Polymerization in vacuum

The entropy of polymerization is negative, i.e., randomly oriented monomer molecules are transformed to a highly ordered chain molecule. In order to have a 

Polymerization Monomer (starting material) Initiator Reaction phase 

Plasma No specific functional group is needed No initiator Gas phase (gas-solid interface) 

Radiation Monomer structure for addition polymerization No initiator Liquid or solid phase 

Parylene Dimer of para-xylene No initiator Gas phase 

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Anionic polymerization of lactams was shown to proceed according to what is called the activated monomer mechanism. With bischloroformates of hydroxy-terminated poly(tetramethyleneglycol) and poly(styrene glycol) as precursors for a polymeric initiator containing N-acyl lactam ends, block copolymers with n-pyrrol-idone and e-caprolactam were obtained by bulk polymerizations in vacuum at 30 and 80 °C, respectively361. ... 

The complexity of polymer deposition, which is depicted in Figure 10.1, could be best understood by comparing corresponding schemes for other (hypothetical) mechanisms. Let us first consider a hypothetical case in which a monomer polymerizes in vacuum and deposits onto an exposed surface without any complication. In other words, if a polymer can be formed in vacuum by free radical polymerization, the polymerization mechanism can be depicted as shown in Figure 10.2. In this case, the chemical structure of a plasma polymer can be predicted from the structure of the monomer, and only unreacted monomer escapes... 

Figure 10.2 Schematic diagram of hypothetical free radical polymerization in vacuum.

It follows from this discussion that all solvents and monomers used must be carefully purified. Hydrocarbons should be stirred over sulphuric acid for many days and ethers refluxed over sodium—potassium alloy or sodium fluorenone before fractionation. Traces of unsaturated materials in aliphatic hydrocarbons can be removed by silica gel. After fractionation, a preliminary drying over calcium hydride can be followed by storage over sodium—potassium alloy for ethers, or a treatment with butyllithium or similar non-volatile reactive organometallic reagent for hydrocarbons. Monomers cannot be treated quite so drastically, but fractionation followed by a pre-polymerization in vacuum over butyl-... 

The metathesis ring-opening polymerization of COT yielded PA as a viscous liquid [67] and substituted COT was polymerized or copolymerized with the formation of soluble materials with moderate conductivity. The other original and accessible method for the production of trans-PA films is ring-opening polymerization of 7,8-bis(trifluoromethy)-tricyclo-(4,2,2,0)-deca-3,7,9-triene. Polymerization in vacuum on a flask surface treated with a catalytic solution resulted in a silvery polymer film. The flotation density of this film reaches 1.1 g/cm and becomes close to the density of PA obtained by other methods. These polymers have an amorphous structure and are completely trans-isomers. They are easily dissolved in common solvents such as acetone and chloroform. A detailed description of the synthesis can be found in Ref. 68-70. 

Poly(methyl methacrylate), polystyrene and their random copolymers were prepared by free radical polymerization in vacuum using AIBN as initiator. 

Polythiophene can be synthesized by electrochemical polymerization or chemical oxidation of the monomer. A large number of substituted polythiophenes have been prepared, with the properties of the polymer depending on the nature of the substituent group. Oligomers of polythiophene such as (a-sexithienyl thiophene) can be prepared by oxidative linking of smaller thiophene units (33). These oligomers can be sublimed in vacuum to create polymer thin films for use in organic-based transistors. 

Fig. 1. Examples of the kinetic curves during ethylene polymerization by chromium oxide catalysts. Support—SiOs temperature—80°C polymerization at constant ethylene pressure in perfect mixing reactor. Curve 1—catalyst reduced by CO at 300°C. Curve 2— catalyst activated in vacuum (400°C) polymerization in the case of (1) and (2) in solvent (heptane) ethylene pressure 10 kg/cm2 02 content in ethylene 1 ppm, HsO 3 ppm. Curves 3, 4, 5, 6—catalyst activated in vacuum (400°C) polymerization without solvent ethylene pressure 19 (curve 3), 13 (curve 4), 4 (curve 5), and 2 (curve 6) kg/cm2 02 content in ethylene 1 ppm, HsO = 12 ppm.

Anionic polymerization of ethylene oxide by living carbanions of polystyrene was first carried out by Szwarc295. A limited number of methods have been reported in the preparation of A-B and A-B-A copolymers in which B was polystyrene and A was poly(oxyethylene)296-298. The actual procedure was to allow ethylene oxide to polymerize in a vacuum system at 70 °C with the polystyrene anion initiated with cumyl potassium in THF299. The yields of pure block copolymers are usually limited to about 80% because homopolymers are formed300. ... 

The poly(glycolide-co-caprolactone) (PGCL) copolymer was mainly synthesized by the ringopening polymerization. A copolymer with 1 1 mole ratio was synthesized by the ring-opening polymerization in the presence of the catalyst Sn(Oct)2 by Lee and coworkers. The polymerization was under vacuum, and heated in an oil bath at 170°C for 20 h. The copolymer was then dried under vacuum at room temperature for 72 h. The schematic reaction equations are shown in Schemes 8.5 and 8.6. 

Alkyl esters often show low reactivity for lipase-catalyzed transesterifications with alcohols. Therefore, it is difficult to obtain high molecular weight polyesters by lipase-catalyzed polycondensation of dialkyl esters with glycols. The molecular weight greatly improved by polymerization under vacuum to remove the formed alcohols, leading to a shift of equilibrium toward the product polymer the polyester with molecular weight of 2 x 10" was obtained by the lipase MM-catalyzed polymerization of sebacic acid and 1,4-butanediol in diphenyl ether or veratrole under reduced pressure. ... 

Both in liquid propene or in toluene the polymerization reactions were quenched with MeOH, and the polymer products were precipitated by pouring the toluene solution into an excess of MeOH. The product was filtered, washed with acidified methanol, and dried in vacuum at 60 °C overnight [39],... 

High-molecular-weight polyesters cannot be made by polymerization in the molten state alone - instead, post-polymerization (or polycondensation) is performed in the solid state as chips (usually under vacuum or inert gas) at temperatures somewhat less than the melting point. The solid-state polycondensation of polyesters is covered in detail in Chapters 4 and 5. 

Koresh and Soffer (1983) developed a hollow-fiber gas separation membrane. In principle, polymeric hollow fibers can be porous (macroporosity) or dense. On thermal treatment in vacuum (pyrolysis) a second structural feature, the so-called ultramicroporosity (Koresh and Soffer 1983) was observed. This is due to small gaseous molecules channeling their way out of... 

After polymerization the rather viscous solution is added dropwise to 50 ml of 0.1 N HCI, whereupon the polymer precipitates.The polymer is filtered, if necessary broken up, extracted in a Soxhiet apparatus with petroleum ether for 5 h, and finally dried to constant weight in vacuum at 50 °C.The yield is quantitative. 

To start the experiment all the tubes are placed in a rack at the same time and allowed to warm to room temperature finally they are placed in a thermostat at 50 °C.The tubes are removed at intervals of 1 h and immediately cooled in an acetone/dry ice bath.The samples that are still fluid are diluted with approximately 50 ml of chloroform and dropped into about 500 ml of stirred heptane or petroleum ether. For the very viscous or solid samples 1-2 g are dissolved in 50-100 ml of chloroform and the solution is added dropwise to 500-1000 ml of heptane or petroleum ether with stirring.The polymers are filtered off and dried to constant weight in vacuum at 50 C.The yield, the limiting viscosity number (measured in chloroform at 20 °C) and the degree of polymerization are plotted against reaction time. 

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