| Popis: |
In this mini-review, the effect of random and block copolymerization on crystallization and properties of biodegradable poly(butylene succinate) is outlined. For random copolymerization, the effect of minor co-monomers can be divided into two categories: In most of the cases, the minor co-monomer units will be excluded from the crystal lattice of the major monomer units, which leads to the decreased melting point, lower crystallinity and slower crystallization kinetics. Consequently, the copolymers will be more flexible. Copolymerization with other aliphatic units results in enhanced biodegradation rate, while copolymerization with aromatic units may depress the biodegradation rate. There is an exceptional case, e.g. in poly(butylene succinate-co-butylene fumarate), where the co-monomer units can cocrystallize with the major monomer units in the whole range of copolymer composition, resulting in almost invariant degree of crystallinity. Whether some content of co-monomer units is included in the crystal lattice of the major monomer units or not is still an open question and deserves further study. Furthermore, block copolymerization is an alternative option to tune the properties, which may open a new window for designing biodegradable polymers, especially thermoplastic elastomers. Block and multiblock copolymers combine the properties of the different blocks and the crystallization behavior depends on the block length and miscibility of the blocks. When the block length is large enough, the melting point of such block will not vary much with its content, which is distinctly different from the random copolymers. Incorporation of more hydrophilic blocks, such as aliphatic polyethers will considerably enhance the hydrolytic degradation rate. |
