Arylamines with electron donating groups such as alkyl and alkoxy groups in the meta position on the aromatic ring change the polymerization temperature of the benzoxazine prepared therefrom and offer an opportunity for an additional crosslinking site (the para position on the aromatic amine can couple to a Mannich base generated by the opening of the oxazine ring of the benzoxazine or a methylene bridge generated by a degradation reaction). Naphthenic amines with an alkyl or alkoxy substituent on the 5.sup.th through the 8.sup.th carbon atom on the naphthalene ring can function similarly. The polymers for benzoxazines prepared from at least 10% substituted aromatic or naphthenic amines are useful due to low polymerization temperatures and higher Tg (glass transition temperature).

FIELD OF INVENTION 
The invention field is benzoxazines. Benzoxazines are an alternative to 
phenolic, epoxy, and other thermosetting resins in many applications due 
to their similar thermal stability and the processing advantages of 
benzoxazines. Benzoxazines offer useful properties including low 
viscosity, little or no release of volatiles during cure, no need for 
harsh catalysts, a high glass transition temperature, high thermal 
stability, -good mechanical properties, and wide molecular design 
flexibility. Substituted aromatic amines offer an additional site on the 
aromatic amine to build the polybenzoxazine's molecular weight and/or to 
provide crosslinking sites. These changes in the polymer should result in 
better thermal stability over some temperature range and improved physical 
properties over some temperature range. 
BACKGROUND OF INVENTION 
The effect of various substituents on the reactivity of aromatic amines in 
some reactions has been studied. The electronegativity of the substituent 
and its position (e.g. ortho, meta, and para) on the amine has an effect 
on the reactivity of the amine in chemical reactions including 
electrophilic aromatic substitution reactions. One set of papers 
discussing this is by M. Miocque and J. M. Vierfond in the Bull. Soc. 
Chim. Fr. (1970), volume 5, pages 1896, 1901, and 1910. 
It is known that one of the degradation products of thermal decomposition 
of aromatic amine containing benzoxazine polymers is the aromatic amine. 
It has been proposed to add acetylene, phthalonitrile and nitrile 
functional groups to an aromatic amine to generate an additional chemical 
bond between the aromatic amine and the rest of the polybenzoxazine 
network. Conceptually, the added chemical bond would decrease the amount 
of aromatic amine volatilized thereby increasing the thermal stability of 
the benzoxazine polymer. This was effective, but the aromatic amines with 
the acetylene, phthalonitrile and nitrile functional groups are difficult 
to prepare and significantly raise the product's cost. 
SUMMARY OF INVENTION 
It has been discovered that aromatic amines with substituents, which 
activate the ring of the aromatic amine for electrophilic aromatic 
substitution reactions at the para position, can sufficiently activate the 
ring so that said para position of the amine competes with the ortho 
position on the phenolic reactant for chemical reaction with the Mannich 
bridge formed during the ring opening polymerization of benzoxazine. 
Naphthenic amines with alkyl and/or alkoxy substituents on the 5.sup.th 
through the 8.sup.th carbon atom of the naphthalene can be substituted for 
the aromatic amine with similar results. Several of the substituents such 
as a meta-methyl group also facilitate ring opening of the benzoxazine 
monomer which is part of the polymerization process for benzoxazines. This 
may lower the polymerization temperature and provide for higher molecular 
weight or crosslinked polybenzoxazines. 
It is desirable that at least 10 or 25 mole percent and more desirably at 
least 50 mole percent of the total amines used to form the benzoxazine 
monomer and benzoxazine polymer are aromatic amines that have substituents 
that activate the aromatic ring for electrophilic substitution reactions 
with the Mannich base in the para position. Preferred substituents are 
electron donating groups such as mono or di-alkyl or mono or di-alkoxy 
groups in the meta position. The substituted aromatic amine may be 
partially or fully replaced with a substituted naphthenic amine. Preferred 
phenolic compounds are mono, di, or polyhydric phenolic molecules which 
can form one or more benzoxazine rings per phenolic molecule. 
