Crosslinking degradation

Enzymes to degrade crosslinked hydroxypropylated starch derivative and xanthan gum polymer systems are available [158,1246]. Specific enzymes are efficient in reducing the near wellbore damage induced by the starch polymer to eventually return permeabilities to the range of 80% to 98% without the use of acid systems. 

Experiments done in the absence of an external stress showed that the effects of degradation crosslinking are significant at relatively short times of UV exposure, and confirmed that the photodegradation is essentially in the surface layers. The oxidized layer thickness appeared to remain more or less constant after a certain exposure. 

Palmgren R, Karlsson S, Albertsson A-C (1997) Synthesis of degradable crosslinked polymers based on l,5-dioxepan-2-one and crosslinker of bis- -caprolactone type. J Polym Sci A Polym Chem 35 1635-1649... 

The G values should be considered as estimates since the molecular weight relations are continuously altered because of the degradation, crosslinking, and branching that occur during irradiation. For example,... 

The three fundamental processes that result from electron modification of polymers are degradation, crosslinking, and grafting. Crosslinking and degradation occur simultaneously. The ratio of their kinetics depends on the chemical structure of the polymer to be modified as well as on the treatment conditions. In general, polymers are divided into those that predominantly crosslink and those that predominantly degrade. 

D. Discharge from a polymer at the electrode generates the polymer radical followed by degradation, crosslinking and branching in the presence of monomer. 

Crosslinking has no specific direct effect on thermal degradation crosslinks can be either weak points (e.g., tertiary carbons in polyester or anhydride-cured epoxies) or thermostable structural units (e.g., trisubstituted aromatic rings in phenolics, certain epoxies, or certain thermostable polymers). Indirect effects can be observed essentially above Tg crosslinking reduces free volume and thus decreases 02 diffusivity. It also prevents melting, which can be favorable in burning contexts. 

Pulse radiolysis studies concerning the polymerization as well as the degradation, crosslinking and radiation resistance of polymers are surveyed. Initiation mechanisms of the radiation-induced polymerization of styrene and other monomers are discussed on the basis of the direct measurements of the reaction intermediates. Optical and kinetic data on the short-lived chemical intermediates produced in the solution of polymers and in the rigid polymers are surveyed and discussed with special reference to the degradation mechanism of polymers. 

Polyfunctional monomers, (III), prepared by Li [4] were used to synthesize cationic polymers having degradable crosslinks for therapy involving the delivery of nucleic acids into cells. 

Title Degradable Crosslinkers and Degradable Crosslinked Hydrogels Comprising Them... 

Harris [4] prepared degradable crosslinked hydrogels with controllable half-lives using hydrolytically unstable imine linkages, (IX). 

An interpretation of these results is that there is little effect of degradation crosslinking or other product formation on chain or group motions involved in the observed transition and modulus behavior up to about 160 hours exposure. This is a reflection of the relatively low crosslink density obtained up to that exposure time. It is anticipated that creep behavior, a low frequency response, would exhibit greater sensitivity to low levels of crosslinking. 

Thermal degradation/crosslinking] polymer temperature too hot/screw speed too low. 

PEG-based star copolymers bearing cationic cores were prepared by Cho et al. using the arm-first ATRP method (Scheme 3.7). ° The PEG-based macromonomer was polymerized with DMAEMA in the presence of a degradable crosslinker to obtain well-defined star-shaped nanoparticles of 120 kDa with degradable and cationic cores. The PEG-based star-shaped... 

Kim, S. Healy, K. E. Synthesis and characterization of injectable poly(N-isopropylacrylatnide-co-acrylic acid) hydrogels with proteolytically degradable crosslinks. Biomacromolecules 2003, 4,1214-1223. 

Table 3 Degradable crosslinking agents used in the preparation of hydrogels... 

Table 4 Syntlietic hydrogels with degradable crosslinkers... 

PHEMA PHEMA was crosslinked by degradable crosslinker, a, n)-diinethacryloyl-P(D,L)-lactide. Hydrolysis of cros-slinker. Barakat el aL, 1994... 

Another consideration in the selection of technology platform is the polymer chosen for the amorphous solid dispersion formulation. The fact that many pharmaceutical polymers degrade, crosslink, or lose functionality at high temperatures has already been discussed. However, the melt viscosity of a polymer is critical to the ability to extrude the amorphous solid dispersion within the capabilities of the extrusion equipment. The melt viscosity as a function of temperature and shear rate varies considerably across pharmaceutical polymers (Chokshi et al. 2005). Formulation melt viscosities in the range of 10-100,000 Pa s are generally acceptable for HME, although the range depends heavily on the torque limit capability of the particular extruder. 

Perfluorinated materials seem to present both a sufficient etch resistance and ease of stripping. Alternatively, a very elegant method allowing an efficient resist stripping process for crosslinked materials is the development of degradable crosslinkers [71]. 

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