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     

Study of hydrogen bonding and thermal properties of polybenzoxazine and poly‐(ε‐caprolactone) blends

The thermal properties of physical blends containing benzoxazine monomer and polycaprolactone (PCL) were monitored by DSC and Fourier transform infrared spectroscopy (FTIR). The ring‐opening reaction and subsequent polymerization reaction of the benzoxazine were facilitated significantly by the presence of a PCL modifier. Hydrogen‐bond formation between the hydroxyl groups of polybenzoxazine and the carbonyl groups of PCL was evident from the FTIR spectra. Only one glass‐transition temperture (T_g) value was found in the composition range investigated, and the T_g value of the resulting blend appeared to be higher in the blend with a greater amount of PCL. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 736–749, 2001     

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     

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     

Ring opening polymerization of epoxides with urea‐derivatives of 4‐aminopyridine as thermally latent anionic initiator

In this study, a series of urea‐derivatives of 4‐aminopyridine (4AP) were evaluated as thermally latent initiators for the anionic ring‐opening polymerization of diglycidyl ether of bisphenol A (DGEBA). The urea‐derivatives were synthesized by the reactions of 4AP with the corresponding iso(thio)cyanates (phenyl isocyanate, tert‐butyl isocyanate, methylene diphenyl diisocyanate, and phenyl isothiocyanate). The ability of the urea‐derivatives as latent initiators was investigated with differential scanning calorimetry (DSC): Upon heating formulations comprised of DGEBA and the urea‐derivatives in a heating rate at 10 °C/min, the resulting DSC profiles indicated exothermic peaks to confirm that DGEBA underwent the polymerization efficiently. The corresponding DSC‐peak top temperatures (T_{peak top}) was higher than that observed for the formulation comprised of DGEBA and pristine 4AP, to clarify that the urea are useful initiators with thermal latency. A possible mechanism for the initiation step involves the thermal dissociation of the urea into 4AP and the corresponding isocyanates. 4AP thus generated readily initiated the ring‐opening polymerization of epoxide. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2518–2522     

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     

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     

Functional 1,3‐benzoxazine bearing 4‐pyridyl group: Synthesis and thermally induced polymerization behavior

1,3‐benzoxazine 1 , bearing 4‐pyridyl moiety on the nitrogen atom, was synthesized from p‐cresol, 4‐aminopyridine, and paraformaldehyde. The efficient synthesis was achieved by adding acetic acid to suppress the strong basicity caused by the presence of 4‐aminopyridine derivatives. Upon heating 1 at 180 °C, it underwent the thermally induced ring‐opening polymerization. The resulting polymer was composed of two types of repeating unit, i.e., (1) Mannich‐type one (‐phenol‐CH₂‐NR‐CH₂‐) that can be expected from the general ring‐opening polymerization of conventional benzoxazines and (2) a typical phenolic resin‐type one (‐phenol‐CH₂‐phenol‐) induced by release of 4‐aminopyridine and paraformaldehyde (unit B). Another structural feature of the polymer was that it possessed a benzoxazine moiety at the chain end. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 410–416     

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 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     

Ring‐opening polymerization of L‐lactide by rare‐earth tris(4‐tert‐butylphenolate) single‐component initiators

The ring‐opening polymerization of L ‐lactide initiated by single‐component rare‐earth tris(4‐tert‐butylphenolate)s was conducted. The influences of the rare‐earth elements, solvents, temperature, monomer and initiator concentrations, and reaction time on the polymerization were investigated in detail. No racemization was found from 70 to 100 °C under the examined conditions. NMR and differential scanning calorimetry measurements further confirmed that the polymerization occurred without epimerization of the monomer or polymer. A kinetic study indicated that the polymerization rate was first‐order with respect to the monomer and initiator concentrations. The overall activation energy of the ring‐opening polymerization was 79.2 kJ mol^?1. ¹H NMR data showed that the L ‐lactide monomer inserted into the growing chains with acyl–oxygen bond cleavage. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6209–6215, 2004     

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     

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     

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     

Functional benzoxazines containing ammonium salt of carboxylic acid: Synthesis and highly activated thermally induced ring‐opening polymerization

