Nanosized Amorphous Calcium Carbonate Stabilized by Poly(ethylene oxide)-b-poly(acrylic acid) Block Copolymers

Abstract

Particles of amorphous calcium carbonate (ACC), formed in situ from calcium chloride by the slow release of carbon dioxide by alkaline hydrolysis of dimethyl carbonate in water, are stabilized against coalescence in the presence of very small amounts of double hydrophilic block copolymers (DHBCs) composed of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) blocks. Under optimized conditions, spherical particles of ACC with diameters less than 100 nm and narrow size distribution are obtained at a concentration of only 3 ppm of PEO-b-PAA as additive. Equivalent triblock or star DHBCs are compared to diblock copolymers. The results are interpreted assuming an interaction of the PAA blocks with the surface of the liquid droplets of the concentrated CaCO3 phase, formed by phase separation from the initially homogeneous reaction mixture. The adsorption layer of the block copolymer protects the liquid precursor of ACC from coalescence and/or coagulation.

The Effect of Additives on Amorphous Calcium Carbonate (ACC): Janus Behavior in Solution and the Solid State

“…[ 9 ] The small molecules phosphoenolpyruvate and 3-phosphoglycerate, which are intermediates of the glycolic pathway, have also been found to be important in stabilizing ACC in the exoskeleton and gastroliths of crustaceans. [ 10 ] Taking inspiration from this strategy, highly carboxylated species including poly(acrylic acid), [ 11 ] a poly(ethylene oxide)-block -poly(acrylic acid) block copolymer, [ 12 ] and poly(aspartic acid) [ 7 , 13 ] have been widely used to extend the lifetime of synthetic ACC in solution, as have magnesium [ 14 , 15 ] and phosphate ions. [ 16 ] Other effective species have included poly(allylamine hydrochloride) (PAH), [ 17 ] poly(styrene sulphonate), [ 11 ] ovalbumin, [ 18 ] and silicate.…”

Solubility and bioavailability of stabilized amorphous calcium carbonate

“…(6) Several techniques have been reported for the synthesis and stabilization of ACC, (4,7) but all known methods use either toxic materials or various organic polymers to stabilize ACC for more than 3 days. (7)(8)(9)(10)(11) To avoid use of such compounds, a novel method for synthetic production of stabilized ACC using phosphoaminoacids was developed recently (12) and was shown to stabilize ACC for more than 4 months under ambient conditions.…”

Nanostructured silica templated by double hydrophilic block copolymers with a comb-like architecture

“…Moreover, the PAA-b-PAMPEO copolymer is here synthesized quickly by using only one polymerization technique, the RAFT (Reversible Addition Fragmentation chain Transfer) polymerization for the two polymeric blocks and it is easy to control the size of the two blocks separately [21]. In comparison, the synthesis of PAA-b-PEO block copolymers was reported in the literature by either anionic polymerization [22][23][24] or atom transfer radical polymerization (ATRP) [25,26]. The anionic pathway is time consuming, because AA cannot be polymerized without protection.…”