A series of poly(aryl ether sulfonephthalazinone)s (PPES-Ps) containing pendent carboxyl groups and

N

-heterocyclicphthalazinone units were derived from phenolphthalin (PPL) and 4-(3-chloro-4-hydroxylphenyl)(2H)-phthalazin-1-one (DHPZ) with 4

4′-dichlorodiphenyl sulfone (DCS)

via

" one-pot” solution polymerization. The structure of the resulting polymers was elaborately controlled by tailoring the feed ratio of the two diphenols to have a balance between the carboxyl content and the thermal resistance. As evidenced by NMR analysis

the structure of the corrsponding polymers along with the carboxyl content is consistent with those designed. PPES-Ps also exhibit high glass transition temperature (

T

g

>

260 °C) and excellent thermal stability as well as good solubility

mainly originating from the rigid

bulky

non-coplanar phthalazinone units. As the content of phthalazinone unit increases

both

T

g

and solubility demostrate an increasing trend. Furthermore

the copolymers with different contents of carboxyl groups are used to reactively toughen 601 epoxy resin. The mechanical and thermal properties of the obtained blending system are investigated in details. The results indicate that the pendant carboxyl groups in PPES-P can efficiently react with the epoxy groups of 601 resin during the thermal curing

leading to cross-linking networks by covalent bonding

which can not only improve the fracture toughness and flexural properties

but also maintain the high

T

g

of 601 epoxy resin. The impact strength of 601 epoxy resin

reactively toughened by PPES-P13 derived from PPL/DHPZ with the molar ratio of 1:3

is 43% higher than that of unmodified 601 resin. Meanwhile

the fracture of impact specimen shows a toughened fracture character

and no phase separation is observed on the crack surface

even with a high concent (15%) of PPES-P

which means that the reactive carboxyl moiety could enhance the compatibility between the high rigid poly(aryl ether)s and the epoxy resins. The 601 resins

reactively modified with PPES-Ps toughening

are thus expected to be useful in multistage toughening of carbon fiber reinforced resin matrix composites.