Siloxanes and Silicones, di-Me, Bu group- and 3-(2-hydroxyethoxy)propyl group-terminated
[CAS 207308-30-3]

Identification

• Classification: Chemical pesticide >> Plant growth regulator
• Name: Siloxanes and Silicones, di-Me, Bu group- and 3-(2-hydroxyethoxy)propyl group-terminated
• CAS Registry Number: 207308-30-3
• EC Number: 805-011-1

chemBlink Chemical Story

Siloxanes and Silicones, di-Me, Bu group- and 3-(2-hydroxyethoxy)propyl group-terminated, identified by CAS Registry Number 207308-30-3, is more commonly described as an asymmetric monocarbinol-terminated polydimethylsiloxane. It consists of a polydimethylsiloxane chain carrying a nonreactive butyl group at one end and a hydroxyalkyl ether group at the other. Unlike an ordinary silicone fluid, it therefore combines the characteristic surface properties of polydimethylsiloxane with a terminal hydroxyl group capable of participating in further chemical reactions.

The substance is best regarded as a polymeric material rather than a single molecular species. Commercial grades may differ in chain length, average molecular weight, hydroxyl content, and viscosity. Consequently, a single molecular formula or molecular weight cannot reliably describe every material sold under this CAS number. This variability is not an impurity in the conventional sense but an inherent feature of functional silicone polymers, whose properties are commonly specified by viscosity and average molecular weight rather than by one exact molecular structure. Commercial examples include grades ranging from relatively low-viscosity liquids to products with average molecular weights of several thousand.

The development of carbinol-functional silicones arose from a central challenge in silicone chemistry. Polydimethylsiloxane possesses low surface energy, excellent flexibility, water repellency, thermal stability, and resistance to weathering. These properties make silicone fluids valuable as lubricants, release agents, antifoams, and surface modifiers. Conventional trimethylsiloxy-terminated silicone oils, however, are largely nonreactive and may migrate, separate, or gradually be lost from an organic polymer matrix.

Introducing a terminal organic hydroxyl group offers a way to overcome this limitation. The hydroxyl group can react with isocyanates, anhydrides, epoxides, or other resin-forming reagents, while the siloxane chain retains its characteristic flexibility and low surface energy. Monocarbinol-terminated polydimethylsiloxanes can consequently be incorporated into polyurethane, polyester, acrylic, and related polymer systems instead of merely being dispersed as unbound silicone oil.

The asymmetric structure is particularly useful. Because only one end of the silicone chain is reactive, the molecule can behave as a chain terminator, pendant modifier, or surface-active segment rather than as a difunctional crosslinker. The butyl-terminated end remains chemically inactive, while the hydroxyethoxypropyl end provides a connection to the organic resin. This controlled functionality allows formulators to introduce silicone characteristics without necessarily producing an extensively crosslinked siloxane network.

One important application is the modification of polyurethane coatings and dispersions. Incorporation of polydimethylsiloxane segments can lower surface energy, improve water resistance, reduce adhesion of contaminants, and impart slip or release properties. Reviews of PDMS-modified waterborne polyurethanes describe silicone modification as a practical method for improving several surface and durability characteristics of polyurethane films. Patented coating systems have specifically used monocarbinol-terminated PDMS to create amphiphilic siloxane-polyurethane materials in which silicone-rich segments preferentially migrate toward the coating surface.

This surface migration can be advantageous in fouling-release, easy-clean, ice-release, lubricious, and water-repellent coatings. The polyurethane or other organic resin supplies adhesion and mechanical strength, while the silicone segment modifies the outermost surface. Patents have described monocarbinol-terminated PDMS in coatings intended to reduce biological fouling, liquid adhesion, and ice accumulation, demonstrating how a relatively small amount of functional silicone can alter interfacial behavior.

Related hydroxy-functional silicones are also used as reactive resin modifiers, paint additives, and mold-release components. Their value lies not in one narrowly defined end use but in their ability to connect two chemically different material families: organic polymers, which generally provide strength and adhesion, and silicones, which provide flexibility, low friction, weather resistance, and low surface energy.

CAS 207308-30-3 therefore represents an important class of modern functional polymers rather than a conventional pure compound. Its scientific and industrial significance comes from molecular end-group design. By placing one reactive alcohol group at the end of an otherwise low-reactivity silicone chain, chemists created a material that can become chemically integrated into coatings and resins while retaining the distinctive interfacial properties of polydimethylsiloxane. It is a clear example of how a small modification at a polymer chain end can fundamentally change the way an entire material is processed and used.

References

1. Gelest, Inc. monoCARBINOL TERMINATED POLYDIMETHYLSILOXANE, asymmetric, product information for CAS 207308-30-3.

2. Ji, X. et al. (2017) “Progress in polydimethylsiloxane-modified waterborne polyurethane,” RSC Advances, 7, pp. 34086–34095.

3. Amphiphilic Siloxane-Polyurethane Fouling-Release Coatings, United States patent application US 2021/0348021 A1.