244
From another perspective, in the post-functionalization of the siloxane copolymers by hydrosilylation there is the risk of incomplete conversion, depending on
the reactivity of the double bond reagent or steric factors, and an un-controlled
crosslinking can be produced by the subsequent condensation involving hydrolysed
Si-H groups. For example, Racles et al. (2014a) only achieved an 89% conversion
in the modification of poly(methylhydrosiloxane) (PMHS) with allyl cyanide
(Table 11.2, entries 1, 2). The residual Si-H bonds are slowly hydrolyzed to Si-OH
groups which can be exploited for subsequent crosslinking by condensation (Racles
et al. 2015a). With this in mind, Kussmaul et al. (2011) partially grafted the Si-H
groups of a poly(dimethyl-co-methylhydro)siloxane (PDMHS) using polar N-allylN-methylaniline (Table 11.2, entry 3), and simultaneously crosslinked with vinylterminated PDMS, which leads to dielectric elastomers.
Racles et al. (2016) also obtained functionalized silicones containing pendant
epoxy, benzaldehyde or DR1 groups from PDMHS (Table 11.2, entries 4–6). The
carbonate functional groups can also be introduced by hydrosilylation (Putzien
et al. 2010; Lowe 2014) (Table 11.2, entry 7). The epoxy groups can be subsequently modified by reaction with aldehydes or amines (Table 11.2, entry 4) (Racles
2010; Racles and Cozan 2012; Racles et al. 2016, 2018). For example, Yang and
Wnek (1992) introduced silyl ketene acetals as pendant groups into PMHS
(Table 11.2, entry 8) and the silicones obtained were further reacted using 4-nitrobenzenesulphenyl chloride.
Ishiwari et al. (2018) showed that end functionalization of PDMS of different
Mw using a triptycene moiety with a 1,8-substitution pattern leads to significant
changes in the rheological, structural and thermal properties of PDMS. The excellent self-assembly capacity of the 1,8-substituted triptycene moiety, which is powerful enough to assemble even an amorphous polymer into a specific ‘2D + 1D’
periodic structure is responsible for this. The physical and structural properties of
PDMS also did not change with the end functionalization with another triptycene
derivate (1,4-Trip, Table 11.2, entry 9), which differs only in the substitution pattern.
The hydrogen terminated PDMS (PDMS-H 2 ) oligomers synthesized through the
cationic ROP of D 4 in the presence of TMDS were subjected to a hydrosilylation
reaction with tert-butyl methacrylate (tBMA) by Yang et al. (2014). PDMS(COOH) 2 was obtained after acidic hydrolysis of the t-butyl ester terminated PDMS
(PDMS-tBMA 2 ) intermediate product (Yang et al. 2014).
A particular case is exemplified in the last entry in Table 11.2 where the vinyl
group belongs to the polysiloxane substrate (poly(methylvinyl)siloxane, PMVS)
and the Si-H group is attached to the functional molecule (Fig. 11.4b). A controlled two-step one-pot synthesis was described by Boehm et al. (2012), who
obtained well-defined polysiloxane block copolymers by the sequential anionic
ROP of D 3 and D 4
V
. Substituents bearing ethoxysilanes or epoxides, as well as long
aliphatic chains, have subsequently been linked to the resulting PDMS-b-PMVS via
hydrosilylation (Table 11.2, entry 10).
The thiol-ene addition (Fig. 11.5) has been used as an alternative pathway for the
modification of polysiloxanes with polar groups (Le Neindre and Nicolaÿ 2014;
Dünki et al. 2015a; Opris 2018) because it is easy to handle and is produced with
C. Racles et al.
From another perspective, in the post-functionalization of the siloxane copolymers by hydrosilylation there is the risk of incomplete conversion, depending on
the reactivity of the double bond reagent or steric factors, and an un-controlled
crosslinking can be produced by the subsequent condensation involving hydrolysed
Si-H groups. For example, Racles et al. (2014a) only achieved an 89% conversion
in the modification of poly(methylhydrosiloxane) (PMHS) with allyl cyanide
(Table 11.2, entries 1, 2). The residual Si-H bonds are slowly hydrolyzed to Si-OH
groups which can be exploited for subsequent crosslinking by condensation (Racles
et al. 2015a). With this in mind, Kussmaul et al. (2011) partially grafted the Si-H
groups of a poly(dimethyl-co-methylhydro)siloxane (PDMHS) using polar N-allylN-methylaniline (Table 11.2, entry 3), and simultaneously crosslinked with vinylterminated PDMS, which leads to dielectric elastomers.
Racles et al. (2016) also obtained functionalized silicones containing pendant
epoxy, benzaldehyde or DR1 groups from PDMHS (Table 11.2, entries 4–6). The
carbonate functional groups can also be introduced by hydrosilylation (Putzien
et al. 2010; Lowe 2014) (Table 11.2, entry 7). The epoxy groups can be subsequently modified by reaction with aldehydes or amines (Table 11.2, entry 4) (Racles
2010; Racles and Cozan 2012; Racles et al. 2016, 2018). For example, Yang and
Wnek (1992) introduced silyl ketene acetals as pendant groups into PMHS
(Table 11.2, entry 8) and the silicones obtained were further reacted using 4-nitrobenzenesulphenyl chloride.
Ishiwari et al. (2018) showed that end functionalization of PDMS of different
Mw using a triptycene moiety with a 1,8-substitution pattern leads to significant
changes in the rheological, structural and thermal properties of PDMS. The excellent self-assembly capacity of the 1,8-substituted triptycene moiety, which is powerful enough to assemble even an amorphous polymer into a specific ‘2D + 1D’
periodic structure is responsible for this. The physical and structural properties of
PDMS also did not change with the end functionalization with another triptycene
derivate (1,4-Trip, Table 11.2, entry 9), which differs only in the substitution pattern.
The hydrogen terminated PDMS (PDMS-H 2 ) oligomers synthesized through the
cationic ROP of D 4 in the presence of TMDS were subjected to a hydrosilylation
reaction with tert-butyl methacrylate (tBMA) by Yang et al. (2014). PDMS(COOH) 2 was obtained after acidic hydrolysis of the t-butyl ester terminated PDMS
(PDMS-tBMA 2 ) intermediate product (Yang et al. 2014).
A particular case is exemplified in the last entry in Table 11.2 where the vinyl
group belongs to the polysiloxane substrate (poly(methylvinyl)siloxane, PMVS)
and the Si-H group is attached to the functional molecule (Fig. 11.4b). A controlled two-step one-pot synthesis was described by Boehm et al. (2012), who
obtained well-defined polysiloxane block copolymers by the sequential anionic
ROP of D 3 and D 4
V
. Substituents bearing ethoxysilanes or epoxides, as well as long
aliphatic chains, have subsequently been linked to the resulting PDMS-b-PMVS via
hydrosilylation (Table 11.2, entry 10).
The thiol-ene addition (Fig. 11.5) has been used as an alternative pathway for the
modification of polysiloxanes with polar groups (Le Neindre and Nicolaÿ 2014;
Dünki et al. 2015a; Opris 2018) because it is easy to handle and is produced with
C. Racles et al.