Riwei Xu

Cross-Linked Quaternized Poly(styrene-b-(ethylene-co-butylene)-b-styrene) for Anion Exchange Membrane: Synthesis, Characterization and Properties

Poly(styrene-b-(ethylene-co-butylene)-b-styrene) triblock copolymer (SEBS) was selected for functionalization and cross-linking reaction to prepare the anion exchange membrane. The cross-linked quaternized SEBS (QSEBS-Cn) membranes were synthesized by simultaneous of quaternization and cross-linking of chloromethylated SEBS with α,ω-difunctional tertiary amines. The spacer groups of (-CH2-)n in diamines did affect the functionalization, micromorphology and properties of the resulting QSEBS-Cn membranes. The ionic conductivity of QSEBS-Cn membranes greatly increased and methanol resistance slightly decreased with increasing the length of spacer groups in the cross-linked structures from -(CH2)- to -(CH2)6-. Compared to the un-cross-linked QSEBS, the QSEBS-Cn membranes behaved much higher mechanical property, service temperature, chemical stability and thermal stability. Moreover, the hybrid composite membrane of QSEBS-C6 with 0.5% of graphene oxide could also be in situ prepared. This hybrid membrane had both relatively high ionic conductivity of 2.0 × 10(-2) S·cm(-1) and high selectivity of 7.6 × 10(4) S·s·cm(-3) at 60 °C due to its low methanol permeability.

Curing kinetics of benzoxazine resin by torsional braid analysis

Abstract Benzoxazine precursor is synthesized and is tested by torsional braid analysis. The phenomena of gelation and glass transitions which occur in the formation of thermosets are found and studied. In particular, two special secondary glass transitions appear at the curing temperature and the time–temperature-transformation spectrum is obtained.

Development of a cross-linked quaternized poly(styrene-b-isobutylene-b-styrene)/graphene oxide composite anion exchange membrane for direct alkaline methanol fuel cell application

A cross-linked quaternized poly(styrene-b-isobutylene-b-styrene)/graphene oxide composite anion exchange membrane has been prepared via intercalation of organo-modified graphene oxide (GOA), and characterized as a promising anion exchange membrane for direct alkaline methanol fuel cell application. In order to further increase the ionic conductivity of the composite membrane, quaternized GOA (GOAN) was introduced into QSIBS. Compared with the Nafion® membrane, the new anion exchange membranes show a comparable ionic conductivity (1.95 × 10−2 S cm−1) but much lower methanol permeability (1.7 × 10−7 cm2 s−1). The QSIBS/0047OAN-0.50 wt% composite membrane has the highest selectivity, which is about 12 times higher than that of the Nafion 115 membrane. The promising performance is attributed to two factors: one is the barrier effect of the quaternized octadecylamine-functionalized graphene oxide sheets, which is unfavourable for methanol crossover; and the other is the presence of interconnected ionic transportation channels between the incorporated modified graphene oxide and polymer, which is favourable for ionic transport.

Synthesis and Characterization of a Novel 2-Oxazoline-Benzoxazine Compound with Incorporated Polyhedral Oligomeric Silsesquioxane

A novel 2-oxazoline-benzoxazine compound (POB) was synthesized and characterized by FT-IR, 1H-NMR, 13C-NMR and MS. Simultaneously, octa(aminophenyl)silsesquioxane was also synthesized and incorporated in POB to prepare the nanocomposites. The 1H-NMR spectra of the formulated POB and OAPS solution showed the reaction of 2-oxazoline ring and amino group at room temperature, the reaction mechanism was suggested for the first time, and finally the product containing benzamidine structure was obtained. DMA results showed that little content of OAPS (0.5 wt%) remarkably enhanced the thermal properties of PolyPOB; however, excessive content of OAPS may be impair the thermal properties of the nanocomposite. It is speculated that the introduced OAPS decreased the packing density of PolyPOB, which led to the decreasing of char yield (at 800°C) with the increasing of OAPS contents. The TEM micrographs indicated that 0.5 wt% content of OAPS dispersed homogenously in PolyPOB matrix, while aggregation will occur in the nanocomposites containing 5 wt% OAPS.

