Comb Graft Copolymers Research Articles

Fully biobased thermoplastic elastomers: Synthesis of highly branched star comb poly(β-myrcene)-graft-poly(l-lactide) copolymers with tunable mechanical properties

Biobased thermoplastic elastomers from renewable resources are gaining increasing attention from academia and industry in recent years. Herein, highly branched star comb graft copolymers consisting of star poly(β-myrcene) (SPM) backbone and semicrystalline poly(l-lactide) (PLLA) branches were successfully synthesized. The structure-properties relationships of the resultant graft polymers varied with graft density and branch length were investigated by DSC, WAXD, POM, SAXS, TEM, AFM and stress-strain test. The microphase separated structure and the relative properties of the copolymers were explored. It was found that the macromolecular architectures had a profound influence on the performances of these obtained graft materials. The crystallization ability of PLLA depended on the content of rubbery backbone and the graft density of these graft copolymers. Besides, the graft density and the branch length influence the tensile toughness of these materials. At the identical PM fraction, the elongations at break of the star comb graft copolymers were larger than those of the linear comb analogues.

Synthesis and Characterization of Graft Copolymers Poly(isoprene-g-styrene) of High Molecular Weight by a Combination of Anionic Polymerization and Emulsion Polymerization

In this work, high molecular weight “comb-shaped” graft copolymers, poly(isoprene-g-styrene), with polyisoprene as the backbone and polystyrene as side chains, were synthesized via free radical emulsion polymerization by copolymerization of isoprene with a polystyrene macromonomer synthesized using anionic polymerization. A small amount of toluene was used in order to successfully disperse the macromonomer. Both a redox and thermal initiation system were used in the emulsion polymerization, and the latex particle size and distribution were investigated by dynamic light scattering. The structural characteristics of the macromonomer and comb graft copolymers were investigated through use of size exclusion chromatography, spectroscopy, microscopy, thermal analysis, and rheology. While the macromonomer was successfully copolymerized to obtain the desired multigraft copolymers, small amounts of unreacted macromonomer remained in the products, reflecting its reduced reactivity due to steric effects. Nevertheless, the multigraft copolymers obtained were very high in molecular weight (5–12 × 105 g/mol) and up to 10 branches per chain, on average, could be incorporated. A material incorporating 29 wt % polystyrene exhibits a disordered microphase separated morphology and elastomeric properties. These materials show promise as new, highly tunable, and potentially low cost thermoplastic elastomers.

Concentrated aqueous synthesis of nanoparticles using comb-graft copolymer stabilisers: the effect of stabiliser architecture

Silver nanoparticles have been synthesised at high concentration (>1 mol L−1) in water using a series of comb-graft copolymers. The copolymers were synthesised and then derivatised from methoxypoly(ethylene glycol) acrylate and maleic anhydride. The degree of polymerisation (number of backbone units), the nature of the adsorption group and length (MW) of the steric component were all found to be critical to the stabilisation of the nanoparticles during synthesis. The results demonstrate that a minimum steric length is required to prevent particle aggregation during synthesis. For Ag particles less than 30 nm in diameter, this corresponded to a polyethylene glycol (PEG) chain with a molecular weight of 454 g mol−1. It was shown that stabiliser molecules with a low number of backbone units were readily displaced, whereas stabilisers that possess numerous adsorption groups bind irreversibly to the particle surface. Adsorption groups were modified to test both chemisorption and physisorption functionality. Chemisorbed species were shown to be more effective stabilisers whereby concentrated Ag nanoparticles were synthesised at a smaller particle size. This was attributed to the adsorption strength and greater diffusive capabilities of the molecule.

Revisiting the Synthesis of a Well-Known Comb-Graft Copolymer Stabilizer and Its Application to the Dispersion Polymerization of Poly(methyl methacrylate) in Organic Media

Polymeric stabilizers are an essential ingredient for the dispersion polymerization of poly(methyl methacrylate) (PMMA) in nonpolar media. In this contribution, we focus on the synthesis of an amphipathic copolymer consisting of pendant poly(12-hydroxystearic acid) (PHS) chains grafted to an insoluble PMMA backbone. This type of steric stabilizer is well established and capable of producing spherically shaped, monodisperse PMMA colloids. Unfortunately, the comb-graft copolymer is not available commercially; furthermore, the multistep synthesis of the desired stabilizer has proven challenging to reproduce. We discuss the practical matter of preparing PHS-graft-PMMA, and report specific techniques developed over several years in our lab. Gel permeation chromatography, mass spectroscopy, and end group analysis of the stabilizer and the precursor macromonomer reveal important, previously unreported details about the chemical synthesis. Our protocol is reproducible and resulted in the production of low polydispersity PMMA particles.

Synthesis of well-defined graft co-polymers via coupled living anionic and living ring-opening metathesis polymerisation

The synthesis of polystyrene (PS) macromonomers functionalised with a norbornene (Nbe) unit and their living ring-opening metathesis polymerisation (ROMP) to produce comb graft co-polymers is described. Macromonomers comprising of one PS chain per Nbe unit and two PS chains per Nbe unit have been synthesised with a variety of chain lengths of PS. These macromonomers have been subjected to ROMP initiated with three different catalysts and the effect of catalyst along with the effect of solvent, concentration and time on the extent and rate of macromonomer polymerisation have been studied. Molecular weight analysis of the comb graft co-polymers by triple-detection size-exclusion chromatography (SEC) with light scattering has greatly improved the ease and accuracy of interpretation of results.

