Table 4.

Comparison of polymerization methods for the synthesis of molecularly imprinted polymers

Method of imprinting	Principle	Advantages	Disadvantages
Bulk polymerization	Functional monomers, templates, initiators, crosslinking agents are uniformly mixed in a certain ratio in a non-polar solvent and sealed in a vacuum for crosslinking polymerization. The resulting bulk polymer is then subjected to crushing and sieving so that the template molecule can be removed from the polymer	Simplicity in synthesis; no requirement for expensive or sophisticated instrumentation; high purity of the produced molecularly imprinted polymers	Low performance; difficulty in template elution; irregular particle in size and shape; time-consuming; fewer binding sites
In-situ polymerization	The synthesis of molecularly imprinted polymers is conducted directly in the column by simple polymerization	In-situ preparation, one-step; continuity and uniformity; good porosity; rapid response to the template is assured	Poor selectivity; slow flow rate; short service life; high column pressure; extensive optimization is required for each new template system
Precipitation polymerization	The precursors are dissolved in a suitable solvent for reactive polymerization and the Molecularly imprinted polymers precipitate out of the reaction system after the formation of solid microspheres that are insoluble in the reaction medium	Imprinted microspheres with uniform size and large specific surface area; high performance; single preparative step	A large amount of template and solvents; high dilution factor; high requirements for solvent viscosity
Suspension polymerization	The reaction precursors, including functional monomers, templates, porogens, cross-linkers, and other substances, dissolved in the selected solvent, followed by the addition of the dispersant. The mixture is further sealed and stirred at high speed	Uniform spherical particles; large scale assembly possible; high reproducibility	Long preparation period; big particle size; specialist surfactant polymers required; poor recognition; the presence of a surfactant and a stabilizer is mandatory
Emulsion polymerization	The template, cross-linker, and functional monomer are first emulsified in water, followed by the addition of stabilizers to the disperse phase to eliminate diffusion in the continuous phase	Uniform particle size; the abundance of binding sites on the molecularly imprinted polymer surface	Complex and expensive synthesis; low purity of the products
Surface imprinting polymerization	Functional monomers are attached to the surface of the matrix carriers (e. g. SiO2, carbon dots, carbon nanotubes, metal–organic framework) by suitable techniques such as chelation or grafting. Then the template is introduced to the monomer to form a pre-polymerization complex, which is further cross-linked on the matrix carrier surface in the presence of the initiator, forming surface molecularly imprinted polymer	Easy to prepare; large imprinted surface; abundant binding sites; controlled size and shape; good reproducibility; high selectivity and sensitivity	The limited yield on large scale preparation
Sol–gel polymerization	Inorganic precursor and template molecules are dissolved in low molecular weight solvent, and the gel is formed by hydrolysis (water) and condensation polymerization	Eco-friendly reaction solvent; good thermal and chemical stability; simple preparation under mild operating conditions;	The difficulty in forming porous silicon; lack of polymerization method and the functional monomer; low sensitivity; the need for high pH hydrolysis