Iranian polymer journal
Volume:19 Issue: 9, 2010

Anon-linear-optical (NLO) chromophore molecule and polyimide (PI) were synthesized. The chemical structures were characterized by 1H NMR and elemental analysis. Then, a polyimide/silica NLO hybrid material with covalent links between the inorganic and the organic networks was synthesized using polyimide, 3-aminopropyltriethoxysilane (APTES) as a coupling agent between the organic and inorganic phases, and the hydrolyzate of tetraethyl ortho-silicate (TEOS) by the sol-gel process. FTIR and 29Si nuclear magnetic resonance spectroscopy were used to characterize the structure of the hybrid. The results revealed that Q3, Q4 and T3 were the major microstructural elements in forming a three-dimensional network structure.The particle size and crystallinity were investigated using transmission electron microscopy (TEM) and X-ray diffraction (XRD). The differential scanning calorimeter (DSC) and thermal gravimetric analysis (TGA) exhibited the glass transition temperature (Tg) and the decomposition temperature (Td) of 5% mass loss in polyimide and hybrid material at 244°C and 344°C, 352°C and 447°C, respectively. A reflective electro-optic (EO) modulator using this polyimide or hybrid was fabricated. The electro-optic (EO) coefficients 33 of the polyimide and hybrid in the EO modulator were determined to be 28 and 22 pm/V (poling voltage of 3.8 kV, 205°C) at 832 nm by an attenuated-total-reflectance (ATR) method and the values retained >94% for more than 100 h at 205°C. The results show that polyimide and hybrid may be useful as EO modulator.

Cure reaction of an epoxy system consisting of diglycidyl ether of bisphenol A (DGEBA) and urea formaldehyde (UF) resin as curing agent was studied in different ratios by using FTIR and non-isothermal DSC techniques. The rate of epoxide conversion was etermined by measuring the reduction of epoxide group absorption peak at 916 cm-1 during curing. The rate of epoxide conversion depends on the weight ratio of DGEBA/UF and also on the temperature of cure reaction. Activation energy (Ea) of cure reaction for DGEBA/UF (50/50, wt%) system was obtained by using the data from non-isothermal DSC technique and Kissinger and Ozawa equations. The Ea values obtained from both methods were close and in the range of 130-132 kJ/mol. The Ea values measured by isoconversional method showed dependence on the degree of conversion (α) and reached a maximum value of 170 kJ/mol at α = 0.4. DGEBA/UF systems were used for paper impregnation and lamination of the impregnated papers on the particle board. Degree of curing, porosity degree and resistance to gases of the laminated products were investigated according to industrial procedure. The best conditions of DGEBA/UF ratio, impregnation process and lamination process are also reported.

Anew kind of reactive toughening agent, defined as liquid crystalline polyurethane(LCPB), having both flexible chain and rigid biphenyl mesogenic groups was synthesized by polyaddition of 2,4-toluenediisocyanate (TDI) with diethylene glycol and 4,4'-dihydroxybiphenyl in DMF. The structure and morphology of the LCPB were investigated systematically by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), wide angle X-ray diffractometry (WAXD) and polarizing optical microscopy (POM), respectively. The POM observation confirmed that the LCPB exhibited nematic texture and good mesophase stability. The LCPB was used to modify the epoxy resin as toughening agents. The mechanical properties, dynamic mechanical behaviour, fracture surface morphology and apparent activation energy (Ea) of the modified systems were systematically investigated. The experimental results revealed that the impact strength of the epoxy resin modified with LCPB reached the highest value of 47.21 kJ/m2, and it is 1.8 times higher than that of the unmodified system when the content of LCPB loading reached 5 wt%. In addition, the tensile strength and the fracture strength also enhanced with increasing concentratio of LCPB. The DMA results showed that the storage modulus in rubbery state and glass transition temperature (Tg) of the modified systems were higher than those of the unmodified system, indicating that the motion of epoxy matrix chains was strongly restricted by the rigidity of mesogenic units, while the Ea at glassy relaxation process of modified system was about 100-120 kJ/mol higher than that of the unmodified system. The effects of reinforcement on mechanisms of the damaging process of the modified systems were investigated by scanning electron microscopy.

