利用动态光散射、透射电镜研究了嵌段共聚物聚苯乙烯 b 聚丙烯酸(PS b PAA)与均聚物聚苯乙烯(PS)在选择性溶剂水中的自组装行为.由于均聚物PS与PS嵌段具有相同的结构单元,均聚物PS参与胶束的形成,和嵌段共聚物的PS链段一同组成胶束的核;在适当的均聚物分子量和含量条件下,PS b PAA PS可以自组装形成单分散的纳米胶束;通过改变体系中均聚物PS的分子量和含量可在较大范围内调变胶束的尺寸. 相似文献
Metallocene-based homogeneous Ziegler–Natta catalysts produce mono-olefin-terminated oligopropenes with narrow molecular weight distributions, controlled stereoregularities, and molecular weights ranging from 100 to 30,000 g/mole in high yield slurry and solution processes. Steric and molecular weight control are influenced by metallocene structures, and by polymerization conditions such as temperature and propene concentration. Predominantly mono-vinylidene-terminated oligopropenes are attractive intermediates, and feedstock for the synthesis of a variety of polypropylene materials, including blends, block and graft copolymers. The key step is the chain end functionalization of the vinylideneterminated oligopropenes via double bond conversion reactions, followed by the controlled synthesis of polypropylene block and graft copolymers. In melt and solution processes the olefinic end groups have been converted into a variety of polar functional groups, e.g. hydroxy, carboxy, succinic anhydride, thiol and acrylic groups. The thiol-terminated oligopropenes are chain transfer agents in radical methylmethacrylate polymerization with chain transfer constant measured to be 0.2. Acrylic monomers and styrene are grown onto the thiol end group via a chain transfer reaction, thus producing a family of block copolymers, e.g. poly(propene-b-methylmethacrylate) and poly(propene-b-styrene). As demonstrated by SEM fracture surface analysis, the poly(propene-b-styrene) block copolymers are efficient dispersing agents for compatibilizing polystyrene/polypropene (70/30) blends. Homo- and copolymerization of acrylic oligopropene macromonomers yield novel classes of graft copolymers with pendant isotactic or atactic oligopropene chains. Hydroxy-terminated oligopropenes are useful initiators in caprolactone polymerization to form poly(propene-b-caprolactone) block copolymers. IR spectroscopic studies demonstrate that succinic anhydride-terminated oligopropenes, obtained by ene-type addition of maleic anhydride to the olefinic oligopropene end group, react with oligomeric diamine-terminated polyamide-6,6 in the melt to yield polypropene-b-polyamide-6,6-b-polypropene triblock copolymers. 相似文献
The historical development of our research on polycondensation that proceeds in a chain-growth polymerization manner ("chain-growth polycondensation") for well-defined condensation polymers is described. We first studied polycondensation in which change of the substituent effect induced by bond formation drove the reactivity of the polymer end group higher than that of the monomer. In this approach, well-defined aromatic polyamides, polyesters, polyethers, and poly(ether sulfone)s were obtained. The second approach was the study of the phase-transfer polymerization of a solid monomer dispersed in an organic solvent. In this type of polymerization, the solid monomer was physically unable to react with another monomer and was carried with the phase transfer catalyst into the solution phase where it reacted with an initiator and the polymer end group in the solvent in a chain polymerization manner. We also found catalyst-transfer polycondensation as a third approach to chain-growth polycondensation. In the Ni-catalyzed polycondensation of 2-bromo-5-chloromagnesiothiophenes, the Ni catalyst transferred to the polymer end group, and a coupling reaction occurred there to yield a well-defined polythiophene. This chain-growth polycondensation was applied to the synthesis of condensation polymer architectures such as block copolymers, star polymers, graft copolymers, and so on. 相似文献
A straightforward, novel strategy based on the in situ functionalization of polymers prepared by nitroxide‐mediated polymerization (NMP), for the use as an extension toward block copolymers and post‐polymerization modifications, has been investigated. The nitroxide end group is exchanged for a thiocarbonylthio end group by a rapid transfer reaction with bis(thiobenzoyl) disulfide to generate in situ reversible addition–fragmentation chain transfer (RAFT) macroinitiators. Moreover, not only have these macroinitiators been used in chain extension and block copolymerization experiments by the RAFT process but also a thiol‐terminated polymer is synthesized by aminolysis of the RAFT end group and subsequently reacted with dodecyl vinyl ether by thiol‐ene chemistry. 相似文献
