Polymerization of myrcene and its copolymerization with butadiene by half-sandwich scandium complexes

(C

5

Me

4

SiMe

3

)Sc(CH

2

SiMe

3

)

2

(THF) (

1

) and Cp′Sc(CH

2

C

6

H

4

NMe

2

-

o

)

2

(

2

: Cp′ = C

5

Me

4

SiMe

3

;

3

: Cp′ = C

5

H

5

)

have been examined. The microstructures and thermal properties of the obtained polymers were characterized by

1

H-NMR

13

C-NMR

GPC and DSC. Significant ligand influence on the catalytic activity

selectivity

and polymer molecular weight has been observed in the homopolymerization of myrcene. The scandium complexes

1

and

2

bearing large C

5

Me

4

SiMe

3

ligand showed relatively low activity (10

4

g polymer mol

Sc

−1

h

−1

) and preferred 3

4-selectivity (74% for

1

and 61% for

2

). The myrcene homopolymers prepared by complexes

1

and

2

have low molecular weight (

M

n

= 1.7 × 10

4

− 5.6 × 10

4

) and relatively high glass transition temperature (−48 and −45 °C). The complex

3

bearing small C

5

H

5

ligand showed high activity (10

5

g polymer mol

Sc

−1

h

−1

) and high

cis

-1

4-selectivity (95%). The myrcene homopolymers prepared by complex

3

have high molecular weight (

M

n

= 7.0 × 10

4

− 2.31 × 10

5

) and low glass transition temperature (

T

g

= −70 °C). By use of complex

3

the copolymerization of myrcene with butadiene was also achieved for the first time to afford a novel family of rubber materials. The copolymerization reaction was completed within 5 min

irrespective of the monomer feed ratio

and the copolymerization activity was raised to as high as 10

5

g polymer mol

Sc

−1

h

−1

. The copolymer composition was in agreement with the co-monomer feed ratio

suggesting that both monomers were completely incorporated into their copolymers. The obtained myrcene-butadiene copolymers showed a random monomer sequence distribution

and the

cis

-1

4 contents of both monomers in the copolymers were more than 92%. All of these copolymers showed a single

T

g

varing with the myrcene/butadiene ratio. The

T

g

s of the copolymers with myrcene content of 19 mol% − 75 mol% fell in a range of −95 °C to −71 °C

which are between those of homopolymyrcene (−70 °C) and homopolybutadiene (−107 °C). The

T

g

of the copolymers decreased with increasing butadiene content. The molecular weight of the myrcene-butadiene copolymers can be controlled simply by changing the monomer/catalyst ratio.