Copolymer microspheres

Expandable VDC copolymer microspheres are prepared by a microsuspension process (191). The expanded microspheres are used in reinforced polyesters, blocking multipair cable, and in composites for furniture, marble, and marine appHcations (192—195). Vinylidene chloride copolymer microspheres are also used in printing inks and paper manufacture (196). 

Soapless seeded emulsion copolymerization has been proposed as an alternative method for the preparation of uniform copolymer microspheres in the submicron-size range [115-117]. In this process, a small part of the total monomer-comonomer mixture is added into the water phase to start the copolymerization with a lower monomer phase-water ratio relative to the conventional direct process to prevent the coagulation and monodispersity defects. The functional comonomer concentration in the monomer-comonomer mixture is also kept below 10% (by mole). The water phase including the initiator is kept at the polymerization temperature during and after the addition of initial monomer mixture. The nucleation takes place by the precipitation of copolymer macromolecules, and initially formed copolymer nuclei collide and form larger particles. After particle formation with the initial lower organic phase-water ratio, an oligomer initiated in the continuous phase is... 

The soapless seeded emulsion copolymerization method was used for producing uniform microspheres prepared by the copolymerization of styrene with polar, functional monomers [115-117]. In this series, polysty-rene-polymethacrylic acid (PS/PMAAc), poly sty rene-polymethylmethacrylate-polymethacrylic acid (PS/ PMMA/PMAAc), polystyrene-polyhydroxyethylmeth-acrylate (PS/PHEMA), and polystyrene-polyacrylic acid (PS/PAAc) uniform copolymer microspheres were synthesized by applying a multistage soapless emulsion polymerization process. The composition and the average size of the uniform copolymer latices prepared by multistage soapless emulsion copolymerization are given in Table 11. 

Chang, M., Colvin, M., and Rembaum, A. (1986) Acrolein and 2-hydroxyethyl methacrylate copolymer microspheres. /. Polym. Sci. Part C Polym. Lett. 24, 603-606. 

Liu et al. prepared palladium nanoparticles in water-dispersible poly(acrylic acid) (PAA)-lined channels of diblock copolymer microspheres [47]. The diblock microspheres (mean diameter 0.5 pm) were prepared using an oil-in-water emulsion process. The diblock used was poly(t-butylacrylate)-Wock-poly(2-cinna-moyloxyethyl) methacrylate (PtBA-b-PCEMA). Synthesis of the nanoparticles inside the PAA-lined channels of the microspheres was achieved using hydrazine for the reduction of PdCl2, and the nanoparticle formation was confirmed from TEM analysis and electron diffraction study (Fig. 9.1). The Pd-loaded microspheres catalyzed the hydrogenation of methylacrylate to methyl-propionate. The catalytic reactions were carried out in methanol as solvent under dihydro-... 

Vojnovic D, Rubessa F, Bogataj M, Mrhar A. Formulation and evaluation of vinylpyrrolidone/vinylacetate copolymer microspheres with griseofulvin. / Microencapsul 1993 10(1) 89-99. 

Polyanhydrides have also been investigated as protein carriers.f Poly(SA) and 20 80 CPH SA copolymer microspheres were foimd to conserve both the primary structure of the released protein [bovine serum albumin (BSA)] and the secondary structure of the encapsulated and released protein, and showed a sustained delivery for approximately 15 and 30 days, respectively. As the CPH content in the copolymer increased, the secondary structure of BSA was not conserved, as indicated by the steep decrease in the a-helix content. 

Wu H, Wang S et al (2011) Chltosan-polycaprolactone copolymer microspheres for transforming growth factor-[beta] 1 delivery. Colloids Surf B 82 602-608... 

Sohier J, Van Dijkhuizen-Radersma R, De Groot K, Bezemer J. Release of small water-soluble drugs from multiblock copolymer microspheres a feasibility study. Eur J Pharm Biopharm 2003 55 221-228. 

