Dilute solution characterization of polyfluoroalkoxyphosphazenes

Results from the dilute solution characterization of polyfluoroalkoxyphosphazenes in Freon ether (E2) solutions are reported. Anomalous viscosity data suggest that polymer aggregation sometimes occurs in E2 and may be caused by the presence of relatively few anomalous polar groups on the polymer backbone. Since small amounts of acetone added to the E2 solutions inhibit aggregate formation, samples are also characterized in an E2-acetone mixed solvent. Light scattering and osmometry indicate that E2 and E2-acetone (9.09% by volume) are theta solvents for the polymers. High molecular weights (M?_w < 3 × 10⁶) and unusually broad molecular weight distributions (M?_w/M?_n < 16) are found. One polymer is fractionated by extracting solutions in 1,1,2-trichloro-1,2,2-trifluoroethane with acetone. Although the samples are highly polydisperse, intrinsic viscosities correlate with number-average molecular weights satisfying the Mark-Houwink relation with the exponent a ≈ 1/2. The z-average mean-square radius of gyration increases linearly with molecular weight so that 〈S²〉_g/M?_w ≈ 0.098. Because of the large polydispersity and unknown form of the distribution function, a quantitative interpretation of characterization results relating dilute solution parameters to polymer skeletal structure is not possible. The tentative conclusion is that the fluoroalkoxy-substituted phosphazene polymers are relatively linear and therefore that the broad distribution of molecular weights must be due to some polymerization mechanism other than branching.     

Molecular weight distribution in radiation-induced polymerization. I. γ-radiation-induced free-radical polymerization of liquid styrene

The kinetics of γ-radiation-induced free-radical polymerization of styrene were studied over the temperature range 0–50°C at radiation intensities of 9.5 × 10⁴, 3.1 × 10⁵, 4.0 × 10⁵, and 1.0 × 10⁶ rad/hr. The overall rate of polymerization was found to be proportional to the 0.44–0.49 power of radiation intensity, and the overall activation energy for the radiation-induced free-radical polymerization of styrene was 6.0–6.3 kcal/mole. Values of the kinetic constants, k_p²/k_t and k_trm/k_p, were calculated from the overall polymerization rates and the number-average molecular weights. Gelpermeation chromatography was used to determine the number-average molecular weight M?_n, the weight-average molecular weight M?_w, and the polydispersity ratio M?_w/M?_n, of the product polystyrene. The polydispersity ratios of the radiation-polymerized polystyrene were found to lie between 1.80 and 2.00. Significant differences were observed in the polydispersity ratios of chemically initiated and radiation-induced polystyrenes. The radiation chemical yield, G(styrene), was calculated to be 0.5–0.8.     

A novel group transfer polymerization of 1-trimethylsiloxy-benzocyclobutene via hetero Diels-Alder reaction

A novel group transfer polymerization via hetero-Diels-Alder reaction is described. When 1-trimethylsiloxybenzocyclobutene ( 1 ) was treated with a catalytic amount of p-anisaldehyde (4-methoxybenzaldehyde) and TASF (tris(dimethylamino)sulfonium difluorotrimethylsilanide) at room temperature for 0.5 h, poly[1,2-phenylene-1-(trimethylsiloxy)ethylene] was obtained quantitatively. The number-average molecular weight of the polymer was M̄_n = 2000 and the molecular weight distribution was narrow (ratio of weight-to number-average molecular weights M̄_w/M̄_n = 1.18). Structural characteristics suggested a polymerization mechanism involving isomerization of 1 to o-quinodimethane and successive hetero-Diels-Alder reaction leading to poly[1,2-phenylene-1-trimethylsiloxy ethylene]. The living-like nature of the polymerization was supported by a monomer addition experiment in which the molecular weight increased according to the increase of the added monomer.     

Polymerization of vinyl chloride with organolithium compounds. V. Fractionation and solution properties of high molecular weight poly(vinyl chloride)

A sample of high molecular weight poly(vinyl chloride) (PVC) was fractionated by classical precipitation fractionation and gel-permeation chromatography (GPC) on a preparative scale. The fractions thus obtained were characterized by light scattering, viscometry, and by the GPC method. The measured weight-average molecular weights M?_w, intrinsic viscosity [η], and polydispersity index M?_w/M?_n values were used for the determination of the Mark-Houwink equation, [η] = KM^a, for PVC in cyclohexanone (CHX) at 25°C valid for molecular weights from 100,000 to 625,000.     

