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Characterization of Biodegradable          Poly(3-hydroxybutyrate-co-         butyleneadipate) Copolymers     Obtained fro...
IntroductionNot biodegradable     plastics Biodegradable    plastics
Polyhydroxyalkanoates (PHA)            R                       O                                   Poly(3-hydroxyalkanoate...
Physical and chemical properties.•   Average molecular weight ranging between 5·104 and1·106 Da•   Enantiomerically pure• ...
PHAs in medicine and pharmaceuticals.      Sutures.              Bone graft substitutes.Temporary heart valves.    Carrier...
Role of PHAs in tissue engineering.
Poly(alkylene dicarboxylate)sAliphatic polyesters , semi-crystalline polymers with a wide variety ofphysical, mechanical p...
Synthesis of new P(HB-co-BA) copolymers via the acidcatalyzed transesterification of PHB and PBA in solution.             ...
What are the microwavesThe microwaves are not ionizing electromagnetic waves having a wavelengthbetween 1 mm (ν = 300 GHz)...
Design For Efficient Energy: Energy requirements should berecognized for their environmental and economic impacts andshoul...
Table 1: Reaction time, composition, yield, molecular weight,sequence length and randomness of P(HB-co-BA) copolyestersobt...
Table 2: Reaction time, composition, yield, molecular weight,sequence length and randomness of P(HB-co-BA) copolyestersobt...
Table 3: Reaction time, composition, yield, molecular weight,sequence length and randomness of P(HB-co-BA) copolyestersobt...
a                   a                   CH     O                             O                       O                    ...
i                 a                 CH                                                                                    ...
HB-A-B                               B-A-B                                                                                ...
As in all the 13C-NMR spectra the triad signals were only partially resolved, we basedour sequence analysis on dyads inten...
Differential scanning calorimetry (DSC)• Performed on PHB and PBA homopolymers and on selected HB-BA  copolymers, namely t...
Differential scanning calorimetry (DSC)Fig. 4: DSC heating curves (20°C/min) of the P(HB-co-BA) copolyesters (Samples B1-B...
MALDI-TOF MS I%                                                  xyz= (HBx-By-Az)Na+           ‡ x-2-2 (x = 2-6)100      ‡...
2-6-6                                                                                                                     ...
Conclusion• By microwave assisted transesterification              were obtained new  biodegradable and biocompatible copo...
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Characterization of biodegradable poly(3 hydroxybutyrate-co-butyleneadipate) copolymers obtained from their homopolymers by microwave-assisted transesterification.

Copolymers containing (R)-3 hydroxybutyric acid (HB), 1,4-butanediol (B), and adipic acid (A) were synthesized by microwave assisted transesterification of biodegradable poly(R-3-hydroxybutyrate) (PHB) and poly(1,4-butyleneadipate) (PBA) in solution at different reaction times, composition of the starting mixture, and amount of 4-toluenesulfonic acid, used as a catalyst. The copolyesters were characterized with regard to their molecular weights, thermal properties, molar composition, and average block length of repeating units by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXS), 1H-NMR, and 13C-NMR, respectively. Random and microblock copolymers could be obtained depending on experimental conditions, with weight-average molecular weight of up to 17000. The glass transition temperature (Tg) of all samples lay in the range between the Tgs of PBA and PHB, while their structure varied from partially crystalline to totally amorphous. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra of copolymers allowed us to ascertain that they were hydroxyl and carboxyl chain-end terminated.

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Characterization of biodegradable poly(3 hydroxybutyrate-co-butyleneadipate) copolymers obtained from their homopolymers by microwave-assisted transesterification.

