Crosslinked microparticles

The question whether the intramolecularly crosslinked microparticles of non-aqueous polymer dispersions are really microgels is also justified, considering non-aqueous dispersions prepared from acrylic copolymers and melamine/formaldehyde crosslinker with particle sizes of about 300 nm. [45, 343]. In any case, these crosslinked polymeric microparticles are useful constituents of high-solids coatings, imparting a yield stress to those solutions which probably involves attractive forces between the microparticles. 

The delivery of proteins from non-crosslinked microparticles has been hampered by the fact that the amount of protein that crosses the gastrointestinal lining is not augmented. Many of these systems only allow the material to be delivered in the vicinity of the intestinal wall. If particular proteins can easily traverse the GI lining, it will have increased in vivo activity. 

Different architectures, such as block copolymers, crosslinked microparticles, hyperbranched polymers and dendrimers, have emerged (Fig. 7.11). Crosslinked microparticles ( microgels ) can be described as polymer particles with sizes in the submicrometer range and with particular characteristics, such as permanent shape, surface area, and solubility. The use of dispersion/emulsion aqueous or nonaqueous copolymerizations of formulations containing adequate concentrations of multifunctional monomers is the most practical and controllable way of manufacturing micro-gel-based systems (Funke et al., 1998). The sizes of CMP prepared in this way vary between 50 and 300 nm. Functional groups are either distributed in the whole CMP or are grafted onto the surface (core-shell, CS particles). 

Another procedure for the preparation of modified thermosets consists of introducing preformed particles in the initial formulation. This technique is also well documented for modified thermoplastics (Paul and Bucknall, 2000). In Chapter 7 different macromolecular architectures such block copolymers, crosslinked microparticles, hyperbranched polymers, and den-drimers, were presented (Fig. 7.11). All these compact molecules can be used as thermoset modifiers. Thermoplastic powders and core-shell polymers are the more accessible preformed molecules. Some examples are given below. 

Hyperbranched polymers (Boogh et al., 1999), and crosslinked microparticles based on acrylates and prepared in organic media (Pascault et al., 2000), give size particles in the range of 20-50 nm. Crosslinked epoxy particles made from a latex can be either small, 30-600 nm (Landfester et al., 2000) or very large 10-100 pm (Jansen et al., 1999). In every case the chemistry of the shell has to be controlled. 

Different ways of toughening thermosets may be employed such as the use of rubber block copolymers (Mulhaupt and Buchholz, 1996) or introduction of microgels (crosslinked microparticles) (Funke et al., 1998). 

Physical properties and loading capacity of starch-based microparticles crosslinked with trisodium trimetaphosphate. Journal of Food Engineering, Vol. 92, 3, 0une 2009), pp. (255-260), ISSN 0260-8774... 

CR Robert, PA Buri, NA Peppas. Effect of degree of crosslinking of water transport in polymer microparticles. J Appl Polym Sci 30 301-307, 1985. 

P Stjarnkvist, I Sjoholm, T Laasko. Biodegradable microspheres. XII. Properties of the crosslinking chains in polyacryl starch microparticles. J Pharm Sci 78 52-56, 1989. 

Polymeric Materials. Photopolymer chemistry is also being used to prepare a variety of polymeric materials including crosslinked fibers and films (83), microporous gels, microporous polymers (84), microparticles (85) and battery electrodes (86) and components. 

Following route A (Fig. 1), Yan Xiao et al. reported the chemoenzymatic synthesis of poly(8-caprolactone) (PCL) and chiral poly(4-methyl-8-caprolactone) (PMCL) microparticles [5]. The telechelic polymer diol precursors were obtained by enzymatic polymerization of the corresponding monomers in the presence of hexanediol. Enzymatic kinetic resolution polymerization directly yielded the (R)-and (S )-enriched chiral polymers. After acrylation using acryloylchloride, the chiral and nonchiral particles were obtained by crosslinking in an oil-in-water emulsion photopolymerization. Preliminary degradation experiments showed that the stereoselectivity of CALB is retained in the degradation of the chiral microparticles (Fig. 2). 

Crosslinked polyacrylamide latexes encapsulating microparticles of silica and alumina have also been prepared by this method [179], Three steps are involved a) formation of a stable colloidal dispersion of the inorganic particles in an aqueous solution containing acrylamide, crosslinker, dispersant, and initiator b) HIPE preparation with this aqueous solution as the dispersed phase and c) polymerisation. The latex particles are polyhedral in shape, shown clearly by excellent scanning electron micrographs, and have sizes of between 1 and 5 pm. 

Singh A, Suri S, Roy K (2009) In-situ crosslinking hydrogels for combinatorial delivery of chemokines and siRNA-DNA carrying microparticles to dendritic cells. Biomaterials 30 (28) 5187-5200... 

Controlled crosslinking of cationic starches improves performance in microparticle-containing papermaking systems.84-86 Superior performance over cationic potato starch was achieved with crosslinked cationic or amphoteric waxy maize, tapioca or potato starch in microparticle systems when the starch cooking was optimized to produce the proper colloidal dispersions.86... 

It is evident from Table 15 that the thermally regenerable capacity of 2.1 meq/g, which is theoretically feasible in the absence of any internal neutralization, is achieved only when crosslinked poly(ethyl acrylate) microparticles are encapsulated in a crosslinked poly(diallylamine hydrochloride) matrix). The resins synthesized by other routes have capacities less than 2.1 meq/g, indicating that internal neutralization could not be avoided completely. 

Precrosslinked particles with low crosslink density exhibit elastic properties and ean be applied for toughening thermoplastics or thermosets. The size of the elastic domains in blends consisting of elastic particles and a polymer matrix can be adjusted precisely, provided that the particles are dispersible. Via functional groups, microparticles can be covalently attaehed to a (thermoset) matrix. The grafting of polymer shells onto elastic microparticles improves the compatibility with the polymer matrix to be modified [3]. Thus, after processing of the polymer alloy discrete elastic particles can be observed as disperse phase in a continuous thermoplastic matrix. 

The microparticles prepared in inverse emulsion form can be dispersed into aqueous media with agitation and the aid of inverting surfactants. Because of their highly crosslinked nature, the size of the kernel microparticles changes very little in solutions of different salinity. Consequently, the rheological properties of the carrier fluid are not affected by the salinity change encountered in... 

One apparent feature of droplets generated in microfluidic devices is their mono-dispersity in size. Formation of droplets containing precursor solutions dispersed in a continuous phase and then initiation of crosslinking, polymerization or phase separation produces monodisperse microparticles of defined compositions. 

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