RADIATION CROSSLINKING OF BRANCHED POLY (VINYL ACETATE)

In the present work, radiation crosslinking of different branched poly (vinyl acetate) have beemstudied and the validity of the relationship between sol fraction and radiation dose: R(S+S~(1/2)=1/U_(1qo)+p′_o/q_oR~βto branched poly(vinyl acetate) have been assured.     

聚丙烯/聚乙烯共混物的辐射凝胶生成动力学研究

本文研究辐照PP/HDPE共混物的溶胶生成分数s与辐照剂量R的关系,结果表明适用于某些纯聚合物辐射交联规律的Charlesby-Pinner关系式和陈-刘-唐关系式皆不适用于PP/HDPE共混体系。张万喜等人曾研究过许多纯聚合物的辐射交联,提出裂解度正比于R~β的假定,β是与高分子结构相关的参数,这个假定可与大多数聚合物的辐射交联实验数据符合。同样的假定被应用于本文的共混体系,不同的是根据共混物结构特点对R~β项进行了必要的修正,即共混物的R~β=∑f_iR~(βI),其中f_i,β_i分别为共混物第i组分的重量分数及β值。用修正后的R~β处理辐照PP/HDPE共混物的实验数据,R(s+√s)～R~β,有很好的线性关系。     

Stereoregularity of poly(2-vinylpyridine) and poly-(4-vinylpyridine)

In order to determine the stereoregularity of poly(4-vinylpyridine), 4-vinylpyridine-β,β-d₂ was synthesized from 4-acetylpyridine. The ¹H-NMR spectra of the deuterated and nondeuterated polymers were measured and analyzed. From the ¹H-NMR spectra of poly(4-vinylpyridine-β,β-d₂), triad tacticity can be obtained, while the ¹H-NMR spectra of nondeuterated poly(4-vinylpyridine) give the fraction of isotactic triad. The ¹³C-NMR spectra of poly(4-vinylpyridine) were also observed, and the spectra of C₄ carbon of polymers were assigned by the pentad tacticities. The fraction of isotactic triad of poly(2-vinylpyridine) and poly(4-vinylpyridine) obtained under various polymerization conditions were determined. The radical polymerization and anionic polymerizations with phenylmagnesium bromide and n-butyllithium as catalysts of 4-vinylpyridine gave atactic polymers.     

EFFECT OF IRRADIATION TEMPERATURE ON GENERAL EQUATION OF SOL FRACTION-DOSE RELATIONSHIP FOR FLUOROPOLYMERS

In this paper, the effect of irradiation temperature on sol fraction-dose relationship of tluoropolymers was studied. It was found that the increasing of irradiation temperature can result in the decreasing of βvalue of fluoropolymer, which increases the crosslinking probability of fluoropolymer. The relationship between crosslinking parameter βand irradiation temperature (T_i)of fluoropolymer is established as follows:β=2.2×10~(-3) T_g+4×10~(-4)(T_g-T_i)+0.206.values of some tluoropolymers calculated from the above expression are in agreement with the experimental values.     

CHARACTERIZATION OF γ-IRRADIATED CRYSTALLINE POLYMERS Ⅰ. CHARACTERIZATION OF γ-RADIATION INDUCED CROSSLINKED POLYAMIDE 1010 BY CRYSTALLIZATION TEMPERATURE*

The effect of ~(50)Co γ-radiation on plain polyamide 1010 (PA1010 Ⅰ) and PA1010 containing dif-ferent amount of crosslinking agent (BMI) (PA1010 Ⅱ) both in vacuum and in air at room tempera-ture was investigated with DSC. It was found that the crystallization temperature T_c of crosslinkedsample determined with DSC at constant cooling rate decreased as the radiation dose increased. Thedifference between crystallization temperatures before and after crosslinking (T_(c_o)-T_(c_R) is linearlyrelated to the radiation dose for PA1010I. Based on the Charlesby-Pinner's equation an expressionwas derived S+S~(1/2)=A+B/(T_(c_o)-T_(c_R)) where S is the sol fraction, A and B are constants. Since thereis evidence that T_c is relative to S only and independent of the way of irradiation, the equation is alsoapplicable to the enhanced γ-irradiation crosslinked PA1010 Ⅱ. Therefore, determination of T_cof crosslinked polymer by DSC offers a convenient approach to study quantitatively the random andespecially non-random crosslinking reaction of crystalline polymer.     