A new method for the polymerization of methyl methacrylate

Dialkyl iodomethylmalonates in the presence of tetrabutylammonium iodide initiate the polymerization of methyl methacrylate, but not of methyl acrylate or acrylonitrile. Typically, at 60°C in 1,3-dimethyltetrahydro-2-1H-pyrimidone (DMPU) as the solvent, poly(methyl methacrylate (PMMA)) is obtained in the number-average molecular weight range of 2 000 to 8 000, the molecular weight distribution being fairly narrow (ratio of weight- to number-average molecular weights M̄_w/M̄_n 1.2–1.3).     

Cationic polymerization of p-methylstyrene initiated by acetyl perchlorate: An approach to living polymerization

The cationic polymerization of p-methylstyrene initiated by acetyl perchlorate at ?78°C led to long-lived (living-like) polymers with a narrow molecular weight distribution (M?_w/M?_n = 1.1–1.4) in methylene chloride containing a common ion salt (n-Bu₄NClO₄) or in a less polar solvent (CH₂Cl₂/toluene, 1/4v/v). Under these conditions, the number-average molecular weight (M?_n) of the polymers increased in proportion to monomer conversion and was regulated by the monomer-to-initiator ratio. When fresh feeds of the monomer were repeatedly added to a completely polymerized solution, the polymerization ensued at the same rate as before and the linear increase in M?_n with monomer conversion continued. The effects of solvent polarity and the common ion salt on the polymerization showed the suppression of the ionic dissociation of the propagating species, resulting in a “nondissociated species,” to be the key factor for the formation of the long-lived polymers.     

Living cationic polymerization of isobutyl propenyl ether as β-substituted vinyl ether

Isobutyl propenyl ether [IBPE; CH₃CH=CH? OCH₂CH(CH₃)₂] was polymerized with a mixture of hydrogen iodide and iodine (HI/I₂ initiator) in n-hexane at ?40°C to yield living polymers with a nearly monodisperse molecular weight distribution (MWD) (M?_w/M?_n ≈ 1.1). The number-average molecular weight (M?_n) of the polymers increased proportionally to IBPE conversion and further increased when a new monomer feed was added to a completely polymerized solution. The M?_n was controlled by the initial concentration of hydrogen iodide if the acid was charged in excess over iodine. In polymerization by iodine alone the M?_n of the polymers obtained in nonpolar solvents (n-hexane and toluene) also increased with conversion, but their MWD was broader (M?_w/M?_n = 1.3–1.4) than in the HI/I₂-initiated systems under similar conditions. The iodine-initiated polymerization in polar CH₂Cl₂ solvent, in contrast, led to nonliving polymers with a broad MWD (M?_n/M?_n = 1.6–1.8) and M?_n, independent of conversion. The living polymerization of IBPE was also compared with that of the corresponding isobutyl vinyl ether, to determine the effect of the β-methyl group in IBPE.     

Living cationic polymerization of 2-vinyloxyethyl phthalimide: Synthesis of poly(vinyl ether) with pendant primary amino functions

Cationic polymerization of 2-vinyloxyethyl phthalimide ( 1 ) in CH₂Cl₂ at ?15°C with hydrogen iodide/iodine (HI/I₂) as initiator led to living polymers of a narrow molecular weight distribution (M?_w/M?_n = 1.1–1.25). The number-average molecular weight of the polymers was in direct proportion to monomer conversion and could be controlled in the range of 1000–6000 by regulating the 1 /HI feed ratio. However, when a fresh monomer was supplied to the completely polymerized reaction mixture, the molecular weight of the polymers was not directly proportional to monomer conversion. The polymerization of 1 by boron trifluoride etherate (BF₃OEt₂) in CH₂Cl₂ at ?78°C gave polymers with relatively high molecular weight (M?_w > 20,000) and broad molecular weight distribution (M?_w/M?_n ～ 2). The HI/I₂-initiated polymerization of 1 was an order of magnitude slower than that of ethyl vinyl ether, probably because of the electron-withdrawing phthalimide pendant. Hydrazinolysis of the imide functions in poly( 1 ) gave a water-soluble poly(vinyl ether) ( 3 ) with aliphatic primary amino pendants.     

