Polysiloxanes

Contact lenses are one of the most successful biomaterials in history with a global market estimated to be worth over $17 billion in 2025. Silicone hydrogel contact lenses dominate the market and are complex biphasic biomaterials with several critical material properties needed for clinical use. Careful consideration of composition and chemistry is needed to identify formulations of lenses meeting all commercial standards with the potential for improved manufacturability, cost, and/or next generation use. Four silicone macromers were investigated in this work with varying symmetry of siloxane units and macromer structure, number of siloxane groups, branching, length, and concentration. Novel silicone hydrogel lenses were produced and evaluated for optical transmittance, elastic modulus, oxygen transmissibility, water content, and surface wettability. Several lenses met commercial standards and demonstrated an increase in oxygen permeability (Dk) and inverse relationship with elastic modulus and siloxane concentration, respectively. A hydrophobic/hydrophilic ratio below 1.4 was needed for a co‐continuous water phase. Substitution of methoxypropyl groups for butyl groups increased hydrophobic microdomains leading to decreased optical quality and mechanical properties. Generally, fluorine‐containing silicone macromers allowed for a wider range of successful compositions, and above a certain hydrophilic composition, the presence of trifluoropropyl groups resulted in improved solubility and optically clear lenses. Data also showed asymmetric siloxane macromers have potential to meet critical lens properties at lower overall siloxane content. New lens materials with wider composition ranges meeting all clinical lens properties is a significant challenge and may significantly expand the field.

Silicone elastomers with elongations approaching 5000% are now available. These elongations are nearly 4 times greater than any commercial elastomer. The new elastomers utilize a cure mechanism which generates elastomeric properties by driving linear polymers to extremely high molecular weights with concomitant formation of intra-chain and inter-chain entanglements rather than covalent cross-linking. When elastomers have elongations significantly above 1500%, they exhibit behavior that is readily differentiated from conventional elastomers .  Tear propagation mechanisms are altered and tear failure occurs at radically greater elongations.  The polymer chemistry relies upon step-growth polymerization of heterobifunctional siloxane macromers produced by anionic ring-opening polymerization.

Ring opening polymerization (ROP) of hexamethylcyclotrisiloxane (D 3) and octamethylcyclotetrasiloxane (D 4) was promoted by acid-treated synthetic and natural silica-aluminates. Silica-alumina (1:3 Si/Al molar ratio) was obtained using a simple and economic route from precipitation of aluminum sulfate solutions. The material was treated in an acidic medium to improve the content of acid sites and successfully tested as inorganic acidic catalyst for ROP of D 3 or D 4 cyclosiloxanes. Natural bentonite was treated and used in a similar manner. Once the ROP reaction completed, the catalyst was easily removed and it was found that the recovered synthetic silica-alumina was active in a second ROP reaction. The effect of the concentration and type of catalyst in respect to the molecular weight and polydispersity of polydimethylsiloxanes was analyzed: increasing the amount of silica-alumina in ROP of D 4 from 0.05 to 0.1 g decreased the average molecular weight (M n = 13–1.8 kDa) associated with an increase in the polydispersity (2.95 vs. 1.81). Analogous results were found with bentonite. These values suggest that an increase in the catalyst concentration led to a lower M n , with a more homogeneous molecular chain dimension.

Today's focus on hybrid organic-inorganic polymers is yielding many new materials. Although polydimethylsiloxanes (Dimethicones) and their many organic derivatives have been used extensively in the cosmetic industry, no polysiloxanes without methyl substitution have been developed for personal care. The Dimethicones are characterized by their ability to improve slip, increase lubricity, reduce tack, and impart water repellency in all types of cosmetic formulations. The insolubility of many surfactants, emollient oils, and waxes in the Dimethicone causes formulation difficulties and restricts the amount of Dimethicone that an be incorporated into a product.

New high complex polymeric structures containing metal chelate sequences alternating, through esteric bridges, with silane units were obtained. The azomethine of 2,4-dihydroxybenzaldehyde with 1,3-bis(aminopropyl)tetramethyldisiloxane has been synthesized and in situ complexed with copper (II), nickel (II), cobalt (II) and cadmium (II). The obtained bis-phenolic chelates were covalently inserted in polymeric linear structures by their polycondensation with bis(p-carboxyphenyl)diphenylsilane as a diacid chloride. The structures of the obtained polymers were confirmed by IR, UV, 1H NMR and elemental analysis. The characterization was made by TGA, DSC, solubility tests and GPC. The electrical conductivity of both chelate monomers and their polymers was investigated, all compounds showing typical semiconducting behaviors.New complex polymeric structures containing metal chelate sequences alternating with silane units of the type: have been synthesized and characterized by IR, UV, 1H NMR, TGA, DSC, GPC, and elemental analysis. The siloxane and silane presences in such structures confer a good solubility. The electrical conductivity of both chelate monomers and their polymers are investigated, all compounds showing typical semiconducting behaviors.

