Sequential Copolymerization Research Articles

P(CL-b-LLA) diblock copolymers grafting onto cellulosic nanocrystals

Cellulose nanocrystals (CNCs) have attracted growing interest as a reinforcement agent in polymer matrices thanks to their biodegradability and excellent mechanical properties. However, due to the polar nature and strong interactions among them, CNCs form aggregates which are difficult to disperse in hydrophobic matrices. To improve CNCs’ dispersion in apolar matrices, we have studied modifications via surface grafting with biodegradable polymers. In this work, CNCs were successfully modified with the P(CL-b-LLA) copolymer via a “grafting onto” method. First, the P(CL-b-LLA) copolymers (Mn molecular weight of 6190 and 10,500 Da) were synthesized by sequential copolymerization of e-caprolactone (CL) and l-lactide (LLA) using stannous octoate and 1-butanol as initiator and co-initiator, respectively. Then, the grafted CNCs, P(CL-b-LLA)-g-CNC, were obtained through the functionalization of copolymers with toluene-2,4-diisocyanate and subsequent covalent linkage to CNCs’ surface in dry toluene. Surface grafting was confirmed using Fourier transform infrared, proton nuclear magnetic resonance (1H NMR), transmission electron microscopy (TEM), and thermogravimetry (TGA). TEM and TGA analyses indicated that the surface modification of the CNCs occurred to a greater extent with the use of the lower molecular weight copolymer. The resulting modified nanoparticles can find applications as filler and compatibilizer in the field of bionanocomposite materials.

NMR analysis of compositional heterogeneity in polysaccharides

Abstract Many copolysaccharides are compositionally heterogeneous, and the composition determined by the usual analytical or spectroscopic methods provides only an average value. For some polysaccharides, the NMR data contain copolymer sequence information, such as diad, triad, and tetrad sequence intensities. In such cases, it is possible to estimate the extent of compositional heterogeneity through NMR. Two general types of methodologies can be used: perturbed Markovian and discrete component approaches. The theoretical bases for these approaches are reviewed in this work, and three examples are shown of the application of these NMR methodologies to copolysaccharides.

Synthesis of polycaprolactone-polyimide-polycaprolactone triblock copolymers via a 2-step sequential copolymerization and their application as carbon nanotube dispersants

Triblock copolymers of polycaprolactone-polyimide-polycaprolactone (PCL-PI-PCL) were synthesized via polycondensation followed by ring-opening polymerization and used as single-walled carbon nanotubes (SWNTs) dispersants.

Kinetics and thermodynamics of living copolymerization processes.

Theoretical advances are reported on the kinetics and thermodynamics of free and template-directed living copolymerizations. Until recently, the kinetic theory of these processes had only been established in the fully irreversible regime, in which the attachment rates are only considered. However, the entropy production is infinite in this regime and the approach to thermodynamic equilibrium cannot be investigated. For this purpose, the detachment rates should also be included. Inspite of this complication, the kinetics can be exactly solved in the regimes of steady growth and depolymerization. In this way, analytical expressions are obtained for the mean growth velocity, the statistical properties of the copolymer sequences, as well as the thermodynamic entropy production. The results apply to DNA replication, transcription and translation, allowing us to understand important aspects of molecular evolution.This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'.

Terpolymer Micelles for the Delivery of Arsenic to Breast Cancer Cells: The Effect of Chain Sequence on Polymeric Micellar Characteristics and Cancer Cell Uptake.

In this study, we developed a micellar platform composed of terpolymers for the encapsulation of inorganic arsenite or arsenous acid (AsIII). For this purpose, a series of terpolymers composed of poly(ethylene oxide) (PEO, block A), poly(α-carboxylate-ε-carprolactone) (PCCL, block B), and poly(ε-caprolactone) (PCL, block C) with either a blocked, i.e., BC or CB, or random, i.e., (B/C)ran block copolymer sequence in the polyester segment was synthesized. The COOH groups on block B were further modified with mercaptohexylamine for AsIII encapsulation. We then investigated how sequence of terpolymers can affect the stability and surface charge of micelles as well as the cellular uptake of their cargo, i.e., AsIII, by MDA-MB-435 cancer cells. 1H NMR spectroscopy in D2O and CDCl3 was also used to study the structure of different terpolymer micelles. Our results showed micelles with ABC sequence to have better stability over those of ACB and A(B/C)ran as reflected by a lower critical micellar concentration. The AsIII-loaded ABC micelles were less negatively charged on the surface than the other two types of terpolymer micelles. In line with this observation, ABC micelles showed a substantially enhanced uptake of AsIII by MDA-MB-435 cancer cells. Stability and surface charge are key parameters that can influence the performance of polymeric micelles as nanodrug carriers. Based on these results, we suggest ABC micelles to have improved characteristics for AsIII delivery compared to ACB and A(B/C)ran micelles.

