Ring-opening Polymerization Temperature Research Articles

Metal salts used as an efficient catalyst to reduce the ring opening polymerization temperature of benzoxazines

An attempt was made to develop low-temperature curing aniline-based benzoxazines (BA-a/BF-a) using various transition metal salts, such as FeCl3, CoCl2, NiBr2, CuCl2, ZnCl2, Zn(OAc)2, CdCl2 and Alkali–Alkaline earth metal salts, such as LiCl, KI and CaCl2 and main group metal salt AlCl3 as an efficient catalyst. The findings of the DSC analysis revealed that the main group and transition metal salts had outstanding catalytic activity and were able to reduce the curing temperature of benzoxazines (BA-a/BF-a). Among the various metal salts, FeCl3, AlCl3, ZnCl2 and Zn(OAc)2 exposed excellent catalytic behavior in lowering the curing temperature of benzoxazines to 145 °C (BA-a) and 150 °C (BF-a) from 217 to 218 °C, respectively. The thermal stability and flame retardant characteristics of the resultant polybenzoxazines (PBz’s), are also studied and included in this work. In the presence of catalysts, the initial degradation temperature almost same, residual char yield increased from 27 to 55%, and the flame retardant properties increased to 39.5 from 28.5 for the resultant PBz’s.

Understanding the Stereochemical Effect on the Properties of Emerging Thermosets: Sustainable Polybenzoxazines

Exploration of the properties of monomers by modulating their stereochemistry is not well reported in polybenzoxazines (PBzs). Isosorbide contains a rigid bicyclic (endo–exo-configuration) core that has shown promise in high-performance thermoplastic polymers. In this report, new chiral PBzs were prepared from industrially available feedstocks, carbohydrate-derived (isosorbide), and lignin- or cashew nut waste-sourced renewable phenols (cardanol and guaiacol). A fully biobased benzoxazine monomer based on a one-step condensation reaction of isosorbide diamine (isa) with phenols was carried out for 15 min under microwave and solvent- and catalyst-free conditions. Structural elucidation of monomers was achieved by two-dimensional (2D) NMR spectroscopy [heteronuclear single quantum correlation (HSQC) and COSY (correlated spectroscopy)]. The “isa”-based monomer revealed a comparable ring-opening polymerization temperature and a good processing window for the widely available bisphenol-A/aniline-based monomer. The resultant polymers showed a higher Tg, better thermomechanical properties, and adhesive strength compared to other classical petrobased PBzs. The current work extends the importance of the major component of the sugar-derived isohexide family member, isosorbide, in polybenzoxazine chemistry and suggests that stereocontrol in the monomer is another approach to affect the thermomechanical properties of this upcoming class of high-performance phenolic polymer.

Synthesis, Dynamic Mechanical Properties, and Shape Memory Effect of Poly(benzoxazine‐ether‐urethane)s

AbstractTwo series of poly(benzoxazine‐ether‐urethane)s (PBEUs) are prepared through thermally activated ring‐opening polymerization (ROP) of bi‐functional benzoxazines containing ether‐urethane moieties. The bi‐functional benzoxazines are synthesized through coupling reaction of hydroxyl‐containing mono‐functional monomers based on phenol,o‐allylphenol,o‐cresol,p‐cresol, diglycolamine, and paraformaldehyde with 1,6‐hexamethylene diisocyanate (HDI) and 2,4‐toluene diisocyanate (TDI), respectively. The ROP temperature of each HDI‐based benzoxazine is higher than that of the counterpart based on TDI, and they are in descending orderortho‐,para‐, and unsubstituted phenol for both series. Due to the difference in structure symmetry between the two series monomers, the variation of polymerization rate with temperature of each TDI‐based benzoxazine is different from that of the counterpart based on HDI. Theortho‐ andpara‐substituted‐phenol‐based PBEUs show lower glass transition temperatures than that of the phenol‐based counterpart. In the vicinity of the glass transition temperature, the HDI‐based PBEUs exhibit thermally induced one‐way dual‐shape memory effect.

