Structure‐property relationship of L‐tyrosine‐based polyurethanes for biomaterial applications

The structure‐property relationship of L ‐tyrosine‐based polyurethanes was demonstrated by using different polyols and diisocyanates. L ‐tyrosine‐based chain extender, desaminotyrosyl tyrosine hexyl ester (DTH), was used to synthesize a series of polyurethanes. Polyethylene glycol (PEG) or poly caprolactone diol (PCL) was used as the soft segment and hexamethylene diisocyanate (HDI) or dicyclohexylmethane 4,4′‐diisocyanate (HMDI) was used with DTH as the hard segment. The polyurethanes were characterized to investigate the effect of structure on different polyurethane properties. From FTIR and DSC, these polyurethanes exhibit a wide range of morphology from phase‐mixed to phase‐separated structure. The decreasing molecular weight of the PEG soft segment leads to relatively more phase mixed morphology whereas for PCL‐based polyurethanes the extent of phase mixing is less with decreasing PCL molecular weight. Results show that PCL‐based polyurethanes are mechanically stronger than PEG‐based polyurethanes but PCL‐based polyurethanes degrade slower and absorb less water compared with PEG‐based polyurethanes. The HMDI‐based polyurethanes are less crystalline and comparatively more hydrophobic than HDI‐based polyurethanes. The characterization results show that the polyurethane properties are directly related to the structure and can be varied easily for a different set of properties that are pertinent for biomaterial applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Porous biodegradable polyester blends of poly(L‐lactic acid) and poly(ε‐caprolactone): physical properties,morphology, and biodegradation

Poly(L ‐lactic acid) (PLLA), poly(ε‐caprolactone) (PCL), and their films without or blended with 50 wt% poly(ethylene glycol) (PEG) were prepared by solution casting. Porous films were obtained by water‐extraction of PEG from solution‐cast phase‐separated PLLA‐blend‐PCL‐blend‐PEG films. The effects of PLLA/PCL ratio on the morphology of the porous films and the effects of PLLA/PCL ratio and pores on the physical properties and biodegradability of the films were investigated. The pore size of the blend films decreased with increasing PLLA/PCL ratio. Polymer blending and pore formation gave biodegradable PLLA‐blend‐PCL materials with a wide variety of tensile properties with Young's modulus in the range of 0.07–1.4 GPa and elongation at break in the range 3–380%. Pore formation markedly increased the PLLA crystallinity of porous films, except for low PLLA/PCL ratio. Polymer blending as well as pore formation enhanced the enzymatic degradation of biodegradable polyester blends. Copyright © 2006 Society of Chemical Industry     

Synthesis and properties of novel biodegradable poly(ε‐caprolactone)/ poly(ethylene glycol)‐based polyurethane elastomers

Elastomeric polyurethanes with tunable biodegradation properties and suitable for numerous biomedical applications were synthesized via reaction of epoxy‐terminated polyurethanes (EUPs) with 1,6‐hexamethylenediamine as curing agent. The EUPs themselves were prepared from glycidol and isocyanate‐terminated polyurethanes made from poly(ε‐caprolactone) (PCL) or poly(ethylene glycol) (PEG) and 1,6‐hexamethylene diisocyanate. All the polymers were characterized by conventional methods, and their physical, mechanical, thermal, and degradation properties were studied. The results showed that the degradation rate and mechanical properties of the final products can be controlled by the amount of PEG or PCL present in the EUP. Increasing the PEG content causes an increase of hydrolytic degradation rate, and increasing the PCL content improves the mechanical properties of the final products. Evaluation of cytotoxcicity showed nontoxic behavior of the prepared samples, but the cytocompatibility of these polymers needs to be improved. Copyright © 2006 Society of Chemical Industry     

Characterization of the mechanical and thermal properties and morphological behavior of biodegradable poly(L‐lactide)/poly(ε‐caprolactone) and poly(L‐lactide)/poly(butylene succinate‐co‐L‐lactate) polymeric blends

