Linear Random Copolymers Research Articles

Metal-Catalyzed Simultaneous Chain- and Step-Growth Radical Polymerization: Marriage of Vinyl Polymers and Polyesters

All polymerization reactions are categorized into two large different families, chain- and step-growth polymerizations, which are typically incompatible. Here, we report the simultaneous chain- and step-growth polymerization via the metal-catalyzed radical copolymerization of conjugated vinyl monomers and designed monomers possessing unconjugated C horizontal lineC and active C-Cl bonds. Especially, almost ideal linear random copolymers containing both vinyl polymer and polyester units in a single polymer chain were formed by the CuCl/1,1,4,7,10,10-hexamethyltriethylenetetramine- or RuCp*Cl(PPh(3))(2)-catalyzed copolymerization of methyl acrylate (MA) for the chain-growth polymerization and 3-butenyl 2-chloropropionate (1) for the step-growth polymerization. In contrast, other transition metal catalysts, such as CuCl with tris[2-(dimethylamino)ethyl]amine or N,N,N',N'',N''-pentamethyldiethylenetriamine and FeCl(2)/PnBu(3), resulted in branched structures via the concomitant chain-growth copolymerization of 1 with MA. The polymerization mechanism was studied in detail by NMR and MALDI-TOF-MS analyses of the polymerizations as well as the model reactions. Furthermore, a series of copolymers changing from random to multiblock polymer structures were obtained by varying the feed ratios of the two monomers. These copolymers can be easily degraded into lower molecular weight oligomers or polymers via methanolysis of the ester-linkages in the main chain using sodium carbonate.

Static partial scattering functions for linear and ring random copolymers

The static partial scattering functions for linear and ring random copolymers of type A–B are investigated. In the case of random distribution of the different kinds of monomers, analytic forms can be derived. Monte Carlo simulations are used to make evaluations on biased distributions of the different kinds of monomers. Results clearly show that the number, fraction and distribution of monomers have significant effect on the scattering intensities at Q × Rg>1, where Q is the magnitude of the scattering vector and Rg is the radius of gyration of the polymer. The scattering function in molten state is also calculated on the basis of random phase approximation.

Macromolecular brushes synthesized by “grafting from” approach based on “click chemistry” and RAFT polymerization

AbstractWell‐defined macromolecular brushes with poly(N‐isopropyl acrylamide) (PNIPAM) side chains on random copolymer backbones were synthesized by “grafting from” approach based on click chemistry and reversible addition‐fragmentation chain transfer (RAFT) polymerization. To prepare macromolecular brushes, two linear random copolymers of 2‐(trimethylsilyloxy)ethyl methacrylate (HEMA‐TMS) and methyl methacrylate (MMA) (poly(MMA‐co‐HEMA‐TMS)) were synthesized by atom transfer radical polymerization and were subsequently derivated to azide‐containing polymers. Novel alkyne‐terminated RAFT chain transfer agent (CTA) was grafted to polymer backbones by copper‐catalyzed 1,3‐dipolar cycloaddition (azide‐alkyne click chemistry), and macro‐RAFT CTAs were obtained. PNIPAM side chains were prepared by RAFT polymerization. The macromolecular brushes have well‐defined structures, controlled molecular weights, and molecular weight distributions (Mw/Mn ≦ 1.23). The RAFT polymerization of NIPAM exhibited pseudo‐first‐order kinetics and a linear molecular weight dependence on monomer conversion, and no detectable termination was observed in the polymerization. The macromolecular brushes can self‐assemble into micelles in aqueous solution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 443–453, 2010

Photochromic Polymer Conjugates: The Importance of Macromolecular Architecture in Controlling Switching Speed within a Polymer Matrix

Naphthopyran−poly(n-butyl acrylate) conjugates with different geometries were assembled using ATRP. First, within a rigid lens matrix, an investigation of the photochromic behavior of various poly(n-butyl acrylate), p(n-BA), homopolymers showed that midplacement of a single dye moiety, made possible using a Y-branching difunctional photochromic initiator, gave superior fade kinetics per chain length of conjugated polymer compared to end-functionalized homopolymers. Furthermore, having the dye pendant from the chain opposed to directly within the chain was also found to be advantageous. Fading kinetics became faster when chain length was increased, except in the case of linear random copolymers made by copolymerization of n-butyl acrylate with a naphthopyran acrylate. A gradient copolymer made with a nonphotochromic difunctional initiator and a naphthopyran methacrylate displayed superior kinetics. Films consisting of ABA triblock copolymers, incorporating the photochromic in the middle of a soft p(n-BA) section, gave slower switching speeds compared to lens samples, with responses that were highly tunable and dependent on the amount of soft section inhabited by the photochromic moiety.