  1. 1. Characterization of Biodegradable Poly(3-hydroxybutyrate-co- butyleneadipate) Copolymers Obtained from Their Homopolymers by Microwave-assisted TransesterificationGiuseppe Impallomenia, Giovanni Marco Carnemollab, Giuseppe Puzzob,Alberto Ballistrerib*, Lucrezia Martinoc, Mariastella Scandolac. a Istituto di Chimica e Tecnologia dei Polimeri, Consiglio Nazionale delle Ricerche, Via P. Gaifami 18, 95126 Catania, Italy. b Dipartimento di Scienze del Farmaco, Università di Catania, Viale A. Doria 6, 95125 Catania, Italy. c Dipartimento di Chimica “G. Ciamician”, Università di Bologna, Via Selmi 2, 40126 Bologna, Italy
  2. 2. IntroductionNot biodegradable plastics Biodegradable plastics
  3. 3. Polyhydroxyalkanoates (PHA) R O Poly(3-hydroxyalkanoates) CH C with R= alkyl or functional group O CH2 nPHASCL: short-chain length PHA 3-5 carbon atomsPHAMCL: medium-chain length PHA 6-14 carbon atoms
  4. 4. Physical and chemical properties.• Average molecular weight ranging between 5·104 and1·106 Da• Enantiomerically pure• Biodegradable and biocompatible Polymer Tg (°C) Tm (°C) Cristallinity (%) Extension at break (%) P(3HB) 15 175 50-80 5P(3HB-co-3HV) -1 145 56 50P(3HB-co-4HB) -7 150 43 444 PP -15 176 50 400
  5. 5. PHAs in medicine and pharmaceuticals. Sutures. Bone graft substitutes.Temporary heart valves. Carrier for drug delivery.
  6. 6. Role of PHAs in tissue engineering.
  7. 7. Poly(alkylene dicarboxylate)sAliphatic polyesters , semi-crystalline polymers with a wide variety ofphysical, mechanical properties and biodegradability.Poly(alkylene dicarboxylate)s, is polymerized through apolycondensation reaction between a diol, HO-R1-OH, and a dicarboxylicacid, HOOC-R2-COOH, forming polyesters like poly(butylene succinate)(PBS) and poly(butylene adipate) (PBA). O O O O O O O O n n PBS PBAAlthough polyesters with relatively high molecular weight have recentlybeen obtained through polycondensation using metal alkoxides ascatalysts high molecular weight is usually difficult to obtain bypolycondensation and synthesized polymers are left with poormechanical properties.
  8. 8. Synthesis of new P(HB-co-BA) copolymers via the acidcatalyzed transesterification of PHB and PBA in solution. CH O O O 3 O CH CH C + O CH CH CH CH O C CH CH CH CH C 2 n 2 2 2 2 2 2 2 2 PHB m PBA 1. PTSA·H2O, Chloroform, Toluene (reflux) 2. Azeotropic CH O O O 3 O CH CH C O CH CH CH CH O C CH CH CH CH C 2 2 2 2 2 2 2 2 2 n m P(HB-co-BA)
  9. 9. What are the microwavesThe microwaves are not ionizing electromagnetic waves having a wavelengthbetween 1 mm (ν = 300 GHz) and 1 dm (ν = 3 GHz), they are located in the area ofthe spectrum between the frequencies of the infrared and the radio waves.The frequency of 2.45 (± 0.05) GHz, corresponding in vacuum at a wavelength (λ) of12.2 cm, is that used for applications in the domestic field, scientific, medical, andfor many industrial processes.
