Simulation study of the morphologies of energetic block copolymers based on glycidyl azide polymer

The morphologies of energetic block copolymers based on glycidyl azide polymer (GAP) were investigated by dissipative particle dynamics simulation. The results show that the morphologies could be used to qualitatively explain the variation in the mechanical properties of poly(azidomethyl ethylene oxide‐b‐butadiene) diblock copolymers (DBCs) and that bicontinuous (B) phases could effectively improve the mechanical properties. Among our designed DBCs, only GAP–acrylic acid, GAP–acrylonitrile, and GAP–vinyl amide could form B phases at very narrow regions of GAP contents. The triblock copolymers with their linear topologies could maintain the B phases in the broader region of GAP contents. We hope these results can provide help in the design and synthesis of new energetic block copolymers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Bis(azidomethyl) oxetane/hydroxyl‐terminated polybutadiene/bis(azidomethyl) oxetane triblock copolymer: Synthesis and characterization

A copolymer consisting of bis(azidomethyl) oxetane and hydroxyl‐terminated polybutadiene was synthesized with different monomer ratios via an activated monomer mechanism. The copolymer thus obtained was characterized with Fourier transform infrared, ¹H‐NMR, molecular weight, and polydispersity measurements. Rhe‐ological and thermal studies were also carried out. The mechanical properties of the gum stock obtained through curing with toluene diisocyanate and crosslinking with pyrogallol at about 50°C were also determined. This was an attempt to combine the useful properties of hydroxyl‐terminated polybutadiene (a nonenergetic binder providing excellent mechanical properties) and poly[bis(azidomethyl) oxetane] (an energetic binder). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and Characterization of Glycidyl Azide‐r‐(3,3‐bis(azidomethyl)oxetane) Copolymers

Glycidyl azide‐r‐(3,3‐bis(azidomethyl)oxetane) copolymers were synthesized by cationic copolymerization of epichlorohydrin and 3,3‐bis(bromomethyl)oxetane, using butane‐1,4‐diol as an initiator and boron trifluoride etherate as a catalyst, followed by azidation of the halogenated copolymer. The main objective of this work is the preparation of an OH‐terminated amorphous polymer with energetic content higher than that of the well‐known glycidyl azide homopolymer. The effect of experimental conditions, i.e., the rate of monomer feeding, on the final molecular weight and functionality of the copolymer has also been investigated. The obtained copolymers were extensively characterized to determine their composition and thermal stability. The heat of reaction for the polymerization of the halogenated key precursors has also been measured. It was found that even though both the operating conditions and the catalytic system were chosen in order to favor a living character of the polymerization, the final product seems to be the result of a combined living and active chain end mechanism. In particular, the latter is responsible for the formation of oligomers and not hydroxyl‐terminated chains. Nevertheless, the average number of OH groups is high enough to allow a cross‐linking of the polymeric chains, by addition of polyisocyanates and subsequent formation of inter‐chain urethanic bonds.     

Probing the compatibility and interaction of energetic binders based on 3,3‐bis(azidomethyl)oxetane with some explosives: thermal,interfacial and simulation studies

Several polymer binders based on 3,3‐bis(azidomethyl)oxetane (BAMO) were studied to explore the compatibility and interaction of the energetic binders with three common energetic oxidants. The compatibilities were studied by differential scanning calorimetry and ratings were obtained according to evaluated standards. The results showed that all the binders based on BAMO had good compatibility with cyclotrimethylenetrinitramine, cyclotetramethylenetetranitroamine and hexanitrohexazaiso‐wurtzitane. The work of adhesion (W_a) between binders and explosives was tested via measurement of contact angle and the results are in the following order: chain‐extended poly(3,3‐bis(azidomethyl)oxetane) (PBAMO) by isophorone diisocyanate (IPDI‐CE) with diethyl bis(hydroxymethyl) malonate (IPDI‐DBM‐CE) > chain‐extended PBAMO by IPDI‐CE > PBAMO. In addition, similar results were found in the binding energies reported by molecular dynamics, and the average values of E_binding for the IPDI‐DBM‐CE system were larger than E_binding for the other systems due to the formation of hydrogen bonds between –COOEt and –NO₂, which improve the bonding abilities. © 2017 Society of Chemical Industry     