Random and Graft Cationic Polyacrylamide Microgel Flocculants

Graft and random microgel copolymeric flocculants of quaternary salt of N,N-dimethylaminoethylacrylate methyl chloride (DMAEA.MCQ) and acrylamide (AM) were synthesized via a free radical mechanism using the γ-radiation technique, and their performance was evaluated on a model dilute titanium dioxide (TiO2) colloid suspension. The time required to form graft and random microgel copolymers increased with increasing DMAEA.MCQ content in the copolymer, indicating the formation of graft copolymers and the crosslinking of linear random copolymers to form microgels (or soft gels). Both graft and random microgel copolymers showed improved reduction in the relative turbidity of the colloid suspension over their nonirradiated counterparts.

Influence of Progressive Cross-Linking on Dewetting of Polystyrene Thin Films

We present dewetting experiments on thin polymer films as a function of cross-linking density. Covalent cross-links were obtained in the glassy state on the basis of azide photochemistry of linear random copolymers of styrene and p-(azidomethyl)styrene, i.e., 106 and 2500 kg/mol with 7% and 1% azide functionality among the polymer backbone, respectively. Upon ultraviolet radiation, azides generate highly unstable nitrene radicals which react with the surrounding polymer backbone, yielding covalent cross-links. We determined the probability for film rupture, defined by the number of holes formed per unit area, and the relaxation time (tauw) of residual stresses which resulted from the film preparation process. For the lower molar mass polymer studied and for azide conversion rates lower than 60%, only partial cross-linking occurred. The effective molar mass of the polymer increased, and consequently, an increase in tauw was observed. The increase in tauw was accompanied by a decrease in hole density, indicating that the still present residual stresses in the films were not able anymore to rupture the films at the high probability of un-cross-linked polymers. For high conversion (>60%), cross-linking was significant enough to lead to the formation of a three-dimensional rubbery network which, in turn, generated an elastic force that counteracted the driving forces. This elastic force eventually inhibited dewetting and the relaxation of residual stresses. Thus, at high conversions, the relaxation time tauw grew exponentially and the number of holes tended toward zero. For the higher molar mass polymer, no changes in the relaxation time tauw were observed for low conversion (<30%). However, at a higher conversion rate, tauw increased drastically, suggesting an almost infinitely long relaxation time at 100% conversion. Consequently, to successfully stabilize thin polymer films by cross-linking, it is preferable to use long polymer chains.

Synthesis of star-like random copolymers from resorcinarene-based octa-functional alkoxyamine initiatorvia nitroxide mediated free radical polymerization

An octa-functional alkoxyamine initiator, with the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) free radical, was synthesized based on resorcinarene, with its efficiency to initiate the nitroxide-mediated free radical copolymerization of styrene and methyl methacrylate (MMA) described. A difunctional analogue of this initiator was also synthesized, using resorcinol as the core molecule. The structures of the resulting initiators were confirmed by homolysis studies based on electron spin resonance spectroscopy and molecular modeling. The polymerization behavior and characteristics of the polymers obtained using these two initiators were also compared. Well-defined star-shaped and linear random copolymers, with low polydispersities and controlled molecular weights, were prepared. The efficiencies of these initiators towards copolymerization, as well as the parameters permitting the formation of well-defined polymers, were also investigated. The reactivity ratios werer a = 0.42 (a = styrene) andr b = 0.33 (b = MMA) for the octa-functional initiator system andr a = 0.45 andr b = 0.39 for the difunctional initiator system.

