Ring-opening Polymerization Of Octamethylcyclotetrasiloxane Research Articles

Synthesis and characterization of β-cyclodextrin centered polysiloxane star polymers

In this study, a macroinitiator of β-CD-ONa was prepared by a substitution reaction of β-cyclodextrin (β-CD) with sodium (Na). The macroinitiator was then used in the ring-opening polymerization of octamethylcyclotetrasiloxane (D4) to obtain a star polymer, in which β-CD is the core and polysiloxane is the arm. FTIR, NMR, TGA, CA, etc., were used to characterize the structure and properties of star polymers. The results indicated that there were four polysiloxane arms attached to each β-CD core, and the star polymer had good thermal stability. With the increase in D4 monomer dosage, the hydrophobicity of the star polymer slightly improved, but the reaction time had no significant effect on hydrophobicity. When the star polymer was coated onto polyethylene terephthalate membrane, the transmittance increased from 87.6% to 92.8%, and the haze did not change significantly. Furthermore, the surface of star polymer porous membranes was prepared by the static breath-figure method using n-hexane as solvent at 30 °C. The results showed uniform pore distribution and increased hydrophobicity.

Ring-opening polymerization of octamethylcyclotetrasiloxane using 3d metal trifluoroacetate complexes

3d-Metal trifluoroacetate complex-catalyzed ring opening polymerization of octamethylcyclotetrasiloxane affords polydimethylsiloxanes whose molecular weight can be controlled by the nature of 3d metal complexes, in particular, by their structural type, and by the polymerization conditions. The best results were achieved using tetranuclear zinc oxotrifluoroacetate as the catalyst at a temperature of 75 °C and a reaction time of 35 h.

Cationic ring opening polymerization of octamethylcyclotetrasiloxane initiated by solid superacid

Kinetics of the cationic ring opening polymerization of octamethylcyclotetrasiloxane (D4) in bulk initiated by solid superacid was studied. The optimalizing experimental conditions were based on preliminary experiments. Higher temperature was beneficial to equilibrium conversion while stirring intensity beyond a certain level displayed no obvious effect on the rate of the reaction. A kinetic model was elicited and kinetic parameters were obtained through optimization. The calculated activation energies were 32.6 and 34.1 kJ mol–1 for D4 and all other annuluses (Dx), respectively.

A convenient method for preparation of hydroxyl silicone oils with ring opening polymerization of octamethylcyclotetrasiloxane (D4)

GRAPHICAL ABSTRACT

Controlled nanoclustering of magnetic nanoparticles using telechelic polysiloxane and disiloxane

Diacrylate-terminated polydimethylsiloxane (PDMS) and disiloxane were synthesized and used for controlling degree of nanoclustering of magnetite nanoparticles (MNPs). PDMS was synthesized via a ring-opening polymerization of octamethylcyclotetrasiloxane (D4), followed by end functionalization with diacrylate groups. Diacrylate-terminated disiloxane was separately synthesized in a similar fashion without the use of D4 in the reaction. They were then reacted with amino-coated MNPs to obtain MNP-embedded siloxane nanoclusters. Transmission electron microscopy showed the formation of MNP-siloxane nanoclusters with the size of 70–200 nm. Degree of MNP nanoclustering can be adjusted by varying the MNP-to-siloxane ratio to obtain hydrodynamic size ranging from 200 to 2400 nm. Using the same ratio of MNPs to the siloxanes, PDMS resulted in the nanoclusters with smaller D h and more stable in toluene than those coated with disiloxane. These novel nanoclusters with controllable size might be ideal candidates for biomedical and other advanced applications after suitable surface modification.

