Abstract
A new polycondensation aromatic rigid-chain polyester macroinitiator was synthesized and used to graft linear poly-2-ethyl-2-oxazoline as well as poly-2-isopropyl-2-oxazoline by cationic polymerization. The prepared copolymers and the macroinitiator were characterized by NMR, GPC, AFM, turbidimetry, static, and dynamic light scattering. The molar masses of the polyester main chain and the grafted copolymers with poly-2-ethyl-2-oxazoline and poly-2-isopropyl-2-oxazoline side chains were 26,500, 208,000, and 67,900, respectively. The molar masses of the side chains of poly-2-ethyl-2-oxazoline and poly-2-isopropyl-2-oxazoline and their grafting densities were 7400 and 3400 and 0.53 and 0.27, respectively. In chloroform, the copolymers conformation can be considered as a cylinder wormlike chain, the diameter of which depends on the side chain length. In water at low temperatures, the macromolecules of the poly-2-ethyl-2-oxazoline copolymer assume a wormlike conformation because their backbones are well shielded by side chains, whereas the copolymer with short side chains and low grafting density strongly aggregates, which was visualized by AFM. The phase separation temperatures of the copolymers were lower than those of linear analogs of the side chains and decreased with the concentration for both samples. The LCST were estimated to be around 45 °C for the poly-2-ethyl-2-oxazoline graft copolymer, and below 20 °C for the poly-2-isopropyl-2-oxazoline graft copolymer.
Highlights
The synthesis of rigid-chain polymers in the middle of the 20th century was a breakthrough in polymer science and technology, which made it possible to obtain new ultrastrong materials
In connection with the above, the objectives of this work are: (i) the development of approaches to the controlled synthesis of copolymers (APEr.ch.-graft-PAlOx), in which thermosensitive PEtOx or PiPrOx are grafted to a rigid-chain aromatic polyester (APEr.ch.); (ii) determination of hydrodynamic and conformational characteristics of the synthesized APEr.ch.-graft-PAlOx; and (iii) the study of the thermal response of aqueous solutions of the synthesized molecular brushes and its dependence on the chemical structure of the side PAlOx chains
2-[4-(2-Br-ethyl)]phenylsulfonylhydroquinone (1) [73] and 2-isopropyl-2-oxazoline [95] were synthesized according to the known procedures. 1-Chloronaphthalene and 1,1,2,2tetrachloroethane (Aldrich) as well as oxazolines were dried over calcium hydride and distilled
Summary
The synthesis of rigid-chain polymers in the middle of the 20th century was a breakthrough in polymer science and technology, which made it possible to obtain new ultrastrong materials. The high rigidity of macromolecules predetermines their elongated state in the direction of the main chain and often provides lyotropic mesomorphism [1,2,3,4,5]. Such features are useful for creating high-strength fibers and films and selfreinforcing plastics, including those with specific optical and conductive properties [6,7,8,9]. Analysis of the various molecular structures showed that the high chain equilibrium and kinetic rigidity is the effect of a specific chemical structure of macromolecules [10,11]. In macromolecules with a comb-like structure, increased rigidity is induced by steric obstacles arising between the side chains, which impede the bending and folding of the main chain as a result of intramolecular thermal movement of the units [11,22,23]
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