Advances in Preparations and Applications of Polymeric Microsphers

The preparative techniques and systems of microspheres with diameters from 0.1 to above 100μm have been well established. Especially in the last decade, remarkable progress has been made in the preparation of very small (several 10 nm) and very large (∼100 μm) uniform microspheres and their applications. Microspheres can be prepared via a polymerization process from monomers and via a granulation process of preformed polymers. Most of researchers are concerned with the preparation of microspheres via a polymerization process, because various microspheres with required functionalities can be obtained economically at high concentration. This trend can be well understood from a large number of published papers. However, the preparative methods have also been developed for the preformed polymers such as natural, biodegradable, and other special polymers, because the microspheres composed of these polymers are difficult to prepare by a polymerization process. In this chapter, the preparative techniques via polymerization process are described, and a couple of examples on their advances are given. The preparative methods via a polymerization process are mainly divided to emulsion polymerization, soap-free emulsion polymerization, suspension polymerization, dispersion polymerization, precipitation polymerization, microemulsion polymerization, miniemulsion polymerization, and seeded polymerization. The characters of these methods, the size range, and the size distribution of obtained microspheres are shown in Fig. 1. Each polymerization system can be divided into a nucleation process and a growing process of the nuclei. These two Figure 1 56Size and size distribution of microspheres prepared by various polymerization methods. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003064978/05298e18-7827-4b3e-b6a4-6dca83c0c4c6/content/fig3_1.tif/> factors are considered to be the key factors for controlling the size, size distribution, and polymer composition. A detailed discussion on polymerization mechanism will be presented in Sec. II.