Critical adsorption of copolymer tethered on selective surfaces.

Critical adsorption behaviors of flexible copolymer chains tethered to a flat homogeneous surface are studied by using Monte Carlo simulations. We have compared the critical adsorption temperature Tc, estimated by a finite-size scaling method, for different AB copolymer sequences with A the attractive monomer and B the inert monomer. We find that Tc increases with an increase in the fraction of monomers A, fA, in copolymers, and it increases with an increase in the length of block A for the same fA. In particular, Tc of copolymer (AnBn)r can be expressed as a function of the block length, n, and Tc of copolymer (AnB)r and (ABm)r can be expressed as a linear function of fA. Tc of random copolymer chains also can be expressed as a linear function of fA and it can be estimated by using weight-average of Tc of different diblocks in the random copolymer. However, the crossover exponent is roughly independent of AB sequence distributions either for block copolymers or for random copolymers.

Effect of molecular architecture and chemical structure on solid-state and barrier properties of heteroatom-containing aliphatic polyesters

A class of multiblock fully-aliphatic copolyesters containing thio-ether linkages has been synthesized by reactive blending.Solid-state properties have been correlated to the chemical structure and the molecular architecture. With the aim of employing these polymers for food packaging, the permeability behavior to CO2 and O2 gas has been analysed.The decrease of the degree of crystallinity, due to the copolymerization, together with the flexibility given by the thio-ether containing sequences, deeply influenced the behavior of the copolymers. The length of the copolymer sequences played the major role in tailoring the polymer characteristics. A decrease in the block length caused a decrease in the crystallinity degree and in the flexibility effect.Finally, the copolyesters here presented have been compared to ether-oxygen containing samples of comparable molecular architecture, to evaluate the effect of the different heteroatom on the polymer properties.

Instantaneous Directional Growth of Block Copolymer Nanowires During Heterogeneous Radical Polymerization (HRP)

Polymeric nanowires that consist of ultrahigh molecular weight block copolymers were instantaneously prepared via one-step surfactant-free heterogeneous radical polymerization (HRP). Under heterogeneous reaction and initiator-starvation conditions, the sequential copolymerization of hydrophilic and hydrophobic monomers facilitates the formation of amphiphilic ultrahigh molecular weight block copolymers, which instantaneously assemble to polymeric nanowires. As polymerization progresses, initially formed nanoparticles exhibit the directional growth due to localized repulsive forces of hydrophilic blocks and confinement of the hydrophobic blocks that adopt favorable high aspect ratio nanowire morphologies. Using one-step synthetic approach that requires only four ingredients (water as a solvent, two polymerizable monomers (one hydrophilic and one hydrophobic), and water-soluble initiator), block copolymer nanowires ∼70 nm in diameter and hundreds of microns in length are instantaneously grown. For example, when 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and styrene (St) were copolymerized, high aspect ratio nanowires consist of ultrahigh (>10(6) g/mol) molecular weight pDMAEMA-b-St block copolymers and the presence of temperature responsive pDMAEMA blocks facilitates nanowire diameter changes as a function of temperature. These morphologies may serve as structural components of the higher order biological constructs at micro and larger length scales, ranging from single strand nanowires to engineered biomolecular networks capable of responding to diverse and transient environmental signals, and capable of dimensional changes triggered by external stimuli.

Living Anionic Polymerization of N-(1-Adamantyl)-N-4-vinylbenzylideneamine and N-(2-Adamantyl)-N-4-vinylbenzylideneamine: Effects of Adamantyl Groups on Polymerization Behaviors and Thermal Properties

The anionic polymerization of N-(1-adamantyl)-N-4-vinylbenzylideneamine (1) and N-(2-adamantyl)-N-4-vinylbenzylideneamine (2) was performed using various initiators, such as oligo(α-methylstyryl)dipotassium, potassium naphthalenide, diphenylmethylpotassium, and diphenylmethyllithium, in THF at −78 °C for 1 h to investigate the effects of adamantyl groups on the polymerization behaviors and thermal properties of the resulting polymers. The well-defined poly(1) and poly(2) with predictable molecular weights and narrow molecular weight distributions were successfully obtained, indicating that the bulky adamantyl groups effectively protected the carbon–nitrogen double bond (C═N) from the nucleophilic attack of the initiators and the propagating chain ends. The stability of the propagating chain end of poly(1) was confirmed by the quantitative efficiencies in the postpolymerization and the sequential copolymerization with tert-butyl methacrylate. A poly(4-formylstyrene) was quantitatively formed by the acidic ...

