Table Of ContentPreface
The pleasingly favourable reception ofthe tetralogy on dendrimer chemistry in
the Topics in Current Chemistry series prompted us to assemble the present fol-
low-up issue “Dendrimers V”.This is also justified by the quickly growing field,
in particular,because the focus had not been directed towards the exciting appli-
cations that dendrimers have found recently.Dendrimer chemistry is experienc-
ing new challenges coming from supramolecular chemistry, nanotechnology,
and biochemistry and the new developments emerging from these interdiscipli-
nary marriages ofdifferent fields are invaluable for the future ofmaterials and
life sciences.This is also reflected in the large number ofrecent publications in
these areas dealing with dendritic molecules.
In this issue,the reader will find contributions from the whole scope ofden-
drimer chemistry,some ofwhich are shorter as they describe new developments
which are currently emerging.We start with the synthesis of hyperbranched
acrylates reviewed by Hideharu Mori and Axel Müller who give profound insight
into the properties ofhyperbranched polymers in solution,the melt and on sur-
faces.The exciting new results in the field ofmetallodendrimers form the focus
of the next chapter written by Kiyotaka Onitsuka and Shigetoshi Takahashi,
which at the same time introduces a “mini-series”ofarticles dealing with den-
drimers containing particular building blocks implementing exactly defined
properties which may lead to function.These are porphyrin-containing den-
drimers which are highlighted by Ken-ichi Sugiura, dendrimers that bear
fullerenes as expertly discussed by Jean-François Nierengarten,and dendrimers
with mechanically bound entities incorporated within their scaffold summar-
ized and beautifully categorized by Kimoon Kim and Jae Wook Lee. Several
reviews deal with the applications ofdendrimers:Kensuke Naka gives an excel-
lent overview on the potential of dendrimers to stimulate and control the
crystallization ofcalcium carbonate,Vincenzo Balzani,Manabu Kawa,Shiyoshi
Yokoyama and their coworkers acted as pioneering authors of three chapters
containing a firework of applications of dendrimers in photochemistry and
their photochemical analysis.Luminescent dendrimers,antenna effects,and the
use ofoptoelectronics are described in depth in these reviews.Finally,the jour-
ney through this volume and the chemistry of dendrimers ends with two in-
triguing biochemistry- and biology-oriented contributions on gene transfection
by Jörg Denning and on antibody dendrimers by Hiroyasu Yamaguchi and Akira
Harada which demonstrate the enormous potential ofdendritic structures and
the broad scope this field has meanwhile developed.
VIII Preface
It is with great pleasure and enthusiasm that we present this fifth volume of
what was originally intended to be a tetralogy.This volume is not only a heavy-
weight because ofits size and the sheer number ofcontributions (eleven!),but
also due to the variety and quality ofits scientific contents.Reflecting the quick-
ly growing field ofdendrimer chemistry,we also regard it as a timely update to
the two „dendrimer bibles“ by Fréchet and Tomalia1and Newkome et al.2which
appeared in print earlier. In this respect, we are looking forward to learning
about the further progress made beyond the results discussed here at the 3rd
International Dendrimer Symposium,September 17th–20th,2003,in Berlin.
Bonn,March 2003 Christoph A.Schalley,
Fritz Vögtle
1 JMJ Fréchet,DA Tomalia (2001) Dendrimers and other Dendritic Polymers.Wiley,Chichester,UK.
2 GR Newkome,CN Moorefield,F Vögtle (2001) Dendrimers and Dendrons.Wiley-VCH,Weinheim,
Germany.