Synthesis Optimization of Novel Cross-Linked Polysiloxane with End-capped Epoxy Groups as Waterproofing Agent for Fabric

Novel cross-linked polysiloxane with end-capped epoxy groups as waterproofing agent for fabric was synthesized by hydrosilylation of polymethylhydrosiloxane and an epoxy groups-terminated polyvinylmethylsiloxane, which was previously prepared via anionic ring-opening polymerization of octamethylcyclotetrasiloxane, 2, 4, 6, 8-Tetramethyl-2, 4, 6, 8-tetravinylcyclotetrasiloxane, and epoxy group-terminated polydimethylsiloxane using tetramethylammonium hydroxide as a catalyst. Synthesis parameters were discussed in detail. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectra confirmed structure of the resultants. X-ray photoelectron spectroscopy analysis further verifies that the cross-linked polysiloxane film was indeed covered on cotton surface. Thermal stability of those polymers was improved with augment of the cross-linking degree.

Synthesis of an adhesion-enhancing polyhydrosiloxane containing acrylate groups and its cross-linked addition-cure silicone encapsulant

A novel adhesion-enhancing polyhydrosiloxane containing acrylate groups (MPMS-PHMS) was prepared via the hydrolysis of 3-methacryloyloxypropylmethyldimethoxysilane and the ring-opening polymerization of octamethylcyclotetrasiloxane and tetramethylcyclotetrasiloxane, and was used as cross-linker for addition-cure silicone encapsulant (ASE) with a large amount of alumina as thermally conductive fillers. The chemical structure of MPMS-PHMS was characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, silicon nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The effect of MPMS-PHMS on the properties of ASE was investigated. The results indicated that when using MPMS-PHMS as cross-linker, the cross-linking density of ASE was much higher than that of ASE using commercial poly(hydromethylsiloxane) cross-linker. It was also found that MPMS-PHMS not only markedly improved the adhesion strength of ASE to aluminum substrate but also significantly enhanced the mechanical properties of ASE. Appropriately increasing cure temperature and prolonging cure time were favorable to improve the adhesion strength of ASE. The optimal content of MPMS-PHMS was 10 phr, and the suitable cure temperature and time were approximately between 130 and 150°C and 2 h, respectively.

Synthesis of vinyl end‐capped polydimethylsiloxane by ring opening polymerization of octamethylcyclotetrasiloxane (D4) catalyzed by rare earth solid super acid SO42‐/TiO2/Ln3+

AbstractRare earth solid super acids SO42−/TiO2/Ln3+ have been successfully developed to synthesize vinyl end‐capped polydimethylsiloxane by ring opening polymerization of octamethylcyclotetrasiloxane (D4) end‐capped with 1,1,3,3‐tetramethyl‐1,3‐divinyldisiloxane. The features of ring opening polymerization reactions have been investigated in detail. The preferable conditions for the ring opening polymerization of D4 are as follows: [Nd3+] = 0.07 mol L−1 and [SO42−] = 1.85 mol L−1 in the immersing solution; the amount of SO42−/TiO2/Nd3+ calcined at 500 °C was 5 wt% of the amount of D4; polymerization at 80 °C for 1 h. The average molecular weights of the products obtained using various rare earth catalysts were in order Nd > La > Sm > Gd, which shows that the light rare earths were more favorable for higher molecular weight products than the heavy ones. According to the polymerization features, a cationic equilibrium reaction mechanism is proposed. © 2013 Society of Chemical Industry

Necklace-shaped Dimethylsiloxane Polymers Bearing a Polyhedral Oligomeric Silsesquioxane Cage Prepared by Polycondensation and Ring-opening Polymerization

Abstract A series of necklace-shaped dimethylsiloxane (DMS) polymers bearing a polyhedral oligomeric silsesquioxane (POSS) cage were synthesized from bifunctional POSS by two different synthetic routes. One-step or two-step polycondensation between POSS and dimethyloligosiloxane dichloride led to necklace polymers with constant chain lengths (n = 2–8). The ring-opening polymerization of octamethylcyclotetrasiloxane (D4) with POSS was also found to provide similar necklace-shaped polymers with dispersed chain lengths of DMS. The thermal properties, decomposition temperature (Td5%), and glass-transition temperatures (Tg) of the polymers were strongly dependent on DMS chain length. The polymers with dispersed chain lengths gave higher Tg’s than the polymers with corresponding constant chain lengths. The highest Td5% reached 478 °C.

