Cellulose containing block copolymers

Summary Solution properties of trimethylcellulose-poly(oxytetramethylene two and star block copolymers with defined molecular weights are reported. The solubility behavior of the concerned block copolymers is mainly governed by the solubility of the trimethylcellulose blocks. The solubility parameters for TMC and POTM indicate that both polymers are incompatible with each other. This is confirmed by the appearance of phase separation in concentrated solutions of corresponding blends even in nonselective solvents. Intrinsic viscosities of the block copolymers are reported and compared to corresponding polymer blend solutions.     

Phase separation in polymer blends comprising copolymers: 7. Statistical theory of block copolymer-homopolymer systems

The miscibility of a homopolymer in corresponding domains of a copolymer predicted by Meier's theory is far less than found experimentally. In this paper, a density gradient model is suggested for describing the segment distribution of the bound and free chains in block copolymer-homopolymer systems. Using this model, Helfand's theory, which has been successful in explaining microphase separation of block copolymers, is extended to polymer blends of homopolymer and corresponding block copolymer with lamellar structure. The calculated free energy of mixing of the system shows that the predicted miscibility is much larger than that obtained by Meier's theory and is in good agreement with the main known experimental results. In particular, on the basis of the present theory, homopolymer can be expected to be solubilized by corresponding blocks in the whole composition range provided that the molecular weight of the former is less than that of the latter.     

Blending of polystyrene with styrene-siloxane block and graft copolymers

A preliminary study on the efficiency of styrene-siloxane block and graft copolymer as toughening additives for polystyrene has been made. Block and graft copolymers of required molecular weight were synthesized for making compatible blends with polystyrene. Compatibility of these systems was evaluated through differential scanning calorimetry, thermo-mechanical analysis, rheovibron studies, and scanning electron microscopy. A good miscibility of block and graft copolymers was confirmed by these methods. Higher work of rupture in these blended polystyrene samples further demonstrates the feasibility of styrene-siloxane block and graft copolymers as good toughening material for a brittle polystyrene matrix. The mechanical properties have been related to the morphology and the amount of siloxane content in the blended polystyrene.     

Phase separation in polymer blends comprising copolymers: 5. Polyisoprene/poly(isoprene-g-styrene) copolymer system

As part of a programme of research into miscibility in polymer blends comprising copolymers, this paper presents the morphology of blends of polyisoprene and poly(isoprene-g-styrene) with complicated but well defined structure. The graft copolymers were prepared by polymerization of styrene initiated by metallated polyisoprene backbone and were fully characterized. All the studied blends of copolymers and polyisoprene of different molecular weights exhibit macrophase separation even when the molecular weight of the homo PI is apparently less than that of the PI segments between neighbourning junction points in the copolymers. The results provide support for the argument that the molecular architecture of a copolymer is an important factor governing its miscibility with corresponding homopolymers. Besides, it is observed that the copolymer with higher proportion of polystyrene shows apparent solubilization in polystyrene matrix of high molecular weight and solubilization varies predictably with the addition of low molecular weight polyisoprene.     

Synthesis and characterization of perfectly alternating polycarbonate‐polydimethylsiloxane multiblock copolymers possessing controlled block lengths

An array of perfectly alternating polycarbonate‐polydimethylsiloxane (PC‐PDMS) multiblock copolymers possessing systematic variations in block molecular weights were successfully produced by coupling preformed PC and PDMS telechelic oligomers using hydrosilylation. Based on gel permeation chromatography results, the multiblock copolymers were essentially void of the oligomeric precursors. Despite the relatively large difference in solubility parameter between PC and PDMS, the multiblock copolymers exhibited significant partial miscibility between the two phases. As expected, the degree of partial miscibility was dependent on the molecular weight of the blocks with the extent of partial miscibility increasing with decreasing block molecular weights. Morphological characterization using small angle X‐ray scattering showed that, at a given PC block molecular weight, the uniformity of the two phase morphology increased with increasing PDMS block molecular weight, which is consistent with a decrease in the extent of phase mixing with increasing PDMS block molecular weight. POLYM. ENG. SCI., 54:1648–1663, 2014. © 2013 Society of Plastics Engineers     

Phase separation in polymer blends comprising copolymers: 5.

Star-shaped block copolymers were used as heat activated adhesives in glass to glass joints. The branches consisted in either AB or ABA poly(styrene-b-isoprene) block copolymers. Tensile shear strengths of simple lap joints were measured for star block copolymers differing in the length or in the number of branches. Values higher than those of the corresponding linear species were obtained. These results were related to the presence of chemical junction points created by coupling the linear copolymers.     

