Synthesis Of Linear Block Copolymers Research Articles

Effect of Block Length and Stereocomplexation on the Thermally Processable Poly(ε-caprolactone) and Poly(Lactic acid) Block Copolymers for Biomedical Applications

The current research concentrates on the synthesis of linear block copolymers with their backbone consisting of hard and soft segments, that is, poly(L-lactic acid) (PLLA)/ poly(D-lactic acid) (PDLA) and poly(e-caprolactone) (PCL), with the detailed investigation of the effect of block length on the thermal, mechanical, and crystallization behavior followed by their processing and biocompatibility evaluation. In the current work, sequential ring opening polymerization has been employed wherein PCL is used as a macroinitiator for the synthesis of diblock (PCL-PDLA and PCL-PLLA) and stereotriblock copolymers (PCL-PLLA-PDLA) of targeted molecular weight, which is confirmed by 1H NMR spectroscopy. The block length of PCL, in the case of diblock copolymer, is fixed; however, that of PLLA or PDLA is varied, and the enantiomeric blends thereof are made to achieve the merits of stereocomplexation. The length of the individual blocks is the same in the case of stereotriblock copolymer. The presence of two crystall...

Polyphosphazenes – Synthetically Versatile Block Copolymers (“Multi‐Tool”) for Self‐Assembly

This microreview outlines recent advances on the synthesis and self‐assembly of polyphosphazene diblock copolymers, a class of versatile polymers (Multi‐Tool) able to generate a great variety of different well‐defined nanomorphologies. Particular focus is placed on the synthesis of linear block copolymers composed of two polyphosphazene chains (PP‐b‐PP′), or hybrid polymers combining one PP chain with a non‐phosphazene segment [i.e. organic blocks such as poly(olefin)s, polyethers, polyesters, etc.]. We also survey the self‐assembly of these macromolecules equipped with crystalline, rigid or chiral PP core‐forming blocks, to show the morphological diversity and structural complexity of the nanostructures generated in thin films or in solution (selective solvent).

One‐Pot Two‐Step (First ROP, Then SET‐LRP) Synthesis of Polycaprolactone‐Polyacrylate Star Block Copolymers

AbstractA one‐pot, two‐step method is applied to the controlled synthesis of polyacrylate‐b‐(polycaprolactone)2 three‐arm AB2‐type star block polymers. First, ring‐opening polymerization (ROP) of ε‐caprolactone is carried out in toluene using either stannous octoate (Sn(Oct)2) or diphenyl phosphate (DPP) as catalyst, and a multifunctional initiator featuring one bromoester and two alcohol groups. Then, single‐electron transfer living radical polymerization (SET‐LRP) of methyl acrylate and isobornyl acrylate is conducted in the same reaction vessel after sequential addition of its typical reactants, apart from the (PCL)2‐Br macroinitiator generated in the first step, in either toluene/toluene + phenol or toluene/dimethyl sulfoxide solvent systems. DPP (the ROP catalyst) from the first step is found to take part in an acid–base reaction with tris[2‐(dimethylamino)ethyl]amine (the SET‐LRP N‐ligand) in the second part, but stoichiometry could be adjusted to avoid interference and keep the controlled nature of the polymerizations. Interestingly, the electrochemically active Sn(Oct)2 ROP catalyst does not interfere with the SET‐LRP process. Well‐defined poly(methyl acrylate)‐b‐(polycaprolactone)2 and poly(isobornyl acrylate)‐b‐(polycaprolactone)2 are thus synthesized through a simple and cost‐effective experimental procedure. The technique also applies to the synthesis of linear block copolymers.

Formation of polystyrene-poly(methyl methacrylate) block copolymers by anion to free radical transformation

This paper describes a new route for the synthesis of linear block copolymers using a combination of anionic and radical propagation reactions. Free radical polymerization of methyl methacrylate is initiated from halogen-containing end-groups incorporated into the terminal units of polystyrene produced by anionic polymerization. Gel-permeation chromatography is used to establish copolymer formation.

The synthesis of block copolymers in a flow system

A method is described for the synthesis of linear block copolymers. The principle of the method is to start off polymerization of a vinyl compound in a system in which the liquid flows down a capillary tube at a regulated rate. Initiation of the reaction is made at a fixed point in the capillary tube, and the radicals so formed are allowed to grow until a specified size is reached. These radicals are then allowed to flow into a large excess of another monomer in which new environment polymerization is completed so that one half of the molecule is synthesized in the capillary and the other in the receiver attached to that capillary. The systems studied are butylacrylate-styrene and acrylonitrile-styrene. In order to achieve the synthesis of reasonable amounts of material for examination a special apparatus has been designed to initiate polymerization photochemically at extremely high rates. This is done by illuminating a 1 mm capillary tube by means of a specially designed elliptical reflector from a capillary mercury arc lamp. The lamp and the capillary are at the two foci of the ellipse. By using this arrangement radical concentrations 10000 times greater than that normally achieved have been obtained, and methods have been developed to demonstrate that it is possible to arrange matters to have a solution of polymer radicals in monomer issuing from the capillary tube. The kinetics of reaction in a flow system have been worked out, and incidentally the method provides an additional means whereby the absolute velocity coefficients of radical polymerization can be determined.