Living cationic polymerization of cis- and trans-ethyl propenyl ethers and synthesis of block copolymers with isobutyl vinyl ether

The cationic polymerization of cis- and trans-ethyl propenyl ethers (EPE, CH₃? CH?CH? O? C₂H₅), initiated by a mixture of hydrogen iodide and iodine (HI/I₂ initiator) at ?40°C in nonpolar media (toluene and n-hexane), led to living polymers of controlled molecular weights and a narrow molecular weight distribution (MWD) (M?_w/M?_n = 1.2–1.3). The geometrical isomerism of the monomer did not affect the living character of the polymerization. ¹³C NMR stereochemical analysis of the polymers showed that the living propagating end is sterically less crowded than nonliving counterparts generated by conventional Lewis acids (e.g., BF₃OEt₂). New block copolymers between EPE (cis or trans) and isobutyl vinyl ether were also prepared by sequential living polymerization of the two monomers.     

Viscosity–molecular weight relationship for fractionated poly(ethylene terephthalate)

Poly(ethylene terephthalate) was separated into 12 fractions of equal size by a stepwise increase in the amount of solvent in the two-phase liquid fractionation system of phenol-tetrachloroethane (PTCE) (1:1) and n-heptane. Various molecular weight parameters of the fractions were measured by osmotic pressure and gel-permeation chromatography. Intrinsic viscosity-molecular weight plots were made for three different solvents at 25°C. Mark-Houwink constants for viscosity-average molecular weight were measured and gave values of K of 2.50, 2.37, and 2.25 × 10^?4 dl/g and values of a of 0.73 for 1:1 PTCE, 3:2 PTCE, and o-chlorophenol, respectively. A comparison with the literature values for this polyester was made, and application of the Mark-Houwink equation to the determination of number-average (M _n) and weight-average (M _w) molecular weight of whole polymers is considered.     

Synthesis of polystyrene-block-polyoxyethylene for use as a stabilizer in the emulsion polymerization of styrene

Five well-defined polystyrene-block-polyoxyethylene copolymers were synthesized by anionic polymerization for use as stabilizers in the emulsion polymerization of styrene. The size of the blocks and their relative weight ratios to each other were the main variables. The molecular weights of the blocks varied from M?_n = 1000–7000 for polystyrene, and M?_w = 3000–9000 for polyoxyethylene. The results of the styrene emulsion polymerization with these block copolymers as stabilizers indicate that for efficient anchoring the block length need not be more than 10 monomer units, possibly even less, and that the polyoxyethylene block M?_w = 3000 is just as capable of stabilizing the polystyrene particle as the higher molecular weight blocks. A very important factor was found to be the weight ratio of the two blocks: block copolymers with a polyoxyethylene content between 75 and 90 wt % were effective stabilizers for the emulsion polymerization of styrene © 1992 John Wiley & Sons, Inc.     

Molecular weight analysis of pitches and polymeric pitches by gel-permeation chromatography

The technique of gel-permeation chromatography (GPC) has been developed as a method for measuring molecular weight distribution in pitch materials. Molecular weight calibration data were obtained from measurements made on GPC fractions collected from a standard pitch. By solubilization of the polymeric portion of pitch through a reduction with lithium in ethylenediamine, the molecular weight range for analysis was extended to in excess of 3000. Mass spectroscopy has been used to further analyze some of the GPC fractions. The GPC calibration data can be employed, with the aid of computer analysis, to determine quantitatively number-average molecular weights M?_n weight-average molecular weights M?_w, and molecular weight distribution D (= M?_w/M?_n) in pitch materials.     

Poly(vinyl fluoride) solution characteristics

Nine unfractionated poly(vinyl fluoride) samples were characterized for molecular weight and polydispersity by means of sedimentation velocity, osmometry, and viscosity measurements. Molecular weights were in the range of 143,000–654,000 and M _w/M _n = 2.5–5.6. The Mark-Houwink (M-H) relation was established as [η] = 6.52 × 10^?5 M^0.80. The M-H exponent is at the Flory-Fox upper limit (0.80), as is characteristic of extended, polar polymers, in good solvents. The unperturbed chain dimensions, characteristic ratio and steric factor were derived by the methods of Stockmayer and Fixman and Kurata and Stockmayer. The steric factor is 1.7, which agrees with data reported for other poly(vinyl halides).     

