lanthanum chloride and their crosslinked structures

Lanthanum chloride (LaCl₃) was incorporated into five kinds of benzoxazines by different preparation methods. The thermal stability and the structures of polybenzoxazines were characterized by thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The evolved gases from the degradation process of polybenzoxazines were analyzed by FTIR. The results showed that the thermal stability and char yields of three kinds of polybenzoxazines containing LaCl₃ can be improved obviously. LaCl₃ has an important effect on the polymerization reactions of benzoxazines. More stable arylamine Mannich bridges were observed in the chemical structures of the polybenzoxazines. It is these structures that can effectively retard the volatilization of aniline derivatives and result in the improvement of the thermal stability of the polybenzoxazines.     

Crosslinked polyamide based on main‐chain type polybenzoxazines derived from a primary amine‐functionalized benzoxazine monomer

Two types of main‐chain type polybenzoxazines with amide and benzoxazine groups as repeating units in the main chain, termed as poly(amide‐benzoxazine), have been synthesized. They have been prepared by polycondensation reaction of primary amine‐bifunctional benzoxazine with adipoyl and isophthaloyl dichloride using dimethylacetamide as solvent. Additionally, a model reaction is designed from the reaction of 3,3′‐(4,4′‐methylenebis(4,1‐phenylene))bis(3,4‐dihydro‐2H‐benzo[e][1,3]oxazin‐6‐amine) with benzoyl chloride. The structures of model compound and polyamides are confirmed by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (¹H NMR) spectroscopies. Differential scanning calorimetry and FTIR are also used to study crosslinking behavior of both the model compound and polymers. Thermal properties of the crosslinked polymers are also studied by thermogravimetric analysis. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Photogenerated base in polymer curing and imaging: Design of reactive styrenic copolymers susceptible to a base-catalyzed β-elimination

A novel family of functionalized styrenic copolymers that are susceptible to a base-catalyzed β-elimination reaction is reported. The reactive copolymers, poly-{(2-phenyl-2-cyanoethoxycarbonyloxystyrene)-co-(4-hydroxystyrene)}, are prepared by chemical modification of poly(4-hydroxystyrene) using 2-phenyl-2-cyanoethyl chloroformate. A photoresist material consisting of the copolymer and bis[[(2-nitrobenzyl)-oxy] carbonyl]-4,4′-trimethylenedipiperidine used as an amine photogenerator affords positive tone images by UV irradiation. The effect of copolymer structure and composition on imaging, thermal stability, and the ease of β-elimination reaction is discussed. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3543–3552 1997     

Shape memory polybenzoxazines based on a siloxane‐containing diphenol

A siloxane‐containing diphenol is synthesized from 1,1,3,3‐tetramethyldisiloxane and o‐allylphenol, followed by the Mannich condensation with aniline, methylamine, and formaldehyde yielding two siloxane‐containing benzoxazines. The onset polymerization temperature of aniline‐based benzoxazine is higher than that of the methylamine counterpart. The dynamic mechanical properties of the polybenzoxazines depend on the structure of the starting primary amines. Both polybenzoxazines exhibit one‐way dual‐shape memory behavior in response to changes in temperature, and they show excellent shape fixity ratios in bending, tension, and tensile stress–strain tests, high shape recovery ratios in bending and tension tests, but relatively low shape recovery ratios in tensile stress–strain test. The network chain segments including the alkylsiloxane units serve as a thermal control switch based on the glass transition temperatures (39 and 53 °C) for the polybenzoxazines. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1255–1266     

High performance benzoxazine monomers and polymers containing furan groups

Furan‐containing benzoxazine monomers, 3‐furfuryl‐3,4‐dihydro‐2H‐1,3‐benzoxazine (P‐FBz) and bis(3‐furfuryl‐3,4‐dihydro‐2H‐1,3‐benzoxazinyl)isopropane (BPA‐FBz), were prepared using furfurylamine as a raw material. The chemical structures of P‐FBz and BPA‐FBz were characterized with FTIR, ¹H NMR, elemental analysis, and mass spectrometry. Formation of furfurylamine Mannich bridge networks in the polymerizations of P‐FBz and BPA‐FBz increased the cross‐linking densities and thermal stability of the resulting polybenzoxazines. P‐FBz‐ and BPA‐FBz‐based polymers also exhibited high glass transition temperatures above 300 °C, high char yields, and low flammability with limited oxygen index values of 31. The dielectric (D_k = 3.21–3.39) and mechanical properties (high storage modulus of 3.0–3.9 GPa and low coefficient of thermal expansion of 37.7–45.4 ppm) of the P‐FBz‐ and BPA‐FBz‐based polymers were superior or comparable to other polybenzoxazines. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5267–5282, 2005     

Improved thermal stability of polybenzoxazines by transition metals

The incorporation of various transition metal salts increases the char formation of polybenzoxazines. It is shown that the effect of the transition metal salt is not simply additive and is independent of the amine and phenol structures. While the metal salts have an insignificant effect on the polymerization, their presence in benzoxazine favors the formation of carbonyl functional groups. It is proposed that reduced flammability of polybenzoxazines is achieved through the evolution of CO₂ during thermal degradation.     

