Distinguishing silicone from modified polyether silicone and identifying polyether defoamer types: A Guide

In the field of fine chemicals, silicone, modified polyether silicone, and polyether defoamers are all widely used surface-active substances, but their compositional structures, performance characteristics, and applicable scenarios differ significantly. Accurately distinguishing between these substances is crucial for optimizing production formulations and improving application effectiveness. This article will systematically elaborate on the core differences between silicone and modified polyether silicone, and detail the classification and identification methods of polyether defoamers, providing technical references for industry applications.

Distinguishing Methods Between Organosilicon and Modified Polyether Silicone

Modified polyether silicone (full name polyether modified silicone) is a composite modification product of silicone and polyether, possessing some advantages of both, and is easily confused with traditional silicone. It can be accurately distinguished from three aspects: component structure, performance characteristics, and identification methods.

(I) Compositional Structure Differences: The Core Demarcation of Essential Attributes

The core component of silicone is siloxane polymer (such as dimethyl silicone oil), with a molecular structure featuring a siloxane bond (Si-O-Si) backbone and hydrophobic groups like methyl groups attached as side chains. It exhibits extreme chemical inertness and does not contain polyether segments. Its molecules are typically hydrophobic, immiscible with water and most organic compounds, and form a dense siloxane cross-linked structure upon curing.

Modified polyether siloxanes are created by incorporating polyether segments (ethylene oxide (EO) and propylene oxide (PO) copolymers) onto the siloxane molecular chain via condensation or addition reactions, forming a "siloxane segment - polyether segment" copolymer structure. The siloxane segment provides high and low temperature resistance and hydrophobicity, while the polyether segment provides hydrophilicity and dispersibility. The molecules possess both hydrophilic and hydrophobic characteristics, and the hydrophilicity/hydrophobicity can be adjusted based on the EO/PO ratio. In short, modified polyether siloxane is an "improved version" of silicone, addressing the shortcomings of traditional silicone, such as poor dispersibility and compatibility, by introducing polyether segments.

(II) Performance Characteristic Differences: Basis for Application Scenario Selection

The performance difference between the two stems directly from their compositional structures, manifesting in the following dimensions:

Hydrophilicity/Hydrophobicity and Compatibility Silicone as a whole exhibits strong hydrophobicity and is difficult to disperse evenly in aqueous systems, requiring emulsifiers to form emulsions for use. It also has poor compatibility with polar systems. Modified silicone polyethers, due to the presence of polyether segments, can be dispersed in both water and oil-based systems, and their compatibility with polar systems such as coatings, inks, and cutting fluids is significantly better than that of silicone.

Defoaming and foam suppressing performance Silicone surfactants exhibit extremely low surface tension, enabling rapid defoaming with minimal dosage, but their foam inhibition persistence is weak and they are prone to failure in high-temperature and strongly acidic environments. Modified polyether siloxanes integrate the rapid defoaming properties of silicones with the long-lasting foam inhibition of polyethers, offering a wider applicable temperature and pH range, and can stably function in systems ranging from 5-150°C and across acidic and alkaline conditions.

Weather resistance and stability Silicone exhibits exceptional weather resistance, resisting UV and ozone degradation, but suffers from low mechanical strength. Modified polyether siloxanes retain the weather resistance of silicone while enhancing tensile strength due to the flexibility of the polyether segments, making them suitable for applications requiring mechanical performance (such as sealants and coating additives).

(III) Practical Identification Methods: Rapid Differentiation in the Laboratory and on Site

Appearance and Solubility Identification At room temperature, traditional silicone defoamers are mostly milky white viscous emulsions (containing emulsifiers), while pure silicone oil is a colorless and transparent oily liquid, insoluble in water and ethanol, and soluble only in a few non-polar solvents. Modified polyether silicones are mostly colorless to pale yellow transparent viscous liquids, partially soluble in water (adjustable according to the EO ratio), and can be uniformly mixed with polar solvents such as ethanol and propylene glycol without stratification. When a small amount of sample is added to water and stirred, the silicone oil will float on the water surface to form an oil film, while the modified polyether silicone can form a uniformly dispersed liquid or a slightly turbid liquid.

Thermal stability test Placing the sample in a 200°C environment for 30 minutes, silicone exhibits strong stability due to the siloxane bond, resulting in minimal weight loss and no noticeable odor, and it maintains its original state after cooling. Modified polyether silicone, however, has weaker high-temperature resistance in its polyether segments, which may undergo slight decomposition accompanied by a small amount of volatile gas, potentially leading to decreased viscosity and color darkening after cooling.

Application Performance Comparison Adding a small amount of silicone to water-based coating systems easily leads to "crawling" and "fish eyes" due to poor compatibility. Modified polyether silicone can be uniformly dispersed without adverse appearance effects, while also providing defoaming and leveling properties. In strong acidic systems (pH≤3), the defoaming effect of silicone significantly diminishes, while modified polyether silicone can still maintain stable defoaming performance.

II. Polyether Defoamer Type Differentiation and Identification Techniques

Polyether defoamers, with ethylene oxide (EO) and propylene oxide (PO) copolymers as their core components, are derived into different types of products by adjusting the initiator type, EO/PO ratio, and segment arrangement. The performance differences are mainly determined by the molecular structure. The following will elaborate on the classification, core differences, and identification methods.

(I) Main Types and Structural Features of Polyether Defoamers

Based on the arrangement of EO/PO in the molecular structure, the type of initiator, and the end-group structure, polyether defoamers are mainly divided into three categories.

Block polyether defoamer Most commonly used basic type, EO and PO are connected in block form, and based on the initiator and segment sequence, they are further divided into two types.

