Solution polymerization procedure

In summary, our synthetic studies led to the development of interfacial and solution polymerization procedures for the preparation of poly(iminocarbonates) of high molecular weight. These procedures have so far been employed for the synthesis of a small number of structurally diverse poly(iminocarbonates). 

Illustrative Procedure 2 Poly(iminocarbonates) by Solution Polymerization (46) Under argon, 1 g of a diphenol and an exact stoichiometric equivalent of a dicyanate were dissolved in 5 ml of freshly distilled THF. 1 mol% of potassium tert-butoxide was added, and the reaction was stirred for 4 hr at room temperature. Thereafter, the poly(iminocarbonate) was precipitated as a gumUke material by the addition of acetone. The crude poly(iminocarbonate) can be purified by extensive washings with an excess of acetone. The molecular weight (in chloroform, relative to polystyrene standards by GPC) is typically in the range of 50,000-80,000. 

Solution polymerizations of 1,3-butadiene were carried out in a high-pressure glass reactor (40 mL) connected with a vacuum system. In a typical procedure, 4 pmol of precatalyst (EAS/precatalyst =100 mol/mol) was dissolved in 20 mL of toluene. The polymerization started by adding 1.08 g of 1,3-butadiene and EAS to the solution in this order. The reaction mixture was stirred at a specific temperature (30 to 70 °C) for 40 min. The resulting solution was poured into acidified methanol (100 mL of a 5% v/v solution of HCl). The polymer was then isolated by filtration and washed with methanol before drying overnight at 40 °C. Polymer yield was determined by gravimetry. 

Both commercial and laboratory-synthesized polymers were used. Those made in the laboratory were generally prepared by solution polymerization, refluxing commercially available monomers in toluene using benzoyl peroxide as the catalyst. Other preparations were made in which azo-bis-isobutyronitrile (AIBN) was used as initiator, ethanol was employed as the refluxing medium, and monomers were especially synthesized in the laboratory. These variations in preparative procedure did not significantly affect the ranking of the polymers with respect to their tendency to crosslink, as reported in Table I. 

Bz s-imidoesters like DMS may be used to couple proteins to PE-containing liposomes by crosslinking with the amines on both molecules (Figure 22.24). However, single-step crosslinking procedures using homobifunctional reagents are particularly subject to uncontrollable polymerization of protein in solution. Polymerization is possible because the procedure is done with the liposomes, protein, and crosslinker all in solution at the same time. 

In other related areas, such as solution polymerization and bulk polymerization, the removal/recycling of solvents or unreacted monomer has been extensively investigated [108-112]. The methods used are based on lateral heat-dependent operations such as evaporation and steam-stripping, or non-lateral heat-dependent operations that include a variety of extraction procedures. 

Polymer Synthesis. General Procedure—All polymers were prepared by free-radical-initiated solution polymerization. Typical quantities utilized were as follows 5.0 g total monomer and 0.02 g AIBN or Vazo 33 in 30-60 mL solvent. More dilute solutions were employed in some cases to eliminate gel formation. In addition, a chain transfer agent, dodecanethiol, was used to control molecular weight in some polymerizations. 

We have prepared two linear soluble polyurethanes P(LAGA-MDI) and P(LAGA-HMDI) by solution polymerization of LAGA with MDI and HMDI respectively in dimethyiacet-amide as a solvent using dibutyltin dilaurate as a catalyst at 75°C over 24 hours According to the procedure used in the preparation of the isosorbide polyurethanes as described in the experimental section. Both polymers have been isolated in quantitative yield in their lactone form by precipitation from chloroform (15). 

Conditions for low temperature solution polymerizations of pyromellitic dianhydride (PMDA) have been developed for a wide variety of aromatic 1,4-phenylene [54, 55] and 4,4 -biphenylene [56-58] diamine monomers in a number of aprotic solvents to give high molecular weight prepolymers referred to as polyamic acids. Since the imidized structures are insoluble, they must be processed in the form of their polyamic acids which are subsequently imidized thermally or by chemical dehydrating agents. Although this procedure is acceptable for thin film or fibers, the fabrication of thick parts is complicated by the water of imidization. 