DETAILED DESCRIPTION OF THE INVENTION 
Polybenzoxazines with improved properties due to the use of a substituted 
arylamine are described. While the char yield of such polybenzoxazines is 
not substantially better than similar benzoxazines from aniline, the 
properties and thermal stability between 200 and 350.degree. C. are 
improved. It is intended to claim not only the polybenzoxazines but the 
monomers used to make them and the processes used in their preparation. It 
is acknowledged that the term polybenzoxazine may be confusing to some 
because a polybenzoxazine typically has no residual benzoxazine containing 
repeat units since the benzoxazine ring is opened as part of the 
polymerization process. A benzoxazine monomer does have at least one 
benzoxazine ring and may have multiple benzoxazine rings. 
Benzoxazine monomers generally have a formula with an oxazine ring pendant 
to a benzene ring such as shown below 
##STR1## 
wherein m can be any integer from 1 to 20 and is preferably an integer 
from 1 to 4 and is most preferably 2 or 3, and R.sub.1 is one of the 
connecting groups such as shown later for the phenolic molecules. 
Furthermore, each benzene ring, as shown by (R.sub.3).sub.p where p is an 
integer from 0 to 3 and R.sub.3 is as defined later, can have one or more 
substituents of the same structure or a mixture of the R.sub.3 structures. 
Preferably R.sub.3 is an alkyl of 1 to 16 carbon atoms such as CH.sub.3, 
C.sub.2 H.sub.5, C.sub.3 H.sub.7 or C.sub.4 H.sub.9, or a mono or poly 
fluorinated alkyl of 1 to 9 carbon atoms such as CF.sub.3, C.sub.2 
F.sub.5, C.sub.3 F.sub.7. R.sub.2 can be anything that when attached to 
NH.sub.2 would generate the amines described later. 
Benzoxazines have been shown to polymerize via a thermally induced 
ring-opening reaction to form a phenolic structure characterized by a 
Mannich base bridge (--CH.sub.2 --NR.sub.1 --CH.sub.2 --) as shown instead 
of the methylene bridge associated with traditional phenolic resins. 
##STR2## 
This thermal polymerization typically evolves very small amounts of 
byproducts because, as the oxazine ring is opened, it attaches to an ortho 
or para position on another aromatic ring generating a hydrogen from the 
attachment to the ring, which is available to form the hydroxyl group of a 
phenol. The major source, if any, of byproducts is side reactions that may 
cleave the Mannich bridge from the phenol or cleave the Mannich bridge. 
This can be controlled by choosing proper polymerization conditions. 
Alternatively the polymerization can be initiated or catalyzed. Cationic 
ring opening polymerization is taught in U.S. patent application Ser. No. 
09/105,859. 
Unfortunately with typical monofunctional benzoxazines the polymer 
molecular weight never gets very high during uncatalyzed thermally 
initiated polymerization as side reactions and thermal degradation limits 
the molecular weight. Therefore many polybenzoxazine producers use 
difunctional or polyfunctional phenols to generate two or more benzoxazine 
rings on the benzoxazine monomer. Using polyfunctional benzoxazines the 
molecular weight of the polymer can be significantly increased and 
crosslinking can be achieved even with significant levels of side 
reactions and impurities. 
Generally an early thermal degradation product, whether during 
polymerization or post polymerization, is the amine of the Mannich bridge. 
This is the focus of this disclosure as decreasing the amount of amine 
generated early in thermal degradation may be the best route to increase 
the thermal stability of the polybenzoxazine. While the attachment of 
additional reactive groups, e.g. acetylene, phthalonitrile and nitrile 
functional groups does decrease the amount of amine released during 
thermal degradation (low temperature) and also increases the char yield of 
the polymer at 800.degree. C., this is a costly component to the recipe. 
An alternative, as explained herein, is to use a reactant that favors 
additional chemical bonds being formed to the amine component or favors 
the generation of more thermally stable byproducts early in the 
polymerization without the use of expensive, reactive substituents 
attached to the aryl amine such as acetylene, phthalonitrile and/or 
nitrile. 
Amines desirable for forming the benzoxazines are aromatic amines with 
substituents that favor electrophilic substitution reactions at the para 
position of the aromatic group. Preferred loci of the substituents are the 
meta positions on the benzene ring. Preferred meta substituents are alkyls 
of 1 to 4 carbon atoms or alkoxy groups of 1 to 4 carbon atoms. Highly 
preferred is meta methyl groups such as found on 3-methyl aniline 
(3-toluidine) and 3,5-dimethyl aniline (3,5-xylidine) and meta methoxy 
groups such as found on 3-methoxy aniline. Methyl is an electron donating 
substituent and activates the para position on the ring for electrophilic 
substitution. Substituents in the para position are not preferred as it is 
difficult to form a covalent bond to the arylamine in the ortho or meta 
positions due to steric hindrance and/or electronic reasons. Substituents 
in the ortho position are not preferred as they are a steric hindrance and 
reduce the reactivity of the oxazine ring in the reaction forming the 
polybenzoxazine. 