Novel in situ carbon nanofiber/polydimethylsiloxane nanocomposites: Synthesis, morphology, and physico‐mechanical properties

AbstractA series of carbon nanofiber (CNF)/polydimethylsiloxane (PDMS)‐based nanocomposites was prepared by anionic ring opening polymerization of octamethylcyclotetrasiloxane (D4) in presence of pristine CNF and amine‐modified CNF. A detailed study of morphology–property relationship of the nanocomposites was carried out in order to understand the effect of chemical modification and loading of filler on property enhancement of the nanocomposites. An elaborate comparison of structure and properties was carried out for the nanocomposites prepared by in situ and conventional ex situ methods. Pronounced improvement in degree of dispersion of the fillers in the matrix on amine modification of CNFs was reflected in mechanical properties of the modified nanocomposites. Maximum upliftment in mechanical properties was observed for in situ prepared amine modified CNF/hydroxyl PDMS nanocomposites. For 8 phr filler loading, tensile strength increased by 370%, while tensile modulus showed an increase of 515% compared with the virgin elastomer. Furthermore, in situ prepared unmodified CNF/hydroxyl PDMS nanocomposites showed an increase of 141°C in temperature of maximum degradation (Tmax) for 8 phr CNF loading. These results were correlated with the morphological analysis through transmission electron microscopic studies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis and Characterization of Highly Cross-Link Polysiloxane Based on 2,4,6,8- Tetramethyl-2,4,6,8- Tetravinylcyclotetrasiloxane

A series of hydrosilyl-terminated polydimethyl-siloxane (HTP) of different molecular weight was cross-linked with 2,4,6,8-tetramethyl-2,4,6,8-tetravinyl-cyclotetra siloxane (D4V) to afford a three dimension cross-link network. They were systematically synthesised through acid-catalyzed ring opening polymerization of octamethyl-cyclotetrasiloxane (D4) followed by hydrosilylation reaction using Platinum complex catalyst. Chemical structure of HTP was characterized using FTIR and H-NMR. Mechanical properties were established using Shore A hardness which were closely related to the cross-link density.

Anionic ring-opening polymerization of octamethylcyclotetrasiloxane in emulsion above critical micelle concentration

Batch anionic ring-opening polymerization of octamethylcyclotetrasiloxane in emulsion using nonionic and cationic emulsifiers was studied. The concentration of emulsifiers was set above their critical micelle concentration. Effects of emulsifier concentration, nonionic/cationic emulsifier ratio and cationic emulsifier/initiator (KOH) ratio on the kinetics, average particle size and distribution and on the average molecular weight and distribution were investigated and discussed. At the beginning of the polymerization, empty micelles, active micelles (polymer particles) and monomer droplets co-exist in emulsion. The transport of monomer from monomer droplets toward empty micelles was confirmed by monomer droplets and empty micelles disappearance and by formation of smaller particles. The transport of monomer from monomer droplets toward polymer particles was not confirmed, since the average polymer particle size did not increase during polymerization. It was proposed, that at lower conversions, monomer diffuses from polymer particle interior to particle surface, while at higher conversions, the monomer diffuses from larger to smaller polymer particles. Emulsifier concentration, nonionic/cationic emulsifier ratio and cationic emulsifier/KOH ratio have an evident effect on the kinetics and on the average molecular weight, thus demonstrating that cationic emulsifier participates to the initiation reaction.

Nucleation loci in the ring-opening polymerization of octamethyl- cyclo-tetrasiloxane in Winsor I system with dodecylbenzene sulfonic acid sodium salt and sulfuric acid

AbstractThe ring-opening polymerization of octamethylcyclotetrasiloxane (OTS) was carried out in an Winsor I system with dodecylbenzene sulfonic acid, sodium salt (DBSNa) as emulsifier and sulfuric acid as initiator, to clarify the mechanism of the polymerization, especially focusing on the nucleation loci, the rate of generation of nonvolatile molecules and the average diameter of generated polymer droplets. In the system where DBSNa concentration is higher than the critical micellar concentration (CMC), nonvolatile molecules were generated in the aqueous phase and their generation rate became higher with an increase in DBSNa concentration, while nonvolatile molecules were not generated at emulsifier concentrations lower than the CMC. These experimental results support that nucleation did not take place in the true aqueous phase, but originated from the micelles.

