Exactly alternating silarylene–siloxane polymers. V. Evaluation of the mechanical properties of crosslinked elastomers

The search for technologically useful elastomers with good thermal stability at elevated temperatures combined with low temperature flexibility has led us and others to the preparation of a series of linear alternating silarylene–siloxane polymers. Because of the very favorable thermal stabilities of these polymers, a detailed study was made of methods for their vulcanization and for the evaluation of their mechanical properties. The results of these investigations are described, including mechanical properties of the vulcanizates both before and after heat aging and before and after immersion in different solvents, as well as their characteristics after prolonged and repeated extension.     

Exactly alternating silarylene—siloxane polymers: 6. Thermal stability and degradation behaviour

The thermal stability and degradation behaviour of a series of twelve different exactly alternating silarylene—siloxane polymers were investigated by several different methods including thermal gravimetric analysis (t.g.a.) in air and in nitrogen, long term (up to 48 h) high temperature (600° and 900°C) isothermal degradation in nitrogen, and rapid pyrolysis in helium. No weight loss was observed by t.g.a. until about 400°C, and two distinctly different mechanisms were observed, one for degradation in nitrogen (a single step process), and the other in air (a three step process). Under nitrogen, black, insoluble, carbon-hydrogen-silicon containing degradation products were obtained, which were stable in pure oxygen to at least 1100°C. In air, pure SiO₂ was obtained after heating to above 730°C. Isothermal investigations revealed that at temperatures of 600°C and above, weight loss by thermal degradation under a nitrogen atmosphere was completed in less than an hour, and the polymeric products which remained thereafter did not change any further even after 48 h at 900°C.     

The synthesis of selenium condensation polymers using bis(2-hydroxyethyl) selenide and bis(2-aminoethyl) selenide

Procedures were developed for the large-scale synthesis of bis(2-hydroxyethyl) selenide and bis(2-aminoethyl) selenide. These bifunctional selenides were converted into a series of polyesters, polyureas, and polyurethanes. Methods of syntheses and properties of these condensation polymers are described.     

Intumescent flame retardants for polymers. I. The poly(acrylonitrile)–ammonium polyphosphate–hexabromocyclododecane system

The influence of ammonium polyphosphate (APP) and hexabromocyclododecane (HBCD) as flame retardant (FR) on poly(acrylonitrile) (PAN) has been examined. The APP–HBCD system behaves as an intumescent flame retardant (IFR) formulation, APP being the char-forming agent and HBCD the blowing agent. A negligible gas-phase mode of action was ascertained for HBCD with this substrate. A synergism between the two FR agents was observed, corresponding to about 50% increased efficacy with respect to the separate effects of the two components. Thermogravimetry (TG), oxygen index (OI), nitrous oxide index (NOI) experiments and phosphorous residue measurements were performed to substantiate the conclusion that a conclusion that a condensed phase mechanism of action accounts for all the facts observed.     

Postpolymerization synthesis of (bis)amide (co)polymers: Thermoresponsive behavior and self-association

A library of novel well-defined (bis)amide-based (co)polymers was prepared through postpolymerization modification of poly(pentafluorophenyl acrylate) with amines including ammonia and amide derivatives of amino acids. Products were characterized using a combination of NMR and FT-IR spectroscopies and size exclusion chromatography; results conformed to the expected structures obtained through quantitative conversion. The series of (bis)amide (co)polymers displayed rich phase behavior in aqueous solution such as thermoreversible gelation at low temperature and high concentration while other samples displayed inverse temperature dependent solubility (lower critical solution temperature (LCST)-type) behavior. A hydrophobically modified polyacrylamide copolymer displayed upper critical solution temperature (UCST) behavior in aqueous solution. Significantly, driven by polymer–polymer hydrogen bonding, copolymers self-associated into highly ordered, regular structures of several tens to hundreds of micrometers in size. Morphologies included sheet-like, rod-like and honeycomb-like structures and depended strongly on the chemical composition of copolymers.     

