Synthesis and morphology of polyethylene‐block‐poly(methyl methacrylate) through the combination of metallocene catalysis with living radical polymerization

Polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) was successfully synthesized through the combination of metallocene catalysis with living radical polymerization. Terminally hydroxylated polyethylene, prepared by ethylene/allyl alcohol copolymerization with a specific zirconium metallocene/methylaluminoxane/triethylaluminum catalyst system, was treated with 2‐bromoisobutyryl bromide to produce terminally esterified polyethylene (PE‐Br). With the resulting PE‐Br as an initiator for transition‐metal‐mediated living radical polymerization, methyl methacrylate polymerization was subsequently performed with CuBr or RuCl₂(PPh₃)₃ as a catalyst. Then, PE‐b‐PMMA block copolymers of different poly(methyl methacrylate) (PMMA) contents were prepared. Transmission electron microscopy of the obtained block copolymers revealed unique morphological features that depended on the content of the PMMA segment. The block copolymer possessing 75 wt % PMMA contained 50–100‐nm spherical polyethylene lamellae uniformly dispersed in the PMMA matrix. Moreover, the PE‐b‐PMMA block copolymers effectively compatibilized homopolyethylene and homo‐PMMA at a nanometer level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3965–3973, 2003     

Highly ordered nanoporous thin films by blending of PSt‐b‐PMMA block copolymers and PEO additives as structure directing agents

Herein, we present a simple method for producing nanoporous templates with a high degree of lateral ordering by self‐assembly of block copolymers. A key feature of this approach is control of the orientation of polymeric microdomains through the use of hydrophilic additives as structure directing agents. Incorporation of hydrophilic poly(ethylene oxide) (PEO) moieties into poly(styrene‐b‐methyl methacrylate) (PSt‐b‐PMMA) diblock copolymers gives vertical alignment of PMMA cylinders on the substrate after solvent annealing. Because of the miscibility between PEO and PMMA, PEO additives were selectively positioned within PMMA microdomains and by controlling the processing conditions, it was found that ordering of PSt‐b‐PMMA diblock copolymers could be achieved. The perpendicular orientation of PMMA cylinders was achieved by increasing the molecular size of the PEO additives leading to an increased hydrophilicity of the PMMA domains and consequently to control the orientation of microdomains in PSt‐b‐PMMA block copolymer thin films. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8041–8048, 2008     

Block‐brush copolymers via ROMP and sequential double click reaction strategy

We report an efficient way, sequential double click reactions, for the preparation of brush copolymers with AB block‐brush architectures containing polyoxanorbornene (poly (ONB)) backbone and poly(ε‐caprolactone) (PCL), poly(methyl methacrylate) (PMMA) or poly(tert‐butyl acrylate) (PtBA) side chains: poly(ONB‐g‐PMMA)‐b‐poly(ONB‐g‐PCL) and poly(ONB‐g‐PtBA)‐b‐poly(ONB‐g‐PCL). The living ROMP of ONB affords the synthesis of well‐defined poly(ONB‐anthracene)₂₀‐b‐poly (ONB‐azide)₅ block copolymer with anthryl and azide pendant groups. Subsequently, well‐defined linear alkyne end‐functionalized PCL (PCL‐alkyne), maleimide end‐functionalized PMMA (PMMA‐MI) and PtBA‐MI were introduced onto the block copolymer via sequential azide‐alkyne and Diels‐Alder click reactions, thus yielding block‐brush copolymers. The molecular weight of block‐brush copolymers was measured via triple detection GPC (TD‐GPC) introducing the experimentally calculated dn/dc values to the software. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of multiblock copolymers composed of poly(5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one) outer blocks and poly(L‐lactide) inner blocks