GP型（甘油聚醚）：以甘油为起始剂，先聚合PO形成疏水链段，再聚合EO形成亲水链段，结构为C₃H₅(O-PO)m-(O-EO)n-OH。特点是消泡速度快、浊点较低，温度超过浊点后从水中析出发挥作用，适合高温体系消泡，但抑泡性较弱，又称“消泡型聚醚”。

GPE type (Foamfoe): Also initiated with glycerol, it adopts an "EO-PO-EO" three-segment block structure, with hydrophilic EO segments at both ends and a hydrophobic PO segment in the middle. It has stronger hydrophilicity and can continuously disperse in aqueous systems, exhibiting excellent foam inhibition performance but a slower defoaming speed. It is often used in fermentation, food processing, and other scenarios that require long-lasting foam inhibition, and is also known as "foam inhibition type polyether."

End-capped polyether defoamer Modification of the terminal hydroxyl groups (-OH) of block polyethers with hydrophobic groups such as alkyl or ester groups to reduce water solubility and enhance spreading ability on foam films after structural modification. The defoaming efficiency is more than 30% higher than that of ordinary block polyethers, making it suitable for high-viscosity systems (such as coatings and adhesives).

Fatty acid ester-based polyether defoamer Polyethers and fatty acids undergo esterification to produce substances that possess both the dispersibility of polyethers and the penetrability of esters. They exhibit superior hydrophilic-lipophilic balance, balanced defoaming and foam inhibiting properties, and good compatibility with oily systems, making them suitable for defoaming in oily systems such as inks and lubricating oils.

(II) Core Differences Between Different Types of Polyether Defoamers

Defoaming and foam suppression performance GP type focuses on "rapid defoaming" and is suitable for sudden foam scenarios; GPE type focuses on "long-lasting foam suppression" and is suitable for continuous foaming systems; end-capped defoamers have the best defoaming efficiency, while fatty acid ester types balance defoaming and foam suppression, with a wider range of applications.

Solubility and Suitable System GPE types exhibit the strongest hydrophilicity, are easily soluble in cold water, and are suitable for water-based low-temperature systems. GP types have decreased solubility at high temperatures, making them suitable for high-temperature water-based systems. End-capped and fatty acid ester types exhibit stronger hydrophobicity and are more suitable for oil-based or high-viscosity systems.

Toxicity and Applications GP and GPE types are non-toxic and odorless, making them suitable for industries with high safety requirements such as food fermentation, pharmaceuticals, and cosmetics. End-capped and fatty acid ester types have slightly higher toxicity due to the presence of modified groups, and are mostly used in non-food fields such as industrial coatings and textile printing and dyeing.

(III) Identification Methods for Polyether Defoamer Types

Cloud Point Test (Distinguishing GP Type from GPE Type) Cloud point is a key characteristic of polyether defoamers, referring to the temperature at which the polyether changes from a dissolved state to a cloudy state in water. GP-type polyethers have a lower cloud point (typically 40-60℃), and quickly precipitate above the cloud point, significantly increasing the turbidity of the solution. GPE-type polyethers have a higher cloud point (typically 80-100℃) due to the longer EO segments, and can remain dissolved in the range of room temperature to 70℃. To test, take a 1% sample aqueous solution, slowly heat and observe the change in turbidity, which can quickly distinguish the two.

Contrast method of solubility : Take a small amount of sample and add it to water and white oil separately: GPE type is easily soluble in water and difficult to dissolve in white oil; end-capped type and fatty acid ester type are difficult to dissolve in water and easily soluble in white oil; GP type is partially soluble in cold water, insoluble in hot water (above the cloud point), and slightly soluble in white oil. The type can be preliminarily classified by bidirectional solubility test.

Application Performance Validation In fermentation systems, GPE-type defoamers can continuously suppress foam formation with a slower defoaming speed; GP-type defoamers can quickly eliminate existing foam, but the foam is prone to recurrence. In oil-based coatings, end-capped and fatty acid ester defoamers exhibit stable defoaming effects, while GP-type and GPE-type defoamers may experience stratification and failure due to poor compatibility.

Infrared Spectroscopy (Precise Identification) Infrared spectroscopy can be used to detect characteristic functional group peaks: End-capped polyethers exhibit significantly reduced or absent hydroxyl characteristic peaks in the 3200-3600 cm⁻¹ region due to the blocking of hydroxyl groups; Fatty acid ester-type polyethers show a characteristic ester peak around 1730 cm⁻¹; GP and GPE types can be distinguished by the difference in characteristic peak intensities corresponding to the EO/PO chain segment ratio.

III. Application Recommendations

The core difference between silicone and modified polyether silicone lies in whether or not they contain polyether segments; the former is hydrophobic and highly inert, while the latter is both hydrophilic and hydrophobic with good compatibility. The classification of polyether defoamers is based on the EO/PO arrangement in the molecular structure, end-group modification, and initiator type, with different types corresponding to different defoaming/antifoaming characteristics and suitable systems.

In practical applications, precise selection is necessary based on the needs of the scenario: GPE-type polyether defoamers are preferred for water-based low-temperature systems, while GP-type are chosen for high-temperature sudden foaming scenarios; end-capped polyether defoamers or modified polyether silicones are suitable for oily or high-viscosity systems; for scenarios with high requirements for weather resistance and dispersibility (such as outdoor coatings and precision instrument cleaning), modified polyether silicones are superior to traditional silicones. Through the identification methods described in this article, various substances can be quickly distinguished, avoiding application effects that are less than ideal and cost waste due to incorrect selection.