Control Of Molecular Weight Distribution Research Articles

Designing hydrolysis-resistant Ti/Zn bimetallic catalyst based on the coordination activation mechanism to synthesize high molecular weight poly (1,5-pentene terephthalate) (PPeT)

The high molecular weight poly (1,5-pentene terephthalate) synthesis and its molecular weight distribution control are still challenging, and one of the critical problems is the lack of efficient catalysts. Based on the coordination activation mechanism, a heavy metal free, hydrolysis-resistant and 1,5-Pentanediol soluble Ti/Zn bimetallic catalyst has been synthesized and characterized. The Ti/Zn bimetallic active center increases electron-absorption effect in catalyst to promote the esterification process, and the diol-metal alkoxide structure increases the production of oligomer ligands, which can effectively improve transesterification efficiency. The optimal polycondensation reaction temperature for PPeT synthesized with Ti/Zn bimetallic catalyst can be reduced to 230 °C, with an average reaction rate of 90.33 g mol−1·min−1. The number average molecular weight of PPeT can be increased to 3.02 × 104 g mol−1, and the polymer dispersive index can be as low as 1.90. As the number average molecular weight increases, poly (1,5-pentene terephthalate) has a tensile strength of 29.80 MPa and an elongation at break of 16.39%. More importantly, Ti/Zn bimetallic catalyst retains excellent catalytic activity after treatment with boiling water and has significantly improved hydrolysis resistance and storage stability. Ti/Zn bimetallic catalyst can significantly increase the molecular weight and melt viscosity of poly (1,5-pentene terephthalate), giving it the potential for a wider range of applications in plastics and fiber fields.

Fault Tolerant Control of Fuzzy Stochastic Distribution Systems With Packet Dropout and Time Delay

The fault diagnosis (FD) and fault tolerant control (FTC) problem of the fuzzy stochastic distribution system (SDS) over packet dropout and time delay is studied. Firstly, the static model of linear fuzzy logic system that approximates the output PDF and the dynamic model with the multiplicative fault in a fuzzy system are established. The random packet dropout and time delay caused by the network are described in a unified framework, in which the lost data is compensated with the latest data received by the buffer. On this basis, an adaptive observer is devised to estimate the unknown multiplicative fault. The design of sliding mode predictive fault tolerant controller is discussed to ensure that the system still has good tracking performance after the fault occurs. Numerical simulations on a molecular weight distribution control system are supplied to prove the effectiveness of the presented scheme. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —The motivation of this paper is to improve the reliability of the fuzzy stochastic distribution system with packet dropout and time delay. This kind of stochastic distribution systems is described by the relationship between the input and the output PDF rather than the normal relationship between the input and the output. When the multiplicative fault occurs in the system, the design of fault diagnosis strategy and fault-tolerant controller becomes an important challenge, especially when the system is subject to packet dropout and time delay. To address the above problems, a new fault diagnosis and fault-tolerant control scheme is proposed, which can accurately estimate the time and size of the fault and obtain the satisfactory fault-tolerant control effect.

Thermal pre-processing before extraction of polyhydroxyalkanoates for molecular weight quality control

