Reactive Polydimethylsiloxanes

Introduction to Reactive Polydimethylsiloxanes (Silicones)

Polydimethylsiloxanes Chemical Structure
Fig­ure 1: Chem­i­cal Struc­ture of Polydimethylsiloxanes

Reac­tive poly­di­methyl­silox­anes, or RPDMS (Reac­tive Sil­i­cones), are a new class of sil­i­cone poly­mers with dis­tinct char­ac­ter­is­tics that are gain­ing increas­ing fame in a wide range of indus­tri­al appli­ca­tions. PDMSs have inter­est­ing prop­er­ties includ­ing low sur­face ener­gy, bio­com­pat­i­bil­i­ty, high ther­mal and oxida­tive sta­bil­i­ty as well as good water resis­tance. RPDMS are more ver­sa­tile and func­tion­al than typ­i­cal poly­di­methyl­silox­anes (PDMS) since they go through mul­ti­ple chem­i­cal reac­tions instead of just one.

Explaining the PDMS Functional Groups

Reac­tive Sil­i­cones are char­ac­ter­ized by the pres­ence of func­tion­al groups that enable chem­i­cal reac­tiv­i­ty. Com­mon reac­tive groups include vinyl, epoxy, amino, and hydrosi­lane func­tion­al­i­ties. Oth­er func­tion­al groups such a amino, hydroxy, and methacry­loxy are also known for their prop­er­ties as raw mate­ri­als. These three func­tion­al groups, avail­able through our Reac­tive Sil­i­cones port­fo­lio, have spe­cif­ic com­pat­i­bil­i­ty with var­i­ous mate­ri­als (Fig­ure 2).

Reactive Silicone Functional Groups with compatibility to different materials
Fig­ure 2. Reac­tive Sil­i­cone Func­tion­al Groups with com­pat­i­bil­i­ty to dif­fer­ent materials

The simul­ta­ne­ous pres­ence of pen­dant organ­ic groups attached to an inor­gan­ic back­bone gives sil­i­cones their unique com­bi­na­tion of phys­i­cal, chem­i­cal, and mechan­i­cal prop­er­ties. The low sur­face ten­sion of liq­uid PDMS results from a com­bi­na­tion of the prop­er­ties of organ­ic side groups (reac­tive) com­bined with the inor­gan­ic back­bone (silox­ane chains).

The methyl groups are able to close­ly pack at the sur­face due to their low inter­mol­e­c­u­lar forces and the large Si-O-Si bond angle as seen in Fig­ure 3A & 3B. The low crit­i­cal sur­face ten­sion of wet­ting of PDMS read­i­ly explains one of the most com­mon fea­tures of sil­i­cone poly­mers: their excel­lent low adhe­sion which pre­vents most mate­ri­als from strong­ly adher­ing to them. Con­verse­ly, their low sur­face ten­sion means that they can wet almost all sur­faces, thus ful­fill­ing the first require­ment of any adhe­sive sys­tem.

Anoth­er inter­est­ing con­se­quence of the prop­er­ties of the silox­ane bond, is the val­ue of n in the com­mon lin­ear trimethyl­siloxy-end­blocked-PDMS, (M‑DIl‑M) which can vary from zero to tens of thou­sands giv­ing a range of vis­cos­i­ty from 0.65 to 2,500,000 cen­tipoise to the poly­mer­ic mate­r­i­al. This rela­tion­ship between vis­cos­i­ty and poly­mer chain length allows PDMS poly­mers to vary in form from ‘water-like’ flu­ids to a flow­able gum which helps with filler dis­per­sion, while retain­ing the same chem­i­cal char­ac­ter. The length of the poly­mer chain is direct­ly pro­por­tion­al to its mol­e­c­u­lar weight. The FM Bi & Mono ter­mi­nal series of JNC’s Reac­tive Sil­i­cones offer a vari­ety of poly­mer length chains, rang­ing from a mol­e­c­u­lar weight (MW) of 1000 up to 15000, to cater to the needs of any appli­ca­tion that needs vis­cos­i­ty adjustment.

