Cyclolinear polysiloxanes. II. Crosslinking and characterization

The synthesis and characterization of two groups of novel networks prepared from cyclolinear polysiloxanes are described. The first group of networks from cyclolinear polysiloxanes (N‐CLPSs) was synthesized by the hydrosilation of vinyl‐terminated cyclolinear polyorganosiloxanes [prepared from diacetoxydiethyltetramethylcyclotetrasiloxane (D₄Et₂OAc₂) or diacetoxytriethylpentamethylcyclopentasiloxane (D₅Et₃OAc₂)] with a copolymer of dimethylsiloxane and methylhydrosiloxane as the crosslinking agent. Hydrosilation was effected with a platinum carbonyl catalyst with a cyclovinylsiloxane moderator. The second group of networks (N‐eCLPSs) was prepared similarly with extended cyclolinear polysiloxanes. The mechanical properties of the novel networks were comparable to those of polydimethylsiloxane networks (N‐PDMS). The oxygen permeabilities were similar to or slightly higher than that of N‐PDMS. The glass‐transition temperatures of D₄Et₂OAc₂‐ and D₅Et₃OAc₂‐based N‐CLPSs were ?67.8 and ?90.8 °C, respectively, whereas the incorporation of polydimethylsiloxane spacers into similar N‐eCLPSs lowered their glass‐transition temperatures to ?109.7 and ?115.0 °C. Upon heating to 800 °C in air, N‐CLPSs yielded more residue than N‐eCLPSs, which in turn yielded more residue than N‐PDMS. These results may have been due to the presence of T units in the cyclic siloxane units, which may have inhibited chain degradation or the formation of volatile products. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4053–4062, 2006     

可交联PVC的合成及其交联反应

N,N-二乙基二硫代氨基甲酸钠(铜试剂,简称NasR)取代PVC链中的部分氯原子,制得不同官能度的功能高分子PVC-SR.在热的作用下,实现了PVC-SR的自交联和PVC-SR/NBR共混体系的共交联.研究了温度、铜试剂用量对取代反应的影响及PVC-SR官能度对交联反应硫化曲线、产物的凝胶含量、玻璃化温度、拉伸性能和压缩永久变形的影响,并初步探讨了交联反应机理.     

Thermooxidative degradation of polyacrolein

Thermooxidative degradation of polyacrolein has been investigated with a derivatograph. It was found that up to 80° a physical process occurs — the evaporation of traces of water and monomer acrolein trapped by the polymer. Exothermic process of dehydration of hydrated aldehyde groups of polyacrolein takes place from 80 to 130°. A very pronounced exothermic process from 130 to 180° with a sharp weight loss is caused by the degradation of ring structures withn<3. The presence of ring structures withn>3 in the polymer shifts the DTA and DTG peaks by 20° to lower temperatures. At temperatures of about 250° and higher side carbonyl groups are thermally oxidized and decarboxylated with a considerable weight loss. All these suggestions were confirmed by infrared spectroscopy.

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Zusammenfassung Die thermooxidative Zersetzung von Polyacrolein wurde mit einem Derivatographen untersucht. Es wurde gefunden, daß bis zu 80° ein physikalischer Vorgang stattfindet — die Verdampfung von Wasserspuren und von im Polymer eingeschlossenem monomerem Acrolein. Der exotherme Vorgang der Dehydratisierung hydratisierter Aldehydgruppen des Polyacroleins vollzieht sich von 80 bis 130°. Ein sehr stark exothermer Vorgang zwischen 130 und 180°, mit scharf ausgeprägtem Gewichtsverlust, wird durch die Zersetzung von Ringstrukturen mitn<3 verursacht. Die Gegenwart von Ringstrukturen mitn>3 im Polymer verschiebt die DTA- und DTG-Peaks um 20° in Richtung der niedrigeren Temperaturen. Bei etwa 250° oder höher liegenden Temperaturen werden Seiten-Carbonylgruppen thermisch oxidiert und decarboxyliert, und zwar unter bedeutendem Gewichtsverlust. All diese Annahmen wurden durch infrarotspektroskopische Untersuchungen unterstützt.

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Résumé Etude de la dégradation thermique oxydante de la polyacroléine à l'aide d'un Derivatograph. On montre qu'un processus physique se produit jusqu'à 80°:l'évaporation des traces d'eau et de l'acroléine monomère encagée dans le polymère. La déshydratation des groupes aldéhydes hydratés de la polyacroléine se produit exothermiquement entre 80 et 130°. Un processus exothermique très prononcé entre 130 et 180°, accompagné d'une brusque perte de poids résulte de la dégradation de la structure annulaire lorsquen<3. La présence dans le polymère de structures annulaires avecn > 3 déplace les pics ATD et TGD de 20° vers les températures inférieures. Aux températures d'environ 250° ou plus, on observe l'oxydation thermique et la décarboxylation des groupes carbonyles latéraux, accompagnée d'une perte de poids considérable. Cette interprétation est confirmée par spectroscopie infrarouge.