THE RADIATION CROSSLINKING OF EPR/SBR BLEND

The radiation crosslinking of EPR/SBR blend has been studied. A relationship between sol fraction and radiation dose for the different weight ratio polymer blends and the method to calculate βb value of EPR/SBR blend system have been established.     

Stereoregularity of poly(alkyl α-chloroacrylates) and mechanism of isotactic polymerization

The catalytic activity of the complexes prepared by the reaction of Grignard reagents with ketones, esters, and an epoxide as polymerization catalysts of methyl and ethyl α-chloroacrylates was investigated. The modifiers which gave isotactic polymers were α,β-unsaturated ketones such as benzalacetophenone, benzalacetone, dibenzalacetone, mesityl oxide, and methyl vinyl ketone, and α,β-unsaturated esters such as ethyl cinnamate, ethyl crotonate, and methyl acrylate. Catalysts with butyl ethyl ketone, propiophenone, and propylene oxide as modifiers produced atactic polymers but no isotactic polymers. It was revealed that the complex catalysts having a structure ? C?C? O? MgX (X is halogen) gave isotactic polymers. The mechanism of isotactic polymerization was discussed. In addition, for radical polymerization of ethyl α-chloroacrylate, enthalpy and entropy differences between isotactic and syndiotactic additions were calculated to give ΔH_i^* ? ΔH_s^* = 910 cal/mole and ΔS_i^* ? ΔS_s^* = 0.82 eu.     

Indirect Measurement of the Cooperative Hydrogen Bonding of Polymers Using NMR Quadrupole Relaxation and PFG Methods

Summary: A general method of measurement of polymer hydrogen bond (HB) cooperativity using a low-molecular weight model ligand named marker and two independent methods of ²H NMR is presented. As marker, a deutero-compound chemically similar to the functional groups of one of the polymers is used, e.g. pyridine-d₅ in the investigated interaction of poly(4-vinylpyridine) with poly(4-vinylphenol) or acetic acid-d₄ in the interaction of polyacrylic acid with poly(4-vinylphenol) reported here. The method is based on the fact that a substantial fraction of the marker, originally bound to the groups of one of the polymers, is liberated by the cooperative interaction between the two polymers. For the establishment of the fraction of the bound marker before and after mixing the polymers, ²H NMR quadrupolar relaxation or ²H PFG NMR diffusion measurement can be used with comparable precision. In both these methods, the results must be normalized to a standard viscosity using the relaxation or diffusion of an added inert compound such as CDCl₃.     

Effect of gamma radiation on fluoropolymers

A series of fluoropolymer films were synthesized by reacting several bisphenol monomers with 1,3‐bis(1,1,1,3,3,3‐hexafluoro‐2‐pentafluorophenyl methoxy‐2‐propyl)benzene via a nucleophilic aromatic substitution to form polyethers. The bisphenols used included two diphenol‐substituted spirodilactams (SDL; aliphatic and aromatic), biphenol, bisphenol A, bisphenol AF, bisphenol O, and bisphenol F to form seven different polymers. Polymers were irradiated by a Gamma beam 651‐PT at a dose rate of 10.5 kGy/h; the absorbed dose in each film was varied between 300 and 1000 kGy. The effect on the chemical structure upon radiation was studied by DSC, TGA, FTIR‐ATR, and NMR after and before irradiation. Thermal analysis showed a lessened thermal stability and a lower T_g after irradiation. Further, irradiation caused a decrease in molecular weight as a result of cleavage of sp³ bonds. These data allowed calculation of the radiochemical yield scission (G_s) for each of these polymers. The SDL aromatic system proved the most radiation‐resistant. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1617–1626, 2009     