Chemically Reactive Functional Silicones

Reactive Silicone: FM-0815J Chemical Structure with Alkoxysilyl Reactive Group

Sila­plane FM-0815J is a monoter­mi­nal type reac­tive sil­i­cone with an Alkoxysi­lyl func­tion­al group. Unlike the oth­er FM prod­ucts, where filler dis­per­sion prop­er­ties only rely on the phys­i­cal bond between the reac­tive group and fillers, FM 0815J’s silox­ane chains and alkoxysi­lyl groups have the abil­i­ty to chem­i­cal­ly bond to the sur­face of the inor­gan­ic filler thus sta­bi­liz­ing the filler dis­per­sion. They are also effec­tive in reduc­ing the vis­cos­i­ty of filler dis­per­sion bet­ter than silane cou­pling agents.

Common Reactive Silicone properties

Anoth­er impor­tant prop­er­ty of sil­i­cones, and one that is par­tic­u­lar­ly rel­e­vant to adhe­sion appli­ca­tions, is their high ther­mal sta­bil­i­ty com­pared to com­mon organ­ic poly­mers. This sta­bil­i­ty towards ther­mal ener­gy opens a new win­dow of oppor­tu­ni­ties for sil­i­cone adhesives. 

Sil­i­cones are also able to build reac­tiv­i­ty on the poly­mer. This allows the build­ing of cured sil­i­cone net­works of con­trolled mol­e­c­u­lar archi­tec­tures with spe­cif­ic adhe­sion prop­er­ties while main­tain­ing the inher­ent phys­i­cal prop­er­ties of the PDMS chains. The com­bi­na­tion of the unique bulk char­ac­ter­is­tics of the sil­i­cone net­works, sur­face prop­er­ties of the PDMS seg­ments, and the speci­fici­ty and con­trol­la­bil­i­ty of the reac­tive groups, pro­duces unique mate­ri­als use­ful as adhe­sives, pro­tec­tive encap­su­lants, coat­ings and sealants.

Over­all, reac­tive sil­i­cones are an essen­tial ingre­di­ent in many prod­ucts such as adhe­sives, sealants and Ther­mal inter­face mate­ri­als, in which their chem­i­cal and phys­i­cal prop­er­ties con­tribute to the pro­duc­t’s per­for­mance. They are main­ly used as a blend­ing ingre­di­ent to improve the flowa­bil­i­ty, filler con­tent and adhe­sion of spe­cial­ty prod­ucts. Aside from the adhe­sive indus­try appli­ca­tion, reac­tive sil­i­cones’ prop­er­ties are also start­ing to be rec­og­nized as a raw mate­r­i­al at the cos­met­ic indus­try .

We sup­port a wide prod­uct range of reac­tive sil­i­cones with mul­ti­ple mol­e­c­u­lar weights and vis­cosi­ties. We can also cus­tomize new grades of mate­ri­als after con­sul­ta­tion with our R&D depart­ment. Take the next step toward mate­r­i­al excel­lence and devel­op­ment – reach out to our team today. 

About Darlene Pudolin

Darlene Pudolin is one of CAPLINQ's Application Engineers specializes in Thermal Interface Materials, Fine & Specialty Chemicals, and Soldering Materials within the company's Technical Marketing unit. Darlene recently joined CAPLINQ in early 2023 but has been an experienced materials quality engineer for 5+ years. She has a broad range of experience in materials solution from Thermal Interface Materials, Cement Chemistry, and Hydrogen Renewable Technology. With a long history of serving customers in Industrial and Research academe, Darlene is passionate on driving solutions about troubleshooting points that best fit the market requirements. Based in the Philippines, Darlene holds a Bachelor's degree in Chemical Engineering from Mapua University and currently doing her Master's degree in Energy Engineering at University of the Philippines Diliman.

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