Chemorheology and thermomechanical characteristics of benzoxazine‐urethane copolymers

Abstract

In this research, processability and some important thermomechanical properties of polybenzoxazine (BA-a) modified with a highly flexible urethane elastomer (PU) are discussed. This copolymer has been reported to show synergy in its glass transition temperature and some mechanical properties thus provides a fascinating group of high temperature polymers with enhanced flexibility. The results reveal that a processing window of the BA-a/PU mixtures is widened with the increasing urethane prepolymer fraction, that is, the liquefying temperature is lowered and the gel point shifted to higher temperature with the amount of the PU. Synergism in glass transition temperature (T g ) of this copolymer was clearly confirmed, i.e., T g 's of the BA-a/PU alloys were significantly greater than those of the parent resins, i.e., BA-a (T g ¼ 166 C) and PU (T g ¼ À 70 C). In addition, flexural modulus was found to systemically decrease from 5.4 GPa of the neat polybenzoxazine to 2.1 GPa at 40% by weight of the PU. Flexural strength of the alloys also shows a synergistic behavior at the BA-a/PU ratio of 90/ 10. Coefficient of thermal expansion of the polymer alloys were also found to show a minimum value at BA-a/PU ¼ 90/10.

Investigation on Rubber-Modified Polybenzoxazine Composites for Lubricating Material Applications

“…It was found that raising the processing temperature increases the rate of crosslinking of the BA-a/ATBN mixture. Consequently, at higher temperature, the mixture reached its gel point more quickly and the gel time was shorter as similarly observed in BA-a/epoxy mixtures ( Ref 13,15). Furthermore, Fig.…”

“…Moreover, an ability of benzoxazine resins to blend with various other resins or polymers results in new resins with a broad range of applications ( Ref 5,10,11). For example, blending between benzoxazine resins and epoxy resins, polyurethanes, and dianhydrides (Ref [12][13][14][15][16] was considered to be a potentially effective measure to enhance thermal or mechanical properties as well as flammability of the polymers. Furthermore, thermosetting copolymers based on benzoxazine resins and rubbers such as amine-terminated acrylonitrile-butadiene (ATBN) and epoxyterminated liquid nitrile rubber (ETBN) have been reported to provide various useful characteristics ( Ref 17,18).…”

Characterizations of polybenzoxazine modified with isomeric biphenyltetracarboxylic dianhydrides

“…Moreover, polybenzoxazine provides some characteristics such as excellent dimension stability, high heat resistance, flame retardance and low moisture absorption as well as good dielectric properties in which cannot be found in traditional phenolic resins [6,7]. Alloying of polybenzoxazine with various other resins or polymers has been reported to economically provide a novel class of resin systems with superior performance [1,4,[8][9][10][11][12][13][14][15]. However, the major shortcoming of polybenzoxazine is its relatively high rigidity.…”

“…Therefore, various efforts have been done to toughen polybenzoxazine such as by easily blending with more flexible monomers or polymers e.g. flexible epoxy resins [9,12], urethane elastomers [8,13], polyimides [14,15] or dianhydrides [16,17]. In recent reports, thermal and thermo-oxidative stabilities of polybenzoxazines have been substantially improved by alloying techniques [8,[15][16][17][18].…”

“…The authors reported that the Bz-BAMPO: DGEBA at 2:1 mole ratio showed degradation temperature (T d ) at 5% weight loss of about 347°C compared to 333°C of Bz-BAMPO. Moreover, thermomechanical properties of bisphenol A and aniline-based polybenzoxazine (PBA-a) modified with highly flexible urethane elastomer (PU) [13] were reported. The obtained T g of the PBA-a: PU copolymers was in a range of 177 to 245°C which was substantially greater than those of the parent polymers, i.e.…”