Linear toluene swell

Other material properties that are of general interest to the polymer chemist are shown in Table 3. Linear toluene swell is indicative of cross-link density in the material. The vinyl-phenyl modified rubber showed the lowest degree of swell. This is due to additional cross-links introduced by the vinyl groups during synthesis. The unmodified rubber was found to swell considerably in toluene and was found to dissolve partially in the solvent. 

Linear toluene swell (% of thickness) per unit density 70 Dissolves 40 19... 

Dry nework modulus G(l) correlated with equilibrium swelling Q in toluene for PDMS networks. The open circles are for model networks made from end-linking linear chains with two... 

In Fig. 7.17, the dry modulus of various PDMS networks is plotted as a function of their equilibrium swelling in toluene. A single curve results for both model networks (open symbols) made by end-linking linear chains with two reactive ends and networks with intentionally introduced defects in the form of dangling ends (filled symbols) made by end-linking mixtures of chains with one and two reactive ends. The data are fit to Eq. (7.91) as the solid lines in Fig. 7.17 and their intersection determines the crossover concentration 0 = 0.2, which is typical for good solvents. 

Figure 7.3 Dependence of equilibrium swelling in toluene on the crosslinking degree of networks prepared by crosslinking with monochlorodimethyl ether of (1) linear polystyrene at the concentration of Co = 0.125mg/mL (2) styrene-0.3% DVB copolymer swollen to a maximum, Q, = 0.111 mg/mL (3) styrene-0.3% DVB copolymer partially swollen to Q = 0.485 mg/mL (4) styrene-1 % DVB copolymer swollen to a maximum, Q, = 0.485 mg/mL. (After [129]).

Figure 7.4 Dependence of equilibrium swelling in toluene on the crosslinking degree of networks prepared by crosslinking linear polystyrene with partially chloromethylated polystyrene containing (1) 3 (2) 11.5 and (3) 14.8% chlorine. (After [129]).

Linear polymers are well known to dissolve only in solvents exhibiting strong affinity to the polymers, and traditional three-dimensional polymers can also swell with only such kind of media. Contrary to this rule hypercrosslinked polystyrene networks swell both with thermodynamically good solvents, such as toluene or methylene dichloride, and with typical precipitating media for linear polystyrene, such as methanol or -hexane (Fig. 7.5, Tables 7.1 and 7.2) [129-131]. 

Figure 7.7 Dependence of swelling ratio in (1) methanol (2) ethanol (3) n-hexane and (4) toluene on the concentration of starting solution for the networks prepared by crosslinking linear polystyrene with monochlorodimethyl ether to 66% crosslinking degree. (Reprinted from [133] with permission of Elsevier Publishing Company.)...

Figure 7.9 Dependence of weight swelling in toluene calculated per gram of starting polystyrene on the crosslinking degree of networks prepared by crosslinking (1-6) linear polystyrene and (7) styrene-1% DVB copolymer with (1) 1,4-bis-chloromethyldiphenyl, (2, 7) monochlorodlmethyl ether, (3) tris- chloromethyl)-mesitylene, (4) p-tgrlylene dichloride (5) l,4-bis(p-chloromethylphenyl)butane and (6) dimethylformal (8) gel-type styrene-DVB copolymers.

If DCPD is copolymerized with other NBE-type monomers like 2-norbornene-5-methylester (NBE-ME), using 4 as catalyst, the Tg of the so obtained copolymers decrease linearly with the NBE-ME content from 145°C (pure DCPD) to 57°C (pure NBE-ME) and the swelling in toluene increases from 100 to >900%, pointing to a sharp decrease in the crosslink density. This and similar experiments with other comonomers suggest a random incorporation of the comonomer into the poly(DCPD) network. 

The crosslink densities of samples irradiated with doses of 50, 122 and 198 kGy, calculated from equilibrium swelling in toluene, are presented in Fig. 11.1. For all samples studied, crosslink densities formed during EB irradiation process are increasing linear function of dose. 

For the first, diisocyanates, such as 4,4 -diphenyl methane diisocyanate, 1,6-hexamethylene diisocyanate and toluene diisocyanate were allowed, as an example, to react with metribuzin to yield a pesticide-isocyanate adduct. This was then allowed to react with poly(vinyl alcohol) to form a copolymer with controlled release properties. (See Equation 4.) Crosslinked systems were also made by using an excess of the diisocyanate prior to the reaction with polyvinyl alcohol. The metribuzin was released faster from the linear preparation than the crosslinked due to its ability to swell with the hydrophilic polymer hydrolysis and diffusion of the herbicide occurred more easily. Only the hydrolyzed or released metribuzin moved the polymer remained immobile. The commercial formulation of metribuzin was found to be non-toxic after 78 days, but the linear polymer version was found to retain activity even after 112 days. Polymer crosslinking can be varied to provide even longer activity times. 

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