An amphiphilic poly(2‐oxazoline) block copolymer consisting of a water‐soluble poly(2‐methyloxazoline) block and a hydrophobic block bearing bipyridine moieties in the side chain was synthesized by living cationic polymerization. This macroligand was applied to atom‐transfer radical polymerization (ATRP) of methyl methacrylate in aqueous solution in the presence of Cu(I)Br and ethyl 2‐bromoisobutyrate as the initiator. High monomer conversion up to 96% was achieved after 3 h of polymerization at 60°C. 相似文献
Thermo-sensitive poly(2-isopropyl-2-oxazoline)s (PiPrOx) were functionalized with end groups of different polarity by living cationic ring-opening polymerization using the initiator and/or termination method as well as sequential block copolymerization with 2-methyl-2-oxazoline. As end groups, methyl, n-nonyl, piperidine, piperazine as well as oligo(ethylenglygol) and oligo(2-methyl-2-oxazoline) were introduced quantitatively. The lower critical solution temperature (LCST) of the aqueous solutions was investigated. The introduction of hydrophobic end groups decreases the LCST, while hydrophilic polymer tails raise the cloud point. In comparison to poly(N-isopropyl acrylamide), the impact of the end group polarity upon the modulation of the LCST was found to be significantly stronger. Surprisingly, terminal oligoethylenegycol units also decrease the LCST of PiPrOx, thus acting as moieties of higher hydrophobicity as compared to the poly(2-oxazoline) main chain. Together with the possible variation of the side group polarity, this allows a broad modulation of the LCST of poly(2-oxazoline)s. 相似文献
Summary: The preparation of polystyrene block methyl methacrylate copolymers (PS-b-PMMA) is described. The polystyrene segment was prepared by anionic polymerization and the methylmethacrylate segment was prepared via free radical autoxidation of a borane agent attached to the styrene chain. 1 The chemistry involves a transformation of the anionic polymerization process to borane chemistry by firstly producing polystyrene with chain end unsaturated alkyl functional groups prepared using a n-butyllithium initiator and termination with allylchlorodimethylsilane. Secondly, the unsaturated macroinitiator end was hydroborated by 9-borabicyclo[3.3.1]nonane (9-BBN) to produce a borane terminated PS. Thirdly, the borane group at the chain end was selectively oxidized and converted to polymeric radicals in the presence of methyl methacrylate which then initiated radical polymerization to produce block copolymers. The polymer obtained was characterized using several chromatographic techniques including LC-CC (liquid chromatography under critical conditions) for the polystyrene segments and two-dimensional chromatography with LC-CC in the first dimension and SEC in the second. The results show that block formation was successful although significant homopolymerization of methyl methacrylate is also obtained. 相似文献
Summary: The combination of enzymatic polymerization with ATRP for the synthesis of branched (block) copolymers was investigated. Heterotelechelic polycaprolactone macroinimer was synthesized in a one‐pot enzymatic procedure by using 2‐hydroxyethyl α‐bromoisobutyrate as a bifunctional initiator. A polymerizable end group was introduced by subsequent in situ enzymatic acrylation with vinyl acrylate. Branched polymers were obtained by subsequent atom transfer radical polymerization (ATRP).
Enzymatic synthesis of heterotelechelic macromonomers and subsequent self condensing vinyl polymerization by ATRP. 相似文献
Summary: A low‐molar‐mass poly(acrylic acid) with a narrow molar‐mass distribution, prepared by SG1 nitroxide‐mediated controlled free‐radical polymerization, was subjected to end‐group analysis to confirm its living nature. 1H and 31P NMR spectroscopy confirmed the presence of the SG1‐based alkoxyamine end group. Furthermore, chain extension with styrene and n‐butyl acrylate demonstrated the ability of the homopolymer to initiate the polymerization of a second block. These results open the door to the synthesis of poly(acrylic acid)‐based block copolymers by direct nitroxide‐mediated polymerization of acrylic acid.
Acrylic acid polymerization using an alkoxyamine initiator based on SG1 (N‐tert‐butyl‐N‐(1‐diethyl phosphono‐2,2‐dimethylpropyl) nitroxide resulting in a homopolymer capable of initiating the polymerization of a second block. 相似文献