Two series of biodegradable polymer blends were prepared from combinations of poly(L ‐lactide) (PLLA) with poly(?‐caprolactone) (PCL) and poly(butylene succinate‐co‐L ‐lactate) (PBSL) in proportions of 100/0, 90/10, 80/20, and 70/30 (based on the weight percentage). Their mechanical properties were investigated and related to their morphologies. The thermal properties, Fourier transform infrared spectroscopy, and melt flow index analysis of the binary blends and virgin polymers were then evaluated. The addition of PCL and PBSL to PLLA reduced the tensile strength and Young's modulus, whereas the elongation at break and melt flow index increased. The stress–strain curve showed that the blending of PLLA with ductile PCL and PBSL improved the toughness and increased the thermal stability of the blended polymers. A morphological analysis of the PLLA and the PLLA blends revealed that all the PLLA/PCL and PLLA/PBSL blends were immiscible with the PCL and PBSL phases finely dispersed in the PLLA‐rich phase. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Melt‐processed biodegradable polyester blends of poly(L‐lactic acid) and poly(ε‐caprolactone): Effects of processing conditions on biodegradation

Biodegradable polyester blends were prepared from poly(L ‐lactic acid) (PLLA) and poly(ε‐caprolactone) (PCL) (50/50) by melt‐blending, and the effects of processing conditions (shear rate, time, and strain) of melt‐blending on proteinase‐K‐ and lipase‐catalyzed enzymatic degradability were investigated using gravimetry, differential scanning calorimetry, and scanning electron microscopy. The proteinase‐K‐catalyzed degradation rate of the blend films increased and leveled off with increasing the shear rate, time, or strain for melt‐blending, except for the shortest shear time of 60 s. The optimal processing conditions of melt‐blending giving the maximum rate of lipase‐catalyzed degradation were 9.6 × 10² s^?1 and 180 s, whereas a deviation from these conditions caused a reduction in lipase‐catalyzed enzymatic degradation rate. At the highest shear rate of 2.2 × 10³ s^?1, PCL‐rich phase was continuous in the blend films, irrespective of the shear time (or shear strain), whereas PLLA‐rich phase changed from dispersed to continuous by increasing the shear time (or shear strain). This study revealed that the biodegradability of PLLA/PCL blend materials can be manipulated by altering the processing conditions of melt‐blending (shear rate, time, or strain) or the sizes and morphology of PLLA‐rich and PCL‐rich domains. The method reported in the present study can be utilized for controlling the biodegradability of other biodegradable polyester blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 831–841, 2007     

Strong resistance of poly (ethylene glycol) based L‐tyrosine polyurethanes to protein adsorption and cell adhesion

Biofouling that involves protein adsorption, cell and bacteria adhesion, and biofilm formation between a surface and biological entities is a great challenge for biomedical and industry applications. In this work, L ‐tyrosine‐derived polyurethanes (L ‐polyurethane) with different molecular weights of poly(ethylene glycol) (PEG) were synthesized, characterized and coated on gold surfaces using spin‐coating. The non‐fouling activity of different L ‐polyurethane films was evaluated by protein adsorption and cell adhesion. Surface plasmon resonance and cell assay results demonstrate that the PEG content in these L ‐polyurethanes contributes excellent resistance to protein adsorption and cell attachments. This work provides alternative and effective biomaterials for potential applications in blood‐contacting devices. Copyright © 2011 Society of Chemical Industry     

Enzymatic degradation of blends of poly(ε‐caprolactone) and poly(styrene‐co‐acrylonitrile) by Pseudomonas lipase