Contents
Hyperbranched (Meth)acrylates in Solution,in the Melt,and Grafted
From Surfaces
H.Mori,A.Müller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Metallodendrimers Composed ofOrganometallic Building Blocks
K.Onitsuka,S.Takahashi . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
An Adventure in Macromolecular Chemistry Based on the Achievements
ofDendrimer Science:Molecular Design,Synthesis,and Some Basic
Properties ofCyclic Porphyrin Oligomers to Create a Functional
Nano-Sized Space
K.Sugiura . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Fullerodendrimers:Fullerene-Containing Macromolecules
with Intriguing Properties
J.-F.Nierengarten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Rotaxane Dendrimers
J.W.Lee,K.Kim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Effect ofDendrimers on the Crystallization ofCalcium Carbonate
in Aqueous Solution
K.Naka . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Luminescent Dendrimers.Recent Advances
V.Balzani,P.Ceroni,M.Maestri,C.Saudan,V.Vicinelli . . . . . . . . . . . 159
Antenna Effects ofAromatic Dendrons and Their Luminescene
Applications
M.Kawa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
Dendrimers for Optoelectronic Applications
S.Yokoyama,A.Otomo,T.Nakahama,Y.Okuno,S.Mashiko . . . . . . . . . 205
Gene Transfer in Eukaryotic Cells Using Activated Dendrimers
J.Dennig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Antibody Dendrimers
H.Yamaguchi,A.Harada . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
Author Index Volumes 201–228 . . . . . . . . . . . . . . . . . . . . . . . . 259
Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
Top Curr Chem (2003) 228:1–37
DOI 10.1007/b11004
Hyperbranched (Meth)acrylates in Solution, Melt,
and Grafted From Surfaces
Hideharu Mori · Axel H.E.Müller
Makromolekulare Chemie II,Bayreuther Institut für Makromolekülforschung
and Bayreuther Zentrum für Kolloide und Grenzflächen,Universität Bayreuth,
95440 Bayreuth,Germany
E-mail:[email protected]
This review summarizes recent advances in the synthesis and characterization of hyper-
branched (meth)acrylates.We will focus on self-condensing vinyl (co)polymerization as an
effective method for the synthesis of hyperbranched polymers. Molecular parameters of
hyperbranched polymers obtained by self-condensing vinyl (co)polymerization are discussed
from a theoretical point of view.Solution properties and melt properties of the resulting
hyperbranched poly(meth)acrylates and poly(acrylic acid)s are reviewed.A novel synthetic
concept for preparing hyperbranched polymer brushes on planar surfaces and nanoparticles
is also described.
Keywords.Hyperbranched polymers,(Meth)acrylates,Self-condensing vinyl polymerization,
Controlled polymerization, Surface-grafted hyperbranched polymers, Polymer brushes,
Hybrid nanoparticles
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Self-Condensing Vinyl Polymerization (SCVP) . . . . . . . . . . . . . 4
2.2 Self-Condensing Vinyl Copolymerization (SCVCP) . . . . . . . . . . . 8
3 Molecular Parameters ofHyperbranched Polymers Obtained
by SCVP and SCVCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1 Molecular Weight Distribution (MWD) . . . . . . . . . . . . . . . . . 9
3.2 Degree ofBranching (DB) . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3 Experimental Evaluation ofDB . . . . . . . . . . . . . . . . . . . . . . 11
4 Solution Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.1 In Organic Solvent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2 In Aqueous Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5 Melt Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
© Springer-Verlag Berlin Heidelberg 2003
2 H.Mori · A.H.E.Müller
6 Surface-Grafted Hyperbranched Polymers . . . . . . . . . . . . . . . 26
6.1 Hyperbranched Polymers Grafted from Planar Surfaces . . . . . . . . 28
6.2 Hyperbranched Polymers Grafted from Spherical Particles . . . . . . 31
6.3 Theoretical Considerations . . . . . . . . . . . . . . . . . . . . . . . . 32
7 Summary and Perspective . . . . . . . . . . . . . . . . . . . . . . . . 33
8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Abbreviations
DB degree ofbranching
g,g¢ contraction factor
g comonomer ratio=[monomer] /[inimer]
0 0
a Mark–Houwink exponent
GPC gel permeation chromatography
MALS multi-angle light scattering
UNICAL universal calibration
NMR nuclear magnetic resonance
MW molecular weight
MWD molecular weight distribution
SCVP self-condensing vinyl polymerization
SCVCP self-condensing vinyl copolymerization
t-BuA tert-butyl acrylate
Pt-BuA poly(tert-butyl acrylate)
MMA methyl methacrylate
PMMA poly(methyl methacrylate)
PAA poly(acrylic acid)
ATRP atom transfer radical polymerization
GTP group transfer polymerization
1
Introduction
In the past decade, the field of arborescent polymers (dendrimers, hyper-
branched,and highly branched polymers) has been well established with a large
variety ofsynthetic approaches,fundamental studies on structure and proper-
ties ofthese unique materials,and possible applications [1–4].Dendrimers are
monodisperse molecules with well-defined, perfectly branched architectures,
made in a multi-step organic synthesis.In contrast,hyperbranched polymers
are made in a one-pot polymerization,making them promising candidates for
industrial applications where ultimate perfection in structural uniformity is less
needed.However,they are less regular in structure and their degree ofbranch-
ing (DB) typically does not exceed 50% ofthat ofdendrimers.
