Preparation and properties of polydimethylsiloxane‐modified epoxy resins

In this work, polydimethylsiloxane (PDMS) with different molecular weight were used to modify diglycidyl ether of bisphenol A (DGEBA). A PDMS‐block‐DGEBA copolymer that acted as a compatibilizer was prepared via DGEBA, hydroxy terminated PDMS, and silane coupling agent in the presence of a catalyst. The reaction mechanisms and compatibilizing effects of the block copolymer were studied by means of Fourier transform infrared (FTIR) spectrum analysis and observation under scanning electron microscopy (SEM). The thermal and mechanical behaviors were analyzed as well. Results indicated that the block copolymer has good compatibilizing effect, and PDMS with low molecular weight could be dispersed in the DGEBA matrix more evenly. Moreover, the PDMS modified DGEBA systems had higher impact strength and lower weight loss rate than those of the pristine DGEBA system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1683–1690, 2000     

On the pyrolysis of a methyl-silsesquioxane in reactive CO2 atmosphere: A TG/MS and FT-IR study

Polymer-derived SiOC-C composites are typically obtained through pyrolysis of a polysiloxane precursor in inert atmosphere. Recent studies have shown that novel SiOC microstructures and compositions can be obtained when the pyrolysis is carried out in a reactive environment, as CO₂, which leads to a selective oxidation of the Si─C bonds leaving a microstructure constituted by a nano-dispersed sp² carbon phase within an SiO₂ matrix. However, little is known about the reaction mechanisms between CO₂ and the preceramic polymer to date. In this work, we investigated the pyrolysis of a methyl-silsesquioxane in reactive (CO₂) and inert (Ar or He) atmosphere by combining TG/MS and FT-IR analysis. The results showed that CO₂ starts to react with the preceramic polymer from ≈750°C when the Si─CH₃ groups start to form Si─CH_x-Si units. The reaction breaks the Si─C bond increasing the amount of the free carbon phase and releasing water vapor, detected by MS, even at temperatures exceeding 900°C. At higher temperatures (≈950°C), CO₂ reacts with the free carbon phase leading to a weight loss and the formation of CO.     

Free-radical emulsion copolymerization of styrene with butadiene and vinyl triethoxysilane with a cumene hydroperoxide redox initiator

The emulsion free-radical copolymerization of vinyl triethoxysilane (VTES) with styrene (St) and butadiene (Bd) was initiated by cumene hydroperoxide and ferrous sulfate at 0 °C. The effects of VTES on the copolymerization conversion, reaction time, gel content, latex particle size, thermal stability, and mechanical properties were thoroughly investigated. The success of this reaction was confirmed by the peaks attributed to both Si─O─Si groups at 1065 cm⁻¹ and the Si─O─C bond at 1046 cm⁻¹. A kinetics analysis showed that the conversion decreased with increasing VTES mass in the monomer feed. Compared with that in the St–Bd copolymer, the latex particle size increased slightly with increasing VTES mass. The Mooney viscosity and gel content results show that a large fraction of precrosslinking molecular chains was formed in the rubber particles. The thermogravimetric analysis results indicate that the thermal stability of the copolymers increased with increasing VTES concentration. The 300% modulus and tensile strength of the St–Bd–VTES copolymer increased with the mass of VTES at first and then decreased after 3 phr VTES, whereas the elongation at break decreased with increasing VTES mass. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47896.     

Synthesis and characterization of hydroxy‐terminated polyether‐polydimethylsiloxane‐polyether (PE‐PDMS‐PE) triblock oligomers and their use in the preparation of thermoplastic polyurethanes

A series of hydroxy‐terminated polyether‐polydimethylsiloxane‐polyether (α,ω‐dihydroxy‐(PE‐PDMS‐PE)) ABA triblock oligomers were synthesized from silanic fluids and methyl polyallyloxide polyethers. The reaction was a one‐step solventless hydrosilylation reaction with chloroplatinic acid (CPA) catalyst in the presence of heat. These ABA oligomers were characterized via ¹H‐NMR, ¹³C‐NMR, ²⁹Si‐NMR, FT‐IR, and GPC to demonstrate that they exhibit a 100% linear ABA structure with a siloxane Si? O chain in the center and polyether ethylene oxide (EO)/propylene oxide (PO) chains on the two sides terminated by hydroxy groups. The triblock oligomers were used to form thermoplastic polyurethanes (TPUs) using two‐step solventless bulk polymerization. The investigation of triblock oligomers impact on TPUs mechanical properties, thermal performance, surface water repellency, and morphology performance were analyzed by Instron material tester, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), water contact angles (WCA), scanning electron microscope (SEM), and transmission electron microscope (TEM). DSC and TGA indicated that PE‐PDMS‐PE modified TPUs had a clear lower T_g under ?120°C and the temperature of 50% weight loss was improved from 280 to 340°C. PE‐PDMS‐PE–modified TPU did not have the marked reduction on mechanical properties than pure polyether produced TPU. Tensile strength was maintained at 13 MPa and elongation was maintained at 300%. SEM and TEM were used to investigate the copolymers’ morphology performance and found that all PO PE‐PDMS‐PE had a pseudo‐three phase separation. WCA analysis confirmed that PE‐PDMS‐PE–modified TPU had significantly improved hydrophobic performance because the silicone structure linked into TPU copolymers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42521.     