Ahighly active Zr-based FI catalyst of bis[N-(3,5-dicumylsalicylidene)cyclohexylaminato]zirconium(IV) dichloride was prepared and used for polymerization of ethylene. The catalyst displayed a very high activity of about 3.2×106 in ethylene polymerization at the monomer pressure of 3 bar using triisobutylaluminium (TIBA) and methylaluminoxane (MAO) as a scavenger and cocatalyst, respectively. The highest activity of the catalyst was obtained at about 35°C. The polymerization activity was increased linearly with increased monomer pressure and [Al]:[Zr] ratio in the range studied. Introduction of bulky cumyl group on ortho position to the phenoxy oxygen prevents the catalyst from coordination to the cocatalyst following its easier coordination of ethylene to the active centres. The existence of bulky substitutions on the catalyst structure resulted in linear increase in its activity with increasing the MAO concentration through ion separation which facilitates the monomer insertion. However, fouling of the reactor was strongly increased with monomer pressure and the amount of MAO used. Ethylene polymerization was carried out using different amounts of hydrogen. The activity of the catalyst was slightly increased with addition of hydrogen; however, the viscosity average molecular weight (Mv) of the obtained polymer was not affected. In order to study the catalyst lifetime service, ethylene polymerization reactions were carried out at different reaction times while the temperature and [Al]/[Zr] molar ratio were kept constant. Despite the high activity, the catalyst showed a short lifetime. Crystallinity and melting point of the obtained polymer were between 55-65% and 125-130°C, respectively. Mv Values of the obtained polymer were dropped as polymerization temperature increased, while higher pressure increased both the crystallinity and the Mv values of the resulting polymer. Meanwhile some specifications of the obtained polymer were investigated.

Asort of novel stimuli-responsive water-soluble polymer-biomolecule conjugate, casein-g-poly(N-isopropylacrylamide) (PNIPAAm), was synthesized by free radical graft copolymerization of N-isopropylacrylamide (NIPAAm) from casein.The graft polymerization was induced by a small amount of t-butyl hydroperoxide(TBHP) in water under general condition. Free radicals on the amino groups of caseinand t-butoxy radicals were generated concurrently, which initiated the graft copolymerization and homopolymerization of NIPAAm, respectively. The graft copolymers and homopolymer of NIPAAm were isolated and the chemical structure of the graftcopolymer was characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The phase-transition behaviours of the graftcopolymers in aqueous solutions were investigated by the turbidity measurements.Casein-g-PNIPAAm did not precipitate at around the isoelectric pH (IP) of casein at25°C and the lowest transmittance was changed as the pH changed. These resultssuggest that the PNIPAAm offers a greater hindrance to the aggregation of casein at25°C and the casein offers a hindrance to the aggregation of PNIPAAm at the temperature of lower critical solution temperature (LCST) and at the pH apart from theIP. In addition, casein almost has no effect on LCST. The graft copolymer is stimulisensitivewith respect to both temperature and pH in aqueous solutions and thepolymeric micelles with different structures can be obtained simply by changing theenvironmental conditions. It associates into core-shell micelles in aqueous solution withcollapsed PNIPAAm as a core as well as inverse core-hair micelles with expandedcasein as a core on changing temperature or pH, indicated by transmission electronmicroscopy (TEM). With the casein being a nature protein and the graft copolymers aremetal ion-free therefore, they may have great potential for biomedical and biomaterialapplications.

