Copolymer solutions 1,4-dioxane

Glasses. The solvents used to form the glass with polymers should be clear in the UV region to allow maximum absorption of radiation by the polymer. The ESR of irradiated solvents should not interfere with that of the polymer. Three solvents were found to be close to ideal tetrahydrofuran (THF) p-dioxane (DX) and tetrahydropyran (TP). All three were purified by repeated distillation and column chromatography. Poly(vinyl chloride) and the copolymer solutions (5-15%, w/v) were prepared from these solvents, degassed, sealed under vacuum (10-6 torr), and irradiated. 

Two blending procedures were employed. In the first, the S 0 P 0 0-Acid and the ethyl acrylate copolymers were separately dissolved in 1,4-dioxane (2% w/v) at room temperature. After complete dissolution, the ethyl acrylate copolymer solutions were added slowly to the vigorously stirred sulfonated polymer solutions at room temperature. In the case of the stoichiometric S 0 P 0 0-Acid (600 EW)/PEA-4VP (630 EW) and S 0 P 0 0 Acid (510 EW)/PEA-4VP (480 EW) blends, a gel-like precipitate was obtained during the addition of the ethyl acrylate copolymer solutions. The mixture was further stirred for 3 hours prior to the freeze-drying step. The freeze-dried samples were kept in a vacuum oven initially at 60 C for one week, then further dried at 180 C for a few days prior to use. 

In the second procedure, after separate dissolution of the macromolecules in dioxane, the ethyl acrylate copolymer solutions were added slowly to the vigorously stirred sulfonated polymer solutions at 90instead of room temperature as in the first procedure. The mixture was further stirred for 3 hours at 90 C. Blend samples were recovered using the same procedure as in the first method. 

The second system described by Lovrien, which belongs to mechanism (2), is poly(methacrylic acid) with pendant azobenzene groups. In aqueous solution, the viscosity was found to increase by ultraviolet irradiation. Matejka et. al, have developed the system to styrene -maleic anhydride copolymer with pendant azobenzene groups. The copolymer exhibited a pronounced photodecrease of the viscosity in 1,4-dioxane solution, i.e. a reversible decrease by 24 - 30 % in the reduced viscosity of the solution after ultraviolet irradiation. In THF, the viscosity decreased by 1 - 8 %. The contraction of the dimensions of the copolymer coil is explained as follows trans to cis isomerization induces a strong dipole in the azo bond. These dipoles become mutually oriented and attract each other so that compact coil conformations are preferred. In the dark, the viscosity of the copolymer solution returned to the original value as shown in Figure 3. The increase rate of the viscosity, however, was much slower, by a factor of 1/2.5 to 1/7, than the rate of cis to trans isomerization of the pendant azobenzene chromophores measured by optical absorption in the dark. The discrepancy requires further examination of the postulated mechanism of the conformational change. 

The PBSt-b-PSt (2.00 g) was dissolved in THE (70 mL). Concentrated hydrochloric acid (7 mL) was added to the copolymer solution. The mixture was heated at 85°C for 4.5 hours. The resulting solution was concentrated to ca. 30 mL by an evaporator, and was poured into water (1 L) to precipitate a polymer. The precipitates were collected by filtration, then freeze-dried with 1,4-dioxane to obtain poly(vinylphenol)-block-polystyrene diblock copolymer (PVPh-b-PSt, 1.593 g). The PVPh-b-PSt (0.70 g) was dissolved in DME (15 mL). Sodium hydride (0.414 g, 17-3 mmol) was added to the copolymer solution at 0°C under nitrogen atmosphere. The suspension was stirred at 0°C for 5 minutes and was further stirred at room temperature for 1 hour. Allyl chloride (1.41 g, 18.4 mmol) in DMF (5 mL) was added to the suspension at 0°C. The mixture was stirred at 0°C for 5 minutes and was further stirred at room temperature for 20 hours. The resulting solution was poured into methanol (1 L) to precipitate a polymer. The precipitates were collected by filtration, then dried in vacuo for several hours. PASt-b-PSt (0.68 g) was obtained. The molecular weight of the PASt-b-PSt was determined to be Mn(PASt-b-PSt) = l4000-b-96600 by IH NMR. 

Isotactic poly(methyl methacrylate/methacrylic acid), a copolymer of methyl methacrylate and methacrylic acid, was synthesized by the partial hydrolysis of isotactic poly(MMA) according to the method of Klesper et al. (10-13). A hydrolyzing mixture of 8 mL dioxane and 4 mL methanolic KOH (10% by weight K0H) was mixed with 250 mg of polymer in closed vials at 85°C for 48 hr. Saponified polymer separated from the solution and adhered to the walls of the vial. The precipitated polymer was dissolved in water and then precipitated again with a few drops of HC1. The solution was warmed and the coagulated polymer removed, washed with water, and dried in vacuo at 50°C. The nmr spectrum indicated approxi-... 

