PMMA encapsulation

Wu, P.S. et al., 2014. Effects of the novel poly(methyl methacrylate) (PMMA)-encapsulated organic ultraviolet (UV) filters on the UV absorbance and in vitro sun protection factor (SPF). 

Dependence of the composite dispersed morphology on PS and PMMA molecular weights. SEM photomicrographs of (A) blend 1 (low-Mw PS/high-Mw PMMA), where PMMA is extracted by acetic acid and PS encapsulates PMMA (B) blend 2 (low-Mw PS/low-Mw PMMA), where PMMA is extracted by acetic acid and PS encapsulates PMMA and (C) blend 3 (high-Mw PS/high-Mw PMMA), where PS is extracted by cyclohexane and PMMA encapsulates PS. In aU cases HOPE is the matrix. The white scale bar denotes 1 pm. The results clearly show that in blends 1 and 2, PS encapsulates PMMA and in blend 3 the PMMA encapsulates PS. (From J. Reignier, B. D. Favis, and M.-Cl. Heuzey, Polymer 44,49-59,2003. With permission.)... 

Duguet, E. et al. (2000) PMMA encapsulation of alumina particles through aqueous suspension polymerisation processes. Macromolecular Symposia, 151,365-370. 

In another recent example, dtrate-capped Au NPs are modified with 1-dodeca-nethiol in a first step. These premade nanoparticles were encapsulated with block copolymers such as poly(styrene-block-acrylic acid) (PS-b-PAA) and poly(methyl-methacrylate-block-acrylic acid) (PMMA-b-PAA) leading to core-shell hybrid materials. The Au NP diameters are 12 and 31 nm with average shell thickness of about 15 nm [121] (Scheme 3.18). 

Trypsin-encapsulated sol-gel (alkoxysilane-based) was fabricated in situ onto the sample reservoir of a PMMA chip. This was employed for enzymatic conversion of NBD-labeled ArgOEt and bradykinin, followed by CE separation of the products. The enzymatic activity of the encapsulated trypsin as given by the Km value was found to be 19 times higher than that of the free trypsin. The stability of trypsin was 1 week at 4°C. This enhanced enzyme stability was possibly caused by the prevention of enzyme autolysis by the sol-gel matrix [1062],... 

In another approach, the polymer is precipitated from the continuous phase onto on stable nanodroplets in an inverse miniemulsion [109], In this case, a miniemulsion with the liquid core material is formed in a continuous phase that consists of a mixture of a solvent and a nonsolvent for the polymer. That way, PMMA nanocapsules encapsulating an antiseptic agent could be produced. 

Block copolymer vesicles, or polymersomes, are of continued interest for their ability to encapsulate aqueous compartments within relatively robust polymer bilayer shells (Fig. 7) [66, 67]. Eisenberg and coworkers were the first to report the formation of block copolymer vesicles from the self-assembly of polystyrene-h-poly(acrylic acid) (PS-h-PAA) block copolymers. They also have described the formation of a wide range of vesicle architectures in solution from the self-assembly of five different block copolymers PS-h-PAA. PS-h-PMMA, PB-h-PAA, polystyrene-h-poly(4-vinyIpyridinium methyl iodide), and polystyrene-h-(4-vinylpyridinium decyl iodide) [68]. Small uniform vesicles, large polydisperse vesicles, entrapped vesicles, hollow concentric vesicles, onions, and vesicles with hollow tubes in the walls have been observed and the formation mechanism discussed. Since vesicles could be prepared with low glass transition polymers such as PB [69, 70] and PPO [71], it has been established than these structures are thermodynamically stable and not trapped by the glassy nature of the hydrophobic part. 

Aizpurua et al. [96] have studied the kinetics of vinyl acetate miniemulsions stabilized with PS or PVAc. Guyot and coworkers [97] used PS as the costabilizer for the mini emulsion encapsulation of pigment. Samer [67] has used PMMA to stabilize MMA miniemulsions for continuous polymerization in a CSTR. 

Poly (methyl methacrylate) or briefly PMMA is a less common encapsulant used for LEDs. PMMA is also known under the name of acrylic glass and under the product name Plexiglas. The relatively low refractive index of PMMA (it = 1.49 in the wavelength range 500 - 650 nm) results in a limited extraction efficiency when used with high-index semiconductors. 

A key paper involving the experimental interfacial aspects of polymer blends discussed the blends of more than two components wherein a polymeric constituent will concentrate at the interface between two of the blend constituents [Hobbs et al., 1988]. Employing the concepts of interfacial relationships, it was shown that a ternary component can concentrate at the interface between the other constituents and allow for compatibilization of dissimilar and incompatible components. As an example, it was shown that in the ternary blend of PMMA/PC/PBT, PC encapsulates PMMA as a dispersed phase in a matrix of PBT. PC, which exhibits partial miscibility with PMMA and PBT thus compatibil-izes PMMA/PBT blends. 

The dyes solvent green, solvent yellow, solvent blue, and solvent red could be encapsulated in PMMA polymer particles [53,54]. Phase separation occurred during the generation of the composite particles, to form dye crystallites encapsulated in a polymer [53]. Due to an interaction with the polymer, a small but significant bathochromic shift of the absorption maxima was observed [54]. 

The acid sensitive photoinitiator Lucirin TPO could effectively be shielded from an acidic environment by encapsulating it into PMMA or PBA-co-PMMA particles [173]. The hybrid particles show a core-shell morphology (Fig. 16c) which is generated by phase separation during the polymerization process. While the photoinitiator is readily soluble in the monomer(s), it becomes insoluble in the polymer. Therefore, Lucirin TPO precipitates during the polymerization and forms an amorphous core surrounded by a polymeric shell. The encapsulation efficiency was determined as about 90%. 

Nanoprecipitation can also be a very efficient method for the encapsulation of an aqueous core with a polymeric shell. Aqueous droplets containing an active component, e.g., the antiseptic chlorohexidine digluconate [193,194], can be obtained by miniemusification. The continuous phase of the miniemulsion consists of a mixture of a solvent (e.g., dichloromethane, DCM) and a non-solvent (e.g., cyclohexane) for the polymer (e.g., PMMA, PCL, or polymethylacrylate PMA). After miniemulsification, the solvent is carefully evaporated in a controlled manner and the polymer precipitates onto the aqueous droplet (Fig. 23), resulting in a core-shell structure of the system. 

The protecting abilities of the polymeric shell around silica particle were shown by subjecting silica/PMMA-co-PBA hybrids to HF treatment. Nearly 90% of the silica was encapsulated and thus not prone to dissolution by HF [126]. 

Fig. 28 Microscopic observation of prepared surface-imprinted magnetic PMMA nanopeirticles. Field emission SEM images of (a) support particles, (b) imprinted particles, and (c) non-imprinted particles, (d) TEM images illustrating the successful encapsulation of Fc304 magnetite. Reprinted with permission from [177]. Copyright 2008 American Chemical Society...

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