Novel Thermoresponsive Polymers Tunable by pH

Abstract

Thermoresponsive polymers that are pH tunable were successfully synthesized by a combination of atom transfer radical polymerization (ATRP) and Cu(I)-catalyzed 1,3-dipolar cycloaddition of azide and alkynes (click chemistry). ATRP was employed to synthesize poly(2-hydroxyethyl methacrylate) (PHEMA), followed by introduction of alkyne groups using pentynoic acid, leading to PHEMA-alkyne. 2-Azidoethylamine, 2-azido-N,N-dimethylethylamine, and 2-azido-N,N-diethylethylamine were added to the PHEMA-alkyne backbone via click chemistry. Molecular weight, molecular weight distribution, and click reaction efficiency were determined by gel permeation chromatography (GPC) and 1H NMR spectroscopy. The average molecular weight (M n) of the resulting polymers ranged from 5.6 × 104 to 7.0 × 104 depending on the molecular architecture. The molecular weight distribution was low (M n/M n = 1.25−1.35). The transmission spectra of the 0.1 wt % aqueous solutions of the resulting polymers with different pH values at 650 nm were measured as a function of temperature. Results showed that the lower critical solution temperature (LCST) could be dramatically affected by solution pH. To give additional evidence for pH-responsive thermal transition, in-situ temperature-dependent 1H NMR measurements in deuterated water (0.01 wt %) were conducted. The LCST values measured by in-situ 1H NMR correlated well with those determined by turbidimetry.

Stimuli‐Sensitive Synthetic Polypeptide‐Based Materials for Drug and Gene Delivery

“…The primary amine‐, secondary amine‐, and dimethylamine‐substituted PPLG show no detectable phase transition within the experimental pH range. This is different from the solution behavior of amino‐functionalized poly(2‐hydroxyethyl methacrylate)s (PHEMA) that are also synthesized by grafting the amino groups to PHEMA via “click” chemistry 257. Sharp pH‐induced phase‐transitions were observed for the primary amine‐ and dimethylamine‐functionalized PHEMA at pH 12.3 and 9.7, respectively.…”

Dual Responsiveness of a Tunable Thermosensitive Polypeptide

“…This temperature responsiveness is not surprising considering the polymer's structural similarities to other known amine containing temperature responsive polymers. 10 …”

Precise Control of Thermoresponsive Properties of Polymers with Hydroxy Groups in the Side Chains

“…21 Briefly, atom transfer radical polymerization (ATRP) was directly employed to prepare PHEMA using a CuCl/bpy catalyst system with 2-bromoisobutyrate (EBiB) as an initiator. The resulting PHEMA was reacted with pentynoic acid to yield PHEMA-alkyne in the presence of DCC.…”