VULCANIZATION KINETICS OF SILICONE RUBBER

Vulcanization rate of silicone rubber with the aid of organic peroxide or hydrosilylation agent was studied by using oscillation disk rheometer. It was found that the process of network formation would take place through one, two or three steps depending on the structure of the reactants. The effect of phenyl group, vinyl terminals on polysiloxane chain and the functionality of silylation agent was also studied.     

STUDY ON THE TOUGHENING MECHANISM OF RUBBER TOUGHENED EPOXY

The following factors affecting the rubber toughened epoxy resin system were studied: 1. kindsof curing agent used, 2. the M_c value of the matrix, 3. the bonding foce between the dispersed phaseand the matrix. Our experimental result indicates that the average chain length between crosslinks(M_c) is a much more important affecting factor. Chemical bonding between the dispersed phaseand the matrix is also important. A toughening mechanism of rubber toughened epoxy has beenproposed. In the material with relatively low crosslinking density, extensive fracture process stripis formed which is induced by the combined stress field near the rubber particles. The chemical bond-ing between the dispersed phase and the matrix may inerease the strength of the local stress field aboutthe rubber particles which is in favor of broading the fracture process area.     

STUDY ON THE EPOXY RESIN TOUGHENED BY HYDROXY-TERMINATED BUTADIENE-ACRYLONITRILE COPOLYMER

Toughened epoxy resin with excellent properties was obtained by adding organic acid anhydride curing agent and hydroxy-terminated butadiene-acrylonitrile copolymer (HTBN), which is cheaper than CTBN. The anhydride reacts with both epoxy groups on epoxy resin and hydroxyl groups on HTBN. As a result the soft long chains of HTBN and the rigid chain of epoxy resin form one network, giving the resin toughness. Two-phase structure of the toughened resin was observed by SEM and TEM.     

Multiple-SO3H functioned ionic liquid as efficient curing agent for phthalonitrile-terminated poly(phthalazinone ether nitrile)

Combined with the advantages of low melting point,high thermal stability and strong acidity,a multipleSO_3H functioned ionic liquid(MIL) was developed successfully as a curing agent to promote the curing reaction of phthalonitrile-terminated poly(phthalazinone ether nitrile)(PPEN-Ph).The curing kinetics over differential scanning calorimetry(DSC) showed that both the initial curing temperature T_(p0') and apparent activation energy Ea'(based on Kissinger equation) were reduced significantly over MIL(207.9℃ and 101.5 kJ/mol) compared to the common curing agent ZnCl_2(268.5℃ and 201.5 kJ/mol).Moreover,under identical curing conditions,the resulting thermosetting resin over former(T_(d5%)=526.1℃) showed better thermal stability than that over latter(T_(d5%)=512.1 ℃).These results indicated that MIL should be a good candidate as a curing agent for phthalonitrile resins.     

Reaction-induced phase separation in rubber-modified epoxy resin

The phase separation mechanism,and structure development during curing of epoxy with a novel liquid rubber-ZR were investigated by time-resolved light scattering,optical microscope and differential scanning calonmetry (DSC) The mixture loaded with curing agent was a single-phase system in the early stage of curing.When the cure reaction proceeded,phase separation took place via the spinodal decomposition induced by polymerization of epoxy resin.This was supported by the characteristic change of light scattering profile with curing time.Cure reaction plays an important role in the progress of phase separation.The bigger the cure reaction rate is,the longer periodic distance will be.The overall two-phase structure was basically locked in when the conversion approached 80% estimated by DSC,and finally the co-continuous two-phase structure was successfully obtained.     

REINFORCEMENT OF POLYDIMETHYLSILOXANE NETWORKS BY NANOCALCIUM CARBONATE

Although a number of investigations have been devoted to the analysis of silica or carbon black filled elastomer networks, little work has been done on the reinforcement of CaCO3 filled elastomer network. In this work, the reinforcement of polydimethylsiloxane (PDMS) network by using CaCO3 nano-particles was investigated. We have found a simultaneous increase of tensile strength, modulus and elongation with the increase in nano-CaCO3 content, which suggests that nano-CaCO3 particles can indeed be used as a reinforcing agent, just like silica or carbon black. Interestingly, the tensile strength,modulus and elongation were seen to leave off for the first time when the content of nano-CaCO3 particles reaches to 80%.PDMS also showed an enhanced elastic modulus and storage modulus with the increase in nano-CaCO3 content, particularly for samples with high nano-CaCO3 content. SEM was used to investigate the dispersion of the filler in PDMS matrix. A better dispersion was found for samples with high nano-CaCO3 content. A great increase of viscosity was found for samples with higher filler content, which is considered to be the reason for the good dispersion thus the reinforcement, because high viscosity will be helpful for breaking the agglomerates of fillers into small size particles under effect of shear. Our work provides a new way for the reinforcement of elastomer by using an adequate amount of nano-CaCO3 particles instead of as mall quantity of silica, which is not only economically cheap but also very effective.     