Ethylene glycol (EG) initiated, hydroxyl‐telechelic poly(L ‐lactide) (PLLA) was employed as a macroinitiator in the presence of a stannous octoate catalyst in the ring‐opening polymerization of 5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one (MBC) with the goal of creating A–B–A‐type block copolymers having polycarbonate outer blocks and a polyester center block. Because of transesterification reactions involving the PLLA block, multiblock copolymers of the A–(B–A)_n–B–A type were actually obtained, where A is poly(5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one), B is PLLA, and n is greater than 0. ¹H and ¹³C NMR spectroscopy of the product copolymers yielded evidence of the multiblock structure and provided the lactide sequence length. For a PLLA macroinitiator with a number‐average molecular weight of 2500 g/mol, the product block copolymer had an n value of 0.8 and an average lactide sequence length (consecutive C₆H₈O₄ units uninterrupted by either an EG or MBC unit) of 6.1. For a PLLA macroinitiator with a number‐average molecular weight of 14,400 g/mol, n was 18, and the average lactide sequence length was 5.0. Additional evidence of the block copolymer architecture was revealed through the retention of PLLA crystallinity as measured by differential scanning calorimetry and wide‐angle X‐ray diffraction. Multiblock copolymers with PLLA crystallinity could be achieved only with isolated PLLA macroinitiators; sequential addition of MBC to high‐conversion L ‐lactide polymerizations resulted in excessive randomization, presumably because of residual L ‐lactide monomer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6817–6835, 2006     

Crystallization and stereocomplexation behavior of poly(D‐ and L‐lactide)‐b‐poly(N,N‐dimethylamino‐2‐ethyl methacrylate) block copolymers

The thermal properties, crystallization, and morphology of amphiphilic poly(D ‐lactide)‐b‐poly(N,N‐dimethylamino‐2‐ethyl methacrylate) (PDLA‐b‐PDMAEMA) and poly (L ‐lactide)‐b‐poly(N,N‐dimethylamino‐2‐ethyl methacrylate) (PLLA‐b‐PDMAEMA) copolymers were studied and compared to those of the corresponding poly(lactide) homopolymers. Additionally, stereocomplexation of these copolymers was studied. The crystallization kinetics of the PLA blocks was retarded by the presence of the PDMAEMA block. The studied copolymers were found to be miscible in the melt and the glassy state. The Avrami theory was able to predict the entire crystallization range of the PLA isothermal overall crystallization. The melting points of PLDA/PLLA and PLA/PLA‐b‐PDMAEMA stereocomplexes were higher than those formed by copolymer mixtures. This indicates that the PDMAEMA block is influencing the stability of the stereocomplex structures. For the low molecular weight samples, the stereocomplexes particles exhibited a conventional disk‐shape structure and, for high molecular weight samples, the particles displayed unusual star‐like shape morphology. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1397–1409, 2011     

Synthesis of a novel liquid crystal rod–coil star block copolymer consisting of poly(methyl methacrylate) and poly{2,5‐bis[(4‐methoxy‐phenyl)oxycarbonyl] styrene} via atom transfer radical polymerization

A bromine capped star‐shaped poly(methyl methacrylate) (S‐PMMA‐Br) was synthesized with CuBr/sparteine/PT‐Br as a catalyst and initiator to polymerize methyl methacrylate (MMA) according to atom transfer radical polymerization (ATRP). Then, with S‐PMMA‐Br as a macroinitiator, a series of new liquid crystal rod–coil star block copolymers with different molecular weights and low polydispersity were obtained by this method. The block architecture {coil‐conformation of the MMA segment and rigid‐rod conformation of 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl] styrene segment} of the four‐armed rod–coil star block copolymers were characterized by ¹H NMR. The liquid‐crystalline behavior of these copolymers was studied by differential scanning calorimetry and polarized optical microscopy. We found that the liquid‐crystalline behavior depends on the molecular weight of the rigid segment; only the four‐armed rod–coil star block copolymers with each arm's M_n,_GPC of the rigid block beyond 0.91 × 10⁴ g/mol could form liquid‐crystalline phases above the glass‐transition temperature of the rigid block. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 733–741, 2005     

Controlled copolymerization of 1‐octene and butyl methacrylate via RAFT and their nonisothermal model‐free thermokinetic decomposition study

Reversible addition fragmentation chain transfer (RAFT) copolymerization of 1‐octene and butyl methacrylate (BMA) was carried out for the first time using 4‐cyano‐4‐(phenylcarbonothioylthio)pentanoic acid as RAFT agent in N,N′‐dimethyl formamide. Poly(1‐octene‐co‐BMA) copolymers with well‐controlled molecular weights and narrow molecular weight distribution were obtained throughout the polymerization. The copolymers have been well characterized by different analytical techniques such as SEC, FT‐IR, NMR, SEM, AFM, XRD, and TG analyses. FT‐IR and NMR analyses confirmed the synthesis of poly(1‐octene‐co‐BMA) copolymers. SEM and AFM analyses demonstrated the wavy‐lamellar morphological structure of the copolymers. Thermogravimetric analysis revealed good thermal stability of poly(1‐octene‐co‐BMA) copolymers synthesized via RAFT mediated polymerization. The thermokinetic parameters were evaluated by adopting model‐free methods of Friedman and Flynn–Wall–Ozawa using the nonisothermal thermogravimetric data. The multivariate nonlinear regression analysis established the most appropriate kinetic model and the corresponding kinetic parameters of thermal decomposition of poly(1‐octene‐co‐BMA) copolymers were also calculated. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2093–2103     