High-temperature elastomers: Glass transition–structure correlations for two systematic series of linear poly(carborane–siloxane)s. I

Nine linear poly(carborane–siloxane) high-temperature elastomers which differ systematically in chemical structure were investigated by torsional braid analysis. The structural variations include two different carborane cage structures in the polymer chain (? CB₁₀H₁₀C? and ? CB₅H₅C? ) and the stepwise increase in the number of ? Si(CH₃)₂? O? linkages associated with each cage in the repeat unit. Poly(dimethylsiloxane) was studied as the compositional limit of both series. The dynamic mechanical relaxations (at about 1 cps) of the materials are reported. These include the melting points of the semicrystalline polymers and the glass transitions and secondary transitions of all the polymers. The glass transition temperatures in each series were systematized using the well-known copolymer composition-versus-glass transition temperature relationship 1/T_g = W₁/T_g1 + W₂/T_g2.     

Synthesis and photoconductivity study of phthalocyanine polymers. I. PAA–CuPc(NO2)2

Cu–dinitro–diamino phthalocyanine was synthesized and converted to the diazonium salt. Polyacrylamide bonded CuPc(NO₂)₂ [PAA–CuPc(NO₂)₂] (I) was synthesized by hot polymerization of acrylamide and this diazonium salt. Polymer(I) is water soluble and contains about 7 mol % CuPc(NO₂)₂ rings, which are covalently bonded to PAA. Polymer(I) shows good photoconductivity, which is much better than that of the corresponding phthalocyanine monomers. By doping with iodine (I₂), the photosensitivity of polymer(I) is increased, which through fluorescence analysis is explained by the fact that a charge–transfer complex (CTC) of polymer(I) with I₂ is formed. The influence of interface layer (IFL) and charge–transportation material (CTM) on the photoconductivity of polymer(I) were also studied.     

Epoxidation of styrene–butadiene block polymers. I

A styrene–butadiene–styrene (20–60–20) linear block polymer was epoxidized in toluene and cyclohexane solutions with peroxyformic acid generated in situ. The epoxidized polymer, containing about 8% oxygen, exhibits greatly improved resistance to ASTM oils. It can be readily compounded with carbon black, and the unvulcanized stock is found to be comparable to vulcanized polychloroprene and nitrile rubber in tensile strength and resistance to ASTM oils and certain chemicals.     

Synthesis and characterization of thermoplastic poly(ester–siloxane)s

Two series of thermoplastic poly(ester–siloxane)s, based on poly(dimethylsiloxane) (PDMS) as the soft segment and poly(butylene terephthalate) as the hard segment, were synthesized by two‐step catalyzed transesterification reactions in the melt. Incorporation of soft poly(dimethylsiloxane) segments into the copolyester backbone was accomplished in two different ways. The first series was prepared based on dimethyl terephthalate, 1,4‐butanediol and silanol‐terminated poly(dimethylsiloxane) (PDMS‐OH). For the second series, the PDMS‐OH was replaced by methyl diesters of carboxypropyl‐terminated poly(dimethylsiloxane)s. The syntheses were optimized in terms of both the concentration of catalyst, tetra‐n‐butyl‐titanate (Ti(OBu)₄), and stabilizer, N,N′‐diphenyl‐p‐phenylene‐diamine, as well as the reaction time. The reactions were followed by measuring the inherent viscosities of the reaction mixture. The molecular structures of the synthesized poly(ester–siloxane)s were verified by ¹H NMR spectroscopy, while their thermal properties were investigated using differential scanning calorimetry. © 2001 Society of Chemical Industry     