A comparative study of poly(l‐lactide)‐block‐poly(ϵ‐caprolactone) six‐armed star diblock copolymers and polylactide/poly(ϵ‐caprolactone) blends

This paper deals with the synthesis of a series of six‐armed star diblock copolymers based on poly(l ‐lactide) (PLLA) and poly(?‐caprolactone) (PCL) by ring‐opening polymerization using stannous octoate as catalyst and the preparation of polylactide (PLA)/PCL linear blends using a solution blending technique, while keeping the PLA‐to‐PCL ratio comparable in both systems. The thermal, rheological and mechanical properties of the copolymers and the blends were comparatively studied. The melting point and the degree of crystallinity were found to be lower for the copolymers than the blends due to poor folding property of star copolymers. Dynamic rheology revealed that the star polymers have lower elastic modulus, storage modulus and viscosity as compared to the corresponding blends with similar composition. The blends show two‐phase dispersed morphology whereas the copolymers exhibited microphase separated morphology with elongated (worm‐like) microdomains. The crystalline structures of the copolymers were characterized by larger crystallites than their blend counterparts, as estimated using Sherrer's equation based on wide‐angle X‐ray diffraction data. © 2016 Society of Chemical Industry     

3,3‐Bis(azidomethyl)oxetane (BAMO) Synthesis via Pentaerythritol Tosyl Derivates

3,3‐Bis(azidomethyl)oxetane (BAMO) is the most widely known azido oxetane in terms of the number of its polymers and copolymers applied as energetic binders e.g. in rocket propellants and plastic formulations of explosive materials. However, this compound continues to be a rather expensive monomer today. The aim of this study was to find a suitable synthetic route to produce this monomer in a large scale and to optimize it. The chosen route of synthesis was based on the application of tosyl pentaerythritol derivatives as the starting material. The BAMO synthesis by this method involves three stages, namely: pentaerythritol tosylation, tritosylpentaerythritol cyclization to 3,3‐bis(tosylmethyl)oxetane (BTMO), and substitution of the BTMO tosyl groups with azido groups. In this work all the stages of the synthesis were optimized. BAMO was obtained in an overall yield of 61 %. The structure of the obtained compounds was verified by two techniques, namely: ¹HNMR and FT‐IR.     

Characterization of block copolymers based on poly[3,3-bis(ethoxymethyl)oxetane] and other novel polyethers

Diblock, triblock, and alternating block copolymers based on poly[3,3-bis(ethoxymethyl) oxetane] [poly(BEMO)] and a random copolymer center block poly(BMMO-co-THF) composed of poly[3,3-bis(methoxymethyl)oxetane] [poly(BMMO)], and poly(tetrahydrofuran) [poly(THF)] were synthesized and characterized with respect to molecular weight. Glass transition temperatures T_g and melting temperatures T_m were characterized via DSC, modulus–temperature, and dynamic mechanical spectroscopy (DMS). These polyethers had T_m between 70°C and 90°C, and T_g between ?55°C and ?30°C. The degree of crystallinity of poly(BEMO) was found to be 65% by X-ray powder diffraction. Tensile properties of the triblock copolymer, poly(BEMO-block-BMMO-co-THF-block-BEMO) were also studied. A yield point was found at 4.1 × 10⁷ dyn/cm² and 10% elongation and failure at 3.8 × 10⁷ dyn/cm² and 760 % elongation. Morphological features were examined by reflected light microscopy and the kinetics of crystallization were studied. Poly(BEMO) and its block copolymers were found to form spherulites of 2–10 μm in diameter. Crystallization was complete after 2–5 min.     

Nonisothermal crystallization behaviors of biodegradable double crystalline poly(butylene succinate)‐poly(ethylene glycol) multiblock copolymers

Nonisothermal crystallization behaviors of both poly(butylene succinate) (PBS) and poly(ethylene glycol) (PEG) segments within PBS‐PEG (PBSEG) multiblock copolymers were investigated by differential scanning calorimetry (DSC). The nonisothermal crystallization kinetics of both PBS and PEG segments were analyzed by Avrami, Ozawa, and Mo methods. The results showed that both of Avrami and Mo methods were successful to describe the nonisothermal crystallization kinetics of PBS and PEG segments. The results of crystallization kinetics indicated that the crystallization rate of PBS segment decreased with PBS segment content and/or L_PBS, while that of PEG segment decreased with M_n,PEG or F_PEG. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40940.     