Aqueous solution properties of pH‐responsive AB diblock acrylamido–styrenic copolymers synthesized via aqueous reversible addition–fragmentation chain transfer

Here we report the synthesis and solution characterization of a novel series of AB diblock copolymers with neutral, water‐soluble A blocks consisting of N,N‐dimethylacrylamide and pH‐responsive B blocks of N,N‐dimethylvinylbenzylamine. To our knowledge, this represents the first example of an acrylamido–styrenic block copolymer prepared directly in a homogeneous aqueous solution. The best blocking order [with poly(N,N‐dimethylacrylamide) as a macro‐chain‐transfer agent] yielded well‐defined block copolymers with minimal homopolymer impurities. The reversible aggregation of these block copolymers in aqueous media was studied with ¹H NMR spectroscopy and dynamic light scattering. Finally, an example of core‐crosslinked micelles was demonstrated by the addition of a difunctional crosslinking agent to a micellar solution of the parent block copolymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1724–1734, 2004     

Preparation of reactive block copolymers and their transformation to hollowed nanostructures

A novel polymeric hollow nanostructure was generated using micellar template method through a three‐step procedure. First, the block copolymers were synthesized via ring‐opening metathesis polymerization by sequentially adding monomers 7‐oxanorborn‐5‐ene‐exo‐exo‐2,3‐dicarboxylic acid dimethyl ester and the mixture of norbornene and 2,3‐bis(2‐bromoisobutyryloxymethyl)‐5‐norbornene in chloroform, and also atom transfer radical polymerization of 4‐(3‐butenyl)styrene was carried out by using the as‐obtained block copolymer poly(7‐oxanorborn‐5‐ene‐exo,exo‐2,3‐dicarboxylic acid dimethylester)‐block‐poly(norbornene‐co‐2,3‐bis(2‐bromoisobutyryloxymethyl)‐5‐norbornene as macroinitiator to afford a graft copolymer bearing poly(4‐(3‐butenyl)styrene) branch poly(7‐oxanorborn‐5‐ene‐exo,exo‐2,3‐dicarboxylic acid dimethylester)‐block‐poly(norbornene‐co‐2,3‐bis(2‐bromoisobutyryloxymethyl)‐5‐norbornene)‐graft‐poly(4‐(3‐butenyl)styrene). Second, the shell‐crosslinked micelles were prepared by ruthenium‐mediated ring‐closing metathesis of poly(4‐(3‐butenyl)styrene) branches in intramicelle formed from the copolymers self‐assembly spontaneously in toluene. Finally, the hollowed spherical nanoparticles were presented by removing the micellar copolymer backbone through the cleavage of the ester bonds away from the crosslinked network of branches. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Stress–strain behavior of low‐density polyethylene/poly(methyl methacrylate) blends with modulated interfaces with a hydrogenated polybutadiene‐block‐poly(methyl methacrylate) diblock copolymer

The stress–strain diagrams and ultimate tensile properties of uncompatibilized and compatibilized hydrogenated polybutadiene‐block‐poly(methyl methacrylate) (HPB‐b‐PMMA) blends with 20 wt % poly(methyl methacrylate) (PMMA) droplets dispersed in a low‐density polyethylene (LDPE) matrix were studied. The HPB‐b‐PMMA pure diblock copolymer was prepared via controlled living anionic polymerization. Four copolymers, in terms of the molecular weights of the hydrogenated polybutadiene (HPB) and PMMA sequences (22,000–12,000, 63,300–31,700, 49,500–53,500, and 27,700–67,800), were used. We demonstrated with the stress–strain diagrams, in combination with scanning electron microscopy observations of deformed specimens, that the interfacial adhesion had a predominant role in determining the mechanism and extent of blend deformation. The debonding of PMMA particles from the LDPE matrix was clearly observed in the compatibilized blends in which the copolymer was not efficiently located at the interface. The best HPB‐b‐PMMA copolymer, resulting in the maximum improvement of the tensile properties of the compatibilized blend, had a PMMA sequence that was approximately half that of the HPB block. Because of the much higher interactions encountered in the PMMA phase in comparison with those in HPB (LDPE), a shorter sequence of PMMA (with respect to HPB but longer than the critical molecular weight for entanglement) was sufficient to favor a quantitative location of the copolymer at the LDPE/PMMA interface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 22–34, 2005     

