DYNAMIC MECHANICAL RESPONSE OF CRAZES IN POLYSTYRENE

Dynamic mechanical analysis was used to study the mechanical properties and microstructureof crazes in polystyrene produced in air or in methanol at different temperatures. A new loss peakwas found at about 82℃,which is assigned to glass transition peak of craze fibrils. The decreaseof glass transition temperature of polymer in craze fibrils is due to the high values of surface tovolume ratio. The glass transition temperature ratio of craze fibrils to bulk material (T_g~l /Tg) hasbeen expressed as a function of the fibrils diameter (d). From T_g~l of craze fibrils,the value of fibrildiameter can be calculated. Annealing the crazed specimen at room temperature makes the fibrilsplastically deform and cause the fibrils to thin slightly,whereas annealing the crazed specimen atthe temperature near T_g of the craze fibrils makes the fibrils bundle together.     

ELASTICITY OF MONOLAYER OF LINOLEIC ACID AND ITS POLYMER

The dynamic elasticity of linoleic acid monolayer on a subphase of10~(-4)mol/L TbCl_3 at various surface pressure has been measured by means of dynamic oscil-lation method in measuring the change of surface pressure caused by periodic compression-expansion cycles of the barrier. The elasticity of monolayer increases with increasing ofsurface pressure linearly. The linoleic acid polymer monolayer has been obtained underUV-irradiation in situ when keeping a constant surface pressure. But the elasticity of theresulting polymerized monolayer is even smaller than that of its corresponding monomermonolayer. The elasticity of the polymerized linoleic acid monolayer decreases with in-creasing polymerization time. The explanation based on entropy has been presented.     

PREPARATION OF MICROGEL-EPOXY RESIN TWO-PHASE POLYMERS BY IN SITU POLYMERIZATION~*

Microgel-epoxy resin two-phase polymers were prepared by in situ copolymerization of ethylenic monomers with unsaturated polyesters. The choice of monomers and the effect of monomer concentration on microgel particle size were discussed. Agglomeration of particles played a significant role in the early stage of polymerization. The microgel dispersion in epoxy resin was stable after the finish of polymerization. Upon curing the particles remained well dispersed.     

INVESTIGATION OF THE TRANSITIONS OF OLIGO-POLYSULFONES BY DSC

The transitions of bisphenol A and phenolphthalein o|igopolysulfones were investigated by DSC. It is found that both the oligomers have three transitions within the temperature range (230-550K) studied. Considering the strong dependence of the appearance of the two transitions, lower and higher than T_g, on the specimens' thermal history, i. e., temperature and time of heat-treatment, and their particular molecular strueture, it is proposed that these two transitions are morphological in origin arid are due to the disordering of relatively short range order of very small regions, and to the disordering of relatively well-ordered intraor/and intermoleeular segments, respectively. Equations for linear relationship between T_g and 1/_n for both the oligomers are given in the paper.     

SYNTHESIS OF BLOCK COPOLYMER BY INTEGRATED LIVING ANIONIC POLYMERIZATION-ATOM TRANSFER RADICAL POLYMERIZATION(ATRP)*

Alpha-trichloroacetoxy terminated polystyrene oligomer (PS-CH_2CH_2OCOCCl_3) and poly-(styrene-b-butadiene)oligomer [P(S-b-B)-CH_2CH_2OCOCCl_3)] were synthesized by living anionic polymeri-zation using n-butyllithium as initiator.Then the PS-CH_2CH_2OCOCCl_3 (PS-Cl_3) or P(S-b-B)-CH_2CH_2O-COCCl_3 (PSB-Cl_3) was used as the macroinitiator in thepolymerization of (meth)acrylates in the presence of CuX/bpy. AB diblock and ABC triblock copolymers were prepared bythe integrated living anionic polymerization (LAP)-atom transfer radical polymerization (ATRP). The structures of the PSB-Cl_3 and the P(S-b-MMA) were identified by FTIR and ~1H-NMR spectrum, respectively. A new way to design blockcopolymers (the combination of LAP and ATRP) was developed.     

