Thermogravimetric investigation of two classes of block copolymers based on poly(lactic-glycolic acid) and poly(ɛ-caprolactone) or poly(ethylene glycol) (original) (raw)

Thermogravimetric investigation of two classes of block copolymers based on poly(lactic-glycolic acid) and poly(ε-caprolactone) or poly(ethylene glycol)

Polymer Degradation and Stability, 2001

The thermogravimetric analysis (TGA) of two classes of multi-block copolymers based on poly(d,l-lactic-glycolic acid) (PLGA) and diol-terminated poly(e-caprolactone) (PCDT) or poly(ethylene glycol) (PEG) segments is reported. These materials, having the structure of poly(ester-carbonate)s, were synthesized by a chain extension reaction. The influence of the length of PCDT or PEG segments and of the molar ratio of d,l-lactic acid (LA) and glycolic acid (GA) residues on thermal stability in air and nitrogen atmosphere has been investigated. For comparison purposes the degradation behaviour of starting oligomers was also studied. TGA under nitrogen shows two degradation processes that can be ascribed to the PLGA and PCDT or PEG segments, respectively. In addition, the thermal stability increases with the LA content in the PLGA blocks. In the tests run under air two degradation steps have also been observed, though the former occurs in general at higher temperatures. #

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

Journal of Applied Polymer Science, 2007

were synthesized in a two-step process with 1-dodecanol (DDC) and stannous octoate as the initiating system. In the firststep reaction, a 50:50 mol % amorphous poly(L-lactide-co-ecaprolactone) [P(LL-co-CL)] copolyester was synthesized via the bulk copolymerization of L-lactide and e-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, 1 H-and 13 C-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 (DH m ), crystallizing temperature (T c ), and heat of crystallizing (DH c ), of the final P(LL-co-CL)-b-PLL diblock copolyester products. T m , DH m , T c , and DH 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.

Effect of composition and synthetic route on the microstructure of biodegradable diblock copolymer, poly(ε-caprolactone-co-L-lactide)-b-poly(ethylene glycol)

Macromolecular Research, 2008

Biodegradable poly(ε-caprolactone-co-L-lactide)-b-poly(ethylene glycol) (PCLA-b-PEG) copolymers were synthesized via solution polymerization by varying the feed composition of ε-caprolactone (ε-CL) and L-lactide (LLA) (ε-CL: LLA=10:0, 7:3, 5:5, 3:7, 0:10). The feed ratio based on weight is in accordance with the copolymer composition except for the case of ε-CL: LLA=3:7 (C3L7), which was verified by 1 H-NMR. Two different approaches were used for the exceptional case, which is an extension of the reaction time or the sequential introduction of the monomer. A copolymer composition of ε-CL: LLA=3:7 could be obtained in either case. The chemical microstructure of PCLA-b-PEG was determined using the 1 3 C-NMR spectra and the effect of the sequential structure on the thermal properties and crystallinity were examined. Despite the same composition ratio of the copolymer, the microstructure can differ according to the reaction conditions.

Diblock Poly (ester)-Poly (ester-ether) Copolymers: I–Synthesis, Thermal Properties and Degradation Kinetics

Industrial & Engineering …

The synthesis and characterization of polycaprolactone (PCL) and poly(dioxanone-methyl dioxanone) (P(DX-co-MeDX)) block copolymers in a range of compositions of the two segments and with varying methyl dioxanone units is herein reported. The thermal properties of the copolymers were studied by differential scanning calorimetry (DSC) which revealed that copolymers exhibited two melting transitions ranging between 48 and 53°C for the PCL segment and 71−79°C for the P(DXco-MeDX) segment. Copolymers exhibited only one crystallization exotherm which decreased as the MeDX content of the copolymer increased, thereby increasing miscibility of PCL and P(DX-co-MeDX) segments, a result also confirmed by scanning electron micrographs (SEM). Lastly, the kinetics of thermal degradation of PCL-b-P(DX-co-MeDX) copolymers were investigated by thermogravimetric analysis (TGA). Thermal degradation was shown to proceed in three distinct steps with the P(DX-co-MeDX) segment degrading in the first stage followed by the PCL segment in the last two stages most likely via unzipping and random polymerization mechanisms. The activation energies of copolymer degradation were determined and were found to decrease with increasing MeDX content of the copolymer. Overall, increasing MeDX content influenced both thermal properties and degradation kinetics through phase mixing of segments in the copolymers.

