Hai-ming Chen

Effect of the interfacial structure on the thermal stability of poly(methyl methacrylate)-silica hybrids

Abstract Poly(methyl methacrylate)–silica hybrid materials, P(MMA-MA5)–SiO 2 or P(MMA-GMA5)–SiO 2 , were synthesized from the in situ reaction of the methyl methacrylate (MMA) with maleic anhydride (MA) or glycidyl methacrylate (GMA), then hydrolyzed with 3-aminopropyl methyl diethoxysilane (APrMDEOS) and tetraethoxysilane (TEOS) by a sol–gel process. The thermal stability and the apparent activation energies ( E a ) of the PMMA moieties in the hybrids under air and nitrogen, evaluated by van Krevelen’s method, were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). P(MMA-GMA5)–SiO 2 hybrids with the flexible chain of the coupling agent had the lower glass transition temperature ( T g ) and E a . Moreover, the structure of the coupling agent influences the thermal and thermo-oxidative degradation of the PMMA within the hybrids.

Organic-inorganic hybrid materials 7 : characterization and degradation of polyvinylimidazole-silica hybrids

Abstract Polyvinylimidazole–silica hybrid materials (PVI–SiO 2 ) containing various proportions of covalently bonded silica were prepared from [3-(methacryloxy)propyl]trimethoxysilane modified polyvinylimidazole (PVI), water and tetramethoxysilane (TMOS) via a sol–gel technique. Infrared (IR), 29 Si and 13 C nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to analyse the structures and properties of hybrids with various proportions of TMOS. The apparent activation energies E a for desorption of water and decomposition of PVI chains in hydroxylated hybrids were respectively around 55 and 35 kJ/mol, while the values were increased by about 10 kJ/mol in dehydroxylated hybrids.

Organic-inorganic hybrid materials. II. Chain mobility and stability of polysiloxaneimide-silica hybrids

Polysiloxaneimide-silica hybrid materials (PSI-SiO 2 ) were obtained using the sol-gel technique by polycondensation of tetramethoxysilane (TMOS) in a polyamic acid solution. IR, 29 Si- and 13 C-NMR spectroscopy, and thermogravimetric analysis were used to study hybrids containing various proportions of TMOS and hydrolysis ratios. The morphology, dynamics, and thermal stability of the hybrids were investigated. The chain mobility of the hybrids was investigated by spin-spin relaxation time (T 2 ) measurements. The apparent activation energy (E a ) for degradation of the hybrids in air was studied by the van Krevelen method. The T 2 value was independent of the silica content whereas that of the E a decreased as silica content increased.

Effect of graphene oxides on thermal degradation and crystallization behavior of poly(L-lactide)

Graphene oxides (GO) were introduced into a poly(L-lactide) (PLLA) to prepare the PLLA/GO composites with different concentrations of the GOs. The main attention of the present work was focused on the thermal degradation and crystallization behaviors of a PLLA matrix induced by GOs. The measurements based on gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) clearly proved the thermal degradation of the PLLA matrix during the melt-processing procedure. Consequently, reduced complex viscosity of the composites was achieved. The crystallization behaviors of the PLLA matrix were comparatively investigated under different crystallization conditions including melt-crystallization (nonisothermal or isothermal crystallization occurring from the melt state) and cold-crystallization (crystallization occurring from an amorphous solid state) using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD). Largely enhanced crystallization ability of the PLLA matrix was achieved. The crystallization conditions and the GO content are key factors which influence the crystallization behavior of the PLLA matrix. This work proved that the stabilization of the PLLA matrix during the melt-processing procedure must be considered when designing and preparing the PLLA/GO materials.