Properties of polypropylene and metallocene-prepared polyethylene blends: Crystallization behavior and interaction parameter

Blends of metallocene linear low-density polyethylene (m-LLDPE) and polypropylene random copolymer (PP) with three different weight ratios of 10/90, 30/70 and 50/50 m-LLDPE/PP were prepared using a twin screw extruder. The crystallization kinetics and spherulite growth rate of the parent polymers and their blends were then studied by using a differential scanning calorimeter (DSC) and a polarized optical microscope, respectively. The temperatures were high enough to allow only PP to crystallize. The equilibrium melting point and fold surface free energy of PP lamella decreased with increasing the m-LLDPE content in the blend, suggesting that there was a limited miscibility between the components. The negative value determined for interaction parameter was also in agreement with this finding.

Influence of Regulator, Temperature and Monomer Proportion on the Microstructure and Sequence Distribution of Random Isoprene-Styrene Copolymer

The linear random isoprene-styrene copolymer (L-SIR) was prepared by solution polymerization with cyclohexane—n-hexane mixture as solvent and n-BuLi as initiator in the presence of the polar regulator—tetrahydrofuran (THF). Microstructures of L-SIR have been studied by 1H-NMR.

Phase separation in polypropylene and metallocene polyethylene blends

Blends of a metallocene linear low density polyethylene (m-LLDPE) and polypropylene random copolymer (PP) have been prepared using a twin screw extruder and characterized by thermal analysis, mechanical properties, and wide angle X-ray scattering to determine their degree of compatibility. The blends were either directly quenched in water from the melt- or slow-cooled to room temperature. In both cases, the two components formed separate phases and crystallized independently. The slow-cooled specimens had higher yield stress, tensile modulus, and lower elongation at break consistent with higher degree of crystallinity. The elongation to break also varied with composition reaching a minimum at 50% consistent with the incompatible nature of the blends. Crystallization kinetics and melting studies confirm that the two components formed separate phases and crystallized independently. POLYM. ENG. SCI., 46:889–895, 2006. © 2006 Society of Plastics Engineers

Ideal tetrafunctional amphiphilic PEG/PDMS conetworks by a dual‐purpose extender/crosslinker. I. Synthesis

AbstractThe synthesis of a new type of amphiphilic conetwork (APCN) consisting of well‐defined hydrophilic poly(ethylene glycol) (PEG) and hydrophobic polydimethylsiloxane (PDMS) segments is described. The conetwork is ideal (the lengths of each PEG and PDMS chain segments, respectively, are identical) and tetrafunctional (exactly four chains emanate from each crosslink site). The synthesis of the conetworks was achieved by the use of a novel dual‐purpose extender/crosslinker Y (bis [(dimethylsilyl)oxy]‐[(etoxydimethylsilyl)oxy]phenylsilane, (SiPh(SiH)2OEt)), in two steps: (1) Synthesis of a new linear random multiblock copolymer (MBC) (AY)n(BY)m, where A is the hydrophilic PEG and B is the hydrophobic segment, and (2) Crosslinking the multiblocks by catalytic condensation of the SiOEt groups in the Y units. The extender/crosslinker fulfills two totally different functions: First, it extends two incompatible hydrophilic and hydrophobic prepolymers (PEG and PDMS) to a random MBC, and, subsequently, it cross‐links the multiblocks to the target APCN. The synthesis and characterization of the extender/crosslinker is also presented. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4953–4964, 2005

Synthesis and flocculation performance of graft copolymer of N -vinylformamide and poly(dimethylaminoethyl methacrylate) methyl chloride macromonomer

A comb-structured polymeric flocculant was synthesized by the aqueous copolymerization of N-vinylformamide (NVF) with poly(dimethylaminoethyl methacrylate) quats (methyl chloride) macromonomer. The effects of temperature and macromonomer concentration on the copolymerization kinetics were determined experimentally. The copolymerization reactivity ratio was measured to be 3.82 and 6.39 for NVF and macromonomers with 50 and 100 repeating units when copolymerized with NVF. The copolymer samples were also subjected to a flocculation performance test and were found to be more effective than linear random cationic copolymers in terms of cationic content, flocculation rate, final turbidity levels, and floc strength.