Stability and behavior of a comb–graft copolymer stabilizing a thin oil emulsion film

Stability and behavior of a comb–graft copolymer stabilizing a thin oil emulsion film

Stability and behavior of a comb-graft copolymer stabilizing a thin oil emulsion film

Amphiphilic polymers are able to adsorb at liquid/liquid interfaces and provide stability for emulsions. Studies on thin liquid films provide a way to measure forces between two approaching interfaces which are responsible for emulsion and foam stability. This paper begins with a brief review of some of the work which examine the effects of polymeric surfactants on stabilizing thin films. Then, a more detailed look at the effects of a graft–comb copolymer on stabilizing an oil-in-water film is given. The stabilizing polymeric surfactant (“polysoap”) comprised a polydimethylsiloxane backbone with hydrophobic alkyl and hydrophilic ethylene/propylene oxide grafts. Electrical compressive stresses were imposed on the films, and their thicknesses were determined from measurements of capacitance and optical interference. Also, larger compressive stresses were applied in order to rupture the films and observe film breakdown behavior. The films were remarkably thick and compressible compared with films formed from simple surfactant or lipid systems. The film properties were relatively insensitive to the surfactant concentration and moderately sensitive to polymeric surfactant purity. The observed thicknesses are shown not to arise from interfacial electrostatic effects or van der Waals forces but from steric interactions. The observed thicknesses are consistent either with strongly stretched chains adsorbed at the interface or with multichain aggregate structures at the interface. The exact mechanism is still unclear. Copyright © 2001 John Wiley & Sons, Ltd.

Electric-field-induced rupture of polymer-stabilized oil films

Water-in-oil emulsions stabilized by polymeric surfactants are robust, but the reasons for their stability are poorly understood. We studied oil films stabilized by a comb–graft copolymer having a poly(siloxane) backbone and poly(ethylene oxide)/poly (propylene oxide) and C16 grafts (Abil EM-90) with a total number-average molecular weight of 62,000. Electric fields imposed in the aqueous phases on either side of the oil films were used to induce rapid rupture, and the response of the film was monitored using optical interference and electrical conductance measurements. Film thickness values ranged between 30 and 50 nm and rupture at field strength values between 2 × 107 and 5 × 107 V/m. Unexpectedly, in some cases, stable pores were formed and the films became electrically conductive. Often the pores persisted for more than 20 min after the voltage had been removed. Since the current was independent of film area, very few pores are involved in conduction. This behavior is similar to that found in lipid films; however, the persistence time is greater for polymer-stabilized films. Because the films are thick, it is possible that pores are formed by multimolecular self-assembly as with pore-forming proteins. Polymer purification also influenced film stability.

A new theoretical formula for the determination of the copolymer composition distribution measured by gel permeation chromatography

AbstractA new theoretical formula, used for the determination of the chemical composition distribution of copolymers, is proposed in this paper. The composition distribution of styrene in chlorinated butyl rubber/polystyrene comb graft copolymer was obtained by gel permeation chromatography utilising a combination of refractive index and ultraviolet detection. It is a more convenient and time‐saving method for the characterization of the molecular structure parameters of a copolymer compared to the conventional experimental method.

Tailored copolymers via coupled anionic and ring opening metathesis polymerization. Synthesis and polymerization of bicyclo[2.2.1]hept-5-ene-2,3- trans-bis(polystyrylcarboxylate)s

The preparation of polystyrene macromonomers containing a norbornene unit and their living ring opening metathesis polymerization (ROMP) to produce comb graft copolymers is described. The ROMP was initiated by the well defined Schrock initiators, Mo(CHR)(NAr)(OR′) 2, where R is (CH 3) 3C or C 6H 5C(CH 3) 2, Ar is 2,6-diisopropylphenyl and R′ is (CH 3) 3C. Well characterized macromonomers and comb graft copolymers with polystyryl grafts with average degrees of polymerization ( DPs) of 4, 7, and 9 were successfully produced. The graft copolymers exhibit single mode molecular weight distributions and narrow polydispersities. Attempts to prepare copolymers with longer polystyryl grafts gave products which exhibited bimodal molecular weight distributions in which one component of the distribution had the same retention time as that of the macromonomer, this observation is rationalized in terms of steric inhibition of the ROMP of such macromonomers.

Synthesis and Application of Tailored Graft Copolymers from Polystyrene Macromonomer

Abstract Comb graft copolymers prepared by macromonomer technique has become applicable for permanent modification of polymer surfaces. In this paper the association and adsorption behavior in solution of the well designed graft copolymer prepared from polystyrene macromonomer and various hydrophilic comonomer was studied and the mechanism of surface accumulation of hydrophilic segment was clarified by surface analysis of polystyrene containing the graft copolymers. Wetting of modified polymer surfaces and the permeability of gases through the film was also discussed.