Determination of block size in poly(ethylene oxide)‐b‐polystyrene block copolymers by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Characterization of block size in poly(ethylene oxide)‐b‐poly(styrene) (PEO‐b‐PS) block copolymers could be achieved by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) after scission of the macromolecules into their constituent blocks. The performed hydrolytic cleavage was demonstrated to specifically occur on the targeted ester function in the junction group, yielding two homopolymers consisting of the constitutive initial blocks. This approach allows the use of well‐established MALDI protocols for a complete copolymer characterization while circumventing difficulties inherent to amphiphilic macromolecule ionization. Although the labile end‐group in PS homopolymer was modified by the MALDI process, PS block size could be determined from MS data since polymer chains were shown to remain intact during ionization. This methodology has been validated for a PEO‐b‐PS sample series, with two PEO of number average molecular weight (M_n) of 2000 and 5000 g mol^?1 and M_n(PS) ranging from 4000 to 21,000 g mol^?1. Weight average molecular weight (M_w), and thus polydispersity index, could also be reached for each segment and were consistent with values obtained by size exclusion chromatography. This approach is particularly valuable in the case of amphiphilic copolymers for which M_n values as determined by liquid state nuclear magnetic resonance might be affected by micelle formation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3380–3390, 2009     

Synthesis and characterization of poly (2-vinylpridine)-b-poly (t-butyl methacrylate)

The synthesis of well defined and monodisperse (M_w/M_n ≤ 1.2) narrow molecular weight distribution poly (2-vinylpyridine)-poly (t-butyl methacrylate) (P2VP-PTBMA) AB block copolymers is carried out by initiation of 2-vinylpyridine polymerization by 1,1-diphenylhexyllithium in THF at-78°C, followed by addition of TBMA and termination at ?78°C using MeOH. The formation of the BAB block copolymer is carried out in a similar fashion except that 1,4-dilithio-1,1,4,4-tetraphenylbutane is used as initiator. The corresponding synthesis of P2VP-PMMA block copolymers is carried in a similar manner, except that 1-2 equivalents of TBMA is used to end-functionalize the living P2VP before the addition of MMA. Without the addition of TBMA, trimodal molecular weight distributions in P2VP-b-PMMA are obtained. All the block copolymers are characterized by Size Exclusion Chromatography (SEC), Nuclear Magnetic Resonance (NMR), and Differential Scanning Calorimetry (DSC). © 1994 John Wiley & Sons, Inc.     

Synthesis of arborescent styrene homopolymers and copolymers from epoxidized substrates

The synthesis of arborescent styrenic homopolymers and copolymers was achieved by anionic polymerization and grafting. Styrene and p‐(3‐butenyl)styrene were first copolymerized using sec‐butyllithium in toluene, to generate a linear copolymer with a weight‐average molecular weight M_w = 4000 and M_w/M_n = 1.05. The pendant double bonds of the copolymer were then epoxidized with m‐chloroperbenzoic acid. A comb‐branched (or arborescent generation G0) copolymer was obtained by coupling the epoxidized substrate with living styrene‐p‐(3‐butenyl)styrene copolymer chains with M_w ≈ 5000 in a toluene/tetrahydrofuran mixture. Further cycles of epoxidation and coupling reactions while maintaining M_w ≈ 5000 for the side chains yielded arborescent copolymers of generations G1–G3. A series of arborescent styrene homopolymers was also obtained by grafting M_w ≈ 5000 polystyrene side chains onto the linear and G0–G2 copolymer substrates. Size exclusion chromatography measurements showed that the graft polymers have low polydispersity indices (M_w/M_n = 1.02–1.15) and molecular weights increasing geometrically over successive generations. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and healing properties of poly(arylene ether sulfone)‐poly(alkyl disulfide) multiblock copolymers

A multiblock copolymer consisting of hard (poly(arylene ether sulfone)) and soft (poly(alkyl disulfide)) segments was successfully synthesized by oxidative coupling of the corresponding thiol‐terminated oligomers. Its structure was confirmed by ¹H and ¹³C NMR spectroscopy. The GPC data (M_w = 82,000, M_w/M_n = 2.7) and inherent viscosity (0.67 dL g⁻¹) indicated the formation of a high‐molecular‐weight multiblock copolymer, while AFM and DSC indicated a microphase‐separated morphology. Tensile testing of the multiblock copolymer films showed a large elongation at break, which is characteristic of microphase‐separated hard/soft multiblock copolymers. Over 90% of the elongation at break of damaged samples (notched or cut) was recovered by UV irradiation. The elongation recovery was proportional to the UV irradiation energy, and the high recovery was achieved by relatively weak irradiation (<170 J cm⁻²). The high content of disulfide bonds in the multiblock copolymer resulted in a lower self‐healing energy. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1358–1365     

