Freeze-dried copolymers

Synthesis. Graft copolymer was formed in aqueous solution by ceric-ion-initiated, radical polymerization of monomer on starch. Polymerization was conducted in an inert, atmosphere. Details of the synthesis procedure may be found in references 41 to 43 In recovering the polymer product, freeze drying was used with care since freeze drying produces a more dissolvable and useful product but can degrade polymers with molecular weights of 1 million or more. Poly(starch-g-(1-amidoethylene)) Poly(starch-g-(1-amidoethylene))... 

EAAm was synthesized in our laboratory as described previously [24]. Copolymers of DMAEMA and EAAm were prepared by free radical polymerization as follows 7.8 g of distilled monomers (mixtures of DMAEMA and EAAm) and 0.02 g of AIBN as an initiator were dissolved in 100 mL of a (50/50 by volume) water/ethanol mixture. The feed compositions for poly(DMAEMA-co-EAAm) are shown in Table 2. The ampoule containing the solution was sealed by conventional methods and inunersed in a water bath held at 75°C for 15 h. After polymerization, all polymers were dialyzed against distilled-deionized water at 4°C and freeze-dried. 

Fig. 16 TEM pictures showing nanoparticles of cholesteryl end-capped poly(NIPA-co-dimethylacrylamide). The nanoparticles were obtained by the dialyzing dimethylfor-mamide solutions of copolymers against water and subsequent freeze-drying. The initial concentrations of the copolymer in dimethylformamide were a-c 0.35 wt%, d 0.1 wt%, e, f 1.2 wt%. a, c-f were obtained for the copolymer with Mw = 3400 b was obtained for the copolymer with Mw = 8000. (Reprinted with permission from Ref. [55]. Copyright 2003 Elsevier)...

For photolysis of the ethylene—carbon monoxide copolymer in solution, the AH-6 lamp and a 20-mm. path-length quartz cell were used. The cell was filled with the solvent, pure n-heptane, and the intensity of the lamp was measured at the experimental temperature. Freeze-dried polymer was then added to make a 2% solution, which absorbed about 25% of the light. The polymer was dissolved, and the solution was mixed by a dry nitrogen stream, which also flushed out any air dissolved in the solvent. The light beam was then allowed to enter the cell, and the photolysis commenced the intensity of the emergent beam was monitored by the photomultiplier tube and the recorder. At the end of the photolysis the cell was filled with pure solvent, and the intensity of the lamp was measured again. The polymer was recovered from solution by evaporating the heptane it was then dissolved in benzene and freeze-dried. 

To check whether vinyl esters of strongly branched acids behave differently, mixtures of vinyl acetate and VV 911 in molar ratios of 1/3, 1/1, and 3/1 were polymerized in bulk to a conversion of about 10%, using benzoyl peroxide as initiator at 50°C. The reaction mixtures were then diluted with benzene, and the polymers were precipitated with methanol. After five further dissolutions in benzene and precipitation with methanol the polymers were freeze dried from their solutions in benzene and analyzed for carbon content. The results given in Figure 1 show that, at least for practical purposes, the assumption that r1 = r2 = 1 is valid, and at any time during the polymerization random copolymers are formed at any vinyl acetate-VV 911 ratio. 

Of this polymer 0.493 g was dissolved in 5 mL of 1,3,3-trimethylazeti-dine and the solution was heated in a sealed tube for 18 hr in 80° C. The reaction mixture was then dissolved in benzene and freeze-dried to give 0.721 g of ABA triblock copolymer. 

Solid-state NMR spectra of whole cells containing poly(hydroxyalkanoic acid) have been observed [39,40], The CP/MAS NMR spectrum of P(3HB-co-3HV) containing 21 mol% 3HV in the freeze-dried cells is found to be qualitatively similar to that of a solution- or melt-cast film of the isolated copolymer [41]. 

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. 

Hydrolysis of styrene-methacrylic anhydride copolymers. One gram samples of the copolymers were suspended in distilled water (150 ml.) and the mixtures were refluxed, with stirring, until solutions were obtained that were stable at room temperature. Copolymers with high styrene contents hydrolyzed slowly and required 108 hr. reaction times. These polymers formed soap-like solutions when completely hydrolyzed. The hydrolyzed polymers were isolated by freeze-drying and were examined by infrared spectroscopy to establish the completeness of hydrolysis. 

The samples were synthesized by the same techniques as those used for the styrene ionomers (12). The protonated styrene-methacrylic acid copolymers were prepared by thermal initiation. The polymerization took place in sealed glass tubes in the bulk at 80 °C after several freeze-thaw cycles. A conversion of 10% was obtained after 19 hr. The polymer was precipitated in methanol and neutralized in a benzene-methanol solution. A similar procedure was used for the deuterated samples except that the unreacted deuterated styrene monomer was evaporated prior to the precipitation. The mixing of the deuterated and protonated styrene copolymers was performed in a benzene solution by stirring for 1 hr. The benzene used as the solvent contained a minimum amount of methanol necessary to dissolve the ionomer (approximately 5-10% for the samples of high ion content). The samples were freeze-dried, then dried further at 60°-80°C under vacuum, and finally compression-molded at Tg - - 30°C. 

The leading electrolyte was 0.01 H HCl buffered to pH 3.8 with -al2uilne (Kodak Lca>oratory euid Bese2urch Products, Rochester, MY) emd contained 0.5% Triton X-100 surfactemt (Bohm emd Haas, Philadelphia, PA). The terminal electrolyte was 0.01 H n-hexanolc acid (Kodak Laboratory 2uid Research Products) emd contained 0.5% Triton X-100 surfactemt. Copolymer seunples were prepared at 2000 ppm by dissolving 20 mg of the freeze-dried polymer In 10 ml of the leading electrolyte or water. 

The rates of solubilization, however, and the apparent homogeneity of the solutions deserve comment. First, the extent of incorporation of the N-alkylacrylamide in the copolymer is not determinable from elemental analysis or NMR measurements because of the low concentration in the feed initially. Second, solubilization of purified, freeze-dried samples is often difficult because of inter- and intramolecular associations. Finally, even under dilute conditions, a time dependence on dissolution is observed with some solutions, which require weeks to reach constant values of apparent viscosity. Optical cloudiness with stringy texture is often observed with the longer alkyl chains at higher concentration. 

Prepare a solution of I-PSSNa macroinitiator (0.050 mmol), MMA (5.0 mmol), copper (I) bromide (0.050 mmol) and 2,2 -bipyridine (1.00 mmol) in a mixed solvent composed of methanol and water (80/20 ratio) and stir at 25 "C for 24 h, under an argon atmosphere. The copolymer is purified by dialysis and recovered via freeze-drying. 

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