Past studies have repeatedly demonstrated the technical feasibility to produce polyhydroxyalkanoate (PHA) using bacterial biomass of mixed microbial cultures (MMCs). Commercial quality grades of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, can be produced with control of average monomer composition. However, demonstration of PHBV production and recovery with quality control of molecular weight (MW) distribution has been lacking in the research literature. Towards this goal, a workflow has been developed for characterizing molecular weight control by thermal treatment pre-processing of dried PHA-rich biomass before solvent extraction. Dimethyl carbonate (DMC) was a suitable solvent in this workflow in the routine evaluation of extractable PHA. From assessments of DMC extraction using differential scanning calorimetry, 125 °C was selected for nominally 100 percent extraction yield independent of polymer 3-hydroxyvalerate (3HV) content (2 to 41 wt.% 3HV) and molecular weight (100 to 1400 kDa). Intrinsic viscosity measurements of PHBV in DMC at 60 °C was used for molecular weight monitoring. Mark-Houwink constants, α (0.738 ± 0.010) and LogK (-2.016 ± 0.025), were estimated for a PHBV co-polymer blend having 36 wt.% 3HV. A model of random scission supported that weight average molecular weight (Mw) was a more robust metric, compared to number average molecular weight (Mn), for assessing the polymer scission rates. During isothermal heat treatment for a given biomass batch, interpreted scission rate was reproducible and commonly, but not always, constant in time. Scission rates between biomass batches were also variable. Measured properties of the polymer in the biomass (thermal stability, biomass PHA content, PHBV grade, initial moisture content) could not be correlated to this observed batch-to-batch variation of scission rate. Molecular weight loss before extraction did not influence the melting temperatures of the co-polymer blends of PHBV evaluated over a wide sub-eutectic range of average 3HV content. Molecular weight changes for these PHBV co-polymer blends were considered to have likely influenced the nature of blend 3HV distribution, and consequently, crystallization behaviour. Molecular weight loss effects on crystallization behaviour at constant PHBV average 3HV wt.% content could then have contributed to the observed variability for glass transition temperatures and melting enthalpies. However, a reproducible correlation between this variability and MW change was not observed.

New Ways for Controlling the Molecular-Weight Characteristics and Branching Distribution in Polyethylene Obtained over Supported Catalysts Containing Bis(imino)pyridyl Complexes of Fe(II) and Bis(imine) Complexes of Ni(II)

The paper describes ways for controlling the molecular structure of polyethylene (PE) produced over supported catalysts containing bis(imino)pyridyl complexes of Fe(II) (LFeCl2) and bis(imine) complexes of Ni(II) (*LFeCl2), which are anchored on silica gel modified by the introduction of alumina (SiO2(Al)). Under variation of polymerization conditions over LFeCl2 /SiO2(Al) catalysts, linear PE with different molecular weight and controllable molecular-weight distribution (MWD) was obtained. Homopolymerization of ethylene over *LNiBr2 /SiO2(Al) catalysts led to the formation of branched PE with the molecular-weight and thermophysical characteristics close to the low-density polyethylene produced by ethylene copolymerization with α-olefins over supported metallocene catalysts and supported Zieglertype catalysts. A method was proposed for constructing the supported bicomponent catalysts containing LFeCl2 and *LNiBr2 complexes anchored on the SiO2(Al) support for the deliberate production of polyethylene with the required molecular structure. There are examples of obtaining the linear PE with bimodal MWD on a bicomponent supported catalyst containing two different LFeCl2 complexes, the PE with controllable branching distribution on a bicomponent catalyst synthesized by anchoring LFeCl2 and *LNiBr2 complexes on the SiO2(Al) support, and an example of modifying the industrial chromium oxide catalyst by introducing the LFeCl2 complex for the control of MWD and branching distribution in the produced polyethylene.

Molecular Weight Distribution Control for Polymerization Processes Based on the Moment-Generating Function.

The molecular weight distribution is an important factor that affects the properties of polymers. A control algorithm based on the moment-generating function was proposed to regulate the molecular weight distribution for polymerization processes in this work. The B-spline model was used to approximate the molecular weight distribution, and the weight state space equation of the system was identified by the subspace state space system identification method based on the paired date of B-spline weights and control inputs. Then, a new performance criterion mainly consisting of the moment-generating function was constructed to obtain the optimal control input. The effectiveness of the proposed control method was tested in a styrene polymerization process. The molecular weight distribution of the styrene polymers can be approximated by the B-spline model effectively, and it can also be regulated towards the desired one under the proposed control method.