In polymer blends, the composition and microcrystalline structure of the blend near surfaces can be markedly different from the bulk properties. In this study, the enzymatic degradation of poly(ε‐caprolactone) (PCL) and its blends with poly(styrene‐co‐acrylonitrile) (SAN) was conducted in a phosphate buffer solution containing Pseudomonas lipase, and the degradation behavior was correlated with the surface properties and crystalline microstructure of the blends. The enzymatic degradation preferentially took place at the amorphous part of PCL film. The melt‐quenched PCL film with low crystallinity and small lamellar thickness showed a higher degradation rate compared with isothermally crystallized (at 36, 40, and 44°C) PCL films. Also, there was a vast difference in the enzymatic degradation behavior of pure PCL and PCL/SAN blends. The pure PCL showed 100% weight loss in a very short time (i.e., 72 h), whereas the PCL/SAN blend containing just 1% SAN showed ～50% weight loss and the degradation ceased, and the blend containing 40% SAN showed almost no weight loss. These results suggest that as degradation proceeds, the nondegradable SAN content increases at the surface of PCL/SAN films and prevents the lipase from attacking the biodegradable PCL chains. This phenomenon was observed even for a very high PCL content in the blend samples. In the blend with low PCL content, the inaccessibility of the amorphous interphase with high SAN content prevented the attack of lipase on the lamellae of PCL. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 868–879, 2002     

Synthesis,characterization, and degradation of a novel L‐tyrosine‐derived polycarbonate for potential biomaterial applications

A novel class of pseudo‐poly(amino acid)s was synthesized with a cyclic dipeptide as new diphenole. Nonpeptide bonds alternating with a peptide bond structure were introduced into the backbone of the pseudo‐poly(amino acid)s. The cyclic dipeptide in this study was obtained from natural L ‐tyrosine. L ‐Tyrosine is a major nutrient amino acid with a phenolic hydroxyl group, so a polycarbonate derived from the cyclic dipeptide should possess more optimum mechanical properties, bioactivity, and biocompatibility. The hydrolytic specimen of the resulting polycarbonate was prepared by a modified solvent evaporation process. Under strongly alkaline conditions, degradation testing was performed. The tyrosine‐derived polycarbonate possessed a low glass‐transition temperature value and a high thermal decomposition temperature value, which formed a broad mean thermal processing range. The most important results of our study were the effects of the polycarbonate degradation on the local pH values, which were smaller than those of other biodegradable polymers [e.g., poly(lactic acid), poly(glycolic acid), and poly(lactic glycolic acid)]. The synthesized polymer and cyclic dipeptide were characterized with Fourier transform infrared, ¹³C‐NMR, and ¹H‐NMR spectroscopy to determine their chemical structures; by differential scanning calorimetry and thermogravimetric analysis to determine the thermal properties of the polymer; by gel permeation chromatography to determine the polymer's molecular weight; and by X‐ray diffraction to determine the polymer's morphology. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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     

Synthesis,characterization, and hydrolytic degradation of biodegradable poly(ether ester)‐urethane copolymers based on ε‐caprolactone and poly(ethylene glycol)

In this article, a new kind of biodegradable poly(ε‐caprolactone)‐poly(ethylene glycol)‐poly(ε‐caprolactone)‐based polyurethane (PCEC‐U) copolymers were successfully synthesized by melt‐polycondensation method from ε‐caprolactone (ε‐CL), poly(ethylene glycol) (PEG), 1,4‐butanediol (BD), and isophorone diisocyanate (IPDI). The obtained copolymers were characterized by ¹H‐nuclear magnetic resonance (¹H‐NMR), FTIR, and gel permeation chromatography (GPC). Thermal properties of PCEC‐U copolymers were studied by DSC and TGA/DTG under nitrogen atmosphere. Water absorption and hydrolytic degradation behavior of these copolymers were also investigated. Hydrolytic degradation behavior was studied by weight loss method. ¹H‐NMR and GPC were also used to characterize the hydrolytic degradation behavior of PCEC‐U copolymers. The molecular weight of PCL block and PEG block in soft segment and the content of hard segment strongly affected the water absorption and hydrolytic degradation behavior of PCEC‐U copolymers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Comparison of the degradation of polycaprolactone and polycaprolactone–(β‐tricalcium phosphate) scaffolds in alkaline medium

