Methanol chain transfer agent

Polymerizations were carried out in a jacketed, 1-gal, stirred, pressure tank reactor. Typical reactions were run by adding water, alcohol, or chain transfer agent, phosphate buffer, and persulfate to the reactor. The reactor was pressurized with CTFE monomer. Sulfite solution was fed at a rate to maintain reaction. Copper and iron ions were used at times as catalysts by adding cupric sulfate or ferrous sulfate.3 The product was filtered, washed with 90 10 water methanol followed with deionized water. The product was dried at 110°C. 

For entries 3-5 the increase in molecular weight observed can be assigned to the increase in the rate of insertion and the rate of termination remains practically the same. An increase of the rate of polymerisation with the steric bulk of the ligand is usually ascribed to the destabilisation of the alkene adduct while the energy of the transition state remains the same. As a chain transfer reaction presumably P-hydride elimination takes place or traces of water might be chain transfer agents. Chain transfer does occur, because a Schulz-Flory molecular weight distribution is found (PDI 2, see Table 12.2). Shorter chains are obtained with a polar ortho substituent (OMe, entry 2) and in methanol as the solvent, albeit that most palladium is inactive in the latter case. 

Further, it turned out to introduce a step of pre-polymerization. In this step the catalyst described just above is used. For the main polymerization, triethylaluminum and trimethylmethoxysilane are added. Hydrogen is used as the chain transfer agent and methanol is added after an appropriate time to stop the polymerization. 

Copolymers are produced by aqueous copolymerization of the monomers in a manner similar to the homopolymerizations. Nonaqueous polymerizations of TFE with PPVE may be conducted in water or in fluorinated solvents at lower temperatures (30-60 °C) using a soluble organic initiator such as perfluoro-propionyl peroxide. The molecular weight is controlled by addition of chain transfer agents such as methanol in nonaqeuous polymerizations or hydrogen in aqeous polymerizations. 

Induction periods of various lengths have been reported for anionic and cationic polymerizations of formaldehyde. It is apparent that the compound that is added as initiator is rarely the actual initiator. Tetraalkyl ammonium acetate used for the potymerization of formaldehyde is a slow initiator but capable of initiating formaldehyde polymerization. Methanol, other alcohols or water, always present in the polymerization mixture, are responsible for the high rates of polymerization. They act as efficient chain transfer agents and alkoxide or hydroxide ions are the actual initiators they initiate by a factor of several powers of ten more efficiently than acetate. 

Commercially, PFA is polymerized by free-radical polymerization mechanism usually in an aqueous media via addition polymerization of TFE and perfluoropropyl vinyl ether. The initiator for the polymerization is usually water-soluble peroxide, such as ammonium persulfate. Chain transfer agents such methanol, acetone and others are used to control the molecular weight of the resin. Generally, the polymerization regime resembles that used to produce PTFE by emulsion polymerization. Polymerization temperature and pressure usually range from 15 to 95°C and 0.5 to 3.5 MPa. 

Poly(methacrylic acid) and poly(acrylic acid) (PAA) were prepared by AIBN initiated polymerization of the freshly distilled monomer in deoxygenated methyl ethyl ketone at 60°C. The incorporation of 9,10-dimethylanthracene (9,10-DMA) end-groups in the polymer was achieved by the addition of the chain transfer agent (1% by weight) to the polymerization mixture. Unreacted 9,10-DMA was separated from the polymer by gel permeation chromatography using a column packed with Sephadex LH-20 and methanol as the eluent. Analysis of the PMA sample by NMR indicates that the polymer produced under these conditions consists of 57% syndiotactic, 33% heterotactic and 10% isotactic triads (15). Solution concentrations were 0.02 M in repeating units of the polymer. 

Although these materials were not soluble, they were easily compression moldable at temperatures around 200°C and all yielded clear, transparent films. However, when a small amount of an organic soluble chain transfer agent (1-dodecanethiol) was used, it was possible to obtain ionomers which were soluble in solvents such as tetrahydrofuran, chloroform and toluene/methanol. 