  10. 10. Design For Efficient Energy: Energy requirements should berecognized for their environmental and economic impacts andshould be minimized. Synthetic methods should be conducted atambient temperature and pressure. Heating mechanisms heat exchange Heating with Microwave Benefits: Energy saving Process Efficiency Restrictions on the use of halogenated solvents
  11. 11. Table 1: Reaction time, composition, yield, molecular weight,sequence length and randomness of P(HB-co-BA) copolyestersobtained from a 50/50 mol % mixture of PHB and PBA with 5% w/w ofcatalyst. Sample Reaction time a (HB)/(BA) b Yield % Mw x 10-3 c Mw/Mn d LHB e LBA f DR g A1 0.5+2 50/50 83 16.9 1.19 28 74 0.05 A2 1+2 53/47 70 17.8 1.46 14.2 28.4 0.10 A3 2+2 49/51 65 17.8 1.37 7.5 23 0.18 A4 3+2 45/55 57 17.6 1.28 6.1 11 0.25 a Reaction times (hours) of the two synthetic steps of hydrolysis and azeotropic dehydration. b Molar composition of the resulting copolyesters as measured by 1H-NMR. c Weight average molecular weights as determined by GPC. d Polydispersity index. e Average block length of HB. f Average block length of BA. g Degree of randomness.
  12. 12. Table 2: Reaction time, composition, yield, molecular weight,sequence length and randomness of P(HB-co-BA) copolyestersobtained from a 75/25 mol % mixture of PHB and PBA with 5% w/w ofcatalyst. Sample Reaction time a (HB)/(BA) b Yield % Mw x 10-3 c Mw/Mn d LHB e LBA f DR g B1 0.5+2 66/34 65 11.4 1.35 23 37 0.07 B2 1+2 64/36 60 11.4 1.31 13 17 0.13 B3 2+2 66/34 47 13.1 1.29 13 13 0.15 B4 3+2 61/39 38 15.7 1.21 5.1 5.4 0.38 a Reaction times (hours) of the two synthetic steps of hydrolysis and azeotropic dehydration. b Molar composition of the resulting copolyesters as measured by 1H-NMR. c Weight average molecular weights as determined by GPC. d Polydispersity index. e Average block length of HB. f Average block length of BA. g Degree of randomness.
  13. 13. Table 3: Reaction time, composition, yield, molecular weight,sequence length and randomness of P(HB-co-BA) copolyestersobtained from a 50/50 mol % mixture of PHB and PBA with 10% w/wof catalyst. Sample Reaction time a (HB)/(BA) b Yield % Mw x 10-3 c Mw/Mn d LHB e LBA f DR g C1 0.5+2 49/51 56 10.6 1.45 9.1 17 0.17 C2 1+2 55/45 42 7.7 1.36 5.6 9.8 0.28 C3 2+2 43/57 35 5.3 1.71 3.5 7.8 0.41 C4 3+2 54/46 30 4.9 1.62 2.2 3.0 0.79aReaction times (hours) of the two synthetic steps of hydrolysis and azeotropic dehydration. b Molar composition ofthe resulting copolyesters as measured by 1H-NMR. c Weight average molecular weights as determined by GPC. dPolydispersity index. e Average block length of HB. f Average block length of BA. g Degree of randomness.
  14. 14. a a CH O O O 3 f,i O CH CH C O CH CH CH CH O C CH CH CH CH C b c 2 d n e 2 f 2 f 2 e 2 g h 2 i 2 i 2 h2 g m e h c b8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 (ppm) Fig. 1: 200 MHz 1H-NMR spectrum in CDCl3 of P(HB-co-39 mol % BA) (Sample B4).
  15. 15. i a CH h 3 O O O f O CH CH C O CH CH CH CH O C CH CH CH CH C b c 2 d n e 2 f 2 f 2 e 2 g h 2 i 2 i 2 h2 g m e a b c g d180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 (ppm) Fig. 2: 50 MHz 13C-NMR spectrum in CDCL3 of P(HB-co-39 mol % BA) (Sample B4).
  16. 16. HB-A-B B-A-B HB-HB-HB B-A-HB A-HB-HB HB-HB-B HB-A-HB A-HB-B B4 B3 B2 B1 174.0 173.5 173.0 172.5 172.0 171.5 171.0 170.5 170.0 169.5 169.0 168.5 (ppm)Fig. 3: 50 MHz 13C-NMR spectral expansion of the carbonyl region of the P(HB-co-BA) copolyester(Samples B1-B4).
