Introduction

Biodegradable polymer materials are a class of polymer compounds that can be catabolized into CO₂ and H₂O under the action of microorganisms, enzymes or chemicals.^[1] Biodegradable AB block copolymers are biodegradable polymers that have hydrophobic chains and hydrophilic chains in their molecular structure. In recent years, biodegradable AB block copolymers have attracted more and more attention from polymer materials scientists, especially as new drug carriers with broad application prospects. The physical and chemical properties of block copolymers can be adjusted by adjusting the ratio of block composition. For example, changing the ratio of the hydrophilic segment to the hydrophobic segment of the polymer, or modifying new blocks that meet the requirements through functional groups at the end of the polymer, so that they are more biodegradable and have good biocompatibility.

The synthesis methods of biodegradable AB block copolymers mainly include anionic catalyzed ring-opening polymerization, cationic ring-opening polymerization and coordination polymerization. Currently, the most commonly used method is tin catalyst ring-opening polymerization of lactone and lactide coordination ring-opening polymerization to obtain amphiphilic AB block copolymers. For example, Zheng et al. used stannous octoate as a catalyst, and methoxy polyethylene glycol (PEG), dihydroxy-terminated PEG and 2-ethylene glycol methoxy polyethylene glycol as initiators to initiate the ring-opening polymerization of caprolactone (CL) at 130 °C to obtain PCL-PEG diblock copolymers.^[2]

Characteristics

It has been found that the self-assembly of biodegradable amphiphilic AB block copolymers in selected solvents can form micelles or micellar aggregates of various morphologies and structures. Polymer morphology is an important factor affecting the physicochemical properties of micellar aggregates. The different surface areas and anisotropy of micellar aggregates with different morphologies affect their applications. So far, polymer scientists have used block copolymers to prepare micelles of various shapes, such as spheres, rods, bubbles, hollows, tubes, worms, flowers, etc.^[3]

Fig. 1. Several typical self-assembly forms of block copolymers: (A) spherical (B) vesicles (C) rod-like (D) ring (E) worm (F) flower-like (J. Am. Chem. Soc. 2007, 129(5): 1113-1121).

Application

Biodegradable AB block copolymers are widely used in pharmaceutical industry, agriculture, etc.

• Pharmaceutical Industry

Biodegradable AB block copolymers are useful as drug release carrier materials in the pharmaceutical industry. As a drug carrier, the biodegradable AB block polymer can release the drug to a specific part of the body with the maximum load, then degrade into non-toxic substances, and finally metabolize it out of the body through its own metabolism. Biodegradable AB block copolymers have been used to deliver anticancer drugs by encapsulating them in polymers and adding targeting agents to reduce their toxicity to healthy cells.

• Agriculture

Biodegradable AB block copolymers are also widely used in agriculture, such as mulch film, greenhouse, silage packaging, etc. Biodegradable polymer materials have little environmental pollution and are conducive to the development of green agriculture. In recent years, many new types of degradable mulch have emerged, such as photodegradable mulch and biodegradable mulch, which are made of biodegradable polymer materials and have been widely used in agricultural production.

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References

1. Anal, A.K. et al. Ionotropic cross-linked chitosan microspheres for controlled release of ampicillin. International Journal of Pharmaceutics. 2006, 312(1-2): 166-173.
2. Zheng, Y. et al. pH- and temperature-sensitive PCL-grafted poly(beta-amino ester)-poly(ethylene glycol)-poly(beta-amino ester) copolymer hydrogels. Macromolecular Research. 2010, 18(11): 1096-1102.
3. Bhargava, P. et al. Temperature-induced reversible morphological changes of polystyrene-block-poly(ethylene oxide) micelles in solution. J Am Chem Soc. 2007, 129(5): 1113-1121.