The polymerization of vinyl acetate in various alcohols has been suggested by many workers. Certainly when methanol is used as a solvent, the solvent concentration has a profound influence on the molecular weight of the polymer [67,99,103]. This effect has been attributed to the formation of acetaldehyde, a well-known chain-transfer agent, by a transesterification reaction involving the monomer [103] ... 

According to another patent, heating 100 parts of diallyl o-phthalate with 2 parts of methanol, 2 parts of carbon tetrachloride, and 0.4 parts of dibenzoyl peroxide for 3.5 hr at 1 lO C results in the isolation of 27 gm of a prepolymer by precipitation with an excess of methanol [105]. After heating 30 gm of the monomer with 10 gm of hexachloroethane for 18 hr with 0.3 gm of dibenzoyl peroxide at 80 C, 12.3 gm of a prepolymer is isolated which could readily be molded. This process affords a greater than 30% yield of prepolymer [106]. Evidently by using a rather large quantity of chain-transfer agent, substantial... 

Among the chain-transfer agents evaluated, are methanol, isopropanol, and 1,3-dioxolane. Of these, methanol has the most modest effect on the molecular weight of the product. A medium containing 30% methanol affords a polymer with an intrinsic viscosity of 1.3dl/gm whereas the product produced in a methanol-free reaction medium has an intrinsic viscosity of 4.5 dl/gm. Isopropanol and 1,3-dioxoIane had much more profound effects on the molecular weight. For example, only 5% of isopropanol in the medium produces a polymer with an inherent viscosity of approximately 0.8, whereas 5% of 1,3-dioxolane in the medium gives a product with an intrinsic viscosity of approximately 0.25 dl/gm. 

Of some interest is the fact that many solvents act as chain transfer agents and are used to control the molar mass of the product. Also Kalb et al. [456] mentioned the possibility of adding telogens (chain-terminating agents) to reduce the intrinsic viscosity of the product. Fie studied the effect using methanol or other alcohols. Polymerization with solvents such as toluene [452] and benzene [456] yielded a low-molar-mass polymer, and the conversion did not increase over 17% even when the pressure was raised to 9 x 10 Pa. 

Table 5.3 summarizes the results of variations of polymerization recipes and reaction conditions and their effects on melt viscosity, flex life, and end groups (measured by infrared spectroscopy). The strong effect of methanol on reducing the melt viscosity (i.e., molecular weight) can be observed from cases 3 and 5. Reaction time and pressure drive up molecular weight as reflected by the increase in melt viscosity. An increase in peroxide initiator lowers the molecular weight, thus lowering the melt viscosity. A comparison of the effectiveness of methanol and cyclohexane as chain transfer agents can be seen in Table 5.4. A small amount of either compound brings forth a drastic reduction in melt viscosity.

The initiator type and the presence/absence of a surfactant determine the phase in which polymerization takes place when a mixture of aqueous and solvent mediums is present. For example, ammonium persulfate (initiator) is water-soluble, therefore indicating that polymerization occurs in the aqueous phase in Table 5.7 systems. In another example l tetrafluo-roethylene and perfluoroethylvinyl ether were polymerized by suspension-polymerization without a surfactant. The reaction medium consisted of water and perfluoro-(2-butyltetrahydrofuran) and the chain transfer agent was methanol. The initiator was a bis-pefluorobutyryl peroxide as a solution in 1,1,2-trichloro-1,2,2-trifluoroethane (F-113) which caused the polymerization to take place in the organic phase of the medium. 

A terpolymer of tetrafluoroethylene, hexafluoro-propylene, and perfluoropropylvinyl ether was re-ported " ] to have superior stress crack resistance than TFE/HFP copolymer. The terpolymer in this development was prepared by the nonaqueous polymerization process described in US Patent numbers 3,528,954 and 4,029,868.In this procedure a halogenated solvent, in which perfluoropropylvinyl ether and a chain transfer agent had been dissolved, acted as the polymerization medium. Methanol was a common example of an effective chain transfer agent. Polymerization was carried out in a stainless steel pressure vessel. The polymer contained 0.2-2% perfluoropropylvinyl ether and 9-17% hexafluoropropylene. 

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