EFFECTS OF SOME PHENYLETHYNYLSILICON COMPOUNDS ON HEAT-CURABLE SILICONE RUBBER Ⅲ 1, 1, 3, 3-TETRAMETHYL-1, 3-DIPHENYLETHYNYL-DISILOXANE*

We have shown that some phenylethynylsilicon compounds are good cure crosslinkersof heat-curable silicone rubber(HCSR). In this paper the effects of 1, 1, 3, 3-tetramethyl-1, 3-diphenylethynyldisiloxane (TMDPDS) as a crosslinker on HCSR were studied. Thevulcanizates with fine mechanical properties could be obtained with suitable amounts ofTMDPDS. Sol fractions, and crosslinking density of vulcanizates and vulcanizationretardation effect of TMDPDS on hydrosilation curing silicone rubber were also discussed.     

CURE OF A MICROGEL-EPOXY RESIN TWO-PHASE POLYMER WITH ETHYLENE DIAMINE

The curing of a microgel-epoxy resin two phase polymer prepared by in situ copolymerization of unsaturated polyester with acrylic monomer was studied. The unsaturated unit reacted with N—H during the cure of the resin with ethylene diamine. The Michael type reaction was ten times more rapid than the addition of N—H to epoxide.This was accounted for the lower apparent activation energy of the curing of the two phase resin.     

PREPARATION OF POLY（ETHYLENEGLYCOL-co-ACRYLIC ACID） MICROSPHERES WITH DIVINYLBENZNE AS CROSSLINKER BY DISTILLATION-PRECIPITATION POLYMERIZATION

Monodisperse poly（poly（ethyleneglycol） methyl ether acrylate-co-acrylic acid） （poly（PEGMA-co-AA）） microspheres were prepared by distillation-precipitation polymerization with divinylbenzene （DVB） as crosslinker with 2,2＇- azobisisobutyronitrile （AIBN） as initiator in neat acetonitrile without stirring. Under various reaction conditions, four distinct morphologies including the sol, microemulsion, microgels and microspheres were formed during the distillation of the solvent from the reaction system. A 2D morphological map was established as a function of crosslinker concentration and the polar monomer AA concentration, in comonomer feed in the transition between the morphology domains. The effect of the covalent crosslinker DVB on the morphology of the polymer network was investigated in detail at AA fraction of 40 vol%. The ratios of acid to ethylene oxide units presenting in the comonomers dramatically affected the polymer-polymer interaction and hence the morphology of the resultant polymer network. The covalent crosslinking by DVB and the hydrogen bonding crosslinking between two acid units as well as between the acid and ethylene oxide unit played key roles in the formation of monodisperse polymer microspheres.     

ON THE ORIGIN OF STRESS PEAK IN UNI-AXIAL STRETCHING OF AMORPHOUS POLYMERS

Rubber of high molar mass, like cis-polybutadiene, shows a stress peak on theenineering stress-strain curve during stretching at room temperature. In this work cis-polybutadiene samples were swollen in a poor solvent, CHCl_3/EtOH (1/1 v/v), for differenttimes. It was found that both the initial modulus and the stress peak on stretching de-creased in magnitude with increasing swelling time and the peak disappeared entirely after1 hour of swelling. On further swelling the initial modulus increased somewhat and a smallstress peak re-appeared after swelling for 2 h. The disappearance of the stress peak afterswelling is interpreted as the result of disruption of cohesional entanglements present in theinitial rubber sample. The re-appearance of a small stress peak and the increase of modu-lus on further swelling are interpreted as being of the same nature as the phenomenon ofanti-plasticization. It is the result of forming some new cohesional entanglements of largerbinding energies through longer range chain segmental motions excited after the disruptionof the previously existing cohesional entanglements in the rubber. Thus an understand-ing of the stress peak on stretching a high molar mass rubber and the phenomenon ofanti-plasticization on molecular level has been put forward.     

CURING KINETICS AND PROPERTIES OF ACRYLIC RESIN CURED WITH AZIRIDINE CROSSLINKER

A kind of aziridine crosslinkers was synthesized and used to crosslink acrylate copolymers. The crosslinkingproperties and curing kinetics of the resin were studied. It was found that with the increase of the content of crosslinker in theemulsion, the mechanical properties and solvent resistance of the resin will be apparently improved, but its glass transitiontemperature (T_g) is very low. The lowest amount of crosslinker used in the acrylic resin emulsion is 0.25%. Curing kineticsstudied by DSC show that this curing reaction occurs readily because the apparent activation energy of the reaction is low(65.1 kJ/mol). These results demonstrate that the aziridine crosslinker is indeed a low temperature crosslinking agent and canbe used at room temperature.     

