Presence Of Chain Transfer Agent Research Articles

Covalently Crosslinked Networks from Telechelic Polycyclooctene with Reinforced Properties

Comprehensive SummaryIntroducing covalently crosslinked network to telechelic polymers can enable the formation of advanced polymeric materials with enhanced material properties. In this contribution, well‐defined telechelic polymers bearing acetoacetate groups were synthesized via Ru‐catalyzed ring‐opening metathesis polymerization of cyclooctene in the presence of chain transfer agents. Given the unique feature of muti‐site reactive acetoacetate end groups, several crosslinked networks were constructed using different crosslinkers under mild conditions. In the Michael addition reaction system, the introduction of di/trifunctional aliphatic acrylate as crosslinkers significantly enhanced the mechanical properties of the generated crosslinked network (tensile strength up to 27 MPa, elongation at break up to 500%). On the other hand, vitrimers with dynamic covalent crosslinked networks were accessed via transamination of vinylogous urethane reaction using telechelic polymers and tris(2‐aminoethyl)amine. These vitrimers presented great mechanical properties and reprocessing properties. These strategies can be potentially applied to construct other types of high‐performance polymeric materials.

Living and Immortal Ring-Opening Polymerization of Cyclic Esters

The limited availability of fossil fuels on the Earth has led researchers to develop new materials that are derived from renewable feedstocks. The polymers produced from the ROP of cyclic esters like (LA and ɛ-CL) are biodegradable, biocompatible, and bioassimilable and thus find major applications in various field. The ROP are catalyzed by the metal-based organometallic catalyst and metal-free organocatalyst. This review exemplifies the living and immortal ROP. The advantage of such polymerization is that they produce polymers with controlled molecular weight distribution. For the immortal ROP, more than one polymer chain grows from the single catalytic site in the presence of chain transfer agents (CTAs), and thus catalyst loading is low, which make the process economically more viable. The nature of CTAs and loading of CTAs with respect to the catalyst is crucial as the catalyst should be effective in the presence of CTAs. The review also discusses functionalized CTAs employed for the polymerization in some instances where functionalized polymers are generated.

Telechelic Oligo(N-Vinylpyrolydone)swith Cumene Based Terminal Groups for Block-Copolymer and Nanoparticle Obtaining

Polymers with terminal epoxy, phosphate, fluoroalkyl groups were obtained by radical polymerization in the presence of chain transfer agents derived from isopropylbenzene. The structure of polymers was confirmed by NMR spectra and functional analysis. Polymers with functional fragment were used for synthesis of polymer-inorganic particles and copolymers with poly(2-ethyl-2-oxazoline) fragment.

Fluorination of nitrile-butadiene rubber without gelation via radical graft polymerization in presence of chain transfer agent

Fluorination could efficiently improve the comprehensive performance of nitrile-butadiene rubber (NBR). However, severe gelation usually occurred in the radical graft polymerization onto the diene-based polymers. Here, a facile approach has been established for the facile fluorination of NBR without gelation via radical graft polymerization in presence of n-dodecylmercaptan (NDM) as chain transfer agent, with 2,2,3,4,4,4-hexafluorobutyl acrylate (F6) as the model fluorinating monomer. The gel content decreased with increasing the feeding ratio of NDM and reached 0 with a feeding ratio of NDM of 50 mol% of the initiator, with a fluorination degree of 0.50%. The graft polymerization mechanism was proposed with the 1H NMR analysis. The proposed strategy is expected to provide a promising approach for the functionalization of diene-based polymers.

Thermokinetic parameter estimation of RAFT solution polymerization of dodecyl methacrylate by reaction calorimetry

The kinetics of RAFT polymerization of a dodecyl methacrylate controlled by a trithiocarbonate as a chain transfer agent (CTA) are studied by measuring the thermal profile in an RC1-RTCal reaction calorimeter. Contrary to classical methods such as electron spin resonance spectroscopy, the equilibrium constants related to the addition and fragmentation steps are estimated for a high degree of polymerization. The estimation method consists of a comparison between the measured thermal profiles and those built from models reflecting the instantaneous balances of mass and energy. The influence of the concentration of the transfer agent on the characteristics of the polymer (molar mass and dispersity) was also studied at different reaction temperatures. An increase in the concentration of CTA decreases the viscosity of the medium due to a more homogeneous distribution of the small sizes of the polymers. The influence of reaction temperature on the characteristics of polymers is reduced in the presence of CTA.

