312
M. Hong
8.4 Summary and Outlook
The development of LPP not only brings about a renaissance in polymerization
catalysis with main-group elements but also provides an efficient, controlled, and
selective strategy for the synthesis of a variety of novel polymeric materials that
cannot be efficiently realized by traditional polymerization techniques. The past two
years have witnessed the unprecedented achievements made to this rapidly expanding
field. In this chapter, these recent advances have been highlighted, with a special
emphasis on the LP-mediated polymerization of polar vinyl monomers and RO(C)P
of cyclic esters, epoxides, and anhydrides.
Compared to the research work reported previously, the current LPPs exhibit
several impressive advantages and also open up a new opportunity for the applications of LP catalysis: (1) Pushing the limits on accessible monomers, such as
the first effective LPPs of SFMAs, [51] epoxides, [71–73] as well as those notable
monomers derived from renewable biomass or natural products (e.g., MC [59], IN
[60], β-AL [61], OCA [69, 70]). (2) Realizing the controlled or even living polymerizations of divinyl acrylic monomers, [42, 46] acrylamides, [48] vinyl phosphonates, [52] epoxides, [72, 73] whose LPPs generally suffered from poor control
previously, via the development of LP catalyst with matched Lewis acidity, basicity,
and steric effects. (3) Enabling the synthesis of UHMW polymers with relatively
low dispersities, as seen in examples of UHMW PMMA by (BHT)Al
i Bu 2 /IAP-1
FLP, [38] SFPMAs by MeAl(BHT) 2 /I
t Bu LP, [51] PPO by Mg(HMDS) 2 /NHO-9
CLA [71]. (4) Establishing robust LP catalysts or convenient methodology for the
facile preparation of well-defined block copolymers, as demonstrated by the utilization of robust (BHT)Al
i Bu 2 /IAP-1 FLP for methacrylic multiblock copolymers with
DHDM features via sequential addition method, [41] one-pot manner to P
n BA-bP
t BA diblock [53] and poly(ether-b-ester-b-ether) triblock copolymers [75] from
n BA/
t BA and anhydride/excess epoxide monomer mixture using MeAl(BHT) 2 /PMe 3
and BEt 3 /
t Bu-P 2 LP, respectively, and a switchable polymerization to ether-estertype multiblock copolymer by switching the monomer selectivity through varying
the amount of BEt 3 and
t Bu-P 2 [74].
The accomplishments made in this time frame also points out several key challenges which are still in need of a solution in the field of LPPs. Currently, successful
LPPs are only limited to heteroatom-containing polar monomers. To the best of our
knowledge, less activated nonpolar monomers, such as conjugated dienes or styrenes
still remain unexplored. Therefore, extending the monomer scope and thus further
broadening the applications of LPPs will undoubtedly continue to be a major focus in
the future research. It would be also of great interest to develop novel LPPs capable of
constructing complex macromolecular structures with controlled topology or highorder sequence, which will be used to create polymeric materials with advanced properties and specific functions. Moreover, at present, highly stereoselective LPP can
only be achieved at low polymerization temperature (e.g., −78 °C) with compromised
activity. The design of new LP catalysts that allow highly stereoselective polymerization under mild conditions could become one of the next challenges to be addressed.
M. Hong
8.4 Summary and Outlook
The development of LPP not only brings about a renaissance in polymerization
catalysis with main-group elements but also provides an efficient, controlled, and
selective strategy for the synthesis of a variety of novel polymeric materials that
cannot be efficiently realized by traditional polymerization techniques. The past two
years have witnessed the unprecedented achievements made to this rapidly expanding
field. In this chapter, these recent advances have been highlighted, with a special
emphasis on the LP-mediated polymerization of polar vinyl monomers and RO(C)P
of cyclic esters, epoxides, and anhydrides.
Compared to the research work reported previously, the current LPPs exhibit
several impressive advantages and also open up a new opportunity for the applications of LP catalysis: (1) Pushing the limits on accessible monomers, such as
the first effective LPPs of SFMAs, [51] epoxides, [71–73] as well as those notable
monomers derived from renewable biomass or natural products (e.g., MC [59], IN
[60], β-AL [61], OCA [69, 70]). (2) Realizing the controlled or even living polymerizations of divinyl acrylic monomers, [42, 46] acrylamides, [48] vinyl phosphonates, [52] epoxides, [72, 73] whose LPPs generally suffered from poor control
previously, via the development of LP catalyst with matched Lewis acidity, basicity,
and steric effects. (3) Enabling the synthesis of UHMW polymers with relatively
low dispersities, as seen in examples of UHMW PMMA by (BHT)Al
i Bu 2 /IAP-1
FLP, [38] SFPMAs by MeAl(BHT) 2 /I
t Bu LP, [51] PPO by Mg(HMDS) 2 /NHO-9
CLA [71]. (4) Establishing robust LP catalysts or convenient methodology for the
facile preparation of well-defined block copolymers, as demonstrated by the utilization of robust (BHT)Al
i Bu 2 /IAP-1 FLP for methacrylic multiblock copolymers with
DHDM features via sequential addition method, [41] one-pot manner to P
n BA-bP
t BA diblock [53] and poly(ether-b-ester-b-ether) triblock copolymers [75] from
n BA/
t BA and anhydride/excess epoxide monomer mixture using MeAl(BHT) 2 /PMe 3
and BEt 3 /
t Bu-P 2 LP, respectively, and a switchable polymerization to ether-estertype multiblock copolymer by switching the monomer selectivity through varying
the amount of BEt 3 and
t Bu-P 2 [74].
The accomplishments made in this time frame also points out several key challenges which are still in need of a solution in the field of LPPs. Currently, successful
LPPs are only limited to heteroatom-containing polar monomers. To the best of our
knowledge, less activated nonpolar monomers, such as conjugated dienes or styrenes
still remain unexplored. Therefore, extending the monomer scope and thus further
broadening the applications of LPPs will undoubtedly continue to be a major focus in
the future research. It would be also of great interest to develop novel LPPs capable of
constructing complex macromolecular structures with controlled topology or highorder sequence, which will be used to create polymeric materials with advanced properties and specific functions. Moreover, at present, highly stereoselective LPP can
only be achieved at low polymerization temperature (e.g., −78 °C) with compromised
activity. The design of new LP catalysts that allow highly stereoselective polymerization under mild conditions could become one of the next challenges to be addressed.