Synthesis and characterizations of the four‐armed amphiphilic block copolymer S[poly(2,3‐dihydroxypropyl acrylate)‐block‐poly(methyl acrylate)]4

The polymers poly[(2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate] (PDMDMA) and four‐armed PDMDMA with well‐defined structures were prepared by the polymerization of (2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate (DMDMA) in the presence of an atom transfer radical polymerization (ATRP) initiator system. The successive hydrolyses of the polymers obtained produced the corresponding water‐soluble polymers poly(2,3‐dihydroxypropyl acrylate) (PDHPA) and four‐armed PDHPA. The controllable features for the ATRP of DMDMA were studied with kinetic measurements, gel permeation chromatography (GPC), and NMR data. With the macroinitiators PDMDMA–Br and four‐armed PDMDMA–Br in combination with CuBr and 2,2′‐bipyridine, the block polymerizations of methyl acrylate (MA) with PDMDMA were carried out to afford the AB diblock copolymer PDMDMA‐b‐MA and the four‐armed block copolymer S{poly[(2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate]‐block‐poly(methyl acrylate)}₄, respectively. The block copolymers were hydrolyzed in an acidic aqueous solution, and the amphiphilic diblock and four‐armed block copolymers poly(2,3‐dihydroxypropyl acrylate)‐block‐poly(methyl acrylate) were prepared successfully. The structures of these block copolymers were verified with NMR and GPC measurements. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3062–3072, 2001     

Syntheses and characterizations of poly[2‐(dimethylamino)ethyl methacrylate]–poly(propylene oxide)–poly[2‐(dimethylamino)ethyl methacrylate] ABA triblock copolymers

A novel, near‐monodisperse, well‐defined ABA triblock copolymer, poly[2‐(dimethylamino)ethyl methacrylate]‐b‐poly(propylene oxide)‐b‐poly[2‐(dimethylamino)ethyl methacrylate], was synthesized via oxyanion‐initiated polymerization. The initiator was a telechelic‐type potassium alcoholate prepared from poly(propylene glycol) and KH in dry tetrahydrofuran. The copolymers produced were characterized by Fourier transform infrared, ¹H NMR, and gel permeation chromatography (GPC). GPC and ¹H NMR analyses showed that the products obtained were the desired copolymers, with narrow molecular weight distributions (ca. 1.09–1.11) very close to that of the original poly(propylene glycol). ¹H NMR, surface tension measurements, and dynamic light scattering all indicated that the triblock copolymer led to interesting aqueous solution behaviors, including temperature‐induced micellization and very high surface activity. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 624–631, 2002; DOI 10.1002/pola.10144     

Thermal‐initiating potentialities of poly(methyl methacrylate) peroxide: Metamorphosis of block‐into‐block copolymer and comparative studies on surface texture and morphology

This is the first report concerning the use of vinyl polyperoxide, namely, poly(methyl methacrylate) peroxide (PMMAP), as a thermal initiator for the synthesis of active polymer PMMAP‐PS‐PMMAP by free‐radical polymerization with styrene. The polymerizations have been carried out at different concentrations of macroinitiator PMMAP. The active polymers have been characterized by ¹H NMR, DSC, thermogravimetric analysis, and gel permeation chromatography. PMMAP‐PS‐PMMAP is further used as the thermal macroinitiator for the preparation of another block copolymer, PMMA‐b‐PS‐b‐PMMA, by reacting the active polymers with methyl methacrylate. The block copolymers have been synthesized by varying the concentrations of the active polymers. The mechanism of block copolymers has been discussed, which is also supported by thermochemical calculations. Studies on the surface texture and morphology of the block copolymer of polystyrene (PS) and PMMA material have been carried out using scanning electron microscopy. Furthermore, in this article, a blend of the same constituent materials (PS and PMMA) in proportions (v/v) similar to that contained in block copolymers has been formulated, and the morphology and surface textures of these materials were also investigated. A comparative microscopical evaluation between two processing methods was done for a better understanding of the processing route dependence of the microstructures. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 546–554, 2001     