Microphase segregation in molten randomly grafted copolymers

We study microphase ordering of molten randomly grafted copolymers (RGCs) by using a mean field theory and the replica method to calculate the quenched average. Our results illustrate that in the weak segregation limit (WSI), the optimal wave vector q* of the lamellar phase formed by molten RGCs, has a temperature dependence different from either linear random copolymers (LRCs) or diblock copolymers (DCPs): when close, but below the microphase separation transition (MST) temperature, q* increases sharply with decreasing temperature; then q* gradually acquires an asymptotic value determined by the length of the branch and the average distance between branch points on the backbone. Our results are compared with recent experiments, and the effects of chain architecture on the microphase separation characteristics of RGCs are delineated. Our results suggest a new method for controlling the microphase spacing by exploiting quenched disorder.

Rapid process for purification of an extracellular β-xylosidase by aqueous two-phase extraction

A rapid process for purification of an extracellular β-xylosidase with high purity was developed. The manipulation involved the precipitation of protein from culture medium and the extraction of enzyme from the resuspended crude protein solution by an aqueous-two phase separation. A linear random copolymer, PE62, with 20% ethylene oxide and 80% propylene oxide was employed in both stages of the purification. The enzyme was precipitated effectively by using 10% (w/v) PE62 and 5% (w/v) Na 2HPO 4. The aqueous two-phase extraction was performed with PE62 (10%)–NaH 2PO 4 (15%) as phase-forming reagent. SDS–PAGE analysis revealed that the purified enzyme is near homogeneity. The yield is about 100% with a purification factor of 8.8-fold. The whole process can be completed within an hour without any column chromatography.

Theoretical study of polymeric mixtures with different sequence statistics. I. Ising class: Linear random copolymers with different statistical sequences and ternary blends of linear random copolymers with homopolymers

We derive a Landau free energy functional for polymeric mixtures containing components with different sequence statistics. We then apply this general field theory to two mixtures that belong to the Ising universality class: mixtures of two different linear random copolymers, and ternary systems of linear random copolymers and two homopolymers. We discuss the instability conditions for the homogeneous state of these mixtures, and calculate the structure factors for different components in the homogeneous state. The structure factors show interesting features which can directly be compared with scattering experiments carried out with selectively deuterated samples. We also work out the eigenmodes representing the least stable concentration fluctuations for these mixtures. The nature of these concentration fluctuations provides information regarding the ordered phases and the kinetic pathways that lead to them. We find various demixing modes for different characteristics of the two mixtures (e.g., average compositions, statistical correlation lengths, and volume fractions).

Theoretical study of polymeric mixtures with different sequence statistics. II. Brazovskii class: Linear random copolymers with diblock copolymers

We use a Landau theory to study the instability of the homogeneous state of a mixture of linear random copolymers and diblock copolymers. Interesting features of the calculated structure factors for different components of the mixture are found, which can be directly compared with scattering experiments with selectively deuterated samples. We also investigate the least stable concentration fluctuations and find four different types of segregation modes at the spinodal depending upon the characteristics of the mixture (e.g., average compositions, statistical correlation lengths and volume fractions). The different segregation modes are also indicative of the kinetic pathways leading to the formation of ordered microstructures. Experiments probing these pathways are suggested.

Entropically driven phase separation of highly branched/linear polyolefin blends

Small-angle neutron scattering (SANS) was used to examine the melt phase behavior of a heavily branched comb PEE polymer blended separately with two linear PEE copolymers. In this case, PEE refers to poly(ethylene-r-ethylethylene) with 10% ethylene units; therefore, the molecular architecture was the only difference between the two components of the blends. The molecular weights of the two linear random copolymers were 60 and 220 kg/mol, respectively. The comb polymer contained an average of 54 long branches, with a molecular weight of 13.7 kg/mol, attached to a backbone with a molecular weight of 10 kg/mol. Three different volume compositions (25/75, 50/50, and 75/25) were investigated for both types of blends. SANS results indicate that all the blends containing the lower molecular weight linear polymer formed single-phase mixtures, whereas all the blends containing the high molecular weight linear polymer phase-separated. These results are discussed in the context of current theories for polymer blend miscibility. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2965–2975, 2000

Synthesis and flocculation performance of graft and random copolymer microgels of acrylamide and diallyldimethylammonium chloride

Graft (from linear homopolymers) and random (from a linear random copolymer) copolymer microgels of diallyldimethylammonium chloride (DADMAC) and acrylamide were synthesized via a free-radical mechanism using a γ-radiation technique. These copolymer microgels were evaluated as flocculants on a model dilute TiO2 colloid suspension using a turbidimeter and a disc centrifuge photosedimentometer, and their performances were compared with the linear homopolymers and their blends. It was found that microgels produced after an appropriate irradiation time showed improved flocculation behavior over their nonirradiated linear counterparts. The graft microgels performed better than the corresponding random microgels. For a γ-radiation dosage of 100 krad/h, the graft microgels obtained by irradiating a 30% DADMAC (by weight) homopolymer blend for 3 h showed the maximum reduction in the relative turbidity of the TiO2 suspension as well as the largest fraction of larger particles flocculated.

