Ingredient Profile: Polyquaternium-6

By: Michael J. Fevola, PhD, Johnson & Johnson Consumer and Personal Products Worldwide

Posted: March 2, 2011, from the March 2011 issue of Cosmetics & Toiletries.

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For more than two decades, DADMAC and other diallyl quaternary ammonium monomers were believed to form a thermodynamically favored, six-membered ring during cyclo-polymerization; however, as modern structural determination techniques such as carbon-13 nuclear magnetic resonance (¹³C NMR) spectroscopy became more accessible in the 1970s, it was proven that these monomers instead form a kinetically favored five-membered ring.² The five-membered ring forms because DADMAC chain propagation occurs rapidly. The growing polymer chain adds across the first C=C bond of the monomer, then quickly adds across the second C=C bond, “locking” the five-membered ring in place before the second allyl group can adopt the conformation required to close the repeat unit as the less strained six-membered ring.

Properties

PQ-6 is typically supplied as a pale yellow, transparent aqueous solution with a neutral to slightly acidic pH and mild aldehydic odor.^{2, 8–10} Most grades supplied to the personal care industry are ca. 40% active polymer solids and have solution viscosities of 7,000–12,000 cP, although the exact solution viscosity of the raw material will depend on polymer molecular weight and concentration. Solutions of PQ-6 are expected to contain residual DADMAC monomer (typical levels of up to 1.5% w/w are possible⁹), NaCl, and by-products of polymerization initiators such as sulfate salts from the decomposition of persulfate initiators.

Applications

The primary industrial applications of PQ-6 are as separation aids in water treatment and mining processes and as additives in paper and textile manufacturing. In the personal care industry, it may be employed as a conditioning agent in rinse-off and leave-on formulations for hair and skin care applications. Most commonly, PQ-6 is found in hair care where it provides lubricity and softness to improve wet and dry combing, reduce static charge buildup, and aid in film formation and style retention. Due to its exceptional chemical stability, PQ-6 is especially preferred for use in high pH and/or highly oxidative formulations such as bleaches, dyes, relaxers and permanent waving products.

Formulation Guidelines

Recommended use levels of active PQ-6 typically range from 0.2–1.2% w/w. Due to its relatively high cationic charge density, PQ-6 readily forms strong physical complexes with anionic surfactants and anionic polymers; therefore, special care must be taken when combining PQ-6 with such ingredients to prevent the formation of insoluble precipitates during processing. To solubilize PQ-6 in the presence of anionic surfactants, either a large excess of anionic surfactant is required, or amphoteric, betaine or nonionic secondary surfactants must be added to the formulation. High loads of secondary surfactants are especially necessary when formulating clear liquid cleansers with PQ-6.

PQ-6 should never be combined directly with solutions of anionic polymers or concentrated anionic surfactants. Instead, commercial PQ-6 solutions are preferably pre-diluted with water and added to formulations following the addition and complete dissolution of all other polymers and surfactants. The portion of the water used to pre-dilute PQ-6 will depend on the level of PQ-6 in the formulation, but it typically is about 5–10 times the % w/w of PQ-6 solution being added to the batch. Alternatively, PQ-6 may be added up front to the water phase when there are no anionic polymers, e.g. thickeners, or anionic surfactants that require dissolution first.