Anchoring group design of polymer dispersants: How to improve the dispersion stability of titanium dioxide through block copolymers?

Titanium dioxide is the core raw material in the field of coating and ink, and its dispersion stability directly affects the covering power, gloss and weather resistance of the coating. However, the surface of titanium dioxide particles is highly polar and easy to agglomerate, which makes it very difficult to disperse in non-polar systems. The block copolymer dispersant has become the key technology to solve this problem through the synergistic interaction between the anchoring group and the solvation chain. The following is an in-depth analysis from molecular design to application effect:

(1) Strong combination of anchoring groups and titanium dioxide surface

The anchoring group of the block copolymer is adsorbed on the surface of titanium dioxide through multiple mechanisms such as ionic bond, hydrogen bond and polarity:

1. Acid group optimization: carboxylic acid (-COOH), sulfonic acid (-SO3H) and other groups can form stable coordination with the hydroxyl group on the surface of titanium dioxide, and experiments show that the dispersant containing sulfonic acid group can increase the adsorption energy by more than 40%.

2.Block structure design: ABA-type structure (such as polyacrylate-B-polystyrene-B-polyacrylic acid) is used, the middle hydrophobic section enhances the compatibility with the organic system, and the hydrophilic sections at both ends strengthen the anchoring-effect.

3. Dynamic adsorption verification: Through atomic force microscopy (AFM) observation, it was found that the adsorption layer thickness of block copolymers on the surface of titanium dioxide can reach 5-8nm, far exceeding the 1-2nm of traditional dispersants.

(2) the three-dimensional barrier effect of the solvation chain

The solvation chain of block copolymers maintains dispersion stability through steric hindrance and entropy repulsion effects:

1. Chain length control: the molecular weight of polyether (such as PEO) or polyester chain segment needs to be controlled in the 5000-20000 range, too short is insufficient steric resistance, too long is easy to lead to chain folding.

2. Responsive design: The introduction of temperature-sensitive chain segments (such as polyn-isopropylacrylamide) triggers the contraction of the chain segments during the coating drying process to form a dense protective layer.

3. Quantitative verification: laser particle size meter test shows that the titanium dioxide paste dispersed by block copolymer has a particle size growth rate of less than 5% after 30 days of storage, while the traditional dispersant system reaches 20%.

(3)Precise regulation of RAFT polymerization technology

With reversible addition-break chain transfer (RAFT) polymerization, precise control of block structure is possible:

1. Narrowing of molecular weight distribution: PDI (polydispersion index) can be controlled at 1.1-1.3 to ensure the consistency of performance of different batches of dispersants.

2. Functional group positioning: anchoring groups (such as maleic anhydride) are introduced in the polymerization process, so that each chain segment contains 3-5 active adsorption points.

3. Industrial case: A company uses the dispersant produced by RAFT method to increase the dispersion efficiency of titanium dioxide in alkyd resin by 200% and shorten the grinding time from 8 hours to 2.5 hours.

(4) Application effect and industry verification

1. Performance improvement data:

Coverage ratio increased from 0.92 to 0.98 (GB/T 9755 standard) 50% solid slurry viscosity reduction from 2500mPa·s to 800mPa·s (Brookfield Viscometer test)

2. Environmental compliance: does not contain APEO and meets the SVHC list requirements of REACH regulations.

Conclusion and action guide

Block copolymer dispersants break through the traditional technical bottleneck through molecular design, and have become the standard choice for high-end coatings and ink formulations. Contact engineers for a customized dispersant solution.