Kwon YM, Kim SW. Biodegradable triblock copolymer microspheres based on thermosensitive sol-gel transition. Pharm Res 2004 21 339-343. 

Tuncel, A., K. Ecevit, et al. (1996). Nonswellable and sweUable ethylene glycol dimethacrylate-acrylic acid copolymer microspheres. Journal of Polymer Science Part A Polymer Chemistry 34(1) 45-55. 

Aminated PS-based latices were prepared by dispersion polymerisation and were characterised. Mixtures of Boc-p-aminostyrene and styrene monomers at various compositions were copolymerised under dispersion conditions in 2-propanol/water 3 1 by volume in the presence of AIBN as free radical initiator at 75C. Copolymer microspheres with uniform size distributions and average diameters between 0.9 and 1.8 micrometres were obtained. Aminated microspheres were obtained by the simple removal of the Boc protective group under acidic conditions, followed by neutralisation, thus leading to p-aminostyrene/styrene copolymers. These chemical treatments, when carried ont nnder mild conditions (room temp, and dilute acid and basic solutions), were efficient without causing any major alteration of the microsphere morphology. X-ray photoelectron spectroscopy analysis of the prepared microspheres showed an increase of amino groups with increase of the Boc-p-aminostyrene in the copolymer feed up to 10 mol %. 26 refs. 

The influence of gamma-sterilisation on the physicochemical properties of a controlled release formulation for insulin-like growth factor-I was investigated. The growth factor was entrapped in lactide-glycolide copolymer microspheres by a water-in-oil-in-water solvent evaporation technique. Microspheres were irradiated and evaluated by SEM and DSC. The stability of the released protein was investigated by circular dichroism and gel electrophoresis. 34 refs. 

Details are given of the targeted delivery of antiinflammatory drugs to inflammatory sites using biodegradable lactic acid-glycolic acid copolymer microspheres. A carbohydrate that serves as a ligand to selectins was attached to the surface of the microspheres to mimic the adhesive behaviour of leukocytes on selectins. 47 refs. 

Details are given of the development of lactic acid-glycolic acid copolymer microspheres for continuous delivery of dexamethasone. The microspheres were prepared using an oil-in-water emulsion technique. Drug loading and release rates were determined by HPLC-UV analysis. 42 refs. 

The effect of morphology on the drug release in blends as well as copolymers of PLLA and PDXO was investigated by Albertsson and coworkers. The microspheres obtained from blends were more compact and crystalline, while the copolymer microspheres had an amorphous structure that affected the hydrolysis under humid conditions. The storage stability of copolymers was studied for 5 months and was found to be less than that of blends [149]. 

Lu, Z.H., Liu, G.J., and Liu, F.T. (2001a) Block copolymer microspheres containing intricate nanometer-sized segregation patterns. Macromolecules, 34, 8814—8817. 

Name(s) acrylic microbeads, VAc/VC copolymer microspheres, ethyl-ene/methyl acrylate copolymer, silicone crosslinked spherical particles, polymethylsilsesquioxane, poly(styrene-co-divinylbenzene)... 

If the structure of the self-assemblies can be immobilized by crosslinking of the spherical parts (the spherical microdomains in the solid state and the core in solution), the crosslinked products should form the core-shell type copolymers (microspheres) (see Figure 1). In fact, poly[st)u-ene(S)-Z>-butadiene (Bu)-Z>-S] block copolymer micelles with cores of polybutadiene (PBu) blocks in dilute solution were stabilized by crosslinking of the chains in the micellar... 

Recently core shell microspheres of NIPAM copolymer gels with sty-rene(St) have been prepared [33]. Because St-NIPAM copolymer microspheres prepared by soap-free emulsion polymerization have an imperfect core shell structure, seeded polymerization of NIPAM was carried out using the St-NIPAM microspheres as seeds to prepare uniform core shell microspheres. The particles obtained are thermosensitive gels and the adhesion between these particles and leukocytes has been investigated. Adsorption of proteins on the particles was also studied using PNIPAM gels [34]. 

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