Synthesis and properties of corresponding polymers of urushiol-based benzoxazine monomers modified by silane

Polybenzoxazine, a new kind of phenolic materials, have the properties of dimensional and thermal stability and do not release any by-products during its curing process, so polybenzoxazine has shown potential for anti-corrosion coating application. In this study, urushiol, a natural phenol obtained from lacquer, was successfully utilized to synthesize a novel urushiol-benzoxazine monomer (UB) via Mannich-like condensation with paraformaldehyde and triethylenetetramine, then the novel benzoxazine monomers were modified by γ-(2,3-epoxypropoxy)propytrimethoxysilane, the structures of UB and urushiol-benzoxazine modified by silane (UBSi) were characterized by Fourier transform infrared spectroscopy (FT-IR) and 1H NMR spectroscopy, and the results of differential scanning calorimetry (DSC) indicated that the ring-opening polymerization temperature of the benzoxazine modified by silane occurred at approximately 210 °C, lower than that of unmodified benzoxazine. Thermal gravimetric analysis (TGA) measurements showed that the temperatures corresponding to 10 and 50% weight loss (T10 and T50) of UB were 354 and 417 °C, respectively; however, the corresponding values of UBSi were 377 and 436 °C. Strain-stress tests indicated that the failure values of strain and stress of UB were 17.27% and 11.45 Mpa, and the corresponding values of UBSi were 14.82% and 12.21 Mpa, respectively. The water absorption of UB curing coating is 3.75%, while that of UBSi30 curing coating drops to 1.27%.

Unique self-catalyzed bio-benzoxazine derived from novel renewable acid-containing diamines based on levulinic acid and furfurylamine: Synthesis, curing behaviors and properties

4,4-bis[5-(aminomethyl)furan-2-yl]pentanoic acid (BAFP), brand new renewable acid-containing diamines, was first utilized as feedstock for preparing fully biomass-based benzoxazine with self-catalytic characteristic. The resulting acid-containing bio-benzoxazine was prepared through Schiff base strategy. The onset ring-opening polymerization temperature of resulting benzoxazine is 173 °C determined by DSC, much lower than that of analogous bisfurfurylamine-based biobenzoxazine free of carboxylic group. The curing kinetics of as-prepared benzoxazine was probed by non-isothermal DSC method. The curing reaction consisted of three stages with overlapped regions with each other. The first stage was ascribed to initiation reaction triggered by protons of acid, with a activation energy of 116.9 KJ/mol calculated by Flynn-Wall-Ozawa method; the second stage was named combination-catalyzed stage for the fact that acid proton and phenolic proton was co-catalyzed the chain propagation, with a activation energy of 118.0 KJ/mol; The third stage was diffusion-controlled curing reaction with a activation energy of 137.3 KJ/mol. More interesting, the calculated apparent activation energy of three reactions decreased with the increase of monomer conversion.

Promoting ring-opening polymerization of benzoxazine and its thermal property through incorporation of pyrogallol-based benzoxazines

Both pyrogallol-furfurylamine-based and pyrogallol-aniline-based di-benzoxazines (PG-FA and PG-A) possess a free hydroxyl and latent catalytic characteristics. To decrease the ring-opening polymerization (ROP) temperature of benzoxazine based on phenol and 4,4′-diaminodiphenylmethane (P-DDM) and increase simultaneously thermal property of its polymer, PG-FA and PG-A as catalysts were introduced into P-DDM. DSC and FTIR tests were used to investigate the effect of PG-FA and PG-A on the ROP of P-DDM; DMA, FTIR and TGA were performed to study their effects on the hydrogen bonds and thermal property of the cured P-DDM (PP-DDM). The results indicate that the ROP temperature of P-DDM remarkably decreased with the incorporation of PG-FA and PG-A. FTIR and DMA results illustrate that the total amounts of hydrogen bonds in PP-DDM increased with the addition of PG-FA or PG-A; however, its fraction of –OH⋯N (intra) and O−⋯+HN (intra) hydrogen bonds decreased. The decrease in –OH⋯N hydrogen bonds made the cross-linked density of polybenzoxazine increase, resulting in that the thermal stability of PP-DDM enhanced with the introduction of PG-FA and PG-A.