Hyperbranched (Meth)acrylates in Solution,Melt,and Grafted From Surfaces 3
As early as 1952, Flory [5, 6] pointed out that the polycondensation of
AB -type monomers will result in soluble “highly branched”polymers and he
x
calculated the molecular weight distribution (MWD) and its averages using a
statistical derivation.Ill-defined branched polycondensates were reported even
earlier [7,8].In 1972,Baker et al.reported the polycondensation ofpolyhydrox-
ymonocarboxylic acids,(OH) R-COOH,where n is an integer from two to six
n
[9].In 1982,Kricheldorfet al.[10] published the cocondensation ofAB and AB
2
monomers to form branched polyesters.However,only after Kim and Webster
published the synthesis of pure “hyperbranched” polyarylenes from an AB
2
monomer in 1988 [11–13],this class of polymers became a topic of intensive
research by many groups.A multitude ofhyperbranched polymers synthesized
via polycondensation ofAB monomers have been reported,and many reviews
2
have been published [1,2,14–16].
The interest in hyperbranched polymers arises from the fact that they com-
bine some features of dendrimers,for example,an increasing number of end
groups and a compact structure in solution,with the ease ofpreparation oflin-
ear polymers by means ofa one-pot reaction.However,the polydispersities are
usually high and their structures are less regular than those of dendrimers.
Another important advantage is the extension ofthe concept ofhyperbranched
polymers towards vinyl monomers and chain growth processes,which opens
unexpected possibilities.
Several strategies for the preparation ofhyperbranched polymers are current-
ly employed.The polymerization reactions are classified into three categories [1,
4,17]: (1) step-growth polycondensation of AB monomers; (2) chain-growth
x
self-condensing vinyl polymerization (SCVP) of AB* initiator–monomers
(“inimers”);(3) chain-growth self-condensing ring-opening polymerization of
Table 1. Classification ofdifferent types ofmonomers for synthesis ofhyperbranched polymers
Step growth
AB
2
Self-condensing vinyl polymerization
Chain growth
AB*
Self-condensing ring-opening polymerization
4 H.Mori · A.H.E.Müller
cyclic inimers.Table 1 compares the step-growth and chain-growth methods.
The most common method is the polycondensation ofAB monomers.Howev-
x
er,vinyl monomers cannot be polymerized by that approach.The recent discov-
ery ofSCVP made it possible to use vinyl monomers for a convenient,one-pot
synthesis of hyperbranched vinyl polymers [18–25]. By copolymerizing AB*
inimers with conventional monomers,the SCVP technique was extended to self-
condensing vinyl copolymerization (SCVCP), leading to highly branched
copolymers where the degree of branching (DB) is controlled by the como-
nomer ratio [26–31]. By using these techniques, a variety of hyperbranched
polymers can be synthesized.The scope ofthis review will cover hyperbranched
(meth)acrylates that have been made using SCV(C)P.
2
Synthesis
2.1
Self-Condensing Vinyl Polymerization (SCVP)
In attempts to synthesizew-styrylpolyisobutylene usingm-/p-(chloromethyl)-
styrene as an initiator and aluminum alkyls/H O as co-initiators,Kennedy and
2
Frisch [32] found significantly less than 100% of vinyl groups in the product.
They concluded that copolymerization ofthe vinyl group ofthe “initiator”with
isobutylene occurred as a “deleterious side reaction”.In a similar experiment,
Nuyken et al.[33] observed the formation ofsoluble polymers with much high-
er than calculated molecular weights (MWs) and broad MWD and attributed
this to the formation of branched copolymers.On the other hand,attempted
copolymerizations of isobutylene with p-(chloromethyl)styrene or p-(chloro-
methyl)-a-methylstyrene initiated with boron trifluoride or EtAlCl were re-
2
ported earlier [34,35].All these results indicate that p-(chloromethyl)styrene
acts both as a cationic initiator and as a monomer.In 1991,Hazer [36,37] poly-
merized macromonomers which carried an azo function at the other terminus
and named them “macroinimers”.