Cobalt‐mediated radical polymerization routes to poly(vinyl ester) block copolymers

Cobalt‐mediated radical polymerizations (CMRPs) utilizing redox initiation are demonstrated to produce poly(vinyl ester) homopolymers derived from vinyl pivalate (VPv) and vinyl benzoate (VBz), and their block copolymers with vinyl acetate (VAc). Combining anhydrous Co(acac)₂, lauroyl peroxide, citric acid trisodium salt, and VPv at 30 °C results in controlled polymerizations that yield homopolymers with M_n = 2.5–27 kg/mol with M_w/M_n = 1.20–1.30. Homopolymerizations of scrupulously purified VBz proceed with lower levels of control as evidenced by broader polydispersities over a range of molecular weights (M_n = 4–16 kg/mol; M_w/M_n = 1.34–1.65), which may be interpreted in terms of the decreased nucleophilicity of these less electron donating propagating polymer chain ends. Based on these results, we demonstrate that sequential CMRP reactions present a viable route to microphase separated poly(vinyl ester) block copolymers as shown by small‐angle X‐ray scattering analyses. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

The effect of structure on the thermoresponsive nature of well‐defined poly(oligo(ethylene oxide) methacrylates) synthesized by ATRP

Statistical copolymers of di(ethylene glycol) methyl ether methacrylate (MEO₂MA) and tri(ethylene glycol) methyl ether methacrylate (MEO₃MA) were synthesized by atom transfer radical polymerization (ATRP) providing copolymers with controlled composition and molecular weights ranging from M_n = 8,300–56,500 with polydispersity indexes (M_w/M_n) between 1.19 and 1.28. The lower critical solution temperature (LCST) of the copolymers increased with the mole fraction of MEO₃MA in the copolymer over the range from 26 to 52 °C. The average hydrodynamic diameter, measured by dynamic light scattering, varied with temperature above the LCST. These two monomers were also block copolymerized by ATRP to form polymers with molecular weight of M_n = 30,000 and M_w/M_n from 1.12 to 1.21. The LCST of the block copolymers shifted toward the LCST of the major segment, as compared to the value measured for the statistical copolymers at the same composition. As temperature increased, micelles, consisting of aggregated PMEO₂MA cores and PMEO₃MA shell, were formed. The micelles aggregated upon further heating to precipitate as larger particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 194–202, 2008     

Nitroxide‐mediated radical copolymerization of methyl methacrylate controlled with a minimal amount of 9‐(4‐vinylbenzyl)‐9H‐carbazole

The controlled nitroxide‐mediated homopolymerization of 9‐(4‐vinylbenzyl)‐9H‐carbazole (VBK) and the copolymerization of methyl methacrylate (MMA) with varying amounts of VBK were accomplished by using 10 mol % {tert‐butyl[1‐(diethoxyphosphoryl)‐2,2‐dimethylpropyl]amino} nitroxide relative to 2‐({tert‐butyl[1‐(diethoxyphosphoryl)‐2,2‐dimethylpropyl]amino}oxy)‐2‐methylpropionic acid (BlocBuilder?) in dimethylformamide at temperatures from 80 to 125 °C. As little as 1 mol % of VBK in the feed was required to obtain a controlled copolymerization of an MMA/VBK mixture, resulting in a linear increase in molecular weight versus conversion with a narrow molecular weight distribution (M_w /M_n ≈ 1.3). Preferential incorporation of VBK into the copolymer was indicated by the MMA/VBK reactivity ratios determined: r_VBK = 2.7 ± 1.5 and r_MMA = 0.24 ± 0.14. The copolymers were found significantly “living” by performing subsequent chain extensions with a fresh batch of VBK and by ³¹P NMR spectroscopy analysis. VBK was found to be an effective controlling comonomer for NMP of MMA, and such low levels of VBK comonomer ensured transparency in the final copolymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Dependence of flory-Huggins χ parameters on the copolymer composition for solutions of poly(methyl methacrylate-ran-n-butyl methacrylate) in cyclohexanone