Alternatively or in combination with the above aromatic amines one can use 
naphthenic amines with alkyl or alkoxy substituents as described above. 
The location of the substituents on the naphthenic amines need not be in 
the meta position but should be on the ring not bonded directly to the 
nitrogen. Thus on the fused rings below the alkyl and/or alkoxy 
substituents could be on the 5.sup.th through 8.sup.th carbon atom. 
##STR3## 
Desirably at least 10 or 25 mole percent and preferably at least 50 mole 
percent of the amines used to form the benzoxazine or incorporated into 
the polybenzoxazine are the above described aromatic amines with para 
directing substituents for electrophilic aromatic substitution reactions 
and/or said naphthenic amines. In the polybenzoxazine polymer desirably at 
least 0.01 mole percent, more desirably at least 0.1 mole percent, and 
preferably at least 0.5 mole percent of the total substituted aromatic 
amines and naphthenic amines have a Mannich bridge or methylene bridge 
attached to the aromatic ring thereof. 
The benzoxazines containing the above substituted aryl amines can be 
prepared by mixing the substituted arylamines with other amines and then 
making the benzoxazines therefrom or benzoxazines prepared primarily or 
entirely of said substituted arylamines can be copolymerized with other 
benzoxazines containing said other amines, e.g. an aromatic amine, 
aliphatic amine, alkyl substituted aromatic or aromatic substituted alkyl 
amine, halogenated aliphatic amine, or halogenated aromatic amine or 
combinations thereof. The amine can also be a polyamine, although the use 
of polyamines will, under some circumstances, yield polyfunctional 
benzoxazine monomers. The amines generally have from about 1 to about 40 
carbon atoms unless they include aromatic rings and then they may have 
from about 6 to about 40 carbon atoms. The amine of di or 
polyfunctionality may also serve as a branch point to connect one 
polybenzoxazine to another. 
The preferred phenolic compounds are diphenols (e.g. bisphenol-A), 
triphenols, etc., e.g. polyphenols, wherein each phenolic group in the 
phenolic compound has on average about 6 to about 20 carbon atoms per 
phenol group but can include monohydric phenols including substituted 
phenols such as cresol. The use of phenols with two or more hydroxyl 
groups reactive in forming benzoxazines may result in branched and/or 
crosslinked products. The groups connecting said phenolic groups into a 
phenol (R.sub.1) can be branch points or connecting groups in the 
polybenzoxazine. 
When n is 2, 3 or 4, examples of the R.sub.1 connecting groups include but 
are not limited to 
##STR4## 
where x can vary from 1 to about 100. It may be desirable that R.sub.1 be 
ortho, meta, or para to the oxygen atom of the benzoxazine monomer of 
Formula B. R.sub.4 can be H, CH.sub.3, or Cl such that the repeat unit is 
from butadiene, isoprene or chloroprene respectively. 
The variable m can be an integer from 0 to 5 and R.sub.3 can be H or 
R.sub.2. Furthermore, each benzene ring, as shown by (R.sub.3).sub.m where 
m is an integer from 0 to 3 and R.sub.3 is as defined later, can have more 
than one substituent of the same structure or a mixture of the R.sub.3 
structures. Preferably R.sub.3 is not the amine or polyamine components of 
R.sub.2. Preferably R.sub.3 is an alkyl of 1 to 9 carbon atoms such as 
CH.sub.3, C.sub.2 H.sub.5, C.sub.3 H.sub.7 or C.sub.4 H.sub.9, or a mono 
or poly fluorinated alkyl of 1 to 9 carbon atoms such as CF.sub.3, C.sub.2 
F.sub.5, C.sub.3 F.sub.7. These R.sub.1 compounds are well known to those 
familiar with phenolic compounds. Generally R.sub.1 can be any of the 
known connecting groups that interconnect two or more phenols. Known 
connecting groups refers to those which are present in commercially 
available phenols, are in experimentally available phenols, and phenols 
whose synthesis are described in the published literature. Examples of 
such phenols include 
##STR5## 
The aldehydes used to form the benzoxazine can be any aldehyde but 
preferably the aldehydes are those having from about 1 to about 10 carbon 
atoms with formaldehyde being highly preferred. 