However,it was Fréchet et al.who recognized the importance of initiator–
monomers (later called “inimers”) to synthesize hyperbranched polymers from
vinyl monomers and in 1995 they named the process “self-condensing vinyl
polymerization”(SCVP) [18].Initiator–monomers (later called “inimers”[38,
39]) have the general structure AB*,where the double bond is designated A and
B* is a group capable of being activated to initiate the polymerization of vinyl
groups.Scheme1 shows initial steps in SCVP.In order to initiate the polymer-
ization,the B* group is activated.Upon activation of a B* group,the polymer-
ization starts by addition ofthe B* group to the double bond ofanother inimer,
resulting in the formation of the dimer,Ab–A*B*.The asterisk indicates that a
structural group can add monomer; it can be either in its active or dormant
form.Lowercase letters indicate that the group has been consumed and can no
longer participate in the polymerization. The resulting dimer has two active
sites,A* (propagating) and B* (initiating),for possible chain growth besides the
vinyl group.Addition of a third monomer unit at either site results in the for-
Hyperbranched (Meth)acrylates in Solution,Melt,and Grafted From Surfaces 5
Scheme 1. Initial steps in SCVP and SCVCP.Capital letters indicate vinyl groups (A and M) and
active centers (A*,B*,M*),lowercase letters stand for reacted ones (a,b,m)
mation of the trimer which can now grow in three directions.Also,oligomers
(i.e.,two dimers) or polymers can react with each other,similar (but mechanis-
tically different) to a polycondensation.The polymerization can also be initiat-
ed by a mono- ofmultifunctional initiator,leading to better control ofMWD and
DB,especially when the inimer is added slowly [40].
AB* inimers used for SCV(C)P are listed in Fig.1.A variety ofacrylate-type
inimers have been reported,including1,2[23–25],3[41],4[42],5[43],6[44],7
[45], and 8 [46]. In general, Cu-based atom transfer radical polymerization
(ATRP) was employed for SCVP ofthese acrylate-type inimers with an acrylate
(A) and a bromoester group (B*) capable of initiating ATRP. For example, it
was demonstrated that the polymerization of the inimer1 catalyzed by CuBr/
4,4¢-di-tert-butyl-2,2¢-bipyridine at 50°C provided a hyperbranched polymer
(DB=0.49) [23,24].In addition,kinetics and mechanism of chain growth for
SCVP of the inimer1and evaluation of the DB of the resulting polymers were
investigated. The significant influence of solubility of the deactivator and of
thepolymerization temperature,which are closely related to the concentration
of Cu(II), on the topology of the resulting polymers has been also reported
[25].However,methacrylate-type inimers9and10as well as the acrylate-type
inimer2could not be successfully polymerized by such Cu-based ATRP despite
variations in ligand and temperature [47].It was speculated that the tertiary
radical sites generated from methacrylate moieties (A) and/or the 2-bro-
moisobutyryloxy moieties (B*) coupled rapidly, forming an excess amount
of deactivating Cu(II) species and prevented polymerization.For the prepara-
tion of hyperbranched methacrylates,Cu-based ATRP with addition of zero-
6 H.Mori · A.H.E.Müller
Fig.1. AB* vinyl inimers (initiator–monomers) used for SCVP and SCVCP
valent copper for9[47],Ni-based controlled radical polymerization for9[48],
Cu-based ATRP for 11 [49], group transfer polymerization (GTP) for 12
[20,50],and photo-initiated radical polymerization for 13 [51] have all been
employed.
For SCVP of styrenic inimers,the mechanism includes cationic (14[18],19
[29]),atom transfer radical (15 [22,27]),nitroxide-mediated radical (16 [21]),
anionic (20 [19]),photo-initiated radical (17 [2],18 [52–55]),and ruthenium-
catalyzed coordinative (21[56]) polymerization systems.Another example in-
Hyperbranched (Meth)acrylates in Solution,Melt,and Grafted From Surfaces 7
Fig.1(continued)
volves vinyl ether-type inimers22and23which undergo cationic polymeriza-
tion in the presence ofa Lewis acid activator,such as zinc chloride [26,57,58].
Self-condensing anionic and cationic ring-opening polymerizations have been
also reported [4,59] (see examples in Table1).
Note that polymerization of compounds13,17,and18is based on a dithio-
carbamate radical formed by UV radiation and the methylmalodinitrile radical
formed by decomposition ofan azo group.These fragments act as reversible ter-
minating/transfer agents,but not as initiators.Hence,these compounds cannot
be regarded as initiator–monomers,but the mechanism is analogous to SCVP.
There are also several accounts of preparing branched polymers from
(meth)acrylate derivatives [60–63], in which polymerization systems can be
regarded as SCVP analogs.
