Abstract Poly(styrene-isobutylene-styrene) (PS-PIB-PS) block copolymers synthesized via living carbocationic polymerization using a di- or tricumyl chloride/TiCl4/pyridine initiating system in 60/40 (v/v) hexane/methyl chloride cosolvents. The kinetics of formation of the PIB block at ? 80°C were found to be first order in isobutylene (IB) concentration, first order in the concentration of initiating sites, second order in TaiCl4 concentration, and a negative fractional order with respect to the pyridine concentration. The rate of polymerization was found to decrease with increasing temperature, indicating an equilibrium between dormant, covalent and active, ionized chain ends, and chain-end concentration studies suggested that there was no contribution by free ions to the rate of propagation. Diagnosis of the livingness of the IB polymerization indicated that at high (≥90%) monomer conversion, β-proton elimination becomes important, causing the timing of addition of styrene to be critical. Addition of styrene at an IB reaction time significantly exceeding the time necessary for complete IB consumption resulted in contamination of the product with a substantial amount of homo-PS; conversely, addition at intermediate IB conversion resulted in slow copolymerization between IB and styrene and the formation of a tapered block copolymer. Addition of styrene at an IB conversion of about 90% resulted in well-defined block copolymers which displayed ordered, phase-separated morphologies consisting of cylinders of PS in a continuous phase of PIB. The block copolymers possessed properties consistent with those of physically crosslinked rubbers. Dynamic mechanical spectroscopy revealed two glass transitions with a broad rubbery plateau extending from about 0 to 100°C, and tensile strengths of up to 25 MPa and elongations to 1000% were observed for some samples. 相似文献
This review focuses on poly(2-oxazoline) containing triblock copolymers and their applications. A detailed overview of the synthetic techniques is provided. Triblock copolymers solely based on poly(2-oxazoline)s can be synthesized by sequential monomer addition utilizing mono- as well as bifunctional initiators for the cationic ring-opening polymerization of 2-oxazolines. Crossover and coupling techniques enable access to triblock copolymers comprising, e.g., polyesters, poly(dimethylsiloxane)s, or polyacrylates in combination with poly(2-oxazoline) based segments. Besides systematic studies to develop structure property relationships, these polymers have been applied, e.g., in drug delivery, as (functionalized) vesicles, in segmented networks or as nanoreactors. 相似文献
Recently, significant progress has been made in the field of living free radical polymerization such as nitroxide-mediated stable free radical polymerization, atom transfer radical polymerization (ATRP), reverse ATRP and reversible addition-fragmentation chain transfer1. Among them, ATRP has been successfully applied to the synthesis of well-defined comb, gradient, star and dendritic macromolecules. Recent advances have been carried toward new initiators, metals and ligands. As a new cl… 相似文献
In this paper, we combine hydrophilic oligoagarose (DPn = 10–15), issued from enzymatic degradation of the natural biopolymer agarose, with polycaprolactone, a synthetic biodegradable and hydrophobic polyester. To synthesize these amphiphilic graft copolymers, we use partially acetylated oligoagarose as macroinitiator in combination with tin (II) octanoate for the bulk polymerization of ε-caprolactone. The grafting was confirmed by NMR and SEC which showed a monomodal distribution. After removal of the acetyl protecting groups, copolymers with 30–60% free hydroxyl groups were soluble in water and insoluble in chloroform, thus indicating that they probably adopt micelle-like structures in aqueous solution with a PCL hydrophobic core and spherical oligoagarose side chains. 相似文献
Summary: Stepwise anionic polymerization, catalytic hydrogenation, and atom transfer radical polymerization were performed to synthesize an amphiphilic ABC triblock copolymer, poly(ethylene‐alt‐propylene)‐block‐poly(ethylene oxide)‐block‐poly(hexyl methacrylate) (PEP‐b‐PEO‐b‐PHMA), with hydrophilic PEO as the middle block. The resulting block copolymers have well‐defined molecular weights and narrow molecular weight distributions as revealed by 1H NMR spectroscopy and gel permeation chromatography.
GPC chromatograms of an ABC triblock copolymer, PEP‐b‐PEO‐b‐PHMA, and its intermediate precursors exhibiting narrow polydispersities. 相似文献