Thermooxidative degradation behavior of poly(silphenylene–siloxane)s

Copolymers of poly(silphenylene–siloxane) with dimethylsiloxane and diphenylsiloxane with various end groups were synthesized through an Si? H/Si? OR polycondensation process. The thermooxidative degradation behaviors of the copolymers were investigated by thermogravimetric analysis and IR spectrometry techniques. All of the polymers were characterized by a two‐step mass loss. The first one, which peaked at 510–545°C in differential thermogravimetric curves, was mostly caused by the main‐chain depolymerization, whereas the second one, which reached its maximum around 650°C, was caused by side‐group oxidation and Si? C bond scission. The main‐chain depolymerization occurred over a temperature range of some 470–580°C, whereas Si? C bond scission and side‐group oxidation occurred over a temperature range of about 585°C to above 720°C. The incorporation of phenyl groups in the end groups greatly retarded the temperature for the degradation onset of the main chain to 120°C higher. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

双(三氯甲基)碳酸酯的合成

介绍双（三氯甲基）碳酸酯的合成机理及３种合成方法：溶剂法,非溶剂法,循环法。     

Electrospinning of poly(dimethyl siloxane) by sol–gel method

Crosslinked poly(dimethyl siloxane) (PDMS) fibers were fabricated by electrospinning in combination with a sol–gel process followed by heat treatment. Before and after heat treatment, the changes in the chemical and thermal properties of the electrospun PDMS fibers were examined by differential scanning calorimetry (DSC), equilibrium swelling tests, and contact angle measurements. There was no significant change in morphology and average diameter of the as‐spun PDMS fibers after heat treatment. The tensile properties of the as‐spun PDMS fibers mat increased with increasing heat treatment temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Epoxy resins. I. The stability of the epoxy–trimethoxyboroxine system

The useful life of a material depends on its environmental exposure. The diglycidyl ether of bisphenol A (DGEBA) cured with trimethoxyboroxine (TMB) was evaluated under various aging conditions. For isothermal aging, the main factor controlling weight loss appeared to be related to the diffusion of the degradation products (E_act = 22.1 kcal/mole). Chemical decomposition kinetic parameters were obtained using vacuum thermogravimetric analysis (TGA) on powder samples. The thermal decomposition activation energy and the reaction order of cured DGEBA were 37.5 kcal/mole and 1.05, respectively. The hydrolytic aging of this material was also kinetically analyzed, and it was concluded that the weight change was controlled by both water diffusion into the sample and diffusion of hydrolysis products from the sample. During hydrolytic aging below the glass transition temperature, the specimens gained weight up to 0.05 g based on 1-g unaged cured resin and then leveled off. At higher temperatures, the specimens initially gained weight and then began to lose weight, reaching a constant weight gain. The activation energies for water diffusion into the cured resin are 19.5 kcal/mole at temperatures above T_g and 21.5 kcal/mole at temperatures below T_g. The main hydrolysis product was boric acid from reaction of the boroxine ring with water. The time-temperature superposition principle was used for the weight loss study on isothermal and isothermal hydrolytic aging. The scale factor in this approach was found to be the ratio of the diffusion coefficient at the temperature of interest to that at a reference temperature.     

Quinone–amine polymers. V. Syntheses and solubilities of several diamine–p-benzoquinone oligomers (PAQ)

Several diamine–p-benzoquinone polymer/oligomers were synthesized to find those that exhibited superior properties, in addition to being able to displace water from wet, rusty steel surfaces. Unfortunately, many of these were found to be insoluble in most commonly used solvents and a few to be insoluble in all 34 solvents used in polymer solubility studies. The reason for this low solubility is believed to be the extremely regular structure of the polymers.     