Isotactic Poly(propylene oxide): A Photodegradable Polymer with Strain Hardening Properties.

Leakage and accumulation of highly stable commercial plastics has led to substantial contamination of the environment. Highly isotactic poly(propylene oxide) (iPPO) was investigated as a potential high-strength thermoplastic with greater susceptibility toward degradation under ambient conditions. Various stereoregular forms of iPPO including enantiopure, enantioenriched, racemic, and stereoblock were synthesized with a single catalyst architecture in the presence of chain transfer agents. These materials were found to possess the same approximate ultimate tensile strength (UTS) via uniaxial tensile elongation analysis (∼75 MPa). A serrated tensile response corresponding to stress oscillations was observed in all forms of iPPO. An investigation on strain rate dependence showed that an increase in strain rate results in the decay and disappearance of the serrated response. Further evaluation of iPPO revealed its dramatic strain hardening afforded an UTS comparable to that of nylon-6,6. Exposing iPPO to UVA light (365 nm) resulted in photolytic degradation. Following 30 days of continuous exposure at 250 μW cm-2, the Mn decreased from 93 kDa to 21 kDa, while samples not exposed to UVA light remained unchanged. Through selective stabilization with antioxidant additives, we believe iPPO could be a suitable replacement for nylon-6,6 in environmentally susceptible applications.

Placing Single-Metal Complexes into the Backbone of CO2-Based Polycarbonate Chains, Construction of Nanostructures for Prospective Micellar Catalysis

The copolymerization of CO2 and epoxides in the presence of chain-transfer agents (CTAs) has provided a well-controlled route to polycarbonate polyols. Upon employing dicarboxylic acid CTAs which c...

Understanding the Role of Shape and Composition of Star-Shaped Polymers and their Ability to Both Bind and Prevent Bacteria Attachment on Oral Relevant Surfaces.

In this study, we have prepared a series of 4- and 6-arm star-shaped polymers with varying molecular weight and hydrophobicity in order to provide insight into the role and relationship that shape and composition have on the binding and protecting of oral relevant surfaces (hydroxyapatite, HAP) from bacteria colonization. Star-shaped acrylic acid polymers were prepared by free-radical polymerization in the presence of chain transfer agents with thiol groups, and their binding to the HAP surfaces and subsequent bacteria repulsion was measured. We observed that binding was dependent on both polymer shape and hydrophobicity (star vs. linear), but their relative efficacy to reduce oral bacteria attachment from surfaces was dependent on their hydrophobicity only. We further measured the macroscopic effects of these materials to modify the mucin-coated HAP surfaces through contact angle experiments; the degree of angle change was dependent on the relative hydrophobicity of the materials suggesting future in vivo efficacy. The results from this study highlight that star-shaped polymers represent a new material platform for the development of dental applications to control bacterial adhesion which can lead to tooth decay, with various compositional and structural aspects of materials being vital to effectively design oral care products.

Preparation of Ultralow Molecular Weight Poly(vinyl chloride) with Submicrometer Particles via Precipitation Polymerization

Poly(vinyl chloride), with ultralow molecular weight, produced by free radical polymerization either at high temperature or in the presence of chain transfer agents, is widely used as special resins and polymer process additives. This paper reports a new process, called self-stabilized precipitation polymerization, in which the polymerization of vinyl chloride monomer (VCM) is conducted in hydrocarbon diluents without addition of any suspending agent or emulsifier. The merits of this novel strategy include: (1) PVC resins with ultra-low number-average molecular weight (Mn) from 4000 to 15000, which is much lower than Mn of those prepared by conventional suspension and emulsion polymerizations, (2) sub-micrometer PVC particles with near spherical morphology, and (3) the very simple post-polymerization separation process. Under mild stirring, polymerization proceeds stably and smoothly. The influences of main process factors, such as solvents, initiator and monomer concentrations, polymerization time, and temperature on both particle morphology and Mn of the polymer products are investigated systematically. The molar ratio of -CH2-CHCl-/-CH=CH-CH2CHCl, a good indicator of structural defects, is about 1000/0.1 which means the low molecular weights do not result from chain transfer to the monomers. Then the mechanism of this polymerization is proposed. In summary, this novel polymerization technology provides a straightforward method for preparing PVC particulate products with low Mn.

