共查询到20条相似文献,搜索用时 31 毫秒
1.
Lian R. Hutchings Jonathon M. Dodds Susan J. Roberts-Bleming 《Macromolecular Symposia》2006,240(1):56-67
We describe here a new strategy for the synthesis of polymers with highly branched architectures. The strategy involves the synthesis by anionic polymerization of well-defined AB2 polystyrene macromonomers with molecular weights from 3,600 to 94,000 gmol−1, which are then converted via a one-pot polycondensation reaction into high molecular weight, long-chain (hyper)branched architectures. Since the Hyperbranched structures are built up from condensation Macromonomers we have coined the term ‘HyperMac’ to describe these branched polymers. In this paper we report the synthesis of the HyperMacs, the optimal conditions for the polycondensation reaction and some preliminary characterization studies. 相似文献
2.
Zheng Y Cao H Newland B Dong Y Pandit A Wang W 《Journal of the American Chemical Society》2011,133(33):13130-13137
Controlled/living radical polymerization (CRP) is a widely used technique that allows the synthesis of defined polymer architectures through precise control of molecular weights and distributions. However, the architectures of polymers prepared by the CRP techniques are limited to linear, cross-linked, and branched/dendritic structures. Here, we report the preparation of a new 3D single cyclized polymer chain structure from an in situ deactivation enhanced atom transfer radical polymerization of multivinyl monomers (MVMs), which are conventionally used for the production of branched/cross-linked polymeric materials as defined by P. Flory and W. Stockmayer nearly 70 years ago. We provide new evidence to demonstrate that it is possible to kinetically control both the macromolecular architecture and the critical gelling point in the polymerization of MVMs, suggesting the classical Flory-Stockmayer mean field theory should be supplemented with a new kinetic theory based on the space and instantaneous growth boundary concept. 相似文献
3.
Effect of a Set of Acids and Polymerization Conditions on the Architecture of Polycarbonates Obtained via Ring Opening Polymerization 下载免费PDF全文
I. Jiménez‐Pardo L. G. J. van der Ven R. A. T. M. van Benthem A. C. C. Esteves G. de With 《Journal of polymer science. Part A, Polymer chemistry》2017,55(9):1502-1511
Polycarbonate‐based polymers with a well‐defined architecture have become interesting materials due to their large range of applications. Ring opening polymerization (ROP) has been largely applied to make branched polycarbonates. The polymer architectures obtained via this method are strictly related with the polymerization mechanisms involved which depend on the polymerization conditions chosen. Hereby, we evaluate the catalytic activity of three acids, fumaric, trifluoroacetic, and methanesulfonic on the Cationic ROP of trimethylene carbonate (TMC) over a trifunctional initiator, trimethylol propane (TMP), under different reaction conditions. In‐detail characterization of the polymers showed the co‐existence of two polymerization mechanisms: the activated monomer (AM), which produces a tri‐armed branched polycarbonate with inclusion of the TMP initiator (TMP‐PTMC), and a combined AM/Activated Chain End (ACE) mechanism, which produces a linear polycarbonate (L‐PTMC). Such mixtures were identified for nearly all the reaction variables investigated, together with other side reactions. Upon optimization of the synthesis, the polymerizations in toluene with TFA at 35 °C and equimolar acid/initiator ratio were optimal, avoiding side reactions, but still resulting in a polymer mixture composed of ~69% TMP‐PTMC and 31% of a polycarbonate linear polymer. The occurrence of such mixed polymer architectures is commonly overlooked in literature regarding CROP of branched polycarbonates. We demonstrate the importance of performing a full characterization for a successful detection of polymer mixtures having different (number of) end‐functionalities, which are critical for further use in advanced applications, such as in the biomedical or pharmaceutical filed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1502–1511 相似文献
4.
《高分子科学》2018,(11)
The synthesis and structure-property correlation of poly(N-(2-hydroxypropyl) methacrylamide) (PHPMA) conjugates with various architectures including random, block, branched or star-like structures and compositions have been thoroughly explored.However, related synthesis and structure-property data are still lacking for comb-like PHPMA. In this work, we report the synthesis of comb-like PHPMA copolymer-doxorubicin (DOX) conjugates with different backbone/side-chain lengths and location of drug moieties.Well-defined comb-like PHPMA-DOX conjugates are obtained via the combination of controlled radical polymerization and fractional precipitation techniques. The influences of structural factors on the biological properties such as cellular uptake, blood circulation and tumor accumulation have been investigated. Long blood circulation and efficient tumor accumulation can be achieved by proper control of the comb number, length and location of drug moieties. These facile comb-like structures possess great potentials in future theranostics for brachytherapy or surgical navigation. 相似文献
5.