Highly active bifunctional cobalt‐salen complexes for the synthesis of poly(ester‐block‐carbonate) copolymer via terpolymerization of carbon dioxide,propylene oxide,and norbornene anhydride isomer: Roles of anhydride conformation consideration

This article describes an efficient synthetic route of defined reactive polyester‐block‐polycarbonate copolymers, utilizing a bifunctional SalenCoNO₃ complex as catalyst for the single‐step terpolymerization of norbornene anhydride (NA), propylene oxide, and carbon dioxide. The geometric isomer of NA plays an important role in polymerization efficacy and the resulting polymer microstructure, including carbonate content, sequence isomer of polycarbonate moiety, and molecular weight. A hydroxyl‐functionalized polyester–polycarbonate block copolymer was synthesized by a thiol‐ene reaction. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 789–795     

Synthesis of PMMA‐b‐PBA block copolymer in homogeneous and miniemulsion systems by DPE controlled radical polymerization

In this research, poly(methyl methacrylate)‐b‐poly(butyl acrylate) (PMMA‐b‐PBA) block copolymers were prepared by 1,1‐diphenylethene (DPE) controlled radical polymerization in homogeneous and miniemulsion systems. First, monomer methyl methacrylate (MMA), initiator 2,2′‐azobisisobutyronitrile (AIBN) and a control agent DPE were bulk polymerized to form the DPE‐containing PMMA macroinitiator. Then the DPE‐containing PMMA was heated in the presence of a second monomer BA, the block copolymer was synthesized successfully. The effects of solvent and polymerization methods (homogeneous polymerization or miniemulsion polymerization) on the reaction rate, controlled living character, molecular weight (M_n) and molecular weight distribution (PDI) of polymers throughout the polymerization were studied and discussed. The results showed that, increasing the amounts of solvent reduced the reaction rate and viscosity of the polymerization system. It allowed more activation–deactivation cycles to occur at a given conversion thus better controlled living character and narrower molecular weight distribution of polymers were demonstrated throughout the polymerization. Furthermore, the polymerization carried out in miniemulsion system exhibited higher reaction rate and better controlled living character than those in homogeneous system. It was attributed to the compartmentalization of growing radicals and the enhanced deactivation reaction of DPE controlled radical polymerization in miniemulsified droplets. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4435–4445, 2009     

Poly(ϵ‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ϵ‐caprolactone) triblock copolymers: Synthesis and self‐assembly in aqueous solutions

Nontoxic and biodegradable poly(?‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(?‐caprolactone) triblock copolymers were synthesized by the solution polymerization of ?‐caprolactone in the presence of poly(ethylene glycol). The chemical structure of the resulting triblock copolymer was characterized with ¹H NMR and gel permeation chromatography. In aqueous solutions of the triblock copolymers, the micellization and sol–gel‐transition behaviors were investigated. The experimental results showed that the unimer‐to‐micelle transition did occur. In a sol–gel‐transition phase diagram obtained by the vial‐tilting method, the boundary curve shifted to the left, and the gel regions expanded with the increasing molecular weight of the poly(?‐caprolactone) block. In addition, the hydrodynamic diameters of the micelles were almost independent of the investigated temperature (25–55 °C). The atomic force microscopy results showed that spherical micelles formed at the copolymer concentration of 2.5 × 10^?4 g/mL, whereas necklace‐like and worm‐like shapes were adopted when the concentration was 0.25 g/mL, which was high enough to form a gel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 605–613, 2007     

Donor–acceptor rod–coil block copolymers comprising poly[2,7‐(9,9‐dihexylfluorene)‐alt‐bithiophene] and fullerene as compatibilizers for organic photovoltaic devices

