Jiasong He

NMR spectroscopic studies of cellobiose solvation in EmimAc aimed to understand the dissolution mechanism of cellulose in ionic liquids.

The dissolution mechanism of cellulose in ionic liquids has been investigated by using cellobiose and 1-ethyl-3-methylimidazolium acetate (EmimAc) as a model system under various conditions with conventional and variable-temperature NMR spectroscopy. In DMSO-d(6) solution, NMR data of the model system clearly suggest that hydrogen bonding is formed between hydroxyls of cellobiose and both anion and cation of EmimAc. The CH(3)COO(-) anion favors the formation of hydrogen bonds with hydrogen atoms of hydroxyls, and the aromatic protons in bulky cation [Emim](+), especially the most acidic H2, prefer to associate with the oxygen atoms of hydroxyls with less steric hindrance, while after acetylation of all hydroxyls in cellobiose the interactions between cellobiose octaacetate and EmimAc become very weak, implying that hydrogen bonding is the major reason of cellobiose solvation in EmimAc. Meanwhile the stoichiometric ratio of EmimAc/hydroxyl is estimated to be between 3:4 and 1:1 in the primary solvation shell, suggesting that there should be one anion or cation to form hydrogen bonds with two hydroxyl groups simultaneously. In situ and variable-temperature NMR spectra suggest the above mechanism also works in the real system.

Definitions of terms relating to the structure and processing of sols, gels, networks, and inorganic-organic hybrid materials (IUPAC Recommendations 2007)

This document defines terms related to the structure and processing of inorganic, polymeric, and inorganic-organic hybrid materials from precursors, through gels to solid products. It is divided into four sections - precursors, gels, solids, and processes - and the terms have been restricted to those most commonly encountered. For the sake of completeness and where they are already satisfactorily defined for the scope of this document, terms from other IUPAC publications have been used. Otherwise, the terms and their definitions have been assembled in consultation with experts in the relevant fields. The definitions are intended to assist the reader who is unfamiliar with sol-gel processing, ceramization, and related technologies and materials, and to serve as a guide to the use of standard terminology by those researching in these areas.

Chemical structure and physical properties of cyclic olefin copolymers (IUPAC Technical Report)

Cyclic olefin copolymers comprise a new class of polymeric materials showing properties of high glass-transition temperature, optical clarity, low shrinkage, low moisture absorption, and low birefringence. There are several types of cyclic olefin copolymers based on different types of cyclic monomers and polymerization methods. In this work, we have analyzed the chemical structure of the currently commercialized cyclic olefin copolymers by 13C NMR, and investigated their glass-transition temperatures and surface characteristics. It was observed that the glass-transition temperature, Tg, of cyclic olefin copolymers depended on the bulkiness of the main chain, and the number of rings had an important role in increasing the bulkiness of cyclic olefin copolymers. Cyclic olefin copolymers with polar substituents such as ester or ether groups showed high surface energy per area and peel strength.

Thermoplastic cellulose-graft-poly(L-lactide) copolymers homogeneously synthesized in an ionic liquid with 4-dimethylaminopyridine catalyst.

An effective method for grafting L-lactide (LA) from unmodified cellulose by ring-opening polymerization (ROP) in homogeneous mild conditions is presented. By using 4-dimethylaminopyridine (DMAP) as an organic catalyst, cellulose-graft-poly(L-lactide) (cellulose-g-PLLA) copolymers with a molar substitution (MS(PLLA)) of PLLA in a range of 0.99-12.28 were successfully synthesized in ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl) at 80 degrees C. The amount and length of grafted PLLA in cellulose-g-PLLA copolymers were controlled by adjusting the molar ratios of LA monomer to cellulose. The structure and thermal properties of cellulose-g-PLLA copolymers were characterized by (1)H NMR, (13)C NMR, wide-angle X-ray powder diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and optical microscopy. The DSC results revealed that the copolymers exhibited a single glass transition temperature, T(g), which sharply decreased with the increase of MS(PLLA) up to MS(PLLA) = 8.28 (DS(PLLA) = 2.19) and increased a little with a further increase of the lactyl content. When MS(PLLA) was above 4.40, the graft copolymers exhibited thermoplastic behavior, indicating the intermolecular and intramolecular hydrogen bonds in cellulose molecules had been effectively destroyed. By using a conventional thermal processing method, fibers and disks of cellulose-g-PLLA copolymers were prepared.