Thermodynamics of information processing at the molecular scale

The thermodynamics of copolymerization processes leading to the formation and replication of copolymers is presented. Copolymers are natural one-dimensional supports of information, which may be coded in the sequence of monomeric units randomly attached or detached during their synthesis. Multivariate fluctuation relations are here established for copolymerization processes synthesizing Bernoulli and first-order Markov chains. Thereof, the thermodynamic entropy production is deduced and shown to depend on quantities characterizing information possibly stored in the copolymer sequence.

Immiscible polydiene blocks in linear copolymer and terpolymer sequences

ABSTRACTSynthesis, molecular, and morphological characterization of two linear diblock copolymers consisting of two polydienes with specific geometric isomerisms and two triblock terpolymers with a combination of the same polydienes with polystyrene are investigated for both lower and very high molecular weights. This work is inspired from a previous research study which demonstrated that linear ABC terpolymers consisting of polystyrene, poly(butadiene), and poly(isoprene), with specific geometric isomerisms for the polydienes, lead to 3‐phase microphase separated systems. We report also the coexistence of the core‐shell double gyroid and the 3‐phase 4‐layer alternating lamellae morphologies with the majority fraction being the lamellar structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1238–1246

Polypeptide-b-Poly(Phenyl Isocyanide) Hybrid Rod-Rod Copolymers: One-Pot Synthesis, Self-Assembly, and Cell Imaging.

Hybrid rod-rod diblock copolymers, poly(γ-benzyl L-glutamate)-poly(4-cyano-benzoic acid 2-isopropyl-5-methyl-cyclohexyl ester) (PBLG-PPI), with determined chirality are facilely synthesized through sequential copolymerization of γ-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) and phenyl isocyanide monomers bearing chiral menthyl pendants using a Ni(cod)(bpy) complex as the catalyst in one-pot. Circular dichroism and absorption spectra reveal that each block of the block copolymers possesses a stable helical conformation with controlled helicity in solution due to the induction of chiral pendants. The two diastereomeric polymers self-assemble into helical nanofibrils with opposite handedness due to the different chiral induction of the L- and D-menthyl pendants, confirmed by transmission electron microscopy (TEM). Deprotection of the benzyl groups of the PBLG segment affords biocompatible amphiphilic diblock copolymers, poly(L-glutamic acid)-poly(4-cyano-benzoic acid 2-isopropyl-5-methyl-cyclohexyl ester) (PLGA-PPI), that can self-assemble into well-defined micelles by cosolvent induced aggregation. Very interestingly, a chiral rhodamine chromophores RhB(D) can be selectively encapsulated into the chiral polymeric micelles, which is efficiently internalized into living cells when directly monitored with a confocal microscope. This contribution will be useful for developing novel rod-rod biocompatible hybrid block copolymers with a controlled helicity, and may also provide unique chiral materials for potential bio-medical applications.

Controlling effective interactions and spatial dispersion of nanoparticles in multiblock copolymer melts

ABSTRACTThe microscopic Polymer Reference Interaction Site Model theory is employed to study, for the first time, the effective interactions, spatial organization, and miscibility of dilute spherical nanoparticles in non‐microphase separating, chemically heterogeneous, compositionally symmetric AB multiblock copolymer melts of varying monomer sequence or architecture. The dependence of nanoparticle wettability on copolymer sequence and chemistry results in interparticle potentials‐of‐mean force that are qualitatively different from homopolymers. An important prediction is the ability to improve nanoparticle dispersion via judicious choice of block length and monomer adsorption‐strengths which control both local surface segregation and chain connectivity induced packing constraints and frustration. The degree of dispersion also depends strongly on nanoparticle diameter relative to the block contour length. Small particles in copolymers with longer block lengths experience a more homopolymer‐like environment which renders them relatively insensitive to copolymer chemical heterogeneity and hinders dispersion. Larger particles (sufficiently larger than the monomer diameter) in copolymers of relatively short block lengths provide better dispersion than either a homopolymer or random copolymer. The theory also predicts a novel widening of the miscibility window for large particles upon increasing the overall molecular weight of copolymers composed of relatively long blocks. The influence of a positive chi‐parameter in the pure copolymer melt is briefly studied. Quantitative application to fullerenes in specific copolymers of experimental interest is performed, and miscibility predictions are made. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1098–1111

