MORPHOLOGY AND DYNAMIC MECHANICAL-PROPERTIES OF AB CROSS-LINKED POLYMERS BASED ON POLYURETHANES

Polyoxypropylene glycol (PPG) (or castor oil) and toluene diisocyanate (TDI) were mixed, and the prepolymer polyurethane (PU) (I) was formed. Vinyl-terminated polyurethane (II) was prepared from (I), and hydroxyethyl acrylate, AB crosslinked polymers (ABCPs) were synthesized from (II) and vinyl monomers such as styrene, methyl methacrylate, vinyl acetate, etc. The dynamic mechanical properties and morphology of ABCPs were measured. The ABCPs based on PPG have double glass transition temperatures (T(g)) on the sigma-vs. temperature curves. They display a two-phase morphology with plastic components forming the continous phase and PU-rich domains forming the separated phase on the electron micrographs. Irregular shapes and a highly polydisperse distribution of PU-rich domain sizes were observed. The crosslink density of ABCPs has a notable effect on the morphology and properties. The average diameter of the PU-rich domains depends on the molecular weight of prepolymer PPG. The highly crosslinked structures will produce large numbers of very small domains. ABCPs based on castor oil show a single T(g) relaxation on the dynamic mechanical spectra. The compatibility between the two components is much better in ABCPs based on castor oil than in those based on PPG, because there is a high crosslink density in the former. Comparison of the dynamic mechanical spectra of ABCP and interpenetrating networks (IPN) based on castor oil with similar crosslink density and composition imply that the two components in ABCP are compatible whereas microphase separation occurs in IPN. An improvement in the compatibility is achieved by the crosslinking between the two networks.

A SIMPLE METHOD FOR PREDICTION OF GAS-PERMEABILITY OF POLYMERS FROM THEIR MOLECULAR-STRUCTURE

A method for the prediction of gas permeabilities (P) through polymers from their chemical structure has been developed on the basis of the ratio of molar free volume to molar cohesive energy, V(f)/E(coh). The permeation of small gas molecules through polymer membranes is dependent on the chain packing density measured by V(f) and segmental motion of polymer chains measured by E(coh). But no simple relationship between P and V(f) or E(coh) alone was found. The permeability data of more than 60 polymers covering 7 orders of magnitude for six gases have been treated with linear regression analysis. All plots of log P vs. V(f)/E(coh) gave good straight lines. It is also found that a linear relationship holds when plotting both the intercepts and slopes of log P vs. V(f)/E(coh) lines against square of the diameters of gas molecules. Therefore, the permeabilities of all the non-swelling gases through a great variety of polymers can be estimated using two correlations above. Moreover, this method is more accurate than others in the literature and may found useful for the selection of gas separation or barrier membrane materials.

WATER-SOLUBLE AND AMPHIPHILIC POLYMERS .6. A STUDY ON THE SURFACE-COMPOSITION OF CAST FILMS OF PST/PMAA AND PEO-PST-PEO BLOCK POLYMERS BY XPS

Thin films of PSt/PMAA and PEO-PSt-PEO block polymers were deposited on a polystyrene substrate by solution adsorption (with or without solvent treatment), and the film surfaces were characterized by means of XPS. Direct solvent - casting of PEO-PSt-PEO from benzene solutions resulted in PSt-rich surfaces, whereas PMAA richer surfaces were obtained for PSt/PMAA films cast from DMF solutions. Moreover, solvent treatment after casting had profound effect on the film surface composition. Treatment with water markedly increased the surface concentration of polar PEO segments. In the case of PSt-PMAA block polymers, the PSt content on the surface increased in the order of water < ethanol < cyclohexane < petroleum ether, the last-named giving films with almost pure PSt surface. It is well worth noticing that the bulk composition had little to do with the surface composition for both PSt/PMAA and PEO-PSt-PEO block polymers within the composition range investigated when subsequent solvent treatment was applied.