Compatibilization of blends containing thermotropic liquid crystalline polymers with sulfonate ionomers

Zinc salts of lightly sulfonated polystyrene ionomers (Zn-SPSs) are shown to be effective compatibilizers for blends of a wholly aromatic liquid crystalline polyester (LCP) with nylon 66 (PA66) and polycarbonate (PC). Zn-SPS is miscible with PC, PA66 and the LCP, though the origins of miscibility are different for the three binary blends. Zn-SPS and PA66 mix because of strong intermolecular attractive interactions between the sulfonate and amide groups, while the ionomer is miscible with PC and the LCP as a result of intramolecular repulsive interactions along the ionomer molecules. The addition of Zn-SPS to LCP/PA66 and LCP/PC blends reduces the dispersed phase size and improves the adhesion between the phases. The compatibilized blends have significantly higher tensile modulus and tensile stress at break than the blends without ionomer.

Crystallization kinetics of maleic anhydride grafted polypropylene ionomers

Abstract Polypropylene (PP) was lightly maleated by solid-state graft polymerization and further neutralized to prepare semicrystalline ionomers, H+-, Na+-, Ca2+- and Mn2+-form maleated PP (mPP). The crystallization kinetics of pure PP and these ionomers have been investigated under isothermal and non-isothermal conditions. Under both conditions, the introduction of pendant groups along the PP chains increases the crystallization rate and does not influence the crystallization mode. The energy required for folding macromolecules to form nuclei becomes smaller in case of ionomers. The facility of nucleation in ionomers by the ionic interactions may result in high crystallization rate, while the decrease of chain diffusion in mPP ionomers has a reverse effect at the same time.

Stable dispersions of reduced graphene oxide in ionic liquids

Starting with graphene oxide, we successfully prepared stable dispersions of reduced graphene oxide (RGO) in three hydrophilic ionic liquids (ILs) at relatively high concentration without using any surfactants/stabilizers.

DEFINITIONS OF TERMS RELATING TO REACTIONS OF POLYMERS AND TO FUNCTIONAL POLYMERIC MATERIALS (IUPAC Recommendations 2003)

The document defines the terms most commonly encountered in the field of polymer reactions and functional polymers. The scope has been limited to terms that are specific to polymer systems. The document is organized into three sections. The first defines the terms relating to reactions of polymers. Names of individual chemical reactions are omitted from the document, even in cases where the reactions are important in the field of polymer reactions. The second section defines the terms relating to polymer reactants and reactive polymeric materials. The third section defines the terms describing functional polymeric materials.

In situ hybrid composites of thermoplastic poly(ether ether ketone), poly(ether sulfone) and polycarbonate

Abstract In order to overcome the poor processability of short-fibre-reinforced thermoplastics and to enhance the mechanical performance of thermoplastics reinforced with thermotropic liquid crystalline polymer (TLCP) fibrils (in situ composites), a new concept of an in situ hybrid composite has been put forward. This group of polymer–matrix composites, basically consisting of a thermoplastic matrix, inorganic fibres of micrometeres in diameter and organic TLCP fibrils of submicrometres in diameter, has hybrid effects of rheology, geometry and mechanics originating from these two reinforcements at two orders of magnitude. In situ hybrid composites, such as TLCP/carbon-fibre-reinforced poly(ether ether ketone), TLCP/carbon-fibre-reinforced poly(ether sulfone) and TLCP/glass-fibre-reinforced polycarbonate systems, show lower melt viscosity and excellent processability, minimized breakage of fibres added, favoured orientation of reinforcing fibres and enhanced tensile strength and modulus, flexural strength and modulus and impact strength, compared to their pristine short-fibre-reinforced composites.

In-situ hybrid composites containing reinforcements at two orders of magnitude

By combining the concepts of the in-situ composite and hybrid composite, a concept of in-situ hybrid composites has been put forward. A composite structure of polyethersulfone reinforced by carbon fibres (CF) and thermotropic liquid crystalline polymer (TLCP) fibrils has been formed in injection-moulded bars by matching the characteristics and processing conditions of the TLCP and the matrix resin. These TLCP fibrils with large intrinsic aspect ratios are generated in-situ in the melt of the resin matrix during the processing of the ternary blends. This technique uses TLCPs to decrease the viscosity of the whole blend systems and to minimize the CF breakage as well. The improved processability is especially beneficial for the processing of advanced engineering plastics. This technique, forming reinforcements at two orders of magnitude in the resultant composites, utilizes these two reinforcements to balance the enhanced mechanical properties of the hybrid composites.