LAMELLAR STRUCTURE OF THERMOTROPIC LIQUID CRYSTALLINE POLYMERS

The lamellar structure of a thermotropic aromatic polyester with flexible spacer has beenstudied by using transmission electron microscopy. It was found that the lamellar structure couldbe observed in the crystalline samples of this semirigid polymer crystallized from different states.The thickness of lamellae is around 10 nm, which is similar to that of the conventional polymersof flexible chain molecules. The molecular chains in the lamellae are oriented in the thicknessdirection as determined by electron diffraction. The possibility of molecular chains folding in the lamellae has been discussed.     

THE DEGREE OF CRYSTALLINITY OF NYLON-1010 BY WAXD

Based on the X-ray scattering intensity theory and using the atomic scattering factorapproximate expression,the correction factors for three main crystalline peaks and an amorphouspeak of Nylon-1010 were calculated and the formula of degree of crystallinity of Nylon-1010 wasderived by graphic multipeak resolution method. The results calculated are compatible with the density measurement and calorimetry.     

THE DEGREE OF CRYSTALLINITY OF MULTICOMPONENT POLYMERS BY WAXD

Based on the X- ray scattering intensity theory, the correction factors of the degree ofcrystallinity formulae of the multicomponent polymers have been clearly defined. The formulae ofthe degree of crystallinity of the multicomponent polymers were derived in terms of WAXDtheory and improved graphic multipeak resolution methods. The results calculated aresatisfactory in comparison with the density measurement.     

GRAFTING OF HYDROPHILIC MONOMERS ONTO POLYURETHANE MEMBRANES BY SOLUTION OR PRE-ABSORBING METHODS FOR ACCELERATION OF CELL COMPATIBILITY*

Two grafting methods, i.e. solution grafting and pre-adsorbing, are introduced to covalently immobilizehydrophilic polymers on segmented polyurethane (SPU) to modify its hydrophilicity and to improve its cell compatibility.Solution grafting results in higher degree of grafting and rougher surface morphology. Cell culture evaluation demonstratesthat the modified membranes thus obtained are disadvantageous to the endothelial cell (ECs) growth probably because thehydrophilic groups on the surface are over-crowded. However, pre-absorbing grafting generates lower degree of grafting,which is detected and confirmed by ATR-FTIR spectra and water conted angle. Scanning electron microscopic (SEM)measurement shows that the latter method produces a plane and smooth morphology, which is similar to the SPU controlsample controlled. When grafting with lower monomer concentration, ECs could grow on SPU-g-PHEA [poly(2-hydroxyethyl acrylate)], SPU-g-PAAm (polyacrylamide), SPU-g-PDMA [poly(2-(dimethylamino)ethyl methacrylate)] orquatemized SPU-g-PDMA surface with elongated cell shapes. Hence, the cell compatibility of SPU is improved and a usefulmethod to construct a cell compatible layer on the polymer surface has been developed.     

STATISTICAL PROPERTIES OF LONG-RANGE CONTACTS IN GLOBULAR PROTEINS

The analysis of residue-residue contacts in protein structures can shed some light on our understanding of the folding and stability of proteins. In this paper, we study the statistical properties of long-range and short-range residue-residue contacts of 91 globular proteins using CSU software and analyze the importance of long-range contacts in globular protein structure. There are many short-range and long-range contacts in globular proteins, and it is found that the average number of long-range contacts per residue is 5.63 and the percentage of residue-residue contacts which are involved in long-range ones is 59.4%. In more detail, the distribution of long-range contacts in different residue intervals is investigated and it is found that the residues occurring in the interval range of 4-10 residues apart in the sequence contribute more long-range contacts to the stability of globular protein. The number of long-range contacts per residue, which is a measure of ability toform residue-residue contacts, is also calculated for 20 different amino acid residues. It is shown that hydrophobic residues (including Leu, Val, Ile, Met, Phe, Tyr, Cys and Trp) having a large number of long-range contacts easily form long-range contacts, while the hydrophilic amino acids (including Ala, Gly, Thr, His, Glu, Gln, Asp, Asn, Lys, Ser, Arg, and Pro) form long-range contacts with more difficulty. The relationship between the Fauchere-Pliska hydrophobicity scale (FPH) and the number of short-range and long-range contacts per residue for 20 amino acid residues is also studied. An approximately linear relationship between the Fauchere-Pliska hydrophobicity scale (FPH) and the number of long-range contacts per residue CL is found and can be expressed as     

