Organic hybrid of chlorinated polyethylene and hindered phenol. I. Dynamic mechanical properties

Dynamic mechanical properties and microstructure of an organic hybrid consisting of chlorinated polyethylene (CPE) and 3,9‐bis[1,1‐dimethyl‐2{β‐(3‐tert‐butyl4‐hydroxy‐5‐methylphenyl)propionyloxy}ethyl]‐2,4,8,10‐tetraoxaspiro[5,5]‐undecane (AO‐80) were investigated. The AO‐80 clearly exhibited two second‐order transitions at 6 and 69 °C in addition to the melting: the transition at lower temperature is assigned to the glass transition, and the transition at higher temperature is considered to be caused by the dissociation of hydrogen bond between the hydroxyl groups of AO‐80. When blending with CPE, part of AO‐80 molecules was dispersed into the CPE matrix, and most of them formed an AO‐80‐rich phase. As a result, a novel transition appeared above the glass‐transition temperature of the CPE matrix. It was assigned to the dissociation of the intermolecular hydrogen bond between the α‐hydrogen of CPE and the hydroxyl groups of AO‐80 within the AO‐80‐rich phase. Dynamic mechanical properties and microstructure of CPE/AO‐80 hybrid were controlled by the thermal treatment. It was found that the CPE/AO‐80 hybrid is a good damping material and shows a shape memory effect. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2285–2295, 2000     

Organic hybrid of chlorinated polyethylene and hindered phenol. II. Influence of the chemical structure of small molecules on viscoelastic properties

The viscoelastic properties and stabilities of those properties of organic hybrids consisting of chlorinated polyethylene (CPE) and tetrakis[methylene‐3‐(3‐5‐di‐tert‐butyl‐4‐hydroxy phenyl)propionyloxy]methane (AO‐60) and triethylene glycol bis[3‐(3‐tert‐butyl‐4‐hydroxy‐5‐methyl phenyl)propionyloxy] (AO‐70) were investigated. The CPE/AO‐70 hybrids show only one transition, whereas for the CPE/AO‐60 hybrids, one novel relaxation appears above the glass‐transition temperature of CPE. This relaxation on the higher temperature side in the mechanical spectrum for CPE/AO‐60 is associated with the appearance of the AO‐60‐rich phase. Furthermore, the stabilities of the viscoelastic properties and microstructures of the organic hybrids consisting of CPE and multifunctional hindered phenols are dominated by the strength of the intermolecular interaction between CPE and phenols and the conformations of the middle skeletal parts of hindered phenols. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1496–1503, 2000     

Organic hybrid of chlorinated polyethylene and hindered phenol. IV. Modification on dynamic mechanical properties by chlorinated paraffin

Binary systems of chlorinated polyethylene (CPE) and chlorinated paraffin (CP) or 3,9‐bis[1,1‐dimethyl‐2{β‐(3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl) propionyloxy}ethyl]‐2,4,8,10‐tetraoxaspiro[5,5]‐undecane (AO‐80) and their ternary systems were investigated by dynamic mechanical analysis, thermal analysis, and infrared spectrum analysis. Adding CP into CPE/AO‐80, in which one novel relaxation appears above the glass‐transition temperature of CPE, can increase not only the peak height but also the minimum value between two peaks. The tan δ value in the middle of the two peaks for CPE/CP/CPE was found to be proportional to the slope (d ln E′/dT) of the E′ curve at an identical temperature. The addition of CP caused changes in many of the hydrogen bonds: a decrease in hydrogen bonds between the hydroxyl groups of AO‐80, a reinforcement of hydrogen bonds between the hydroxyl groups of AO‐80 and α‐hydrogens of CPE, and the formation of other hydrogen bonds between the carbonyl groups of AO‐80 and α‐hydrogens of CPE. Those changes are useful to improve the temperature dependence of tan δ and to enhance the stability of the dynamic mechanical properties. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 23–31, 2001     

Crystallization of a vitrified hindered phenol within chlorinated polyethylene and its effects on dynamic mechanical properties

