Studies of cyclic and linear poly(dimethyl siloxanes): 13. Static dielectric measurements and dipole moments

The static dielectric permittivities, refractive indices and densities of undiluted oligomeric cyclic and linear dimethyl siloxanes and narrow fractions of cyclic and linear poly(dimethyl siloxanes) have been measured for number-average molar masses M?_n in the range $\text{160 <}\text{M}\text{?}{}_{\mathrm{n}}\text{< 7700}$ at temperatures from 298 to 313 K. Measured total dielectric polarizations have been resolved into their electronic, atomic and orientation components and dipole moments have been derived. The dipole moments of cyclic oligomers ((CH₃)₂SiO)_x (for example, with x = 4, 5) are markedly lower than the dipole moments of the corresponding linear oligomers containing the same number of siloxane bonds. However, for x ? 10, the dipole moments of cyclic dimethyl siloxanes are identical, within experimental error, to those of the corresponding linear dimethyl siloxanes. Measured static dielectric permittivities of the dimethyl siloxanes and poly(dimethyl siloxanes) in solution in cyclohexane are markedly different from the corresponding values for the undiluted siloxanes. These differences are interpreted as resulting from the specific solvent effects.     

Studies of cyclic and linear poly(dimethyl siloxanes): 5. Diffusion behaviour in dilute solution

The diffusion coefficients of cyclic and linear oligomeric and polymeric dimethyl siloxanes, containing number-average numbers of skeletal bonds in the range $\text{6 <}\text{n}\text{?}{}_{\mathrm{n}}\text{< 650}$, have been measured in toluene solution at 298K. Impermeable diffusion behaviour was observed for all the siloxanes studied, in agreement with previous findings for ethylene oxide and hexamethylene oxide oligomers and polymers. The ratio of the friction coefficients $\text{f}{}_{\mathrm{r}}\text{f}{}_{\mathrm{l}}$ for the ring (r) and linear (l) dimethyl siloxanes was found to be $\text{8}\text{3κ}$ (within the limits of experimental error) over the whole range of molecular weights studied. Values of the expansion factor α_f for the linear poly(dimethyl siloxanes) (obtained from the diffusion measurements) were found to be approximately equal to the corresponding values for α_η (found previously by viscometric studies) for small values of the excluded volume parameter z; and α_f was larger than α_η for large z, as predicted by first-order perturbation theory. Mean-square radii of gyration 〈s²_G〉 were calculated from the diffusion data for both cyclic and linear poly(dimethyl siloxanes) assuming Gaussian statistics, and found to be in good agreement with the corresponding values obtained by neutron scattering. However, the values of 〈s²_G,l〉 for the short chain poly(dimethyl siloxanes) did not agree with the corresponding values of 〈s²_O,l〉, calculated using the rotational isomeric state model of Flory, Crescenzi and Mark. This discrepancy is thought to arise from deviations from Gaussian behaviour, and considerably better agreement between experiment and theory was achieved by using appropriate values of a function ψ_l(x), which relates radii of gyration and impermeable hydrodynamic diffusion radii.     

Studies of cyclic and linear poly(dimethyl siloxanes): 3. Neutron scattering measurements of the dimensions of ring and chain polymers

The dimensions of both cyclic and linear poly(dimethyl siloxanes) in dilute solution in benzene-d₆ have been measured by small-angle neutron scattering. The mean-square radii of gyration of the linear polymers are consistent with values predicted from published data, including experimental molar cyclization equilibrium constants. The average dimensions of the cyclic poly(dimethyl siloxanes) in fractions containing z-average numbers of bonds $\text{n}\text{?}{}_{\mathrm{z}}$ in the range $\text{130 <}\text{n}\text{?}{}_{\mathrm{z}}\text{< 550}$, were found to be considerably smaller than those of the corresponding linear polymers. The neutron scattering results give a value for the ratio of the z-average radii of gyration for linear and ring poly(dimethyl siloxanes) (containing the same number of monomer units) $\text{〈s}{}^2\text{〉}{}_{\mathrm{z,l}}\text{<s}{}^2\text{〉}{}_{\mathrm{z,r}}\text{= 1.9 ± 0.2}$. This ratio may be compared with the value of 2.0 predicted theoretically for ‘flexible’ high molecular weight linear and cyclic polymers, unperturbed by excluded volume effects.     