The design and fabrication of scaffolds and biodegradable devices using slow‐degrading polymers and composites (degradation/resorption > 2 years) involve the necessity for long‐term in vitro and in vivo studies. If multiple designs and materials need to be tested, then this would use much time and financial resources. Accelerated degradation systems aim to achieve comparable degradation profiles within a shorter period of time. This investigation considers the hydrolytic degradation of polycaprolactone (PCL) and PCL–calcium phosphate (CaP) scaffolds in 5 mol L^?1 NaOH at 37 °C. The scaffolds degrade via surface erosion, which proceeds in a consistent and predictable manner. The hydrolytic degradation of PCL‐based scaffolds alone is slow, governed by their high molecular weights, crystallinity, hydrophobicity, surface‐to‐volume ratio and porosity. The incorporation of CaP significantly increases the degradation rate. Copyright © 2007 Society of Chemical Industry     

Largely improved tensile extensibility of poly(L‐lactic acid) by adding poly(ε‐caprolactone)

Poly(L ‐lactic acid) (PLLA) has good biocompatibility, biodegradability and physical properties. However, one of the drawbacks of PLLA is its brittleness due to the stiff backbone chain. In this work, a largely improved tensile toughness (extensibility) of PLLA was achieved by blending it with poly(ε‐caprolactone) (PCL). To obtain a good dispersion of PCL in the PLLA matrix, blends were prepared via a solution‐coagulation method. An increase in extensibility of PLLA of more than 20 times was observed on adding only 10 wt% of PCL, accompanied by a slight decrease in tensile strength. However, annealing of the samples led to a sharp decrease of extensibility due to phase separation and a change of crystalline structure. To conserve the good mechanical properties of PLLA/PCL blends, the blends were crosslinked via addition of dicumyl peroxide during the preparation process. For the crosslinked blend films, the extensibility was maintained nearly at the original high value even after annealing. Morphological analysis of cryo‐fractured and etched‐smoothed surfaces of the PLLA/PCL blends was carried out using scanning electron microscopy. Differential scanning calorimetry and polarized light microscopy experiments were used to check the possible change of crystallinity, melting point and crystal morphology for both PLLA and PCL after annealing. The results indicated that the combination of solution‐coagulation and crosslinking resulted in a good and stable dispersion of PCL in the PLLA matrix, which is considered as the main reason for the observed improvement of tensile toughness. Copyright © 2010 Society of Chemical Industry     

Synthesis and characterization of biodegradable polyurethanes based on L‐cystine/cysteine and poly(ϵ‐caprolactone)

Tunable biodegradable polyurethanes (PUs) with favorable mechanical properties were synthesized from 1,6‐hexamelthylene diisocyanate (HDI) as the hard segment, poly(?‐caprolactone) (PCL) as the soft segment, and L ‐cystine ester as chain extender. The structure of PUs was confirmed by FTIR and ¹H‐NMR. The results of differential scanning calorimeter, thermogravimetric analysis, dynamic mechanical analysis, and tensile test revealed that the thermal and mechanical properties of PUs were strongly influenced by the molecular weight of soft segment PCL. In the presence of glutathione, the disulfide group cleaved into thiols, realizing the PUs degraded and the molecular weight decreased. For PU [550], it remained only 50% of the original M_w. Evaluation of cell viability demonstrated the nontoxicity of the PUs, which facilitated their potential in biomedical applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Novel biodegradable amphiphilic poly(ε‐caprolactone)/poly(N‐vinylpyrrolidone) blends via successive in situ polymerizations

In this study, biodegradable blends of poly(ε‐caprolactone) (PCL) and poly(N‐vinylpyrrolidone) (PVP) were prepared by a new strategy in the following steps: (1) free radical polymerization of N‐vinyl‐2‐pyrrolidone (NVP) in ε‐caprolactone (CL); (2) ring‐opening polymerization of ε‐caprolactone in the presence of PVP to obtain the target blends. The structure of the blends was confirmed by FTIR and ¹H NMR, and the molecular weight of PCL and PVP were determined by GPC. SEM study revealed that this polymerization method could decrease the disperse phase size and improve the interphase when compared with solution‐blending method. The phase inversion occurred when PVP content was 15–20 wt %. Subsequently, the PCL sphere dispersed in PVP matrix and its size decreased with the increase of PVP content. The contact angle results showed that PVP has a profound effect on hydrophilic properties of PCL/PVP blends. PCL/PVP blends are believed to be promising for drug delivery, cell therapy, and other biomedical applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hydrolytic degradation and crystallization behavior of linear 2‐armed and star‐shaped 4‐armed poly(l‐lactide)s: Effects of branching architecture and crystallinity