A New Molecular Theory of Non‐Linear Viscoelasticity for Vitrifiable (or Crystallizable) Thermoplastic Polyurethane Elastomers

The molecular theory of non‐linear viscoelasticity for vitrifiable thermoplastic polyurethane elastomers (VTPUE) is a refinement and extension of viscoelastic theory of thermoplastic elastomers and polyurethanes to glassy transition, a structural model and a mechanism of vitrification for glassy polymers were proposed. Five kinds of constituent chains with Nagai chain constraint consisting of soft‐domains, hard‐domains, and entanglements are used as the elementary structural and statistical ensemble units for the correlation of molecular and phase‐domain structures to the static and dynamic mechanical behaviors. So the influences of non‐Gaussian in character, the phase separation of domain, the network topology of structure, the affined deformation of constituent chains, and the thermal history are all taken into account in the constituent chains of the theory. Free energies of deformation for the VTPUE segment copolymer were calculated by the statistical mechanics with the probability distribution functions of the sizes for the five kinds of constituent chains. Then the static constitutive equations and modulus of four types of deformation and the dynamic shear viscosity, modulus and loss tangent of VTPUE are derived from the proposed theory. The theory is successful in relating the molecular chain parameters C₁₀₀, C₀₂₀, and C₂₀₀ to the constitutive equations and modulus under large deformations and the micro‐domain structure to the complex shear viscosity and modulus and the loss tangent. The dynamic shear modulus and loss tangent of VTPUE are related to the domain structures through the fraction of hard segments (W_h), the molecular weight of soft segment (M_ns), and the growth dimensional parameters of hard and soft domains (β). Two series of linear VTPUE copolymers (ES and ET) with different fractions(W_h) of hard segments and molecular weight (M_ns) of soft segments were prepared. Their static and dynamic mechanical properties were studied by uni‐axial extension and dynamic analysis tests. Then the constitutive equation at uni‐axial extension and the expressions of shear modulus and loss tangent are verified by these experimental data, and excellent agreement between the theory and experiments is achieved. It is shown, that the proposed theory can predict the viscoelastic behavior of vitrifiable thermoplastic polyurethanes.     

Huggins constant k′ for flexible chain polymers

The Huggins constant k′ in the expression for the viscosity of dilute nonelectrolytic polymer solutions, η = η(1 + [η] c + k′[η]²c² + …), is calculated. For polymers in the theta condition, k′ is estimated to be 0.5 < k_θ′ ≤ 0.7. For good solvent systems, the Peterson-Fixman theory of k′ has been modified; the equilibrium radial distribution function in the original theory is replaced with a parametric distribution for interpenetrating macromolecules in the shear force field. Comparison of the modified theory with experimental k′ for polystyrenes and poly(methyl methacrylates) of different molecular weights in various solvents shows good agreement. An empirical equation which correlates the Huggins constant k′ and the viscosity expansion factor α_η for polymers has been found to coincide well with the modified theory.     

PEO/PVAc共混体系辐射交联反应中溶胶分数与辐照剂量间的关系

In this paper, the relationship between T_m and composition of PEO/PVAc blend were studied and the Flory-Huggins parameter of the blend system were calculated. The experimental results show that this blend system is compatible and have only one glass transition temperature (T_g), so we can extend the relationship between sol fraction (S) and radiation dose (R) of linear polymer to the PEO/PVAc system. The Bb value of PEO/PVAc system were calculated, which is in good agreement with the experimental value.     