About 20 g of a mixture of 4-vinylphenyldialkyl/arylsilane and styrene was introduced into an ampule of 25 ml capacity in the presence of AIBN (0.2 mole%). The polymerization procedure was the same as that used for homopolymerization. However, the conversion was limited to about 10% (about 4 h). The copolymer was isolated by precipitation of the methylene chloride solution into methanol and dried under vacuum at 40 °C for 6 h. 

The use of a precision digital density meter as supplied by Mettler Instruments (Anton Paar, Ag.) appeared attractive. Few references on using density measurements to follow polymerization or other reactions appear in the literature. Poehlein and Dougherty (2) mentioned, without elaboration, the occasional use of y-ray density meters to measure conversion for control purposes in continuous emulsion polymerization. Braun and Disselhoff (3) utilized an instrument by Anton Paar, Ag. but only in a very limited fashion. More recently Rentsch and Schultz(4) also utilized an instrument by Anton Paar, Ag. for the continuous density measurement of the cationic polymerization of 1,3,6,9-tetraoxacycloundecane. Ray(5) has used a newer model Paar digital density meter to monitor emulsion polymerization in a continuous stirred tank reactor train. Trathnigg(6, 7) quite recently considered the solution polymerization of styrene in tetrahydrofuran and discusses the effect of mixing on the reliability of the conversion data calculated. Two other references by Russian authors(8,9) are known citing kinetic measurements by the density method but their procedures do not fulfill the above stated requirements. 

Polymerization Procedure. The polymerization apparatus consisted of a simple tube with two constrictions. The THF breakseal was attached between the two constrictions. The catalyst solution was prepared in a serum capped nitrogen purged bottle from weighed amounts of oxonium salt and methylene chloride. This solution was made up so that the final catalyst concentration was 3.25 X 10 3M, and the THF concentration was 7.6M (62.5% v/v THF). This insured a fluid mixture throughout the polymerization. Under these conditions the equilibrium conversion to polymer was 27.5%—i.e., the equilibrium monomer concentration of THF was 5.6M. 

CDT Polymerization. Following the general polymerization procedure described above, 1,5,9-cyclododecatriene was polymerized using 100 ml. of 1.57M solution of monomer in benzene and initiated by 2.0 ml. each of the catalyst Components A and B. The reaction was terminated after 30 minutes, and the product was isolated, processed, and analyzed for the low molecular weight extractable macrocyclic fraction as before. 

Ehenol antioxidant. The general procedures and equipment required ave been reported in detail (12). The polymerization procedure consisted of adding catalyst solution to a nitrogen-blanketed mixture of the... 

Anionic graft-polymerization of paraformaldehyde onto starch and dextrin has been effected in methyl sulfoxide solution, polymerization being initiated by the carbohydrate potassium alcoholate formed from the reaction of the carbohydrate with naphthalene potassium, a metallation procedure not previously described for carbohydrates.220... 

The catalyst and metal alkyl cocatalyst can be brought into contact in a number of ways, depending on the commercial process. In a slurry or solution polymerization process, it is most convenient to simply feed a solution of the cocatalyst directly into the reactor, where it comes in contact with the catalyst in dilute solution and in the presence of ethylene and any comonomer. This procedure allows for continuous adjustment of the cocatalyst concentration for control of polymer properties. 

Polymerization Procedure and Characterization. Cyclic ethers and formals were polymerized by adding a measured amount of monomer into the initiator solution at 0°C. The polymer was precipitated with methanol or ethyl ether and freeze-dried from benzene or fractionated by chloroform. The block copolymer of styrene and tetrahydrofuran was dissolved in 1-butanol and refluxed for 12 hours with sodium metal. The solution was washed with water, and the 1-butanol was distilled off. The residual polymer was freeze-dried from benzene, and poly-THF was extracted with 2-propanol in a Soxhlet apparatus. 

Many different approaches have been used to synthesize star-block copolymers including anionic, cationic, radical, and condensation polymerization techniques, and even combinations of them [9]. The majority of the molecules produced thus far were prepared by anionic polymerization procedures. The dominant way of preparing star-block copolymers by anionic polymerization is the coupling of preformed diblock or triblock living copolymer chains with a suitable compound to produce the central linking point. In this way divinylbenzene (DVB) was first used in order for a central core to be created [ 10]. This was achieved by adding a predetermined amount of the divinyl compound to a solution of living diblock chains (Scheme 1). 

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