Copolymer solutions tetrahydrofuran

Figure 13.6 Film cast from a 1 2 mixture of poly(styrene-co-butadiene) and poly(2-vinyl pyridine-co-butadiene) with about 15 mol% butadiene content (10 wt% solution of the copolymers in tetrahydrofuran). Dark areas, poly(styrene-co-butadiene) light areas, poly (2-vinyl pyridine-co-butadiene) [15]. Courtesy of Dr A. Schindler...

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. 

A solution of Viton poly(VDF-co-HFP) copolymer in tetrahydrofurane, mixed with HMDA, at room temperature for one day produces gel forma-... 

GopolymeriZation Initiators. The copolymerization of styrene and dienes in hydrocarbon solution with alkyUithium initiators produces a tapered block copolymer stmcture because of the large differences in monomer reactivity ratios for styrene (r < 0.1) and dienes (r > 10) (1,33,34). In order to obtain random copolymers of styrene and dienes, it is necessary to either add small amounts of a Lewis base such as tetrahydrofuran or an alkaU metal alkoxide (MtOR, where Mt = Na, K, Rb, or Cs). In contrast to Lewis bases which promote formation of undesirable vinyl microstmcture in diene polymerizations (57), the addition of small amounts of an alkaU metal alkoxide such as potassium amyloxide ([ROK]/[Li] = 0.08) is sufficient to promote random copolymerization of styrene and diene without producing significant increases in the amount of vinyl microstmcture (58,59). 

Resist solutions of o-cresol novolac-siloxane copolymers were prepared as 15 w/v % solutions of the polymer in 2-methoxyethyl acetate using 20 wt % (based on polymer) of the positive sensitizer. Poly(hydroxystyrene) and 2-methyl resorcinol copolymers were spun into films from 2-methyl tetrahydrofuran. Solutions were filtered through successive 1.0, 0.5 and 0.2 pm filters and stored in... 

Anhydrous Copolymerization of NIPAAM and N-Acryloxysuccinimide (NASI). In a modification of the procedure of Poliak et al., (4), NIPAAM (5 g, 44 mmol), NASI (0.372 g, 2.2 mmol) and 2,2 azobisisobutyronitrile (AIBN, 0.021 g, 0.13 mmol) were dissolved in 50 ml of dry tetrahydrofuran. The magnetically stirred solution was degassed, heated to 50 C for 24 hours under positive nitrogen pressure, and allowed to cool. The reaction mixture was filtered (0.45 i teflon filter) and the filtrate volume reduced by half. Ether was added with mixing to precipitate the copolymer. 

Figures 6 and 7 illustrate the preposed mechanism in OC. Using the specific example of a separation of a styrene n-butyl methacrylate copolymer, the first SEC separates the copolymer according to molecular size in solution. At any desired retention time, the flow in the first instrument is stopped and an injection made into the second instrument of a single molecular size "slice" of the chrcoiatogram. The solvent running in the second instrument is a mixture of tetrahydrofuran (THF) and n-heptane. THF is a solvent for both styrene cuid n-butyl methacrylate portions of the polymer molecules. However, n-heptane is a nonsolvent for the styrene-rich portions. As a result, vrfien the injection is made into the second instrument, the styrene-rich molecules will shrink relative to the n-butyl methacrylate-rich molecules. An immediate size distribution will be present vrfiich will reflect the composition differences. The smaller styrene-rich molecules will enter more pores of the column packing than their n-butyl methacrylate-rich counterparts and so be fractionated. Furthermore, since the styrene-rich molecules "hate" the mobile phase, they should find the surface area of the packing more "sticky" than the n-butyl methacrylate-rich molecules. Thus, again the styrene-rich molecules should be retarded relative to the others. According to this picture, the mechanisms of size exclusion, adsorption and partition are thus able to act synergistic ally to accomplish a composition separation.

Graft copolymers were prepared by polymerizing ethylene oxide onto the PVN polyradical anion (10), The latter was obtained by reaction of PVN with cesium in tetrahydrofuran solution. The copolymers were extracted with water to remove the PEO homopolymer which was formed as a byproduct. Experimental details and evidence for bond formation between ethylene oxide and the aromatic moiety were presented elsewhere (//). 

