Chemistry Reference
In-Depth Information
NHBoc
BocHN
BocHN
NHBoc
BocHN
NHBoc
O
O
BocHN
NHBoc
O
O
O
O
O
O
O
O
HN
NH
1. Deprotection
2. Dendronization
O
O
O
O
O
O
n
BocHN
NHBoc
MG1
PG1
O
O
O
O
O
N
1
O
n
O
O
PG2
1. Deprotection
2. Dendronization
1. Deprotection
2. Dendronization
1
PG2
PG3
PG4
1
NHBoc
BocHN
O
O
BocHN
NHBoc
O
O
O
O
HN
NH
O
O
O
O
MG2
SCHEME 4.1
Synthesis of a homologous series of dendronized polymers (
PG1
-
PG4
)
according to a powerful attach-to protocol and structure of macromonomer
MG2
used to
compare the two
PG2
s synthesized according to the attach-to and macromonomer protocol,
respectively. Compound
1
is the key building block used for dendronization, which is based on
active ester amidation.
The main characterization effort involved methods providing qualitative insights
concerning the growth processes. These comprised gel permeation chromatography
(GPC),
13
C NMR spectroscopy, and atomic force microscopy (AFM) apparent height
measurements. To be on the safe side all the samples were also checked by a
quantitative method based on UVabsorption. In them the unreacted terminal amines
of the dendronized polymers were converted into UV labels with high extinction
coefficient by reacting them with an excess of Sanger reagent [17]. Finally, the NMR
spectra of the second-generation polymers obtained by the attach-to route were
compared to those obtained by the macromonomer route starting from
MG2
(Scheme 4.1). For details the reader is referred to Ref. [14].
After having discussed so much about thickening and thickness of polymer chains
it is time to provide some experimental insight into this matter. Figure 4.4 shows the
AFMheight image recorded in tappingmode of a sample containing four dendronized
polymers
(structures derived fromM1 in Scheme 4.1) at the same time. As
can be seen, each object can unambiguously be assigned to a particular generation.
Since absolute heights are difficult to determine by the AFM, TEM images of low
angle shadowed samples were also recorded [19].
PG1-PG4