Intermolecular interactions in random copolymer systems depend on the copolymer composition as being observed as a miscibility window in the random copolymer blends. The copolymer composition dependencies of the Flory-Huggins χ parameter and the heats of mixing ▵H_M(∞) at infinite dilution were studied for the solutions of poly(methyl methacrylate-ran-n-butyl methacrylate) (MMAnBMA) in cyclohexanone (CHN). The copolymer composition dependencies of χ obtained from osmotic pressures and of ▵H_M(∞) measured with a microcalorimeter were concave curves. This suggests that the random copolymers MMAnBMA interact with CHN more attractively than do the homopolymers PMMA and PnBMA. This is caused by the repulsion effect between the MMA and nBMA segments. The equation-of-state theory extended to the random copolymer systems by us reproduced fairly well these thermodynamic properties. The χ parameter for the PMMA/PnBMA blends was calculated using the equation-of-state theory with the MMA/nBMA intersegmental parameters employed for the above random copolymer solutions in CHN. The χ value calculated thus was in satisfactory agreement with that obtained from the random copolymer solutions using the Flory-Huggins theory extended to multicomponent systems. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of novel poly(cycloalkyl methacrylate) bearing fused‐ring structure and its copolymers

A new family of cycloaliphatic fused‐ring acrylic polymers based on 8‐hydroxymethyltricyclo[5.2.1.0^2,6]decane (TCD) has been synthesized by free‐radical polymerization. TCD‐methacrylate (TCD‐MA) was synthesized by reacting TCD with methacrylic acid in toluene via transesterification with p‐toluenesulfonic acid as a catalyst. TCDMA was polymerized in toluene with benzoyl peroxide as a free‐radical initiator at 80 °C. Copolymers were synthesized by polymerizing TCDMA with styrene and methyl methacrylate. The composition of the comonomers was varied from 0 to 100%. Homo‐ and copolymers were characterized by Fourier transform infrared (FTIR) and ¹³C NMR spectroscopy. Molecular weight determination by gel permeation chromatography showed that the polymers were obtained in very high molecular weights in the range of M_n > 50,000 and M_w > 80,000 with relatively low polydispersity. The composition analysis of both the copolymer series were determined by ¹H NMR. The thermal properties of the homo‐ and copolymers were studied with differential scanning calorimetry and all the polymers were found to be amorphous. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5617–5626, 2004     

Synthesis of amphiphilic poly(methyl methacrylate‐ b‐ethylene oxide) copolymers from monohydroxy telechelic poly(methyl methacrylate) as macroinitiator

The synthesis of well‐defined poly(methyl methacrylate)‐block‐poly(ethylene oxide) (PMMA‐b‐PEO) dibock copolymer through anionic polymerization using monohydroxy telechelic PMMA as macroinitiator is described. Living anionic polymerization of methyl methacrylate was performed using initiators derived from the adduct of diphenylethylene and a suitable alkyllithium, either of which contains a hydroxyl group protected with tert‐butyldimethylsilyl moiety in tetrahydrofuran (THF) at ?78 °C in the presence of LiClO₄. The synthesized telechelic PMMAs had good control of molecular weight with narrow molecular weight distribution (MWD). The ¹H NMR and MALDI‐TOF MS analysis confirmed quantitative functionalization of chain‐ends. Block copolymerization of ethylene oxide was carried out using the terminal hydroxyl group of PMMA as initiator in the presence of potassium counter ion in THF at 35 °C. The PMMA‐b‐PEO diblock copolymers had moderate control of molecular weight with narrow MWD. The ¹H NMR results confirm the absence of trans‐esterification reaction of propagating PEO anions onto the ester pendants of PMMA. The micellation behavior of PMMA‐b‐PEO diblock copolymer was examined in water using ¹H NMR and dynamic light scattering. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2132–2144, 2008     

Glycoconjugated polymer: Synthesis and characterization of poly(vinyl saccharide)‐block‐polystyrene‐block‐poly(vinyl saccharide) as an amphiphilic ABA triblock copolymer

