250
Dascalu et al. (2015) reported the anionic ROP of F 3 and D 4 catalyzed by TMAH,
in presence of DVTMDS, which yielded siloxane copolymers end-capped with
vinyl groups. Different F 3 :D 4 ratios led to a range of polymers with trifuoropropyl
side-groups of 28 to 58 mol% that were crosslinked with tetrakis(dimethylsiloxy)
silane by Pt-catalyzed hydrosilylation reaction. The dielectric permittivity increased
up to 6.4 with the trifuoropropyl content, apart with increased T g values (up to
-88.6 °C) and low Y (0.019 MPa), while the maximum lateral actuation strain was
5.4% at 7.8 V/μm of applied electric field. In line with this, Dünki et al. (2015a, b)
chemically modified a high Mw polymethylvinylsiloxane-α,ω-diol using
3- mercaptopropionitrile and subsequently crosslinked with a bifunctional thiol
(2,2′-(ethylenedioxy)diethanethiol). A noticeable increase in dielectric permittivity
(10 at 10
6
Hz), a significant actuation strain (20.5% at 10.8 V/μm) and self-healing
capacity of the elastomer were observed. However, dielectric losses and conductivities increased, while the value of maximum E BD was low.
Sun et al. (2019a) studied the influence of the dipole structure and its interaction
on the electromechanical and actuation performance of homogeneous silicone
dielectric elastomers. Poly(dimethylmethylvinyl)siloxane with different molar content of pendant vinyl groups synthesized by anionic polymerization were reacted
with three different dipoles (carboxyl, ester and hydroxyl) using photochemical
thiol-ene click reaction to prepare homogenous dielectric elastomers. The combined
effects of dipolar moment, mobility and interactions of carboxyl, ester and hydroxyl
dipoles had a significant influence on actuated, dielectric and mechanical properties.
The simultaneous improvement of the dielectric and mechanical properties of silicone rubber was further optimized by Sun et al. (2019b). First, a carboxyl modified
polysiloxane was obtained by a photochemical thiol-ene click reaction. The functional silicone was further mixed with a silanol terminated PDMS followed by the
crosslinking of PDMS-OH using an amino support crosslinking agent. Thus, the
dual crosslinking network obtained includes the chemically crosslinked PDMS-NH 2
network and the network formed by hydrogen (H)-bonds between PMVS-COOH
and PDMS-NH 2 .
The modification of polysiloxanes with sulfonyl groups in various proportions
via thiol-ene chemistry was reported by Dünki et al. (2017) as a viable way to tune
the dielectric permittivity within a wide range (5–22.7), while keeping the T g below
RT, which opens up possible applications in actuators capacitors and flexible
electronics.
An alternatively efficient method to increase the electromechanical response is
mixing two polymers, one of them with high dielectric permittivity which can be
accompanied by a decrease in the Y values. The high ε’ component is in many cases
of an organic nature, such as a PU elastomer with permittivity of 15.5 at 10 Hz
(Gallone et al. 2010) or a un-doped poly(3-hexylthiophene) with permittivity >2000
at 1 Hz (Carpi et al. 2008b, a). When the PEGs (PEG600 and PEG1500) were mixed
by Liu et al. (2012) using a liquid silicone (Silastic DC3481), immiscibility between
PEG and PDMS was observed despite good electromechanical performance. Trying
to overcome this drawback, Razak et al. (2015) synthesized PEG-PDMS block
copolymers and mixed them with a commercial silicone (MJK 4/13). The
C. Racles et al.
Dascalu et al. (2015) reported the anionic ROP of F 3 and D 4 catalyzed by TMAH,
in presence of DVTMDS, which yielded siloxane copolymers end-capped with
vinyl groups. Different F 3 :D 4 ratios led to a range of polymers with trifuoropropyl
side-groups of 28 to 58 mol% that were crosslinked with tetrakis(dimethylsiloxy)
silane by Pt-catalyzed hydrosilylation reaction. The dielectric permittivity increased
up to 6.4 with the trifuoropropyl content, apart with increased T g values (up to
-88.6 °C) and low Y (0.019 MPa), while the maximum lateral actuation strain was
5.4% at 7.8 V/μm of applied electric field. In line with this, Dünki et al. (2015a, b)
chemically modified a high Mw polymethylvinylsiloxane-α,ω-diol using
3- mercaptopropionitrile and subsequently crosslinked with a bifunctional thiol
(2,2′-(ethylenedioxy)diethanethiol). A noticeable increase in dielectric permittivity
(10 at 10
6
Hz), a significant actuation strain (20.5% at 10.8 V/μm) and self-healing
capacity of the elastomer were observed. However, dielectric losses and conductivities increased, while the value of maximum E BD was low.
Sun et al. (2019a) studied the influence of the dipole structure and its interaction
on the electromechanical and actuation performance of homogeneous silicone
dielectric elastomers. Poly(dimethylmethylvinyl)siloxane with different molar content of pendant vinyl groups synthesized by anionic polymerization were reacted
with three different dipoles (carboxyl, ester and hydroxyl) using photochemical
thiol-ene click reaction to prepare homogenous dielectric elastomers. The combined
effects of dipolar moment, mobility and interactions of carboxyl, ester and hydroxyl
dipoles had a significant influence on actuated, dielectric and mechanical properties.
The simultaneous improvement of the dielectric and mechanical properties of silicone rubber was further optimized by Sun et al. (2019b). First, a carboxyl modified
polysiloxane was obtained by a photochemical thiol-ene click reaction. The functional silicone was further mixed with a silanol terminated PDMS followed by the
crosslinking of PDMS-OH using an amino support crosslinking agent. Thus, the
dual crosslinking network obtained includes the chemically crosslinked PDMS-NH 2
network and the network formed by hydrogen (H)-bonds between PMVS-COOH
and PDMS-NH 2 .
The modification of polysiloxanes with sulfonyl groups in various proportions
via thiol-ene chemistry was reported by Dünki et al. (2017) as a viable way to tune
the dielectric permittivity within a wide range (5–22.7), while keeping the T g below
RT, which opens up possible applications in actuators capacitors and flexible
electronics.
An alternatively efficient method to increase the electromechanical response is
mixing two polymers, one of them with high dielectric permittivity which can be
accompanied by a decrease in the Y values. The high ε’ component is in many cases
of an organic nature, such as a PU elastomer with permittivity of 15.5 at 10 Hz
(Gallone et al. 2010) or a un-doped poly(3-hexylthiophene) with permittivity >2000
at 1 Hz (Carpi et al. 2008b, a). When the PEGs (PEG600 and PEG1500) were mixed
by Liu et al. (2012) using a liquid silicone (Silastic DC3481), immiscibility between
PEG and PDMS was observed despite good electromechanical performance. Trying
to overcome this drawback, Razak et al. (2015) synthesized PEG-PDMS block
copolymers and mixed them with a commercial silicone (MJK 4/13). The
C. Racles et al.