WO2008149380A2

WO2008149380A2 - A process for solvent-less synthesis of benzoxazine (bz)

Info

Publication number: WO2008149380A2
Application number: PCT/IN2008/000349
Authority: WO
Inventors: Jayashree Bijwe; P. V. Gurunath
Original assignee: Indian Institute Of Technology
Priority date: 2007-06-05
Filing date: 2008-06-03
Publication date: 2008-12-11
Also published as: WO2008149380A3

Abstract

This invention relates to a process for solvent less synthesis of benzoxazine which comprises in taking a phenol in molar combination with primary amine and aldehyde so as to form a ring of oxazine, heating said reactants to a temperature above the boiling point of water.

Description

TITLE

A process for solvent-less synthesis of Benzoxazine (BZ)

FIELD OF INVENTION

This invention relates to a process for solvent-less synthesis of Benzoxazine (BZ) (Monomer of Polybenzoxazine (PBZ).

BACKGROUND OF INVENTION

Phenolic polymers/ thermosets are widely used in the industries as ablative materials, electrical appliances, kitchen appliance handles etc. due to its combination of thermal, mechanical and electrical insulation properties along with very good cost to performance ratio. Phenolics are used as laminated sheets for various applications due to its mechanical properties and water repellency nature. Another major use is in the friction material industries for brake-pads, shoes, repellency nature. Another major use is in the friction material Industries for brake-pads, shoes, linings, blocks, clutches etc. where their binding capacity for multiple ingredients, very good friction and wear performance apart from other above-mentioned properties and hence enjoy the monopoly.

Synthesis of this family of resins is based on two classes of monomers viz, phenols & aldehydes. The variation in the type of monomers or their ratio or curing conditions such as temperature or catalyst such as temperature or catalysts leads to different properties of the phenolic resins. The synthesis involves corrosive catalysts such as acids, alkalis, etc. Thermal curing accelerated by popular curing agents such as hexamine leads to the product with adequate cross- linking and hence desired properties. This, however, leads to a serious and unavoidable problem of evolution of noxious volatiles. Moreover, the precursor of phenolic resin (mixture of oligomer and curing agent) which is commercially available and is used for polymerization, suffer a major disadvantage of very short shelf life which leads to problems of storage & transportation. It undergoes slow in situ polymerization even at little elevated temperature in the humid environment. Once partially cured, it has to be discarded since it is no longer free flowing powder required for final molding.

Polybenzoxazine, recently added family of themosets offers a solution to these problems associated with phenolic resins. Synthesis of this class of resins, which are not commercially available, is based on three classes of monomers viz. Phenol, aldehyde and amine. Their synthesis does not involve any corrosive catalyst as in case of phenolics and polymerization is based on heat induced strained Benzoxazine ring opening. Most interesting feature is about the infinite shelf life up to temperature of 100⁰C. Benzoxazine do not form any condensation products since the cross linking takes place through ring opening reaction. This removes any chance of voids, cracks or shrinkage of the final product.

Benzoxazines (BZ), precursors of Polybenzoxazines (PBz) have been synthesized based on mainly two routes. One uses solvents such as dioxane, alcohol, etc. to dissolve the reactants such as phenol, aldehyde and a primary amine. British patent no. 694489 uses this route to synthesize 3, 4-dihydro- l ,3 Benzoxazine from phenols and substituted phenols. Para-fomaldehyde (which is a solid and oligomer of formaldehyde and decomposes to form formaldehyde molecules) and an aliphatic primary amine. The solvent is then evaporated off or by the precipitation of product by mixing it with a non solvent. Thus this method is not cost effective since it involves solvents and extra step of solvent removal and long reaction duration (5-6 hours of refluxing at a temperature of 1 10⁰C).

Another cost effective route (solvent-less process) has been reported in the US patent no. 5543516 where no external solvent was used except the solvency of reactants for each other. A phenolic derivative either monohydric or dihdydric with one free ortho position, an aldehyde and a primary amine were used. This single step process involves heating of the reactants to their melting temperature. The solvent less process claims to have reduced reaction time and obviously more cost effective.

Although this solvent-less process reduced the overall reaction time and is more cost effective, it suffered a drawback related to the problems of complete removal of residual Para formaldehyde. This becomes a concern especially when material needs to be molded in pure form. It take several hours to get rid of residual Para formaldehyde which otherwise creates bubbles in the final product. The methods reported thus suffer from various drawbacks & need to be addressed. The objectives of the present work are as follows.

OBJECTS OF THE INVENTION:

An object of this invention is to propose a process for solvent-less synthesis of benzoxnzine (BZ) which obviates the disadvantages associated with the removal of residual para formaldehyde.