Synthesis and characterization of a series of wholly aromatic copolyesters containing 2‐(α‐phenylisopropyl)hydroquinone moiety

Two series of new wholly aromatic thermotropic copolyesters containing the 2‐(α‐phenylisopropyl)hydroquinone (PIHQ) moiety have been synthesized and their basic properties such as glass transition temperature (T_g), melting temperature (T_m), thermal stability, crystallinity, and liquid crystallinity were studied by differential scanning calorimetry (DSC), thermogravimetry (TG), and wide‐angle X‐ray diffractometry (WAXD) and on a polarizing microscope. The first series was prepared from acetylated PIHQ, terephthalic acid (TPA), and 2,6‐naphthalenedicarboxylic acid (NDA), and the second series from acetylated PIHQ, TPA, and 1,1′‐biphenyl‐4,4′‐dicarboxylic acid (BDA). The T_g values (152–168°C) of the two series are not much different, although the values for the first series appear slightly higher. The T_m values (287–378°C) and the degree of crystallinity of the first series are appreciably greater than those of the second series. Such differences can be explained by the geometric structure of NDA and BDA moieties. All of the present polyesters are thermotropic and nematic. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 881–889, 1999     

Novel,environmentally friendly crosslinking system of an epoxy using an amino acid: Tryptophan‐cured diglycidyl ether of bisphenol A epoxy

Tryptophan, an amino acid, has been used as a novel, environmentally friendly curing agent instead of toxic curing agents to crosslink the diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The curing reaction of tryptophan/DGEBA mixtures of different ratios and the effect of the imidazole catalyst on the reaction have been evaluated. The optimum reaction ratio of DGEBA to tryptophan has been determined to be 3:1 with 1 wt % catalyst, and the curing mechanism of the novel reaction system has been studied and elucidated. In situ Fourier transform infrared spectra indicate that with the extraction of a hydrogen from NH₃⁺ in zwitterions from tryptophan, the formed nucleophilic primary amine and carboxylate anions of the tryptophan can readily participate in the ring‐opening reaction with epoxy. The secondary amine, formed from the primary amine, can further participate in the ring‐opening reaction with epoxy and form the crosslinked network. The crosslinked structure exhibits a reasonably high glass‐transition temperature and thermal stability. A catalyst‐initiated chain reaction mechanism is proposed for the curing reaction of the epoxy with zwitterion amino acid hardeners. The replacement of toxic curing agents with this novel, environmentally friendly curing agent is an important step toward a next‐generation green electronics industry. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 181–190, 2007     

Film-forming characteristics and thermal stability of low viscosity benzoxazines derived from melamine

A novel class of low-viscosity benzoxazines has been synthesized from melamine and formaldehyde with phenol or bisphenol A. The striking feature of the class of benzoxazines is the subtle combination of their inherently low viscosity at room temperature, good film-forming characteristics and high chemical and thermal stability mainly due to the introduction of melamine into the network of the polymers. The structure of the benzoxazines has been confirmed by proton nuclear magnetic resonance spectroscopy and fourier transform infrared spectroscopy. Thermal properties of polybenzoxazine have been studied by differential scanning calorimetry, dynamic mechanical analysis and thermogravimetric analysis. Transparent polybenzoxazine films were easily obtained under solvent-free conditions, exhibiting significantly improved toughness compared to the conventional polybenzoxazines. Our research may open a new path for overcoming the present drawbacks of polybenzoxazines such as high brittleness, the difficulties in preparing films and poor processibility via tailoring the structures and properties of amine in the benzoxazines.     

Novel polyimides with p-nitrophenyl pendant groups. Synthesis and characterization

Polyimides derived from a new dianhydride with p-nitrophenyl pendant groups have been synthesized and their properties compared with those of a reference series, without side groups. The polymers were obtained by combination of the novel monomer with aromatic diamines, in a two-step procedure that involved the synthesis of poly(amic acid) or poly(amic silyl ester) intermediates and the cyclization of them to polyimides by thermal treatment. The introduction of the polar nitro groups caused significant increase of the T_gs. On the contrary, the thermal stability was reduced because of the breakdown of C_Ar—NO₂ linkages around 400^oC. A slight decrease in mechanical properties was observed, due to the bulkiness of the side groups, that also produced an important decrease in the strength of the β relaxation, as determined by dynamic mechanical analysis. The solubility of the current polyimides in organic solvents was as poor as that of the parent unsubstituted polymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3377–3384, 1999     

ESR study on chemical crosslinking reaction mechanisms of polyethylene using a chemical agent. III. Effect of amine type antioxidants

