St-Cl/H 2 , 1/48 for St-OSi/H 2 , and 1/34 for St-NSi 2 /H 2 . It is intriguing that the k tr /k p
values are significantly lower than those seen for styrene and p-MS under similar
reaction conditions. The bulky, protected functional groups may reduce the
frequency of the chain transfer reaction.
The terminal functional group at the polymer chain end provides direct evidence
for the chain transfer reaction. Figure 15 shows the
1
H NMR spectra (with an inset
of a magnified region and chemical shift assignments) of PP-t-St-OSi polymer
(M n ¼ 22.0 Â 10
3 , M w /M n ¼ 2.0) and the corresponding PP-t-St-OH. In addition
to three major peaks (δ ¼ 0.95, 1.35, and 1.65 ppm) for the CH 3, CH 2 , and CH
groups in the PP backbone, there are three minor chemical shifts at 0.25, 2.61, and
6.75–7.18 ppm (with an intensity ratio near 6/2/4) shown in Fig. 15a, corresponding
to –OSi(CH 3 ) 2 (t-Bu), –CH 2 –Ph, and –CH 2 –C 6 H 4 –OSi, respectively. The chemical
shift for the silane protecting group completely disappears in Fig. 15b, indicating
the occurrence of a very effective deprotection reaction during the sample workup
step by using HCl solution. The equally split chemical shifts for the phenyl protons,
combined with no detectable side product, further indicate the terminal
p-alkylphenol moiety. The same clean
1 H NMR results were also observed in
both PP-t-St-Cl and PP-t-St-NH 2 cases.
Overall, the experimental results strongly indicate a clean and effective reaction
scheme. The combination of the facile in-situ chain transfer to St-f/H 2 during the
catalytic polymerization of propylene and the subsequent complete deprotection
reaction during the sample workup step affords a very interesting reaction scheme
for the preparation of chain-end-functionalized i-PP with a Cl, OH, or NH 2 terminal
group via a one-pot reaction process.
3 Polyolefin Block and Graft Copolymers
In addition to the preparation of functional polyolefins with side chain and chainend functional groups (discussed above), the reactive groups (i.e., borane, p-MS,
and pendant styrene units) in the polyolefin also provide convenient routes for
preparation of polyolefin graft and block copolymers [52, 59–65], containing both a
polyolefin block (PE, PP, s-PS, etc.) and functional polymer block (acrylic
polymers), with good control of the molecular structure. In other words, instead
of obtaining a functional group from a reactive group, the same reactive group can
produce a functional polymer chain with hundreds and thousands of polar groups,
which significantly increases the efficiency of the reactive group. In fact, the
incorporated borane and p-MS groups have been transformed into “living” radical
and anion macro-initiators, respectively, for initiating graft-from polymerization
with well-controlled molecular structures. On the other hand, the incorporated DVB
unit resembles a styrene monomer that can involve the subsequent polymerization
reactions [49, 66]. A broad range of polyolefin graft and block copolymers have
been prepared that have high functional (polar) group concentrations without
compromising desirable polyolefin properties, such as crystallinity, melting
262
T.C.M. Chung
values are significantly lower than those seen for styrene and p-MS under similar
reaction conditions. The bulky, protected functional groups may reduce the
frequency of the chain transfer reaction.
The terminal functional group at the polymer chain end provides direct evidence
for the chain transfer reaction. Figure 15 shows the
1
H NMR spectra (with an inset
of a magnified region and chemical shift assignments) of PP-t-St-OSi polymer
(M n ¼ 22.0 Â 10
3 , M w /M n ¼ 2.0) and the corresponding PP-t-St-OH. In addition
to three major peaks (δ ¼ 0.95, 1.35, and 1.65 ppm) for the CH 3, CH 2 , and CH
groups in the PP backbone, there are three minor chemical shifts at 0.25, 2.61, and
6.75–7.18 ppm (with an intensity ratio near 6/2/4) shown in Fig. 15a, corresponding
to –OSi(CH 3 ) 2 (t-Bu), –CH 2 –Ph, and –CH 2 –C 6 H 4 –OSi, respectively. The chemical
shift for the silane protecting group completely disappears in Fig. 15b, indicating
the occurrence of a very effective deprotection reaction during the sample workup
step by using HCl solution. The equally split chemical shifts for the phenyl protons,
combined with no detectable side product, further indicate the terminal
p-alkylphenol moiety. The same clean
1 H NMR results were also observed in
both PP-t-St-Cl and PP-t-St-NH 2 cases.
Overall, the experimental results strongly indicate a clean and effective reaction
scheme. The combination of the facile in-situ chain transfer to St-f/H 2 during the
catalytic polymerization of propylene and the subsequent complete deprotection
reaction during the sample workup step affords a very interesting reaction scheme
for the preparation of chain-end-functionalized i-PP with a Cl, OH, or NH 2 terminal
group via a one-pot reaction process.
3 Polyolefin Block and Graft Copolymers
In addition to the preparation of functional polyolefins with side chain and chainend functional groups (discussed above), the reactive groups (i.e., borane, p-MS,
and pendant styrene units) in the polyolefin also provide convenient routes for
preparation of polyolefin graft and block copolymers [52, 59–65], containing both a
polyolefin block (PE, PP, s-PS, etc.) and functional polymer block (acrylic
polymers), with good control of the molecular structure. In other words, instead
of obtaining a functional group from a reactive group, the same reactive group can
produce a functional polymer chain with hundreds and thousands of polar groups,
which significantly increases the efficiency of the reactive group. In fact, the
incorporated borane and p-MS groups have been transformed into “living” radical
and anion macro-initiators, respectively, for initiating graft-from polymerization
with well-controlled molecular structures. On the other hand, the incorporated DVB
unit resembles a styrene monomer that can involve the subsequent polymerization
reactions [49, 66]. A broad range of polyolefin graft and block copolymers have
been prepared that have high functional (polar) group concentrations without
compromising desirable polyolefin properties, such as crystallinity, melting
262
T.C.M. Chung