Poly , frontal

The biocompatibility of implantable polyanhydride disks was studied in the brain of rats, rabbits, monkeys, and eventually in human clinical trials. Wafers of poly(CPP SA) and poly (FAD SA) were implanted in the frontal lobes of rats, rabbits, and monkeys. In all these studies, the animals receiving the implants showed no behavioral changes or neurological deficits, indicating that the polymers were not invoking a systemic or local toxicity. To determine how the body metabolized the poly(CPP SA), radio-labeled copolymers were implanted in the brains of rats. Seven days after the implantation, 40% of the " C SA-labeled polymer had been excreted as CO2, 10% was excreted along with the urine, 2% with the feces, and 10% still in the implanted device. In the same period only 4% of the " C CPP-labeled polymer was excreted along with the urine and feces. 

Isothermal frontal polymerization (IFP) is a self-sustaining, directional polymerization that can be used to produce gradient refractive index materials. Accurate detection of frontal properties has been difficult due to the concentration gradient that forms from the diffusion and subsequent polymerization of the monomer solution into the polymer seed. A laser technique that detects tiny differences in refractive indices has been modified to detect the various regions in propagating fronts. Propagation distances and gradient profiles have been determined both mathematically and experimentally at various initiator concentrations and cure temperatures for IFP systems of methyl methacrylate with poly(methyl methacrylate) seeds and wilh the thermal initiator 2,2 -azobisisobutryonitrile. 

A Rayleigh-Taylor instability (Taylor, 1950 Rayleigh, 1899), which also appears as fingers. can ensue if the resulting polymer is molten at the front temperature, such as with -butyl acrylate. The more dense molten polymer streams down from the reaction zone and destroys the front (Figure 11.9). The only current method to study fronts with polymers that are molten at the front temperature is to add a filler, such as silica gel. However, Pojman et al. (1997a) suspected that silica gel could affect the molecular weight distribution, so there is no way on earth (literally ) to study a pure poly(n-butyl acrylate) front. Instead, they carried out a frontal... 

Savostyanov, V. S. Kritskaya, D. A. Ponomarev, A. N. Pomogailo, A. D. 1994. Thermally Initiated Frontal Polymerization of Transition Metal Nitrate Acrylamide Complexes, J. Poly. Sci. Part A Poly. Chem. 32, 1201-1212. 

Lewis and Volpert continue the discussion of the isothermal form of frontal polymerization in Chapter 5. Isothermal frontal polymerization is also a localized reaction zone that propagates but because of the autoacceleration of the rate of free-radical polymerization with conversion. A seed of poly(methyl methacrylate) is placed in contact with a solution of a peroxide or nitrile initiator, and a front propagates from the seed. The monomer diffuses into the seed, creating a viscous zone in which the rate of polymerization is faster than in the bulk solution. The result is a front that propagates but not with a constant velocity because the reaction is proceeding in the bulk solution at a slower rate. This process is used to create gradient refractive index materials by adding the appropriate dopant. 

Most work has been with free-radical systems but other chemistries can be used. Begishev etal. studied frontal anionic polymerization of e-caprolactam [18, 19], and epoxy chemistry has been used as well [20-23]. Mariani ctal. demonstrated frontal ring-opening metathesis polymerization [17]. Fiori et al. produced polyacrylate-poly(dicydopentadiene) networks frontally [24], and Pojman etal. studied epoxy-acrylate binary systems [25]. Polyurethanes have been prepared frontally [13,14, 26]. Frontal atom transfer radical polymerization has been achieved [16] as well as FP with thiol-ene systems [27]. Recent work has been done using FP to prepare microporous polymers [28-30], polyurethane-nanosilica hybrid nanocomposites [31], and segmented polyurethanes [32]. 

M.R. Jr. (2004) Photoinduced cationic ring-opening frontal polymerizations of oxetanes and oxiranes. J. Poly. Sci., Part A Polym. Chem., 42, 1630-1646. 

In order to study poly(n-butyl acrylate) fronts, Pojman et al. added ultrafine silica gel to increase the monomer viscosity (74). To determine the inherent molecular weight distribution (MWD) of poly(n-butyl acrylate) produced frontally, it was necessary to perform a front without silica gel. Because of the Rayleigh-Taylor instability, the only way to accomplish this with a thermoplastic-forming monomer such as n-butyl acrylate is to eliminate the driving force for the collapse of the more dense polymer layer, i.e., eliminate the force of gravity. An experiment was launched on the 1996 Conquest / rocket... 

Used to facilitate multiple repositioning of the lateral tape without tearing the back sheet, frontal tapes are made of PP film and attached to the front of the diaper with adhesive. Their use has helped to reduce the thickness of the poly film without the risk of potential tears associated with the opening of the lateral tapes from the back sheet. In premium diapers, a special loop system has been developed in order to use Velcro type fasteners (also called the hook and loop system). This loop tape can use a locked loop or a brushed loop in order to provide a softer texture or a stronger grip. 

Figure 19 The molecular weight distribution for frontally prepared poly (methacrylic acid) and after the anhydride linkages were cleaved with morpholine. Adapted from Pojman, J. A. Willis, J. R. Khan, A. M. ...

Fiori et were the first to perform frontal urethane poly-... 

All the investigators Mariani and his co-workers prepared poly(iV,iV-dimethylacrylamide) hydrogels and super water absorbent hydrogels frontally.Gavini et al. evaluated FP to prepare dmg controlled release systems based on polyacrylamide. They tested the sodium salt of diclofenac as the dmg to... 

With the development of DESs, they have been applied on some polymerization reactions that are carried out at relatively high temperatures. In these synthetic processes, the eutectic mixtures can act as true solvent-template reactant systems, and thus the DES is at the same time the precursor, the template, and the reactant medium for the fabrication of the desired polymeric material with a defined morphology or chemical composition. Monte and co-workers have reported i) the frontal polymerizations carried out in the eutectic mixtures ChCl/Acrylic acid and ChCl/Mac, " ii) the synthesis of poly(octane-diol-co-citrate) elastomers using eutectic mixtures of 1,8-octanediol and lidocaine at temperatures below 100 C (see Figure 20.3.4), " and iii) the synthesis of poly(acrylic acid)-carbon nanotube composites in the eutectic mixture ChCl/Aciylic acid. " ... 

Figure 14. The morphology of poly(acrylamide) produced frontally, as seen by SEM. Green density 1.14 g cvnr 4% K2S2O8...

The most pernicious convective instability occurs with monomers that produce a molten polymer at the front, such as n-butyl acrylate, styrene and methyl methacrylate. A Rayleigh-Taylor instability (2, 25 ), which also appears as fingers as the more dense molten polymer streams down from the reaction zone and destroys the front (Figure 16). The only currently available methods to study frontal polymerization with thermoplastics are to add a crosslinking monomer to produce a thermoset or to increase the viscosity with a viscosifier such as ultrafine silica gel (CAB-O-SBL). To prepare pure poly(n-butyl acrylate) frontally, Pojman et al resorted to performing the reaction under weightless conditions of a sounding rocket (26 ). 

The use of tributylboron as an initiator which bonds acrylic monomers to dental tissue has been advocated by Masuhara for some time (28). His "Enamite" - a solution of 2-hydroxy-3-beta-naphthoxy-propyl methacrylate, methyl methacrylate, poly(methyl methacrylate), and tri-n-butylboron - is said to show unusually high adhesion to enamel, and, reduced occlusal caries (29). This system has also been used in orthodontics for binding brackets to the frontal face of teeth. 

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