Efficient Visible-Light-Driven RAFT Polymerization Mediated by Deep Eutectic Solvents under an Open-to-Air Environment

In this work, we investigate the effects of deep eutectic solvents (DESs) on a facile reversible addition–fragmentation chain-transfer (RAFT) polymerization driven by visible light. A DES composed of tetrabutylammonium chloride (TBACl) and ethylene glycol served as a nonvolatile medium for a variety of monomers, including methyl methacrylate, methyl acrylate, dimethylacrylamide, and styrene. We first employed the polymerization-through pathway to overcome oxygen inhibition in an open-to-air environment using methyl methacrylate as the model compound. The photoiniferter polymerization using trithiocarbonates as the chain transfer agent (CTA) in DESs exhibited enhanced polymerization rates and achieved a narrow molecular weight distribution. Interestingly, even dithiobenzoate, the CTA with low efficiency for photoiniferter polymerization, exhibited a nearly 4.5-fold increase in the apparent polymerization rate constants when compared to the reaction in dimethyl sulfoxide. Moreover, the stability of the CTAs was increased in DESs for efficient control of molecular weight distribution and preservation of functional chain ends. We then surveyed photocatalysts for photoelectron/energy transfer (PET) RAFT polymerization and found that eosin Y was compatible with DESs. The PET-RAFT polymerization using dithiobenzoate in DESs showed even higher polymerization rates than the photoiniferter polymerization and enabled the polymerization under natural sunlight. Besides methyl methacrylate, other monomers also exhibited an increased polymerization rate in DESs, comparable to reactions in ionic liquids. These results suggest that DESs are effective and green media to facilitate photo-induced RAFT polymerization without additives or tedious degassing processes.

General route to design polymer molecular weight distributions through flow chemistry

The properties of a polymer are known to be intrinsically related to its molecular weight distribution (MWD); however, previous methodologies of MWD control do not use a design and result in arbitrary shaped MWDs. Here we report a precise design to synthesis protocol for producing a targeted MWD design with a simple to use, and chemistry agnostic computer-controlled tubular flow reactor. To support the development of this protocol, we constructed general reactor design rules by combining fluid mechanical principles, polymerization kinetics, and experiments. The ring opening polymerization of lactide, the anionic polymerization of styrene, and the ring opening metathesis polymerization are used as model polymerizations to develop the reactor design rules and synthesize MWD profiles. The derivation of a mathematical model enables the quantitative prediction of the experimental results, and this model provides a tool to explore the limits of any MWD design protocol.

Continuous flow photoinduced phenothiazine derivatives catalyzed atom transfer radical polymerization

Continuous flow photoinduced organocatalyzed atom transfer radical polymerizations (O-ATRP) are investigated by using phenothiazine derivatives as organic photoredox catalysts. A series of phenothiazine derivatives with different substituents are designed and synthesized. The structure-reactivity relationship is examined in both batch and tubular reactor by employing methyl methacrylate (MMA) and ethyl α-bromophenylacetate (EBP) as the monomer and initiator. By transferring the polymerization from the batch reactor to the tubular reactor, the accelerated apparent polymerization constants, better control of molecular weights and narrower molecular weight distributions are achieved. The effect of the inner diameter of the tubular reactor on O-ATRP is explored and it suggests that 1.5 mm and 2.0 mm are the optimized inner diameter based on the consideration of polymerization controllability. By applying this continuous flow photoinduced O-ATRP protocol, poly(methyl methacrylate) (PMMA) and block copolymers are synthesized with varied molecular weights.

Optimal control of molecular weight and particle size distributions in a batch suspension polymerization reactor

Mechanistic modelling is an engineering approach to simulate reasonable physical and chemical processes to develop a model to describe the behaviour of a system. Mathematical models are commonly adopted to explore the physical limits of a process, and are applied to process development, optimization and control. In this work, the population balance model and the moment technique have been utilized to model a suspension polymerization reactor and predict the dynamic evolution of particle size and molecular weight distributions. These distributions are two important factors that affect the physical, rheological and mechanical properties of a polymer, and its final product quality. The cell average technique has been applied to solve the population balance equation, and demonstrate the model predictive capability by comparing its predictions with those obtained from experimental data published in the literature. In addition, the effects of initiator, chain transfer agent, stabilizer concentrations, temperature, and agitation rate on the final particle size and molecular weight distributions have been investigated. An optimal control strategy has been used to obtain the desired molecular weight distribution by manipulating the initiator concentration, concentration of the chain transfer agent and its addition time, and controlling the reactor temperature. Also, the impeller speed and initial value of the stabilizer have been utilized to achieve the desired final particle size distribution. The simulation results indicate that the control objectives have been achieved, and show that the proposed controllers are robust to a mismatched model.