Adhesive properties of star-shaped block copolymers

Star-shaped block copolymers were used as heat activated adhesives in glass to glass joints. The branches consisted in either AB or ABA poly(styrene-b-isoprene) block copolymers. Tensile shear strengths of simple lap joints were measured for star block copolymers differing in the length or in the number of branches. Values higher than those of the corresponding linear species were obtained. These results were related to the presence of chemical junction points created by coupling the linear copolymers.     

Effect of multiblock copolymers in polymer blends

The use of multiblock copolymers for the compatibilization of immiscible polymer blends is controversially discussed in the literature. Investigations have been carried out to estimate the effect of multiblock copolymers containing segments of a liquid crystalline polyester (LCP) and polysulfone (PSU) segments in blends of the based homopolymers. One goal was to determine whether multiblock copolymers provide an opportunity for compatibilizing PSU/LCP blends. By using PSU/LCP multiblock copolymers with different molecular weights of the blocks in the appropriate binary, solution-casted blends, it was shown that the interpenetration of the polysulfone phase of the block copolymer and the PSU matrix leads to an improved miscibility of the blend. This effect is retained in ternary blends of PSU, LCP, and the multiblock copolymer, assuming a certain critical molecular weight of the multiblock copolymer segments. In addition, some mechanical characteristics of PSU/LCP melt blends such as the E-modulus and fracture strength are improved by adding long-segmented multiblock copolymers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2293–2309, 1997     

Star-shaped block copolymers. IV. Emulsifying activity in the water–oil emulsions

Water–organic solvents emulsions based on toluene, n hexane, n-dodecane, and decaline are stabilized by new A(B)₂ star-shaped block copolymers. B is a polyoxirane block and A a polydiene or polyvinyl one. The influence of the molecular parameters of the copolymers has been studied; low-molecular-weight (±5000) copolymers containing 50% of polyoxirane have the originality to generate both O/W and W/O stable emulsions. The importance of the molecular architecture of block copolymers on their stabilizing efficiency has been put in evidence. For instance, 7/3 water–toluene emulsions are more efficiently stabilized by star-shaped block copolymers, whereas linear block copolymers give better results for 3/7 water–toluene emulsions.     

Synthesis of amphiphilic triarm star block copolymers

We describe the synthesis and the characterization of amphiphilic triarm star block copolymers based on polystyrene, poly(methyl methacrylate), poly(ε caprolactone), poly(l lactide) and poly(ethylene oxide) blocks. This synthesis has been achieved by a new route consisting in 2 successive initiation steps on a core molecule (a 1,1-diphenyl-ethylene derivative bearing a protected hydroxy function) located at the end of a first block. Some results on adsorption onto TiO₂ and micellization studies are given. Preliminary results on solid state indicate an increase of the miscibility of the different incompatible blocks. Received: 3 November 1997/Revised version: 1 December 1997/Accepted: 2 December 1997     

Properties of block versus random copolymers

Physical and mechanical properties of block copolymers are compared and correlated with the corresponding random copolymers. The important properties of melting point, transition temperatures, tensile strength, modulus, and elastic properties depend upon the structural arrangement of the molecular units comprising the polymer strecture. All available data suggest overwhelmingly that properties of block copolymers are superior to those of random copolymers. A block copolymer can have properties characteristic of each of the homopolymers from which it is derived as well as a set of properties due to the polymer strcture as a whole. Block copolymers have an advantage over random copolymers in that a crystalline polymer can be modified without significant reduction of its melting point, modulus, tensile strength, and elastic properties, and by suitable selection of a second component it affords a means of “building in” a particular property.     

Effect of chain topology on the self-organization and the mechanical properties of poly(n-butyl acrylate)-b-polystyrene block copolymers

A series of well defined ABA, 3-arm star and bottle brush type copolymers, containing soft poly(n-butyl acrylate) (PBA) blocks and hard blocks of polystyrene (PS) were synthesized by atom transfer radical polymerization (ATRP). Small angle X-ray scattering was used to study the phase separation in these systems and dynamic mechanical analysis and tensile tests were performed to characterize their thermo-mechanical properties. The specific molecular architecture has a major effect on the copolymers self-organization and material properties. The linear ABA type copolymers showed micro phase separation and thermoplastic elastomer (TPE) behavior only at very high PS content. The change of molecular architecture from linear to 3-arm star type resulted in an improved phase separation at lower PS content and better thermoplastic elastomer properties. In contrast the specific brush type molecular architecture seems to prevent the micro phase separation of the PBA and PS components, resulting in amorphous bulk material with single glass transition temperature.     