Synthesis and characterization of novel mussel-inspired benzoxazines bythiol-benzoxazine chemistry

A catechol-based benzoxazine copolymer is reported via a new approach using an oxazine-thiol reaction. The main chain benzoxazine precursor was obtained via the classic benzoxazine synthesis methodology using the raw chemicals catechol, formaldehyde, and 4,7,10-trioxa-1,13-tridecanediamine. The countercomponent was synthesized from poly(ethylene glycol) methyl ether via the Fischer esterification reaction. The obtained reactive catechol-based benzoxazine was then reacted in mild conditions with polymeric thiol precursor to obtain a copolymer structure. The precursors and the resulting structure were characterized by thermal and spectral analyses using DSC, TGA, FT-IR,$^{\, 1}$H NMR, and GPC. Film formation was also demonstrated with unreacted oxazine ring units in the copolymer, and the ring opening polymerization temperature was lower than that corresponding to the benzoxazine precursor.

Sustainable Framework of Chitosan–Benzoxazine with Mutual Benefits: Low Curing Temperature and Improved Thermal and Mechanical Properties

Polybenzoxazines (PBzs) are emerging as a highly promising and superior class of thermoset polymers for a variety of applications. However, it remains a significant challenge to substantially lower the ring-opening polymerization (ROP) temperature with an ease in processability. On the other hand, biomacromolecule chitosan (CS) is explored extensively, but its practical applications have been precluded by poor thermal and mechanical properties. Here, we developed a fully biobased copolymer of vanillin benzoxazine (V-fa) monomer with CS, which is effective in providing mutual benefits, effective lowering in ROP temperature of benzoxazine (70 °C), and an enhanced thermal stability of CS (by 85 °C, and with char yield of ∼32%). To understand this unusual lowering in ROP temperature, we investigated the structural interaction mechanism between solvated CS and V-fa using in situ NMR studies. The analysis of fully intercalated co-structure demonstrated that there is a strong preference for ROP over Schiff base ...

Counterion Effect of Amine Salts on Ring‐Opening Polymerization of 1,3‐Benzoxazines

AbstractThe effect of nucleophilicity of counterions of amine HX salts as catalysts on the ring‐opening polymerization (ROP) of 1,3‐benzoxazines is investigated. The significant reduction observed for the ROP temperature is related to the nucleophilicity of counterions and found to show a general trend as I− > Br− > Cl−, as studied by differential scanning calorimetry and Fourier transform infrared spectroscopy. Moreover, the latent character of the amine salts is also demonstrated by tracking the benzoxazine–amine salt mixtures using 1H NMR spectroscopy. The spectral analysis gives evidences for the dormant nature of the amine HX salts toward benzoxazine at room temperature in solvent. Besides, thermal stabilities of the cured benzoxazine monomers with and without catalysts are investigated by thermogravimetric analysis.

Ring-Opening Polymerization of 1,3-Benzoxazines via Borane Catalyst.

Tris(pentafluorophenyl)borane was used as Lewis acid catalyst to lower the ring opening polymerization temperature (ROP) of 1,3-benzoxazines. Dynamic scanning calorimeter studies revealed that on-set ROP temperatures were decreased as much as 98 °C for model benzoxazine compounds. Catalytic polymerization was traced by both FTIR and 1H NMR, and revealed that tris(pentafluorophenyl)borane acted rapidly and fast curing achieved. Moreover, thermal properties of resulting polybenzoxazines were investigated by thermogravimetric analysis (TGA) and found out that the catalyst has high impact on char yield and even 3 mol % catalyst augmented char yields up to 13%.

Ammonium salt catalyzed ring-opening polymerization of 1,3-benzoxazines

The effect of amine HCl salts as catalysts on the ring-opening polymerization (ROP) of simple 1,3-benzoxazines was investigated. The catalyst effects on the structure of the final polymer was examined and compared. The curing process for each salt-benzoxazine mixture was monitored by using Differential Scanning Calorimetry (DSC) and it was found that amine salts cause clear reduction in ROP temperature. As followed by 1H NMR investigations, the ring-opening of oxazine can take place even at r.t. when suitable solvent is used. Moreover, the analysis gave evidences that amine HCl salts act as nucleophilic catalyst and their efficiency is dependent on ionization ability and solubility of the salts. Thermal stability of the final polymers was also analyzed using Thermal Gravimetric Analysis (TGA).

