Reversibly Crosslinked Networks of Nanoparticles in Metallocene‐Catalyzed Olefin Polymerization

A hierarchic build‐up of functional nano‐ and microparticles allows the generation of smart organic supports for metallocene catalysts. Latices, well defined in size and surface structure, are made by emulsion polymerization using poly(ethylene oxide)‐containing surfactants. Micron‐sized catalyst beads are formed by reversible loading/crosslinking with a metallocene/methylaluminoxane complex. As a result of the network fragmentation during ethylene polymerization, the catalysts achieve very high productivities, hard polyethylene particles and homogeneous distributions of nanometer‐sized fragments in the product.     

马来酸类可聚合乳化剂的合成及其在细乳液聚合中的应用

采用三步法合成了可聚合乳化剂马来酸单十六醇酯丙基磺酸钠.并用正交实验法优化了马来酸单十六醇酯合成工艺条件,结果表明反应的最佳条件为:催化剂质量分数1%,反应时间3.0h,反应温度90℃,马来酸酐与十六醇的摩尔比1.1:1.苯乙烯-丙烯酸丁酯细乳液聚合使用该乳化剂与传统乳化剂相比,在较低温度下(65℃)具有较高的转化率,且所得乳液具有较好的电解质稳定性,乳胶膜的耐水性也得到提高.     

A Missing Reaction Step in Dithiobenzoate-Mediated RAFT Polymerization

The debate on the mechanism of dithiobenzoate-mediated RAFT polymerization may be overcome by taking the so-called “missing step” reaction between a highly reactive propagating radical and the three-arm star-shaped product of the combination reaction of an intermediate RAFT radical and a propagating radical into account. The “missing step” reaction transforms a propagating radical and a not overly stable three-arm star species into a resonance-stabilized RAFT intermediate radical and a stable polymer molecule. The enormous driving force behind the “missing step” reaction is estimated via DFT calculations of reaction enthalpies and reaction free enthalpies.     

A Facile Strategy for the Preparation of Azide Polymers via Room Temperature RAFT Polymerization by Redox Initiation

A new vinyl aryl azide monomer, 4‐azidophenyl methacrylate (APM), has been synthesized and characterized by ¹H NMR and FT‐IR spectroscopy. The thermal stability of APM has been investigated by temperature‐dependent FT‐IR spectroscopy and ¹H NMR, and the monomer has been demonstrated to be quite stable at ambient temperature. Reversible addition–fragmentation chain transfer (RAFT) homopolymerization and copolymerizations of APM with methyl acrylate, methyl methacrylate, and styrene have been carried out at room temperature using a redox initiator, benzoyl peroxide (BPO)/N,N‐dimethylaniline (DMA). The results show that the polymerizations bear all the characteristics of controlled/living free‐radical polymerizations. Moreover, the cycloaddition of azido group to carbon–carbon double bond can be avoided in the polymerization process at room temperature.

     

异丁烯聚合催化体系研究 Ⅰ.均聚与共聚反应

用苯甲酰氯(BC)／TiCl4引发异丁烯(IB)聚合及与苯乙烯(St)的共聚反应，得到分子量高、分布窄的聚异丁烯及其共聚物，并控制了BC的高活性。对IB均聚及其与ST共聚反应影响因素(体系浓度、残余水、第3组分三乙胺(TEA))进行优化，得到最佳条件为：[BC]=2．6mmol／L、[TEA]／[BC]=1.0(均聚)和n(TiCl4)／n(BC)=80、[TEA]／[BC=4．0(共聚)，BC／TiCl4／TEA是最佳体系，对水不敏感，可以制备分子量高及分子量分布(MWD)为1．5(均聚)和2．0(共聚)的窄分布聚合物(GPC曲线均为单峰)。     

Formation of Hexagonally Packed Hollow Hoops and Morphology Transition in RAFT Ethanol Dispersion Polymerization

Similar to the traditional self‐assembly strategy, polymerization induced self‐assembly and reorganization (PISR) can produce a myriad of polymeric morphologies through morphology transitions. Besides the chain length ratio (R) of the hydrophobic to the hydrophilic blocks, the chain mobility in the intermediate nano‐objects, which is a requisite for morphology transition, is a determining factor in the formation of the final morphology. Although various morphologies have been fabricated, hexagonally packed hollow hoops (HHHs) with highly ordered internal structure have not, to the best of our knowledge, been prepared by PISR. In this article, the fabrication of HHHs through morphology transition from large compound vesicles to HHHs is reported. HHHs with highly regular internal structure may have significance in theoretical research and practical applications of nanomaterials.