The reinforcement of polystyrene and poly(methyl methacrylate) interfaces using alternating copolymers

Asymmetric double cantilever beam studies are presented that document the ability of alternating copolymers to strengthen a polymer/polymer interface. For polystyrene/poly(methyl methacrylate) interfaces, these results show that the alternating copolymer is the least effective sequence distribution of a linear copolymer at strengthening the polystyrene/poly(methyl methacrylate) interface, where the copolymers that are compared all have similar molecular weight and composition. The results also demonstrate that the effect of copolymer molecular weight on the ability of the copolymer to strengthen an interface is controlled by the balance between the increased entanglements and decreased miscibility of the copolymer with the homopolymers with increasing molecular weight.     

Synthesis of ABC miktoarm star block copolymers from a new heterotrifunctional initiator by combination of ATRP and ROP

We described the obtention of well-defined ABC star block copolymers through the use of a new heterotrifunctional initiator. That way, well-defined PCL-arm–PS-arm–PLLA star block copolymers have been synthesized from a heterotrifunctional initiator bearing two hydroxyl groups able to initiate ROP of CL and LLA (using Sn(Oct)₂ as coinitiator) and a bromide function able to initiate ATRP of styrene.     

Adhesion characteristics of imide-aryl ether ether ketone block copolymers with poly(ether-imide)

Imide-aryl ether ether ketone block copolymers were prepared and the adhesion characteristics with poly(ether-imide) were investigated. The copolymers were prepared via the poly(amic alkyl ester) precursor to the polyimides which is hydrolytically stable and may be isolated and characterized prior to imidization. Solutions of the copolymers were cast and cured to effect the imidization, producing clear tough films which showed two transitions, indicative of a multiphase morphology. Mixtures of the copolymers with poly(ether-imide) also produced clear films, and the shift in the T_g of the aryl ether ether ketone component of the block copolymer indicated miscibility with the poly(ether-imide) within this phase. This miscibility of the poly(ether-imide) with the aryl ether ether ketone component of the block copolymer produced significant improvements in the adhesion of the thermoplastic poly(ether-imide) with the rigid polyimide copolymer.     

Mechanical relaxations of nylon–polyurea block copolymers

Dynamic mechanical analysis from ?150 to +150°C has been carried out on seven block copolymers that were prepared by the in situ anionic polymerization of caprolactam in the presence of a preformed polyurea. The various relaxations have been identified and activation energies calculated. Some polymer–polymer miscibility of the polyurea and amorphous nylon copolymer segments is indicated by the compositional dependence of the α relaxation.     

Synthesis and aggregation behavior of four types of different shaped PCL‐PEG block copolymers

Biodegradable, amphiphilic, linear (diblock and triblock) and star‐shaped (three‐armed and four‐armed) poly[(ethylene glycol)‐block‐(ε‐caprolactone)] copolymers (PEG–PCL copolymers) were synthesized by ring‐opening polymerization of ε‐caprolactone (CL) with stannous octoate as a catalyst, in the presence of monomethoxypoly(ethylene glycol) (MPEG), poly(ethylene glycol) (PEG), three‐armed poly(ethylene glycol) (3‐arm PEG) or four‐armed poly(ethylene glycol) (4‐arm PEG) as an initiator, respectively. The monomer‐to‐initiator ratio was varied to obtain copolymers with various PEG weight fractions in a range 66–86%. The molecular structure and crystallinity of the copolymers, and their aggregation behavior in the aqueous phase, were investigated by employing ¹H‐NMR spectroscopy, gel permeation chromatography and differential scanning calorimetry, as well as utilizing the observational data of gel–sol transitions and aggregates in aqueous solutions. The aggregates of the PEG–PCL block copolymers were prepared by directly dissolving them in water or by employing precipitation/solvent evaporation technique. The enthalpy of fusion (ΔH_m), enthalpy of crystallization (ΔH_crys) and degrees of crystallinity (χ_c) of PEG blocks in copolymers and the copolymer aggregates in aqueous solutions were influenced by their PEG weight fractions and molecular architecture. The gel–sol transition properties of the PEG–PCL block copolymers were related to their concentrations, composition and molecular architecture. Copyright © 2006 Society of Chemical Industry     