Synthesis and properties of novel block copolymers containing poly(lactic-glycolic acid) and poly(ethyleneglycol) segments

Biomaterials, 1995

A synthetic process for obtaining high-molecular-weight block copolymers containing poly(lacticglycolic acid) and poly(ethylene glycol) segments has been established. This process involves the reaction of poly(ethylene glycols) with phosgene, followed by polycondensation of the resulting u,obis(chloroformates) with poly(lactic-glycolic acid) oligomers. The copolymers have been characterized for their molecular weight, solubility properties, water absorption and preliminarily thermal behaviour. All evidence points to the conclusion that the process described is a general one, enabling biodegradable polymers to be obtained tailor-made according to specific requirements.

Preparation of poly(ethylene glycol)-block-poly(caprolactone) copolymers and their applications as thermo-sensitive materials

Journal of Biomedical Materials Research, 2004

The polymerization of ⑀-caprolactone (⑀-CL) was initiated by the terminal alcohol of methoxy poly(ethylene glycol) (MPEG) as an initiator via activated ring-opening polymerization in the presence of HCl ⅐ Et 2 O as a monomer activator. The molecular weights of the poly(⑀-caprolactone) (PCL) in MPEG-PCL diblock copolymers controlled with the feed ratio of ⑀-CL to MPEG. The polymerization was preceded by living fashion with no termination or chain transfer. This polymerization procedure offered MPEG-PCL diblock copolymers with well-defined structures. The gelto-sol transitions of MPEG-PCL diblock copolymer solutions were also examined. The diblock copolymers synthesized with various MPEG and PCL lengths were dissolved in water at 80°C in various concentrations. The polymer solutions formed gel at room temperature. The formed gel became fluids again by increasing the temperature. The gel-to-sol transition showed strong dependence on the length of the MPEG and PCL diblock segments. When the polymer solution was injected into rat, it became a gel at body temperature. The formed gel maintained for 1 month. We confirmed that MPEG-PCL diblock copolymers with well-defined structures served as new thermo-sensitive biomaterials.

Changes in chemical and thermal properties of the tri-block copolymer poly( l -lactide- b -1,5-dioxepan-2-one- b - l -lactide) during hydrolytic degradation

Polymer, 2000

Hydrolysis of the novel tri-block copolymer poly(l-lactide-b-1,5-dioxepan-2-one-b-l-lactide) of different compositions has been studied in buffered salt solution at 37ЊC and pH 7.4. Specifically, polymer weight loss, composition changes, molecular weight changes, thermal properties and release of lactic acid and 3-(2-hydroxyethyl)-propanoic acid have been detected. The degradation was found to start immediately after the sample was immersed into the aqueous buffer solution. The rate of degradation was influenced only by the original molecular weight, the copolymer composition had no significant effect. The heat of fusion and T g increased with degradation time due to an increased amount of l-lactide (l-LA) in the polymer matrix. The GC-MS analysis showed that up to 70% of the theoretical amount of 3-(2hydroxyethyl)-propanoic acid and 10-20% of lactic acid was released after 23 weeks of degradation.

Thermal degradation behavior of a carboxylic acid-terminated amphiphilic block copolymer poly(ethylene)-b-poly(ethylene oxide

Journal of Thermal Analysis and Calorimetry, 2011

The thermal degradation of an amphiphilic block copolymer poly(ethylene)-b-poly(ethylene oxide)-carboxylic acid terminated (PE-b-80%PEO–CH2COOH) and its salt obtained as intermediary product from chemical oxidation of the end group of poly(ethylene)-b-poly(ethylene oxide) (PE-b-80%PEO) has been studied using a thermogravimetric mass spectrometry (TG/MS) coupled system. The isothermal fragmentation of PE-b-80%PEO–CH2COOH showed a more complex fragmentation pattern than PE-b-80%PEO owing to the simultaneous occurrence of the polyether block and the carboxylic end group fragmentations. This led to the appearance of four overlapping ion current peaks of fragments with m/z 44 and two peaks relative to m/z 18 at different times by acid-terminated copolymer. For the PE-b-80%PEO copolymer, two ion current peaks associated to m/z 44 and one large peak relative to m/z 18 fragments were detected. The intermediary product (PE-b-80%PEO–CH2COO− K+) showed differences related to the fragmentation behavior. It has more defined ion current signals and presented characteristic peaks attributed to m/z 43 fragment at the very beginning of the thermal degradation process, which it not detected in the acid copolymer.

