Silicon‐containing benzoxazines and their polymers: Copolymerization and copolymer properties

A silicon‐containing benzoxazine BATMS‐Bz (1,3‐bis(3‐aminopropyl)tetramethyldisiloxane‐benzoxazine) was used for polybenzoxazine modification by means of formation of benzoxazine copolymers with 3,4‐dihydro‐3‐phenyl‐2H‐1,3‐benzoxazine (Ph‐Bz) and 3‐furfuryl‐3,4‐dihydro‐2H‐1,3‐benzoxazine (F‐Bz), respectively. Ph‐Bz/BATMS‐Bz copolymers showed a positive deviation due the presence of intermolecular hydrogen bonding. However, this effect was not observed with F‐Bz/BATMS‐Bz copolymers. Meanwhile, BATMS‐Bz incorporation exhibited significant effect on toughening polybenzoxazines. It is therefore demonstrated that BATMS‐Bz is a high performance modifier to simultaneously enhance the T_g and toughness of polybenzoxazines. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1007–1015, 2007     

Diethylphosphonate‐containing benzoxazine compound as a thermally latent catalyst and a reactive property modifier for polybenzoxazine‐based resins

A diethylphosphonate‐containing benzoxazine compound (DEP‐Bz) to be used as a multi‐functional reaction agent for preparation of high performance polybenzoxazine thermosetting resins has been reported. The chemical structure of DEP‐Bz has been characterized with FTIR, ¹H NMR, and elemental analysis. The phosphonate groups of DEP‐Bz could convert into phosphonic acid groups which could catalyze the ring‐opening addition reaction of benzoxazines, to demonstrate the thermally latent catalytic effect of DEP‐Bz on the polymerization of benzoxazine compounds. Moreover, DEP‐Bz could also serve as a reactive‐type modifier for polybenzoxazines and other thermosets. DEP‐Bz modified polybenzoxazine resins have shown relatively low reaction temperature (about 190 °C), high mechanical strength with a storage modulus of about 3.0 GPa, and high flame retardancy with a limit oxygen index of about 32. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3523–3530     

Synthesis and study of the thermal crosslinking of bis(m‐aminophenyl) methylphosphine oxide based benzoxazine

Bis(m‐aminophenyl)methylphosphine oxide based benzoxazine (Bz‐BAMPO) was obtained using a three‐step synthetic method from the aromatic diamine and 2‐hydroxybenzaldehyde as starting materials. The structure and purity of the monomer was confirmed by elemental analysis, FTIR, ¹H NMR, ¹³C NMR and ³¹P NMR spectra. The curing kinetics of Bz‐BAMPO was investigated by nonisothermal differential scanning calorimetry (DSC) at different heating rates and by FTIR spectroscopy. The isoconversional method was used to evaluate the dependence of the effective activation energy on the extent of conversion. The evolving factor analysis (EFA) method was applied to the spectroscopic FTIR data obtained in monitoring benzoxazine homopolymerizations. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7162–7172, 2008     

Synthesis of novel tri‐benzoxazine and effect of phenolic nucleophiles on its ring‐opening polymerization

A trifunctional benzoxazine, 1,3,5‐tris(3‐phenyl‐3,4‐dihydro‐2H‐benzo[1,3]oxazin‐6‐yl)benzene (T‐Bz) was synthesized and in an effort to reduce its curing temperature (curing maxima at 238 °C), it was mixed with various phenolic nucleophiles such as phenol (PH), p‐methoxy phenol (MPH), 2‐methyl resorcinol (MR), hydroquinone (HQ), pyrogallol (PG), 2‐naphthol (NPH), 2,7‐dihydroxy naphthalene (DHN), and 1,1'‐bi‐2‐naphthol (BINOL). The influence of these phenolic nucleophiles on ring‐opening polymerization temperature of T‐Bz was examined by DSC and FTIR analysis. T‐Bz undergoes a complete ring‐opening addition reaction in the presence of bi‐ and trifunctional phenolic nucleophiles (MR/HQ/PG/DHN) at 140 °C (heated for 3 h) and forms a networked polybenzoxazine (NPBz). The NPBzs showed a high thermal stability with T_d20 of 350–465 °C and char yield of 67–78% at 500 °C; however, a diminutive weight loss (6.9–9.8%) was observed at 150–250 °C (T_d5: 215–235 °C) due to degradation of phenolic end groups. This article also gives an insight on how the traces of phenolic impurities can alter the thermal properties of pure benzoxazine monomer as well as its corresponding polymer. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2811–2819     

