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Novel carbon nanofiber (CNF) -filled bismalemide composites were fabricated by a thermokinetic mixing method. The thermal and mechanical properties of composites containing 1 wt % and 2 wt % CNFs were investigated. Thermogravimetric analysis demonstrated that minimal improvement in thermal stability of the nanocomposites was obtained by the addition of CNFs. Dynamic mechanical analysis showed an increase in storage modulus (E 0 ) and glass transition temperature (T g ) upon incorporation of nanofibers. Limiting oxygen index (LOI) has also been found to increase with incorporation of CNFs. Morphological studies of fractured surfaces of the composites has been carried out by scanning electron microscopy to determine the effect of fiber content and dispersion on the failure mechanism. In general, good dispersion was observed, along with agglomeration at some points and some fiber matrix interfacial debonding. A decrease in mechanical strength has been observed and debonding was found as the main failure mechanism. Further research outlook is also presented.

A series of block copolymers that contain rigid liquid crystal forming blocks of poly(p-phenylene terephthalamide) (PPTA) and flexible blocks of hexamethylene adipamide (PA 6,6) have been synthesized. The polymers have been prepared in a one-pot procedure by addition of PA 6,6 monomers to an amine-terminated PPTA oligomer via a low-temperature polycondensation reaction in N-methyl-2-pyrrolidone. Via this method block copolymers are formed that were characterized by inherent viscosity measurements, size exclusion chromatography (SEC), NMR, Soxhlet extraction, and TGA. The molecular weights of the synthesized rod-coil block copolymer materials are estimated from their intrinsic viscosities by a semiempirical model that combines both the intrinsic viscosity relations of the homopolymers and the mean-square end-to-end distance of the rodcoil copolymer.

In this study, a new series of semiflexible liquid crystalline (LC) polyesters and poly(ester‐amide)s were synthesized and characterized. Polymers based on 4‐hydroxybenzoic acid (4‐HBA), 6‐hydroxy‐2‐naphthoic acid (HNA), suberic acid (SUA), and sebacic acid (SEA) were modified with hydroquinone (HQ) and different concentrations of 4‐acetamidophenol (AP) to obtain a polyester and two poly(ester‐amide)s, respectively. All polymers were successfully prepared using conventional melt‐condensation techniques. The polymers were characterized by inherent viscosity measurements, SEC, hot‐stage polarizing microscopy, DSC, and TGA. The mechanical behavior was investigated using DMTA and tensile testing. All linear polymers have Tgs in the range of 50–80 °C and melt between 120 and 150 °C. Our polymers display good thermooxidative stabilities (5% wt loss at ∼ 400 °C) and exhibit homogeneous nematic melt behavior over a wide temperature range (ΔN ∼ 250 °C). The liquid crystal phase was lost when high concentrations of nonlinear monomers such as 3‐HBA (>27 mol %) and resorcinol (RC) (>23 mol %) were incorporated. The LC polyester based on 4‐HBA/HNA/HQ/SUA/SEA could easily be processed into good quality films and fibers. The films display good mechanical properties (E′ ∼ 4 GPa) and high toughness, that is, ∼ 15% elongation at break, at room temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6565–6574, 2008

We present results of the phase behavior in sulfuric acid and a structural investigation in the solid state by DSC and SAXS of a series of rod−coil multiblock copolymers comprised of alternating poly(p-phenylene terephthalamide) (PPTA) and polyamide 6,6 (PA 6,6) blocks. These polymers were synthesized via a low-temperature polycondensation reaction as described in the first paper of this series. Concentrated solutions of the copolymers in sulfuric acid show a liquid crystalline phase if the mole fraction of PPTA exceeds 0.5. The critical concentration for the transition from the isotropic to the liquid crystalline state increases with increasing amount of flexible PA 6,6 segments. Comparison of the phase behavior of the copolymer with that of PPTA provides strong evidence that the coils in the copolymer are significantly stretched in the nematic solutions. Without solvent, DSC experiments show that the crystallization of the PA 6,6 is to a large extent suppressed by the presence of PPTA, but the degree of crystallization increases upon annealing. SAXS experiments revealed that, although some block copolymers show a peak in the SAXS data, there is no evidence for long-range lamellar order in any block copolymer due to the absence of higher order peaks.

The focus of this study is on incorporating pendant sulfonate groups along the backbone of a liquid crystalline polyester (LCPE) with the aim to improve the dispersion of single wall carbon nanotubes (SWNTs) and nanodiamonds (NDs). Two LCPE matrices, one sulfonated (LCPE‐S) and one nonsulfonated reference polymer (LCPE‐R), were successfully synthesized via a melt condensation method using aromatic and aliphatic AB, AA, and BB‐type monomers. Upon the introduction of SWNT and ND particles, the glass transition temperature (Tg) of the sulfonated LCPE increased from 21.5 °C to 41.0 °C and 41.9 °C, for SWNTs and NDs, respectively. When sulfonate groups were absent, a decrease in Tg was observed. The storage modulus (E′) followed a similar trend, i.e., E′ increased from 1.3 GPa to 5.2 GPa and 3.4 GPa, upon the addition of NDs and SWNTs. The LCPE‐S showed a lower thermal stability due to the loss of sulfonate groups, i.e. the 5% weight loss temperature (T d5%) is ∼280 °C for LCPE‐S vs. 333 °C for LCPE‐R. The decomposition temperature increased somewhat upon addition of the nanoparticles. The ability of dispersing carbon‐based nanostructures combined with an accessible melt processing window makes sulfonated LCPs attractive matrices towards preparing nanocomposites with improved thermal and mechanical properties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.

Five semi‐flexible thermotropic liquid crystalline (LC) polyesters and poly(ester‐amide)s were synthesized and used as matrix resins for Twaron™ aramid‐based ballistic fabrics. The ballistic performance was investigated as a function of the neat resin content. For the most successful liquid crystalline polyester system, the effect of blending with styrene‐ethylene‐butylene‐styrene (SEBS) and polyvinyl butyrate (PVB) rubber was also explored. The best neat resin V50 values were obtained for 20 wt% LC polyester (LCPE)‐Twaron™ composites, that is, 418 m.s−1, whereas SEBS/LCPE and PVB/LCPE modifications resulted in maximum V50 values of 460 and 466 m.s−1, respectively. It was found that the ballistic impact resistance is strongly influenced by the elastic modulus of the resin component and to a lesser extent to the level of adhesion between the resin and fabric. The effect of resin content, resin strength, elongation‐at‐break, and resin toughness on the ballistic impact resistance was found to be small. The best ballistic protection could be obtained when the Young's modulus of the LC resin was in the range of 0.01–1 GPa. This result seems to be in agreement with existing inter‐yarn friction models. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers