AN EXPERIMENTAL STUDY ON THE SOL/GEL PHASE TRANSITION OF LINEAR POLYMER IN THE PRESENCE OF CROSSLINKERS

The sol/gel phase diagrams were studied for two systems: polyacrylamide/Cr (III) and polyacrylamide/glyoxal. Sol or gel phase could be distinguished according to the concentrations of polymer and crosslinker. The boundary polymer concentration did not depend on the types of gelation and decreased with increasing polymer dimension (molecular weight and conformation). The gelation, which is basically interchain bonding, requires the occurrence of entanglement. The overlap concentration is thus considered as the minimum polymer concentration required for gelation.

EFFECT OF POLYMERIZATION CONDITIONS ON THE MOLECULAR WEIGHT OF POLYPHENYLSILSISQUIOXANE

Samples of polyphenylsilsisquioxane (PPSQ)using CaF_2 or MgF_2 as the main catalysts hadbeen prepared under different polymerization conditions. The results were treated on anorthogonal design L_9 (3~4). All weight-average molecular weights (M_W ) of PPSQ had beenmeasured by gel permeation chromatography (GPC). Effects of polymerization conditionsincluding reaction temperature, composition of the dual catalysts (CaF_2 or MgF_2 and DCC),mixture of solvents and reaction time on M_W of PPSQ have been discussed. The quantity of thecatalysts is the most important factor that affects M_W of PPSQ. Reaction temperature is thesecond important factor. Appropriate polymerization condition has been established to get PPSQwith high M_W.

COMPUTER SIMULATION OF POLYMER SOLUTION THERMODYNAMICS

The statistical counting method for the computer simulation of the thermodynamic quantities of polymer solution has been reviewed. The calculating results for a single athermal chain confirm the theory of the renormalization group. The results for the athermal solution are consistent with the scaling law of the osmotic pressure with the exponent 2.25. The results for a single chain with the segmental interaction are in a good agreement with the exact results obtained by the direct counting method. The results for the polymer solution show us that the Flory-Huggins parameter is strongly dependent on both the polymer concentration and the interaction energy between segments. (Author abstract) 15 Refs.

DETERMINATION OF PHASE INVERSION POINT IN THE EMULSIFICATION OF POLYMERS

Phase inversion emulsification technique is a recently developed method to achieve waterborne dispersions of polymer resin. It is found that the electrical and rheological properties of the system experience abrupt changes in the vicinity of the phase inversion point (PIP). Before PIP, the system is a Newtonian fluid. At PIP, the continuous phase transforms from polymer resin to water phase with the result that the electrical resistance of the system drops abruptly. Meanwhile, the system at PIP exhibits high viscoelasticity originated from the formation of a physical gel alike structure among the waterborne particles. Besides, the morphology evolution is observed by Scanning Electron Microscopy (SEM).

A STUDY ON CONFORMATIONAL STRUCTURE OF MODEL COMPOUND OF NOVEL SIDE CHAIN LIQUID CRYSTALLINE POLYMER BY USING HIGH RESOLUTION SOLID STATE ^(13)C-NMR

^(13)C-NMR chemical shifts of model compound of a novel side chain liquid crystalline polymer, poly 2.5-his (4-alkoxybenzoyloxy) styrene , have been assigned in this study. Moreover, by using high-resolution solid-state CP/MAS (cross polarization/magic angle spinning) technique, the spectrum shows that in the crystalline state the ester linkage has a conformation nearly perpendicular to the either side of ring planes, and that the alkoxy groups are not fully in zigzag form. The possible conformational changes around the mesogens from the solid state to the mesophase are discussed.

MORPHOLOGICAL AND KINETIC STUDIES OF PHASE TRANSITIONS OF A SIDE-CHAIN LIQUID CRYSTALLINE POLYMER

The morphological changes of a side-chain liquid-crystalline polymethacrylate during isotropization and liquid-crystallization transitions were studied by means of polarizing microscopy. These transitions were found to be composed of the initiation of a new phase at local places of the old phase matrix and the growth of the new phase: domains. The kinetics of the liquid-crystallization of the polymer from an isotropic melt to a smectic mesophase was also investigated. The isothermal process of the transition can be described by the Avrami equation. The values of the Avrami exponent were found to be around 2.6. which is lower than the value usually obtained for crystallization transition of polymers, but larger than that reported for liquid-crystallization transition of main-chain polymers. These results may indicate the difference in growth geometry of new phase during transition between crystallization and liquid-crystallization in general and between liquid-crystallization of main-chain and side-chain polymers. It was found that the liquid-crystallization of the used side-chain polymethacrylate may occur at small undercoolings with high transformation rate similar to that of main-chain polymers and small-molecule liquid crystals, while the crystallization of polymers can only proceed at large undercoolings. These phenomena can be explained by the idea that the surface free energy of nucleus during liquid-crystallization transition is less than that for crystallization, and evidence was obtained from analysis of the temperature dependence of the transformation rate.

EFFECT OF POLYMERIZATION CONDITIONS ON THE LADDERLIKE STRUCTURE OF POLYPHENYLSILSESQUIOXANE

The ladderlike structure of PPSQ synthesized by-using four kinds of catalysts (MgF2, LiF, KOH and DCC) at different polymerization conditions has been investigated by IR and NMR. In the system using MgF2 as the main catalyst, the most important factor which affects the ladderlike structure of PPSQ is the composition of the dual catalysts, MgF2 and DCC. PPSQ prepared by using KOH as the catalyst has the highest regularity of ladderlike structure among all samples. PPSQ with different degree of ladder regularity can be obtained by choice of polymerization conditions.

TRANSITIONS AND MODRPHOLOGY OF MAIN-CHAIN LIQUID CRYSTALLINE POLYMERS WITH X-SHAPED MESOGENS

The transitions and morphology of a series of main-chain liquid crystalline polymer with X-shaped mesogens were studied by means of DSC,SALS and polarizing microscopy techniques. Aneven-odd effect was observed for samples with different size of the substituents on the mesogenends. The isotropization process was similar to that of main-chain polymers with rod-likemesogens. No crystallization was detected for specimens cooling down from their isotropic meltstate. However two of the samples may crystallize in cooling process directly from the liquidcrystalline state.

MORPHOLOGICAL STUDIES OF A THERMOTROPIC SIDE-CHAIN LIQUID CRYSTALLINE POLYMER DURING MESOPHASE TRANSITIONS

The morphological features of a side-chain liquid crystalline polymer during the mesophase transitions were investigated by using the DSC technique. The polymer used was polyacrylate with mesogens of three benzene rings attached to the main chain through a flexible spacer. A special two-phase texture was observed in the transition temperature range. Similar to main-chain liquid crystalline polymers the transition process of the side-chain liquid crystalline polymer was composed of an initiation of the new phase at local places of the old phase matrix and a growth process of the new phase domains.

PREPARATION OF WATERBORNE ULTRAFINE PARTICLES OF EPOXY RESIN BY PHASE INVERSION TECHNIQUE

Waterborne ultrafine particles of epoxy resin were prepared by phase inversion technique. The results of SEM revealed that the particles diameter was in the range of 50 to 100 nm and the effects on amount of water required at phase inversion point were also discussed.

CONFORMATIONAL CHARACTERISTICS OF POLY(ACRYLIC ACID) AND POLY(METHACRYLIC ACID)

A full-relaxation optimization of molecule and the Dreiding force field are employed to obtain the geometry parameters and the conformational energy surfaces of meso or racemic dyad of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA). Three different carbonyl-bond orientations of side-groups resulted in the differences in depth of potential wells in their energetic contours for a meso or a racemic dyad. These discrepancies are interpreted as a result of various fine structures corresponding to grid search conformations as well as thereby different interactions. The analysis on the most stable conformations of PMAA confirmed that the ester groups are nearly perpendicular to the plane defined by the two adjacent skeletal bonds but may possibly change their relative orientations to meet the requirement of lower energy during the conformational state transition. For each polymer, two global energy maps of a meso and a racemic dyad were finally constructed from the superposition of energy data for the three kinds of side-group orientations by the Boltzmann factors. From an ensemble average, the proposed scheme with three rotational isomeric states (RIS) allowed us to access the experimentally unperturbed dimensions of PAA chain via the configurational statistical mechanics. Although the calculation was based on the short-range, local interactions, it was interested to note that the experimental characteristic ratios just fell within the range calculated for atactic chains.

MOLECULAR SIMULATION TECHNIQUE ON POLYMERIC MATERIALS

Molecular simulation, or molecular modeling, is recently fast emergingas an important technique of both the research in polymer science and thedesign of polymeric materials. Not only single chain behavior but also bulkproperties of amorphous, crystalline, and liquid crystalline poly-mers can be investigated by this technique. In other fields of science such

MOLECULAR DYNAMICS SIMULATION OF THE RELAXATION OF A FULLY EXTENDED POLYETHYLENE CHAIN

Molecular dynamics simulation of the relaxation at 300 K of a fully extended polyethylene chain of 800 CH2 units has been carried out by following the changes in morphology, van der Waals energy, radius of gyration in the sense of mechanics and gyration radius in the sense of Flory, population of transconformation and orientation factor. The relaxation went through three stages: (1) relaxation from the morphology of a straight rod of 100 nm length to the morphology close to a random coil of gyration radius 5.9 nm in 110 ps; (2) collapse of the morphology of a coil to a highly compact globule close to a sphere of gyration radius 1.3 nm after 178 ps as the result of intersegmental van der Waals attractive interactions; (3) lateral ordering of the folded chain segments in the globule without appreciable changes in the chain dimension up to 1600 ps, the time limit of present simulation. Nearly complete relaxation of local segmental orientation was performed much faster than the relaxation of globule chain orientation even for a single chain of low degree of polymerization and at a temperature some 155 degrees C above its T-g. The lateral ordering of the chain segments during the period 178 to 680 ps of the simulation time was found to obey the Avrami equation with an Avrami index of 1.44.

