Charge-Shifting Polycations with Tunable Rates of
Hydrolysis: Effect of Backbone Substituents on Poly[2-(dimethylamino)ethyl
acrylates]
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Abstract
While polycations
based on 2-(dimethylamino)ethyl methacrylate
and 2-(dimethylamino)ethyl acrylate are used in applications ranging
from biomaterials to wastewater treatment, few studies have considered
the remarkable differences in the hydrolytic stabilities of the respective
ester groups. Here, we describe how the nature of nonmethyl α-substituents
affect the rates of ester hydrolysis of such polymers, with an emphasis
on the resulting shift of net polymer charge from cationic toward
anionic. We introduce 2-(dimethylamino)ethyl 2-hydroxymethyl acrylate
(DHMA) as a new, very hydrolytically labile, cationic monomer that
can be used to form homopolymers as well as a means to tune copolymer
hydrolysis. DHMA synthesis and free radical polymerization are described,
including reactivity ratios for hydroxyl-protected derivatives of
DHMA and 2-(dimethylamino)ethyl acrylate (DMAEA). Hydrolyses of PDHMA,
P[DHMA-<i>co</i>-DMAEA], PDMAEA, and PDMAEMA in pH 5 and
7 buffer are reported. The presence of the hydroxymethyl α-substituent
in PDHMA led to rates of hydrolysis 2–3 orders of magnitude
faster than the already rapid hydrolysis of PDMAEA. Furthermore, hydrolysis
rates of P[DHMA-<i>co</i>-DMAEA] copolymers were shown to
increase as the DHMA mole fraction increased. As a result, a new route
to adjusting the charge-shifting rates of such polycations in aqueous
media is described