INHIBITION OF 3H-THYMIDINE INCORPORATION IN PIG KIDNEY CELLS BY FAR-RED LIGHT*

E xposure of pig kidney cells in monolayer culture to far-red light (FRL), near 750 nm, was found to increase the incidence of chromatid aberrations and aberrant cells [1]. Dose–response curves for cell populations predominantly in early S reached a maximum at incident energies of ca. 50 mJ cm^-2. We show here that the incorporation of tritiated thymidine by the nuclei of pig kidney cells in monolayer also is inhibited by FRL, with a similar dose-response maximum.     

DETECTION OF T_g BY MODULATED DIFFERENTIAL SCANNING CALORIMETRY

The glassy transition of the polyethylene terephthalate (PET) sampleswhich have been subjected to solvent induced crystallization (SINC) was investigated bymodulated differential scanning calorimetry (MDSC) and density measurement. The dif-ferential of heat capacity signal, d C_p/dT from MDSC, was used to monitor the SINCprocess. It reveals that the T_g temperature shifts to higher value with the advancement ofSINC. When the toluene-immersing time was longer (168h), the detection of T_g becomemore difficult, because some smaller peaks emerged at the lower temperatures and theseare explained as the movement of small segments in the amorphous region. These observedresults are due to the morphology and structure introduced by the SINC process.     

THE PHOTOPOLYMERIZATION OF MMA INITIATED BY 3-ARYLOYLCOUMARIN COMPOUNDS

A bulk photopolymerization of methyl methacryhte (MMA) initiated by 3-benzolocoumarin (Sen. 1)——triethylamine (TEA) coinitiated has been studied. Results were compared with a well known photoinitiator system, benzopbenone (BP)——TEA. The mechanism of the reaction has been discussed.     

A DYNAMIC MECHANICAL ANALYSIS STUDY OF THE TRANSITION BEHAVIOUR OF I-PP/EPDM BLENDS

The transition behaviour of the blends of isotactic polypropylene (i-PP) with ethylene-propylene terpolymer (EPDM) containing 42 wt% propylene was investigated by dynamic mechanical analysis technique (DMA). Owing to its high propylene content, EPDM is compatible with i-PP to some degree. The interaction between the two components was strengthened. As expected, for partially compatible system the glass transition temperature of i-PP in the blends shifted to lower temperature. It was found that there existed two transitions, αEPDM and βEPDM, for the EPDM used in this work. The former was considered to be the glass transition of the random chain segments of EPDM, while the latter the local motion of the long ethylene sequences in EPDM. The unusual transition behaviour of αEPDM in the blends was explained in terms of the greater thermal expansion of EPDM and the compatibility of the two components. On the other hand, the βEPDM changed with the composition of the blends in a regular manner.     

STEREOCHEMICAL CONTROL IN PROPYLENE POLYMERIZATION CATALYZED BY UNBRIDGED METALLOCENE CATALYSTS*

Two unbridged metallocene catalysts, bis (2, 4, 7-trimethylindenyl)zirconium dichloride (met-I) and bis(2, 4, 6-trimethylindenyl) zirconium dichloride (met-II), which are different in the position o f substituents on the six-membered ringof the indenyl ligands were synthesized. The effect of substituents in the two metallocenes on the propylene polymerizationwas studied in the presence of methylaluminoxane (MAO) and triisobutylaluminium (TIBA). From the analysis ofmicrostructure determined by ~(13)C-NMR, it was demonstrated that the polymers produced by met-II have higher [mmmm]isotactic sequences than that of met-I. Using a mechanism based on model statistical analysis, it was found that chain-endmodel was dominant for met-I. However, met-II obeys the concurrent two-sites model during polymerization, which can beattributed to the existence of "racemic-like" conformer in its system.     

