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screening and accessibility of hydrogen bonding interactions (because they are direc-
tional) as well as the competition between self-association and complementary
association. In some cases, single hydrogen bonding groups at the chain ends
phase separate from the bulk polymer (Lillya et al. 1992; Sivakova et al. 2005).
This is particularly possible when hydrogen bonding interactions occur in multiple
directions, facilitating the organization of the chain ends (Kautz et al. 2006).
4.3.1. Block Copolymers Involving Single Hydrogen Bonding Groups
Hydrogen bonding block copolymers containing single hydrogen bonding groups
have attracted attention because of the simplicity of their preparation via anionic
polymerization techniques of commonly available monomers. One specific template
is poly(vinylpyridine), which is often blended with complementary poly(methacrylic
acid) (Jiang et al. 2003) or poly(4-hydroxystyrene). Anionic polymerization pos-
sesses a limitation in these cases that is due to the sensitivity of anionic polymeriz-
ation to protic functionality. Thus, protecting group strategies are often employed.
In the case of 4-hydroxystyrene, silyl protecting groups are employed; in the case of
methacrylic acid residues, tert-butyl ester protecting groups are employed. Another
strategy involves postpolymerization modification. Liu and Jiang (1995) introduced
carboxylic acid groups and hydroxyl groups into styrene-ethylene-butylene-
styrene polymers via Friedel -Crafts acylation and subsequent oxidation or redu-
ction of the ketone functional groups. Other strategies involve protecting group
chemistry. In the case of 4-hydroxystyrene based blocks, a silyl protected
monomer is polymerized and deprotected after completion of the polymerization.
Block copolymers containing complementary monomers such as 2-vinylpyridine
and 4-hydroxystyrene or methacrylic acid were shown to produce novel morphologies
in which the complementary segments are mixed in domains, which are phase sep-
arated from the bulk polymer (Asari et al. 2005). Jiang et al. (2003) blended poly
(styrene-b-butadiene-b-tert-butyl methacrylate-co-methacrylic acid) (SBT/A) with
poly(styrene-b-2-vinylpyridine) (SV) to obtain a compatibilized blend. The degree
of hydrogen bonding interaction was varied through controlling the level of hydroly-
sis of the tert-butyl methacrylate residues to methacrylic acid residues. For partially
hydrolyzed SBT polymers (18-51% hydrolyzed), blending with SV led to a tran-
sition from a double gyroid or lamellar morphology (SBT/A-A/TBS) to hcp V-
T/A cylinders in B lamella alternating with S lamella. Asari and colleagues (2006)
conducted a similar study where poly(2-vinylpyridine-b-isoprene-b-2-vinylpyridine)
triblocks with a mole fraction of vinylpyridine of 0.07 and poly(styrene-b-4-
hydroxystyrene) with a 4-hydroxystyrene mole fraction of 0.14 were blended in
either a 1:1 or 2:1 2-vinylpyridine/4-hydroxystyrene ratio. Archimedean tile mor-
phologies resulted, which consisted of rows of vinylpyridine with 4-hydroxystyrene
cylinders staggered between polyisoprene and polystyrene lamella for the 1:1 ratio or
hexagons of polystyrene in an polyisoprene matrix with poly(2-vinylpyridine) with
poly(4-hydroxystyrene) cylinders at the corners of the styrene hexagons (Fig. 4.2).
Asari et al. established the 4-hydroxystyrene/2-vinylpyridine hydrogen bonding