Sabrina Paillet Armelle Roncin Gérald Clisson Gaëlle Pembouong Laurent Billon Christophe Derail Maud Save 《Journal of polymer science. Part A, Polymer chemistry》2012,50(14):2967-2979
Branched and star‐branched polymers were successfully synthesized by the combination of two successive controlled radical polymerization methods. A series of linear and star poly(n‐butyl acrylate)‐co‐poly(2‐(2‐bromoisobutyryloxy) ethyl acrylate) statistical copolymers, P(nBA‐co‐BIEA)x, were first synthesized by nitroxide‐mediated polymerization (NMP at T > 100 °C). The subsequent polymerization of n‐butyl acrylate by single electron transfer‐living radical polymerization (SET‐LRP at T = 25 °C), initiated from the brominated sites of the P(nBA‐co‐BIEA)x copolymer, produced branched or star‐branched poly(n‐butyl acrylate) (PnBA). Both types of polymerizations (NMP and SET‐LRP) exhibited features of a controlled polymerization with linear evolutions of logarithmic conversion versus time and number‐average molar masses versus conversion for final Mn superior to 80,000 g mol?1. The branched and star‐branched architectures with high molar mass and low number of branches were fully characterized by size exclusion chromatography. The Mark–Houwink Sakurada relationship and the analysis of the contraction factor (g′ = ([η]branched/[η]linear)M) confirmed the elaboration of complex PnBA. The zero‐shear viscosities of the linear, star‐shaped, branched, and star‐branched polymers were compared. The modeling of the rheological properties confirmed the synthesis of the branched architectures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
6.
Coates GW Hustad PD Reinartz S 《Angewandte Chemie (International ed. in English)》2002,41(13):2237-2257
Coordination-insertion polymerization systems have long been superior to their anionic, cationic, and radical polymerization counterparts with regard to stereochemical control. However, until five years ago, these metal-based insertion methods were inferior to ionic and radical mechanisms in the category of living polymerization, which is simply a polymerization that occurs with rapid initiation and negligible chain termination or transfer. In the last half decade, the living insertion polymerization of unactivated olefins has emerged as a powerful tool for the synthesis of new polymer architectures. Materials available today by this route range from simple homopolymers such as linear and branched polyethylene, to atactic or tactic poly(alpha-olefins), to end-functionalized polymers and block copolymers. This review article summarizes recent developments in this rapidly growing research area at the interface of synthetic and mechanistic organometallic chemistry, polymer chemistry, and materials science. While special emphasis is placed on polymer properties and novel polymeric architectures, most of which were inaccessible just a decade ago, important achievements with respect to ligand and catalyst design are also highlighted. 相似文献
7.
Hierarchical comb brush architectures via sequential light‐mediated controlled radical polymerizations 下载免费PDF全文
Benjaporn Narupai Justin E. Poelma Christian W. Pester Alaina J. McGrath Edward P. Toumayan Yingdong Luo John W. Kramer Paul G. Clark Paresh C. Ray Craig J. Hawker 《Journal of polymer science. Part A, Polymer chemistry》2016,54(15):2276-2284
A novel strategy for the synthesis and characterization of branched polymer brushes by sequential light‐mediated controlled radical polymerizations is described. Initially, linear brushes are prepared by surface‐initiated copolymerization of methyl methacrylate and 2‐hydroxyethyl methacrylate (HEMA). In a subsequent step, the HEMA side chains are functionalized with initiating groups for secondary graft polymerization, leading to hierarchical, branched architectures. The increased steric bulk due to the polymer side chains results in a dramatic increase in film thickness when compared to the starting linear brushes. This strategy also allows chemical gradient and complex three‐dimensional structures to be obtained by employing grayscale photomasks in combination with controlled radical polymerization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2276–2284 相似文献
8.
Hao Tang Jin Tang Yi Shen Wen-Xuan Guo Min Zhou Rui-Hua Wang Ni Jiang Zhi-Hua Gan Qing-Song Yu 《高分子科学》2018,36(11):1225-1238
The synthesis and structure-property correlation of poly(N-(2-hydroxypropyl) methacrylamide) (PHPMA) conjugates with various architectures including random, block, branched or star-like structures and compositions have been thoroughly explored. However, related synthesis and structure-property data are still lacking for comb-like PHPMA. In this work, we report the synthesis of comb-like PHPMA copolymer-doxorubicin (DOX) conjugates with different backbone/side-chain lengths and location of drug moieties. Well-defined comb-like PHPMA-DOX conjugates are obtained via the combination of controlled radical polymerization and fractional precipitation techniques. The influences of structural factors on the biological properties such as cellular uptake, blood circulation and tumor accumulation have been investigated. Long blood circulation and efficient tumor accumulation can be achieved by proper control of the comb number, length and location of drug moieties. These facile comb-like structures possess great potentials in future theranostics for brachytherapy or surgical navigation. 相似文献
9.