Polybenzoxazine-POSS Nanocomposites

Publisher Summary POSS exhibits an intramolecular hybrid structure that can be incorporated into the polymers without further surface treatment. Many kinds of POSS compounds are employed to modify polybenzoxazine resin. The POSS is well dispersed in the poly(BA-a) matrix, the poly(BA-a)-POSS composites exhibit higher glass transition temperatures, better thermal degradation temperature, and higher char yield than pristine polybenzoxazine resin. Great efforts are taken to find facile synthesis routes of POSS compounds to obtain inexpensive, designed POSS structures. On the other hand, many synthesis methods, especially click reaction, which received increasing attention from the field of polymer science, can be employed to prepare novel POSS compounds and POSS containing PBZ resin. These newly reported novel POSS compounds and benzoxazine monomers can be used to prepare PBZ resin with better overall properties. Designed POSS compounds and benzoxazine monomers will definitely lead to a bright future for the study of PBZ-POSS nanocomposites. The concept of utilizing POSS to modify polybenzoxazine resin aimed to obtain high performance PBZ-POSS nanocomposites is an exciting area that is just beginning to be explored. The tailorability and versatility of the POSS compounds make them ideally suited for this purpose. The incorporation of POSS into some polymers has offered the opportunity to develop new types of materials that combine many desirable properties; POSS-containing polymer is still one of the hottest spots in the field of organic–inorganic hybrid materials.

Viscoelastic Properties and Determination of Plateau Modulus for Ziegler‐Natta Catalyzed Ethylene‐Propylene Random Copolymer

The viscoelastic behavior of ethylene‐propylene random copolymer with ultra‐high molecular weight (UHPPR) and broad molecular weight distribution (MWD), produced with Ziegler‐Natta catalyst, was investigated by means of oscillatory rheometry at 180°C, 200°C, and 220°C. The loss modulus (G″) curves of 180°C and 200°C present a pronounced peak at 38.10 rad/s and 84.70 rad/s, respectively, while the peak of G″ curve at 220°C locates beyond 100 rad/s. Compared with UHPPR, G″(ω) curves at 180°C and 200°C for Ziegler‐Natta catalyzed ethylene‐propylene random copolymer (PPR) with conventional molecular weight and broad MWD, did not show a peak at 0.01–100 rad/s, respectively. This fact indicates that high molecular weight is responsible for a peak of G″ curves for UHPPR. On the other hand, the activation energy of crossover relaxation time τ c (ΔH a,c) and terminal relaxation time τm (ΔH a,m) is 57.4 kJ/mol and 57.7 kJ/mol, respectively, and shows the same dependence of temperature, which also gives another evidence of the presence of a peak in the G″(ω) curves at 180°C and 200°C. For UHPPR, the plateau modulus (G N 0) which was determined to be 4.51×105 Pa and 3.67×105 Pa at 180°C and 200°C, respectively, decreases with increasing temperature and is independent of molecular weight and MWD. The entanglement points of each molecular chain for UHPPR are much higher than those for PPR with conventional molecular weight, which is a partial reason why the melt viscosity increases with increase of molecular weight.

Chapter 37 – Recent Progress in Polybenzoxazine/POSS Hybrid Materials

This chapter is intended to review recent advances in the field of polybenzoxazine (PBZ) resin modified by polyhedral oligomeric silsequioxane (POSS) and related compounds. After a brief introduction of POSS, the types of POSS precursors used in polybenzoxazine/POSS (PBZ/POSS) hybrid materials are classified and the main synthetic approaches for each type of POSS precursors are reviewed. The methods of incorporating POSS into PBZ/POSS hybrid materials are summarized, and the most-cited papers of PBZ/POSS hybrid materials are listed for further study. The PBZ/POSS hybrid materials have been classified for the purpose of research and are discussed separately. Most of the research reveals that the incorporation of the POSS into polybenzoxazine matrixes can result in significant improvements in mechanical properties, thermal stability, radiation resistance, and that the dielectric constant of materials can be reduced. Considering the tailorability and versatility of the POSS compounds, PBZ/POSS hybrid materials will be developed further, especially for functional properties such as radiation resistance, UV resistance, a low dielectric constant etc.