Designing Hydrogels by ATRP - In-Situ Gelling Polymers: For Biomedical Applications - page 90

Fig. 7 Mechanical properties of supersoft elastomers with modules in the range of 1 kPa. The
material obtained from loose crosslinking of bottlebrushes. Reprinted with permission from
American Chemical Society [ 230 ]
Fig. 8 Supersoft elastomer network formed via physical crosslinking and the resulting compli-
ance data. Reprinted with permission from Elsevier [ 231 ]
very densely grafted side chains [ 15 , 16 ]. Such molecular brushes typically have a
backbone with DP bb ca. 300-5,000 and correspondingly the same number of short
side chains with DP sc ca. 20-100. Brushes with the longest backbone may exhibit
plateau in the range 1 kPa and after slight crosslinking form permanent supersoft
elastomers that cannot flow (as shown in Fig. 7 ). The alternative pathway is graft-
ing side chains from a loose network backbone, containing initiating sites.
As noted above supersoft elastomers can be prepared with permanent chemical
crosslinkage but can also be formed by physical crosslinking, as in thermoplastic
elastomers. Figure 8 presents a structure consisting of 3 arm stars bottlebrushes
that can phase separate to form such a network and also the resulting mechanical
properties of the thermoplastic network. Each arm of the star had a methacrylate
backbone of DP bb = 300 grafted with soft P n BA with DP sc = 35. Each arm was