Characterization of the thermo- and pH-responsive assembly of triblock copolymers based on poly(ethylene glycol) and functionalized poly(ε-caprolactone)

Acta Biomaterialia, 2011

A series of novel triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(e-caprolactone)bearing benzyl carboxylate on the a-carbon of e-caprolatone were synthesized through ring opening polymerization of a-benzyl carboxylate-e-caprolactone by dihydroxylated PEG. The debenzylation of the synthesized copolymer, i.e., poly(a-benzyl carboxylate-e-caprolactone)-b-PEG-b-poly(a-benzyl-carboxylate-e-caprolactone) (PBCL-b-PEG-b-PBCL), in the presence of hydrogen gas using different levels of catalyst, was carried out to achieve copolymers with various degrees of free a-carboxyl to a-benzyle-carboxylate groups on the hydrophobic block. Incomplete reduction of PBCL led to the formation of poly(a-carboxyl-co-benzyl caboxylate-e-caprolactone) PCBCL in the lateral blocks at 27%, 50% and 75% carboxyl group substitution. The molecular weight and polydispersity of the resultant copolymers were estimated by 1 H NMR and MALDI-TOF. Synthesized triblock copolymers formed stable micelles at low concentrations (critical micellar concentrations (CMC) of 0.34-12.5 lg ml À1 ). Polymers containing carboxyl groups in their structure showed a pH-dependent increase in CMC. As the pH was raised from 4.0 to 9.0, CMC increased from 0.76 to 1.06 lg ml À1 , for 27% debenzylated polymer, and from 1.30 to 2.20 lg ml À1 , for 50% debenzylated polymers. In contrast, the CMC in polymers without carboxyl group was independent of pH (0.55 lg ml À1 ). Different changes in micellar size as a function of temperature was observed depending on the degree of debenzylation on the PCBCL block: polymers with 27% degree of debenzylation illustrated a rise in micelle size from 38to55nmasthetemperatureincreasedabove29°C,whilepolymerswith5038 to 55 nm as the temperature increased above 29°C, while polymers with 50% debenzylation showed a decrease in micelle size, from 38to55nmasthetemperatureincreasedabove29°C,whilepolymerswith5052 to 38 nm, with increase in temperature. A similar trend was observed at pH 4.5, 7.0 and 9.0 for polymers containing carboxyl groups on their hydrophobic block. The temperature for the onset of size change and/or the extent of aggregate size change was found to be dependent on the pH of the medium and the polymer concentration. The results point to a potential for the formation of thermo-and pH-responsive micelles from triblock copolymers of PEG and carboxyl substituted caprolactone. The results also imply a potential for the 27% debenzylated PCBCL-b-PEG-b-PCBCL copolymers to form a biodegradable thermoreversible gel with a transition temperature a few degrees below 37°C.

ABA triblock copolymers of poly(N-isopropylacrylamide-co-5,6-benzo-2-methylene -1,3-dioxepane) (A) and poly(ethylene glycol) (B): synthesis and thermogelation and degradation properties in aqueous solutions

Colloid and Polymer Science, 2016

Novel hydrolytically degradable thermosensitive triblock copolymers with poly(ethylene glycol) (PEG) m i d d l e-c h a i n a n d r a n d o m c o p o l y m e r s o f Nisopropylacrylamide and 5,6-benzo-2-methylene-1,3dioxepane as side blocks were synthesized by the reversible addition-fragmentation chain transfer (RAFT) copolymerization of the two monomers in the presence of the bisester of [S-1-dodecyl-S′-(α,α′-dimethyl-α″-acetic acid)] trithiocarbonate and α,ω-dihydroxy PEG of 10,000 Da molecular weight as the RAFT macroagent. The polymers prepared were structurally characterized by gel permeation chromatography (GPC), 10 wt% PBS solution, as proved by both GPC and 1 H NMR measurements. Under these conditions, the gel completely dissolved and lost its thermogelation ability up to 60°C in less than 24 days.