Polybenzoxazines from renewable diphenolic acid

The novel benzoxazine monomers, DPA‐Bz and MDP‐Bz from renewable diphenolic acid (DPA), which mimics the structure of bisphenol A (BPA), were synthesized by traditional approaches. The structure and purity of the monomers was confirmed by FTIR, ¹H NMR, and ¹³C NMR spectra. The thermally activated polymerization of the MDP‐Bz and DPA‐Bz afforded thermosetting polybenzoxazines with higher T_g's, 270 °C and 208 °C respectively, and higher crosslinking density compared to BPA‐Bz, due to the transesterification or esterification reactions occurred during curing process. These reactions are in accordance with the number of independent reactions determined analyzing by SVD the chemical rank of the IR spectra data matrices recorded along the homopolymerization reactions monitored at 200 °C. Spectral and concentration profiles of the active chemical species involved in these processes were obtained by MCR‐ALS. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Highly thermal conductive benzoxazine‐epoxy interpenetrating polymer networks containing liquid crystalline structures

A diamine‐based benzoxazine monomer (Bz) and a liquid crystalline epoxy monomer (LCE) are synthesized, respectively. Subsequently, a benzoxazine‐epoxy interpenetrating polymer network (PBEI) containing liquid crystalline structures is obtained by sequential curing of the LCE and the Bz in the presence of imidazole. The results show that the preferential curing of LCE plays a key role in the formation mechanism of liquid crystalline phase. Due to the introduction of liquid crystalline structures, the thermal conductivity of PBEI increases with increasing content of LCE. When the content of LCE is 80 wt %, the thermal conductivity reaches 0.32 W m^?1 K^?1. Additionally, the heat‐resistance of PBEI is superior to liquid crystalline epoxy resin. Among them, PBEI55 containing equal weight of Bz and LCE has better comprehensive performance. Its thermal conductivity, glass transition temperature, and the 5 % weight loss temperature are 0.28 W m^?1 K^?1, 160 °C, and 339 °C, respectively. By introducing boron nitride (BN) fillers into PBEI55, a composite of PBEI/BN with the highest thermal conductivity of 3.00 W m^?1 K^?1 is obtained. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1813–1821     

A novel benzimidazole moiety‐containing benzoxazine: Synthesis,polymerization, and thermal properties

A novel benzoxazine‐containing benzimidazole moiety (P‐PABZ) was synthesized from 2‐(4‐aminophenyl)‐1H‐benzimidazole‐5‐amine and characterized. With the aid of differential scanning calorimetry and in situ Fourier transform infrared, we found the thermal polymerization of P‐PABZ in bulk started around 140 °C and its favored polymerization pathway. Compared to the benzoxazine derived from 4,4′‐diamine diphenyl methane (P‐MDA), P‐PABZ exhibited lower processing temperature, and the corresponding polymers had higher glass transition temperature and enhanced thermal stability. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Polyaddition of bifunctional 1,3‐benzoxazine and 2‐methylresorcinol

A polyaddition system consisted of a bifunctional N‐n‐propyl benzoxazine and 2‐methylresorcinol ( MR ) that proceeds at ambient temperature has been developed. In this system, the aromatic ring of MR acted as a bifunctional monomer, reacting with a two equivalent amount of benzoxazine moieties via their ring‐opening reaction. The polyaddition gave the corresponding linear polymer bearing phenolic moieties bridged by Mannich‐type linkage in the main chain. The linear polymer had a high glass transition temperature, which was comparable to that of the linear polybenzoxazine synthesized by the ring‐opening polymerization of a monofunctional N‐n‐propyl benzoxazine. The employment of a bifunctional N‐allyl benzoxazine in the polyaddition system resulted in the formation of the corresponding polymer with allyl pendants, which exhibited improved heat resistance due to its thermally induced crosslinking reaction. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3867–3872     

Hydrogen‐bonding characteristics and unique ring‐opening polymerization behavior of Ortho‐methylol functional benzoxazine

Monofunctional benzoxazine with ortho‐methylol functionality has been synthesized and highly purified. The chemical structure of the synthesized monomer has been confirmed by ¹H and ¹³C nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT‐IR) and elemental analysis. One‐dimensional (1D) ¹H NMR is used with respect to varied concentration of benzoxazines to study the specific nature of hydrogen bonding in both ortho‐methylol functional benzoxazine and its para counterpart. The polymerization behavior of benzoxazine monomer has been also studied by in situ FT‐IR and differential scanning calorimetry, experimentally supporting the polymerization mechanism of ortho‐methylol functional benzoxazine we proposed before. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3635–3642     

Synthesis of polybenzoxazine/clay nanocomposites by in situ thermal ring‐opening polymerization using intercalated monomer