MECHANICAL RELAXATION TIME OF A TWO-COMPONENT EPOXY NETWORKLiClO_4 POLYMER ELECTROLYTE

The mechanical relaxation time of a two-component epoxy network-LiClO_4 system as a polymer electrolyte was investigated. The network is composed of diglycidyl ether of polyethylene glycol (DGEPEG) and triglycidyl ether of glycerol (TGEG), wherein LiCIO_4 was incorporated and acts as both the ionic carrier and the curing catalyst. As the relaxation time is informative to the segmental mobility, which is known to be essential for ionic conductivity, the average relaxation times of the specimens were determined through master curve construction. Experimental results showed that the salt concentration, molecular weight of PEG in DGEPEG and DGEPEG/TGEG ratio have profound effect on the relaxation time of the specimen. Among these factors , the former reinforces the network chains, leading to lengthen the relaxation time, whereas the latter two are in favour of the chain flexibility and show an opposite effect. The findings was rationalized in terms of the free volume concept.     

A MORPHOLOGICAL STUDY OF POLY（DIVINYLBENZENE-co-ACRYLIC ACID） IN CROSSLINKING PRECIPITATION POLYMERIZATION

Divinylbenzene-80 （DVB-80） and polar monomer acrylic acid （AA） having hydrogen bonding at a total monomer loading of 5 vol% were precipitated-copolymerized in a variety of organic solvents with 2,2＇-azobis（isobutyronitrile） （AIBN） as initiator. The experiments were investigated from a two-dimensional matrix, i.e., the actual crosslinking degree of DVB varying from 0 to 80% and the solvent composition varying from 0 to 100% of toluene mixture with acetonitrile, when the mixture of acetonitrile and toluene was used as the reaction solvent. Under various reaction conditions, six distinct morphologies including soluble polymers, swellable microgels, coagulum, irregular microparticles, and nano-/micrometer microspheres were formed and the structures of these polymer architectures were described. A morphological map was utilized to discuss the effects of both crosslinking degree of DVB and composition of solvent on the transitions between morphology domains. The results demonstrated that the microspheres are formed by an internal contraction due to the marginal solvency of the continuous phase and the crosslinking of the polymer network through the covalent bonding from DVB as well as the interchain hydrogen-bonding between the carboxylic acid units.     

Preparation, Curing Reactivity and Thermal Properties of Titanium-doped Silicone Resins

Novel titanium-doped silicone resins were synthesized from low-cost silane monomers and tetrabutyl titanate as raw materials and hydrochloric acid as catalyst, with titanium element as dopant into principal chain of Si-O-Si. The resins were characterized by means of FTIR, 1 H NMR and 13 C NMR spectra, their thermal properties and curing properties were investigated and their corresponding films were determined. The results show that the thermal stability and storage stability of the resins were influenced by the types of silane monomers containing different carbon atomicities of organic group. The thermal stability of the titanium-doped silicone resin with a molar ratio of silane monomer B(n-propyl triethoxysilane) to silane monomer C(n-octyl triethoxysilane) being 1:1 is superior to that of the resin with a molar ratio of silane monomer B to silane monomer C being 1:3. However, the storage stability of the former is inferior to that of the latter.This work also showed that the synthesized titanium-doped silicone resins have the highest thermal stability up to 450―500 °C with an atomicity molar ratio of 1:4 of titanium to silicon in the reactants. But the best storage stability of the resin prepared from the reactants with an atomicity molar ratio of 1:6[n(Ti):n(Si)] was obtained. The effect of the type and content of curing agent on the curing properties of the resin was also studied. Moreover, thermal mechanism and curing mechanism were proposed in this work.     

NANOMECHANICAL MAPPING OF CARBON BLACK REINFORCED NATURAL RUBBER BY ATOMIC FORCE MICROSCOPY

Atomic force microscopy （AFM） has the advantage of obtaining mechanical properties as well as topographic information at the same time. By analyzing force-distance curves measured over two-dimensional area using Hertzian contact mechanics, Young＇s modulus mapping was obtained with nanometer-scale resolution. Furthermore, the sample deformation by the force exerted was also estimated from the force-distance curve analyses. We could thus reconstruct a real topographic image by incorporating apparent topographic image with deformation image. We applied this method to carbon black reinforced natural rubber to obtain Young＇s modulus distribution image together with reconstructed real topographic image. Then we were able to recognize three regions; rubber matrix, carbon black （or bound rubber） and intermediate regions. Though the existence of these regions had been investigated by pulsed nuclear magnetic resonance, this paper would be the first to report on the quantitative evaluation of the interfacial region in real space.     