V、Mo修饰SBA-15分子筛结构与催化性质的DFT计算预测

采用密度泛函方法,计算了介空分子筛SBA-15及V和Mo原子修饰后分子筛的几何参数及红外光谱,与实测值比较,确定了分子筛的合理模型。通过分析模型化合物的前线分子轨道,推测了V和Mo原子修饰前后分子筛表面的酸碱中心及氧化还原性质。最后,由计算得到分子筛表面VO4和MoO5基团的Mayer键级推测,当此类催化剂参与酸碱和氧化还原反应时,基团上的三种化学键(MO─Si、M─OSi和MO)中,MO─Si键最容易断裂打开,参加化学反应。     

Random coil dimensions of poly(diethyl siloxane)

A sample of high molecular weight poly(diethyl siloxane), [Si(C₂H₅)₂O]_x, (PDES) was separated into a series of fractions by means of liquid-liquid precipitations. Four of the fractions were studied by osmometry and viscometry in toluene at 25°C. The resulting values of the number-average molecular weight, second virial coefficient, and intrinsic viscosity indicate that the unperturbed dimensions of PDES are essentially the same as those of poly(dimethyl siloxane) (PDMS) of the same chain length. Thus, differences in intramolecular interactions between these two chains have little effect on their unperturbed dimensions. Most pertinent in this regard are interactions between the side chains, which are favourable in trans conformations in both PDES and PDMS. These favourable interactions in trans conformations would be enhanced in the case of the ethyl groups in PDES, but this effect is apparently offset by a comparable increase in favourable interactions between ethyl groups and oxygen atoms in the competing gauche conformations.     

Rheology of crosslinked entangled polymers: Shear stiffening in oscillatory shear

Polyborosiloxane (PBS) was synthesized from boric acid and hydroxyl-terminated polydimethylsiloxane (PDMS). The oscillatory shear behavior of PBS formed by PDMS with different molecular weight was studied. The relaxation time of PBS was calculated by Doi-Edwards model. Finally, the shear-stiffening mechanism of reversibly crosslinked entangled polymer was obtained. Shear stiffening occurs at lower shear frequencies, which is mainly due to crosslinking bonds and friction between molecules hindering the movement of molecules. The increase in storage modulus at high frequencies is attributed to the resistance caused by entanglement in the stretching process of molecular chains. In addition, the molecular weight is greater and the degree of shear stiffening is higher. Such a conclusion is useful to further study the application of shear stiffening. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48421.     

The effect of layered silicates on the crosslinking reaction of silanol‐terminated polysiloxane

The effect of incorporation of clay nanoparticles on the vulcanization reaction of silanol‐terminated polysiloxane was studied. Three different types of commercial clays were investigated as reinforcement, namely: Cloisite 20 A (organically modified with nonpolar aliphatic chains), Cloisite 30B (modified with aliphatic chains containing hydroxyl‐end groups) and Nanofil 116, an unmodified montmorillonite as a reference. Nanoclays were found to increase the rate of curing, assessed by viscosity measurements, in all the examined systems and the acceleration rate is proportional to the content of the additive. Moreover, an increase of the area of peaks corresponding to the formation of Si? O? Si bonds (900–1200 cm^?1) was recorded by FTIR spectroscopy for pure and reinforced poly(dimethylsiloxane) (PDMS). Temperature modulated differential scanning calorimetry was also used for accurately monitoring the curing reaction of organoclay/PDMS hybrids, through the heat capacity and the enthalpy of cold crystallization measurements. For pure PDMS low reaction rate was observed during the first 200 min, followed by fast acceleration. A linear increase of the reaction rate as a function of time was observed for the organoclay/PDMS hybrids. POLYM. ENG. SCI., 55:957–965, 2015. © 2014 Society of Plastics Engineers     

Synthesis of polydimethylsiloxane‐block‐polystyrene‐block‐polydimethylsiloxane via polysiloxane‐based macroinitiator in supercritical CO2