Thermoseparating water/polymer system: a novel one-polymer aqueous two-phase system for protein purification.

In this study we show that proteins can be partitioned and separated in a novel aqueous two-phase system composed of only one polymer in water solution. This system represents an attractive alternative to traditional two-phase systems which uses either two polymers (e.g., PEG/dextran) or one polymer in high-salt concentration (e.g., PEG/salt). The polymer in the new system is a linear random copolymer composed of ethylene oxide and propylene oxide groups which has been hydrophobically modified with myristyl groups (C(14)H(29)) at both ends (HM-EOPO). This polymer thermoseparates in water, with a cloud point at 14 degrees C. The HM-EOPO polymer forms an aqueous two-phase system with a top phase composed of almost 100% water and a bottom phase composed of 5-9% HM-EOPO in water when separated at 17-30 degrees C. The copolymer is self-associating and forms micellar-like structures with a CMC at 12 microM (0.01%). The partitioning behavior of three proteins (lysozyme, bovine serum albumin, and apolipoprotein A-1) in water/HM-EOPO two-phase systems has been studied, as well as the effect of various ions, pH, and temperature on protein partitioning. The amphiphilic protein apolipoprotein A-1 was strongly partitioned to the HM-EOPO-rich phase within a broad-temperature range. The partitioning of hydrophobic proteins can be directed with addition of salt. Below the isoelectric point (pI) BSA was partitioned to the HM-EOPO-rich phase and above the pI to the water phase when NaClO(4)was added to the system. Lysozyme was directed to the HM-EOPO phase with NaClO(4), and to the water phase with Na-phosphate. The possibility to direct protein partitioning between water and copolymer phases shows that this system can be used for protein separations. This was tested on purification of apolipoprotein A-1 from human plasma and Escherichia coli extract. Apolipoprotein A-1 could be recovered in the HM-EOPO-rich phase and the majority of contaminating proteins in the water phase. By adding a new water/buffer phase at higher pH and with 100 mM NaClO(4), and raising the temperature for separation, the apolipoprotein A-1 could be back-extracted from the HM-EOPO phase into the new water phase. This novel system has a strong potential for use in biotechnical extractions as it uses only one polymer and can be operated at moderate temperatures and salt concentrations and furthermore, the copolymer can be recovered.

Ionic conductivity of polymer electrolytes based on phosphate and polyether copolymers

Linear polyphosphate random copolymers (LPC) composed of phosphate as a linking agent with poly(ethylene glycol) (PEG) and/or poly(tetramethylene glycol) (PTMG) were synthesized to increase local segmental motion for improved ion transport. Ionic conductivity and thermal behavior of LPC series–LiCF 3SO 3 complexes were investigated with various compositions, salt concentrations and temperatures. The PEG(70)/PTMG(30)/LiCF 3SO 3 electrolyte exhibited ionic conductivity of 8.04×10 −5 S/cm at 25°C. Salt concentration with the highest ionic conductivity was considerably dependent on EO/TMO compositions in LPC series–salt systems. Relationship between solvating ability and chain flexibility with various compositions and salt concentrations was investigated through theoretical aspects of the Adam–Gibbs configurational entropy model. Temperature dependence on the ionic conductivity in LPC6 series–salt systems suggested the ion conduction follows the Williams–Landel–Ferry (WLF) mechanism, which is confirmed by Vogel–Tamman–Fulcher (VTF) plots. The ionic conductivity was affected by segmental motion of the polymer matrix. VTF parameters and apparent activation energy were evaluated by a non-linear least square minimization method. These results suggested that the solvating ability of the host polymer might be a dominant factor to improve the ionic conductivity rather than chain mobility.