     

A Novel Continuous Industrial Process for Producing Hydroxyapatite Nanoparticles

Fluidinova, a recent start‐up high technology engineering company, has developed and is now commercializing a novel continuous industrial reactor NETmix for the manufacture of high added value products, such as nanomaterials, microemulsions, and pharmaceutical products. Through this technology, Fluidinova, in cooperation with Instituto de Engenharia Biomédica, has developed and patented the industrial process for the synthesis of a new high quality product consisting of hydroxyapatite nanoparticles with extremely high purity and crystallinity to be used as biocompatible nanomaterial for biomedical and pharmaceutical applications, to improve the quality of the already existing hydroxyapatite based medical devices, such as bone grafts, coated implants, and drug delivery systems.     

Model prediction of batch emulsion copolymerization as a function of conversion: A sensitivity analysis

Recently a model has been developed capable of predicting absolute monomer concentrations and their ratios in the polymer, aqueous, and monomer droplet phases as a function of conversion in batch emulsion copolymerizations without using any adjustable parameters. In this article the sensitivity of model predictions of composition drift toward deviations of 10% in all model parameters (maximum swellabilities of monomer in the polymer phase, water solubilities, reactivity ratios, and monomer and polymer densities) was estimated using the monomer combination methyl methacrylate-styrene as an example. From the sensitivity analysis it can be concluded that the reactivity ratios are the most important parameters affecting composition drift. The effects of deviations in maximum swellabilities and monomer and polymer densities on composition drift can be neglected, while the water solubility is important only in those cases where the amount of monomer in the aqueous phase cannot be neglected as compared with the total monomer amount. © 1994 John Wiley & Sons, Inc.     

Controlled (Co)Polymerization of Methacrylates Using a Novel Symmetrical Trithiocarbonate RAFT Agent Bearing Diphenylmethyl Groups

Herein, we report a novel type of symmetrical trithiocarbonate chain transfer agent (CTA) based diphenylmethyl as R groups. The utilization of this CTA in the Reversible Addition-Fragmentation chain Transfer (RAFT) process reveals an efficient control in the polymerization of methacrylic monomers and the preparation of block copolymers. The latter are obtained by the (co)polymerization of styrene or butyl acrylate using a functionalized macro-CTA polymethyl methacrylate (PMMA) previously synthesized. Data show low molecular weight dispersity values (Đ < 1.5) particularly in the polymerization of methacrylic monomers. Considering a typical RAFT mechanism, the leaving groups (R) from the fragmentation of CTA should be able to re-initiate the polymerization (formation of growth chains) allowing an efficient control of the process. Nevertheless, in the case of the polymerization of MMA in the presence of this symmetrical CTA, the polymerization process displays an atypical behavior that requires high [initiator]/[CTA] molar ratios for accessing predictable molecular weights without affecting the Đ. Some evidence suggests that this does not completely behave as a common RAFT agent as it is not completely consumed during the polymerization reaction, and it needs atypical high molar ratios [initiator]/[CTA] to be closer to the predicted molecular weight without affecting the Đ. This work demonstrates that MMA and other methacrylic monomers can be polymerized in a controlled way, and with “living” characteristics, using certain symmetrical trithiocarbonates.     

Polymerization behavior of 2,2,6,6-tetramethylpiperidinyl methacrylate: A monomer carrying a hindered amine group

Copolymers of 2,2,6,6-tetramethylpiperidinyl methacrylate (TPMA) with styrene (S) and with methyl methacrylate (MMA) were synthesized using AIBN as initiator. S–TPMA copolymers from feed ranging from 0.10–0.80 mole fractions TPMA and MMA-TPMA copolymers from feed of 0.04–0.85 mole fractions TPMA were used in the determination of monomer reactivity ratios r₁, r₂. Four different methods were employed in the calculations of r₁ and r₂ and all calculated results were in good agreement with each other. The structure of S–TPMA copolymers was inferred to be of an alternating nature while that of MMA–TPMA copolymers was random. Both copolymers are potential hindered amine light stabilizers (HALS) and are expected to be less extractable from, and more compatible with, polystyrene and poly(methyl methacrylate) base polymers.     

Chain Transfer in Degenerative RAFT Polymerization Revisited: A Comparative Study of Literature Methods

Under the validity of the degenerative transfer mechanism, the activation/deactivation process in reversible addition‐fragmentation chain transfer (RAFT) polymerization can be formally quantified by transfer coefficients, depending on the chemical structure of the participating radicals and dormant species. In the present work, the different literature methods to experimentally determine these RAFT transfer coefficients are reviewed and theoretically re‐evaluated. The accuracy of each method is mapped for a broad range of reaction conditions and RAFT transfer reactivities. General guidelines on when which method should be applied are formulated.

     

Mechanism of Dithiobenzoate‐Mediated RAFT Polymerization: A Missing Reaction Step

Summary: The debate on the mechanism of dithiobenzoate‐mediated RAFT polymerization may be resolved by including the reaction between a propagating radical and the star‐shaped combination product from irreversible termination into the kinetic scheme. By this step, a highly reactive propagating radical and a not overly stable three‐arm star species are transformed into the resonance‐stabilized RAFT intermediate radical and a very stable polymer molecule. The time evolution of concentrations is discussed for the main‐equilibrium range of CDB‐mediated methyl acrylate polymerization.