High-resolution gel-permeation chromatography

The resolution attainable in gel-permeation chromatography (GPC) was investigated by using columns packed with polystyrene gel particles of about 5 μ diameter and mixtures of two monodisperse poly-α-methylstyrene samples studied previously. The resolution of GPC was found comparable to that of the sedimentation velocity method and slightly better than that of precipitation chromatography. Standard polystyrene samples obtained from Pressure Chemical Co. also were measured with the same columns. It was found that weight-average to number-average molecular weight ratios (M?_w/M?_n) of these samples with molecular weight in the range 97,000–411,000 are smaller than 1.006. For samples with molecular weight of 10,000–51,000 and 498,000–860,000, M?_w/M?_n is larger than 1.006, and the width of molecular weight distributions of these samples differed. In particular, molecular weight distributions of samples with molecular weights 19,800 and 51,000 were shown to be bimodal. It is therefore concluded that GPC is useful for samples of very narrow molecular weight distribution if high-resolution columns are used.     

Anionic homopolymerization of ferrocenylmethyl methacrylate

Anionic polymerization of ferrocenylmethyl methacrylate (FMMA) was investigated using high-vacuum techniques. Initiators used included n-butyllithium, sodium naphthalide, potassium naphthalide, Grignard reagents (both C₂H₅MgBr and C₆H₅MgBr), sodium methoxide, and lithium aluminum hydride. FMMA polymerization was readily initiated by each of the above initiators with the exception of sodium methoxide. The molecular weight of poly(ferrocenylmethyl methacrylate) could be controlled by varying the monomer-to-initiator ratio when lithium aluminum hydride was used in tetrahydrofuran (THF). In this system, poly(ferrocenylmethyl methacrylate), soluble in benzene or THF, was prepared with M?_n as high as 277,000 with a relatively narrow molecular weight distribution compared to samples prepared by radical-initiated polymerization. The Mark-Houwink values of K and a, determined in THF, were K = 4.94 × 10^?2 and a = 0.53 (when M = M?_n) and K = 3.72 × 10^?2 and a = 0.51 (when M = M?_w). It is clear that the polymer is moderately coiled in THF.     

High-pressure synthesis of cyclic phenylacetylene oligomer

New conjugated oligomers were prepared by reacting phenylacetylene under high pressure of 0.11 to 0.92 GPa at 100–200°C for 0–5 h. The number-average molecular weight M?_n, the weight-average molecular weight M?_w, and the oligomer yield increased with pressure, tem-perature, and time. The average molecular weight of the oligomer showed the maximum value (M?_n: 830, M?_w: 2400) under 0.92 GPa, the maximum pressure, where phenylacetylene was oligomerized at a constant temperature. The structure of the oligomer was investigated from ESR, infrared, UV–VIS, field desorption mass (FDMS) spectra, and ¹³C NMR spec-trum. Analysis of the FDMS spectrum revealed that the molecular weight of the oligomer was multiple of the monomer. ¹³C NMR spectrum of the oligomer showed the absence of sp-carbon (? C?). We found that the oligomer had a cyclic structure. The cyclic oligomers of pentamer or more were new compounds. © 1995 John Wiley & Sons, Inc.     

Vinylic polymerization of norbornene by Pd(II)-catalysis in the presence of ethylene

Pd(II) catalysts with nitrilo ligands and BF₄⁻ counter ions give the best results in vinylic polymerization of norbornene. Absolute molecular weight determination of polynorbornene (PN) by means of light scattering and the three-dimensional shape of PN were also investigated. By correlation of molecular weights M̄_w with intrinsic viscosity (Staudinger-index) [η], yield a close to 0.5 exponent for the Mark-Houwink equation with solvents chlorobenzene and cyclohexane at 25°C expected for polymer molecules with confined conformation. The vinylic polymerization of norbornene with [(CH₃CN)₄Pd][BF₄]₂ ( I ) in nitromethane in the presence of ethylene results in PN with narrow molecular weight distribution. No termination and transfer reactions were found, nor any incorporation of ethylene could be detected.     