Studies of cyclic and linear poly(dimethyl siloxanes): 2. Preparative gel permeation chromatography

A preparative gel permeation chromatographic (g.p.c.) instrument has been constructed and used to separate broad fractions of cyclic poly(dimethyl siloxanes) into sharp fractions with heterogeneity indices $\text{M}\text{?}{}_{\mathrm{w}}\text{M}\text{?}{}_{\mathrm{n}}\text{= 1.05 ± 0.02}$. The number-average molecular weights $\text{M}\text{?}{}_{\mathrm{n}}$ of the cyclic polymer fractions obtained were as high as 50 000, corresponding to number-average numbers of skeletal bonds $\text{n}\text{?}{}_{\mathrm{n}}$ up to 1300. The concentrations of linear poly(dimethyl siloxanes) in all but the highest molecular weight cyclic polymer fractions prepared are believed to be negligible. The preparative g.p.c. instrument was also used to obtain some sharp fractions of linear poly(dimethyl siloxanes).     

Synthesis and ring‐opening polymerization of macrocyclic aromatic sulfide oligomers

A series of macrocyclic(arylene sulfide) oligomers were synthesized by reaction of 4,4′‐oxybis(benzenethiol) with a number of difluoro compounds in dimethylformamide (DMF) in the presence of anhydrous K₂CO₃ under high dilution conditions. The difluoro compound can be 4,4′‐difluorobenzophenone, bis(4‐fluorophenyl)sulfone or 1,3‐bis(4‐fluorobenzoyl)benzene. Detailed structural characterization of these oligomers by matrix‐assisted laser desorption and ionization‐time of flight‐mass spectroscopy (MALDI‐TOF‐MS) demonstrated their cyclic nature. The MALDI‐TOF‐MS technique has proved to be a powerful tool to analyze these cyclics. These cyclic oligomers are amorphous and highly soluble in DMF and N,N′‐dimethyl acetamide. Moreover, these cyclic(arylene sulfide) oligomers readily underwent ring‐opening polymerization in the melt at 285 °C in the presence of 2,2′‐dibenzothiazole disulfide, affording linear, high molecular weigh poly(aromatic sulfide)s. These polymers are insoluble in most common solvents. Copyright © 2004 Society of Chemical Industry     

Synthesis, characterization, and catalytic properties of polysiloxanes with pendant 4-(3-pyridinyl)butyl and 4-(1-oxypyridin-3-yl)butyl groups

New silane monomers with the pendant 4-(3-pyridine)butyl group have been synthesized by hydrosilation of 3-(3-butenyl)pyridine with Me _n Si(OEt)_3-n H (n=0, 1) using a platinum catalyst. Only -addition products were observed. The products were characterized by elemental analysis, infrared,¹H- and¹³C-NMR spectroscopy, and gas chromatography-mass spectrometry. Hydrolysis-polycondensation of the difunctional monomer with a basic catalyst, Me₄NOH, gave a mixture of cyclic oligomers, principally cyclic tetramer, and linear homopolymer. Under similar reaction conditions, the trifunctional monomer gave crosslinked material which was soluble in common organic solvents. The linear homopolymer and crosslinked polymer were trimethylsilyl end-blocked with hexamethyldisilazane. The cyclic and end-blocked polymers were characterized by elemental analysis and spectroscopic methods. Molecular weights of the polymers were obtained by end-group analysis using¹H-NMR spectral data, size exclusion chromatography, and direct insertion-probe mass spectrometry. The cyclic, linear, and crosslinked materials were N-oxidized withm-chloroperoxybenzoic acid and characterized by spectroscopic methods. The polymeric N-oxide derivatives were shown to be effective transacylation catalysts in the synthesis of mixed carboxylic acid anhydrides in immiscible solvents (H₂O/CH₂Cl₂) under phase-transfer conditions. The implications of the results on the mechanism of catalysis are discussed.     

