“Grafting through” polymerization involving surface-bound monomers

“Grafting through” polymerization represents copolymerization of free monomers in solution and polymerizable units bound to a substrate. Free polymer chains are formed initially in solution and can incorporate the surface-bound monomers, and thereby, get covalently bonded to the surface during the polymerization process. As more growing chains attach to the surface-bound monomers, an immobilized polymer layer is formed on the surface. We use a combination of computer simulation and experiments to comprehend this process for monomers bound to a flat impenetrable substrate. We concentrate specifically on addressing the effect of spatial density of the surface-bound monomers on the formation of the surface-attached polymers. We employ a lattice-based Monte Carlo model utilizing the bond fluctuation model scheme to provide molecular-level insight into the grafting process. For experimental validation, we create gradients of density of bound methacrylate units on flat silicon wafers using organosilane chemistry and carry out “grafting through” free radical polymerization initiated in bulk. We report that the proximity of the surface-bound polymerizable units promotes the “grafting through” process but prevents more free growing chains to “graft through'' the polymerizable units. The “grafting through” process is self-limiting in nature and does not affect the overall density of the surface-bound polymer layer, except in case of the highest theoretical packing density of surface-bound monomers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 263–274     

High-conversion polymerization. IV. A definition of the onset of the gel effect

The gel effect in free radical polymerization of vinyl monomers has been recognized as the result of the increased viscosity of the reaction solution of polymer in monomer, which causes a decrease in the rate of the termination reaction. This effect manifests itself as an increase in the rate of polymerization over that rate to be expected in its absence. Definition of the onset of the gel effect has become necessary for several purposes. Previously, it has been common to define the onset phenomenologically, i.e., in terms of the increase in the rate of polymerization. It is proposed here that the onset of the gel effect is best defined on a fundamental basis, i.e., as occurring at that conversion at which the rate of segmental diffusion of the polymeric radicals equals the rate of their translational diffusion. Experimental evidence is presented that shows that the small minima predicted by this definition do exist for both rates and degrees of polymerization. Measurements of the viscosities of solutions of polymers in their monomers suggest that the polymer concentrations at which the “chain-entanglement” phenomena are observed are the same as those for the onset of the gel effect for styrene, methyl methacrylate, and butyl methacrylate.     

获得环境响应聚合物胶束和空心球的途径

概述了本研究组近年来发展的几种制备环境敏感的聚合物纳米胶束和空心球的新方法,包括通过聚合物间的氢键相互作用构建“非共价键合胶束”的自组装方法,将聚合物自组装与单体的原位聚合相结合的方法以及利用接枝共聚物中的主链和支链间的络合作用诱导胶束化和胶束与空心球的可逆转化等.讨论了这些聚合物纳米微球和空心球对温度、pH及离子强度等的响应特性.     

The decomposition of potassium persulphate used as initiator in emulsion polymerization

The decomposition rate of potassium persulphate in various aqueous solutions was measured by isotachophoresis using pure water, sodium dodecyl sulphate (SDS) solution, emulsifier-free polystyrene emulsion, SDS solution containing acrylamide monomer or an SDS-containing emulsion polymerization system for styrene. “Free” SDS molecules in the monomolecular dispersed state were found to increase markedly the decomposition rate, whereas those which formed micelles and became adsorbed onto polystyrene particles did not increase it. The acceleration phenomenon in the former case disappeared in the presence of a small amount of monomer.     

Configurational rules governing the stereochemical control of chiral initiators in ring-opening polymerizations of heterocyclic monomers

Configuration rules were established for the polymerization of cyclic monomers with chiral initiators. The latter recognize in the monomer an asymmetric carbon of homochiral configuration. The chirality of the initiator is defined by the “local” asymmetry of the ligand and by the overall asymmetry of the particular arrangement of catalytic aggregates. Two types of process called “homosteric” and “antisteric,” which apply to the polymerization of resolvable monomers and achiral monomers of meso structure, are defined. These configurational rules have a general character and are verified in many examples of differently substituted three- or four-membered cyclic monomers (oxiranes, thiiranes, β-lactones). Stereoelective polymerization appears to be an original method for the determination of the absolute configuration of some monomers of unknown chirality.     

Sono‐RAFT Polymerization in Aqueous Medium

The ultrasonic irradiation of aqueous solution is demonstrated to be a suitable source of initiating radicals for a controlled radical polymerization when conducted in the presence of a thiocarbonylthio‐containing reversible addition–fragmentation chain transfer (RAFT) agent. This allows for a highly “green” method of externally regulated/controlled polymerization with a potentially broad scope for polymerizable monomers and/or polymer structures.     