Synthesis and characterization of temperature and pH-responsive pentablock copolymers

A family of amphiphilic ABCBA pentablock copolymers based on commercially available Pluronic^® F127 block copolymers and various amine containing methacrylate monomers was synthesized via Cu(I) mediated controlled radical polymerization. The block architecture and chemical composition of the pentablock copolymers were engineered to exhibit both temperature and pH responsive self-assembly by exploiting the lower critical solution temperature of the poly(ethylene oxide)/poly(propylene oxide) blocks and the polycationic property of the poly(amine methacrylate) blocks, respectively. In aqueous solutions, the pentablock copolymers formed temperature and pH-responsive micelles. Concentrated aqueous solutions of the copolymer formed a pH-responsive, thermoreversible gel phase. The controlled radical synthesis route yielded well-defined copolymers with narrow molecular weight distributions with the benefit of mild reaction conditions. Small angle X-ray scattering, laser light scattering, cryogenic transmission electron microscopy and dynamic mechanical analysis have been used to characterize the self-assembled structures of the micellar solution and gel phases of the aqueous copolymer system. These copolymers have potential applications in controlled drug delivery and non-viral gene therapy due to their tunable phase behavior and biocompatibility.     

Miscibility of poly(vinyl acetate) and vinyl acetate-ethylene copolymers with styrene-acrylic acid and acrylate-acrylic acid copolymers

Poly(vinyl acetate) and vinyl acetate-ethylene (VAE) copolymers compose one of the more important polymeric materials, widely employed in coating and adhesive applications. A new class of miscible polymer blends involving poly(vinyl acetate) and VAE with styrene-acrylic acid and acrylate-acrylic acid copolymers has been found. Experimental windows of miscibility as a function of the ethylene content for VAE copolymers and the acrylic acid content of the acrylate-acrylic acid copolymers are observed (acrylate = methyl acrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate). Employing well-established analog heat of mixing measurements, predicted windows of miscibility were compared with experimental results. Fair qualitative agreement was observed and supported the hypothesis that specific rejection arguments can be employed to explain the observed miscibility. Failure to quantitatively predict miscibility based on the analog heat of mixing measurements may be due to the higher association tendencies of the model compounds relative to acrylic acid units in the high molecular weight polymers. No miscible combinations were found for methyl methacrylate-acrylic acid copolymers or acrylate-methacrylic acid copolymers in admixture with poly(vinyl acetate) or the VAE copolymers, thus indicating the sensitivity of phase behavior to minor structural changes. VAE (30 wt % ethylene) copolymers were also noted to be miscible with several polymers previously noted to be miscible with poly(vinyl acetate), namely, poly(vinylidene fluoride), poly(ethylene oxide), and nitrocellulose. © 1995 John Wiley & Sons, Inc.     

Precise preparation of four-arm-poly(ethylene glycol)-block-poly(trimethylene carbonate) star block copolymers via activated monomer mechanism and examination of their solution properties

The polymerization of trimethylene carbonate (TMC) in the presence of HCl·Et₂O via activated monomer mechanism was performed to synthesize 4a-PEG-b-PTMC star block copolymers composed of poly(ethylene glycol) (PEG) and poly(trimethylene carbonate) (PTMC) using four-arm (4a) PEG as an initiator. The TMC conversion and molecular weight of PTMC increased linearly with the polymerization time or the feed ratios of the TMC to 4a-PEG in the presence of HCl·Et₂O in CH₂Cl₂ at 25 °C. The obtained PTMC had molecular weights close to the theoretical value calculated from TMC to PEG molar ratio and exhibited monomodal GPC curve. We prepared successfully 4a-PEG-b-PTMC star block copolymers without metal catalyst at room temperature via living ring-opening polymerization (ROP) of TMC from 4a-PEG as an initiator in the presence of HCl·Et₂O as a monomer activator. The CMCs of the 4a-PEG-b-PTMC star block copolymers determined from fluorescence measurements. The CMCs of the 4a-PEG-b-PTMC star block copolymers decreased in the order of the increase in the PTMC segment. The partition equilibrium constant, K_v, which is an indicator of the hydrophobicity of the micelles of the 4a-PEG-b-PTMC star block copolymers in aqueous media, increased with the increase in the PTMC segment. In conclusion, we confirmed that the 4a-PEG-b-PTMC star block copolymers form micelles and hence may be potential hydrophobic-drug delivery vehicles.