Highly functionalized polycyclosiloxanes and their polymerization into thermally reversible living rubbers

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to the preparation of silicone networks by methods that permit the formation of a specific predetermined final structure determined solely by the compositon of preformed difunctional and polyfunctional units included in a pregel state.
The process involves the living ring-opening copolymerization of polycyclosiloxanes and polysiloxanes, most notably, cyclosiloxanes.
All chainlink units of the polycyclosiloxane, except for those that define the functionality of the cross-links, are sites for disproportionation of the network.
When such networks are formed using reactants with a very small ratio of polyfunctional to difunctional units, in the presence of a very active acid catalyst, the rubbers that are formed behave in a living manner.
The rubbers are observed to grow when fed with monomer, are self-healing, and may be "killed" by adding reagents to inactivate the catalyst.
Such compositions are observed to flow readily at elevated temperatures, acting as thermally reversible gels.
The polycyclosiloxanes used in the process of the present invention contain polyfunctional siloxane units which serve as linking groups which become cross-linking sites for network formation.
The polyfunctional siloxane units contain at least 3, and as many as 8 or more, Si--O bonds which are interconnected by a common backbone consisting of silicon-carbon, carbon-carbon and/or carbon-oxygen bonds exclusively.
These Si--O bonds are reactive, forming sites available for crosslinking.
The number and functionality of the cross-link sites of the network may be predetermined and controlled by the proportion of polycyclosiloxane and polysiloxane "monomers" used as the network-forming reactants.
The network may be prepared at room temperature, in the presence of a strong acid.
The network is thermally reversible.
It may be heated and melted.
Upon cooling, the structure returns to its initial rubbery state.
The network results in the formation of a truly "living" rubber