Studies of cyclic and linear poly(dimethyl siloxanes): 1. Limiting viscosity number-molecular weight relationships

The limiting viscosity numbers of ten cyclic and ten linear poly(dimethyl siloxane) fractions have been measured in a π-solvent (butanone at 293K) and in two ‘good’ solvents (toluene and cyclohexane at 298K). The dimethyl siloxane fractions studied were in the molecular weight range $\text{800 <}\text{M}\text{?}{}_{\mathrm{w}}\text{< 17 000}$. The data obtained are compared with related studies published in the literature. The ratio of the limiting viscosity numbers [η]_r and [η]_l of the cyclic and linear poly(dimethyl siloxanes) with $\text{M}\text{?}{}_{\mathrm{w}}\text{> 2500}$ was found to be 0.67 in butanone at 293K. This value is identical (within experimental error) to the theoretical ratio $\text{[η]}{}_{\mathrm{r}}\text{[η]}{}_{\mathrm{l}}\text{= 0.66}$ predicted by Bloomfield and Zimm and others for ring and chain polymers in π-solvents. The ratio $\text{[η]}{}_{\mathrm{r}}\text{[η]}{}_{\mathrm{l}}$ was found to be somewhat smaller for the higher molecular weight polymers in the ‘good’ solvents.     

Studies of cyclic and linear poly(dimethyl siloxanes): 9. Quasi-elastic light scattering and concentration dependences of diffusion coefficients

The concentration dependences of the diffusion coefficients (D) of linear and cyclic poly(dimethyl siloxanes) (PDMS) in toluene at 298K are reported. Three cyclic/linear pairs of fractions with molar masses in the range 300 to 23 500 g mol^?1 were used. The values of D obtained by quasielastic scattering were in good agreement with those measured by the classical boundary-spreading technique. Analysis of the concentration dependences in terms of the theory of Pyun and Fixman indicates that the solute molecules show a minimum of interpenetration in toluene at 298K.     

Synthesis and thermoelastic characterization of PDMSM networks

Summary The synthesis of poly(dimethyl silmethylenes) with two hydroxyl endgroups is described. Networks produced by endlinking with tetraethoxysilane were characterized, and thermoelastic data were estimated. f_e/f and dln2>_o/dT of these networks are much smaller than those of poly(dimethyl siloxanes).     

The kinetics of hydrolytic polymerization of ε-caprolactam. V. Equilibrium data on cyclic oligomers

The concentrations of the cyclic oligomers (C_i; i = 3, 4, 5, and 6) in the polymeric products of ε-caprolactam were determined by high-performance liquid chromatography. The equilibrium data on the oligomers were obtained as a function of the polymerization temperature and initial water concentration. The concentration of each oligomer in the equilibrated polymer was found to increase with the temperature and/or initial water concentration. A set of the kinetic equations to express the oligomer formation during the polymerization was also proposed.     

Study on the mechanism of the formation of polyhedral oligomeric silsesquioxanes by the 2D correlation infrared spectral

Synthesis of polyhedral oligomeric silsesquioxanes (POSS) by the hydrolytic condensation reaction of trifunctional organosilanes [e.g., RSiCl₃ or RSi(OR)₃] may have achieved success. However, the exact formation mechanism of POSS, especially, an evolution process in the reaction still remains unclear. In this work, a real-time FTIR was carried out to trace the synthesis process of POSS. It was found that linear siloxanes, cyclic siloxanes, and cage-like polysiloxanes were formed during the reaction. With the help of generalized two-dimensional (2D) correlation analysis, we obtained exact sequential change among the three siolxanes, with the linear silicons formed initially. Following this was the emergence of cyclic siloxanes, and finally the cage-like polysiloxanes. Consequently, we not only proved the existence of the linear and cyclic siloxanes but also accurately detected the sequential change of the siloxanes in the process, which exhibited an intact and visual evolution process of POSS formation. Based on this, the reaction mechanism is presented. Finally, the chemical structure of cage-like products was further characterized by ²⁹Si-NMR and GPC measurements. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Role of specific interactions on fiber formation in the electrospinning of poly(vinyl phenol)/poly(vinyl pyrrolidone) blend solutions