A novel approach for synthesis of poly(norbornene)‐co‐poly(styrene) block copolymers via metathesis polymerization and free‐radical polymerization

AbstractIt is successfully realized that block copolymers are synthesized via metathesis polymerization followed by free‐radical polymerization. This method is performed using styrene (St) and norbornene, one block is synthesized using the Grubbs second generation catalyst in the presence of chain transfer agents, and the subsequent polymerization of St is initiated by azo compounds to complete the additional blocks in the copolymers. The use of free‐radical polymerization instead of controlled radical polymerization or ionic polymerization can be potentially superior for industrialization. As a result, the molecular weights of the block copolymers ranging from 10.4 to 54.3 kDa and polydispersity indices ranging from 1.30 to 1.91 are obtained. In principle, this new method can be potentially useful to prepare a broad range of block copolymers with cyclic olefin groups in the main chains, which may be used in some particular applications.

Effects of addition mode on Zn–Co double metal cyanide catalyst for synthesis of oligo(propylene‐carbonate) diols

Zn–Co double metal cyanide (DMC) complexes are promising catalytic systems for copolymerization of epoxide and CO2. In the work reported, Zn–Co DMC catalysts were prepared by parallel‐flow dropping, forward dropping and reverse dropping methods, aiming to provide an insight into the effect of addition mode on catalyst structure and catalytic performance. Catalytic properties were evaluated using the copolymerization reaction of propylene oxide (PO) and CO2 in the presence of chain transfer agent. The results indicated that the factors that affect crystalline state are different for different modes. And excess zinc chloride is the prerequisite for organic ligands to be retained in the catalyst and affect the structure. In addition, a catalyst with flower‐like morphology was obtained with the parallel‐flow dropping method which provided larger surface area. An appropriate O/Zn value ensured abundant active PO which would suppress the backbiting process by forming consecutive PO units adjacent to CO2 units. Oligo(propylene‐carbonate) diols with average molecular weight of 1020 g mol−1, CO2 incorporation of 24.92% and WPC of 5.14 wt% were obtained at 80 °C and 2 MPa.

Highly Efficient One-Pot Synthesis of COS-Based Block Copolymers by Using Organic Lewis Pairs.

A one-pot synthesis of block copolymer with regioregular poly(monothiocarbonate) block is described via metal-free catalysis. Lewis bases such as guanidine, quaternary onium salts, and Lewis acid triethyl borane (TEB) were equivalently combined and used as the catalysts. By using polyethylene glycol (PEG) as the macromolecular chain transfer agent (CTA), narrow polydispersity block copolymers were obtained from the copolymerization of carbonyl sulfide (COS) and propylene oxide (PO). The block copolymers had a poly(monothiocarbonate) block with perfect alternating degree and regioregularity. Unexpectedly, the addition of CTA to COS/PO copolymerization system could dramatically improve the turnover frequency (TOF) of PO (up to 240 h−1), higher than that of the copolymerization without CTA. In addition, the conversion of CTA could be up to 100% in most cases, as revealed by 1H NMR spectra. Of consequence, the number-average molecular weights (Mns) of the resultant block copolymers could be regulated by varying the feed ratio of CTA to PO. Oxygen-sulfur exchange reaction (O/S ER), which can generate randomly distributed thiocarbonate and carbonate units, was effectively suppressed in all of the cases in the presence of CTA, even at 80 °C. This work presents a versatile method for synthesizing sulfur-containing block copolymers through a metal-free route, providing an array of new block copolymers.

Employing a Sugar-Derived Dimethacrylate to Evaluate Controlled Branch Growth during Polymerization with Multiolefinic Compounds

Radical copolymerization of divinyl monomers in the presence of chain transfer agents leads to soluble hyperbranched polymers. In this work, hyperbranched poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) with degradable cross-linker branch points derived from glucarodilactone methacrylate was prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization to provide insight into hyperbranch formation during copolymerizations of multiolefinic compounds. The number-average molecular weight of the polymers increased nonlinearly with monomer conversion, implying that the incorporation of the divinyl cross-linker led to chain branching and a rapid increase in molecular weight at high conversion. The degree of branching was varied by controlling the feed ratio of monomer to cross-linker to chain transfer agent. Hydrolytic degradation of the sugar-derived dilactone branch points was examined under acidic, neutral, and basic aqueous conditions. To provide fundamental insight into...