Styrene (St) was polymerized with α,α′‐bis(2′,2′,6′,6′‐tetramethyl‐1′‐piperidinyloxy)‐1,4‐diethylbenzene ( 1 ) as an initiator (bulk, [St]/] 1 ] = 570) at 120 °C for 5.0 h to obtain polystyrene having 2,2,6,6‐tetramethylpiperidiloxy moieties on both sides of the chain ends ( 2 ) with a number‐average molecular weight (M_n) of 14,300 and a polydispersity index [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] of 1.14. 4‐Vinylbenzyl glucoside peracetate ( 3a ) was polymerized with 2 as a macromolecular initiator and dicumyl peroxide (DCP) as an accelerator in chlorobenzene at 120 °C. The polymerization with the [ 3a ]/[ 2 ]/[DCP] ratio of 30/1/1.2 for 5 h afforded a product in a yield of 73%; it was followed by purification with preparative size exclusion chromatography to provide the ABA triblock copolymer containing the pendant acetyl glucose on both sides of the chain ends ( 4a ; M_n = 21,000, M_w/M_n = 1.16). Similarly, the polymerization of 4‐vinylbenzyl maltohexaoside peracetate produced the ABA triblock copolymer containing the pendant acetyl maltohexaose on both side of the chain end ( 4b ; M_n = 31,800, M_w/M_n = 1.11). Polymers 4a and 4b were modified by deacetylation into amphiphilic ABA triblock copolymers containing the pendant glucose and maltohexaose as hydrophilic segment, 5a and 5b , respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3978–3985, 2006     

Synthesis of poly(ethylene‐co‐vinyl alcohol)‐g‐polystyrene graft copolymer and their applications for ordered porous film and compatibilizer

A series of new functional poly(ethylene‐co‐vinyl alcohol)‐g‐polystyrene graft copolymers (EVAL‐g‐PS) with controlled molecular weight (M_n = 38,000–94,000 g mol^?1) and molecular weight distribution (M_w/M_n = 2.31–3.49) were synthesized via a grafting from methodology. The molecular structure and component of EVAL‐g‐PS graft copolymers were confirmed by the analysis of their ¹H NMR spectra and GPC curves. The porous films of such copolymers were fabricated via a static breath‐figure (BF) process. The influencing factors on the morphology of such porous films, such as solvent, temperature, polymer concentration, and molecular weight of polymer were investigated. Ordered porous film and better regularity was fabricated through a static BF process using EVAL‐g‐PS solution in CHCl₃. Scanning electron microscopy observation reveals that the EVAL‐g‐PS graft copolymer is an efficient compatibilizer for the blend system of low‐density polyethylene/polystyrene. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 516–524     

Adiabatic compressibility of solutions of ethylene–propylene copolymers in hydrocarbon solvents

Adiabatic compressibility measurements are reported on solutions in hydrocarbon solvents of a low M_w high ethylene content, and of both high and low M_w low ethylene content ethylene–propylene copolymers. In all solutions the observed adiabatic compressibility was lower than the solvent value by an increment which was a function of the solvent type. Comparison of the data for a high and low molecular weight sample of the same copolymer indicates no molecular weight effects. Changes in the composition of the copolymer, as indicated by NMR spectroscopy, have only a slight effect on the adiabatic compressibility. The dominant feature of these studies is the apparent correlation of the chain length of the alkane solvent with the decrement in the compressibility.     

Synthesis of poly(p‐phenylene) macromonomers and multiblock copolymers

Rigid‐rod poly(4′‐methyl‐2,5‐benzophenone) macromonomers were synthesized by Ni(0) catalytic coupling of 2,5‐dichloro‐4′‐methylbenzophenone and end‐capping agent 4‐chloro‐4′‐fluorobenzophenone. The macromonomers produced were labile to nucleophilic aromatic substitution. The molecular weight of poly(4′‐methyl‐2,5‐benzophenone) was controlled by varying the amount of the end‐capping agent in the reaction mixture. Glass‐transition temperatures of the macromonomers increased with increasing molecular weight and ranged from 117 to 213 °C. Substitution of the macromonomer end groups was determined to be nearly quantitative by ¹H NMR and gel permeation chromatography. The polymerization of a poly(4′‐methyl‐2,5‐benzophenone) macromonomer [number‐average molecular weight (M_n) = 1.90 × 10³ g/mol; polydispersity (M_w)/M_n = 2.04] with hydroxy end‐capped bisphenol A polyaryletherketone (M_n = 4.50 × 10³ g/mol; M_w/M_n = 1.92) afforded an alternating multiblock copolymer (M_n = 1.95 × 10⁴ g/mol; M_w/M_n = 6.02) that formed flexible, transparent films that could be creased without cracking. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3505–3512, 2001     

