SAMPE Journal - July/August 2022 - 57

INTRODUCTION
Since the first synthesized in 1940s, benzoxazine
resins have been attract strong attention in
scientific research and industrial application. They
not only have excellent mechanical properties,
good thermal stability, and flame retardancy, and
outstanding dielectric properties as traditional
high-performance thermosetting resin, they also
have very flexibility in molecules design, undergo
near-zero volumetric shrinkage upon curing, and
have low water absorption. These properties make
benzoxazines an attractive alternative to traditional
phenolic resins, epoxies, and even bismaleimide
resins for industrial applications, such as in printed
circuit boards, aerospace structural composites,
and other fields. During the curing process, it is
believed that the oxazine ring opens and attacks
the amino group or hydroxy group of another ring
opening product to form a complicated network,
thus form a thermoset polymer. Often, this
process needs a catalyst or very high temperature
to promote the complete reaction. On the other
hand, the crosslink density is lower comparable
to other high performance thermo-setting resins,
thus they tended have lower thermal properties,
and benzoxazine without any additional functional
group generally yield a char yield less than 50% at
800°C under nitrogen.1-8
There are two major ways to address this
issue. One is synthesis of benzoxazine monomer
with additional functional group that would take
part in the crosslink network. Those functional
groups could come from phenol or amine, or
both,
including cyano group9
,
allyl
acetylene group,12 maleimide group,13
group14 among others15-17
group10-11
and furan
benzoxazine with another kind of resin that have
its own unique characteristic, such as epoxies18
and bismaleimides19
.
Functionalized amine based benzoxazines,
such as allylamine, propargylamine and furfuryl
amine has been developed and investigated before.
Those
benzoxazine
generally
will
have more
favorable property over simple benzoxazine resin.
For example, furfuryl amine based benzoxazine
have higher Tg and char yield compared to those
without14
; for propargyl amine derived it could also
achieve even higher Tg than simple Benzoxazine
due to the increasing of network density generated
by the reaction involved acetylene functional
groups12
,
. Another way is to blend
the said shortcoming of benzoxazine resin and it
is a favorable route over the modification of the
benzoxazine matrix itself. Epoxy resin is widely
available and easy to handle, and easily mixed with
benzoxazines at relatively low temperature. And the
Tg could be boosted with the blend over the polymer
product of benzoxazine itself. For example, the
Tg of polymerized bisphenol A benzoxazine from
141°C to about 156°C4
. Bismaleimide is another
excellent thermo-setting resin, and mainly used in
aerospace industry. However, it has high melting
point, and it is hardly dissolved in a common polar
solvent. The process of bismaleimide difficult. But
the resin could be melted into some benzoxazine
resins at a temperature below its melting point.
For example, Matrimid 5292A has a melting point
at 159°C, however, it could be melted into selected
benzoxazine resin at around 110°C - 130°C. The
additional of bismaleimide could great increase the
polymerized benzoxazine resin. There is numerous
data suggest the Tg could increase by 20 to 80°C
when a benzoxazine resin containing about 16%
BMI13
. BMI also could boost the thermal stability of
the polymer product. And with both functionalized
benzoxazine and additional of other thermosetting
resin, there is an even great chance to have even
better result.
The brittleness of polybenzoxazines limits its
application. There are various materials has been
used to improve its toughness. Those material
include linear polymer, such as PES, liquid rubber,
incorporate a long chain into the structure of
benzoxazine. Often, those additional would
decrease its stability.
Most commercially available benzoxazine are
derived from bisphenols with aniline. Due to the
relatively low cured Tg of those polybenzoxazine
resins, the application of those benzoxazine in
high temperature composite is limited. To broad
the portfolio of our benzoxazine products, a few
functionalized benzoxazines that derived from
propargyl amine and furfuryl amine have been
developed, and their homo-polymerization and copolymerization
properties has been investigated.
. In addition, furfuryl amine is a renewable
source, and it would make the benzoxazine more
attractive in the age of increasing environmental
awareness.
Resin blend or alloy is another way to improve
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EXPERIMENTATION
Material and Testing instrument
All commercial benzoxazine were obtained
internally or synthesized according to manufacture
procedure. All propargylamine based benzoxazines
(PPA) were made from the phenol or bisphenol
and formalin solution in refluxing chloroform. All
furfuryl amine based benzoxazines (FA) were made
from the bisphenol/phenol, furfuryl amine and
paraformaldehyde in either toluene or xylene. The
JULY AUGUST 2022
|
SAMPE JOURNAL |
57
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SAMPE Journal - July/August 2022

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