1,3‐Benzoxazine monomers having ammonium salt of carboxylic acid have been developed. These 1,3‐benzoxazines 1a and 1b were easily synthesized from the corresponding tetrabutylammonium salts of glycine and β‐alanine, respectively. The glycine‐derived benzoxazine 1a exhibited remarkably high reactivity, which allowed its thermally induced ring‐opening polymerization in bulk at 100 °C, at which N‐methyl‐1,3‐benzoxazine 1d did not undergo the polymerization at all. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Ring‐opening polymerization of 1,4‐dioxan‐2‐one initiated by lanthanum isopropoxide in bulk

Lanthanum isopropoxide (La(OiPr)₃) has been synthesized and employed for ring‐opening polymerization of 1,4‐dioxan‐2‐one in bulk as a single‐component initiator. The influences of reaction conditions such as initiator concentration, reaction time, and reaction temperature on the polymerization were investigated. The kinetics indicated that the polymerization is first‐order with respect to the monomer concentration. The Mechanistic investigations according to ¹H NMR spectrum analysis demonstrated that the polymerization of PDO proceeded through a coordination‐insertion mechanism with a rupture of the acyl‐oxygen bond of the monomer rather than the alkyl‐oxygen bond cleavage. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5214–5222, 2008     

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     

Synthesis,characterization, and polymerization of brominated benzoxazine monomers and thermal stability/flame retardance of the polymers generated

Novel monofunctional brominated benzoxazine 3‐(2,4,6‐tribromophenyl)‐3,4‐dihydro‐2H‐1,3‐benzoxazine (P‐bra) and bifunctional brominated benzoxazine 6,6′‐bis(3‐(2,4,6‐tribromophenyl)‐3,4‐dihydro‐2H‐1,3‐benzoxazinyl) isopropane (B‐bra) were prepared and highly thermally stable polybenzoxazines were obtained by the thermal cure of the corresponding benzoxazines monomers. The chemical structures of these novel monomers were confirmed by FITR, ¹H‐NMR and elemental analysis. FTIR spectra and differential scanning calorimetry (DSC) suggested that the polymerization was thermally initiated and occurred via ring‐opening of the monomer in each case. Thermogravimetric analysis (TGA) indicated that brominatation could have a profound effect on increasing char yield and on thermal degradation temperatures. The results of UL‐94 burn test showed that the polybenzoxazines prepared from P‐bra and B‐bra had good flame retardance. Copyright © 2009 John Wiley & Sons, Ltd.     

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     

Synthesis and characterization of poly(urethane‐benzoxazine) films as novel type of polyurethane/phenolic resin composites

Poly(urethane‐benzoxazine) films as novel polyurethane ( PU )/phenolic resin composites were prepared by blending a benzoxazine monomer ( Ba ) and PU prepolymer that was synthesized from 2,4‐tolylene diisocyanate (TDI) and polyethylene adipate polyol (MW ca. 1000) in 2 : 1 molar ratio. DSC of PU/Ba blend showed an exotherm with maximum at ca. 246 °C due to the ring‐opening polymerization of Ba, giving phenolic OH functionalities that react with isocyanate groups in the PU prepolymer. The poly(urethane‐benzoxazine) films obtained by thermal cure were transparent, with color ranging from yellow to pale wine with increase of Ba content. All the films have only one glass transition temperature (T_g ) from viscoelastic measurements, indicating no phase separation in poly(urethane‐benzoxazine) due to in situ polymerization. The T_g increased with the increase of Ba content. The films containing 10 and 15% of Ba have characteristics of an elastomer, with elongation at break at 244 and 182%, respectively. These elastic films exhibit good resilience with excellent reinstating behavior. The films containing more than 20% of Ba have characteristics of plastics. The poly(urethane‐benzoxazine) films showed excellent resistance to the solvents such as tetrahydrofuran, N,N‐dimethyl formamide, and N‐methyl‐2‐pyrrolidinone that easily dissolve PU s. Thermal stability of PU was greatly enhanced even with the incorporation of a small amount of Ba . © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4165–4176, 2000