The minimum concentration (C_i) required for electrospinning polymeric fibers from solutions of mixtures of poly(vinyl phenol) and poly(vinyl pyrrolidone) has been experimentally determined for different blend compositions. This minimum concentration C_i has its lowest value when the polymers are mixed in a 1/1 molar ratio. This article shows different results that seem to indicate that the strong hydrogen bonding interactions between the two polymers and the corresponding higher apparent molecular weight cause the reduction of the C_i value. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Microwave dielectric relaxation and molecular dynamics in binary mixtures of poly(propylene glycol) 2000 and poly(ethylene glycol)s of varying molecular weight in dilute solution

Molecular dynamics of binary mixtures of poly(propylene glycol) (PPG) and poly(ethylene glycol)s (PEGs) of varying molecular weight due to molecular interactions, chain coiling and elongation in dilute solution under various conditions, ie varying number of monomer units of PEG, method of mixing of polymers and solvent environment, has been explored using microwave dielectric relaxation times. The average relaxation time τ_o, relaxation time corresponding to segmental motion τ₁ and group rotations τ₂, of a series of binary mixtures of poly(propylene glycol) 2000 and poly(ethylene glycol) of varying molecular weight (ie PPG 2000 + PEG 200, PPG 2000 + PEG 300, PPG 2000 + PEG 400, and PPG 2000 + PEG 600 mixed by equal volume in the pure liquid states, and PPG 2000 + PEG 1500, PPG 2000 + PEG 4000 and PPG 2000 + PEG 6000 mixed equal weights in solvent) have been determined in dilute solution in benzene and carbon tetrachloride at 10.10 GHz and 35 °C. A comparison of the results of these binary systems of highly associating molecules shows that the molecular dynamics corresponding to rotation of a molecule as a whole and segmental motion in dilute solutions are governed by the solvent density when the solutes are mixed in their pure liquid state. Furthermore, the molecular motion is independent of solvent environment when the polymers are added separately in the solvent for the preparation of binary mixtures. It has also been observed that there is a systematic elongation of the dynamic network of the species formed during mixing of pure liquid polymers in lighter environment of solvent with increasing PEG monomer units, while the elongation behaviour of the same species in the heavier environment of carbon tetrachloride solvent is in contrast to the elongation behaviour of the polymeric species formed in pure PEG. The role of rotating methyl side‐groups in the PPG molecular chain has been discussed in term of the breaking and reforming of hydrogen bonds in complex polymeric species for the segmental motion. In all these mixtures, the relaxation time corresponding to group rotations is independent of the solvent environment and constituents of the binary mixtures. The effect of chain flexibility and coiling in these binary mixtures is discussed by comparing the relaxation times of the mixtures with their individual relaxation times in dilute solutions measured earlier in this laboratory. © 2001 Society of Chemical Industry     

Synthesis of copolymers from 3,5-dioxo-4,10-dioxatricyclo-[5.2.02,6]dec-8-ene and vinyl monomers by photopolymerization and their biological activities

Photocopolymerizations of 3,5-dioxo-4,10-dioxatricyclo[5.2.0^2,6]dec-8-ene (DDTD) with methacrylic acid (MA) acrylamide (AAm) and vinyl pyrrolidone (VP) were carried out in 2-butanone using dimethoxy benzoin (DMB) as an initiator at 25°C. The structures of the polymers obtained from photopolymerizations of corresponding monomer pairs were confirmed to be poly(DDTD-co-MA), poly(DDTD-co-AAm) and poly(DDTD-co-VP) by ¹H NMR and ¹³C NMR spectroscopies, and the average molecular weights were determined by gel permeation chromatography (GPC). The weight average molecular weights (M_w) of the polymers were in the range 9500–17300. The polymers were soluble in water, dimethyl sulphoxide (DMSO) and dimethyl formamide (DMF). The contents of DDTD units in the copolymers were 19, 37 and 45%. The in vitro cytotoxicities of the polymers were evaluated using mouse mammary carcinoma (FM-3A), mouse leukaemia (P-388) and human histiocytic lymphoma (U-937) cell lines. The in vivo antitumour activities of the polymers were estimated by the survival time of sarcoma 180 tumour-bearing mice. The in vivo antitumour activities of the polymers were greater than those of 5-fluorouracil (5-FU) and monomeric DDTD at a dose of 0·8mgkg^-1. Poly(DDTD-co-AAm) and poly(DDTD-co-VP) showed higher antitumour activity than 5-FU and monomeric DDTD at all doses tested. © 1998 SCI.     

