Poly(N-isopropylacrylamide)-Modified Styrene-Butadiene Rubber as Thermoresponsive Material

Narrowly distributed (N‐isopropylacrylamide) (NIPAM) polymers are prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization. After successful cleavage of the trithiocarbonate end groups (thiol generation), they can be grafted to styrene‐butadiene rubber (SBR) by a radical thiol‐ene reaction leading to various grafted SBR‐copolymers. During the grafting reaction, no crosslinking or branching of the SBR can be observed. Measurements of the contact angle of water show that the lower critical solution temperature (LCST) properties of the PNIPAM fraction affect the SBR. Films of the graft‐copolymer exhibit a distinct hydrophilicity below the LCST, while they show hydrophobic behavior above the LCST. Rheological measurements reveal a physical crosslinking of the functionalized SBR due to nanophase separation of the PNIPAM chains (hard phase) in the unpolar SBR. Compared with blends of SBR and PNIPAM, the PNIPAM‐grafted SBR possesses a much finer distribution of the PNIPAM domains (10–30 nm) within the matrix. In addition, two novel difunctional chain‐transfer agents are used, leading to difunctional PNIPAM, enabling a covalent crosslinking of SBR. Styrene‐butadiene rubber (SBR) is used in a thiol‐ene reaction with poly(N‐isopropylacrylamide) PNIPAM (PNI) possessing a thiol end group. The products show nanophase separation with phase sizes depending on the PNIPAM content. PNI‐SBRs can change their surface wettability depending on the temperature. Furthermore, difunctional PNIPAM is used in a crosslinking reaction with SBR.