Authors: Normie Jean Sajor1,  Jonathan Briones1, Juanito Raphael Foronda1, Klaud Jenssen Haygood1, and Gil Nonato Santos1*
1 Physics Department, De La Salle University, 2401 Taft Avenue, Manila, Philippines
*Corresponding author: gil.santos@dlsu.edu.ph

ABSTRACT: Abstract
We investigated the anticorrosive, hydrophobic and anti-barnacle properties of polyaniline and graphene (PANI/G) nanocomposite filler in the coating matrix applied to ship hulls. Various formulations of graphene were integrated to polyaniline matrix through in situ polymerization. It was observed that the 0.5%, 1.0%, and 2.5% by weight graphene formulation performed better than the counterparts with higher amount of graphene content as barrier protection. The various coating formulations were applied directly to the metal coupons. It was also observed that the PANI/G nanocomposite exhibited a hydrophilic property. The addition of polysiloxane to the mixture resulted in a hydrophobic surface with a contact angle of 108 degrees. Results show the absence of barnacle growth on metal samples coated with PANI/G/polysiloxane formulation.  It is proposed that this anti-barnacle property is due to the hydrophobicity of the surface.

Key words: PANI, graphene, polysiloxane, HVPG,

Ring opening polymerization (ROP) of hexamethylcyclotrisiloxane (D 3) and octamethylcyclotetrasiloxane (D 4) was promoted by acid-treated synthetic and natural silica-aluminates. Silica-alumina (1:3 Si/Al molar ratio) was obtained using a simple and economic route from precipitation of aluminum sulfate solutions. The material was treated in an acidic medium to improve the content of acid sites and successfully tested as inorganic acidic catalyst for ROP of D 3 or D 4 cyclosiloxanes. Natural bentonite was treated and used in a similar manner. Once the ROP reaction completed, the catalyst was easily removed and it was found that the recovered synthetic silica-alumina was active in a second ROP reaction. The effect of the concentration and type of catalyst in respect to the molecular weight and polydispersity of polydimethylsiloxanes was analyzed: increasing the amount of silica-alumina in ROP of D 4 from 0.05 to 0.1 g decreased the average molecular weight (M n = 13–1.8 kDa) associated with an increase in the polydispersity (2.95 vs. 1.81). Analogous results were found with bentonite. These values suggest that an increase in the catalyst concentration led to a lower M n , with a more homogeneous molecular chain dimension.

Ring opening polymerization (ROP) of 1,3,5-tri-n-hexyl,1,3,5-trimethylcyclotrisiloxane (D 3 Hexa) and 1,3,5-tri-n-heptyl,1,3,5-trimethylcyclotrisiloxane (D 3 Hepta) was promoted by acid-treated synthetic silica–alumina to obtain Gaussian homo asymmetric polysiloxanes. M w was above 70 kg/mol, meaning that homo asymmetric bulky side-group polysiloxane chains with high molecular weight were obtained. The material was treated in an acidic medium to improve the contents of acid sites and successfully tested as an inorganic acidic catalyst for ROP of D 3 Hexa and D 3 Hepta cyclosiloxanes. The samples of poly(meth-ylhexylsiloxane) (PMHS) and poly(methylheptylsiloxane) (PMHepS) obtained were structurally characterized mainly by 29 Si NMR. All the experimental values including the refractive index increment (dn/dc), the second virial coefficient (A 2), the square root of the mean square radius of gyration (hRMS radius 2 i 1=2), the average molecular weight (M w), the average molecular numeral (M n), and the weight polydispersity (M w /M n) were obtained using a gel perme-ation chromatography/light scattering (GPC/LS) coupled system. The A 2 experimental value for the two polymers (between 4 and 6.5 9 10-4 mol/mL g 2) indicated that tol-uene was a good solvent. In addition, PMHS and PMHepS hRMS radius 2 i 1=2 were greater than 30 nm, indicating that larger chains of high molecular weight were obtained. Keywords Gaussian homo asymmetric polysiloxanes Á Bulky side group Á Polysiloxane chains Á Ring opening polymerization Á Silica–alumina Á GPC/LS coupled system