Tadeusz Biela Adam Kowalski Jan Libiszowski Andrzej Duda Stanisław Penczek 《Macromolecular Symposia》2006,240(1):47-55
Recent advances in the controlled ring-opening polymerization of aliphatic cyclic esters are briefly reviewed. Particular attention is paid to the high molecular weight linear, branched, and star-shaped poly(lactide)s and poly(ε-caprolactone) synthesis. It is concluded that despite the plethora of initiating and/or catalytic systems applied for this purpose the best results so far were achieved with Al- and Sn(II) derivatives. Analytical methods employed for aliphatic polyesters of various architectures characterization, including SEC-MALLS, LC-CC, and fluorescence spectroscopy, are also discussed. 相似文献
10.
Madhavaiah Chandra 《Tetrahedron》2007,63(35):8576-8580
Branched DNA constructs have found wide application in DNA-based nanotechnology. Several reports describe the generation of branched DNA structures with variable numbers of arms to self-assemble with pre-designed architectures. Branched DNA is generated by using designed rigid crossover DNA molecules as building blocks. Alternatively, branched DNAs can also be generated by using synthetic branch points derived either from nucleoside or non-nucleoside building blocks. Herein, we report the synthesis of modified uridine derivatives as branching monomer for the synthesis of branched DNA and first studies of their self-assembling properties. 相似文献
11.
Tamara Alhilfi Pierre Chambon Steve P. Rannard 《Journal of polymer science. Part A, Polymer chemistry》2020,58(10):1426-1438
Ambient temperature-initiated anionic polymerization has generated branched polystyrenes of varying molecular weights and architectures by inclusion of a distyryl branching comonomer into a conventional sec-Butylithium-initiated polymerization of styrene. Primary chain length control within the branched polymers, and restriction of the branching points to varying segments of the primary chains, led to variations of glass transition temperature with no direct correlation to the branched polymer molecular weight but a strong relationship to the length of individual chains comprising the branched macromolecules. 相似文献
12.
Piet D. Iedema Johan J. M. Slot Dong‐Min Kim Huub C. J. Hoefsloot 《Macromolecular theory and simulations》2004,13(5):400-418
Summary: Hyperbranched molecules like low‐density polyethylene (ldPE) adopt a huge variety of molecular architectures. Previous work has shown that it is possible to computationally synthesize these architectures and to characterize them according to radius of gyration. Here, a method is presented and applied on ldPE to characterize populations using rheological quantities in terms of comb‐shaped and Cayley tree structures. Interbranch segments are assigned seniority and priority values that quantify their behavior in relaxation and elastic deformation processes. New general‐purpose algorithms have been developed to derive the full bivariate seniority/priority distribution using a representation from the graph theory of branched architectures. This paper describes the computation of bivariate chain length/degree of branching distributions (CLD/DBD) using a Galerkin finite element method for two scission mechanisms: linear and topological scission. The DBD is calculated using pseudo‐distributions. Random scission is treated with fragment length and branch point redistribution functions as obtained from scission statistics of branched molecules, preferentially yielding short and long fragments. Reactor populations of ldPE architectures are then obtained using computational synthesis. The seniority and priority distributions calculated indeed prove to be an adequate characterization method. They show good comparison, although not a complete overlap, with size characterization using a variant of the radius of gyration. It was possible to calculate a full bivariate seniority/priority fraction distribution, but due to the limited sample size its surface was not smooth. Subsequent work has shown the consequences for the prediction of rheological properties.
13.
丙烯腈可控/"活性"自由基聚合研究进展 总被引:4,自引:0,他引:4
可控/"活性"自由基聚合能有效控制聚合物的分子量及其分布,并且能调控其微观拓扑结构。聚丙烯腈及其共聚物具有良好的成纤成膜性能,是一类应用十分广泛的聚合物。本文综述了可控/"活性"自由基聚合法合成聚丙烯腈及其共聚物的研究现状与进展,从氮氧自由基法(NMP)、引发转移终止剂法(iniferter)、原子转移自由基聚合(ATRP)和可逆加成-断裂链转移(RAFT)聚合等方面对丙烯腈均聚物和共聚物的合成研究作了全面的总结,提出了存在的问题,并且对今后的研究方向作了展望。 相似文献
14.
