John Carlton Saam

Direct polyesterifcation in aqueous emulsion

SummaryCertain diols can undergo polycondensation in aqueous emulsion with either dicarboxylic acids or aliphatic aldehydes to give polyester or polyyacetals. The process occurs under mild conditions and requires water insoluble liquid monomers, the presence of a sulfonate surfactant and mobile cations which can ion exchange at the oil-water interface. An acidic catalyst is not necessary. The degrees of polymerization are modest but they exceed those normally expected of polyesterifcations in such an environment. The driving force is thought to be the heat of condensation of the water produced as vapor in the oil phase.

Emulsion Polymerized Polydimethylsiloxane

Abstract The observations are consistent with the formation of grafts of hydrophilic silicates to the silanol chain ends at the surface of the PDMS emulsion particles prior to removal of the water. The silicates may be introduced into the system directly or through the alkaline colloidal silica, which contains appreciable amounts of dissolved silicates. Monomeric, or possibly dimeric, silicate grafted to more than one chain end could migrate to the interior of the PDMS emulsion particle to form further crosslinks. Grafts to higher molecular weight silicates and silicate grafts bearing anionic change would be solvated with water and tend to remain at the oil-water interface. These grafts can provide additional stabilization to the cured particles. The dialkyltin carboxylate is pictured as playing a role in the grafting and crosslinking process. Evaporation of the water would eventually cause collapse of the stabilizing elements surrounding the PDMS particles to allow contact between particles of silica and...

Room-Temperature-Cured Polydimethylsiloxane Elastomers from Aqueous Dispersion

Abstract The observations are consistent with the formation of grafts of hydrophilic silicates to the silanol chain ends at the surface of the PDMS emulsion particles prior to removal of the water. The silicates may be introduced into the system directly or through the alkaline colloidal silica, which contains appreciable amounts of dissolved silicates. Monomeric, or possibly dimeric, silicate grafted to more than one chain end could migrate to the interior of the PDMS emulsion particle to form further crosslinks. Grafts to higher molecular weight silicates and silicate grafts bearing anionic charge would be solvated with water and tend to remain at the oil-water interface. This could provide steric as well as ionic stabilization to the PDMS particles, and the system would no longer respond to electrolytes as a simple, ionically stabilized, hydrophobic colloid but more as a hydrophilic colloid resembling silica. The role of the dioctyltin dilaurate is to interact in the water phase with the water-soluble ...

Properties of Polystyrene-Polydimethylsiloxane Block Copolymers

Block copolymers of polystyrene and polydimethyIsiloxane formed when hexamethylcyclotrisiloxane polymerized from the “living” ends of polystyryllithium. Little of the complicating intra- or intermolecular chain scission usually encountered in anionic siloxane polymerization occurred and essentially pure block copolymers were obtained. These were of the AB or BAB variety (where B signifies polydimethyIsiloxane and A polystyrene) depending on the functionality of the alkyllithium initiator used in formation of the polystyryHithium. The block copolymers, owing to the disparity in solubility between the A and B blocks, showed a tendency to form microphases in the bulk. The BAB block copolymers upon conversion to (BAB)X multi-block systems gave strong thermoplastic elastomers which could be deposited as films from solution or directly molded without any added re-enforcing fillers or cross-linking. Micro- phase formation was also observed in the multi-block copolymers.

Strain induced crystallization in stereoregular poly[methyl (3,3,3-trifluoropropyl) siloxane] networks

Abstract Elastomeric networks based on poly[methyl(3,3,3-trifluoropropyl)siloxane] having a minimum level of stereo-regularity crystallize and self-reinforce when stretched at room temperature. The effect is especially pronounced in networks where the cross-links are uniformly spaced. The polymers are made by modification of a recently described anionic ring opening copolymerization of prescribed mixtures of cis- and trans-1,3,5-trimethyl-1,3,5-tris (3′, 3′, 3′-trifluoropropyl) cyclotrisiloxane. This provides polymers enriched in stereoregularity with nearly monodisperse molecular weight distributions and reactive groups at the chain ends. The end-linked networks show markedly enhanced mechanical properties due to self-reinforcement from strain-induced crystallization. In addition to applied strain, self-reinforcement depends on temperature and the amount of stereoregularity introduced to the polymer. Strained specimens having high levels of stereoregularity and pre-existing crystallinity exhibit plastic ...

Network Development in Films Cast from Emulsions of Polydimethylsiloxane

A current trend in the coatings industry is to shift from solvent based systems to emulsions. In elastomeric coatings cross-linking must occur at some stage during the drying of the latex to obtain useful films. It is also particularly desirable for cross-linking to occur at room temperature. This paper describes such a system based on polydimethylsiloxane (PDMS). It consists of an anionically stabilized emulsion of high molecular weight PDMS terminated with silanol (1), colloidal silica and dialkytin-dicarboxyl-ate curing agent (2). Network formation begins at room temperature before the films are dried and rubbery coherent films form before all the water evaporates from the system. This paper describes the cure process and offers an interpretation of the observed phenomena.