Novel in situ polydimethylsiloxane-sepiolite nanocomposites: Structure-property relationship

A series of novel in situ polydimethylsiloxane (PDMS)-sepiolite nanocomposites were synthesized by anionic ring opening polymerization of octamethylcyclotetrasiloxane. These nanocomposites were characterized by Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy, Wide Angle X-Ray Diffraction (WAXD), Transmission Electron Microscopy (TEM), mechanical and dynamic mechanical properties and thermogravimetry. This paper highlights the structure-property relationship of in situ PDMS-sepiolite nanocomposites and a way to improve the mechanical, dynamic mechanical and thermal properties of silicone rubber. Comparison of these physico-mechanical properties with those of the ex situ nanocomposites reflects greater degree of filler dispersion for the in situ nanocomposites. Increasing amount of the filler reduced the size of the crystalline domains in PDMS matrix, which was evident from the X-Ray and the dynamic mechanical analysis. However, the polymer-filler interaction was even more prominent to negate the effect of the deterioration of the properties due to decrease in size of the microcrystallites. The polymer-filler interaction was reflected in the improved mechanical and thermal properties which were the consequences of proper dispersion of the filler in the polymer matrix. The modulus improvement of the rubber-clay nanocomposites was examined by using Guth and Halpin-Tsai model. The temperature of maximum degradation was raised by 167 °C and improvement of 210% in tensile strength and 460% in modulus at 100% elongation was observed. These results were correlated with the data obtained from WAXD and TEM studies.

Microwave-Irradiated Ring-Opening Polymerization of Octamethylcyclotetrasiloxane in the Presence of Water

α, ω-dihydroxyl polydimethylsiloxane (DHPDMS) was prepared via anionic ring-opening polymerization of octamethyl cyclotetrasiloxane (D4) under microwave irradiation (MI) in the presence of water. The conversion and polymerization rate were calculated by the gravimetric method. The effect of microwave power on the polymerization was investigated. FTIR was used to verify the DHPDMS prepared at different irradiation times. The results show that the conversion is the highest when the initial microwave power is preset at 700 W. Compared with conventional heating (CH), the polymerization rate and equilibrium conversion are both enhanced by the introduction of microwave irradiation. The species and concentration of the cyclosiloxane mixture caused by backbiting reaction were determined by gas chromatography/mass spectrometry (GC/MS). The lower concentration of cyclosiloxane in the polymer prepared under MI indicates that side reactions have been reduced and a pure polymer obtained. The molecular weight and polydispersity index (PDI) measured by GPC show that under MI, the molecular weight of DHPDMS is lower and PDI is narrower than those under CH.

Cationic Ring Opening Polymerization of Octamethylcyclotetrasiloxane Initiated by Acid Treated Bentonite

Cationic ring opening polymerization of octamethylcyclotetrasiloxane (D 4) initiated by acid treated bentonite was investigated. The experimental conditions were chosen on the basis of preliminary experiments. Higher temperature was found beneficial for the reaction process while stirring intensity beyond a certain level showed no obvious effect on the reaction rate. Polymers were characterized by Fourier transform infrared, proton nuclear magnetic resonance ( 1H-NMR) and gel permeation chromotography. The width of molecular mass distribution was found ranging between 1.2 and 1.4, which is extraordinarily narrow compared with that of cationic polymerizations reported elsewhere (>1.9). The results were believed due to the absence of free proton and counter ion which simplifies the polymerization process and the huge steric hindrance provided by bentonite particles which keeps the propagation of polysiloxane onto the surface of bentonite particles in a much more regular way. A feasible mechanism is proposed and seems to be supported well by experiments. Additionally, from the results of α, ω-dihydrogen terminated polysiloxanes prepared, the possibility of applying this potential environmentally friendly heterogeneous catalyst in industrial polymerization of cyclosiloxanes is anticipated.

