Lightly crosslinked poly

In practice the type of support used most widely is a lightly crosslinked poly(styrene-divinylbenzene) system usually in the form of spherical beads —50-500 pm in diameter produced by suspension polymerisation [51]. Typically the level of the crosslinking comonomer divinylbenzene used is only —0.5-2.0 vol%. This is crucial in terms of structural analysis by NMR, since such lightly crosslinked systems can swell considerably in suitable solvents (up to —15 fold), such that the local environment around a functional group attached to the polymer network can approach closely to that in isotropic solution (see later). 

MECHANICAL BEHAVIOR OF LIGHTLY CROSSLINKED POLY/ETHYLENE GLYCOL MONOMETHACRYLATE/ AND POLY/DIETHYLENE GLYCOL MONOMETHACRYLATE/ IN THE MAIN TRANSITION AND RUBBER-LIKE REGIONS. 

V. F. G. Cooke and D. H. Thorpe, Additive for Low Profile Polymerizable Unsaturated Polyester Molding Composition, U.S. Pat. 4,125,702 (1978). Lightly crosslinked poly(vinyl chloride)-suspension-sized particles dispersed in unsaturated polyester-styrene. 

To test this hypothesis, a lightly crosslinked poly(ferrocenyldipropylsilane) gel (4 mol % of 3) was synthesized, and swollen in THF to measure the degree of swelling. The /7-propyl substituted gel, 6, was found to swell ca. 10 times more than the analogous methyl substituted gel 5b (2240% and 248% respectively). It is clear that the swelling of these polymer gels can be dramatically influenced by the substituents at silicon. 

When the five mol percent crosslinked poly(acrylic acid) release curve was compared (Figure 5) to that for a very lightly crosslinked (less than one percent)... 

Figure 5. Release of insulin from lightly crosslinked (Polycarbophil) and 5 mol% crosslinked poly(acrylic acid).

Westover et al. 95 prepared lightly crosslinked nitrated poly(4-hydroxystyrene) microspheres for pH sensors. The microspheres were produced using SPG membranes followed by suspension polymerization and they showed diameters between 1 and 2 micrometers. 

Poly(MA) is 70-90% hydrolyzed and lightly crosslinked with allyl acrylate. 

Zhang QM, Li X, Islam MR, Wei M, Serpe Ml (2014) Light switchable optical materials from azobenzene crosslinked poly (N-isopropylacrylamide)-based microgels. J Mater Chem C 2 6961... 

More recently, lightly crosslinked, suspension-sized particles have been evaluated. Chemically, networks based on polybutadiene, poly-styrene, or poly(vinyl chloride) have been suggested. These particles are swellable in the unsaturated polyester-styrene mix, but are substantially insoluble in it. On curing the polyester, an IPN is formed. 

The bottom diagram of Fig. 6.17 shows the liquidus line of the VT diagram for the rubber rrorty-l,4-poly(l-chlorobutadiene). Instead of length , the extension ratio a is plotted. The solidus line should be somewhere to the left of the liquidus line, but it is never reached in an actual experiment. Equilibrium is lost soon after the first crystals appear and upset the network of the lightly crosslinked rubber. 

We previously mentioned that warm irradiation compared to cold irradiation results in higher ductility and lower strength. In addition, the crosslink density of warm irradiated UHMWPE is lower than that of cold irradiated UHMWPE at the same dose level. This could be due to the biphasic morphology developed in UHMWPE after warm irradiation, which is evidenced by the dual peak melting peaks. We speculate that the biphasic morphology is a result of the nonstatistical distribution of crosslinks that is known to occur at high irradiation temperatures with poly-ethylenes [12, 16, 17]. One of the phases, possibly the continuous one, may be lightly crosslinked and maintain the mechanical properties of the uncrosslinked UHMWPE. The... 

Absorbency has both physical and chemical aspects. The unique character of water determines the properties of materials most able to accept, transport, and ultimately retain aqueous solutions. The absorbent process begins at the interface between the incoming fluid and the absorbent structure. With disposable absorbent articles, the coverstock has the responsibility of receiving and transmitting the fluid insult to the underlying absorbent core. The state-of-the-art core is air-laid cellulose fiber mixed with absorbent polymer. The capillary system of the fibrous batt has appreciable physical absorption capacity in addition to the ability to transport fluid to the absorbent polymer. Many water soluble polymers have been made into absorbent compositions, but the industry standard has become lightly crosslinked partially neutralized poly(acrylic acid). 

The equiibrium and dynamic swelling behavior of lightly crosslinked copolymers of 2-hydroxyethyl methacrylate and acidic monomers have been studied as a function of pH at a constant Ionic strength of 0.1 M at 37°C. These gels showed pH-dependent equilibrium swelling behavior. Poly(2-hydroxyethyl methacrylate-co-acrylic acid) networks swelled as a function of time with rates dependent on pH. 

Light scattering of polymer networks is of importance because of the expectation that the structural make-up of a network will determine its time-dependent and equilibrium mechanical behavior. Evidence for this can be found in the work of Ilavsky on PHEMA gels (12) as well as in the work of Blokland (19) on chemically crosslinked poly-urethanes. 

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