Polydimethylsiloxane‐block‐polystyrene‐block‐polydimethylsiloxane (PDMS‐b‐PS‐b‐PDMS) was synthesized by the radical polymerization of styrene using a polydimethylsiloxane‐based macroazoinitiator (PDMS MAI) in supercritical CO₂. PDMS MAI was synthesized by reacting hydroxy‐terminated PDMS and 4,4′‐azobis(4‐cyanopentanoyl chloride) (ACPC) having a thermodegradable azo‐linkage at room temperature. The polymerization of styrene initiated by PDMS MAI was investigated in a batch system using supercritical CO₂ as the reaction medium. PDMS MAI was found to behave as a polyazoinitiator for radical block copolymerization of styrene, but not as a surfactant. The response surface methodology was used to design the experiments. The parameters used were pressure, temperature, PDMS MAI concentration and reaction time. These parameters were investigated at three levels (?1, 0 and 1). The dependent variable was taken as the polymerization yield of styrene. PDMS MAI and PDMS‐b‐PS‐b‐PDMS copolymers obtained were characterized by proton nuclear magnetic resonance and infrared spectroscopy. The number‐ and weight‐average molecular weights of block copolymers were determined by gel permeation chromatography. Copyright © 2004 Society of Chemical Industry     

Preparation and properties of UV-curable polydimethylsiloxane urethane acrylate

A new type of a UV-curable polyurethane acrylate resin based on hydroxyterminated polydimethylsiloxane (PDMS) soft segments with molecular weight 1800 and 2,4-toluene diisocyanate (TDI)/2-hydroxyethyl methacrylate (HEMA) hard segments were synthesized. The reactivity of 2,4-TDI with the hydroxy groups of silanol and HEMA was discussed by means of IR measurements. The characteristic absorption peaks of the —NCO groups of 2,4-TDI in the para- and ortho-position should decline with increasing the reaction time. The measurements of fundamental physical properties of this type of UV-curable materials had been widely studied in addition to the effects of using various reactive diluents and some pigments. This kind of resin with good optical, electrical insulating, and adhesive properties on various matrices, could be improved in chemical properties and reduced in viscosity while promoting the coating processability by mixing with various reactive diluents. The excellent adhesive properties on glass plates can be attributed to the similar structure between the PDMS soft segments and glass which makes the application in the coating industry possible.     

Synthesis of Polyyttriocarbosilane and its Conversion to Yttrium-Containing Ceramic

The polyyttriocarbosilane (PYCS) with various quantities of yttrium was obtained by reacting yttrium acetylacetonate (Y(AcAc)₃) with polycarbosilane (PCS). The molecular weight, softening point, and Si–H bond content of the resulting PYCS are controlled by the Y(AcAc)₃:PCS weight ratio, reaction temperature and reaction time. The main chain of the PYCS is made up of alternating carbon and silicon atoms with small amount of Si–O–Y presented in the main chain and Si–H groups at the side chain. The pyrolysis process of PYCS was investigated by TG and XRD. The results reveal that the polymer-to-ceramic transition of the PYCS occurs in three steps. The final ceramics obtained at 1,800?°C contain a large number of β-SiC crystallites and a small amount of α-SiC crystallites.     

‘Optical and FT Infrared Absorption Spectra of Soda Lime Silicate Glasses Containing nano Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and Effects of Gamma Irradiation

The optical absorption spectra of undoped soda lime silicate glass together with two glasses doped with either (1 % nano Fe₂O₃ ) or with both (1 % Nano Fe₂O₃ + 5 % cement dust) have been measured from 200 to 2400 nm before and after gamma irradiation with a dose of 8 Mrad. The undoped glass reveals strong UV absorption with two distinct peaks which are attributed trace ferric iron ions present as impurity. Upon gamma irradiation , this base glass exhibits three peaks at 240,310 and 340 nm and the resolution of an induced broad visible band centered at 530 nm. The two doped glasses show an additional small visible band at about 440 nm and followed by a very broad band centered at 1050 nm. Upon gamma irradiation, the two doped samples reveal the decrease of the intensities of the spectrum. The two additional bands are related to ferric (Fe⁺³) ions to the band at (440 nm) while and the broad band at 1050 nm is due to ferrous iron (Fe⁺²) ions. The decrease of the intensities of the UV-visible spectrum upon irradiation can be related to of capturing freed electrons during irradiation . Infrared spectra of the glasses reveal repetitive characteristic absorption bands of silicate groups including bending modes of Si–O–Si or O–Si–O, symmetric stretching , antisymmetric stretching and some other peaks due to carbonate , molecular water , SiOH vibrations . Upon gamma irradiation, the IR spectra reveal a small change in the base spectrum while the IR spectra of the two doped glasses remain unchanged. The change of the IR spectrum of the base glass is related to suggested changes in the bond angles or bond lengths of the mid band structural units. The doped glasses show resistance to gamma irradiation because the nano Fe₂O₃ can capture released electrons and positive holes.     