For the first time attention to the highly important role played by the thermodynamic factors in the formation of macromolecules during copolymerization was drawn almost a quarter of a century ago [52], When investigating the copolymerization of styrene with methacrylic acid in a solution of CCI4 and in a solution of dioxane in the region of low conversions, the authors established that copolymers with the same composition had an identical microstructure regardless of the solvent type and of the monomer molar ratio... 

Hydrolysis of the poly(r-BMA) blocks is achieved by dissolving the triblock copolymer (1 g) in dioxane (100 ml) at room temperature. Cone, hydrochloric acid (1.5 ml) is added, and the resulting mixture is heated (100 °C) and stirred for 18 h. After cooling to room temperature the solution is concentrated down to approx. 10 ml which are poured into cold (0 °C) diethylether (100 ml).The precipitate is filtered off, washed with methanol and dried in vacuo to constant weight.The result is an acrylic acid-b-styrene-b-acrylic acid triblock copolymer. 

Fig. 3.35 Time dependence of the intensity of scattered light, / after mixing 1% micellar solutions of a PS-PB-PS triblock (A/ = 105 kg mol1, 40% PS) in 1,4-dioxane with an equal amount of heptane ( ) 1 % unimer solution of the same copolymer in 1,4-dioxane/40 vol% heptane with an equal amount of 1.4-dioxane (O) (Bednar et til. 1988).

Materials. The monomer l-(N-2-ethylmethacrylcarbamoyl)-5-fluoroura-cil, [EMCF], was prepared from 5-fluorouracil, [5-FU], and 2-isocya-natoethylmethacrylate as described previously (4). Copolymers of [EMCFI were prepared with methyl acrylate, [MA], and with methyl methacrylate, EMMA], in dioxane solution using AIBN as the initiator. The polymerization conditions have been described previously (1.5). The copolymers used in this study had the monomer ratios shown below. 

Using anionic polymerization in THF solution and with diphenylmethylsodium as initiator, Grosius et al.2ls have synthetized block copolymers poly(vinyl-2-pyridine)-poly(vinyl4-pyridine). They have studied by low-angle X-ray scattering the structure of a copolymer V 2 P V 4 P with molecular weight of the blocks 15000 and 8000 respectively. In octanol, they have found a lamellar and a cylindrical structure as a function of solvent concentration. In THF, dioxan, and benzene they have only found a cylindrical structure. 

Block copolymers with a hydrophobic polyvinyl block and a hydrophobic polypeptide block (BG, SG, SC, SL, BCK and SCK copolymers) exhibit well organized meso-phases in dioxane, 1,2-dichloroethane, 2,3-dichloro 1-propene, etc., solutions. These mesophases are observed for solvent concentrations smaller than about 60% and for dry samples obtained by evaporation of the solvent at a slow rate. 

Up to now we have not found reaction conditions permitting exclusive production of insoluble copolymer, which is the desired product in commercial copolymerization of trioxane. Conversion of a large portion of the dioxolane into soluble copolymer could not even be avoided by slow and gradual addition of the comonomer to a homopolymerization run of trioxane in methylene dichloride (9). The same result was obtained in solution copolymerization of trioxane with 8 mole % of 1,3-dioxacycloheptane (dioxepane), and even 1,3-dioxane—which is not homopolymerizable and is a very sluggish comonomer—formed a soluble copolymer in the initial phase of copolymerization (trioxane 2.5M 1,3-dioxane 0.31M SnCb 0.025M in methylene dichloride at 30°C.). 

Since our aim is to crosslink the copolymers under conditions where the polymer is present as single molecules, it would be highly undesirable to have aggregates in the solutions. In dry dioxane at 25°C. the following results were obtained for the copolymer containing 9.5 mole % HEMA ... 

The first self-assembling block copolymers were PS-fe-PMPS- -PS synthesised by Matyjaszewski and Moller. They observed micellar aggregates by ATM after casting dilute dioxane solutions (a solvent selective for the PS block) of the copolymer. The observed micelles were taken to have internal PMPS cores and were measured at 25-30nm in diameter [73], The hrst self-assembling amphiphilic polysilane block copolymers to be investigated was the PMPS-PEO multi-block copolymer with normal distribution PMPS blocks and uniform low polydispersity PEO blocks. After dialysis aqueous dispersions of this copolymer formed micellar as well as vesicular structures [78, 79] as shown in Eig. 19. 

Wetting Measurements. Wetting measurements with water were made on copolymer films formed by evaporation of 3% by weight solutions of the copolymer from t-butanol, p-dioxane, and toluene. The films were formed on glass microscope slides and were the order of 10 microns in thickness. The films were allowed to form over a 24-hour period in a drying box at a relative humidity of 20%. 

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