A general theory of kinetics and thermodynamics of steady-state copolymerization

Kinetics of steady-state copolymerization has been investigated since the 1940s. Irreversible terminal and penultimate models were successfully applied to a number of comonomer systems, but failed for systems where depropagation is significant. Although a general mathematical treatment of the terminal model with depropagation was established in the 1980s, a penultimate model and higher-order terminal models with depropagation have not been systematically studied, since depropagation leads to hierarchically-coupled and unclosed kinetic equations which are hard to solve analytically. In this work, we propose a truncation method to solve the steady-state kinetic equations of any-order terminal models with depropagation in a unified way, by reducing them into closed steady-state equations which give the exact solution of the original kinetic equations. Based on the steady-state equations, we also derive a general thermodynamic equality in which the Shannon entropy of the copolymer sequence is explicitly introduced as part of the free energy dissipation of the whole copolymerization system.

Force–velocity relation for copolymerization processes

A study is reported of copolymerization processes subjected to an external force in the light of recent advances on the kinetics and thermodynamics of copolymer growth. Different processes are considered: the free copolymerization of Bernoulli and first-order Markov chains and copolymerization with a template. For every process, the dependence on the force is analyzed for the elongation rate, the growth velocity, the disorder in the copolymer sequence, the thermodynamic entropy production, as well as related quantities. It is shown that disorder in the copolymer sequence can generate forces of entropic origin. They are characterized by the value of their stall force in the force–velocity relation of the corresponding process.

Living Anionic Polymerization of Benzofulvene in Hydrocarbon Solvent

SummaryAnionic polymerization of benzofulvene (BF) quantitatively proceeded with sec‐BuLi in benzene at 0∼55 °C. The resulting poly(BF) s possessed predicted molecular weights based on the molar ratios between monomer and initiator and narrow molecular weight distributions (Mw/Mn < 1.1). The result of postpolymerization demonstrated that the propagating chain end anion of poly(BF) was stable in benzene at 0 °C for at least 1 h. Anionic sequential copolymerization of isoprene and BF was also performed in benzene to afford a well‐defined polyisoprene‐b‐poly(BF) in quantitative yield. The 13C NMR analysis revealed that the poly(BF) obtained with sec‐BuLi in benzene at 0 °C possessed 76% of the 1,4‐structure and 24% of the 1,2‐structure.

ChemInform Abstract: Reading Polymers: Sequencing of Natural and Synthetic Macromolecules

AbstractReview: [81 refs.

Monomer Sequence Control via Living Anionic Copolymerization: Synthesis of Alternating, Statistical, and Telechelic Copolymers and Sequence Analysis by MALDI ToF Mass Spectrometry

Diphenylethylene (DPE) is a monomer which has attracted significant interest from both academia and industry. DPE can undergo (co)polymerization by living anionic polymerization but is incapable of forming a homopolymer due to steric hindrance. Herein the copolymerization of DPE and 1,1-bis(4-tert-butyldimethylsiloxyphenyl)ethylene (DPE-OSi) with styrene or butadiene is described in order to produce (functional) copolymers with controlled comonomer sequences—either alternating or telechelic. The copolymer sequences are inherently controlled by relative reactivity ratios, which in turn can be tuned by both monomer structure and the polarity of the polymerization solvent. The compositions of the copolymers prepared in this study were analyzed by 1H NMR spectroscopy and MALDI ToF mass spectrometry, the latter offering a unique opportunity to demonstrate perfect alternating sequences and insight into other sequences such as telechelic polymers.

Nanoporous hypercrosslinked polymers containing Tg enhancing comonomers

Hypercrosslinked polymers containing functionalized alternating copolymer sequences of substituted stilbene or styrene and N-aryl substituted maleimides have been synthesized. Alternating copolymers containing these comonomers possess semi-rigid structures, and incorporation of these units into the precursor polymer particles for hypercrosslinking leads to a systematic increase in Tg and chain stiffness of these materials as the concentration of the comonomers is increased. Surface area and porosity of the subsequent hypercrosslinked polymers were investigated using nitrogen adsorption/desorption isotherms at 77 K. These hypercrosslinked polymers exhibit BET surface areas ranging from 1058 m2/g at 25 mol% alternating copolymer incorporation down to loss of measurable surface area at ca. 60% incorporation. The experimental surface area results correlate with predictions from simulations and serve as model systems for future studies on specifically functionalized hypercrosslinked polymer particles.

Sequential amphiphilic and pH responsive hyperbranched copolymer: influence of hyper branching/pendant groups on reversible self assembling from polymersomes to aggregates and usefulness in waste water treatment

Hyperbranched copolymers self assembled from polymersomes to aggregates and encapsulated both hydrophilic/hydrophobic molecules but with varied retention proficiency depending upon the medium pH.