Synthesis and characterization of thermosetting polyacetylene-terminated silicone resins

A novel polyacetylene-terminated silicone (PTS) resins possessing low curing temperature and high heat resistance has been prepared by Grignard reaction using m-diacetylenylbenzene (DEB), 1,3,5-triacetylenylbenzene(TEB), and dichlorosilane as original materials. The reaction of the functional groups was characterized by in situ Fourier transform infrared spectrometer. The experimental results indicated that Si─H and C≡CH bonds are almost exclusively involved in the crosslinking reaction, while ─C≡C─ bonds only partially react. Further, Si─H and C≡CH bonds can participate in the curing reaction at relatively low temperatures, but ─C≡C─ bonds require higher temperature, indicating the higher activity of Si─H and C≡CH bonds than ─C≡C─ bonds. As determined by differential scanning calorimetry, PTS resins have low peak exothermic temperature at 184.5 °C, which is lower than MSP resin (~ 210 °C); in addition, rheological test showed that PTS resins have a very wide processing window from 40 to 163.3 °C, indicating that the PTS resins have excellent processability with a low curing temperature and wide processing window. What is more, TGA results of thermal-cured PTS resins revealed that T_d5 (5% weight loss temperature) of PTS-H10 reached the highest of 684.4 °C. Compared with PTS-H0 resin, there is an increase of 124.2 °C and the remarkably increased heat resistance correlated with a higher m-DEB input ratio. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48783.     

Crystallization and Enthalpy Relaxation of Physically Associating, End-Linked Polymer Networks: Telechelic Pyrene-Labeled Polydimethylsiloxane

Summary The effects of physical crosslinking or gelation and molecular weight on the crystallization behavior of polydimethylsiloxane (PDMS) are determined by thermal analysis of telechelic, pyrene-end-labeled PDMS and its precursor, telechelic, amine-end-labeled PDMS. The pyrene-end-labeled PDMS forms physical crosslinks while the amine-end-labeled PDMS does not. The presence of physical crosslinks leads to a major reduction in PDMS crystallinity achieved during a 5 °C/min quench that is a striking function of molecular weight. In going from the amine-end-labeled PDMS to the pyrene-end-labeled PDMS, a 25 kg/mol sample exhibits a reduction in PDMS crystallinity from 59% to 30% while a 4-7 kgimol sample exhibits a reduction in PDMS crystallinity by more than an order of magnitude, from 53% to 2 to 4%, with the latter value depending on the extent of physical crosslinking achieved by the pyrenyl units at the start of the cooling cycle. The PDMS melting temperature is a strong function of physical crosslinking, while the PDMS glass transition temperature is invariant with molecular weight and type of end unit. However, the extent of enthalpy relaxation or physical aging of the PDMS achieved during a brief quench is reduced in the presence of pyrenyl end units and thus physical crosslinking.     

Rheological behaviors of fumed silica/low molecular weight hydroxyl silicone oil

The structure and viscoelastic properties of fumed silica gels in low molecular weight hydroxyl silicone oil were investigated by means of steady and dynamic rheology. It is found that the fumed silica/hydroxyl silicone oil suspension exhibits shear‐thickening under steady shear and “strain‐thickening” under oscillatory shear condition. Effects of hydroxy groups on the rheological behavior of silicone oil suspension with highly dispersed hydrophilic amorphous silica were investigated by infrared, ¹H‐NMR, and rheological test. The results show that the hydroxy groups on this system play an important role on the formation of shear thickening behavior of the suspension solution. At the same particle diameter and mass fraction, the amount of hydroxy groups on this system has a strong effect on increasing the viscosity of the suspension, which is likely due to multiassociation hydrogen bonding between liquid molecules and silanol groups on fumed silica surfaces (Si? OH). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40722.     

环硅氧烷开环聚合反应中端羟基生成模型

微量水条件下进行环硅氧烷阴离子开环聚合，一步制备羟基聚硅氧烷.在此基础上，对端羟基的生成机理及催化剂在聚合过程中的转化关系进行分析，建立了聚合过程中端羟基生成的动力学模型.运用该模型和实验数据，可以估算链转移速率常数，并得到链转移速率常数与温度关系的阿累尼乌斯方程，求得活化能为116 kJ&#8226;mol^-1.模型可用来预测端羟基生成的动力学行为.     