Heteroarm Star‐Like Micelles Formed from Polystyrene‐block‐poly(2‐vinyl pyridine)‐block‐poly(methyl methacrylate) ABC Triblock Copolymers in Toluene

Polystyrene‐block‐poly(2‐vinyl pyridine)‐block‐poly(methyl methacrylate) ABC triblock copolymers were synthesized by sequential living anionic polymerization. Their solution properties were investigated in toluene, which is a bad solvent for the middle block. Spherical micelles are formed, which consist of a poly(2‐vinyl pyridine) dense core bearing polystyrene and poly(methyl methacrylate) soluble chains at the corona. These micelles exhibit the architecture of heteroarm star copolymers obtained by “living” polymerization methods. The aggregation numbers strongly depend on the length of the insoluble P2VP middle block, thus remarkably affecting the size of the micelles.     

原子转移自由基聚合反应及其进展

活性自由基聚合是目前高分子科学中最为活跃的研究领域之一,原子转移自由基聚合反应是实现活性聚合的一种颇为有效的途径,可实现众多单体的活性可控自由基聚合。此文综述有关原子转移自由基聚合反应及其最新进展。     

In situ gamma ray-initiated polymerization to stabilize surface micelles

Surfactant molecules containing hydrophobic long alkyl chains and hydrophilic groups can organize into various micellar structures both in bulk solution and at interface. However, because of the dynamical nature of surfactant micelles, efforts directed at fixing their structures in bulk solution by polymerization have met with limited success. Herein, we report a unique and simple method of stabilizing surface micelles of a low molecular weight surfactant 11-acryloyloxyundecyltriethylammonium bromide (AUTEAB) through in situ intramicellar polymerization on the mica surface. Atomic force microscopy (AFM) observations show that the cylindrical micellar structure formed by AUTEAB monomers at the mica/water interface is preserved after the in situ polymerization, and the stability of the polymerized surface micelles is greatly enhanced compared with that of the unpolymerized ones.     

Ionic Polymerization of Vinyl Aromatic Monomers

The ionic polymerization of vinyl monomers possessing aromatic and heterocyclic functional groups has not been studied in any systematic fashion. Only in a few isolated cases have detailed mechanistic and structural studies been reported. The anionic polymerization of a number of vinylanthracene monomers has recently been investigated and some rationalization of this system is presented. The cationic and anionic polymerization of the N-, 3-, and 2-vinylcarbazole series of monomers is discussed in some detail. The important role of vinyl aromatic/vinyl heterocyclic monomers, i.e., diphenylethylene and the vinylcarbazoles, in elucidating the mechanistic aspects of cationic polymerization, “change transfer” polymerization, and photoionic polymerization is considered.     

Etude theorique de la reactivite des ions libres intervenant dans la polymerisation anionique de quelques monomeres vinyliques

The reactivities have been calculated for free ions involved in anionic polymerization of vinyl monomers. The copolymerization constants k_AB available in the literature are compared to the stabilization energies involved in the reaction of carbanions with the same monomer. The reactivities of carbanions of living poly (2-vinyl pyridine), poly styrene and poly (substituted styrenes) with respect to 1-1,diphenylethylene have been computed. The rate constants of homopolymerisation have been compared with the variation of π energy between the “monomer” and “carbanion” states of these monomers. The occurrence of side-reactions during the polymerization of vinyl-pyridine has been investigated using quantum chemistry methods.     

Synthesis and applications of olefin-contaning polymers

The problems of ionic coordination polymerization of higher α-olefins are summarized briefly. During the polymerization such monomers as 3-methyl-butene-1, vinylcyclohexane and others isomerize into unreactive isomers, and the rate of polymerization and final yield of polymer are sharply decreased as compared with the polymerization of lower olefins. The modification of polypropylene by ionic coordination copolymerization of propylene with higher α-olefins and polar monomers is considered. Significant modification of carbochain polymers may be obtained by the insertion of heteroatoms in the backbone. New possibilities for chemical “modification” of olefins by direct interaction with sulphur and the unusual aspects of the polymerization of olefin sulfides are also considered. The subsequent transformation of polyolefin sulfide gives polymers which have properties drastically differing from those of polyolefins. In conclusion, some new application areas are described.     

Polymerization of amphiphilic quaternary ammonium salts of acrylic,methacrylic, and ethacrylic acids

The polymerization behavior of dodecyltri-methylammonium methacrylate, and hexadecyltrimethylammonium acrylate, methacrylate and ethacrylate as amphiphilic monomers bearing a polymerizable double bond outside the micelle shell was investigated in micellar solution. Although the monomers did not have spontaneous polymerizability, they polymerized in the presence of both oil-soluble and water-soluble radical initiators, in spite of the difference of the expected location solubilizing initiator molecules. The profit based on micelle-forming of the monomer on the polymerization in water disappeared by the addition of sodium chloride into the polymerizing system due to the increased dissociation between cationic micelles and the polymerizable counter ions.     

Classical and metallocene catalytic systems: Comparison between the stereochemical mechanisms of α-olefin polymerization

Classical Ziegler-Natta and Kaminsky-Ewen catalysts promoting polymerization of hydrocarbon monomers are compared considering the reactivity and the stereochemical mechanisms of polymerization. It is suggested that also the “active sites” of heterogeneous catalysts could be cationic.     