ONE''''POT REACTION OF TRIVALENTPHOSPHORUS COMPOUNDS (Ⅰ)——A NOVEL ONE-STEP REACTION OF ADDITION,REDUCTION AND CYCLIZATION OF SUBSTITUTED β-NITROSTYRENE WITH O,O-DIALKYL PHOSPHITES

In this paper the reaction of substituted β-nitrostyrene with O,O-dialkyl phosphite under cocatalysis of trimethylsilyl chloride (TMS-C1) and triethylamine (or other acidbinding agent) has been first studied and the new cyclization reaction leading to the formation of product Ⅱ, as a new class of derivatives of 1-hydroxyindoles, difficultly accessible or inaccessible with usual methods has been observed. In the related reaction it is surprising that when the Arbuzov rearrangement occurs under mild conditions, the addition, reduction and cyclization as a one-pot reaction take place simultaneously with the formation of products Ⅰ, Ⅱ, Ⅲ. By controlling the reaction conditions the products were formed almost in specificity, and thus the most interesting cyclic products Ⅱ_(a-h) containing phosphorus-carbon bond were obtained. Their structures were confirmed by elemental analysis, IR, ~1H or ~(31)p NMR and MS spectra. The crystal structure of representative compound Ⅱ_h was determined by X-ray diffract     

GRAFTING OF POLYSTYRENE ONTO A NANOMETER SILICA SURFACE BY MICROEMULSION POLYMERIZATION

The grafting of polystyrene onto a nanometer silica surface by microemulsion polymerization is described. Silicawas functionalized with 3-methacryloxypropyltrimethoxysilane coupling agent before polymerization. A mixture of ionic andnon-ionic surfactants as well as water-soluble and oil-soluble initiators were used. The effect of the amount of silica and ionicsurfactant on the graft polymerization was studied. The graft polymerization procedure for styrene was also applied to methylmethacrylate. Composite particles with a core-shell structure were obtained and the yield and grafting efficiency of monomerwere high.     

A MODEL STUDY ON MODE OF BONDING OF CISPLATIN WITH DNA

The interaction of cis-[Pt(NK_3)_2Cl_2] with nucleosides, as constituents of DNA, was studled by spectrophotometric, ~(13)C NMR and CNDO/2 methods. The apparent stability constants of the complexes formed and the initial rate of formation were determined. The sites of binding of nucleoside (or nucleotide) with Cisplatin were ascertained and the electronic structure of the model coordination compounds of Cisplatin and guanine was calculated by MO approach. On the basis of the obtained results, the mechanism of the antitumour action of Cisplatin was discussed, and a new possible mode of bonding of Cisplatin with DNA was proposed.     

HALOMETHYLATION OF POLYSTYRENE AND SUBSEQUENT PYRIDINATION VIA A HOMOLYTIC PATHWAY

Chloromethylation of polystyrene （PS） with two different chloromethylating systems methylal/thionyl chloride and paraformaldehyde/trimethylchlorosilane was studied. Soluble chloromethylated polystyrene with a degree of substitution of 89% was obtained. The Conant-Finkelstein reaction on the chloromethylated PS afforded soluble iodomethylated polystyrene with a degree of substitution as high as 96%. The reaction conditions of Minisci were employed to radically pyridinate PS via its iodomethylated derivative. Polyelectrolytes were formed which could be converted to normal polymers by treatment with a 20% aqueous solution of NaOH.     

EFFECTS OF COUPLING AGENTS ON THE CRYSTALLIZATION BEHAVIOR OF PP/T-ZnOw COMPOSITES

The objectives of this paper are to understand the crystallization behavior of polypropylene(PP)composites with surface modified tetra-needle-shaped zinc oxide whisker(T-ZnOw).T-ZnOw was surface modified with different coupling agents,such as silane coupling agents(KH-550,KH-560)and titanate coupling agent(NDZ-105),in order to improve the compatibility between PP and T-ZnOw.DSC and POM were used to characterize the melt and crystallization behavior and the crystalline structures of the composites,respectively.The results show that the surface modified T-ZnOw acts as a nucleating agent of PP crystallization,depending on the coupling agent used for modification.KH-550 and KH-560 have more apparent role in improving the interfacial interaction than NDZ-105 and induce PP crystallization at higher temperature and with smaller spherulites size.The results also suggest that the crystallization behavior depends on not only the content of coupling agent,but also the content of the surface modified T-ZnOw used in the composites.