Since its introduction, click chemistry has received a considerable amount of interest. In this contribution, the term click chemistry and the reactions that fall under this term are briefly explained. The main focus of this review is on the application of click chemistry in conjunction with living radical polymerization for the synthesis of advanced macromolecular architectures. Therefore the most powerful living radical polymerization (LRP) techniques are discussed and an overview of click chemistry in the different synthetic schemes is given. A large number of examples are shown that include the synthesis of block copolymers, star-shaped polymers, surface modified particles, and polymer-protein conjugates. The enormous potential of LRP/click chemistry is probably best exemplified by the synthesis of different miktoarm star copolymers, to which a separate section is dedicated. 相似文献
15.
Martina Schömer Christoph Schüll Holger Frey 《Journal of polymer science. Part A, Polymer chemistry》2013,51(5):995-1019
Hyperbranched polymers, dendritic macromolecules with branch‐on‐branch structures, have become an important polymer class since the early 1990s. They combine several advantages of the perfectly branched dendrimers with easy accessibility, typically in a one‐step synthesis. Hyperbranched polyethers are a particularly interesting class of chemically stable and often biocompatible materials. Multifunctional hyperbranched polyethers with controllable molar mass and comparably low polydispersities can been prepared using hydroxyl‐functional epoxides or oxetanes for polymerization via anionic and cationic polymerization mechanisms. Here, we review the progress in the preparation, characterization, and application of these uniquely versatile aliphatic polyether polyols. Their unusual mechanical, thermal, and solution properties render them useful for a variety of applications, for example, as building blocks for various complex macromolecular architectures or in biomedical applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
16.
This review summarizes recent advances in the controlled radical polymerization of N-vinyl monomers, such as N-vinylcarbazole, N-vinylindole derivatives, N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylformamide, N-vinylacetoamide derivatives, N-vinyl(na)phthalimides, N-vinylimidazolium salts, and N-vinyltriazoles. Recent significant progress of controlled radical polymerization of these N-vinyl monomers has allowed for the synthesis of well-defined functional polymers having various architectures, including block copolymers, branched polymers (stars, star block copolymers, miktoarm star copolymers, and graft copolymers), and hybrids. Characteristic properties, assembled structures, and three-dimensional architectures of these functional polymers derived from N-vinyl monomers are briefly introduced. 相似文献
17.
α-萘基丁二亚胺氯化镍/MAO制备双(宽)峰聚乙烯 总被引:5,自引:0,他引:5
合成了一种新型α 二亚胺镍配合物———α 萘基丁二亚胺氯化镍 ,此配合物作为催化剂在MAO的活化下催化乙烯聚合得到支化聚乙烯 ,聚合活性高达 7 18× 10 5gPE molNi·h ,1 3C NMR、FTIR测试结果表明制备的聚乙烯含有末端双键 ;GPC结果表明所制备的聚乙烯分子量呈双 (宽 )峰分布 ,其原因有两个 ,一是此催化剂能产生分子量较低的α 烯烃 ,在聚合过程中一部分α 烯烃会“就地”与乙烯原位共聚形成分子量较高的聚合物 ,二是此催化剂存在立体异构体 ,而不同异构体在MAO活化下形成的活性中心的配位环境不同 ,因而得到的聚乙烯的分子量也不同 .研究了聚合温度、聚合压力、铝镍摩尔比 (nAl nNi)对催化活性、聚乙烯分子量、支化度的影响 .聚乙烯的分子量随聚合温度的升高而下降 ,支化度增大 ,熔点则降低 . 相似文献
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《先进技术聚合物》2018,29(3):1161-1169
Chain shuttling polymerization has provided new pathway for introduction of different architectures in a single chain. Unlike the commercially available ethylene/1‐octene block copolymers, synthesis and microstructure of linear/branched polyethylene with blocky nature is not extensively studied. In this work, such block copolymers are synthesized based on reversible transfer of growing chains between an ansa metallocene and α‐diimine catalysts, forming linear and branched structures from ethylene, respectively. Investigation of thermal properties reveals that application of 550 equivalent of chain shuttling agent makes blocky structures that show the most deviation from the longstanding relationship between melting temperature and crystallinity or density, alongside with turning broad molecular distribution into unimodal. Thermal fractionation by successive self‐annealing demonstrates formation of broad distribution of linear blocks, as comprehended through appearance of uniform melting peaks at lower temperatures. Corresponding dynamic mechanical properties and crystalline structures reveal soft elastomeric properties, specifically at temperatures around −50°C, opposed to the purely linear chains or linear/branched blends. Correspondingly, blend samples demonstrate significant morphological change upon treatment with a suitable solvent for the branched fraction, contrary to the blocky microstructures. 相似文献