Preparation of Thermochromic Films from Latexes Made by Miniemulsion Polymerization

AbstractThermosensitive‐thermochromic pigments are classified as smart materials capable of detecting and/or responding to environmental stimuli, and specifically in this study, changes in temperature that induce a change in the color of the material. This study aims to obtain nanoparticles of poly(styrene‐co‐butyl acrylate) and poly(styrene‐co‐methyl methacrylate), containing thermosensitive‐thermochromic pigments that are incorporated into the monomer droplets in miniemulsion polymerization. Miniemulsion polymerization has the advantage that the pigment particles can be dispersed directly in the monomer droplets and are encapsulated when the miniemulsion droplets are polymerized. Using controlled/living radical polymerization (or Reversible Deactivation Radical Polymerization), it is possible to produce polymers with better control of microstructure and narrower molecular weight distributions. Nitroxide‐mediated polymerization (NMP) is conducted using the BlocBuilder initiator, as well as a conventional free radical polymerization (FRP) using potassium persulfate (KPS) and 2,2‐azobis(2‐methylpropionitrile) (AIBN). Stable latexes containing the thermosensitive‐thermochromic pigments are obtained by both NMP and FRP. Films are made from the latexes and shown to exhibit thermochromic behavior.

Partitioning effect of nitrogen catalyst into polymerizing particles on dispersion reversible chain transfer catalyzed polymerization (dispersionRTCP) of methyl methacrylate in supercritical carbon dioxide and organic solvents

Reversible chain transfer catalyzed polymerization (RTCP) in dispersion polymerization system (dispersion RTCP) of methyl methacrylate (MMA) was performed with N-iodosuccimide (NIS) as a nitrogen catalyst in supercritical carbon dioxide (scCO2). The solubility of NIS in scCO2 can be controlled by tuning the pressure, and this led to promote NIS partitioning into polymerizing particles. As a result, the molecular weight distribution control was successfully improved by decreasing the NIS solubility in the medium by tuning the scCO2 at a low pressure of 20 MPa. On the other hand, at the same NIS concentration, a solution RTCP of MMA in toluene as a homogeneous polymerization system did not proceed with a controlled/living manner. The importance of NIS partitioning into the polymerizing particles was also confirmed in hexane as well as scCO2 medium. From these results, it was clarified that the NIS catalyst partitioning into the polymerizing particles as main polymerization loci is a key factor to control the molecular weight distribution in the dispersion RTCP of MMA in scCO2. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 613–620

Perylene as a visible light photoredox catalyst for photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of MMA

The organic photocatalyst, perylene, was used to mediate photoinduced electron transfer (PET) reversible addition-fragmentation chain transfer polymerization (RAFT) of methyl methhacrylate (MMA) under light irradiation in N,N-dimethylformamide (DMF) at 25°C with 4-cyanopentanoic acid dithiobenzoate (CPADB) as chain transfer agent (CTA). Kinetic studies confirmed that the polymerization obeyed the first order kinetic m'odel. The production of PMMAs with a good control of molecular weights (Mn,GPC) and narrow polymer molecular weight distribution (Mw/Mn) were obtained. It is found that well-controlled PET RAFT polymerization of MMA can be manipulated even with the amount of perylene decreasing to ppm level. No polymer was obtained in the absence of light irradiation, implying that the model of PET RAFT polymerization of MMA is an ideal light “on”-“off” switchable system. Furthermore, the speed of PET RAFT polymerization of MMA was also finely tunable by the external light irradiation intensity. The resultant PMMA macro-CTA was characterized by 1H nuclear magnetic resonance spectrum (1H NMR) and gel permeation chromatography (GPC). The accessibility of the high end group fidelity was further demonstrated by chain extension experiments.