Alternating copolymerization of carbon dioxide and cyclohexene oxide catalyzed by silicon dioxide/Zn?CoIII double metal cyanide complex hybrid catalysts with a nanolamellar structure

Air‐stable hybrid catalysts of silicon dioxide/double metal cyanide complexes (Si‐DMCCs) based on Zn₃[Co(CN)₆]₂ (ZHCC) were prepared by an in situ sol–gel method. The Si‐DMCCs showed low crystallinity and a nanolamellar structure with a thickness of ～40–60 nm. In particular, a lamellar structure of regular hexagonal shape was observed for Si‐DMCCs with low SiO₂ content. These catalysts had very high catalytic activity for alternating copolymerization of cyclohexene oxide (CHO) and carbon dioxide. A turnover number of 11,444, turnover frequency of 3815 h^?1, and apparent efficiency of 7.5 kg polymer/g ZHCC (～24.0 kg polymer/g Zn) were achieved at 3.8 MPa and 100 °C. The poly(cyclohexenylene carbonate) (PCHC) polymers obtained were completely atactic with a molecular weight (M_n) of ～10 kg/mol and polydispersity of 2.0–3.0. The PCHCs had a structure of nearly alternating CHO and CO₂ units, with a molar fraction of carbonate units of 0.44–0.47. Preliminary investigations of the mechanism suggest that nucleophilic attack by neighboring oxygen atoms is involved in copolymerization initiation with Zn? Co^III DMCCs. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3128–3139, 2008     

Surface properties and photoactivity of TiO2 treated with electron beam

The improvement of the TiO₂-photoactivitiy by electron beam treatment (1 MeV) as a function of the absorbed radiation dose (MGy) is reported. The radiation-induced effects in the TiO₂ crystal structure, e.g. change of the Ti³⁺/Ti⁴⁺ ratio, increase of the photoactivity, etc. were investigated. Three methods were implemented in this respect: for the change of the TiO₂ crystal structure X-ray photoelectron spectroscopy and photoluminescence spectroscopy were applied. The photocatalytic activity of the EB-treated TiO₂ was tested by taking the degree of methylene blue photodegradation as a measure of the achieved effect. The obtained experimental data of all testing methods showed that in TiO₂ at an absorbed dose of 0.5 MGy optimum changes in crystal structure of the catalyst occur, resulting in the highest photocatalytic efficiencies.     

Cyclodextrins in polymer synthesis: free radical polymerization of cyclodextrin host‐guest complexes of methyl methacrylate or styrene from homogenous aqueous solution

The polymerization of methylated β‐cyclodextrin (m‐β‐CD) 1 : 1 host‐guest compounds of methyl methacrylate (MMA) ( 1 ) or styrene ( 2 ) is described. The polymerization of complexes 1 a and 2 a was carried out in water with potassium peroxodisulfate (K₂S₂O₈)/sodium hydrogensulfite (NaHSO₃) as radical redox initiator at 60°C. Unthreading of m‐β‐CD during the polymerization led to water‐insoluble poly(methyl methacrylate) (PMMA) ( 3 ) and polystyrene ( 4 ). By comparison, analogously prepared polymers from uncomplexed monomers 1 and 2 in ethanol as organic solvent with 2,2′‐azoisobutyronitrile (AIBN) as radical initiator showed significantly lower molecular weights and were obtained in lower yields in all cases. Polymerization of m‐β‐CD complexed MMA in water, initiated with 2,2′‐azobis(N,N ′‐dimethyleneisobutyroamidine) dihydrochloride, occurred much faster than the polymerization of uncomplexed MMA in methanol under similar conditions. Furthermore, it was shown, that the precipitation polymerization of complexed MMA from homogeneous aqueous solution can be described by equations (P_n^–1 ∝ lsqb;Irsqb;^0.5) similar to those for classical polymerization in solution.     

Association of hydrophobically α,ω‐end‐capped poly(2‐methyl‐2‐oxazoline) in water