The effect of antioxidant on the reaction mechanism of chemical crosslinking of polyethylene with dicumyl peroxide (DCP) at high temperatures was investigated by electron spin resonance (ESR). The crosslinking reactions were induced by the alkyl radicals in polyethylene (PE) formed by the thermal decomposition of DCP above 120°C. The type and the content of radicals were much changed for amine type antioxidants on PE crosslinking. It was confirmed that the radicals originated from DCP decomposition reacted preferentially with the amine type antioxidants to produce the nitroxyl radical and that the antioxidants retarded the initiation reaction of the PE crosslinking reaction. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 349–356, 1999     

Thermal characterization and solid‐state 13C‐NMR investigation of blends of poly(N‐phenyl‐2‐hydroxytrimethylene amine) and poly(N‐vinyl pyrrolidone)

The miscibility and thermal properties of poly(N‐phenyl‐2‐hydroxytrimethylene amine)/poly(N‐vinyl pyrrolidone) (PHA/PVP) blends were examined by using differential scanning calorimetry (DSC), high‐resolution solid‐state nuclear magnetic resonance (NMR) techniques, and thermogravimetric analysis (TGA). It was found that PHA is miscible with PVP, as shown by the existence of a single composition‐dependent glass transition temperature (T_g) in the whole composition range. The DSC results, together with the ¹³C crosspolarization (CP)/magic angle spinning (MAS)/high‐power dipolar decoupling (DD) spectra of the blends, revealed that there exist rather strong intermolecular interactions between PHA and PVP. The increase in hydrogen bonding and in T_g of the blends was found to broaden the line width of CH—OH carbon resonance of PHA. The measurement of the relaxation time showed that the PHA/PVP blends are homogeneous at least on the scale of 1–2 nm. The proton spin‐lattice relaxation in both the laboratory frame and the rotating frame were studied as a function of the blend composition, and it was found that blending did not appreciably affect the spectral densities of motion (sub‐T_g relaxation) in the mid‐MHz and mid‐KHz frequency ranges. Thermogravimetric analysis showed that PHA has rather good thermal stability, and the thermal stability of the blend can be further improved with increasing PVP content. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 237–245, 1999     

Cure kinetics modeling and thermomechanical properties of cycloaliphatic epoxy‐anhydride thermosets modified with hyperstar polymers

Hyperstar polymers (HSPs) with hyperbranched aromatic polyester core and arms consisting of block copolymers of poly(methyl methacrylate) and poly(hydroxyethyl methacrylate) have been used as polymeric modifiers in cycloaliphatic epoxy‐anhydride formulations catalyzed with tertiary amines, with the purpose of enhancing the impact strength of the resulting materials without compromising other thermal and mechanical properties.> In this work, the effect of these polymeric modifiers on the curing kinetics, processing, thermal‐mechanical properties and thermal stability has been studied using thermal analysis techniques such as DSC, TMA, DMA, and TGA. The morphology of the cured materials has been analyzed with SEM. The curing kinetics has been analyzed by isoconversional procedures and phenomenological kinetic models taking into account the vitrification during curing, and the degradation kinetics has been analyzed by means of isoconversional procedures, summarizing the results in a time‐temperature‐transformation (TTT) diagram. The results show that HSPs participate in the crosslinking process due to the presence of reactive groups, without compromising significantly their thermal‐mechanical properties. The modified materials show a potential toughness enhancement produced by the formation of a nano‐grained morphology. The TTT diagram is shown to be a useful tool for the optimization of the curing schedule in terms of curing completion and safe processing window, as well as for defining storage stability conditions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1227–1242     

Methylol‐functional benzoxazines as precursors for high‐performance thermoset polymers: Unique simultaneous addition and condensation polymerization behavior

A new class of high‐performance resins of combined molecular structure of both traditional phenolics and benzoxazines has been developed. The monomers termed as methylol‐functional benzoxazines were synthesized through Mannich condensation reaction of methylol‐functional phenols and aromatic amines, including methylenedianiline (4,4′‐diaminodiphenylmethane) and oxydianiline (4,4′‐diaminodiphenyl ether), in the presence of paraformaldehyde. For comparison, other series of benzoxazine monomers were prepared from phenol, corresponding aromatic amines, and paraformaldehyde. The as‐synthesized monomers are characterized by their high purity as judged from ¹H NMR and Fourier transform infrared spectra. Differential scanning calorimetric thermograms of the novel monomers show two exothermic peaks associated with condensation reaction of methylol groups and ring‐opening polymerization of benzoxazines. The position of methylol group relative to benzoxazine structure plays a significant role in accelerating polymerization. Viscoelastic and thermogravimetric analyses of the crosslinked polymers reveal high T_g (274–343 °C) and excellent thermal stability when compared with the traditional polybenzoxazines. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012