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« » MOM (). , 80° . 80 130° . 130–180° n<3. n>3 DTA DTG 20°. 250° . - .

     

热可逆共价交联反应及其研究进展

梗概评述了环戊二烯（ＣＰＤ）与双环戊二烯（ＤＣＰＤ）之间Ｄｉｅｌｓ－Ａｌｄｅｒ反应的特点,以及将其引作大分子间交联键的思路;以此为基础详细讨论了热可逆共价交联聚合物的分析方法。制备路线,以及利用这一反应目前所达到的研究水平和成就 。     

Crosslinking Reaction of Type Aa Involving Intramolecular Cyclization

An alternative way is proposed to approach crosslinking reactions of Type A _a by taking into consideration intramolecular cyclization. The sol fraction for postgelation is investigated to deduce the equilibrium number distribution of n-mer, with the Flory-Stockmayer distribution as a criterion. Furthermore, scaling study leads directly to a generalized scaling law.     

Crosslinking Reaction in the Formation of Porous Clays

Clay minerals are a class of hydrous layer aluminosilicates of the so-called phyllosilicate^[1] family made up of two basic types of layers, the SiO₄ tetrahedral sheet and the Al₂(OH)₆[or Mg₃(OH)₆] octahedral sheet, many of which posses interlayer cations capable of exchanging reaction with other cations. The preparation of porous clays are based on this reactivity of exchangeable interlayer cations by using the intercalation of polycations such as Al₁₃⁷⁺ oligomers^[2] into the galleries of clay minerals to form a microporous materials^[3] Here we reported a study on the interlayered crosslinking of a 2:1 type montmorillonites with a hydrolysed polycations Al in the formation of porous clays. Na-montmorillonite gel (Na-mont, particle size<2 μ) were purified by using sedimentation of Na-bentonite fines (400 mesh, Zhejiang, China) and subsequent extensively washing to remove any soluble Na⁺. Hydrolysed polycations Al was prepared by NaOH hydrolysis of AlCl₃ solutions in a condition^[2] of OH/Al=2.0 and then aging at 70-90℃ for 4 h by the following process^[3].     

Reaction of diisocyanates with alcohols. II. Catalyzed reactions

In a previous work we reported a procedure to calculate rate constants for the primary and secondary reactions (urethane and allophanate formation, respectively) between isocyanate and alcohols. In the present paper the same procedure is applied to the catalyzed reaction, thus defining the selectivity for a series of catalysts.     

Lead removal and recovery from battery industry wastewaters by soluble starch xanthate

Treatment, removal and recovery of lead (3 mg/L) from battery industry wastewaters have been investigated utilising a chemical precipitation process with soluble starch xanthate (SX) at pH 5-6. A reactant ratio, i.e., SX/Pb(II) = 6 mol/mol, a reaction time of 15 min., the addition of 15 mg/L of a cationic polyelectrolyte and a final filtration gave residual lead concentrations in the liquid phase less than 0.2 mg/L, well below the maximum limit established by the EU Directive. Lead was extracted from the obtained sludge by oxidation with sodium hypochlorite or hydrogen peroxide solutions. The amounts of oxidant needed were quantified as 13.5 mol NaClO/mol Pb and one order of magnitude larger, for H2O2, the latter due to the competitive disproportion reaction of the oxidant. The metal extraction was quantitative using sodium hypochlorite; when hydrogen peroxide was used, the formation of insoluble PbSO4 (Anglesite) gave a 80% metal extraction. In both cases molar ratios between sulphate and lead ions in the extracted solutions were in the range 2.1-2.2, in agreement with the stoichiometries of the reactions. Lead can be quantitatively recovered from the extracted (NaClO) solutions, for reuse, after a chemical precipitation process with 1M NaOH at pH 9-9.5, in the form of hydrocerussite [Pb3(CO3)2(OH)2].     

Reaction of inorganic cyanates with halides. II. Reactions of chlorohydrins

The reaction of ethylene and trimethylene chlorohydrins with cyanate ion in anhydrous dimethylformamide (DMF) forms 2-oxazolidinone and tetrahydro-2H-1, 3-oxazin-2-one, respectively. These are the major products over a wide concentration range, and at initial chlorohydrin concentration of 1 M and lower, the yields are high enough to make the reaction useful for synthesis of oxazine and oxazolidine derivatives. The corresponding reaction with tetramethylene chlorohydrin gave tetrahydrofuran as the major product with the by-products being polymeric. Pentamethylene and hexamethylene chlorohydrins yield linear polyurethanes when allowed to react with cyanate in DMF. Examination of the relative rates of reaction of these chlorohydrins indicate that the mechanism by which urethanes are formed (both cyclic and polymeric) is an S_N2 displacement of chloride by cyanate ion to give an isocyanate intermediate which then reacts with an alcohol group to form urethane.     