Synthesis and characterization of poly(ϵ‐caprolactone)–poly(L‐lactide) diblock copolymers with an organic amino calcium catalyst

The quasiliving characteristics of the ring‐opening polymerization of ?‐caprolactone (CL) catalyzed by an organic amino calcium were demonstrated. Taking advantage of this feature, we synthesized a series of poly(?‐caprolactone) (PCL)–poly(L ‐lactide) (PLA) diblock copolymers with the sequential addition of the monomers CL and L ‐lactide. The block structure was confirmed by ¹H‐NMR, ¹³C‐NMR, and gel permeation chromatography analysis. The crystalline structure of the copolymers was investigated by differential scanning calorimetry and wide‐angle X‐ray diffraction analysis. When the molecular weight of the PLA block was high enough, phase separation took place in the block copolymer to form PCL and PLA domains, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2654–2660, 2006     

Structure of Urethane Copolymers of 3,3‐Bis(azidomethyl)oxetane and 3‐Azidomethyl‐3‐methyloxetane

Polyurethane copolymers of 3,3‐bis (azidomethyl) oxetane (BAMO) and 3‐azidomethyl‐3‐methyloxetane (AMMO) with molecular structures of types B(AB)n, A(AB)n, (BB)n and ABn with different ratios of oligomeric units were investigated, where A is the non‐crystallizable “soft” block of oligoAMMO and B is the “hard” block of oligoBAMO and the included urethane diol fragments. The amorphous‐crystalline structures of copolymers BAMO and AMMO were elucidated by wide angle X‐ray diffraction measurements. The influences of the molecular structure and the ratio of oligomeric units on the structural parameters were identified. The degree of crystallinity is in a range from 8 to 22 % and sizes of the crystallites were determined. The defectivenesses of first and second kind in the structure were evaluated, which show high values of the first kind defectiveness (approx. 20 %), which describes the displacement of theoretical lattice sites and the existence of unequal sizes of the lattice sites, and minor values for the second kind defectiveness (approx. 3 %), which describes the lattice site disorder in large distances. Small‐angle X‐ray diffraction measurements were used to investigate the domain structures of copolymers BAMO and AMMO. The distribution and sizes of the crystallites in the structures of the copolymers were calculated.     

Polyurethanes based on 2,2‐Dinitropropane‐1,3‐diol and 2,2‐bis(azidomethyl)propane‐1,3‐diol as potential energetic binders

On the base of 2,2‐bis(azidomethyl)propane‐1,3‐diol (BAMP) and 2,2‐dinitropropane‐1,3‐diol (DNPD) four different polyurethanes were synthesized in a polyaddition reaction using hexamethylene diisocyanate (HMDI) and diisocyanato ethane (DIE). The obtained prepolymers were mainly characterized using vibrational spectroscopy (IR) and elemental analysis. For determination of low and high temperature behavior, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used. Investigations concerning friction and impact sensitivities were carried out using a BAM drop hammer and friction tester. The energetic properties of the polymers were determined using bomb calorimetric measurements and calculated with the EXPLO5 V6.02 computer code. The obtained values were compared with the glycidyl azide polymer (GAP). The compounds turned out to be insensitive toward friction (>360 N) and less sensitive toward impact (40 J). The good physical stabilities, along with their sufficient thermal stability (170–210 °C) and moderate energetic properties renders these polymers into potential compounds for applications as binders in energetic formul;ations. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43991.     