Phase separation in semicrystalline blends of poly(phenylene sulfide) and poly(ethylene terephthalate). II. Effect of poly(phenylene sulfide) homopolymer solubilization of PPS‐graft‐PET copolymer on morphology and crystallization behavior

The morphology and crystallization behavior of poly(phenylene sulfide) (PPS) and poly(ethylene terephthalate) (PET) blends compatibilized with graft copolymers were investigated. PPS‐blend‐PET compositions were prepared in which the viscosity of the PPS phase was varied to assess the morphological implications. The dispersed‐phase particle size was influenced by the combined effects of the ratio of dispersed‐phase viscosity to continuous‐phase viscosity and reduced interfacial tension due to the addition of PPS‐graft‐PET copolymers to the blends. In the absence of graft copolymer, the finest dispersion of PET in a continuous phase of PPS was achieved when the viscosity ratio between blend components was nearly equal. As expected, PET particle sizes increased as the viscosity ratio diverged from unity. When graft copolymers were added to the blends, fine dispersions of PET were achieved despite large differences in the viscosities of PPS and PET homopolymers. The interfacial activity of the PPS‐graft‐PET copolymer appeared to be related to the molecular weight ratio of the PPS homopolymer to the PPS segment of the graft copolymer (M_H/M_A). With increasing solubilization of the PPS graft copolymer segment by the PPS homopolymer, the particle size of the PET dispersed phase decreased. In crystallization studies, the presence of the PPS phase increased the crystallization temperature of PET. The magnitude of the increase in the PET crystallization temperature coincided with the viscosity ratio and extent of the PPS homopolymer solubilization in the graft copolymer. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 599–610, 2000     

Preparation and characterization of biodegradable poly(lactic acid)‐ block‐poly(ε‐caprolactone) multiblock copolymer

Biodegradable copolymers of poly(lactic acid)‐block‐poly(ε‐caprolactone) (PLA‐b‐PCL) were successfully prepared by two steps. In the first step, lactic acid monomer is oligomerized to low molecular weight prepolymer and copolymerized with the (ε‐caprolactone) diol to prepolymer, and then the molecular weight is raised by joining prepolymer chains together using 1,6‐hexamethylene diisocyanate (HDI) as the chain extender. The polymer was carefully characterized by using ¹H‐NMR analysis, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). The results of ¹H‐NMR and TGA indicate PLA‐b‐PCL prepolymer with number average molecular weights (M_n) of 4000–6000 were obtained. When PCL‐diols are 10 wt%, copolymer is better for chain extension reaction to obtain the polymer with high molecular weight. After chain extension, the weight average molecular weight can reach 250,000 g/mol, as determined by GPC, when the molar ratio of –NCO to –OH was 3:1. DSC curve showed that the degree of crystallization of PLA–PCL copolymer was low, even became amorphous after chain extended reaction. The product exhibits superior mechanical properties with elongation at break above 297% that is much higher than that of PLA chain extended products. Copyright © 2009 John Wiley & Sons, Ltd.     

Ethylene/1‐pentene copolymers synthesized using the metaloxycarbene complex catalyst system [(CO)5W=C(Me)OZr(Cp)2Cl]/MAO

Ethylene/1‐pentene copolymers were prepared using a [(CO)₅W= C(Me)OZr(Cp)₂Cl] (1)/MAO catalyst system. 1‐Pentene incorporation in the copolymer was monitored using ¹³C‐NMR spectroscopic methods. The weight average molecular weights (M_w) of the copolymers were between 142,000 and 629,000 g/mol, with polydispersity indexes (PDIs) ranging from ≈ 2 to 90, as analyzed by size exclusion chromatography (SEC). Melting and crystallization temperatures, determined using differential scanning calorimetry (DSC) and crystallization analysis fractionation (CRYSTAF), decreased linearly as the amount of 1‐pentene in the copolymer increased. SEC‐FTIR revealed that the 1‐pentene is predominantly incorporated in the low molecular weight fraction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5121–5133, 2004     