A new class of polybenzoxazine/montmorillonite (PBz/MMT) nanocomposites has been prepared by the in situ polymerization of the typical fluid benzoxazine monomer, 3‐pentyl‐5‐ol‐3,4‐dihydro‐1,3‐benzoxazine, with intercalated benzoxazine MMT clay. A pyridine‐substituted benzoxazine was first synthesized and quaternized by 11‐bromo‐1‐undecanol and then used for ion exchange reaction with sodium ions in MMT to obtain intercalated benzoxazine clay. Finally, this organomodified clay was dispersed in the fluid benzoxazine monomers at different loading degrees to conduct the in situ thermal ring‐opening polymerization. Polymerization through the interlayer galleries of the clay led to the PBz/MMT nanocomposite formation. The morphologies of the nanocomposites were investigated by both X‐ray diffraction and transmission electron microscopic techniques, which suggested the partially exfoliated/intercalated structures in the PBz matrix. Results of thermogravimetric analysis confirmed that the thermal stability and char yield of PBz nanocomposites increased with the increase of clay content. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of polymers bearing 1,3‐benzoxazine moiety in the side chains from poly(allylamine) and their crosslinking behaviors

A polymer bearing 1,3‐benzoxazine moiety in the side chain was synthesized successfully from poly(allylamine) based on a stepwise strategy consisted of three steps: (1) treatment of poly(allylamine) with salicylaldehyde to convert the amino group in the side chain into the corresponding o‐(iminomethyl)phenol moiety, (2) reduction of the o‐(iminomethyl)phenol to obtain the corresponding o‐(aminomethyl)phenol moiety, and (3) formation of 1,3‐benzoxazine moiety by the reaction of the o‐(aminomethyl)phenol with formaldehyde. The content ratio of benzoxazine moieties and o‐(aminomethyl)phenol moieties in the polymer were tunable by varying amount of formaldehyde. The presence of o‐(aminomethyl)phenol moieties exhibited a significant promoting effect on the crosslinking reaction. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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     

Synthesis of high thermal stability polybenzoxazoles via ortho‐imide‐functional benzoxazine monomers

We report our work for preparing cross‐linked polyimide via a series of imide functional benzoxazine resins as precursors. The structures of synthesized monomers have been confirmed by ¹H NMR and FT‐IR. Among this class of benzoxazine monomers, the ortho‐imide functional benzoxazine resins show useful features both in the synthesis of benzoxazine monomers and the properties of the corresponding thermosets. For the cross‐linked polyimides based on ortho‐imide functional benzoxazine, an additional route is adopted to form a more thermally stable cross‐linked polybenzoxazole with the release of carbon dioxide. The ortho‐imide functional benzoxazine resins show the possibility to form high performance and even super high performance thermosets with low cost and easy processability. The thermal properties are evaluated by DSC and TGA. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1330–1338     

Carboxylic acid‐containing benzoxazines as efficient catalysts in the thermal polymerization of benzoxazines

The autocatalytic thermal polymerization behavior of three benzoxazine monomers containing carboxylic acid functionalities is reported. Several mixtures of these carboxylic monomers and 3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine were prepared and their thermal polymerization behavior was analyzed by differential scanning calorimetry. The acid character of these reactive monomers increases the concentration of oxonium species, thus catalyzing the benzoxazine ring opening reaction. In this way the polymerization temperature decreased by as much as 100 °C in some cases. The existence of decarboxylation processes at high temperatures has been established by FTIR‐ATR and related to the increase in thermal stability observed by TGA in some cases. A relationship between the presence of carboxylic groups in the resulting materials and their flame retardancy behavior has also been established. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6091–6101, 2008     

Acceleration effect of N‐allyl group on thermally induced ring‐opening polymerization of 1,3‐benzoxazine

Thermally induced ring‐opening polymerization of monofunctional N‐allyl‐1,3‐benzoxazine 1a was compared with that of N‐(n‐propyl)‐1,3‐benzoxazine 1b to clarify an unexpected effect of allyl group to promote the polymerization, that is, in spite of the comparable bulkiness of allyl group to n‐propyl group, the polymerization of 1a was much faster than that of 1b . Such a difference in polymerization rate was also observed similarly in the comparison of thermally induced polymerization of a bifunctional N‐allyl‐benzoxazine 2a with that of a bifunctional N‐(n‐propyl) analogue 2b . These observations implied a certain contribution of an electron‐rich C? C double bond of the N‐ally group to promotion of the ring‐opening reaction of 1,3‐benzoxazine into the corresponding zwitterionic species, which would involve a mechanism to stabilize the cationic part of the zwitterionic species based on “neighboring group participation” of the C? C double bond. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and crosslinking reaction of a novel polymer containing benzoxazine and phenyleneethynylene moieties in the main chain