Catalytic effect of trifluoroacetamido group on thermally induced ring-opening polymerization of 1,3-benzoxazine and formation of arylamine Mannich bridge structure

The autocatalytic ring-opening polymerization behavior of trifluoroacetamido group containing benzoxazine (FBA) is reported and its curing process was monitored by in situ proton nuclear magnetic resonance and Fourier transform infrared spectra analysis. The ring-opening polymerization temperature of FBA is significantly lower than that of typical 1,3-benzoxazine (BA), which can be attributed to higher stability of benzoxazine zwitterionic ion intermediate due to strong electron-withdrawing effect of trifluoroacetamido substituent. Arylamine Mannich bridge structure is found to form during polymerization, thereby enhancing the thermal stability of FBA homopolymer (poly-FBA). Differential scanning calorimetric analysis indicates that FBA effectively catalyzes the copolymerization of FBA and BA monomers at a temperature even lower than the polymerization temperature of pure FBA monomer, and the resultant copolymer exhibits higher glass transition temperature than either FBA or BA homopolymer, indicating promising possibility of FBA as reactive comonomer of polybenzoxazine systems for curing acceleration and performance improvement.

Calcium silicate/poly(ethylene terephthalate) biomaterials via ring-opening polymerization

Calcium silicate/poly(ethylene terephthalate) (CS/PET) composites were synthesized via ring-opening polymerization (ROP). CS raw material was synthesized by coprecipitation of calcium nitrate tetrahydrate and tetraethyl orthosilicate. Commercial grade PET was cyclodepolymerized under high dilution technique to cyclic oligo(ethylene terephthalate) (C-OET) raw material. The CS/PET pre-composites were prepared by mixing 60:40 (C6P4) and 50:50 (C5P5) wt% of CS powder and C-OET with the presence of 3 mol% of dibutyl tinoxide catalyst (with respect to the cyclic) then shaped the pre-composites into cylindrical pellets. The presented C-OET in the pre-composites was ring-opening polymerized to obtain PET film covering on the CS grains with the different reaction temperatures as 180, 200 and 250 °C under vacuum for 24 h. Thermogravimetric analysis indicated that the ROP-PET content in the C5P5 and C6P4 composites were about 46–48 and 35–38 wt%, respectively. The melting points (Tm) of ROP-PET of all composites were in a range of 233–246 °C. Compressive strength of the CS/PET composites was significantly increased from 4.8 MPa of the neat CS to 31.0 MPa for the C5P5 composites at the ROP temperature of 250 °C. The CS/PET composites faster induced the continuous-phase formation of hydroxyapatite (HAp) nanocrystals on their surfaces than the HAp/polymer composites. The induction occurred within 7-day soaked in the simulated body fluid (SBF) solution, indicating the bioactivity of the CS/PET composites.

Synthesis and characterization of fluid 1,3‐benzoxazine monomers and their thermally activated curing

AbstractNovel mono‐ and difunctional aliphatic oxyalcohol‐based benzoxazines have been synthesized and characterized in detail. Molecular structures of the monomers were investigated by spectral analysis. The obtained benzoxazine monomers exhibit fluidic behavior, which makes them particularly useful for many applications compared to other traditional benzoxazines. Differential scanning calorimetry was used to monitor the thermal crosslinking behavior of synthesized monomers. Mono‐ and bifunctional benzoxazine monomers exhibited low curing exhothermic peak with the onset around 173 and 180 °C, respectively. Relatively, low ring‐opening polymerization temperature was due to the hydroxyl groups present in the structure of the monomers. The hydrogen bonding of hydroxyl groups may cause alignment of the monomers in the liquid state. Thermal stabilty of the polybenzoxazines was studied by thermogravimetric analysis. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009

Synthesis and ring-opening polymerization of macrocyclic (arylene thioether ketone) oligomers

Macrocyclic (arylene thioether ketone) oligomers together with a linear poly(phenylene sulfide ketone) oligomer were synthesized by a one-step reaction. The macrocycles and linear oligomer were fully characterized by 13C-NMR, H-NMR, matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), differential scanning calorimetry (DSC) and FT-IR. Uncatalyzed, simultaneously ring-opening polymerization (ROP) of the macrocycles and the mixture of macrocycles and linear oligomer were carried out under dynamic heating conditions. The ROP temperature of the macrocycles decreased upon mixing it with the linear oligomer. The ROP conditions and mechanism were investigated and discussed. The macrocycles and their mixture show potential applications in high temperature adhesives and sealants. Copyright © 2006 John Wiley & Sons, Ltd.