Amphiphilic diblock copolymers poly(2‐hydroxyethylmethacrylate)‐b‐(N‐phenylmaleimide) and poly(2‐hydroxyethylmethacrylate)‐b‐(styrene) using the macroinitiator poly(HEMA)‐Cl by ATRP: Preparation,characterization, and thermal properties

In recent years, much attention has been given to the development of specialty polymers from useful materials. In this context, amphiphilic block copolymers were prepared by atom transfer radical polymerization (ATRP) of N‐phenylmaleimide (N‐PhMI) or styrene using a poly(2‐hydroxyethylmethacrylate)‐Cl macroinitiator/CuBr/bipyridine initiating system. The macroinitiator P(HEMA)‐Cl was directly prepared in toluene by reverse ATRP using BPO/FeCl₃ 6 H₂O/PPh₃ as initiating system. The microstructure of the block copolymers were characterized using FTIR, ¹H‐NMR, ¹³C‐NMR spectroscopic techniques and scanning electron microscopy (SEM). The thermal behavior was studied by differential scanning calorimetry (DSC), and thermogravimetry (TG). The theoretical number average molecular weight (M_n,th) was calculated from the feed capacity. The microphotographs of the film's surfaces show that the film's top surfaces were generally smooth. The TDT of the block copolymer P(HEMA)₈₀‐b‐P(N‐PhMI)₂₀ and P(HEMA)₉₀‐b‐P(St)₁₀ of about 290°C was also lower than that found for the macroi′nitiator poly(HEMA)‐Cl. The block copolymers exhibited only one T_g before thermal decomposition, which could be attributed to the low molar content of the N‐PhMI or St blocks respectively. This result also indicates that the phase behavior of the copolymers is predominately determined by the HEMA block. The curves reveal that the polymers show phase transition behavior of amorphous polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of novel rod–coil diblock copolymers of poly(methyl methacrylate) and liquid crystalline segments of poly(2,5‐bis[(4‐methoxyphenyl)oxycarbonyl] styrene)

Liquid crystalline diblock copolymers with different molecular weights and low polydispersities were synthesized by atom transfer radical polymerization of methyl methacrylate (MMA) and 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene (MPCS) monomers. The block architecture (coil‐conformation of MMA segment and rigid‐rod of MPCS segment) of the copolymer was experimentally confirmed by a combination of ¹H nuclear magnetic resonance and gel permeation chromatograph techniques. The liquid crystalline behaviour of the copolymer was studied using differential scanning calorimetry and polarized optical microscope. It was found that the liquid crystalline behaviour was dependent on the number average molecular weight of the rigid segment. Only those copolymers with M_n(GPC) of the rigid block above 9200 g mol^?1 could form liquid crystalline phases higher than the glass transition temperature of the rigid block. The random copolymers MPCS‐co‐MMA were also synthesized by conventional free radical polymerization. The molar content of MPCS in MPCS‐co‐MMA had to be higher than 71% to maintain liquid crystalline behaviour. © 2003 Society of Chemical Industry     

Synthesis and characterization of brush copolymers based on methoxy poly(ethylene glycol) and poly(ε‐caprolactone)

Brush copolymers composed of methoxy poly(ethylene glycol) (MPEG) and poly(ε‐caprolactone) (PCL) have been synthesized by the ring‐opening polymerization of ε‐caprolactone initiated by hydroxyl function of thermally esterified MPEG‐citrate in presence of stannous octoate. Citric acid (CA) acts as spacer between brush‐like MPEG and the long chain of PCL. Existence of hydrophobic domains as cores of the micelles were characterized by ¹H NMR spectroscopy and further confirmed with fluorescence technique using pyrene as a probe. Critical micelle concentration (CMC) of the synthesized copolymer decreased from 0.019 to 0.0031 mg/mL on increasing the fraction of PCL. Along with the physicochemical study, the brush copolymers were explored for the preparation of nanoparticles by nanoprecipitation technique. The morphology and geometry of micelles were investigated by using DLS, AFM, and TEM. Hydrodyanamic dimensions of micelles were around 118 and 178 nm with the core size of 8–10 nm, which further aggregated to form secondary micelle of 60–90 nm. Such assembled polymeric micelles with its flexible dendritic MPEG corona could hold a promise for the immobilization (encapsulation) of hydrophobic drugs and subsequently promote sustained release so that it can be a good vehicle for anti‐cancer drug deliverance. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of pH on the hydrolytic degradation of poly(ε‐caprolactone)‐block‐poly(ethylene glycol) copolymers