As is well known, benzoxazine monomers are made from the reaction of three 
reactants, aldehydes, phenols, and primary amines by procedures using a 
solvent or solventless systems. U.S. Pat. No. 5,543,516, hereby 
incorporated by reference, sets forth a generally solventless method of 
forming benzoxazine monomers. An article by Ning and Ishida in Journal of 
Polymer Science, Chemistry Edition, vol. 32, page 1121 (1994) sets forth a 
procedure using a solvent which can be used to prepare benzoxazine 
monomers. The procedure using solvents is generally common to the 
literature of benzoxazine monomers.

EXAMPLES 
In the-first study methyl groups, weak activators towards electrophilic 
aromatic substitution, were added as substituents groups to various sites 
on the aromatic amine groups. More strongly activating substituent groups, 
such as hydroxyl groups, are difficult though possible to incorporate due 
to the necessity of forming closed benzoxazine rings during the monomer 
synthesis. Adding a methyl or methoxy group to the para position of the 
aromatic amine should block the ring from reaction since the meta 
positions are unfavored for electrophilic substitution reactions due to 
the ortho/para directing nature of the nitrogen. Addition of a methyl 
group in the ortho position will likely decrease the activation of the 
open para position relative to the meta position and will serve to 
illustrate the effects of steric hindrance on the polymerization. Adding 
methyl groups to one or both meta positions should increase the activation 
of the para position enough to either compete with the traditional ortho 
position on the phenolic group for electrophilic substitution reactions or 
dominate and serve as the only site of reaction. 
Monofunctional benzoxazine monomers were synthesized from 4-t-butyl-phenol 
(para substituted)(4TBUPH) or 2,4-dimethyl phenol (ortho and para 
substituted)(24DMP) with a series of aromatic amines. The para substituted 
phenol would be similar to bisphenol A and would have one available ortho 
position for polymerization with a Mannich bridge. The ortho and para 
substituted phenol would have no available ortho positions after forming a 
benzoxazine and thus a benzoxazine formed from this phenol should not be 
readily polymerizable. The aromatic amines include aniline, o-toluidine 
(ot), m-toluidine (mt), p-toluidine (pt), and 3,5-xylidine (35x). These 
represent nonsubstituted, ortho substituted, meta substituted, para 
substituted, and dimeta substituted aniline. 
All the compounds were used as received from Aldrich Chemical Co. without 
further purification. The monofunctional benzoxazines were synthesized via 
a solventless method discussed in full detail in the Ph.D. Thesis of J. 
Liu from Case Western Reserve in 1995. The phenol, paraformaldehyde, and 
amine were added to an open container in stoichiometric amounts (1:2:1). 
The reactants were mixed for 20 minutes at 120.degree. C. The crude 
reaction product was dissolved in diethyl ether and washed with 2N NaOH 
solution at least ten times and rinsed with deionized water. The purified 
products were dried over sodium sulfate and the solvent was removed under 
vacuum. The compounds were sequentially recrystallized from methanol twice 
and finally ethanol once. The residual ethanol was removed under vacuum at 
room temperature for 24 hours. 
Benzoxazine monomers were prepared from the above reactants. They will be 
designated as the hyphenated combination of the abbreviations for the 
phenol and the aromatic amine. They include (24DMP-ot) a needle-like 
crystalline powder, (24DMP-mt) a light tan crystalline powder, (24DMP-pt) 
a white plate-like crystalline powder, (24DMP-35x) a white crystalline 
powder, (4TBUPH-a) a white crystalline powder, (4TBUPH-ot) a white 
needle-like crystalline powder, (4TBUPH-mt) a light tan crystalline 
powder, (4TBUPH-pt) a white plate-like crystalline powder, (4TBUPH-35x) a 
yellowish viscous liquid. 
The benzoxazine monomers were reacted (e.g. hopefully polymerized) in NMR 
tubes with and without phenolic initiators under an argon atmosphere. The 
partially reacted materials were dissolved in deuterated chloroform and 
used for .sup.1 H and .sup.13 C NMR spectroscopy. The molecular weight of 
the resulting polymers was determined via size exclusion chromatography 
(SEC). The samples for molecular weight determination were prepared by 
diluting the NMR solution with HPLC grade tetrahydrofuran (THF). 