The effects of heat treatment below the melting point of 3,9‐bis{1,1‐dimethyl‐2[β‐(3‐tert‐butyl‐4‐hydroxy‐5‐methylphenyl)propionyloxy]ethyl}‐2,4,8,10‐tetraoxaspiro[5,5]‐undecane (AO‐80) on the thermal and dynamic mechanical properties and microstructure of chlorinated polyethylene (CPE) filled with vitrified AO‐80 particles were investigated. The initial AO‐80 was a complete crystal, whereas AO‐80 obtained by cooling from its melting state was amorphous. The vitrified AO‐80 particles could crystallize again in a CPE matrix by an annealing treatment, but this crystal was different from the initial AO‐80 in the microstructure. In addition, the incorporation of CPE chains caused a dramatic increase in the modulus. As a result, the AO‐80 crystal particles that contained some CPE chains acted as multifunctional crosslinks, and the CPE/AO‐80 hybrid was found to be a new type of elastomer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 209–215, 2004     

Influence of the catalyst and polymerization conditions on the long‐chain branching of metallocene‐catalyzed polyethenes

A study was made on the effects of polymerization conditions on the long‐chain branching, molecular weight, and end‐group types of polyethene produced with the metallocene‐catalyst systems Et[Ind]₂ZrCl₂/MAO, Et[IndH₄]₂ZrCl₂/MAO, and (n‐BuCp)₂ZrCl₂/MAO. Long‐chain branching in the polyethenes, as measured by dynamic rheometry, depended heavily on the catalyst and polymerization conditions. In a semibatch flow reactor, the level of branching in the polyethenes produced with Et[Ind]₂ZrCl₂/MAO increased as the ethene concentration decreased or the polymerization time increased. The introduction of hydrogen or comonomer suppressed branching. Under similar polymerization conditions, the two other catalyst systems, (n‐BuCp)₂ZrCl₂/MAO and Et[IndH₄]₂ZrCl₂/MAO, produced linear or only slightly branched polyethene. On the basis of an end‐group analysis by FTIR and molecular weight analysis by GPC, we concluded that a chain transfer to ethene was the prevailing termination mechanism with Et[Ind]₂ZrCl₂/MAO at 80 °C in toluene. For the other catalyst systems, β‐H elimination dominated at low ethene concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 376–388, 2000     

Synthesis and characterization of near‐monodisperse electron acceptor homopolymers of 2‐[(3,5‐dinitrobenzoyl)oxy]ethyl methacrylate

Homopolymers of 2‐(trimethylsiloxy)ethyl methacrylate of degrees of polymerization from 5 to 50 were synthesized by group transfer polymerization in tetrahydrofuran (THF) using 1‐methoxy‐1‐(trimethylsiloxy)‐2‐methyl propene as the initiator and tetrabutylammonium bibenzoate as the catalyst. These polymers were first converted to poly[2‐(hydroxy)ethyl methacrylate]s by removal of the trimethylsilyl‐protecting groups by acidic hydrolysis, and subsequently transformed to poly{2‐[(3,5‐dinitrobenzoyl)oxy]ethyl methacrylate}s by reaction with 3,5‐dinitrobenzoyl chloride in the presence of triethylamine. Gel permeation chromatography in THF and proton nuclear magnetic resonance (¹H NMR) spectroscopy in CDCl₃ and d₆ dimethyl sulfoxide were used to characterize the polymers in terms of their molecular weight and composition. The molecular weights were found to be close to the values expected from the polymerization stoichiometry and the molecular weight distributions were narrow, with polydispersity indices around 1.1. The hydrolysis and reesterification steps were found to be almost quantitative for all polymers. Differential scanning calorimetry and thermal gravimetric analysis were also employed to measure the glass transition temperatures (T_g 's) and decomposition temperatures, which were determined to be approximately 80 and 320 °C, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1457–1465, 2000     

Viscoelastic properties of an organic hybrid of chlorinated polyethylene and a small molecule

The dynamic mechanical properties of an organic hybrid consisting of chlorinated polyethylene (CPE) and N,N‐dicyclohexyl‐2‐benzothiazolyl sulfenamide (DZ) were investigated. All the CPE/DZ hybrids showed a single loss tangent (tan δ) peak in the mechanical spectra. The peak area under the tan δ/temperature curves around the mechanical loss peak was examined to characterize the damping properties of the CPE/DZ hybrids. We found that there exists a bending point in the relation between the glass‐transition temperature (T_g) and DZ content and that the value of T_g is saturated in the higher DZ contents, suggesting that excess DZ molecules show self‐aggregation and are reorganized. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1341–1347, 2000     

The synthesis of poly[6,8‐dioxabicyclo[3.2.1]octane‐b‐(ethylene glycol)‐b‐6,8‐dioxabicyclo[3.2.1]octane] by controlled cationic ring‐opening polymerization

The triblock copolymer poly[6,8‐dioxabicyclo[3.2.1]octane‐b‐(ethylene glycol)‐b‐6,8‐dioxabicyclo[3.2.1]octane] was prepared by the controlled cationic ring‐opening polymerization of 6,8‐dioxabicyclo[3.2.1]octane (6,8‐DBO) from a macroinitiator. The macroinitiator, poly(ethylene glycol) (PEG) di(1‐chloroethyl ether), was prepared via the addition of HCl to PEG divinyl ether and was characterized with ¹³C NMR, ¹H NMR, and gel permeation chromatography (GPC). Upon preparation, a small fraction of the chain ends underwent a cyclization reaction to form inactive chain ends. When the macroinitiator was used in polymerizations of 6,8‐DBO with ZnI₂ as an activator, linear kinetic plots were observed, a linear increase in the copolymer molecular weight with conversion was seen, and the molecular weight distributions of the copolymer samples remained constant at about 1.40. Confirmation of the triblock structure of the final product was obtained with ¹H NMR spectra, ¹³C DEPT spectra, and GPC chromatograms. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4081–4087, 2000     

Anionic polymerization of styrenic macromonomers of polyisoprene,polybutadiene, and polystyrene

Anionic polymerization and high‐vacuum techniques were used to prepare a series of well‐defined polyisoprene, polybutadiene, and polystyrene polymacromonomers. The procedure involved (1) the synthesis of styrenic macromonomers in benzene by the selective reaction of the corresponding macroanion with the chlorine of 4‐(chlorodimethylsilyl)styrene (CDMSS) and (2) the in situ anionic polymerization of the macromonomer without previous isolation. The synthesis of the macromonomers [polyisoprene macromonomer: 11 samples, weight‐average molecular weight (M_w) = 1000–18,000; polybutadiene macromonomer: 5 samples, M_w = 2000–4000; and polystyrene macromonomer: 2 samples, M_w = 1300 and 3600] was monitored by size exclusion chromatography with refractive index/ultraviolet detectors. Selectivity studies with CDMSS indicated that polybutadienyllithum had the highest selectivity, and polystryryllithium the lowest. From kinetic studies it was concluded that the polymerization half‐life times were longer but comparable to those of styrene, and they appeared to only slightly depend on the molecular weight of the macromonomer chain (at least for low degrees of polymerization of the polymacromonomer and for M_w < 7000 for the macromonomer side chain). Dependence on the polymerization degree of the polymacromonomer product was also observed. All the prepared polymacromonomers were characterized by size exclusion chromatography with refractive index, ultraviolet and two‐angle laser light scattering detectors, and NMR spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1038–1048, 2005     

Micelles with highly branched nanoporous interior: Solution properties and binding capabilities of amphiphilic copolymers with linear dendritic architecture

