Synthesis and Characterization of ABA-Type Triblock Copolymers Using Novel Bifunctional PS, PMMA, and PCL Macroinitiators Bearing p-xylene-bis(2-mercaptoethyloxy) Core

Syntheses of novel bifunctional poly(methyl methacrylate) (PMMA)-, poly(styrene) (PS)-, and (poly ε-caprolactone) (PCL)-based atom transfer radical polymerization (ATRP) macroinitiators derived from p-xylene-bis(1-hydroxy-3-thia-propanoloxy) core were carried out to obtain ABA-type block copolymers. Firstly, a novel bifunctional ATRP initiator, 1,4-phenylenebis(methylene-thioethane-2,1-diyl)bis(2-bromo-2-methylpropanoat) (PXTBR), synthesized the reaction of p-xylene-bis(1-hydroxy-3-thia-propane) (PXTOH) with α-bromoisobutryl bromide. The PMMA and PS macroinitiators were prepared by ATRP of methyl methacrylate (MMA) and styrene (S) as monomers using (PXTBR) as the initiator and copper(I) bromide/N,N,N',N″,N″-pentamethyldiethylenetriamine (CuBr/PMDETA) as a catalyst system. Secondly, di(α-bromoester) end-functionalized PCL-based ATRP macronitiator (PXTPCLBr) was prepared by esterification of hydroxyl end groups of PCL-diol (PXTPCLOH) synthesized by Sn(Oct)2-catalyzed ring opening polymerization (ROP) of ε-CL in bulk using (PXTOH) as initiator. Finally, ABA-type block copolymers, PXT(PS-b-PMMA-b-PS), PXT(PMMA-b-PS-b-PMMA), PXT(PS-b-PCL-b-PS), and PXT(PMMA-b-PCL-b-PMMA), were synthesized by ATRP of MMA and S as monomers using PMMA-, PS-, and PCL-based macroinitiators in the presence of CuBr/PMDETA as the catalyst system in toluene or N,N-dimethylformamide (DMF) at different temperatures. In addition, the extraction abilities of PCL and PS were investigated under liquid-liquid phase conditions using heavy metal picrates (Ag+, Cd2+, Cu2+, Hg2+, Pb2+, and Zn2+) as substrates and measuring with UV-Vis the amounts of picrate in the 1,2-dichloroethane phase before and after treatment with the polymers. The extraction affinity of PXTPCL and PXTPS for Hg2+ was found to be highest in the liquid-liquid phase extraction experiments. Characterizations of the molecular structures for synthesized novel initiators, macroinitiators, and the block copolymers were made by spectroscopic (FT-IR, ESI-MS, 1H NMR, 13C NMR), DSC, TGA, chromatographic (GPC), and morphologic SEM.

Acrylic AB and ABA block copolymers based on poly(2-ethylhexyl acrylate) (PEHA) and poly(methyl methacrylate) (PMMA) via ATRP

Acrylic block copolymers have several advantages over conventional styrenic block copolymers, because of the presence of a saturated backbone and polar pendant groups. This investigation reports the preparation and characterization of di- and triblock copolymers (AB and ABA types) of 2-ethylhexyl acrylate (EHA) and methyl methacrylate (MMA) via atom transfer radical polymerization (ATRP). A series of block copolymers, PEHA-block-PMMA(AB diblock) and PMMA-block-PEHA-block-PMMA(ABA triblock) were prepared via ATRP at 90 °C using CuBr as catalyst in combination with N,N,N',N″,N″-pentamethyl diethylenetriamine (PMDETA) as ligand and acetone as additive. The chemical structure of the macroinitiators and molar composition of block copolymers were characterized by (1)H NMR analysis, and molecular weights of the polymers were analyzed by GPC analysis. DSC analysis showed two glass transition temperatures (T(g)), indicating formation of two domains, which was corroborated by AFM analysis. Small-angle X-ray scattering (SAXS) analysis of AB and ABA block copolymers showed scattering behavior inside the measuring limits indicating nanophase separation. However, SAXS pattern of AB diblock copolymers indicated general phase separation only, whereas for ABA triblock copolymer an ordered or mixed morphology could be deduced, which is assumed to be the reason for the better mechanical properties achieved with ABA block copolymers than with the AB analogues.