Control of molecular weight distribution in synthesis of poly(2-hydroxyethyl methacrylate) using ultrasonic irradiation

Poly(2-hydroxyethyl methacrylate) (PHEMA) was synthesized using ultrasonic irradiation without any chemical initiator. The effect of the ultrasonic power intensity on the time course of the conversion to polymer, the number average molecular weight, and the polydispersity were investigated in order to synthesize a polymer with a low molecular weight distribution (i.e., low polydispersity). The conversion to polymer increased with time. A higher ultrasonic power intensity resulted in a faster reaction rate. The number average molecular weight increased during the early stage of the reaction and then gradually decreased with time. A higher ultrasonic intensity resulted in a faster degradation rate of the polymer. The polydispersity decreased with time. This was because the degradation rate of a polymer with a higher molecular weight was faster than that of a polymer with a lower molecular weight. A polydispersity below 1.3 was obtained under ultrasonic irradiation. By changing the ultrasonic power intensity during the reaction, the number average molecular weight can be controlled while maintaining low polydispersity. When the ultrasonic irradiation was halted, the reactions stopped and the number average molecular weight and polydispersity did not change. On the basis of the experimental results, a kinetic model for synthesis of PHEMA under ultrasonic irradiation was constructed considering both polymerization and polymer degradation. The kinetic model was in good agreement with the experimental results for the time courses of the conversion to polymer, the number average molecular weight, and the polydispersity for various ultrasonic power intensities.

Beyond Dispersity: Deterministic Control of Polymer Molecular Weight Distribution.

The breadth of the molecular weight distributions (MWD) of polymers influences their physical properties; however, no synthetic methods allow precise control of the exact shape and composition of a distribution. We report a modular strategy that enables deterministic control over polymer MWD through temporal regulation of initiation in nitroxide-mediated polymerization reactions. This approach is applicable to any controlled polymerization that uses a discrete initiator, and it allows the use of MWD composition as a parameter to tune material properties.

Organocatalyzed continuous flow ring-opening polymerizations to homo- and block-polylactones

TBD catalyzed continuous flow ring-opening polymerizations of ε-caprolactone and δ-valerolactone were exemplified as the model investigation system of organocatalytic synthesis of polyesters in the simple PTFE tubular microreactor (MR). In contrast to the batch reactor (BR), significant benefits of utilizing continuous flow strategy were achieved including higher level control of molecular weights and molecular weight distributions as well as faster polymerizations (kapp(CL) = 0.00602 (MR) vs 0.00286 min−1 (BR); kapp(VL) = 0.159 (MR) vs 0.079 min−1 (BR)). Furthermore, more easily and efficiently block copolymerizations were conducted in the integrated-microreactor by sequential introduction of monomers to well-defined poly(δ-valerolactone)-block-poly(ε-caprolactone) and poly(ε-caprolactone)-block-poly(δ-valerolactone).

Rapid ambient temperature living radical polymerization of methyl methacrylate and styrene utilizing sodium hypophosphite as reducing agent

ABSTRACTA facile, safe, and inexpensive reducing agent, sodium hypophosphite (NaH2PO2·H2O), has been successfully used to perform ambient temperature living radical polymerizations of methyl methacrylate (MMA) and styrene (St). The rapid radical polymerizations were readily obtained at 25°C, i.e., MMA reached a conversion of ca 90% after 2.5 h, and St reached a conversion of ca 80% after 40 h. The polymerizations of MMA and St exhibited excellent living/controlled nature, as evidenced by pseudo first‐order kinetics of polymerization, linear evolution of molecular weights with increasing monomer conversions, and narrow molecular weight distributions. The various experimental parameters—ligand, solvent, and molar ratio of NaH2PO2·H2O to CuSO4·5H2O—were varied to improve the control of polymerization, molecular weight, and molecular weight distribution. 1H NMR analyses and chain‐extension reactions confirm the high chain‐end functionality of the resultant poly(methyl methacrylate) and polystyrene. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42123.