Association of polyacrylonitrile prepared by low-temperature,solution polymerization with an organometallic catalyst

The weight-average molecular weights of polymers of acrylonitrile prepared by a free-radical initiator and an organometallic catalyst have been determined by lightscattering measurements in N,N-dimethylformamide, dimethyl sulfoxide, and dimethylacetamide at 25°C. and in dimethyl sulfoxide at 140°C. The apparent molecular weights of the polymers prepared with the NaAlEt₃S(i-Pr) catalyst in DMF at ?78°C. (referred to as high-melting polymers) changed from 54,800, 82,700, and 480,000 when measured in DMF at 25°C. to 36,000, 41,600, and 225,000 when measured in DMSO at 140°C., whereas the molecular weights of the free-radical polymers remained unchanged. Furthermore, from results obtained in DMSO at 140°C., The intrinsic viscosity–molecular-weight relationships were found to be identical for the high-melting and the free-radical polymer and in substantial agreement with an equation reported by Cleland and Stockmayer. The apparent decrease in molecular weight of the high-melting polymer from 25 to 140°C. indicates rather clearly that the high-melting polymers are associated in DMF at 25°C. The “aggregates,” even though present only at low concentrations, raised the weight-average molecular weight markedly but affected the number-average molecular weight only slightly, thus giving a high M?_w/M?_n ratio. It appears likely that when temperature and solvent are such that association does not occur, linear PAN's will have approximately the same intrinsic viscosity–molecular weight relationship (subject of course to slight change by polydispersity). The often reported abnormal molecular weight of samples prepared by solution polymerization especially at low temperatures, may be attributed to branching, or to an association, as reported here. The nature of association of PAN in dilute solution is also discussed.     

Polymerization by oxidative coupling. IV.. Synthesis and properties of poly(2-methyl-6-phenylphenylene ether)

Copper-amine catalyst systems which polymerize 2-methyl-6-phenylphenol to high molecular weight polymer are described. With CuCl and N,N,N ′,N′-tetramethyl-1,3-butanediamine (TMBD), an intrinsic viscosity of 1.56 dl/g was obtained. Faster rates of polymerization resulted with a CuBr-TMBD catalyst. Catalysts from other tertiary amines and mixtures of tertiary amines also produced high polymer. Pyridine and diethylamine catalyst were less active. Samples of polymer were isolated at different stages of the polymerization. Measurements of viscosity, osmotic pressure, light scattering, gel permeation, hydroxyl groups, nitrogen content, and chemical reactivity were made on the samples. Below a molecular weight value of M?_n 60,000, M?_n/M?_w was 2.0. At higher molecular weights, there was a broadening in molecular weight distribution. No major change in the molar concentration of the “;head” endgroups with increasing molecular weight was detected by infrared analysis. However, nitrogen analyses, chemical reactivity studies, and the M?_n/M?_w ratio suggested the chemical nature of the “head” end had changed. The relationships between intrinsic viscosity in chloroform at 25°C and M?_n and M?_w for unfractionated polymer samples are log [η] = ?4.26 + 0.84 log M?_n and log [η] = ?3.86 + 0.70 log M?_w.     

Modelling free-radical copolymerization kinetics—evaluation of the pseudo-kinetic rate constant method, 1. Molecular weight calculations for linear copolymers

The moment equations for binary copolymerization in the context of the terminal model have been solved numerically for a batch reactor operating over a wide range of conditions. Calculated number- and weight-average molecular weights were compared with those found using pseudo-kinetic rate constants with the method of moments and with the instantaneous property method for homopolymerization. With the pseudo-kinetic rate constant method under polymerization conditions where number-average molecular weights (M̄_n) are below about 10³ the error in calculating M̄_n exceeds 5%. The error increases rapidly with decrease in molecular weight for M̄_n < 10³. M̄_n measured experimentally for polymer chains (homo- and copolymers) have error limits of greater than ±5% at the 95% confidence level. Therefore, for all practical purposes, the pseudo-kinetic rate constant method is valid for M̄_n greater than 10³. Errors in calculating weight-average molecular weights (M̄_w) or higher averages are always smaller than those for M̄_n when applying the pseudo-kinetic rate constant method. The assumptions involved in molecular weight modelling using the pseudo-kinetic rate constant approach are thus proven to be valid, and therefore it is recommended that the pseudo-kinetic rate constant method be employed with the instantaneous property method to calculate the full molecular weight distribution and averages for linear chains synthesized by multicomponent chain growth polymerization.