2,4-dimethyl phenol-Based Monomers and Polymers 
All of the 24DMP based benzoxazine monomers showed a distinct melting peak 
in the DSC analysis except for 24DMP-a, which was a viscous liquid at room 
temperature. A calorimetric analysis of the 24DMP based benzoxazines 
showed an exotherm which decreased as a function of the number of methyl 
substituents in the meta position of the arylamine ring increased i.e. 
benzoxazines from meta-toluidine had a lower temperature exotherm than 
benzoxazines from nonsubstituted aromatic amines and benzoxazines from 
3,5-xylidine showed a still lower exotherm. Since benzoxazines from 24DMP 
are not believed to be ring opening polymerizable, the presence of a 
reaction exotherm in these materials is surprising. The low heats of 
reaction suggest that these exotherms may simply represent the ring 
opening and/or cleaving reactions. The results on benzoxazines from 
meta-toluidine and 3,5-xylidine may be due to polymerization to para 
activated positions on the arylamine ring or another side reaction. 
After reaction of the 24DMP-based monomers under argon in the NMR tubes for 
3 hours at 200.degree. C., the molecular weight distribution was 
determined via SEC. The retention time of the monomer species is about 
30.2 minutes. 24DMP-ot and 24DMP-pt showed only a small shoulder in the 
SEC plot at around 29.2 minutes which is typical for an open-ring 
monomeric species. This is consistent with the ortho-toluidine and 
para-toluidine not being reactive in electrophilic aromatic substitution 
reactions by the Mannich bridge from the oxazine ring opening and not 
forming dimers or oligomers. The 24DMP-mt showed peaks associated with the 
monomeric and open ring but additionally exhibits a peak centered at 28.4 
minutes from a larger molecular weight species. The higher molecular 
weight species were also present in the 24DMP-35x. The higher molecular 
weight species are primarily dimeric in nature with smaller additional 
amount of higher oligomers such as trimers and tetramers. These dimers and 
oligomers are evidence that there is a reaction difference in the 
benzoxazines formed with para- directing substituents on the aromatic 
amine. 
NMR analysis of the monomers after the polymerization basically confirmed 
the SEC analysis. It was observed that 24DMP-mt showed resonance at 4.27 
ppm, which has been previously assigned to the open ring methylene protons 
of a Mannich base having the structure 
##STR6## 
Another prominent resonance corresponding to a methylene proton of a open 
ring Schiff base can be observed at 8.52 ppm. It has the structure 
##STR7## 
The oxazine rings of 24DMP-mt evidently started to open during the 
temperature regime employed, although a considerable amount of monomer 
remains after 3 hours. These open ring products participated in a cleavage 
reaction at this elevated temperature, which produces the Schiff base. 
Thus while the meta-toluidine is more active toward electrophilic para 
substitution reactions the meta substituent may lower the ring opening 
temperature allowing more side reactions to occur with meta-toluidine than 
with aniline, ortho-toluidine, or para-toluidine. 
Blocking the preferred site of reaction on the phenol, i.e. the site ortho 
to the hydroxyl group, with a methyl substituent in 24DMP was effective in 
preventing the ring-opening polymerization from occurring in 24DMP-ot and 
24DMP-pt. Activating the arylamine ring with methyl substituents at one or 
both meta positions facilitated the formation of the open-ring species at 
lower temperatures. The presence of methyl substituents in the meta 
positions must allow for sufficient electron density to be pushed into the 
oxazine ring, without the formation of more stable hyperconjugated 
resonance structures, such that the oxazine rings are less stable against 
ring opening. 
Since higher molecular weight species were observed for 24DMP-mt and 
24DMP-35x, it is necessary to determine if the site of reaction has simply 
shifted to the arylamine ring or if another polymerization/degradation 
reaction is taking place. Based on a .sup.1 H NMR resonance near 4.34 ppm 
associated with the methylene protons of the Mannich bridge, and the lack 
of open ortho and para positions on the phenol for addition of the Mannich 
bridge, it is assumed the reaction site for the Mannich bridge was shifted 
to the para position on the arylamine ring. This type of linkage will be 
referred to as an arylamine Mannich bridge. 
