Block and star block copolymers by mechanism transformation. VIII Synthesis and characterization of triblock poly(LLA-b-St-b-MMA) by combination of ATRP and ROP

Switching from Single to Simultaneous Free-Radical and Anionic Polymerization with Enamine-Based Organic Electron Donors

Although most monomers can polymerize through different propagation pathways, polymerization-initiating systems that can switch from one mode to another are rare. In this study, we demonstrate that enamine-based organic electron donors (OEDs) constitute the first systems able to initiate either free-radical or anionic polymerization under simple, mild, and safe conditions. While direct electron-transfer reduction of monomers by OEDs results in the initiation of anionic chain-growth polymerization, introduction of a competing oxidant with a higher reduction potential than the monomer switches the former anionic propagation to a clean radical-propagation process. The benefit of this dual-mode activator is highlighted in the synthesis of an interpenetrating polymer network through simultaneous initiation of radical and anionic propagation processes.

Phase manipulation of topologically engineered AB-type multi-block copolymers

Recent advances in the fundamental understanding of the ordered phases of multi-block copolymers (MBCPs) at the molecular level have attracted considerable scientific interest in recent years. Herein, by employing molecular dynamics simulation, we focus on the four typical systems: linear alternating, branch-like, star-like AB-type MBCPs and linear copolymers filled with nanoparticles (NPs). First, we establish the phase diagram for the linear tetrablock copolymers (ABAB) as a function of the composition ratio between A- and B-block, exhibiting six typical phase states. Furthermore, increasing the mutual repulsive interaction strength, the temperature and the periodic dynamic shearing cycle result in the merging of spheres, presenting a clear beginning of the order-to-order transition (OOT) behavior. Second, we examine the branch-like and star-like copolymers and find that increasing branch density significantly leads to the occurrence of phase transition. Particularly, we illustrate that the sphere configurations of the MBCPs can be described in terms of tail, loop and bridge conformations. Increasing the number of distinct blocks in linear alternating copolymers results in an enhancement of the bridge conformation, in which case some spheres are separated to smaller ones. Furthermore, for the tail conformation, we present a unified theoretical framework to rationalize the topological state of the chain arrangements of spheres and infer that the entanglements within the internal reaction layer between different A-blocks result in the inhomogeneous distribution of the spheres sizes even with controlled molecular weight and composition ratio between each block. Finally, we find that the ABAB tetrablock copolymers filled with moderate spherical NPs exhibit a clear OOT from spheres to double gyroid or cylinders. We infer that the maximum amount of the B-block within the second and/or third layers for the filled spherical NPs connects different NPs effectively, leading to the complicated OOT behavior. Generally, this fundamental study could provide some guidelines for designing and fabricating high performance BCPs by manipulating the formation of the ordered phases.

An intrinsic internal standard substrate of Au@PS-b-P4VP for rapid quantification by surface enhanced Raman scattering

Reliable quantification by surface enhanced Raman scattering (SERS) highly depends on the development of a reproducible substrate with excellent anti-interference capability and precise calibration methods.

Copolymerization of l-lactide/trimethylene carbonate by organocatalysis: controlled synthesis of comb-like graft copolymers with side chains with different topologies

Synthesis of comb-like graft copolymers of lcP(LLA-co-TMC) from an organocatalyst/PB–OH system: including lcP(TMC-b-LLA), lcP(LLA-grad-TMC) and lcP(LLA-ran-TMC).

The crystallinity, thermal properties and microscopic morphology of di-block copolymers of l-lactide and several acrylates

Di-block copolymers of l-lactide and (meth)acrylate were synthesized from PLLA macroinitiators, and the microphase separation of copolymers was observed.

Self-assembly morphology effects on the crystallization of semicrystalline block copolymer thin film

Self-assembly morphology effects on the crystalline behavior of asymmetric semicrystalline block copolymer polystyrene-block-poly(L-lactic acid) thin film were investigated. Firstly, a series of distinctive self-assembly aggregates, from spherical to ellipsoid and rhombic lamellar micelles (two different kinds of rhombic micelles, defined as rhomb 1 and rhomb 2) was prepared by means of promoting the solvent selectivity. Then, the effects of these self-assembly aggregates on crystallization at the early stage of film evolution were investigated by in situ hot stage atomic force microscopy. Heterogeneous nucleation initiated from the spherical micelles and dendrites with flat on crystals appeared with increasing temperature. At high temperature, protruding structures were observed due to the thickening of the flat-on crystals and finally more thermodynamically stable crystallization formed. Annealing the rhombic lamellar micelles resulted in different phenomena. Turtle-shell-like crystalline structure initiated from the periphery of the rhombic micelle 1 and spread over the whole film surface in the presence of mostly noncrystalline domain interior. Erosion and small hole appeared at the surface of the rhombic lamellar micelle 2; no crystallization like that in rhomb 1 occurred. It indicated that the chain-folding degree was different in these two micelles, which resulted in different annealing behaviors.