WATER-SOLUBLE AND AMPHIPHILIC POLYMERS .7. SYNTHESIS AND CHARACTERIZATION OF A NOVEL COMB-TYPE AMPHIPHILIC POLYMER PAMC16S

A novel comb-like amphiphilic polymer, poly (2-acrylamidohexadecylsulfonic acid) (PAMC16S), was synthesized by free radical polymerization of the corresponding amphiphilic monomer in 1,4-dioxane-water mixed solvents. Depending on the ratio of water/dioxane in the solvent, the reaction proceeded by either precipitation polymerization or micellar polymerization. The molecular weight of the polymer obtained under similar conditions decreased and subsequently increased with the increase of water content in the mixed solvent. The polyion nature of PAMC16S was confirmed by viscosity data of ethanolic solutions. In addition, the polymer was characterized by solubility, IR, TG and wide angle X-ray diffraction methods.

EQUATION OF STATE FOR POLYMERS

In the theoretical study on equation of state for polymers, much attention has been paid to the polymer in liquid state, but less to that in solid state. Therefore, some empirical and semi-empirical equations of state have been used to describe its pressure-volume-temperature (P-V-T) relations.

CHARACTERIZATION OF GAMMA-RADIATION CROSS-LINKED CRYSTALLINE POLYMERS BY CRYSTALLIZATION TEMPERATURE

The effect of gamma-radlatlon on plain crystalline polymers and crystalline polymers containing different amounts of difunctional monomer both in vacuum and in air at room temperature has been investigated with DSC. It was found that the crystallization temperature T_c of crosslinked sample measured on DSC at a constant cooling rate decreases with increasing radiation dose. The difference between T_c before and after crosslinking (T_(c_0)-T_(c_R)) is linearly related to the radiation dose for plain polymer....

Studies on two coordination polymers [M(mu(4)-pz25dc)](n) (M = Cd or Zn, pz25dc=pyrazine-2,5-dicarboxylato) with three-dimensional pillared-layer three-nodal framework: Synthesis, structural characterization, strong optical non-linearities and optical limiting properties

Two isomorphous new candidates [M(mu(4)-pz25dc)](n) (M = Cd, 1; Zn, 2; pz25dc = pyrazine-2,5-dicarboxylato)for nonlinear optical (NLO) materials have been synthesized hydrothermally and characterized crystallographically as pillared-layer three-nodal frameworks with one four-connected metal nodes and two crystallographically different four-connected ligand nodes. Their optical non-linearities are measured by the Z-Scan technique with an 8 ns pulsed laser at 532 nm. These two coordination polymers both exhibit strong NLO absorptive abilities [alpha(2) = (63 +/- 6) x 10 (12) mW (1) 1, ( 46 +/- 6) x 10 (11) mW (1) 2] and effective self-focusing performance [n(2) = (67 +/- 5) x 10 (18) 1, (13 +/- 3) x 10 (18) m(2) W (1) 2] in 1.02 x 10 (4) 1 and 1.05 x 10 (4) mol dm (3) 2 DMF solution separately. The values of the limiting threshold are also measured from the optical limiting experimental data. The heavy atom effect plays important role in the enhancement of optical non-linearities and optical limiting properties. (C) 2009 Elsevier B. V. All rights reserved.

Review of Artificial Muscle Based on Contractile Polymers

An artificial muscle with strength and speed equal to that of a human muscle may soon be possible. Polymer gels exhibit abrubt volume changes in response to variations in their external conditions -- shrinking or swelling up to 1000 times their original volume. Through the conversion of chemical or electrical energy into mechanical work, a number of devices have already been constructed which produce forces up to 100N/cm2 and contraction rates on the order of a second. Through the promise of an artificial muscle is real, many fundamental physical and engineering questions remain before the extent or limit of these devices is known.

Dynamic Model and Control of an Artificial Muscle Based on Contractile Polymers

A dynamic model and control system of an artificial muscle is presented. The artificial muscle is based on a contractile polymer gel which undergoes abrupt volume changes in response to variations in external conditions. The device uses an acid-base reaction to directly convert chemical to mechanical energy. A nonlinear sliding mode control system is proposed to track desired joint trajectories of a single link controlled by two antagonist muscles. Both the model and controller were implemented and produced acceptable tracking performance at 2Hz.