The .sup.1 H NMR resonance assigned to the Mannich bridge methylene protons 
is small in 24DMP-35x suggesting that either few para sites on the 
arylamine ring have served as sites for polymerization or the para 
positions reacted with the Mannich bridges subsequently cleaving during 
the cure. Numerous resonances in the region of 3.7 to 3.9 ppm are greatly 
enhanced. A resonance at 3.85 ppm can be assigned to the formation of a 
bisphenolic methylene structure as shown below. 
##STR8## 
.sup.13 C NMR spectroscopy of 24DMP-mt and 24DMP-35x lacks any significant 
resonances at 79.3 and 50.2 ppm associated with the methylene carbons in 
the oxazine ring. This indicates near complete loss of the oxazine ring 
structure. The large resonance at 48.6 ppm in 24DMP-mt is assigned to the 
open ring Mannich base methine carbon. A resonance corresponding to the 
methylene carbon of the aromatic Schiff bass species mentioned previously 
is located at 162.5 ppm. In the case of 24DMT-mt a resonance corresponding 
to the phenolic Mannich bridge carbon appears near 49.0 ppm. A new 
resonance appeared at 54.7 ppm which can be assigned to the other carbon 
in the arylamine Mannich bridge which is attached to the para position on 
the arylamine ring, since the chemical shift is within 0.2 ppm of the 
value predicted by simple .sup.13 C chemical shift calculations. 
A resonance appears near 30.5 ppm in both 24DMP-mt and 24DMP-35x. This 
resonance can be assigned to the methylene carbon in the bisphenolic 
methylene structure mentioned previously. The relative intensity of this 
peak between 24DMP-mt and 24DMP-35x agrees with the .sup.1 H NMR data. A 
second prominent resonance appears near 32.2 ppm. This is attributable to 
a methyl carbon in an N-methyl Mannich base species. A strong resonance 
near 29.1 ppm is assigned to a methylene carbon in a methylene bridge 
between an ortho position on a phenolic molecule and a position 
(presumably the activated para position) on the aromatic ring. 
4-t-butyl phenol-Based Monomers 
In order to determine if the ring-opening polymerizations of benzoxazine 
can occur with attachment to arylamine sites when there is a free ortho 
site on the phenolic ring concurrently available, a series of monomers 
based on 4-t-butyl phenol was synthesized. The t-butyl protecting group 
was selected to simulate the bulkiness of the isopropylene linkage of 
Bisphenol-A. 
The DSC thermograms of the 4TBUPH-based benzoxazines are similar to those 
of the 24DMP-based benzoxazines. Addition of a methyl substituent on the 
meta position of the arylamine ring decreased the peak exotherm 
temperature and increases the heat of reaction. SEC was used to determine 
the molecular weight distribution of the oligomeric species after 
190.degree. C. for 2 hours and 200.degree. C. for 1 hour (a typical step 
cure for difunctional benzoxazine resins). As with the 24DMP the molecular 
weight of the polymerized species increased as the para position of the 
arylamine ring is increasingly activated for electrophilic aromatic 
substitution reactions. It was observed that the 4TBUPH-ot monomer did not 
polymerize well which is probably due to thermal degradation. The low 
basicity of o-toluidine (ot) and steric hindrance around the amine may 
hinder polymerization. 
1H NMR analysis indicated that the benzoxazine rings were not completely 
reacted (opened) even after an hour at 200.degree. C. The 4TBUPH-mt 
monomer shows a distinguishing resonance at 3.85 ppm which corresponds to 
the methylene protons of the bisphenolic methylene species. This side 
reaction evidently occurs even when there are free ortho sites on the 
phenolic ring. It produces: 
##STR9## 
13C NMR analysis confirmed significant amounts of monomer remain for 
4TBUPH-ot while almost none remains for 4TBUPH-mt. Around 30.8 ppm a small 
resonance appears in 4TBUPH-35x due to the formation of bisphenolic 
methylene linkages. 
Bisphenol A Based Benzoxazines 
Difunctional benzoxazines were synthesized via a solventless synthesis 
method discussed in J. Liu's Ph.D. thesis. The Bisphenol-A, 
paraformaldehyde, and arylamine were added to an open container in 
stoichiometric amounts (1:4:2). The reactants were mixed for 20 minutes at 
120.degree. C. The crude reaction products were dissolved in diethyl ether 
and washed with 2N NaOH solution and rinsed with deionized water. The 
purified products were dried over sodium sulfate and the solvent was 
removed under vacuum. 