The α,ω‐end‐capped poly(2‐methyl‐2‐oxazoline) (C_n‐POXZ‐C_n) have been synthesized by a one‐pot process using cationic ring‐opening polymerization with an appropriate initiator and terminating agent. The polymers bearing different alkyl groups C₁₂ and C₁₈ have molecular weight in the range of 2.4 × 10³ to 14 × 10³ with a small polydispersity index. The solution behavior of the free chains has been analyzed in a nonselective solvent, dichloromethane, by small‐angle neutron scattering and dynamic light scattering. These amphiphilic polymers associate in water to form flower‐like micellar structures. Critical micelle concentrations, investigated by fluorescence technique, are in the range of 0.03–0.5 g L^?1 and are dependent on the hydrophilic/lipophilic balance. The structural properties of the aggregates have also been investigated by viscometry. Intrinsic viscosities of these polymers are in the same range as that of the precursors poly(2‐methyl‐2‐oxazoline) (POXZ) and mono‐functionalized polymers. Large viscosity increase corresponding to intermicellar bridging was observed in the vicinity of the micelle overlap concentration. Addition of hydroxypropyl β‐cyclodextrin (HβCD) has dissociated the aggregates and the intrinsic viscosities of the HβCD‐end‐capped chains have become comparable with the ones of POXZ precursor chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2477–2485, 2010     

Radiation chemical studies of protein reactions: Effect of radiation on the breaking of secondary bonding in protein

The effect of radiation on the breaking of secondary bonding in protein was studied by measuring the viscosity change at different radiation doses and urea concentrations. An experimental equation for the viscosity change was obtained, and the observed behavior was explained on the basis of the molecular mechanism. The general equation for the viscosity change is given by η_red = A(X ? Be^?kx) + C log R, where η_red is the reduced viscosity of the solution, R is the dose of γ-radiation, X is the concentration of urea, and A, B, C, and k are adjustable constants.     

Radiation grafting of acrylonitrile on ethylene-propylene diene terpolymer rubber: Optimization of grafting parameters and oil resistance properties

Radiation induced grafting of acrylonitrile (ACN) on ethylene-propene diene terpolymer (EPDM) rubber film was investigated by mutual radiation grafting technique. Effect of experimental variables viz. radiation dose, dose rate, type of solvent and monomer content on extent of grafting was studied. From the kinetic studies a mathematical relation R _g α[M]^0.7 D ^0.68 showing non-linear relationship for rate of grafting with monomer concentration and dose was deduced. The grafted samples showed increased hardness and oil resistance.     

Quantification of radiation induced crosslinking in a commercial, toughened silicone rubber, TR55 by H MQ-NMR

Radiation induced degradation in a commercial, filled silicone composite has been studied by SPME/GC-MS, DMA, DSC, swelling, and multiple quantum NMR. Analysis of volatile and semi-volatile species indicates degradation via decomposition of the peroxide curing catalyst and radiation induced backbiting reactions. DMA, swelling, and spin-echo NMR analysis indicate an increase in crosslink density of near 100% upon exposure to a cumulative dose of 250 kGray. Analysis of the sol fraction via Charlesby-Pinner analysis indicates a ratio of chain scission to crosslinking yields of 0.38, consistent with the dominance of the crosslinking observed by DMA, swelling and spin-echo NMR and the chain scissioning reactions observed by MS analysis. Multiple quantum NMR has revealed a bimodal distribution of residual dipolar couplings near 1 krad/s and 5 krad/s in an approximately 90:10 ratio, consistent with bulk network chains and chains associated with the filler surface. Upon exposure to radiation, the mean 〈Ω_d〉 for both domains and the width of both domains increased. The MQ-NMR analysis provided increased insight into the effects of ionizing radiation on the network structure of silicone polymers.     

"一步法"合成多级孔SAPO-34分子筛

以TPOAC和硅溶胶为硅源,合成了多级孔SAPO-34分子筛,总比表面积达到649 m²·g^-1。详细考察了TPOAC和硅溶胶的配比对多级孔SAPO-34外比表面的影响,通过XRD、BET、SEM、NH₃-TPD等对其结构进行表征,结果表明多级孔SAPO-34的外比表面积可调变,晶体外观有较多缺陷位置,弱酸量减少,强酸位有变弱的趋势。在TPOAC与硅溶胶的投料比为3:2,晶化时间为10 d,投料比为n_Al2O3:n_P2O5:n_Si:n_TEAOH:n_H2O=1:0.9:0.5:2:60时,合成的多级孔SAPO-34的外比表面积达到最大,为100 m²·g^-1。