“Linear” aliphatic polyesters composed of two poly(l ‐lactide) arms attached to 1,3‐propanediol and “star‐shaped” ones composed of four poly(l ‐lactide) arms attached to pentaerythritol (2‐L and 4‐L polymers, respectively) with number‐average molecular weight (M_n) = 1.4–8.4 × 10⁴g/mol were hydrolytically degraded at 37°C and pH = 7.4. The effects of the branching architecture and crystallinity on the hydrolytic degradation and crystalline morphology change were investigated. The degradation mechanism of initially amorphous and crystallized 2‐L polymers changed from bulk degradation to surface degradation with decreasing initial M_n; in contrast, initially crystallized higher molecular weight 4‐L polymer degraded via bulk degradation, while the degradation mechanism of other 4‐L polymers could not be determined. The hydrolytic‐degradation rates monitored by molecular‐weight decreases decreased significantly with increasing branch architecture and/or higher number of hydroxyl groups per unit mass. The hydrolytic degradation rate determined from the molecular weight decrease was higher for initially crystallized samples than for initially amorphous samples; however, that of 2‐L polymers monitored by weight loss was larger for initially amorphous samples than for initially crystallized samples. Initially amorphous 2‐L polymers with an M_n below 3.5 × 10⁴g/mol crystallized during hydrolytic degradation. In contrast, the branching architecture disturbed crystallization of initially amorphous 4‐L polymers during hydrolytic degradation. All initially crystallized 2‐L and 4‐L polymers had δ‐form crystallites before hydrolytic degradation, which did not change during hydrolytic degradation. During hydrolytic degradation, the glass transition temperatures of initially amorphous and crystallized 2‐L and 4‐L polymers and the cold crystallization temperatures of initially amorphous 2‐L and 4‐L polymers showed similar changes to those reported for 1‐armed poly(l ‐lactide). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41983.     

Miscibility,morphology and thermal properties of poly(para‐dioxanone)/poly(D,L‐lactide) blends

BACKGROUND: Poly(para‐dioxanone) (PPDO) is a biodegradable polyester with excellent biodegradability, bioabsorbability, biocompatibility and mechanical flexibility. However, its high cost and relatively fast degradation rate have hindered the development of commercial applications. Blending with other polymers is a simple and convenient way of modifying the properties of aliphatic polyesters. Poly(D ,L ‐lactide) (PDLLA) is another polyester that has been extensively studied for biomedical applications due to its biocompatibility and suitable degradation rate. However, to our knowledge, blends of PPDO/PDLLA have not been reported in the literature. RESULTS: A series of biodegradable polymers were blended by solution co‐precipitation of PPDO and PDLLA in various blend ratios. The miscibility, morphology and thermal properties of the materials were investigated. DSC curves for all blends revealed two discrete glass transition temperatures which matched the values for pure PPDO and PDLLA. SEM images of fracture surfaces displayed evidence of phase separation consistent with the DSC results. The contact angles increased with the addition of PDLLA. CONCLUSION: PPDO/PDLLA blends exhibit two distinct glass transition temperatures that remain nearly constant and correspond to the glass transition temperatures of the homopolymers for all blend compositions, indicating that blends of PPDO and PDLLA are immiscible. Images of the surface obtained using SEM were also suggestive of a two‐phase material. The crystallinity of the PPDO phase in the blends was affected by the PDLLA content. The mechanical properties of the blends changed dramatically with composition. Adding PDLLA makes the blends less hydrophilic than PPDO. Copyright © 2008 Society of Chemical Industry     

Thermosensitive PCL‐PEG‐PCL hydrogels: Synthesis,characterization, and delivery of proteins