New epoxy resins. I. The stability of epoxy–trialkoxyboroxines triaryloxyboroxine system

A polymer with high aromaticity and/or cyclic ring structures chain backbone usually has high heat, thermal, and flame resistance. Two diglycidyl ethers of bisphenols were prepared from 4,4′ isopropylidenediphenol (DGEBA) and 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) for evaluation. Four boroxines—trimethoxyboroxine (TMB), triethoxyboroxine (TEB), triisopropoxyboroxine (TIPB) and triphenoxyboroxine (TPB)—were used as the curing agents. DGEBA and DGEBF cured with various boroxines indicate that the trend for their respective glass transition temperature (T_g's), degradation temperatures (T_d's), and gel fractions are TMB-cured epoxy ≈ TEB-cured epoxy < TIPB cured epoxy < TPB cured epoxy. The DGEBF system usually has a higher T_g, T_d, gel fraction, oxygen index (OI), and char yield than the related DGEBA system. DGEBF/DGEBA (80/20 mol ratio) shows a synergistic effect in regard to char formation. This effect exists not only in the copolymer system but also in blended homopolymers of the separately cured resins. A modified mechanism for the polymerization of phenyl glycidyl ether (PGE) with TMB has been proposed.     

The effect of segment length on some properties of thermoplastic poly(ester–siloxane)s

A series of novel thermoplastic elastomers, based on poly(dimethylsiloxane) (PDMS) as the soft segment and poly(butylene terephthalate) (PBT) as the hard segment, were synthesized by catalyzed two‐step, melt transesterification reactions of dimethyl terephthalate and methyl esters of carboxypropyl‐terminated poly(dimethylsiloxane)s (M?_n = 550–2170 g mol^?1) with 1,4‐butanediol. The lengths of both the hard and soft segments were varied while the weight ratio of the hard to soft segments in the reaction mixture was maintained constant (57/43). The molecular structure, composition and molecular weights of the poly(ester–siloxane)s were examined by ¹H NMR spectroscopy. The effectiveness of the incorporation of the methyl‐ester‐terminated poly(dimethylsiloxane)s into the copolymer chains was verified by chloroform extraction. The effect of the segment length on the transition temperatures (T_m and T_g) and the thermal and thermo‐oxidative degradation stability, as well as the degree of crystallinity and hardness properties of the synthesized TPESs, were studied. Copyright © 2003 Society of Chemical Industry     

The characterization of styrene–β-pinene polymers

Styrene was polymerized with β-pinene at 30°C and ?50°C in methylene dichloride and in m-xylene solvents. The styrene-to-terpene ratio on pyrolysis suggests that the polymers made at 30°C are copolymers, whereas most of the polymers made at ?50°C are not copolymers. On the other hand, ethylene, ethane, and propylene analysis suggests that more of the polymers made at ?50°C are copolymers.     

Synthesis and characterization of poly(N‐isopropylacrylamide)s initiated with siloxane oligomer–(NH4)2Ce(NO3)6 redox pair

Poly(N‐isopropylacrylamide)s (PNIPAAM)s were synthesized via free‐radical polymerization using a ceric ammonium nitrate, Ce(IV)–α‐ω‐dihydroxy(polydimethylsiloxane) (Tegomer H‐Si 2111, PDMS) redox pair in hexane at 30°C in a nitrogen atmosphere. The dependence of the initiation and termination steps on the [NIPAAM]/[Ce(IV)] and [NIPAAM]/[PDMS] ratios were studied using gravimetry and FTIR, ¹H‐NMR, UV‐vis, and GFAA spectroscopy techniques. Gravimetric results indicated that, in the case of high concentrations of PDMS, the percentage of the solid portions of the products decreased while the amount of the oligomeric NIPAAM chains increased, that is, as the amount of PDMS in hexane was increased, the number of the short NIPAAM chains having PDMS segments at the two ends, also increased. UV‐vis results showed that the LCST of PNIPAAM initiated with Ce(IV) alone was higher than those of the ones that were synthesized using common initiator systems such as an ammonium persulfate–N,N,N′,N′‐tetramethylethylenediamine redox pair and azobis(isobutyronitrile). Further, it was observed that both siloxane blocks and ? NH? groups forming coordination bonds with free Ce(IV) ions and/or metal–ligand complexes had an important effect on the aggregation process of the chains. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1248–1254, 2003