This article describes the solution behavior of model amphiphilic linear‐dendritic ABA block copolymers that self‐assemble in aqueous media and form micelles with highly branched nanoporous cores. The materials investigated are constructed of poly(ethylene glycol), PEG, with molecular weight 5,000 or 11,000 as the water‐soluble B block and poly(benzyl ether) monodendrons [G] of second and third generation as the hydrophobic A fragments. The process of self‐assembly in aqueous media and the character of the micellar core are investigated by fluorescence spectroscopy using pyrene as the molecular probe. The data obtained by different methods indicate that the critical micelle concentrations (cmc) for these systems are between 1.1 × 10⁻⁵ and 2.0 × 10⁻⁵ mol/L for [G‐2]‐PEG5000‐[G‐2] and between 7.08 × 10⁻⁶ and 7.94 × 10⁻⁶ mol/L for [G‐3]‐PEG11000‐[G‐3]. It is found that the ratio of the first and third vibronic bands (I₁/I₃ ) in the fluorescence spectrum of the encapsulated pyrene changes from 1.77 to 1.32 when the concentration of [G‐2]‐PEG5000‐[G‐2] increases from 1.1 × 10⁻⁶ mol/L to 1.1 × 10⁻⁴ mol/L. For [G‐3]‐PEG11000‐[G‐3] these changes are between 1.77 and 1.17 in the same concentration range. The hybrid copolymers form host‐guest complexes with several polyaromatic compounds (phenanthrene, pyrene, perylene and fullerene, C₆₀) that are stable over extended periods of time (more than 12 months). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2711–2727, 2000     

Preparation and characterization of macroporous poly(N‐isopropylacrylamide) hydrogels for the controlled release of proteins

Macroporous, temperature‐sensitive poly(N‐isopropylacrylamide) (PNIPAAm) hydrogels were synthesized with poly(ethylene glycol)s (PEGs; molecular weight = 2000–6000) as the pore‐forming agents. The influence of the molecular weight and PEG content on the responsive kinetics of these macroporous hydrogels was investigated. The PEG‐modified PNIPAAm hydrogels were characterized by the swelling ratio, deswelling–reswelling kinetics, Fourier transform infrared, and differential scanning calorimetry. The morphology of these hydrogels was analyzed with scanning electron microscopy. The prepared macroporous hydrogels exhibited some unique properties in comparison with the gels with low molecular weight PEGs (molecular weight < 2000) as the pore‐forming agents. In addition, a preliminary study on the controlled release of bovine serum albumin from these macroporous hydrogels was carried out. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 152–159, 2003     

The copolymerization of propylene with higher,linear α‐olefins

Propylene was copolymerized with the linear α‐olefins 1‐octene, 1‐decene, 1‐tetradecene, and 1‐octadecene. The metallocene catalyst Me₂Si(2‐Me Benz[e]Ind)₂ZrCl₂, in conjunction with methylalumoxane as a cocatalyst, was used to synthesize the copolymers. The copolymers were characterized by ¹³C and ¹H NMR with a solvent mixture of 1,2,4‐trichlorobenzene (TCB) and benzene‐d₆ (9/1) at 100 °C. Thermal analyses were carried out to determine the melting and crystallization temperatures, whereas the molecular weights and molecular weight distributions were determined by gel permeation chromatography with TCB at 140 °C. Glass‐transition temperatures were determined with dynamic mechanical analysis. Relationships among the comonomer type and amount of incorporation and the melting/crystallization temperatures, glass‐transition temperature, crystallinity, and molecular weight were established. Moreover, up to 3.5% of the comonomer was incorporated, and there was a decrease in the molecular weight with increased comonomer content. Also, the melting and crystallization temperatures decreased as the comonomer content increased, but this relationship was independent of the comonomer type. In contrast, the values for the glass‐transition temperature also decreased with increased comonomer content, but the extent of the decrease was dependent on the comonomer type. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4110–4118, 2000     

Producing bimodal molecular weight distribution polymers through facile one‐pot/one‐step RAFT polymerization

Well‐defined bimodal molecular weight distribution (MWD) polystyrene and polystyrene‐b‐poly(acrylonitrile) were successfully synthesized using a pair of mono/difunctional trithiocarbonate RAFT agents 1 and 2 via one‐pot RAFT polymerization. The kinetics of RAFT polymerization for styrene in bulk with a molar ratio of [St]₀:[AIBN]₀:[ 1 ]₀:[ 2 ]₀ = 1200:1:2.5:2.5 was studied at 75°C. The results indicated that the system showed excellent controllability and “living” characteristics to both higher and lower molecular weight fractions, providing an efficient and facile way to producing bimodal MWD (co)polymers with both controlled molecular weight (MW) and MWD in molecular level, and the plausible mechanism was discussed in this work. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Solution characterization of the novel organometallic polymer poly(ferrocenyldimethylsilane)