Modular, Flexible, and Continuous Plant for Radical Polymerization in Aqueous Solution

The European project F3 Factory aims at designing small to medium scale plants consisting of standardized container assemblies for delocalized production of various chemicals. Within the framework of the F3 Factory project, the design of a modular, multiproduct, and continuous plant for manufacturing water‐soluble polymers is addressed. Free radical polymerization in aqueous solution is examined through two industrial cases: polymerization of acrylic acid (AA) in the presence of chain transfer agent (CTA) and copolymerization of AA with one comonomer. A methodology for performing the transition from batch recipes to continuous operations is proposed. Offline and inline monitoring of monomer consumption is achieved using Raman spectroscopy combined with chemometrics. A modular pilot plant meeting the requirements of F3 Factory project is designed and demonstrated at INVITE (Bayer, Leverkusen). The two polymerization processes are successively operated in the same pilot plant separated by an intermediate extensive washing. For each process, several polymer grades are produced by modification of reaction conditions (inlet flow of CTA or reactor temperature). Transition dynamics are characterized using inline monitoring. The flexibility of the modular plant is demonstrated.image

Preparation of oligo‐N‐isopropylacrylamide brushes with OH and COOH end‐groups via surface‐initiated NMP

AbstractFunctional brushes have recently emerged as an extremely versatile way to modify surface properties in a robust and controlled way. In this study, well‐defined, high density oligo‐N‐isopropylacrylamide (oligoNIPAM) brushes with OH and COOH end‐groups were fabricated through a reliable strategy by the combination of the self‐assembly of bimolecular macroazoinitiator on silicon surface and surface‐initiated nitroxide mediated polymerization of N‐isopropylacrylamide in the presence of chain transfer agent (i.e., 2‐mercaptoethanol or 3‐mercaptopropionic acid). The living polymerization produced silicon substrate‐coated with functional oligoNIPAM with a target molecular weight and a grafting density as high as 8.14 chains nm−2. The functional oligoNIPAM brushes can be employed for the adsorption of biomacromolecules such as DNA and proteins. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

RAFT polymerization of N‐vinyl pyrrolidone using prop‐2‐ynyl morpholine‐4‐carbodithioate as a new chain transfer agent

AbstractRAFT polymerization of N‐vinyl pyrrolidone (NVP) has been investigated in the presence of chain transfer agent (CTA), i.e., prop‐2‐ynyl morpholine‐4‐carbodithioate (PMDC). The influence of reaction parameters such as monomer concentration [NVP], molar ratio of [CTA]/[AIBN, i.e., 2,2′‐azobis (2‐methylpropionitrile)] and [NVP]/[CTA], and temperature have been studied with regard to time and conversion limit. This study evidences the parameters leading to an excellent control of molecular weight and molar mass dispersity. NVP has been polymerized by maintaining molar ratio [NVP]: [PMDC]: [AIBN] = 100 : 1 : 0.2. Kinetics of the reaction was strongly influenced by both temperature and [CTA]/[AIBN] ratio and to a lesser extent by monomer concentration. The activation energy (Ea = 31.02 kJ mol−1) and enthalpy of activation (ΔH‡= 28.29 kJ mol−1) was in a good agreement to each other. The negative entropy of activation (ΔS‡ = −210.16 J mol‐1K‐1) shows that the movement of reactants are highly restricted at transition state during polymerization. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Synthesis of poly(N-isopropylacrylamide) with a low molecular weight and a low polydispersity index by single-electron transfer living radical polymerization