A novel polymer, poly( 1 ) containing benzoxazine and phenyleneethynylene moieties in the main chain with number‐average molecular weights ranging from 1400 to 9800 was obtained quantitatively by the Sonogashira–Hagihara coupling polymerization of the corresponding iodophenyl‐ and ethynylphenyl‐substituted monomer 1 . Poly( 1 ) was heated at 200 °C under N₂ for 2 h to obtain the cured polymer, poly( 1 )′ via the ring‐opening polymerization of the benzoxazine moieties. The structures of the polymer before and after curing were confirmed by ¹H‐NMR, IR, and UV–vis absorption and reflectance spectroscopies. Poly( 1 )′ was thermally more stable than monomer 1 and poly( 1 ). A specimen was prepared from a mixture of poly( 1 ) and phenol‐diaminodiphenylmethane type benzoxazine 2 by heating at 200 °C for 2 h under N₂. The poly( 1 )/ 2 resin was thermally stable than bisphenol‐A type benzoxazine resin 3 . Poly( 1 ) exhibited XRD peaks corresponding to the d‐spacings of 1.26–0.98 and 0.40 nm, assignable to the repeating monomer unit and alignment of polymer molecules, respectively. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2581–2589     

Thermally curable polyvinylchloride via click chemistry

Novel side‐chain benzoxazine functional polyvinylchloride (PVC‐Benzoxazine) was synthesized by using “Click Chemistry” strategy. First, approximately 10% of chloro groups of PVC were converted to azido groups by using NaN₃ in N,N‐dimethylformamide. Propargyl benzoxazine was prepared independently by a ring closure reaction between p‐propargyloxy aniline, paraformaldehyde, and phenol. Finally, azidofunctionalized PVC was coupled to propargyl benzoxazine with high efficiency by click chemistry. The spectral and thermal analysis confirmed the presence of benzoxazine functionality in the resulting polymer. It is shown that PVC containing benzoxazine undergoes thermally activated curing in the absence of any catalyst forming PVC thermoset with high thermal stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3512–3518, 2008     

Thermally curable benzoxazine monomer with a photodimerizable coumarin group

A new monomer, 4‐methyl‐9‐p‐tolyl‐9,10‐dihydrochromeno[8,7‐e][1,3]oxazin‐2(8H)‐one, possessing both benzoxazine and coumarin rings in its structure was synthesized by the reaction of 4‐methyl‐7‐hydroxycoumarin, paraformaldehyde, and p‐toluidine in methanol at 40 °C and characterized with spectral analysis. Upon photolysis around 300 nm, this monomer underwent dimerization via the [2πs+2πs] cycloaddition reaction. Photodimerization reactions were investigated with UV and ¹H NMR spectroscopy measurements. The thermal ring‐opening reaction of the benzoxazine ring was demonstrated with differential scanning calorimetry measurements. The thermal behavior of the cured product was also investigated with thermogravimetric analysis. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1670–1676, 2007     

Promoting effect of thiophenols on the ring‐opening polymerization of 1,3‐benzoxazine

Thiophenol and p‐nitrothiophenol were evaluated as promoters for the ring opening polymerization of benzoxazine. The ring‐opening polymerization of p‐cresol type monofunctional N‐phenyl benzoxazine 1a with 10 mol % of thiophenols proceeded at 150 °C, leading to the high conversion of 1a more than 95% within 5 h, whereas the polymerization of 1a without thiophenols did not proceed under the same conditions. The promotion effect of the thiophenols on curing of bisphenol‐A type N‐phenyl benzoxazine 1b was also investigated. In the differential scanning calorimetric (DSC) analysis of the polymerization of 1b at 150 °C without using any promoters, an exothermic peak attributable to the ring‐opening reaction of benzoxazine was observed after 8 h. In contrast, in the DSC analysis of the polymerization of 1b with addition 20 mol % of p‐nitrothiophenol, an exothermic peak was observed within 2 h, to clarify the significant promoting effect of p‐nitrothiophenol. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2523–2527     

BF3·OEt2 in alcoholic media,an efficient initiator in the cationic polymerization of phenyl‐1,3‐benzoxazines

3‐Phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine ( m ₁ ) underwent cationic ring opening polymerization using BF₃·OEt₂ in alcoholic solution under mild conditions. The polymerization of m ₁ proceeds through an intermediate hemiaminal ether leading mainly to the formation of polybenzoxazines with diphenylmethane bridges, and not only the classical Mannich‐type ones. During the first stages of the reaction, low‐molecular weight soluble oligomers containing benzoxazine rings are formed. At longer polymerization times, the propagation proceeds conventionally through the phenolic active sites. This polymerization mechanism is extensible to other substituted 3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazines but fails in the case of 3‐alkyl‐3,4‐dihydro‐2H‐1,3‐benzoxazines or when the phenyl group in Position 3 have a substituent in the p‐position. Spectroscopic studies and kinetic experiments using model reactions and deuterium labeled benzoxazines, allow proposing a plausible different polymerization mechanism. These soluble benzoxazine‐containing polymers can be conveniently processed and impregnated on appropriate substrates before underwent crosslinking producing materials with comparable properties to those of conventional bis‐benzoxazines. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5075–5084