Conformation of 1,2-Dimethoxyethane in Water

To understand the conformation of 1,2-dimethoxyethane (DME) in water, a system of two kinds of molecules, DME and H_2O, was focused. The interaction of various conformers of DME with water was studied by means of ab initio molecular orbital calculation with 6-31G (d) basis set. It is shown that there are two forms of interactions between the two molecules in the system, the close touched (H_2O attaches to the two oxygen atoms of DME) and the open touched (H_2O attaches to one oxygen atom of DME) structures. The conformation of DME is remarkably influenced by the interactions. Instead the ttt conformer is preferred in the gas state, with a close touched H_2O the tgt conformer becomes the most stable one. The obtained hydration energies show that the stabilized order of DME conformers by water is tgt>tgg′>ttt.

PHOTOINDUCED GRAFTING OF ACRYLIC AND ALLYL MONOMERS ON POLYETHYLENE SURFACE

Photoinduced grafting of acrylic and allyl monomers on polyethylene surface was generally studied by using benzophenone (BP) as a photoinitiator. The grafting process was carried out either in vapor-phase or in solution of the monomers. In the vapor-phase reaction with a filter used to cut off the short wavelength UV light, allyl amine is the most reactive of the four monomers used and acrylic amide is comparatively more reactive than acrylic acid and allyl alcohol. Acetone, as a solvent and carrier for initiator and monomers, however, shows its reactivity to participate the reaction. The solution grafting with a filter is much faster than the corresponding vapor-phase reaction, and a fully covered surface by the grafted polymer can be achieved in this way.

A NEW TYPE LOW SHEAR RATE VISCOMETER FOR HIGH MOLECULAR WEIGHT POLYMER

In this paper, the effects of shear rate on the intrinsic viscosity measurement of partially Hydrolysed Polyacrylamide (HPAM) in salt solution were studied with homemade multibulb viscometer and low shear rate rheometer. The critical shear rate of HPAM in salt solution for high molecular weight HPAM was determined. A low shear rate capillary viscometer was designed in which the [eta] approached to value at zero shear rate can be obtained for HPAM -salt system. The effect of molecular weight on shear rate dependence of viscosity was also studied.

SEM OBSERVATION OF THE CRAZING FOR POLYPHENYLQUINOXALINE FILMS DURING IN SITU STRETCHING

The crazing of polyphenylquinoxaline (PPQ-E) films during in situ stretching has been observed by SEM. The crazing phenomena and craze morphology of PPQ-E films were interpreted. The strain values at critical crazing and yielding and the craze stability of PPQ-E samples depend on the thermal-dealing condition for the samples. From the point of view of cohesional entanglements and energy absorbed by samples, the experiment results were explained.

THE EFFECT OF HOT DRAWN ON THE PHYSICAL AGING OF ATACTIC POLYSTYRENE

The physical aging behavior of atactic polystyrene (aPS) films achieved under different drawing conditions has been studied by optical birefringence and modulate differential scanning: calorimeter (m.d.s.c.). The results show that on annealing at specific temperature below glass transition temperatue (T-g), the enthalpy relaxation (Delta H) and T-g decrease with increasing of birefringence (Delta n). On the other baud, the effect of molecular draw ratio (MDR) is confusing: Delta H and T-g decrease with increasing of MDR in the early stage of aging, but the MDR's effect become unobvious with the development of aging. It may be concluded that the ordered domain generated by the drawing below or above glass transition temperature will affect the development of physical aging behavior. The viewpoint of cohesional entanglement is used to account for the above observations.

MELTING AND CRYSTALLIZATION BEHAVIOR OFAN AROMATIC POLY (AZOMETHINE ETHER) WITH NON-LINEARLY SHAPED MOLECULAR CONFORMATIONS

The melting and crystallization behavior have been investigated for an aromatic poly (azomethine ether)with non-linearly shaped molecular conformations. This polymer was found to undergo multiple melting processes and its phase transition behavior was influenced sensitively by the thermal history of sample. A significant difference between the polymer chain aggregation abilities of samples cooled from the different states was observed. The possible molecular morphology and aggregation models for describing the structures of this polymer were proposed and discussed. The crystallization behavior of the samples cooled from the partially isotropic state and the influence of cooling rate on it have also been examined with DSC.

MODULUS-COMPOSITION DEPENDENCE FOR BLENDS OF PVC WITH SEGMENTED POLYURETHANES OF DIFFERENT SOFT SEGMENTS

The dynamic mechanical modulus at 25℃ for blends of segmented polyurethanes with PVC was studied by using suitable mechanics models of multi-component systems. The analysis indicates that the blend morphology was mainly determined by soft segment structure of polyurethanes. The PPO-PU/PVC blends show typical two-phase morphology and their modulus-composition relations may be described by Halpin-Tsai model for domain-matrix two-phase systems.While the PCL-PU / PVC, PTMA-PU/PVC and PTMO-PU/PVC blends fit the Kerner's packed grain composite model. These results may imply that the modulus-composition relationship is sensitive to the interactions between the components and the mixture morphology of the blends.