The successful synthesis is described for a donor–acceptor rod–coil block copolymer comprising blocks of poly[2,7‐(9,9‐dihexylfluorene)‐alt‐bithiophene] (F6T2) and polystyrene functionalized with fullerene (PS(C₆₀)) (F6T2‐b‐PS(C₆₀)). This new material was obtained by combining Suzuki polycondensation with radical addition fragmentation chain transfer. The block copolymer was characterized by nuclear magnetic resonance, gel permeation chromatography, and optical spectroscopy methods. Photophysical data for (F6T2‐b‐PS(C₆₀)) and a related block copolymer (F6T2‐b‐PS(PCBM)) (PCBM, phenyl‐C61‐butyric acid methyl ester) are reported and their performance as compatibilizers in bulk heterojunction organic solar cells is assessed. It is demonstrated that the addition of the rod–coil block copolymers to the active layer extends the operational stability of organic photovoltaic devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 888–903     

Preparation and characterization of biodegradable poly(trimethylenecarbonate‐ε‐caprolactone)‐block‐poly(p‐dioxanone) copolymers

A series of poly(trimethylenecarbonate‐ε‐caprolactone)‐block‐poly(p‐dioxanone) copolymers were prepared with varying feed rations by using two step polymerization reactions. Poly(trimethylenecarbonate)(ε‐caprolactone) random copolymer was synthesized with stannous‐2‐ethylhexanoate and followed by adding p‐dioxanone monomer as the other block. The ring opening polymerization was carried out at high temperature and long reaction time to get high molecular weight polymers. The monofilament fibers were obtained using conventional melting spun methods. The copolymers were identified by ¹H and ¹³C NMR spectroscopy and gel permeation chromatography (GPC). The physicochemical properties, such as viscosity, molecular weight, melting point, glass transition temperature, and crystallinity, were studied. The hydrolytic degradation of copolymers was studied in a phosphate buffer solution, pH = 7.2, 37 °C, and a biological absorbable test was performed in rats. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2790–2799, 2005     

Synthesis and characterization of biodegradable A–B–A triblock copolymers containing poly(ϵ‐caprolactone) A blocks and poly(trans‐4‐hydroxy‐L‐proline) B blocks

Novel, biodegradable poly(?‐caprolactone)‐block‐poly(trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline)‐block‐poly(?‐caprolactone) triblock copolymers were synthesized by ring‐opening polymerization from dihydroxyl‐terminated macroinitiator poly(trans‐4‐hydroxy‐N‐benzyloxycarbonyl‐L ‐proline) (PHpr) and ?‐caprolactone (?‐CL) with stannous octoate as the catalyst. The molecular weights were characterized with gel permeation chromatography and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. With an increase in the contents of ?‐CL incorporated into the copolymers, a decrease in the glass‐transition temperature (T_g) was observed. The T_g values of copoly(4‐phenyl‐?‐caprolactone) and copoly(4‐methyl‐?‐caprolactone) were higher than T_g of copoly(?‐caprolactone). Their micellar characteristics in an aqueous phase were investigated with fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The block copolymers formed micelles in the aqueous phase with critical micelle concentrations in the range of 1.00–1.36 mg L^?1. With higher molecular weights and hydrophobic components in the copolymers, a higher critical micelle concentration was observed. As the feed weight ratio of antitriptyline hydrochloride (AM) to the polymer increased, the drug loading increased. The micelles exhibited a spherical shape, and the average size was less than 250 nm. The in vitro hydrolytic degradation and controlled drug release properties of the triblock copolymers were also investigated. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4268–4280, 2006     

Hydrolytic degradation of polyisobutylene and poly‐L‐lactide–based multiblock copolymers

The hydrolytic degradation of a series of poly‐L ‐lactide (PLLA)‐polyisobutylene (PIB) multiblock copolymers was studied in phosphate buffer solution (pH = 7.4) at 37 °C. The multiblock copolymers were synthesized by chain extension of PLLA‐b‐PIB‐b‐PLLA triblock copolymers, which were obtained by ring‐opening polymerization of L ‐lactide initiated by hydroxyallyl telechelic PIB. The degradation strongly depended on the PLLA segment length. At constant PIB segment length, the multiblock copolymer with the shortest PLLA segment length (DPn = 10), showed significant weight loss after 8 weeks, whereas weight loss for DPn = 36 was only observed after 24 weeks. The gel‐permeation chromatographic analysis showed a similar decrease in the number‐average molecular weight (M_n) with time further supporting the weight loss data. Dynamic mechanical analysis showed a decrease in ultimate stress and modulus with time. The crystallinity of multiblock copolymers changed significantly with degradation time as indicated from differential scanning calorimetric analysis. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3767–3774, 2010