The synthesis of aniline/o-anisidine copolymer was described by enzymatically oxidative polymerization of aniline (An) and o-anisidine (As) using poly (sodium 4-styrene ulphonate) (SPS) as a template. The enzyme horseradish peroxidase (HRP) was used as a catalyst with a stoichiometric amount of hydrogen peroxide as an oxidant at pH 4. 3 in 0. 01 M sodium phosphate buffer solution medium. The UV-vis spectra of An/As copolymer (1:1) exhibited more similarity to the spectral features of o-anisidine. To address the effect of monomer ratio in the synthesized copolymer, the polymerization was carried out in different ratios of o-anisidine to aniline. The resultant An/As copolymer was characterized by FTIR and UV-vis techniques. The results showed that the enzymatic polymerization produced a real copolymer containing aniline and o-anisidine units. The similarity of the UV-vis spectra of the copolymer to enzymatically synthesized poly (o-anisidine) confirmed that the amount of monomeric unit of o-anisidine was higher than aniline. This was due to a much higher reactivity of the former. Thus, as expected, this copolymer spectral characteristics were more similar to the enzymatically synthesized poly (o-anisidine). UV-Vis and FTIR spectra confirmed that the undoped form of An/As copolymer, unlike the chemically synthesizedد copolymer, has formed a complex with SPS. This biomimetic approach offered an unsurpassed easiness in the synthesis, processability, stability and environmental compatibility.

High solid content nanocomposites based on poly(methyl methacrylate-co-butyl acrylate)/nanosilica was synthesized via miniemulsion polymerization in a semi-continuous operation. Oleic acid was used to act as a coupling agent between silica surfaces and polymer. Latexes with solid content of 42% were obtained, containing 5% by weight nano-SiO2 with respect to polymer. FTIR Results show the modified structure of silica with oleic acid and confirm the presence and bonding of modified silica on the polymer structure. Morphological investigations were performed using TEM analysis. The results of microscopic images confirm the nanocomposite structure where the nanoparticles of silica are coated with the polymer nanolayers. Thermal analysis including DSC and TG/DTA was used to investigate Tg, thermal stability and thermal decomposition of the samples. The nanocomposite latex is compared with the neat latex of the same monomer structure. The results of DTA analysis show an increase of about 8°C in the degradation temperature. DSC Analysis shows that the glass transition temperature of the nanocomposite is higher than that of pure acrylic latex. Moreover, the samples with improved hardness are compared with blank latex sample. All analyses demonstrate the well located silica nanoparticles inside the latex polymeric structure.

Maleic anhydride-heptene-1-styrene terpolymer has been synthesized and modified with allyl alcohol and methylmethacrylate in order to prepare a new cross-linked functional polymer sorbent. The synthesized terpolymer, monoallyl ester of terpolymer and synthesized cross-linked sorbent were characterized by Fourier transform infrared and 1H NMR spectroscopies. The synthesized cross-linked polymer sorbent has a network structure and contains carboxylic acid, carbonyl and ester groups, all of which are capable of interacting with metal ions. The sorption performance of uranyl ions under optimum sorption conditions was evaluated. The analytical characteristics of the sorbent, such as, the solution pH, sorption degree and sorption capacity, have been established and the optimum sorption conditions have been determined. The sorption degree reaches a maximum at pH 6 (73.5%) and the maximum experimental sorption capacity of the sorbent for uranyl ions has been estimated as 1.8 mmol.g-1 (486 mg.g-1). Sorption isotherms of uranyl ions onto prepared polymer sorbent have been measured and the equilibrium data have fitted well to the Langmuir and Freundlich isotherm models. Langmuir and Freundlich isotherm constants and correlation coefficients for the present system are calculated and compared. The obtained values of the Langmuir and Freundlich equations parameters (qmax = 2.03 mmol.g-1, KL = 2.56, KF = 1.33, n = 2.35) specify a sufficiently high sorption activity of the synthesized sorbent towards uranyl ions. Uranyl ions are desorbed from the sorbent by treatment with 20-25% hydrochloric and nitric acids.