and biological ones. Physical stimuli (light, temperature, ultrasound, as well as
magnetic, mechanical and electrical fields) usually influence the chain dynamics
(they change the energy level of the polymer–solvent system), chemical stimuli
(co-solvent, ionic strength, pH, various non-ionic compounds), they impact intermolecular interactions while biological stimuli (enzymes, receptors) change the
molecule functioning (e.g., enzymatic or receptor properties) [1–4].
Two strategies for SRPS design can be used. One of them assumes a direct
application of stimuli-sensitive polymers while, in the case of the other one, the
polymer is combined with a stimuli-sensitive compound(s) and plays only a role of a
passive matrix or a carrier [1]. In this chapter, only the systems containing active
polymers will be discussed. Taking into account this limitation, the subject is still very
broad as the polymer sensitivity to a specific stimulus can be achieved in different
manners, including changes in the hydrophilic–hydrophobic balance, conformations
of macromolecules, solubility, degradation, and bond cleavage [1, 5]. One of the most
spectacular stimuli-responsive systems in nature is the protein of the egg white, which
turns into gel in high temperature, with the presence of salts or changes in pH. The sol–
gel transition resulting from protein denaturation is irreversible, while from applied
engineering systems it is expected to exhibit reversible transitions, ideally without
hysteresis. A variety of homo- and co-polymers and many different ways of their
synthesis open a gate to a vast array of different responsive materials and devices, such
as micro-valves and attenuators, lenses with the adjustable focal lengths, sensors, drug
carriers, smart textronics and many others. Furthermore, polymer properties can be
modified at different levels of the hierarchy, starting from a chemical structure (e.g., a
type and sequences of co-monomers) and isomerism (stereo-regularity, cis-trans
isomerism) to supramolecular structures. A particularly attractive possibility is to
form various polymer topologies (such as stars, combs and brushes, ladder-like,
dendrimers, hyperbranched and networks) and to locate stimuli-responsive groups in
different parts of a macromolecule [1, 5–9].
Depending on the chemical structure, including substitution by functional groups
and topology, polymer systems with sensitivity to different stimuli can be achieved.
Moreover, it is also possible to create dual and multi-stimuli-responsive polymers
that simultaneously respond to more than one stimulus. Depending on the polymer
architecture, different parameters are used to control the threshold value of a
stimulus. In the case of linear chains, these are molecular mass, length and a type of
side groups, a substitution degree, a co-monomer composition and end groups (for
telehelic macromolecules) [10–14]. As regards dendrimers, this is a generation of
dendrimer and functionality of their cores that determines the size of a polymer
molecule and the number of ending groups [15–28]. For star-like and brush-like
polymers, crucial parameters include the number of arms, their length and space
distribution. Space distribution is especially important in the case of arms made of
block co-polymers (including systems capable of sol–gel transition resulting from
aggregation of star-like macromolecules) and so-called mictoarms (stars containing
arms made of different polymers) [29–38]. It is also possible to design SRPS in a
form of permanent gel. The continuity of a polymer network (nano- and microgels
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magnetic, mechanical and electrical fields) usually influence the chain dynamics
(they change the energy level of the polymer–solvent system), chemical stimuli
(co-solvent, ionic strength, pH, various non-ionic compounds), they impact intermolecular interactions while biological stimuli (enzymes, receptors) change the
molecule functioning (e.g., enzymatic or receptor properties) [1–4].
Two strategies for SRPS design can be used. One of them assumes a direct
application of stimuli-sensitive polymers while, in the case of the other one, the
polymer is combined with a stimuli-sensitive compound(s) and plays only a role of a
passive matrix or a carrier [1]. In this chapter, only the systems containing active
polymers will be discussed. Taking into account this limitation, the subject is still very
broad as the polymer sensitivity to a specific stimulus can be achieved in different
manners, including changes in the hydrophilic–hydrophobic balance, conformations
of macromolecules, solubility, degradation, and bond cleavage [1, 5]. One of the most
spectacular stimuli-responsive systems in nature is the protein of the egg white, which
turns into gel in high temperature, with the presence of salts or changes in pH. The sol–
gel transition resulting from protein denaturation is irreversible, while from applied
engineering systems it is expected to exhibit reversible transitions, ideally without
hysteresis. A variety of homo- and co-polymers and many different ways of their
synthesis open a gate to a vast array of different responsive materials and devices, such
as micro-valves and attenuators, lenses with the adjustable focal lengths, sensors, drug
carriers, smart textronics and many others. Furthermore, polymer properties can be
modified at different levels of the hierarchy, starting from a chemical structure (e.g., a
type and sequences of co-monomers) and isomerism (stereo-regularity, cis-trans
isomerism) to supramolecular structures. A particularly attractive possibility is to
form various polymer topologies (such as stars, combs and brushes, ladder-like,
dendrimers, hyperbranched and networks) and to locate stimuli-responsive groups in
different parts of a macromolecule [1, 5–9].
Depending on the chemical structure, including substitution by functional groups
and topology, polymer systems with sensitivity to different stimuli can be achieved.
Moreover, it is also possible to create dual and multi-stimuli-responsive polymers
that simultaneously respond to more than one stimulus. Depending on the polymer
architecture, different parameters are used to control the threshold value of a
stimulus. In the case of linear chains, these are molecular mass, length and a type of
side groups, a substitution degree, a co-monomer composition and end groups (for
telehelic macromolecules) [10–14]. As regards dendrimers, this is a generation of
dendrimer and functionality of their cores that determines the size of a polymer
molecule and the number of ending groups [15–28]. For star-like and brush-like
polymers, crucial parameters include the number of arms, their length and space
distribution. Space distribution is especially important in the case of arms made of
block co-polymers (including systems capable of sol–gel transition resulting from
aggregation of star-like macromolecules) and so-called mictoarms (stars containing
arms made of different polymers) [29–38]. It is also possible to design SRPS in a
form of permanent gel. The continuity of a polymer network (nano- and microgels
224
M. Kozanecki et al.