Block copolymer compatibilizers for polystyrene/poly(dimethylsiloxane) blends

Symmetric polystyrene (PS)–poly(dimethylsiloxane) (PDMS) diblock copolymers were mixed into a 20% dispersion of PDMS in PS. The effect of adding the block copolymer on the blend morphology was examined as a function of the block copolymer molecular weight (M_n,bcp), concentration, and viscosity ratio (η_r). When blended together with the PS and PDMS homopolymers, most of the block copolymer appeared as micelles in the PS matrix. Even when the copolymer was preblended into the PDMS dispersed phase, block copolymer micelles in the PS matrix phase were observed with transmission electron microscopy after mixing. Adding 16 kg/mol PS–PDMS block copolymer dramatically reduced the PDMS particle size, but the morphology, as examined by scanning electron microscopy, was unstable upon thermal annealing. Adding 156 kg/mol block copolymer yielded particle sizes similar to those of blends with 40 or 83 kg/mol block copolymers, but only blends with 83 kg/mol block copolymer were stable after annealing. For a given value of M_n,bcp, a minimum PDMS particle size was observed when η_r ～ 1. When η_r = 2.6, thermally stable, submicrometer particles as small as 0.6 μm were observed after the addition of only 3% PS–PDMS diblock (number‐average molecular weight = 83 kg/mol) to the blend. As little as 1% 83 kg/mol block copolymer was sufficient to stabilize a 20% dispersion of 1.1‐μm PDMS particles in PS. Droplet size reduction was attributed to the prevention of coalescence caused by small amounts of block copolymer at the interface. The conditions under which block copolymer interfacial adsorption and interpenetration were facilitated were explained with Leibler's brush theory. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 346–357, 2002; DOI 10.1002/polb.10098     

Preparation and microstructural analysis of poly(lactic‐alt‐glycolic acid)

Alternating copolymers of glycolic (G) and lactic (L) acid were prepared by the condensation of the preformed dimers: L_LG and L_racG. By size exclusion chromatography (THF, PS standards), poly(L_LG) exhibited a molecular weight (M_n) of 15.6 kg mol^?1, with a weight average molecular weight (M_w) of 26.9 kg mol^?1 and a PDI of 1.72. The M_n for poly(L_racG) was 9.2 kg mol^?1, with a M_w of 12.9 kg mol^?1 and a PDI of 1.40. The NMR spectra of poly(L_LG) were consistent with an isotactic microstructure. NMR spectra of the racemic poly(L_racG) were consistent with an atactic structure. The methylene region of the ¹H NMR spectrum showed a tetrad level of resolution of the nearby stereochemical relationships, for example, iii. Resonances for other groups in both the ¹H and ¹³C NMR spectra gave only a triad level of resolution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4704–4711, 2008     

Titanium‐mediated [CpTiCl2(OEt)] ring‐opening polymerization of lactides: A novel route to well‐defined polylactide‐based complex macromolecular architectures

Among three cyclopentadienyl titanium complexes studied, CpTiCl₂(OEt), containing a 5% excess CpTiCl₃, has proven to be a very efficient catalyst for the ring‐opening polymerization (ROP) of L ‐lactide (LLA) in toluene at 130 °C. Kinetic studies revealed that the polymerization yield (up to 100%) and the molecular weight increase linearly with time, leading to well‐defined PLLA with narrow molecular weight distributions (M_w/M_n ≤ 1.1). Based on the above results, PS‐b‐PLLA, PI‐b‐PLLA, PEO‐b‐PLLA block copolymers, and a PS‐b‐PI‐b‐PLLA triblock terpolymer were synthesized. The synthetic strategy involved: (a) the preparation of OH‐end‐functionalized homopolymers or diblock copolymers by anionic polymerization, (b) the reaction of the OH‐functionalized polymers with CpTiCl₃ to give the corresponding Ti‐macrocatalyst, and (c) the ROP of LLA to afford the final block copolymers. PMMA‐g‐PLLA [PMMA: poly(methyl methacrylate)] was also synthesized by: (a) the reaction of CpTiCl₃ with 2‐hydroxy ethyl methacrylate, HEMA, to give the Ti‐HEMA‐catalyst, (b) the ROP of LLA to afford a PLLA methacrylic‐macromonomer, and (c) the copolymerization (conventional and ATRP) of the macromonomer with MMA to afford the final graft copolymer. Intermediate and final products were characterized by NMR spectroscopy and size exclusion chromatography, equipped with refractive index and two‐angle laser light scattering detectors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1092–1103, 2010