A comparison of poly(ether imide)s from diamines with 2-aminophenoxy or 4-aminophenoxy units: Synthesis, characterization and properties

A series of new 3- and 4-ring bis(2-aminophenoxy) aromatic diamines were prepared. These, and corresponding, conventional bis(4-aminophenoxy) diamines were reacted with several aromatic bis(ether anhydride)s to form poly(ether imide)s. The diamines with 4-aminophenoxy groups gave high-molecular-weight polymers that were cast into films with good mechanical properties. In contrast, in almost all cases, diamines with 2-aminophenoxy groups only gave low-molecular-weight powdery products that could not be cast into coherent films. The low-molecular-weight products, prepared from stoichiometrically equal amounts of monomers, were examined by mass spectrometry and shown, in most cases, to consist primarily of cyclic oligomers; traces of linear oligomers were identified in some samples. Apart from a polyimide prepared from pyromellitic dianhydride and 4,4′-bis(2″-aminophenoxy)biphenyl, the only products found to contain significant proportions of linear oligomers were those prepared with a stoichiometric imbalance of monomers. End groups of the various linear oligomers were identified. The 2-aminophenoxy groups predispose the oligomers to cyclize as amic acids, and to remain as cyclics on imidization. In some cases [1+1] cyclic oligomers were observed although the most common species were the [2+2] cyclic dimers.     

Miscibility of oligomeric poly(dimethyl siloxanes) with long-chain unbranched alkanes: 2. Unsymmetrical cloud point curves

Previously obtained cloud point curves for mixtures of oligomeric poly(dimethyl siloxanes) (weight fraction W₁) with oligomeric polyethylenes have been supplemented by the use of samples of higher molecular weight. Initial flat regions at low-medium W₁ as well as a slight shoulder at extremely high W₁ are now considered to be due to crystallization, since the temperatures at which they occur are the melting points of the oligoethylenes. The actual cloud point curves were of an unsymmetrical dome shape, the form of which could not be simulated by using a concentration-independent interaction parameter g in the Flory-Huggins equation. However, spinodals calculated by assuming a quadratic dependence of g on composition were of the same shape as the experimental cloud point curves. The critical compositions calculated on this basis were also close to the experimental ones.     

Syntheses of cyclic poly(lactones) by zwitterionic ring opening polymerization catalyzed by N‐heterocyclic carbene

Synthesis of cyclic biopolymers from renewable monomers remains a big challenge because of lack of efficient catalysts. The organocatalyst of N‐heterocyclic carbene (NHC), (+)‐1‐methyl‐3‐menthoxymethyl imidazol‐2‐ylidene, is used to prepare cyclic polylactones including poly(ε‐caprolactone) (poly(ε‐CL)), poly(δ‐valearolactone) (poly(δ‐VL)), and poly(ε‐caprolactone‐co‐δ‐valearolactone) (poly(ε‐CL‐co‐δ‐VL)) via zwitterionic ring opening polymerization. The NHC catalyst is founded a highly efficient organic catalyst for the polymerization. The resulting cyclic polymers show a melting temperature (T_m) in a range of 20–60°C, which is dramatically lower than the T_m of cyclic poly(lactide) (T_m = 120–150°C). The resulting copolymer, cyclic poly(ε‐CL‐co‐δ‐VL) owns high molecular weight comparing with corresponding linear poly(ε‐CL‐co‐δ‐VL) produced by other catalysts. The synthesized cyclic homo and copolymers were characterized by ¹H‐, ¹³C‐NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry–thermogravimetric analysis and matrix‐assisted laser desorption ionization‐time of flight mass spectrometry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Gasification of silicone fluids under external thermal radiation. Part I. Gasification rate and global heat of gasification