Carbon nanotubes induced poly(vinylidene fluoride) crystallization from a miscible poly(vinylidene fluoride)/poly(methyl methacrylate) blend

Different contents of carbon nanotubes (CNTs) were introduced into a miscible poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend. The interfacial affinity between CNTs and components of the blend was evaluated by calculating the interfacial tension. The dispersion and microstructure of CNTs in the nanocomposites were investigated through scanning electron microscope and rheological measurement. The effect of CNTs on the crystallization of PVDF was comparatively investigated through nonisothermal and isothermal crystallization processes. The results showed that CNTs exhibited stronger interfacial affinity to PMMA. Homogeneous dispersion of CNTs in the nanocomposites was achieved. Largely enhanced crystallization temperature and increased crystallinity of PVDF were obtained by adding CNTs during the nonisothermal crystallization process. The results obtained from the isothermal crystallization process proved that CNTs induced the concentration fluctuation in the sample, which resulted in the formation of spherulites with different types, i.e., the banded spherulites and compact spherulites. Furthermore, both the crystallization temperature and the content of CNTs exhibited great influence on the crystalline morphology of PVDF.

Characterization and degradation of hydrogen-bonded acidic polyamideimides linked by disiloxanes

Hydrogen-bonded acidic poly(siloxane amideimide)s (PSAIs) were synthesized by partial imidization of 3,3′,4,4′-benzophenone- tetracarboxylic dianhydride (BTDA) with 2,2′,bis(3-amino-4-hydroxyphenyl) hexafluoropropane (AHHFP) and 1,3-bis(3-aminopropyl)tetramethyldisiloxane (APrTMDS). Infrared (IR) and 13C nuclear magnetic resonance (NMR) spectroscopies characterized the structure of PSAI copolymers. The apparent activation energy Ea of degradation of PSAI copolymers in air was studied by thermogravimetry and compared with unmodified polyamideimide (PAI). The higher Ea of the PSAIs in air than that of the PAI suggests that the disiloxane enhanced the stability of the polyamideimide, and the smaller spin–spin relaxation time T2 of the PSAI copolymers than that of the PAI reveals that the PSAI had more closely packed structure with increasing APrTMDS.

Tuning the interaction of an immiscible poly(L-lactide)/poly(vinylidene fluoride) blend by adding poly(methyl methacrylate) via a competition mechanism and the resultant mechanical properties

In this work, a mutually miscible third polymer, i.e. poly(methyl methacrylate) (PMMA), was introduced into an immiscible poly(L-lactide) (PLLA)/poly(vinylidene fluoride) (PVDF) (60/40, wt/wt) blend. The interactions between PMMA and both components of the immiscible blend were first theoretically predicted by calculating the interfacial tensions and then experimentally proven by characterizing the glass transition and crystallization behaviors of the components. The results showed that although PMMA was miscible with PLLA and PVDF, it exhibited stronger interaction with PVDF and had a tendency to merge together with the PVDF component during the melt-compounding processing. There was a competition effect between PLLA and PVDF when they absorbed PMMA. Consequently, the interaction between PVDF and PLLA was enhanced by the bridge effect of PMMA. Furthermore, the migration and diffusion of PMMA carried a part of the PLLA component into the PVDF component (or carried some PVDF component into the PLLA component), forming a so-called occlusion structure. The mechanical properties were measured and the results showed that, at appropriate PMMA content (20–30 wt%), the ternary blends exhibited excellent fracture toughness. The enhanced interaction between components and the formation of the occlusion structure were suggested to be the main toughening mechanisms. This work demonstrated that the microstructure and mechanical properties of the immiscible polymer blends could be tuned by adding a mutually miscible third polymer via a competition mechanism and therefore it provided an alternative strategy for preparing microstructure-/property-controllable materials.

Fracture Behavior of Poly(trimethylene terephthalate) Toughened by Maleic Anhydride Grafted Styrene-Ethylene-Butadiene-Styrene Block Copolymer

Maleic anhydride grafted styrene-ethylene/butadiene-styrene block copolymer (SEBS-g-MA) was introduced into poly(trimethylene terephthalate) (PTT) to prepare the PTT/SEBS-g-MA blends. The results showed that SEBS-g-MA exhibited dispersed particles and the particle sizes changed with the variation of its content. Furthermore, the crystallization behavior of PTT matrix was restricted by adding SEBS-g-MA. Mechanical properties measurements proved that PTT could be toughened by SEBS-g-MA and the toughening effect was greatly dependent upon the SEBS-g-MA content and the measurement conditions. The toughening mechanism was mainly attributed to the largely enhanced resistance of the crack propagation during the fracture process.