A low molecular weight of polytetrahydrofuran was accidentally found in an anodic solution, when an electric current was passed through a solution of styrene with tetrabutylammonium perchlorate in tetra-hydrofuran (23), At the cathode styrene was polymerized and no copolymers were observed in either solution. A possible explanation of the initiation of polymerization can be offerend to account for the preliminary experimental results obtained. It may have been caused by interaction of the perchlorate radical formed at the anode [Eq. (11)] with tetrahydrofuran, providing an axonium ion. 

An anionic technique by indirect grafting was proposed for N-metallation of Nylon by Yamaguchi (153-155), in which alcali metals dissolved in liquid ammonia displace the amidic hydrogen atoms. Nylon derivatives and graft copolymers can be synthetized from the N-metallated Nylon (153). For ethylene oxide as grafting monomer, the metallated fibers were soaked in a tetrahydro-furan solution of the monomer, at 60° C (154). Methyl methacrylate is grafted on Nylon with a conversion over 90% by this technique (155). Other procedures involve the use of sodium methoxide in methanol solution and subsequent anionic graft copolymerization of acrylonitrile in a tetrahydrofuran solution (156). 

Takahashi et al.67) prepared ionene-tetrahydrofuran-ionene (ITI) triblock copolymers and investigated their surface activities. Surface tension-concentration curves for salt-free aqueous solutions of ITI showed that the critical micelle concentration (CMC) decreased with increasing mole fraction of tetrahydrofuran units in the copolymer. This behavior is due to an increase in hydrophobicity. The adsorbance and the thickness of the adsorbed layer for various ITI at the air-water interface were measured by ellipsometry. The adsorbance was also estimated from the Gibbs adsorption equation extended to aqueous polyelectrolyte solutions. The measured and calculated adsorbances were of the same order of magnitude. The thickness of the adsorbed layer was almost equal to the contour length of the ionene blocks. The intramolecular electrostatic repulsion between charged groups in the ionene blocks is probably responsible for the full extension of the... 

Braun and co-workers [46] reported that reductive dechlorination of PVC using tri-n butyl tinhydride ( -Bu3SnH) leads to vinylchloride-ethylene copolymers. Copolymers were characterised by casting film from tetrahydrofuran (THF) solution in a potassium bromide disk. It is thought that the IR absorption peak at 750 cm"1 is ascribed to the (CH2)3 sequences and the peak at 720 cm"1 is due to the (CH2)n>5 sequences. As the dechlorination starts, the peak at 750 cm"1 due to CH2 sequences appears and intensifies with reaction time. The intensity of the peaks at 690 and 615 cm"1 due to the C-Cl stretching vibration slowly decreases. If the reduced PVC contains more than 46 wt% chlorine, only the absorption peak at 750 cm"1 appears in the IR spectra. If the chlorine content is less than 46 wt%, the peak at 720 cm"1 weakens. In this case the (CH2)n>5 sequences become more prominent than the -(CH2)3-sequences [46]. 

We have studied the dispersibility of several pure PVAc-styrene graft copolymers with one PS branch in various selective solvents mainly at room temperature5. The experiment was done with two kinds of dried samples one was recovered from a tetrahydrofuran solution by pouring it into water and the other from a benzene solution which was poured into n-hexane. Let us refer to the former sample as A and the latter sample as B. Due to the difference in solubility of each polymer sequence in those solvents, sample A is supposed to have approximately such a microstructure that PVAc chains are extended and PS chains collapsed, while sample B has the inverse structure. A similar tendency was also pointed out by Merrett12. The results are summarized in Table 2. 

Douy has synthetized polystyrene-polybutadiene (SB) block copolymers of various molecular weights and compositions66 by anionic polymerization, under high vacuum, in tetrahydrofuran dilute solution (less than 5%), at low temperature (—70 °C), and with cumyl potassium as initiator. Resulting from the polymerization conditions, the microstructure of the polybutadiene block is 90% 1,2 and 10% 1,4. 

Symmetric BSB copolymers containing between 20 and 80% polybutadiene and covering a large range of molecular weights haw been synthetized by Douy in tetrahydrofuran solution at a low temperature (—70°) using a bifunctional initiator (a-methylstyrenepotassium dianion)66,88. ... 

High Performance Size Exclusion Chromatography. The Hewlett-Packard 1090 liquid chromatograph was used with the HP 1040 diode array or HP 1037A refractive index (and HP 3392 integrator) detectors. A fifty A (5 mm, 300 x 7 mm) Polymer Laboratories PL gel (polystyrene-divinylbenzene copolymer gel) column was used and standards were as described in Chum et al. (13). Tetrahydrofuran solutions of oil and oil fractions were analyzed. 

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