Transient gasification rates and fluid temperatures were measured for polydimethylsiloxane fluids ranging in viscosity from 0.65 cS to 60 000 cS in a nitrogen atmosphere at external radiant fluxes from 20 kW/m² to 70 kW/m². A detailed energy balance for each fluid sample was conducted to determine its global heat of vaporization. Two major energy loss corrections were identified and quantified. The absorption of incident radiation by the volatile products from short chain oligomers was measured and found to substantially reduce the incident flux to the sample surface; the energy loss due to re-radiation was determined to be a substantial factor in reducing the net heat flux to the sample for long chain length fluids. Other energy losses, e.g. heat loss to the substrate, were observed but were less significant. The average gasification rate for each fluid increased linearly with increasing external radiant flux. The global heat of gasification increases with an increase in the chain length (molecular weight) for the siloxane oligomers. These agreed well with calculated values. The global heat of gasification for 50 cS fluid is about 1200 kJ/kg and its value remains nearly constant for all higher molecular weight dimethylsiloxanes. Pyrolysis rates for siloxane fluids are very sensitive to trace catalysts. Measurements of the global heat of gasification for ultra-clean polymers resulted in significantly higher values (3000 kJ/kg). The gasification of siloxanes occurs via two modes or combinations thereof: (1) volatilization of molecular species native to the polymer, and (2) volatilization of thermal degradation products. The former process dominates for low molecular weight siloxanes (η<10 cS) and the latter process dominates for high molecular weight siloxanes (η>1000 cS). For the intermediate molecular weight siloxanes, both volatilization and degradation processes occur. © 1998 John Wiley & Sons, Ltd.     

Synthesis and characterization of low‐molecular‐weight poly(2,6‐dimethyl‐1,4‐phenylene oxide) in water

Low‐molecular‐weight poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) with unimodal polydispersity was synthesized by oxidative polymerization of 2,6‐dimethylphenol in the presence of Cu‐ethylene diamine tetraacetic acid catalyst in water. A series of low‐molecular‐weight PPO oligomers with M_n ranged from 360 to 3500 were obtained. It was found that the molecular weight and polydispersity were affected by reaction time, reaction temperature, and catalyst concentration. Based on the detector response‐elution volume curve and the molecular weight from gel permeation chromatography, a possible molecular weight growth mechanism was proposed. The structure and properties of low‐molecular‐weight PPO oligomers were characterized by atomic absorption spectroscopy, differential scanning calorimetry, Ubbelohde viscometer, and nuclear magnetic resonance spectroscopy. Compared to the commercial low‐molecular‐weight PPO, PPO oligomers synthesized in water had a much lower residual copper content. The relationships between T_g and M_n at relatively low‐molecular weight are in good agreement with the equation proposed by Fox and Loshack. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Formation of microcapsules of medicines by the rapid expansion of a supercritical solution with a nonsolvent

The rapid expansion from a supercritical solution with a nonsolvent (RESS‐N) was applied to the formation of polymeric microcapsules containing medicines such as p‐acetamidophenol, acetylsalicylic acid, 1,3‐dimethylxanthine, flavone, and 3‐hydroxyflavone. A suspension of medicine in carbon dioxide (CO₂) containing a cosolvent and dissolved polymer was sprayed through a nozzle to atmospheric pressure. The pre‐expansion pressure was 10–25 MPa, and the temperature was 308–333 K. The polymers were poly(L ‐lactic acid) (molecular weight = 5000), poly(ethylene glycol) (PEG; PEG4000, molecular weight = 3000; PEG6000, molecular weight = 7500; and PEG20000, molecular weight = 20,000), poly(methyl methacrylate) (molecular weight = 15,000), ethyl cellulose (molecular weight = 5000), and PEG–poly(propylene glycol)–PEG triblock copolymer (molecular weight = 13,000). The solubilities of the polymers as coating materials and these medicines as core substance were very low in CO₂. However, the solubilities of these polymers in CO₂ significantly increased with the addition of low molecular weight alcohols as cosolvents. After RESS‐N, polymeric microcapsules were formed according to the precipitation of the polymer caused by a decrease in the solvent power of CO₂. This method offered three advantages: (1) enough of the coating polymers, which were insoluble in pure CO₂, dissolved; (2) the microparticles of the medicine were encapsulated without adhesion between the particles because a nonsolvent was used as a cosolvent and the cosolvent remaining in the mixture was removed by the gasification of CO₂; and (3) the polymer‐coating thickness was controlled with changes in the feed composition of the polymer for drug delivery. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 742–752, 2003