The benzoxazine monomers will be described by hyphenated abbreviations for 
the phenol and the aromatic amine used in their preparation. BA will be 
the abbreviation of Bisphenol A. The amines are aniline (a), o-toluidine 
(ot), m-toluidine (mt), p-toluidine (pt), and 3,5-xylidine (35x). 
The BA-a was a white powder. The BA-ot was a white powder. The BA-mt was a 
light tan powder. The BA-pt was white crystalline powder. Due to the 
higher melting temperature of p-toluidine compared to the other amines, 
the monomer forming reaction was carried out at a higher temperature of 
135.degree. C. The BA-35x was a yellowish white powder. 
The curing (polymerization) reaction for the benzoxazines was 140.degree. 
C. for 30 min, 160.degree. C. for 30 min, 170.degree. C. for 45 min, 
180.degree. C. for 45 min, 190.degree. C. for 75 min, and 200.degree. C. 
for 90 min. The ring content before polymerization for the monomers was 
from about 83 to about 95% of the theoretical amount. FTIR analysis of the 
monomers with bands such as 1232 cm.sup.-1 for asymmetric C--O--C stretch, 
1030 cm.sup.-1 characteristic of the --CH.sub.2 --O stretch of the 
aromatic ether and 947 cm.sup.-1 associated with the --C--O--C cyclic 
acetal vibrational mode or a C--H out of plate deformation confirmed the 
formation of the benzoxazine rings. 
The curing exotherms for most of the BA-based benzoxazines were not unusual 
except for BA-mt and BA-35x. The curing of BA-mt and BA-35x exhibited two 
peaks, one large narrow peak centered at 231 C and another small broad 
peak centered at 246. BA-35xt also exhibited peaks at 218 and 239 C. These 
two different peaks suggest reactions at two different sites, said 
reactions having different kinetics. 
Cured samples of the different polybenzoxazines were filed down into flat, 
round disks and placed in hermetic aluminum pans. The temperature was 
ramped at 10.degree. C./min under a nitrogen atmosphere. The thermal 
stability of the cured benzoxazines was measured by thermogravimetric 
analysis (TGA) using a TA Instruments Hi-Res 2950 Thermogravimetric 
Analyzer equipped with a Evolved Gas Analysis (EGA) furnace. The flow cell 
and transfer line were heated to 300.degree. C. to prevent condensation of 
the evolved gases. FTIR spectra of the evolved gases were obtained on a 
Biorad FTS-60A FTIR Spectrometer. 
BA-ot had the least stability with a 5% weight loss at 288.degree. C. BA-a 
and BA-pt had a 5% weight loss at 315 and 305.degree. C. respectively. The 
meta-substituted BA-mt and BA-35x possess the highest 5% weight loss 
temperature of 350.degree. C. This is the highest 5% weight loss 
temperature reported for a neat Bisphenol-A based benzoxazines 
incorporating arylamines, without reactive substituent functionalities on 
the amine. The ultimate char yield at 800.degree. C. of the 5 compounds 
are all similar at about 30-31%. This result is expected since no new 
chemical functionalities have been added. Only when the possibility of 
forming more stable cyclic structures is introduced will the char yield be 
significantly enhanced. 
The glass transition temperatures of the various polymerized benzoxazines 
are BA-ot, 114; BA-a, 170; BA-pt, 158; BA-mt, 210; and BA-35x, 245.degree. 
C. 
Gases were also collected from the series of benzoxazines during 
degradation reactions and analyzed by GC/MS. For the traditional 
benzoxazine polymer the pendant arylamine group is the most easily 
volatilized upon cleavage of the Mannich bridge and therefore is the 
predominant species in the evolved gases. The BA-ot generated the most 
free amine species. For BA-mt the evolved amine was analyzed to find that 
both the activated 4 and 6 positions appear to have reacted. In the 
BA-35x, the 4 position dominated over the more sterically hindered 2 
position. 
The benzoxazine monomers and polymers disclosed herein would be useful as 
matrix resins in molding compounds, fiber reinforced boards for 
electronics, as adhesives or potting resins for electronic applications, 
as flame retardant adhesives or in flame retardant composites for 
airplanes and other transportation vehicles. 
While in accordance with the patent statutes the best mode and preferred 
embodiment have been set forth, the scope of the invention is not limited 
thereto, but rather by the scope of the attached claims.