Mechanism of plasma-initiated polymerization: Concerning the nature of solvent effects on the lifelike polymerization of water-soluble vinyl monomers

To provide a satisfactory basic understanding of the solvent effect of plasma-initiated polymerization, we have carried out several kinds of polymerizations of various water-soluble vinyl monomers. It has been shown that aqueous solution of such vinyl monomers underwent the polymerizations induced by methyl isobutyrate (MIB) plasma-exposed glass surface. The invisible ultrathin polymer film trapping an active radical species deposited on the plasma-exposed glass surface apparently induced the polymerizations. The efficiency, however, was largely dependent on the solvent used: the solvent can be considered to act as “an initiation-activator” for the lifelike postpolymerization. The nature of the solvent effect was ascribed to the physicomechanical property such as swelling ability and/or solubility toward the ultrathin film formed on the glass surface. Thus it has been suggested that the choice of good-balanced combination between the structural feature of the plasma-induced ultrathin polymer film and the solvent as an initiation-activator is important to achieve activity of a desired solution polymerization.     

Pd(II) -catalyzed addition polymerizations of strained polycyclic olefins

Cationic Pd(II) -complexes with weakly coordinating ligands were used for the olefin addition polymerization of strained polycyclic olefins. The cyclic structure of the monomers remained intact during the reaction which contrasts with products obtained from the olefin metathesis polymerization. The Pd(II) -catalyzed polymerizations showed the features of a “living” polymerization, when norbornene and selected exo-substituted norbornene derivatives were used as the monomers. Endo- and exo-dicyclopentadiene, exo-1,2-dihydrodicyclopentadiene, endo, exo-1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene and endo, exo-1,4,5,8-dimethano-1,4,4,a,5,8,8a-hexahydronaphthalene were converted into the corresponding rigid polymers. The exo-substituted monomers were found to polymerize at a higher rate than the corresponding or similar endo-substituted monomers. The polymerization of norbornadiene and the subsequent thermal elimination of cyclopentadiene resulted in the formation of polyacetylene.     

Block polymers of isocyanates and vinyl monomers by homogeneous anionic polymerization

The “living” polymer method was used to prepare block polymers of vinyl monomers and isocyanates at low temperatures in toluene–tetrahydrofuran mixtures. Vinyl monomers and diisocyanates, which have one hindered isocyanate group, as in 2,4-toluene diisocyanate, form block polymers which contain pendant reactive isocyanate groups. These block polymers can be crosslinked with water, diols, diamines, etc. The polymerization is apparently limited to block polymer formation, since the polyisocyanate anion is incapable of initiating the polymerization of common vinyl monomers.     

Facile syntheses of surface-functionalized micelles and shell cross-linked nanoparticles

Block copolymer micelles and shell cross-linked nanoparticles (SCKs) presenting Click-reactive functional groups on their surfaces were prepared using two separate synthetic strategies, each employing functionalized initiators for the controlled radical polymerization of acrylate and styrenic monomers to afford amphiphilic block copolymers bearing an alkynyl or azido group at the α-terminus. The first route for the synthesis of the azide-functionalized nanostructures was achieved via sequential nitroxide-mediated radical polymerization (NMP) of tert-butyl acrylate and styrene, originating from a benzylic chloride-functionalized initiator, followed by deprotection of the acrylic acids, supramolecular assembly of the block copolymer in water and conversion of the benzylic chloride to a benzylic azide. In contrast, the second strategy utilized an alkynyl-functionalized reversible addition fragmentation transfer (RAFT) agent directly for the RAFT-based sequential polymerization of tetrahydropyran acrylate and styrene, followed by selective cleavage of the tetrahydropyran esters to give the α-alkynyl-functionalized block copolymers. These Click-functionalized polymers, with the functionality located at the hydrophilic polymer termini, were then self-assembled using a mixed-micelle methodology to afford surface-functionalized “Clickable” micelles in aqueous solutions. The optimum degree of incorporation of the Click-functionalized polymers was investigated and determined to be ca. 25%, which allowed for the synthesis of well-defined surface-functionalized nanoparticles after cross-linking selectively throughout the shell layer using established amidation chemistry. Functionalization of the chain ends was shown to be an efficient process under standard Click conditions and the resulting functional groups revealed a more “solution-like” environment when compared to the functional group randomly inserted into the hydrophilic shell layer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5203–5217, 2006     

Synthesis of novel polymeric materials based on aliphatic polyesters by combination of different controlled polymerization methods

Combination of the living ring-opening polymerization (ROP) of ε-CL and lactides with the “controlled” free radical polymerization of styrene and methacrylic monomers is a versatile strategy for the synthesis of well-defined block and graft copolymers. In this respect, the dual “living” polymerization strategy in which two different functional groups on a single molecule used to initiate the two controlled mechanisms is particularly efficient. Combination of ROP and step-growth polymerization is another versatile methodology for the preparation of a large variety of new materials, e.g. polyimide nanofoams, polyester/silica hybrid materials and star and branched polyesters by dendritic initiation.