Another object of this invention is to propose a process for solvent- less synthesis of benzoxnzine (BZ) which makes the process more efficient. Still another object of this invention is to propose a process for solvent-less synthesis of benzoxnzine (BZ) which reduces the visocity of reaction melt to improve its processibility.

Another object of this invention is to propose a process for solvent-less synthesis of benzoxnzine (BZ), which replaces fraction of di-functionaJ phenols with mono-functional phenols to lower the viscosity of the reaction melt.

A further object of this invention is to propose a process for solvent- less synthesis of benzoxnzine (BZ), which produces the final copolymer with higher heat of polymerization wherein reduction in viscosity enhances the final crosslinking.

Yet another object of this invention is to propose a process for solvent-less synthesis of benzoxnzine (BZ) and whereby the process is feasible at most of the ambient conditions. A further object of this invention is to propose a process for solvent- less synthesis of benzoxnzine (BZ)which makes the product of PBZ processable even by heating the monomer with and without the option of pressure.

A still further object of this invention is to propose a process for solvent-less synthesis of benzoxnzine (BZ) which makes the final product without bubbles.

STATEMENT OF INVENTION

According to this invention there is provided a process for solvent less synthesis of benzoxazine which comprises in taking a phenol in molar combination with primary amine and aldehyde so as to form a ring of oxazine, heating said reactants to a temperature above the boiling point of water.

DESCRIPTION OF INVENTION: In Benzoxazine synthesis depending upon the functionality of phenol, it is possible to get thermoplastic or thermoset. By utilizing di functional phenol, a thermoset is obtained whereas mono functional phenol results in a thermoplastic polymer. In synthesizing the di functional Benzoxazine, the viscosity increases with the reaction progress pose a problem for further advancement of the reaction thereby leaving the residues of starting material which will interfere with the processing/ molding of the product of polymer. To counter this problem, replacing a fraction of di-functional phenols with mono- functional phenol lowers the viscosity of the reaction melt thereby allowing advancement of reaction. The resulting product would be a copolymer. The reduction in viscosity also enhances the final cross- linking as evidenced by the higher heat of the polymerization for the copolymers.

In the previously reported solvent less methods para-formaldehyde was used as one of the reactants for synthesizing Benzoxazine. Removal process of its residue required a long evacuation time. Moreover, the para-formaldehyde releases sudden burst of formaldehyde when its decomposition temperature is reached. This disturbs the ratio of reactants which may either affect the yield or leave behind the un-reacted reactants in the monomer which will interfere with the molding of the Benzoxazine. This may lead to trapping of bubbles in the polymer product. By utilizing formalin an aqueous solution of formaldehyde, in stead of Para-formaldehyde, the process becomes more efficient in terms of completion. The reaction progress is aided by the progressive and controlled release of formaldehyde. The product thus obtained can be molded without bubbles.

The precursors of Bz synthesis are; phenol, aldehyde and primary amine. The phenol is taken in a molar combination with primary amine along with aldehyde so as to form a ring of oxazine. The reactants are heated at a temperature which is above the boiling point of water. The physical state of the reactants dictates the method of measurement and mixing of the reactants. The reactants as said earlier are mixed in a molar ratio so as to form oxazine ring and heated. BZa, BZpmt, BZppt, Bzppt are the resins that can be synthesized.

This method enjoys the benefits of ease in processibility due to control of viscosity of oxazine melt as a consequence of using combination of phenol and d-hydric phenol. This leads to fast completion of the reaction. The reaction involves progressive release of formaldehyde from aqueous medium for reaction advancement rather than sudden release of formaldehyde as in the case of paraformaldehyde usage (prior art). The chances of leaving behind un- reacted formaldehyde HCHO are nil as evidenced from NMR and IR studies. The reactants may be stirred continuously to facilitate the advancement of the reaction. The pressure to be utilized is also less than what reported in the literature.

Thus, using formalin in this solvent-less process removed the problems related to trapping of bubbles in the melt of product, while use of combination of dihydric phenol and mono hydric phenol led to reduction in the viscosity and hence increased the processibility. Overall the process becomes more energy efficient. The process can be tailored to have entirely different product in terms of final chemical structure of materials depending upon the functionality of the phenol and amine.

In general.

-aqueous solution of any aldehyde (having general formula RCHO) can be employed.

-primary amines (aliphatic, aromatic and their substituted or mixed derivatives); diamines aliphatic, aromatic and their substituted or mixed derivatives) and combination of mono and diamines can be used.

-phenols with free ortho position (monohydric, dihydric and poly hydric) or their combination an be used.