Surface and mechanical properties of microporous membranes of poly(ethylene glycol)–polydimethylsiloxane copolymer/chitosan

Poly(ethylene glycol)–polydimethylsiloxane (PEG–PDMS) block copolymers were prepared via a condensation reaction between PEG diacid and PDMS diol. PEG diacid was synthesized from the reaction between hydroxy-terminated PEG and succinic anhydride. PDMS diol was prepared from the ring-opening polymerization of octamethylcyclotetrasiloxane (D 4) followed by hydrosilylation with allyl alcohol. The copolymers were incorporated into chitosan in order that good water swellability and wettability of chitosan were retained due to hydrophilic PEG blocks, whereas PDMS block in the copolymers functioned as a toughening modifier. Percent crosslinking of 66–84 was observed once 5–10 wt% of the copolymers was incorporated. As compared to the unmodified sample, the copolymer-containing chitosan exhibited the decreases in both water contact angles and the rate of water vapor permeability. The studies on tensile properties indicated that incorporation of copolymers into chitosan improved the flexibility of the films.

Preparation and properties of polydimethylsiloxane-modified chitosan

Preparation and properties of polydimethylsiloxane (PDMS)-modified chitosan are discussed herein. A series of PDMS with systematically varied molecular weights were first prepared via acid-catalyzed ring opening polymerization of octamethylcyclotetrasiloxane (D 4) to obtain PDMS prepolymers. They were subsequently functionalized with allyl glycidyl ether to obtain epoxy functional groups at PDMS terminals. Their chemical structures and molecular weights were characterized using 1H NMR, 13C NMR and FTIR, and thermal properties were determined by DSC. The reaction of the epoxidized PDMS and chitosan was carried out in an acidic aqueous solution. Increasing the molecular weights of PDMS and/or its concentrations improved flexibility and water swellability due to the formation of PDMS microphase. Water contact angle and water vapor permeability measurements indicated that incorporation of the PDMS enhanced its hydrophobicity as compared to the unmodified one.

Modification of epoxy–novolac resins with polysiloxane containing nitrile functional groups: synthesis and characterization

Synthesis of the statistical epoxidized polycyanopropylmethylsiloxane-co-polydimethylsiloxanes (PCPMS-co-PDMS) has been demonstrated. The modified polysiloxanes were prepared via a two-step method; (1) the ring-opening polymerization of octamethylcyclotetrasiloxane (D 4) and tetramethylcyclotetrasiloxane (D 4H), (2) hydrosilylation reaction of the polysiloxane prepolymers with allyl cyanide and allyl glycidyl ether. Molar ratios of D 4H and D 4 were varied to produce the modified polysiloxanes with differences in polarity. 1H-NMR, 29Si-NMR, 13C-NMR and FTIR were used to monitor the formation of the modified polysiloxanes and DSC was used to study their thermal behaviors ( T g, −118 to −68 °C). The use of the modified polysiloxanes as an elastomeric component in epoxy–novolac networks was also investigated. TEM and their transition temperatures suggested that the epoxy–novolac networks with high content of PDMS modifiers exhibited microphase separation. The fracture toughness properties of the networks with the polysiloxane modifiers were improved over the controls without polysiloxanes.

Kinetics of the Anionic Ring Opening Polymerization of Cyclosiloxanes Initiated with a Superbase

Kinetics of the anionic ring opening polymerization of octamethylcyclotetrasiloxane, D4, and hexamethylcyclotrisiloxane, D3, in toluene solution initiated by hexapyrrolidinediphosphazenium hydroxide, P2Pyr6+OH− were studied. Reactions are first order both in monomer and in initiator. The specific rate of the D3 polymerization is higher than that of D4 by about 2–3 orders of magnitudes. Activation energies are 18.1 kcal mol−1 for D4 and 11 kcal mol−1 for D3. The back-biting reaction leading to decamethylcyclopentasiloxane, D5, was followed in the polymerization of D4. This reaction is retarded by the presence of monomer. The kinetics is interpreted in terms of a mechanism in which the active propagation center appears mostly as a monomer separated ion pair, which is also the intermediate in the propagation step.