Alkoxylation of hydridophosphorane. II. Reaction of hydridophosphorane with benzenesulphenic esters

The spirophosphorane 4 underwent reaction with a series of benzene-sulphenic esters 3 to give the corresponding isolable alkoxyphosphoranes. The reactivities of benzenesulphenic esters 3 in this reaction were seen to be dependent on steric hindrance of the R groups. The yields of alkoxyphosphoranes were influenced by the reaction temperature. The probable mechanism was suggested in terms of experimental observations.     

Crosslinking,filler, or transition constraint of polymer networks. II

The theory of Part I is developed by application to filler reinforcement of NR and SBR. For unswollen but prestretched networks it quantifies entire stress–strain curves and applies new concepts of extensibility and strain hardening. Constraint of swelling is expressed by a constant φ, termed linkage reinforcement, and by an effective hard fraction C_h per cubic centimeter of compound. For rubber–filler swelling v_c the modified Flory functions F(v_c) in part 1 need 3% correction. Then, relative to gum fix points 1/F₀(v_r): where C_h ≤ 1.15C for filler concentrations C per cubic centimeter of compound. The effective C_h comprises the volume fraction C* of bonded particles and 5–10 Å of surface–bound rubber that has been stretched hard by swelling. When needed, the actual crosslink density and intrinsic linkage reinforcement φ₀ can be obtained by dividing by (1 + 2.5C_φ) where C_φ = (C ln φ)/(1 + 2.5C). The case C_h ≤ 1.15C with Graphon or inert fillers is identified and assessed by equations: Results C_h > 1.15C are invalid, but then C_h ≈ 1.15C* ≈ 1.15C, e.g., for carbon blacks. Even Graphon is distinguished from inert fillers at low concentrations C by substantial constraint reinforcement F₀(v_r)/F(v_c) > 1. For prestressed dry rubber a modulus G, network extensibility α_b ? 1, and upturn coefficient μ_h express the whole curve; G and μ_h show identical constraint strength distributions. Network extensibility α_b ? 1 is the microbreaking strain (prestretch); for pure elastomer it is elongation at break. The relation of stress F to extension ratio α is: where C₂* = 0.7 and j = 0.4 from NR/MPC data. Strain-hardening coefficients h are obtained from μ_h by the theory given in Part I. Hard modulus components G_h = 0.7 ln (h/h₀) vanish as h → h₀ (gum) = 110. After high prestresses the residual ln-(h^*/h₀) due to strong carbon-rubber linkages implies G_h* = 0.42 kg/cm², i.e., ca. 10% of the normal cure crosslinks.     

Crosslinking of poly(arylene ether ketones). II. Crystallization kinetics

Results of crystallization kinetics study and x-ray diffraction are in good agreement with our previous rheological and mechanical results. Poly(arylene ether ketones), which are modified by sulfur at concentrations below approximately 2% by weight, have higher crystallization rates owing to the decrease in molecular weight caused by chain scission and/or the presence of sulfur that acts as a nucleating agent. However, all the observed differences in mechanical properties can be rationalized only by the nucleation effect of the sulfur. Upon aging of the sulfur-modified samples, cross linking occurs, leading to decreases in crystallization rates.     

The Reaction Mechanism of the Transetherification and Crosslinking of Melamine Resins

Melamine formaldehyde resins (MFR) are well known resins in the wood board and paper coating market. Etherified MFR's are applied as crosslinkers in the automotive coating industry. In Europe the growth of the market and the research activities are relatively small. On the other side in comparison to other polymers outstanding properties are possible to realize. So the development of new melamine ether resins (MER) was started. MER is a partly methylolated and fully etherified resin with a highly stable “thermoplastic” processing range. The MER's themselves are transparent granulates with enough stability for storage and transport. The crosslinking reaction can be started either by thermal or acidic catalytic activation, without losses of formaldehyde. Transetherifications with oligomeric diols can lead to more elastic and higher molecular melamine polyether resin (MPER) structures. The reaction mechanism and the crosslinking kinetics of the partly methylolated melamine ethers of methanol in comparison to the fully methylolated hexamethylol melamine ether will be discussed in this paper.     

Chemistry of novolac resins. II. Reaction of model phenols with hexamethylenetetramine

It is proposed that the reactions of hexamethylenetetramine (HMTA) with 2,4-xylenol and with 2,6-xylenol occur by different pathways. The rate of reaction and the final product distribution depend on the initial xylenol : HMTA ratio and are different in the two systems. Measured by HMTA consumption, with 2,4-xylenol the reaction rate increased with increasing xylenol : HMTA ratios, whereas with 2,6-xylenol the rate of reaction decreased with increasing 2,6-xylenol : HMTA ratio. In systems which contain both 2,4- and 2,6-xylenol, a strong preference for reaction of the HMTA with the ortho site of 2,4-xylenol was noted. This preference was apparent even in mixtures in which 2,6-xylenol was present in greater amounts than 2,4-xylenol. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1389–1398, 1997