In this work, a biodegradable and injectable in situ gel‐forming controlled drug delivery system based on thermosensitive poly(ε‐caprolactone)‐poly(ethylene glycol)‐poly(ε‐caprolactone) (PCL‐PEG‐PCL) hydrogels was studied. A series of PCL‐PEG‐PCL triblock copolymers were synthesized and characterized by ¹H‐NMR and gel permeation chromatography (GPC). Thermosensitivity of the PCL‐PEG‐PCL triblock copolymers was tested using the tube inversion method. The in vitro release behaviors of two model proteins, including bovine serum albumin (BSA) and horseradish peroxidase (HRP), from PCL‐PEG‐PCL hydrogels were studied in detail. The in vivo gel formation and degradation of the PCL‐PEG‐PCL triblock copolymers were also investigated in this study. The results showed that aqueous solutions of the synthesized PCL‐PEG‐PCL copolymers can form in situ gel rapidly after injection under physiological conditions. The PCL‐PEG‐PCL hydrogels showed the ability to control the release of incorporated BSA and HRP. The released HRP was confirmed to conserve its biological activity by specific enzymatic activity assay. The in vivo gel formation and degradation studies indicated that PCL‐PEG‐PCL copolymers hydrogels can sustain at least 45 days by subcutaneous injection. Therefore, owing to great thermosensitivity and biodegradability of these copolymers, PCL‐PEG‐PCL copolymers hydrogels show promise as an in situ gel‐forming controlled drug delivery system for therapeutic proteins. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Phosphorylcholine end‐capped poly‐ε‐caprolactone: A novel biodegradable material with improved antiadsorption property

In this study, the synthesis, characterization, and properties of a novel biodegradable polymer with improved hemocompatibility were introduced. It was synthesized by end‐capping poly‐ε‐caprolactone (PCL) with phosphorylcholine (PC) groups. The polyester backbone provided the mechanical stability and biodegradability, while the PC‐end groups improved its hemocompatibility. The obtained polymer was characterized using ¹H NMR, ³¹P NMR, FTIR, and GPC, its crystallization behavior was studied by DSC. Compared with original PCL, the resulting polymer (PC‐PCL) showed a lower crystallization capability and a faster degradation rate in PBS. The degradation rate of the polymer blends of PCL/PC‐PCL increased with increasing PC‐PCL content. The results of water contact angle measurements revealed a more hydrophilic surface property of PC‐PCL than neat PCL. The hemocompatibility of PC‐PCL was estimated using rabbit platelet‐rich plasma, a better resistance to platelet adhesion and activation was observed. During the human blood plasma contacting process, PC‐PCL showed a prolonged activated partial thromboplastin time over neat PCL. Material–cell interaction was evaluated with human umbilical vein endothelial cell, the result indicated that PC‐PCL may to some extent have an antihyperplasia property, compared with neat PCL. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 989–997, 2007     

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     

Miscibility of block copolymers of poly(ε‐caprolactone) and poly(ethylene glycol) with poly(3‐hydroxybutyrate) as well as the compatibilizing effect of these copolymers in blends of poly(ε‐caprolactone) and poly(3‐hydroxybutyrate)

Atactic poly(3‐hydroxybutyrate) (a‐PHB) and block copolymers of poly(ethylene glycol) (PEG) with poly(ε‐caprolactone) (PCL‐b‐PEG) were synthesized through anionic polymerization and coordination polymerization, respectively. As demonstrated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) measurements, both chemosynthesized a‐PHB and biosynthesized isotactic PHB (i‐PHB) are miscible with the PEG segment phase of PCL‐b‐PEGs. However, there is no evidence showing miscibility between both PHBs and the PCL segment phase of the copolymer even though PCL has been block‐copolymerized with PEG. Based on these results, PCL‐b‐PEG was added, as a compatibilizer, to both the PCL/a‐PHB blends and the PCL i‐PHB blends. The blend films were obtained through the evaporation of chloroform solutions of mixed components. Excitingly, the improvement in mechanical properties of PCL/PHB blends was achieved as anticipated initially upon the addition of PCL‐b‐PEG. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2600–2608, 2001