Method for preparing a siloxane-based elastomer composition

#The invention relates to a method for the preparation of a siloxane-based elastomer composition comprising at least one elastomer, said elastomer composition comprising poly(alkylene oxide) groups present in the elastomer as alkoxy-terminated grafts of polysiloxane units and linked to the polysiloxane units by silicon-carbon bonds.

#Polysiloxanes, in particular poly(dimethyl siloxane) (PDMS), are highly suitable for use as a membrane or matrix regulating the permeation rate of drugs in various drug forms, in particular in implants and IU systems. Polysiloxanes are physiologically inert, and a wide group of drugs are capable of penetrating polysiloxane membranes, which also have the required strength properties.

#It is known from the literature that the adding of poly(ethylene oxide) groups, i.e. PEO groups, to a PDMS polymer may increase the permeation rate of drugs. Publication K L Ullman et al., Journal of Controlled Release 10 (1989) 251-260, describes membranes prepared from a block copolymer which contains PEO and PDMS and the penetration of various steroids through these membranes. It is noted in the publication that an increasing PEO amount in the block polymer tends to increase the penetration of hydrophilic steroids, while the penetration of lipophilic steroids decreases. The block copolymer described in the publication is very complicated in its structure and preparation, and would therefore not be facile in more extensive technical production. Furthermore, said copolymer and thus prepared membrane contains urea groups and hydrolyzable urethane groups, which are undesirable in long-term medical applications as a possible site for degradation or reaction.

#The invention relates to a method as described above. The elastomer composition prepared by said method is used for example as a membrane or matrix for controlling the permeation rate or diffusion rate of a pharmaceutically active drug. Said membrane or matrix may be used for example in intravaginal devices, intrauterine devices, intracervical devices and implants. The pharmaceutically active drug may be for example a hormone such as an antiprogestin, a progestin, an estradiol or an androgen.

#General Description of the Elastomer Composition

#The term “elastomer composition” may stand for one single elastomer, in which case the polysiloxane units which contain poly(alkylene oxide) groups are present in the said elastomer.