Synthesis, characterization and properties of chitosan modified with poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers

Synthesis of poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers is discussed herein. Siloxane prepolymer was first prepared via acid-catalyzed ring-opening polymerization of octamethylcyclotetrasiloxane (D₄) to form polydimethylsiloxane (PDMS) prepolymers. It was subsequently functionalized with hydroxy functional groups at both terminals. The hydroxy-terminated PDMS can readily react with acid-terminated poly(ethylene glycol) (PEG diacid) to give PEG-PDMS block copolymers without using any solvent. The PEG diacid was prepared from hydroxy-terminated PEG through the ring-opening reaction of succinic anhydride. Their chemical structures and molecular weights were characterized using ¹H NMR, FTIR and GPC, and thermal properties were determined by DSC. The PEG-PDMS copolymer was incorporated into chitosan in order that PDMS provided surface modification and PEG provided good water swelling properties to chitosan. Critical surface energy and swelling behavior of the modified chitosan as a function of the copolymer compositions and contents were investigated.     

Effect of alloying element on microstructure,mechanical property,and oxidation resistance of Zr─Me─C (Me═Si/Y) coatings

Accident-tolerant fuels (ATFs) are proposed to provide improved safety response to a loss of coolant accident (LOCA) scenario while maintaining good operational characteristics under normal conditions. In this work, Zr─Me─C (Me═Si or Y) was proposed as candidate coatings for ATF applications. The influence of Si and Y with varied concentration on microstructural evolution, mechanical property, and oxidation resistance of Zr─Me─C coatings were investigated. Based on combined results of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy, it was found that Si or Y doped ZrC_0.55 coatings presented tunable composition and microstructure. Improved air oxidation and spallation resistance were achieved with the incorporation of Me atoms, attributing to the formation of SiO₂ and ZrSiO₄ and/or the stabilization of zirconia. Under a simulated LOCA condition, decreased weight gains of 13.6 at.% Si and 22.5 at.% Y coated Zry-4 alloys were achieved. nc-ZrSiC/nc-ZrSi (13.6 at.% Si) coating exhibited enhanced mechanical property and oxidation resistance in both high-temperature air and LOCA conditions, which could be regarded as potential candidate for the applications in ATFs.     

Influence of Temperature on the Properties of Polycarbosilane

A polycarbosilane precursor of SiC fiber was synthesized at high temperature under high pressure from liquid polysilane (LPS), which was obtained by thermal decomposition of poly(dimethylsilane). The effect of reaction temperature on the Si–H bond content, degree of linearity, Si–Si bond content, molecular weight, molecular weight distribution, elemental composition, softening point, and yield of the polycarbosilane (PCS) was studied spectroscopically (FTIR, UV, ¹H-NMR, and ²⁹Si-NMR) and by gel permeation chromatography (GPC). The results showed that the molecular weight, yield and softening point of the PCS increased, the molecular weight distribution broadened, and the Si–Si bond content and degree of linearity decreased when the reaction temperature increased. The Si–H bond content increased when the thermolysis reaction temperature was less than 450°C and decreased when the temperature was over 460°C. Increasing of the reaction temperature affected the composition with a general decrease in the amount of carbon, hydrogen and oxygen in the product. A middle molecular weight region of PCS in the GPC appears when the reaction temperature approaches 450°C; and, the as-synthesized PCS was stable with low Si–Si bond content. Synthetically, the conversion process is initially the formation of PCS by thermal decomposition of LPS, which is followed by an increase in molecular weight via condensation of PCS molecules.     

醇溶剂提取松木木质素及其结构表征

为进一步理解有机溶剂对木质素的提取率以及结构的影响,系统地研究了6种有机醇溶剂(甲醇、乙醇、正丙醇、乙二醇、1,3-丙二醇和1,4-丁二醇)在提取过程中溶剂极性等特性对木质素收率的影响;同时采用SEM(扫描电镜)、GPC(凝胶渗透色谱仪)、NMR等方法进一步探讨了不同醇溶剂对木质素形貌、分子量与官能团等的影响。结果表明,在所研究的6种有机醇溶剂中,极性、碳链长度与羟基数目对木质素收率、形貌、分子量、官能团等具有显著的影响;羟基数相同时,碳链越长、极性越弱,木质素的收率越高,重均分子量相对越大;一元醇溶剂体系提取的木质素中C、H元素的含量随着碳链长度的增长而降低,而二元醇体系中提取的木质素中C、H元素的含量呈相反的变化趋势;同等碳数的有机醇溶剂随羟基数增多,木质素的收率降低,重均分子量也相应减小。