Predictive PDF control in shaping of molecular weight distribution based on a new modeling algorithm

The aims of this work are to develop an efficient modeling method for establishing dynamic output probability density function (PDF) models using measurement data and to investigate predictive control strategies for controlling the full shape of output PDF rather than the key moments. Using the rational square-root (RSR) B-spline approximation, a new modeling algorithm is proposed in which the actual weights are used instead of the pseudo weights in the weights dynamic model. This replacement can reduce computational load effectively in data-based modeling of a high-dimensional output PDF model. The use of the actual weights in modeling and control has been verified by stability analysis. A predictive PDF model is then constructed, based on which predictive control algorithms are established with the purpose to drive the output PDF towards the desired target PDF over the control process. An analytical solution is obtained for the non-constrained predictive PDF control. For the constrained predictive control, the optimal solution is achieved via solving a constrained nonlinear optimization problem. The integrated method of data-based modeling and predictive PDF control is applied to closed-loop control of molecular weight distribution (MWD) in an exemplar styrene polymerization process, through which the modeling efficiency and the merits of predictive control over standard PDF control are demonstrated and discussed.

Sn(OTf)2 catalyzed continuous flow ring-opening polymerization of ε-caprolactone

A simple PTFE tubular microreactor based platform was successfully developed to conduct Sn(OTf)2 catalyzed ε-caprolactone polymerization with better control of reaction conditions, faster polymerizations and narrower molecular weight distributions.

Synthesis of amphiphilic homopolymers with high chain end functionality by SET–LRP

ABSTRACTSingle electron transfer‐living radical polymerization (SET–LRP) of two amphiphilic acrylates, 2‐methoxyethyl acrylate up to [M]0/[I]0 = 1,000 and di(ethylene glycol) 2‐ethylhexyl ether acrylate up to [M]0/[I]0 = 200, is accomplished with good control of molecular weight and molecular weight distribution in 2,2,2‐trifluoroethanol at 25 °C using hydrazine activated Cu(0) wire as catalyst, methyl 2‐bromopropionate as initiator, and Me6‐TREN as ligand. The chain end functionality of the resulting polymers has been analyzed by MALDI‐TOF spectrometry to demonstrate the synthesis of perfect or near‐perfect chain‐end functional amphiphilic homopolymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 294–303

Photoinduced Electron Transfer–Reversible Addition–Fragmentation Chain Transfer (PET-RAFT) Polymerization of Vinyl Acetate and N-Vinylpyrrolidinone: Kinetic and Oxygen Tolerance Study

Photoinduced electron transfer–reversible addition–fragmentation chain transfer (PET-RAFT) polymerization was employed for the polymerization of unconjugated monomers, including vinyl acetate, vinyl pivalate, N-vinylpyrrolidinone, dimethyl vinylphosphonate, vinyl benzoate, and N-vinylcarbazole, in the presence of low concentration (ppm range) of photoredox catalyst, fac-[Ir(ppy)3], under low energy visible light irradiation. Kinetic studies of vinyl acetate indicated excellent control of molecular weights and molecular weight distributions (Mw/Mn = 1.09–1.2), even with high monomer conversion (>75%), in different catalyst concentrations. High molecular weights of poly(vinyl acetate) (Mn > 100 000 g/mol) and poly(N-vinylpyrrolidinone) (Mn > 40 000 g/mol) with low dispersities (Mw/Mn < 1.25) were obtained in bulk polymerizations. Moreover, the online kinetic study using Fourier transform near-infrared (FTNIR) showed comparable kinetic rates for the polymerizations in the absence and presence of relatively l...