Ammonio Methacrylate Copolymer

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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Ratio of ethyl acrylate groups to methyl methacrylate groups to trimethylammonioethyl methacrylate groups is about 1:2:0.2 as being Type A or 1:2:0.1 as being Type B. 

Poly(ethyl acrylate, methyl methacrylate, trimethylammonioethyl methacrylate chloride) (1:2:0.2); 

Ethyl acrylate–methyl methacrylate–trimethylammonioethyl methacrylate chloride copolymer (1:2:0.2); 

Poly(ethyl acrylate, methyl methacrylate, trimethylammonioethyl methacrylate chloride) (1:2:0.1); 

Ethyl acrylate–methyl methacrylate–trimethylammonioethyl methacrylate chloride copolymer (1:2:0.1) CAS RN®: 33434-24-1. 

1 DEFINITION 

Ammonio Methacrylate Copolymer is a polymerized copolymer of ethyl acrylate, methyl methacrylate, and a low content of methacrylic acid ester with quaternary ammonium groups (trimethylammonioethyl methacrylate chloride). The Assay requirements differ for the two types as set forth in the accompanying table. 

2 IDENTIFICATION

Change to read: 

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K (CN 1-May-2020) 

B. Meets the requirements of the Assay 

3 ASSAY 

Procedure 

Sample: 1 g of Ammonio Methacrylate Copolymer Type A, or 2 g of Type B, previously dried 

Titrimetric system 

(See Titrimetry 〈541〉.) 

Mode: Direct titration 

Titrant: 0.1 N perchloric acid VS 

Endpoint detection: Potentiometric 

Analysis 

Sample: Sample 

Dissolve the Sample in 75 mL of glacial acetic acid at about 50° within 30 min. After the solution cools down to room temperature, add 25 mL of 0.6% cupric acetate in glacial acetic acid. Titrate this solution and a blank, and make any necessary corrections. Each mL of 0.1 N perchloric acid is equivalent to 20.772 mg of ammonio methacrylate (C₉H₁₈ClNO₂) units. 

Acceptance criteria 

Type A: 8.85%–11.96% 

4 IMPURITIES 

Inorganic Impurities 

Residue on Ignition 〈281〉: NMT 0.1% 

Organic Impurities 

Procedure: Limit of Monomers 

Sodium perchlorate solution: 35 mg/mL of sodium perchlorate (NaClO₄ .H₂O) 

Mobile phase: Dilute phosphoric acid with water to obtain a solution with a pH of 2.0. Mix 4 volumes of this solution with 1 volume of methanol. 

Standard stock solution: 1.6 mg/mL of ethyl acrylate and 0.2 mg/mL of methyl methacrylate in methanol 

Standard solution: Dilute 1 mL of the Standard stock solution with methanol to 100 mL. Add 10 mL of this solution to 5 mL of the Sodium perchlorate solution. This solution contains about 10.67 µg/mL of ethyl acrylate and 1.33 µg/mL of methyl methacrylate. Sample solution: Dissolve 5 g of Ammonio Methacrylate Copolymer in methanol, and dilute with the same solvent to 50 mL. Add 5 mL of the Sodium perchlorate solution dropwise to 10 mL of this solution while continuously stirring. Remove the precipitated polymer by centrifugation. Use the clear supernatant. Calculate the concentration of Ammonio Methacrylate Copolymer, in mg/mL, as C . U 

Chromatographic system 

(See Chromatography 〈621〉, System Suitability.) 

Mode: LC 

Detector: UV 202 nm 

Column: 4.6-mm × 12-cm; packing L1 

Flow rate: 2 mL/min 

Injection size: 50 µL 

System suitability 

Sample: Standard solution 

[Note—The relative retention times for ethyl acrylate and methyl methacrylate are 1.00 and 1.14, respectively.] 

Suitability requirements 

Resolution: NLT 1.0 between the pair of analytes 

Relative standard deviation: NMT 5.0% for each analyte 

Analysis 

Samples: Standard solution and Sample solution 

Calculate the percentage of ethyl acrylate (or methyl methacrylate) in the portion of Ammonio Methacrylate Copolymer taken: 

Result = (r_U/r_S) × (C_S/C_U) × F × 100 

r_U = peak response of ethyl acrylate (or methyl methacrylate) from the Sample solution 

r_S = peak response of ethyl acrylate (or methyl methacrylate) from the Standard solution

C_S = concentration of ethyl acrylate (or methyl methacrylate) in the Standard solution (µg/mL) 

C_U = concentration of Ammonio Methacrylate Copolymer in the Sample solution (mg/mL) 

F = conversion factor, 10-3 mg/µg 

Acceptance criteria 

Ethyl acrylate: NMT 100 ppm 

Methyl methacrylate: NMT 50 ppm 

5 SPECIFIC TESTS 

Loss on Drying 〈731〉: Dry a sample in a vacuum at 80° for 5 h: it loses NMT 3.0% of its weight. 

Viscosity—Rotational Methods 〈912〉 

Sample solution: Place 52.5 g of isopropyl alcohol and 35.0 g of acetone in a conical ask with a ground-glass joint. Add a quantity of Ammonio Methacrylate Copolymer, equivalent to 12.5 g of solids on the dried basis, while stirring until the polymer has dissolved completely. 

Analysis: Equip a suitable rotational viscometer with an adapter comprising a cylindrical spindle rotating within an accurately machined chamber (or tube).1 Pipet the Sample solution in the specied volume, which is recommended by the instrument manufacturer, into the chamber (or tube), and ensure that the temperature of the test specimen is at 20 ± 0.1°. The cylindrical spindle rotates at the value of rpm, which corresponds to a rate of shear of approximately 37 s−1.2 Measure the apparent viscosity following the instrument manufacturer’s directions. 

Acceptance criteria: 1–15 mPa · s 

6 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in tight containers, and store at a temperature not exceeding 30°. 

Labeling: Label it to state whether it is Type A or Type B. 

USP Reference Standards 〈11〉 

USP Ammonio Methacrylate Copolymer, Type A RS 

Poly(ethyl acrylate, methyl methacrylate, trimethylammonioethyl methacrylate chloride) (1:2:0.2); 

Ethyl acrylate–methyl methacrylate–trimethylammonioethyl methacrylate chloride copolymer (1:2:0.2). 

USP Ammonio Methacrylate Copolymer, Type B RS 

Poly(ethyl acrylate, methyl methacrylate, trimethylammonioethyl methacrylate chloride) (1:2:0.1); 

Ethyl acrylate–methyl methacrylate–trimethylammonioethyl methacrylate chloride copolymer (1:2:0.1). 

¹ A commercial device is available from Brookeld as an ultra-low (UL) viscosity adapter. The adapter comprises a 0.4-cm diameter shaft, an accurately machined chamber (or tube) with an internal diameter of 2.8 cm and a depth of 13.5 cm, and a cylindrical spindle 2.5 cm in diameter and 9.1 cm in height. 

² For the Brookeld UL adapter, the cylindrical spindle rotates at 30 rpm, which corresponds to a rate of shear of approximately 37 s−1.