It is to be noted that before and after the reaction, the particle size of the
BA/MM6 system (113 and 99 nm, respectively) was much smaller than that of
MBA/MM6 system (220 and 333 nm, respectively), both with PEREX 1.0 wt%. BA
lacks methyl group and hence is able to form compact particles. The molecular
weight of the copolymers was very high, with M n values ranging from 4.95 Â 10
4 to
1.64 Â 10
5 (M w values were from 1.01 Â 10
5 to 1.98 Â 10
5 ).
T g values of three graft copolymers (PBMA-g-PLAm with SDS 3.0 wt%) are
35
C for m ¼ 4, 37
C for m ¼ 6, and 40
C for m ¼ 8. The T g value of PBMA is
20
C and, hence, these T g values were much enhanced by the graft chain; for longer
graft chains, T g gradually increased. Physical properties are given in Table 3 for
three graft copolymer samples of PBMA-g-PLAm (SDS 3.0 wt%, PLA component
34 wt%). The physical strength is higher with the longer graft chain (m ¼ 8) than
with the shorter graft chain (m ¼ 4), whereas the elongation property is higher with
the shorter chain than with the longer chain. That is, when the total amount of the
PLA component is equal, the longer graft chains (yet with a smaller number of
chains) govern the bulk nature of the copolymer rather than the shorter graft chains
(even though there is a larger number of chains). This is a good example to
demonstrate the property relationship between the graft chain length and the
number of graft chains. All of graft copolymers are very elastic, soft materials as
can be seen from the elongation data (Table 3) [41, 42].
3 Green Catalysts: Enzyme-Catalyzed Synthesis
and Degradation of Polyesters
Enzymes are natural catalysts obtained from living systems. Generally, enzymatic
reactions have the following characteristics: (1) high catalytic activity; (2) reaction
under mild conditions with respect to temperature, pressure, solvent, pH of
medium, etc., bringing about energetic efficiency; and (3) high reaction selectivity
of regio-, enantio-, chemo-, and stereoregulation, giving rise to perfectly structurecontrolled products. If these in vivo characteristics could be realized for in vitro
enzymatic polymer synthesis (“enzymatic polymerization”) [13, 20], we may
expect the following advantages: (1) perfect control of polymer structures; (2) creation of polymers with a new structure; (3) a clean, selective process without
formation of by-products; (4) a low loading process with energy savings; and
(5) biodegradable properties of the product polymers in many cases. These are
indicative of the “green” nature of enzymatic catalysis for developing new polymeric materials. In fact, many of these expectations have been realized [13, 14,
16–23]. Enzymatic polymerization has been reviewed recently in a special
volume [46].
Lipase (triacylglycerol acylhydrolase, EC 3.1.1.3) is an enzyme that catalyzes
the hydrolysis of a fatty acid glycerol ester in vivo by bond cleavage; however, it
was disclosed that lipase catalyzes a polymerization reaction to give polyesters
Green Polymer Chemistry: Recent Developments
153
BA/MM6 system (113 and 99 nm, respectively) was much smaller than that of
MBA/MM6 system (220 and 333 nm, respectively), both with PEREX 1.0 wt%. BA
lacks methyl group and hence is able to form compact particles. The molecular
weight of the copolymers was very high, with M n values ranging from 4.95 Â 10
4 to
1.64 Â 10
5 (M w values were from 1.01 Â 10
5 to 1.98 Â 10
5 ).
T g values of three graft copolymers (PBMA-g-PLAm with SDS 3.0 wt%) are
35
C for m ¼ 4, 37
C for m ¼ 6, and 40
C for m ¼ 8. The T g value of PBMA is
20
C and, hence, these T g values were much enhanced by the graft chain; for longer
graft chains, T g gradually increased. Physical properties are given in Table 3 for
three graft copolymer samples of PBMA-g-PLAm (SDS 3.0 wt%, PLA component
34 wt%). The physical strength is higher with the longer graft chain (m ¼ 8) than
with the shorter graft chain (m ¼ 4), whereas the elongation property is higher with
the shorter chain than with the longer chain. That is, when the total amount of the
PLA component is equal, the longer graft chains (yet with a smaller number of
chains) govern the bulk nature of the copolymer rather than the shorter graft chains
(even though there is a larger number of chains). This is a good example to
demonstrate the property relationship between the graft chain length and the
number of graft chains. All of graft copolymers are very elastic, soft materials as
can be seen from the elongation data (Table 3) [41, 42].
3 Green Catalysts: Enzyme-Catalyzed Synthesis
and Degradation of Polyesters
Enzymes are natural catalysts obtained from living systems. Generally, enzymatic
reactions have the following characteristics: (1) high catalytic activity; (2) reaction
under mild conditions with respect to temperature, pressure, solvent, pH of
medium, etc., bringing about energetic efficiency; and (3) high reaction selectivity
of regio-, enantio-, chemo-, and stereoregulation, giving rise to perfectly structurecontrolled products. If these in vivo characteristics could be realized for in vitro
enzymatic polymer synthesis (“enzymatic polymerization”) [13, 20], we may
expect the following advantages: (1) perfect control of polymer structures; (2) creation of polymers with a new structure; (3) a clean, selective process without
formation of by-products; (4) a low loading process with energy savings; and
(5) biodegradable properties of the product polymers in many cases. These are
indicative of the “green” nature of enzymatic catalysis for developing new polymeric materials. In fact, many of these expectations have been realized [13, 14,
16–23]. Enzymatic polymerization has been reviewed recently in a special
volume [46].
Lipase (triacylglycerol acylhydrolase, EC 3.1.1.3) is an enzyme that catalyzes
the hydrolysis of a fatty acid glycerol ester in vivo by bond cleavage; however, it
was disclosed that lipase catalyzes a polymerization reaction to give polyesters
Green Polymer Chemistry: Recent Developments
153