PERFORMANCE IMPROVEMENT OF POLYMERS BY THE ADDITION OF GRAFTED NANO-INORGANIC PARTICLES

An irradiation grafting method was applied for the modification of nanoparticles so that the latter can be added topolymeric materials for improving their mechanical performance using existing compounding techniques. The followingitems are discussed in this paper: (a) chemical interaction between the grafting monomers and the nanoparticles duringirradiation, (b) properties including modulus, yield strength, impact strength and fracture toughness of the resultantcomposites, and (c) possible morphological changes induced by the addition of nanoparticles. Though irradiation graftingpolymerization, nanoparticle agglomerates turn into a nano-composite microstructure (comprised of the nanoparticles and thegrafted, homopolymerized secondary polymer), which in turn builds up a strong interfacial interaction with the surrounding,primary polymeric matrix during the subsequent mixing procedure. Due to the fact that different grafting polymers broughtabout different nanoparticle/matrix interfacial features, microstructures and properties of the ultimate composites could thusbe tailored. It was found that the reinforcing and toughening effects of the nanoparticles on the polymer matrix can be fullybrought into play at a rather low filler loading in comparison to conventional particulate filled composites.     

DETERMINATION OF DEGREE OF CRYSTALLINITY OF NYLON 1212 BY WIDE-ANGLE X-RAY DIFFRACTION

Based on the X-ray scattering intensity theory and using the approximate expression for the atomic scattering factor, the correction factors for three crystalline peaks and an amorphous peak of Nylon 1212 were calculated and the formula of degree of crystallinity of Nylon 1212 was derived by a graphic multipeak resolution method. The degree of crystallinity calculated from the WAXD method is compatible with those obtained by density and calorimetry methods.     

TURNING-OVER OF THE ELECTRIC DIPOLE IN A POLYMER*

The transition from the biexciton to the exciton can turn over the direction of the electric dipole of a polymericmolecule. This turning-over action combined with the photoinduced polarization reversion can be used as a switch. Theswitching speed is governed by the relaxation time of the turning-over process, which can be determined by a dynamicalsimulation.     

LIGHT-SCATTERING STUDY OF POLYELECTROLYTE HOLLOW CAPSULES

Silver halide (AgX) microcrystal was used as template to synthesize hollow polyelectrolyte capsules. These hollow capsules were characterized by laser light scattering (LLS) used to measure the size of the capsules in solution. The ratio of hydrodynamic radius (Rh) from dynamic LLS to the radius of gyration (Rg) from static LLS is almost unity, revealing that the entities are hollow in solution. The results suggest that the LLS method can be regarded as a good complement to the confocal laser scanning microscopy (CLSM) method for the characterization of small hollow capsules, and it possesses the advantage of not needing fluorescence labeling.     

STRUCTURAL CHARACTERIZATION OF POLYETHYLENES BY DSC ANALYSIS AFTER CRYSTALLIZATION SEGREGATION*

The molecular structure of polyethylene (PE) samples with various comonomers including propylene, 1-buteneand 1-hexene was investigated by DSC and ~(13)C-NMR techniques. The density of the samples varies from 0.948 g/cm~3 to0.917 g/cm~3, and the molecular weight determined by the GPC method is in the range of 1～2×10~5. The branch point contentof the samples was determined by ~(13)C-NMR measurements and was found to be less than 20 per 1000 C atoms along themain chain. Crystallization segregation DSC technique (CSDSC) was used to characterize the branch point distribution or thesegment length distribution of PEs. The crystallization segregation was performed in a successive annealing process atdecreasing temperatures. The interval of two successive annealing temperatures was 6 K, and the time length of eachannealing step was 2.5 h. The CSDSC results clearly indicate that all the PE samples used, including some metallocene PEs,more or less exhibit their non-uniformity in segment length distribution, and bimodal or multimodal CSDSC curves wereusually observed. For quantitative characterization of the CSDSC curves and the segment length distribution two parameters,the average melting point, T_(mAV), and the root-mean-square deviation of melting temperature, (ΔT_(mAV)~2)~(1/2), were proposed.T_(mAV) is corresponding to the average segment length due to branching and (ΔT_(mAV)~2)~(1/2) gives information about the width ofthe segment length distribution. Experimental results show that both the degree of average melting temperature depressionand the width of the distribution seem to increase with increasing the branching content and are dependent on the type ofcomonomers. Very good reproducibility and additivity of the CSDSC method were evidenced experimentally. It wasconcluded that the CSDSC technique is a sensitive and convenient method for characterizing the segment length distribution of branched polyethylenes and will be of great interest in structure-property relationship studies of crystalline polymers.