Ingredient Profile—Polyquaternium-7

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

Posted: April 5, 2011, from the April 2011 issue of Cosmetics & Toiletries.

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and indicate the ratio of the rate constant for a reactive propagating species adding its own type of monomer (k₁₁ or k₂₂) to the rate constant of its addition to the other monomer (k₁₂ or k₂₁). In the ideal case, r₁ = r₂ ≈ 1, meaning that both monomers M₁ and M₂ will react at similar rates regardless of whether there is an M₁ or M₂ on the growing chain end, and the resulting copolymer will contain a random distribution of the two monomers.

However, if M₁ reacts preferentially over M₂ (i.e., r₁ > 1 and r₂ < 1), more M₁ will be consumed earlier in the reaction. Thus, copolymer chains formed early in the reaction will be rich in M₁ and those formed later in the reaction will be rich in M₂, a phenomenon known as compositional drift. When compositional drift occurs, the resulting copolymer product will be a heterogeneous mixture of individual copolymer chains of varying comonomer composition; such heterogeneity will influence the properties and performance of the copolymer product.

AM-DADMAC copolymerization: For the copolymerization of AM (M₁) and DADMAC (M₂), the reactivity ratios differ by up to two orders of magnitude, with reported values of r₁ = 4.8–7.1 and r₂ = 0.03–0.22.⁸ Thus, if AM and DADMAC are simply mixed and reacted together in a batch copolymerization, significant compositional drift will occur, resulting in a PQ-7 product with a heterogeneous distribution of AM and DADMAC in the copolymer chains. To obtain PQ-7 with a more uniform comonomer distribution, semi-batch copolymerization processes must be employed, wherein the more reactive AM monomer is slowly fed into the copolymerization reaction to ensure uniform consumption of both monomers and a more homogeneous comonomer distribution in the final product (see Figure 4).^{9, 10}

PQ-7 for personal care applications is usually produced via the aqueous solution copolymerization of AM and DADMAC in a semi-batch process like that shown in Figure 4, where AM monomer and initiator are fed continuously into a reactor initially charged with water, DADMAC, a portion of AM, a portion of initiator, and other additives—e.g., chelating agents, pH adjusters, etc. This reaction is conducted in an oxygen-free environment, either under vacuum or nitrogen blanket, at temperatures of 30–60°C and is initiated using common radical initiators such as persulfate salts or water-soluble azo compounds.

A critical step in the process is the monomer-scavenging treatment that occurs following the polymerization. In this step, the PQ-7 solution is treated with excess initiator or other compounds at higher temperatures (70–80°C) to eliminate any unreacted monomer in the product. While the (co)polymers are essentially nontoxic, the unreacted AM monomer is a neurotoxin,3 and only PQ-7 materials with residual levels of less than 10 ppm AM have been indicated as safe by the Cosmetic Ingredient Review expert panel.¹¹ In practice, many suppliers of personal care grade PQ-7 strive to maintain residual AM levels of < 1 ppm to ensure it is virtually undetectable in finished goods.

Properties