The single-electron transfer living radical polymerization (SET-LRP) method in the presence of chain transfer agent was used to synthesize poly(N-isopropylacrylamide) [poly(NIPAM)] with a low molecular weight and a low polydispersity index. This was achieved using Cu(I)/2,2′-bipyridine as the catalyst, 2-bromopropionyl bromide as the initiator, 2-mercaptoethanol as the chain transfer agent (TH), and N,N-dimethylformamide (DMF) as the solvent at 90 °C. The copper nanoparticles with diameters of 16 ± 3 nm were obtained in situ by the disproportionation of Cu(I) to Cu(0) and Cu(II) species in DMF at 22 °C for 24 h. The molecular weights of poly(NIPAM) produced were significantly higher than the theoretical values, and the polydispersities were less than 1.18. The chain transfer constant (Ctr) was found to be 0.051. Although the kinetic analysis of SET-LRP in the presence of TH corroborated the characteristics of controlled/living polymerization with pseudo-first-order kinetic behavior, the polymerization also exhibited a retardation period (k > ktr). The influence of molecular weight on lower critical solution temperature (LCST) was investigated by refractometry. Our experimental results explicitly elucidate that the LCST values increase slightly with decreasing molecular weight. Reversibility of solubility and collapse in response to temperature well correlated with increased molecular weight of poly(NIPAM). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

SET-LRP of N-isopropylacrylamide in the presence of chain transfer agent

In this study, single electron transfer-living radical polymerization (SET–LRP) of N-isopropylacrylamide (NIPAM) in the presence of 2-mercaptoethylamine chain transfer agent (CTA) was carried out by Cu(0) generated in situ from the disproportionation of CuBr/2,2′-bipyridine (2,2′-bpy) in N,N-dimethylformamide (DMF) at 90 °C. Analysis of polymerization kinetics in the presence of CTA showed that the premature termination of growing polymer chains leads to retardation. The apparent rate constant of polymerization (k) decreased from 4.49 × 10−4 to 2.59 × 10−4 min−1 with increasing CTA concentration. The initiator efficiency (Ieff) and the chain transfer constant (Cs) were found to be 0.524 and 0.286, respectively. The molecular weights of poly(N-isopropylacrylamide) [poly(NIPAM)] produced were significantly higher than the predicted values, and the polydispersities were less than 1.22. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Connection of polymer chains using diepoxide in CO2/propylene oxide copolymerizations

When a small amount of vinylcyclohexene dioxide ([diepoxide]/[cat] = 60, 0.14 w% propylene oxide) is additionally added in CO2/propylene oxide copolymerization catalyzed by a highly active catalyst, cobalt(III) complex of a Salen-type ligand tethered by four quaternary ammonium salts (2), some polymer chains are connected consequently resulting in an increased molecular weight of up to Mw = 606000 and broadened molecular weight distribution. The same chain-connecting process is also applicable in the presence of chain transfer agent, tricarballylic acid (C3H5(CO2H)3), 1,2,3,4-butanetetracarboxylic acid (C4H6(CO2H)4), or adipic acid (C4H8(CO2H)2), although a higher amount of diepoxide is needed. Gel permeation chromatography reveals multi-modal distributions along with a tail at a high molecular weight portion due to formation of the connected chains. The shape of the chain transfer agent varies the chain topology, but the rheological properties are not influenced by the topology change. The poly(propylene carbonate)-block-poly(ethylene glycol) copolymer, which is obtained by feeding poly(ethylene glycol)-OH as a chain transfer agent, becomes tough in the tensile properties and shows a high shear sensitivity in the rheological properties when some chains are connected using diepoxide.

Synthesis of Telechelic Polyisoprene via Ring-Opening Metathesis Polymerization in the Presence of Chain Transfer Agent

Telechelic polyisoprene was synthesized via the ring-opening metathesis polymerization (ROMP) of 1,5-dimethyl-1,5-cyclooctadiene (DMCOD) in the presence of cis-1,4-diacetoxy-2-butene as a chain transfer agent (CTA). This method afforded telechelic polymer in excellent yield, and the acetoxy groups were successfully removed to yield α,ω-hydroxy end-functionalized polyisoprene with potential for subsequent reactions. Efficient, quantitative incorporation of CTA was achieved, and NMR spectroscopy was utilized to confirm the chemical identity of the polymer end groups. Polymerization of discrete DMCOD monomer generated polyisoprene with excellent regioregularity in the polymer backbone. Successful ROMP of sterically challenging DMCOD in the presence of a CTA for chain end-functionalization was borne out through screening of a variety of Ru-based olefin metathesis catalysts.