The in‐vitro hydrolytic behavior of diblock copolymer films consisting of poly(ε‐caprolactone) (PCL) and poly(ethylene glycol) (PEG) was studied at pH 7.4 and pH 9.5 at 37°C. The degradation of these films was characterized at various time intervals by mass loss measurements, GPC, ¹H‐NMR, DSC, FTIR, XRD, and SEM. A faster rate of degradation took place at pH 9.5 than at pH 7.4. Analysis of the molecular weight profile during the course of degradation revealed that random chain scission of the ester bonds in PCL predominates at the initial induction phase of polymer degradation. There was also an insignificant mass loss of the films observed. Mass spectroscopy was used to determine the nature of the water soluble products of degradation. At pH 7.4, a variety of oligomers with different numbers of repeating units were present whereas the harsher degradation conditions at pH 9.5 resulted in the formation of dimers. From the results, it can be proposed that a more complete understanding of the degradation behavior of the PCL‐b‐PEG copolymer can be monitored using a combination of physiological and accelerated hydrolytic degradation conditions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Stereocomplex‐induced gelation properties of polylactide/poly(ethylene glycol) diblock and triblock copolymers

The ring‐opening polymerization of L ‐ or D ‐lactide was realized in the presence of dihydroxyl or monomethoxy poly(ethylene glycol) (PEG) with a number‐average molecular weight of 2000. The resulting low‐molar‐mass poly(L ‐lactide) (PLLA)/PEG and poly(D ‐lactide) (PDLA)/PEG triblock and diblock copolymers were characterized with nuclear magnetic resonance (NMR), differential scanning calorimetry, size‐exclusion chromatography, and X‐ray diffractometric analysis. Bioresorbable hydrogels were successfully prepared from aqueous solutions containing both copolymers because of interactions and stereocomplexation between the PLLA and PDLA blocks. Gelation was evaluated with the tube inverting method and rheological measurements. A phase diagram was realized with gel–sol transitions as a function of concentration. The rheological properties of the hydrogels were investigated under various conditions through changes in the copolymer concentration, temperature, time, and frequency. It was concluded that the hydrogels constituted a dynamic and evolutive system because of the continuous formation/destruction of crosslinks and degradation. Further studies are underway to elucidate the degradation behavior and the potential of these substances as drug carriers or cell culture scaffolds. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study of novel biodegradable thermo‐sensitive hydrogels of methoxy‐poly(ethylene glycol)‐block‐polyester diblock copolymers

A series of biodegradable thermo‐sensitive hydrogels were synthesized by ring‐opening polymerization of methoxy‐poly(ethylene glycol) (mPEG) and various ester monomers, i.e. D ,L ‐lactide, glycolide, β‐propiolactone, δ‐valerolactone and ε‐caprolactone. The copolymers were characterized using ¹H NMR spectroscopy and gel permeation chromatography. The micelle properties were also measured. The results indicated that the diblock copolymers formed nano‐micelles at low concentrations in aqueous phase. The lower critical solution temperatures of the diblock copolymers were above 35 °C at 1 wt%. As the temperature increased above room temperature, the diblock copolymer solutions underwent a sol‐to‐gel phase transition, which was manifested in viscosity increases, indicative of the formation of a gel. The mPEG–polyester diblock copolymer solutions exhibited sol‐gel transition behavior as a function of temperature and polymer concentration. Copyright © 2010 Society of Chemical Industry     

Micellization of pH‐sensitive poly(butadiene)‐block‐poly(2 vinylpyridine)‐block‐poly(ethylene oxide) triblock copolymers: Complex formation with anionic surfactants

The micellization of three tailor‐made triblock copolymers, such as PB₁₀₀–P2VP₁₀₀–PEO₁₀₄, PB₁₈₅–P2VP₁₀₈–PEO₁₅₄, and PB₃₇–P2VP₁₁₅–PEO₂₄₁, having similar total molecular weights and constant poly(2‐vinylpyridine) (P2VP) sequence lengths, was investigated as a function of pH and sodium dodecyl sulfate (SDS) concentration. At pH 7 the formation of intermicellar aggregates was observed, especially for copolymers of low poly(ethylene oxide) (PEO) content. A pH decrease from 7 to 3 leads to a particle size increase due to the electrostatic repulsion of the protonated P2VP chains. The influence of the PEO sequence length was also observed for zeta potential values. At pH 3, in the absence of SDS, core–shell–corona micelles are formed whereas in the presence of small amount of SDS (degree of neutralization DN = 0%–50%), a complex is formed between SDS and the protonated P2VP which leads to the shrinkage of the shell and thus to a decrease of the micellar sizes. For higher DN values, the micellar sizes increase due to the formation of large agglomerates and a transition occurs from a monomodal to a bimodal size distribution. Furthermore, it turned out that secondary aggregation, such as intermicellar aggregation, can completely be avoided if the degree of polymerization (DPn) of the water‐soluble block is significantly higher than the DPn of the water‐insoluble sequence. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45313.     