Illustration of the novel understanding of the RAFT mechanism in dithiobenzoate‐mediated RAFT polymerization.     

Combining RAFT Radical Polymerization and Click/Highly Efficient Coupling Chemistries: A Powerful Strategy for the Preparation of Novel Materials

This paper highlights the powerful combination of reversible addition–fragmentation chain transfer (RAFT) radical polymerization and various click/coupling chemistries. This is not an exhaustive review but rather an overview demonstrating the impressive possibilities that the “marriage” of these two synthetic approaches offers in modern macromolecular design and synthesis.

     

Novel Thiophenic Copolymer as a Multi-Purpose Macromolecular Intermediate

The preparation of a new thiophenic dimer partially derivatized with a bromohexylic chain is described. Its polymerization under mild oxidative conditions leads to a polythiophene with a degree of functionalization of 50% and highly soluble in organic solvents. The product has been fully characterized by FT-IR, ¹H and ¹³C NMR using one and two-dimensional techniques as well as by SEC and thermal analysis. Solvatochromic effects of the new polymer have been investigated in different mixtures, underlining its self-assembling capability even in solvated states.     

Additional Retardation in RAFT Polymerization: Detection of Terminated Intermediate Radicals

The reversible addition‐fragmentation chain transfer (RAFT) polymerization of N‐acryloylmorpholine (NAM) is performed using three dithioesters (DT) as chain transfer agents (CTA) that incorporate a morpholine (morpholine‐DT), a biotin (biotin‐DT), or a sugar (sugar‐DT) moiety in the R group. PolyNAM chains of controlled characteristics are synthesized. An unexpected behavior is observed with morpholine‐DT, described as an ‘additional retardation’, which is especially visible when low molar masses are targeted ( < 5 000 g · mol⁻¹). In that particular case, further investigations using MALDI‐TOF mass spectrometry show the presence of terminated intermediate radicals (IRs), which corroborates the assumption based on a specific protection of IR according to the nature of the α‐chain‐end.

     

RAFT Polymerization and Thiol Chemistry: A Complementary Pairing for Implementing Modern Macromolecular Design

Reversible addition fragmentation chain transfer (RAFT) polymerization is one of the most extensively studied reversible deactivation radical polymerization methods for the production of well‐defined polymers. After polymerization, the RAFT agent end‐group can easily be converted into a thiol, opening manifold opportunities for thiol modification reactions. This review is focused both on the introduction of functional end‐groups using well‐established methods, such as thiol‐ene chemistry, as well as on creating bio‐cleavable disulfide linkages via disulfide exchange reactions. We demonstrate that thiol modification is a highly attractive and efficient chemistry for modifying RAFT polymers.

     

Parametric Analysis of the Intermediate Concentration in a RAFT Polymerization and its Influence upon the Polymerization Kinetics

Summary: A kinetic analysis of living/controlled radical polymerizations in bulk mediated by RAFT is presented. The main objective is to show how the kinetics of the RAFT process and, in particular, of the RAFT intermediate radical is affecting the overall polymerization rate. Namely, three different cases are analyzed: (i) slow fragmentation of the RAFT intermediate; (ii) cross‐termination of the RAFT intermediate with other radicals; and (iii) slow re‐initiation of the RAFT agent leaving group. Simplified analytical formulas are derived for the time‐dependent concentrations of the involved species as well as for conversion. They are supported by numerical simulations and are qualitatively compared to literature experimental findings. Criteria are also given to judge the influence of the RAFT reaction kinetic rate constants on the different phenomena observed experimentally in RAFT polymerization, namely inhibition and retardation. Since these criteria are given by using non‐dimensional groups, they can be readily applied to a broad spectrum of experimental conditions.

Logarithmic non‐dimensional concentration for the radicals (r) and intermediate radicals (q) versus the non‐dimensional polymerization time ( ).     

A One‐Step Route to CO2‐Based Block Copolymers by Simultaneous ROCOP of CO2/Epoxides and RAFT Polymerization of Vinyl Monomers

The one‐step synthesis of well‐defined CO₂‐based diblock copolymers was achieved by simultaneous ring‐opening copolymerization (ROCOP) of CO₂/epoxides and RAFT polymerization of vinyl monomers using a trithiocarbonate compound bearing a carboxylic group (TTC‐COOH) as the bifunctional chain transfer agent (CTA). The double chain‐transfer effect allows for independent and precise control over the molecular weight of the two blocks and ensures narrow polydispersities of the resultant block copolymers (1.09–1.14). Notably, an unusual axial group exchange reaction between the aluminum porphyrin catalyst and TTC‐COOH impedes the formation of homopolycarbonates. By taking advantage of the RAFT technique, it is able to meet the stringent demand for functionality control to well expand the application scopes of CO₂‐based polycarbonates.