Bisphenol A and phenol were mixed in the ratio of 85: 15 to 75:25. Formalin and m-toluidine were combined in the ratio of 1:2. The later mixture was combined with the phenols in the ratio 1 :2 ratio. The reaction was carried out as per conditions described earlier. The product Benzoxazine was molded to Polybenzoxazine. The resulting thermoset has the structure shown in Fig.1 and the softening temperature of the material is between (185-200) ⁰C. The tensile strength of the material is around 27-30 MPa.

Bisphenol A and phenol were mixed in the ratio of 85: 15 to 75:25. Formalin and p-toluidine were combined in the ratio of 1 :2. The later mixture was combined with the phenols in the ratio 1 :2 ratio. The reaction was carried out as per conditions described earlier. The product Benzoxazine was molded in Polybenzoxazine. The resulting thermoset has the structure show in Fig. 2 and the softening temperature of the material is between (155- 17O)⁰C. The tensile strength of the material is around 20-25MPa.

Bisphenol A and phenol were mixed in the ratio of 85: 15 to 75:25. Formalin and o-toluidine were combined in the ratio of 1 :2. The later mixture was combined with the phenols in the ratio were combined in the ratio of 1 :2. The reaction was carried out as per conditions described earlier. The product Benzoxazine was molded to Polybenzoxazine. The resulting thermoset has the structure show in Fig. 3 and the softening temperature of the material is between (120- 13O)⁰C. The tensile strength of the material is around 1 - 2 MPa.

Further objects and advantages of this invention will be more apparent from the ensuing examples:

EXAMPLE 1

Bisphenol-A: Phenol (12.5% of bisphenol), Aniline (200% of bisphenol), formalin (400%) are taken in a reaction vessel and heated above boiling point of water. The melt reaction mixture becomes bubble-free indicating complete removal of formaldehyde.

EXAMPLE 2 Bisphenol-A: Phenol ( 12.5% of bisphenol), o-Toluidine (200%) formalin (400%) are taken in a reaction vessel and heated above boiling point of water. The melt reaction mixture becomes bubble-free indicating complete removal of formaldehyde.

EXAMPLE 3

Bisphenol-A: Phenol (12.5% of bisphenol), m-Toluidine (200%), formalin (400%) are taken in a reaction vessel and heated above boiling point of water. The melt reaction mixture becomes bubble-free indicating complete removal of formaldehyde.

EXAMPLE 4

Bisphenol-A: Phenol (12.5% of bisphenol), p-Toluidine (200%), formalin (400%) are taken in a reaction vessel and heated above boiling point of water. The melt reaction mixture becomes bubble-free indicating complete removal of formaldehyde.

EXAMPLE 5

Bisphenol-A, Aniline (200%), formalin (400%) are taken in a reaction vessel and heated above boiling point of water. The melt reaction mixture becomes bubble-free indicating complete removal of formaldehyde. The reaction completion was confirmed by the formation of transparent bubble-free homogeneous melt of product.

EXAMPLE 6

Bisphenol-A, o-Toluidine (200%) formalin (400%) are taken in a reaction vessel and heated above boiling point of water. The melt reaction mixture becomes bubble-free indicating complete removal of formaldehyde. EXAMPLE 7

Bisphenol-A, m-Xoluidine (200%)/ formalin (400%). are taken" in a reaction vessel and heated above boiling point of water. The melt reaction mixture becomes bubble-free indicating complete removal of formaldehyde.

EXAMPLE 8

Bisphenol-A, p-Toluidine (200%), formalin (400%) are taken in a reaction vessel and heated above boiling point of water. The melt reaction mixture becomes bubble-free indicating complete removal of formaldehyde.

It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims:-

Claims

WE CLAIM:

1. A process for solvent less synthesis oϊ benzoxazine which comprises in taking a phenol in molar combination with primary amine and aldehyde so as to form a ring of oxazine, heating said reactants to a temperature above the boiling point of water.

2. A process as claimed in claim 1 wherein the aldehye comprises aqueous solution of aldehyde (having general formula RCHO).

3. A process as claimed in claim 1 wherein the primary amines comprise-primary amines (aliphatic, aromatic and their substituted or mixed derivatives); diamines aliphatic, aromatic and their substituted or mixed derivatives) and combination of mono and diamines.

4. A process as claimed in claim 1 wherein the phenols comprises phenols with free ortho position (monohydric, dihydric and polyhydric) or their combination.

5. A process as claimed in claim 1 wherein formalin and p-toluidene, o-toluidene or m-toluidene are mixed in the ratio 1 :2 and added in a ratio of 1 :2 to a mixture of Bisphenol A and phenol present in a ratio of 85: 15 to 75:25, and heated to above the boiling point of water, the resulting benzoxazine being molded to po Iy be nzoxazi n e .

6. A process for solvent less synthesis of benzoxazine substantially as herein described.