Enrique M. Vallés

Anionic Ring Opening Polymerization of ε-Caprolactone Initiated by Lithium Silanolates

Ring-opening homo- and co-polymerization reactions of ϵ-caprolactone were performed by employing anionic polymerization (high vacuum techniques) and lithium silanolates (LS) as initiators. LS were obtained by reaction between hexamethyl(cyclotrisiloxane) and sec-Bu–Li+, or from living poly(dimethylsiloxanyl)lithium chains. The results indicated that LS are efficient initiators for the ring-opening polymerization of ϵ-caprolactone, providing the respective homogeneous polymers in good yields.

Polymers in Ophthalmology

Ophthalmological sciences are disciplines focused in the health of the eyes and related structures, as well as vision, visual systems, and vision information processing in humans; dealing with the anatomy, physiology and diseases of the eye. Along time a wide variety of materials, including metals, ceramics and polymers, have been developed and used in different ophthalmic applications. Although, modern ophthalmic devices and drug platforms are made with polymeric materials. Applications of polymers in ophthalmology include vitreous replacement fluids, contact lenses, intraocular lenses, artificial orbital walls, artificial corneas, artificial lacrimal ducts, glaucoma drainage devices, viscoelastic replacements, drug delivery systems, sclera buckles, retinal tacks and adhesives, and ocular endotamponades. Both synthetic and natural polymeric biomaterials are used in ophthalmological applications, although in the lasts years most efforts were focused in natural and biocompatible materials, such as gelatin, hyaluronan, chitosan, gums, etc.; developing, tablets, films, suspensions, nanosystems, inserts, etc. This chapter attempts to offers an insight into the importance of polymers in the design and development of pharmaceuticals platforms used in ocular therapeutics.

Efficiency of Different Chain-Linking Agents in the Synthesis of Long-Chain Branched Polypropylene: Molecular, Thermal, and Rheological Characterization

ABSTRACT Long-chain branched polypropylenes were synthesized from a maleic anhydride grafted polypropylene (PPg). Different levels of branching were generated by reactive processing using four chain-linking agents: glycerol, 1,4-butanediol, 1,4-phenylenediamine, and the epoxy resin bisphenol-A diglycidyl ether. The results from Fourier transform infrared and size-exclusion chromatography confirm the grafting of the chain-linking agents onto grafted polypropylene and the generation of long-chain branches. In addition, the rheological and morphological results show that 1,4-phenylenediamine produces the largest increment of branching at significantly lower concentrations than the other chain-linking agents. Moreover, 1,4-phenylenediamine gives place to branched polypropylenes with narrower distribution of molecular structures. GRAPHICAL ABSTRACT