Telechelic glycidyl epoxide siloxanes substituted with either methyl, cyclopentyl, or cyclohexyl groups were cured thermally with corresponding telechelic aliphatic amine. Also, the three glycidyl epoxide functionalized siloxanes were homopolymerized via a photo-initiated cationic mechanism. Both the UV and thermal curing were performed by formulating with reactive diluents. The mechanical properties, viscoelastic behavior, and coatings properties of the thermally cured siloxanes were studied. In addition, the X-ray measurements were performed. The rate of polymerization increased with the increasing size of substituent on the siloxane backbone. The hardness, adhesion, and solvent resistance increased as the bulk of the substituent increased in the siloxane backbone. The release properties for adhesion and readhesion increased with increase in steric bulk of the backbone substituents. Crosslink density reduced and oxygen permeability increased with increase in siloxane substituent size. There was also an increase in the advancing and the receding contact angles with the increase in substituent size. The inverse dependency of substituent size and free volume was observed in the d-spacing of the X-ray data. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 358-369, 2010

Siloxanes with either methyl, cyclopentyl, or cyclohexyl groups were functionalized with methacrylate groups, then UV-cured using a free radical photo-initiator and a reactive diluent. Hexanediol dimethacrylate (0.1 wt%) was used as the reactive diluent. After curing, the mechanical, the viscoelastic, the coating, and the release properties of the cured films were studied. In addition, the oxygen permeability and the X-ray diffraction scans were evaluated. The crosslink density reduced with increase in siloxane substituent size. The oxygen permeability was dependent on crosslink density, and increased with increasing substituent size. The increase in permeability, and thus free volume, was supported by X-ray studies which showed an increase in d-spacing with increasing alkyl size. The hardness, adhesion, and solvent resistance increased as the size of the substituent increased (methyl to cyclopentyl to cyclohexyl) in the siloxane backbone. The adhesion and re-adhesion forces increased with an increase in size of the backbone substituents. There was also an increase in the advancing and the receding contact angles with the increase in substituent size.

Both random and block siloxane copolymers were synthesized with methyl, and cyclopentyl, or cyclohexyl substituents. Random copolymers were obtained by hydrolytic condensation of dimethyldichlorosilane and dicyclopentyldichlorosilane or dicyclohexanedichlorosilane. Block polymers were prepared using cyclic oligomers via a ring opening polymerization (ROP). Amberlyst-15 was used as the catalyst for ROP. The synthesized polymers were characterized by H-1-NMR, C-13-NMR, Si-29-NMR, FT-IR, and GPC. The glass transition temperatures of the siloxanes were measured using DSC and DMA. The random and block structures were identified via NMR. As expected, The T-g of the copolymers were intermediate between those of the homopolymers.

The effect of oil length of alkyds and substitution of siloxane backbone has been studied for alkyd–siloxane hybrids. A series of nine alkyd–siloxane hybrids were synthesized by either varying the oil length of the alkyd or the siloxane backbone substitution. Three linseed oil-based alkyds with either a long, medium, or short oil length were grafted with three hydride-terminated siloxanes substituted with methyl, cyclopentyl, or cyclohexyl groups. A hydrocoupling reaction was used to couple the telechelic siloxane with the hydroxyl functionality of the alkyds using Wilkinson’s catalyst. The reaction was monitored by the disappearance of siloxane hydride signal using Fourier transform infrared. Characterization of siloxane–alkyd hybrids was performed using 1 H-NMR, 13 C-NMR, and gel permeation chromatography. The hybrids were formulated with a Co, Zr, and Ca drier package and auto-oxidatively cured without using any solvent. The tensile, viscoelastic, and coating properties were evaluated for the cured films. The crosslink density, flexibility, and reverse impact resistance were found to increase as a function of oil length. Tensile modulus, elongation-to-break, glass transition temperature, drying time, and fracture toughness decreased with increase in oil length. For the alkyd–siloxane hybrids, the mechanical and rheological properties were dependant on the size of the substituents. The larger-sized cyclopentyl and cyclohexyl groups resulted in better mechanical and rheological properties than the methyl-containing siloxanes.

Methacrylic functionalized siloxanes were prepared in a two-step process. In the first step, a series of telechelic glycidyl epoxy siloxanes were prepared, substituted with either methyl, cyclopentyl, or cyclohexyl groups. In the second step, the telechelic glycidyl epoxy groups were reacted with methacrylic acid. The reaction was monitored via acid value, and when the acid value was ⩽10, the reaction was terminated. Characterization of the methacrylic telechelic siloxane polymers were performed using 1H NMR, 13C NMR and FT-IR. The methacrylated siloxanes were formulated with a free radical photo-initiator, UV-cured, and the rate of polymerization was monitored via photo-differential calorimetry. After curing, viscoelastic properties, and oxygen-permeability were evaluated. In addition, X-ray was used to evaluate the structure of the cured films. The rate of polymerization was dependent on substituent and increased with increasing substituent size. The oxygen permeability was dependent on crosslink density, and increased with increasing substituent size. The increase in permeability, and thus free volume was supported by X-ray studies which showed an increase in d-spacing with increasing alkyl size.

A synthetic route was developed to prepare thermosetting methyl, cyclopentyl, and cyclohexyl substituted polysiloxanes with epoxide or amino end groups. Cycloalkene (cyclopentene or cyclohexene) and dichlorosilane gas were reacted at 180 degrees C, and at high pressure (2 MPa) to produce dicycloaliphatic dichlorosilane. Hydrolytic condensations of the dichlorosilanes were performed affording low molecular weight cyclic siloxane oligomers. Base catalyzed ring opening polymerization of the cyclic oligomers afforded the hydride -terminated polysiloxanes. The hydride-terminated polysiloxanes were then functionalized with glycidyl epoxide or aliphatic amine groups via hydrosilation reactions. The oligomers and polymers were characterized by H-1 NMR, C-13 NMR, Si-29 NMR, FTIR, and GPC. The molecular weight of polydimethylsiloxane, polydicyclopentylsiloxane, and polydicyclohexylsiloxane oligomers were (M) over bar (n) = 1000, 1200, and 1500, respectively. The polydispersity index of all the cyclic oligomers was approximate to 1.15. Differential scanning calorimetry (DSC) was used to evaluate the crosslinking reaction and the glass transition temperature of the thermally cured systems. Crosslinking occurred at 120 degrees C and the T-g of the methyl, cyclopentyl, and cyclohexyl functionalized siloxanes were found to be at -104, -93, and -82 degrees C, respectively.

A new class of silicone has been developed for coatings or as coating additives. Cycloaliphatic silane monomers were prepared and reacted into more easily handled cyclic oligomers. These cyclic oligomers were ring-opened into siloxane polymers. The polymers were functionalized with a variety of groups, including: amino, glycidyl epoxide, cyclohexene epoxide, acrylic, and alkoxysilane. The cycloaliphatic silicones have been designed for a number of different curing conditions: (1) ambient temperature-cure (amino and glycidyl epoxide), (2) cationic ultraviolet (UV)-cure (cyclohexene epoxide), (3) radical UV-cure (acrylic), and (4) moisture-cure (alkoxysilane). The end usages thus far have been focused on silicone coatings; however, usage as coating additives will be a focus for future research. The cycloaliphatic silicone has been UV-cured with mixed sol–gel precursors for usage as aerospace coatings. The cycloaliphatic silicones have also been ambient temperature-cured for release coatings, and have application as anti-fouling coatings. The inherent low surface energy makes the cycloaliphatic silicones prime candidates for surface tension additives.