Hydrogen bonding: a critical parameter in designing silicone copolymers

Structure-property relations in polydimethylsiloxane (PDMS) containing segm ented copolymers with model hard segments capable of forming hydrogen bondi ng, such as urea, N-methylurea and urethane have been investigated. High mo lecular weight silicone containing copolymers with these hard segments were prepared from PDMS oligomers with number average molecular weights ranging from 890 to 3750 g/mol. Due to major differences in the solubility paramet ers between PDMS and polar hard segments, all copolymers are expected to di splay good microphase separation. It was demonstrated that mechanical and t hermal properties of these copolymers are directly linked to the strength o f the hydrogen bonding in the hard segments. As expected, siloxane-urea cop olymers displayed much higher tensile strengths when compared with siloxane -N-methylurea and siloxane-urethane copolymers with similar compositions. ( C) 2001 Elsevier Science Ltd. All rights reserved.