Synthesis and characterization of diblock,triblock, and multiblock copolymers containing poly(3‐hydroxy butyrate) units

A poly[(R,S)‐3‐hydroxybutyrate] macroinitiator (PHB‐MI) was obtained through the condensation reaction of poly[(R,S)‐3‐hydroxybutyrate] (PHB) oligomers containing dihydroxyl end functionalities with 4,4′‐azobis(4‐cyanopentanoyl chloride). The PHB‐MI obtained in this way had hydroxyl groups at two end of the polymer chain and an internal azo group. The synthesis of ABA‐type PHB‐b‐PMMA block copolymers [where A is poly(methyl methacrylate) (PMMA) and B is PHB] via PHB‐MI was accomplished in two steps. First, multiblock active copolymers with azo groups (PMMA‐PHB‐MI) were prepared through the redox free‐radical polymerization of methyl methacrylate (MMA) with a PHB‐MI/Ce(IV) redox system in aqueous nitric acid at 40°C. Second, PMMA‐PHB‐MI was used in the thermal polymerization of MMA at 60°C to obtain PHB‐b‐PMMA. When styrene (S) was used instead of MMA in the second step, ABCBA‐type PMMA‐b‐PHB‐b‐PS multiblock copolymers [where C is polystyrene (PS)] were obtained. In addition, the direct thermal polymerization of the monomers (MMA or S) via PHB‐MI provided AB‐type diblocks copolymers with MMA and BCB‐type triblock copolymers with S. The macroinitiators and block copolymers were characterized with ultraviolet–visible spectroscopy, nuclear magnetic resonance spectroscopy, gel permeation chromatography, cryoscopic measurements, and thermogravimetric analysis. The increases in the intrinsic viscosity and fractional precipitation confirmed that a block copolymer had been obtained. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1789–1796, 2004     

Synthesis and characterization of poly(L‐lactide‐co‐ϵ‐caprolactone)‐b‐poly(L‐lactide) biodegradable diblock copolyesters: Effect of the block lengths on their thermal properties

Poly(L ‐lactide‐co‐ε‐caprolactone)‐b‐poly(L ‐lactide) [P(LL‐co‐CL)‐b‐PLL] diblock copolyesters were synthesized in a two‐step process with 1‐dodecanol (DDC) and stannous octoate as the initiating system. In the first‐step reaction, a 50:50 mol % amorphous poly(L ‐lactide‐co‐ε‐caprolactone) [P(LL‐co‐CL)] copolyester was synthesized via the bulk copolymerization of L ‐lactide and ε‐caprolactone, which was followed by the polymerization of the PLL crystalline block at the end chain in the second‐step reaction. The yielded copolyesters were characterized with dilute‐solution viscometry, gel permeation chromatography, ¹H‐ and ¹³C‐NMR, and differential scanning calorimetry methods. The molecular weights of the P(LL‐co‐CL) copolyesters from the first‐step reaction were controlled by the DDC concentrations, whereas in the second‐step reaction, the molecular weights of the P(LL‐co‐CL)‐b‐PLL diblock copolyesters depended on the starting P(LL‐co‐CL) copolyester molecular weights and L ‐lactide/prepolymer molar ratios. The starting P(LL‐co‐CL) copolyester molecular weights and PLL block lengths seemed to be the main factors affecting specific thermal properties, including the melting temperature (T_m), heat of melting (ΔH_m), crystallizing temperature (T_c), and heat of crystallizing (ΔH_c), of the final P(LL‐co‐CL)‐b‐PLL diblock copolyester products. T_m, ΔH_m, T_c, and ΔH_c increased when the PLL block lengths increased. However, these thermal properties of the diblock copolyesters also decreased when the P(LL‐co‐CL) block lengths increased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007