Thickening behavior of thermo‐associative water soluble multiblock copolymers under redox RAFT polymerization

Abstract

In this study, the synthesis of thermo‐associative water soluble multiblock copolymers is reported. A trithiocarbonate functionalized polyacrylamide (PAM) was prepared and subsequently utilized in the preparation of three series of thermo‐associative copolymers by addition of N‐isopropylacrylamide (NIPAM) and acrylamide (AM) until reaching a nonablock copolymer with four thermo‐associative blocks distributed into the backbone of polymer. Reactions were performed at 25 °C using a tertbutyl hydroperoxyde (TBHP) and ascorbic acid (As.Ac.) as redox initiator, and S,S′‐Bis (α,α’‐dimethyl‐α”‐acetic acid)‐trithiocarbonate (DMAT) as chain transfer agent. The targeted molecular weight (MnTheo) of PAM was maintained constant (10,000 g/mol) while the expected Mntheo of polyN‐isopropylacrylamide (PNIPAM) was varied from 10,000, 15,000, and 20,000 g/mol, respectively. The synthesized copolymers were characterized by infrared (IR), nuclear magnetic resonance (NMR), size exclusion chromatography (SEC) for determining the structure of materials, whereas ultraviolet (UV) analysis allowed to get access to the cloud point temperature (Tcp) of polymers. Rheological analyses were carried out for examining the effect of thermo‐responsive block on the thickening behavior of aqueous polymer solutions. These analyses were performed at different concentration from 1 to 20 wt. % varying the temperature of measurements from 25, 30, 40, 50, 60, and 70 °C. Results confirmed the influence of the size of thermo‐responsive blocks on the viscosity of these copolymers.

Synthesis and rheological properties of water soluble ionic copolymers as modifier fluids at high temperature and saline media

“…This could lead to the development of intermolecular interactions which induced an increase the viscosity of the aqueous polymer solution. 57,58 Moreover, results from 1 H NMR measurements of copolymer (A 50 N 50 ) were performed at different temperature from 25 to 60 C showed similar spectra for all analyses (See Figure S2). This finding differs to rheological measurements and can be attributed to the probable formation of alternating structure PAM-alt-PNIPAM where the location of highly soluble PAM moieties impede the phase transition of the thermo-responsive PNIPAM fragments.…”

“…It is well known that the lower concentration solution temperature (LCST) of PNIPAM is close to 32°C and could enable a phase separation of macromolecule chains above LCST values conducting to the formation of hydrophobic fragments. This could lead to the development of intermolecular interactions which induced an increase the viscosity of the aqueous polymer solution 57,58 . Moreover, results from 1 H NMR measurements of copolymer (A 50 N 50 ) were performed at different temperature from 25 to 60°C showed similar spectra for all analyses (See Figure S2).…”

“…The influence of salts on the LCST of PNIPAM was widely investigated. Recently, Maldonado‐Textle et al reported the effect of salt on the SEC traces of alternating and block copolymer composed of PAM and PNIPAM, respectively 58 . It is worth to mentioning that the rheological measurements of saline solutions of copolymer (A 50 N 50 ) at 20 and 25 wt% of salt are not performed due to the phase separation to the mixture.…”

“…Recently, Maldonado-Textle et al reported the effect of salt on the SEC traces of alternating and block copolymer composed of PAM and PNIPAM, respectively. 58 It is worth to mentioning that the rheological measurements of saline solutions of copolymer (A 50 N 50 ) at 20 and 25 wt% of salt are not performed due to the phase separation to the mixture. Through elimination of interactions between water molecules and amine groups of PNIPAM, these moieties (previously soluble) change to hydrophobic segments which lead to the formation of intramolecular interactions inducing a reduction to the hydrodynamic volume of polymer chains, therefore the viscosity of these saline polymer solutions decreases.…”

Hydroxyapatite/hyperbranched polyitaconic acid/chitosan composite scaffold for bone tissue engineering

“…[38][39][40][41][42] Recently, the controlled/living radical polymerization has been investigated for itaconic acid monomer and its derivatives especially by using the reversible addition-fragmentation chain transfer (RAFT) process which is considered one of the easiest and most adaptable controlled/living radical polymerization systems due to its straightforward reaction procedure, broad range of applicable monomers, and high level of controllability. [43][44][45][46][47][48] In the current publication, a modified composite scaffold hydroxyapatite/hyperbranched polyitaconic acid/ chitosan (HAP/HBP-RAFT-PI/CS) was prepared. Accordingly, Itaconic acid monomer was RAFT polymerized using a hyperbranched macroinitiator (HBP-RAFT) to form polyitaconic acid (HBP-RAFT-PI) which was further involved by blending with hydroxyapatite and chitosan in the synthesis of a biocompatible anti-cancerous composite scaffold with a modified physicochemical and biological properties.…”