A series of four well‐defined poly(ferrocenyldimethylsilane) (PFS) samples spanning a molecular weight range of approximately 10,000–100,000 g mol⁻¹ was synthesized by the living anionic polymerization of dimethyl[1]silaferrocenophane initiated with n‐BuLi. The polymers possessed narrow polydispersities and were used to characterize the solution behavior of PFS in tetrahydrofuran (THF). The weight‐average molecular weights (M_w ) of the polymers were determined by low‐angle laser light scattering (LALLS), conventional gel permeation chromatography (GPC), and GPC equipped with a triple detector (refractive index, light scattering, and viscosity). The molecular weight calculated by conventional GPC, with polystyrene standards, underestimated the true value in comparison with LALLS and GPC with the triple detection system. The Mark–Houwink parameter a for PFS in THF was 0.62 (k = 2.5 × 10⁻⁴), which is indicative of fairly marginal polymer–solvent interactions. The scaling exponent between the radius of gyration and M_w was 0.54, also consistent with marginal polymer–solvent interactions for PFS in THF. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3032–3041, 2000     

Synthesis of maleic anhydride grafted polyethylene and polypropylene,with controlled molecular structures

This article discusses a new chemical route to prepare maleic anhydride (MA) grafted polyethylene and polypropylene polymers with controlled molecular structure, that is, MA grafted content and polymer molecular weight and composition distributions. The chemistry involves a free radical graft reaction of maleic anhydride with poly(ethylene‐co‐p‐methylstyrene) and poly(propylene‐co‐p‐methylstyrene) copolymers. Under a suspension reaction condition, the grafting reaction takes place selectively on the p‐methylstyrene units in the copolymer, due to high reactivity of p‐methyl group and favorable mixing between p‐methylstyrene units and chemical reagents in the swollen amorphous phases. The resulting polymer shows no detectable molecular weight change during the reaction, and the MA grafted content increases with the increase of initiator and p‐methylstyrene concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1337–1343, 2000     

Synthesis and characterization of poly(phenylacetylene)s carrying oligo(ethylene oxide) pendants

A group of new amphiphilic poly(phenylacetylene)s bearing polar oligo(ethylene oxide) pendants, poly{4‐[2‐(2‐hydroxyethoxy)ethoxy]phenylacetylene} ( 1 ), poly(4‐{2‐[2‐(2‐hydroxyethoxy)‐ethoxy]ethoxy}phenylacetylene) ( 2p ), poly(3‐{2‐[2‐(2‐hydroxyethoxy)ethoxy]ethoxy}phenylacetylene) ( 2m ), poly(4‐{2‐[2‐(2‐methanesulfonyloxyethoxy)ethoxy]ethoxy}phenylacetylene) ( 3 ), poly(4‐{2‐[2‐(p‐toluenesulfonyloxyethoxy)ethoxy]ethoxy}phenylacetylene) ( 4 ), poly(4‐{2‐[2‐(2‐trimethylsilyloxy‐ethoxy)ethoxy] ethoxy}phenylacetylene) ( 5 ), and poly(4‐{2‐[2‐(2‐chloroethoxy)ethoxy]ethoxy}phenylacetylene) ( 6 ), were synthesized with organorhodium complexes as the polymerization catalysts. The structures and properties of the polymers were characterized with IR, UV, NMR, and thermogravimetric analysis. 1 , 2p , and 2m , the three polymers containing pendants with hydroxyl groups, were oligomeric or insoluble. The organorhodium complexes worked well for the polymerization of the monomers without hydroxyl groups, giving soluble polymers 3 – 6 with a weight‐average molecular weight up to ～160 × 10³ and a yield up to 99%. Z‐rich polymers 3 – 6 could be prepared by judicious selections of the catalyst under optimal conditions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1153–1167, 2006     

RAFT‐mediated batch emulsion polymerization of styrene using poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride] trithiocarbonate as both surfactant and macro‐RAFT agent

Poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride] trithiocarbonate, which contains the reactive trithiocarbonate group and the appending surface‐active groups, is used as both surfactant and macromolecular reversible addition‐fragmentation chain transfer (macro‐RAFT) agent in batch emulsion polymerization of styrene. Under the conditions at high monomer content of ～20 wt % and with the molecular weight of the macro‐RAFT agent ranging from 4.0 to 15.0 kg/mol, well‐controlled batch emulsion RAFT polymerization initiated by the hydrophilic 2‐2′‐azobis(2‐methylpropionamidine) dihydrochloride is achieved. The polymerization leads to formation of nano‐sized colloids of the poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride]‐b‐ polystyrene‐b‐poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride] triblock copolymer. The colloids generally have core‐shell structure, in which the hydrophilic block forms the shell and the hydrophobic block forms the core. The molecular weight of the triblock copolymer linearly increases with increase in the monomer conversion, and the values are well‐consistent with the theoretical ones. The molecular weight polydispersity index of the triblock copolymer is below 1.2 at most cases of polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A successive route to amphiphilic graft copolymers with a hydrophilic poly(3‐hydroxypropyl methacrylate) backbone and hydrophobic polystyrene side chains

A successive method for preparing novel amphiphilic graft copolymers with a hydrophilic backbone and hydrophobic side chains was developed. An anionic copolymerization of two bifunctional monomers, namely, allyl methacrylate (AMA) and a small amount of glycidyl methacrylate (GMA), was carried out in tetrahydrofuran (THF) with 1,1‐diphenylhexyllithium (DPHL) as the initiator in the presence of LiCl ([LiCl]/[DPHL]₀ = 2), at −50 °C. The copolymer poly(AMA‐co‐GMA) thus obtained possessed a controlled molecular weight and a narrow molecular weight distribution (M_w /M_n = 1.08–1.17). Without termination and polymer separation, a coupling reaction between the epoxy groups of this copolymer and anionic living polystyrene [poly(St)] at −40 °C generated a graft copolymer with a poly(AMA‐co‐GMA) backbone and poly(St) side chains. This graft copolymer was free of its precursors, and its molecular weight as well as its composition could be well controlled. To the completed coupling reaction solution, a THF solution of 9‐borabicyclo[3.3.1]nonane was added, and this was followed by the addition of sodium hydroxide and hydrogen peroxide. This hydroboration changed the AMA units of the backbone to 3‐hydroxypropyl methacrylate, and an amphiphilic graft copolymer with a hydrophilic poly(3‐hydroxypropyl methacrylate) backbone and hydrophobic poly(St) side chains was obtained. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1195–1202, 2000     

Melt polycondensation of L‐lactic acid with Sn(II) catalysts activated by various proton acids: A direct manufacturing route to high molecular weight Poly(L‐lactic acid)

Poly(L ‐lactic acid) (PLLA) was produced by the melt polycondensation of L ‐lactic acid. For the optimization of the reaction conditions, various catalyst systems were examined at different temperature and reaction times. It was discovered that Sn(II) catalysts activated by various proton acids can produce high molecular weight PLLA [weight‐average molecular weight (M_w ) ≥ 100,000] in a relatively short reaction time (≤15 h) compared with simple Sn(II)‐based catalysts (SnO, SnCl₂ · 2H₂O), which produce PLLA with an M_w of less than 30,000 after 20 h. The new catalyst system is also superior to the conventional systems in regard to racemization and discoloration of the resultant polymer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1673–1679, 2000     

Living radical copolymerization of styrene/maleic anhydride

Styrene/maleic anhydride (MA) copolymerization was carried out using benzoyl peroxide (BPO) and 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO). Styrene/MA copolymerization proceeded faster and yielded higher molecular weight products compared to styrene homopolymerization. When styrene/MA copolymerization was approximated to follow the first‐order kinetics, the apparent activation energy appeared to be lower than that corresponding to styrene homopolymerization. Molecular weight of products from isothermal copolymerization of styrene/MA increased linearly with the conversion. However products from the copolymerization at different temperatures had molecular weight deviating from the linear relationship indicating that the copolymerization did not follow the perfect living polymerization characteristics. During the copolymerization, MA was preferentially consumed by styrene/MA random copolymerization and then polymerization of practically pure styrene continued to produce copolymers with styrene‐co‐MA block and styrene‐rich block. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2239–2244, 2000