  17. 17. As in all the 13C-NMR spectra the triad signals were only partially resolved, we basedour sequence analysis on dyads intensities. Designating with IA-B, IA-HB, IHB-B, and IHB-HBthe intensity of signals due to A-B, A-HB, HB-B and HB-HB sequences in the 13C-NMRspectra, and considering the copolyesters as terpolymers made up of the threecomonomers HB, B, and A the average block length of BA and HB units (LBA, LHB), anddegree of randomness (DR) may be defined as: LBA = IA-B/IA-HB + 1 LHB = IHB-HB/IHB-B + 1 DR = 1/LBA + 1/LHB For a random copolymer of 1:1:1 composition, these parameters are expected to assume the values LBA = 3, LHB = 1.5 and DR = 1
  18. 18. Differential scanning calorimetry (DSC)• Performed on PHB and PBA homopolymers and on selected HB-BA copolymers, namely those of series B.• Each sample was preliminarily heated to 210°C to erase previous thermal history, then it was analyzed after both controlled cooling at 10°C/min and after quench cooling.• All copolymers show melting endotherms except sample B4, why this copolymer has the highest degree of randomness and it is reasonable that in this sample the development of crystallinity is inhibited. Copolymers B1, B2 and B3 show a melting endotherm at temperatures higher than PBA Tm. This implies that the crystal phase concerned is stable in a range where PBA crystals cannot exist, hence it is likely due to melting of PHB-type crystals. This attribution is plausible for these B series copolymers that are rich in HB units (61-66 mol %).• The melting temperature of such PHB-type crystals is lower than Tm of the corresponding homopolymer, showing that these microblock copolymers behave, in this respect, similarly to random copolymers.
  19. 19. Differential scanning calorimetry (DSC)Fig. 4: DSC heating curves (20°C/min) of the P(HB-co-BA) copolyesters (Samples B1-B4) and of thereference PHB and PBA homopolymers, after controlled cooling at 10 °C/min.
  20. 20. MALDI-TOF MS I% xyz= (HBx-By-Az)Na+ ‡ x-2-2 (x = 2-6)100 ‡ x-3-3 (x = 0-6) x-4-4 (x = 0-6) x-5-5 (x = 0-6) x-6-6 (x = 0-3) x-7-7 (x = 0-1) ^ x-2-1 (x = 4-7) x-1-2 (x = 4-11) + x-4-3 (x = 0-7) x-3-2 (x = 2-8) x-2-3 (x = 1-11) + x-5-4 (x = 0-7)  x-3-4 (x = 0-9) + x-6-5 (x = 0-5) x-4-5 (x = 0-7) + x-7-6 (x = 0-3) 50 ‡ ^   ‡  ^   ‡ ‡   ^    ^ 0 580 780 980 1180 1380 1580 Mass (m/z)Fig. 5: MALDI-TOF mass spectrum of P(HB-co-57 mol % BA) (sample C3) in the mass range580-1580 m/z.
  21. 21. 2-6-6 3-6-6 I% 4-6-5 + 8-3-4 2-7-6 + 6-4-5 100 6-5-4 + 10-2-3 5-5-5 1-6-7 3-5-6 0-7-7 7-4-4 50 0 2-7-6 + 6-4-5 5-5-5 I% 6-5-4 + 10-2-3 4-6-5 + 8-3-4 7-4-4 9-4-3 + 13-1-2 3-5-6 100 3-6-6 10-3-3 9-3-3 2-6-6 1-6-7 50 0-7-7 0 1405 1426 1447 1468 1489 1510 Mass (m/z)Fig. 10: MALDI-TOF mass spectra of samples P(HB-co-57 mol % BA) (sample C3, upper trace)and P(HB-co-46 mol % BA) C4 (sample C4, lower trace) in the mass range 1405-1510 m/z.
  22. 22. Conclusion• By microwave assisted transesterification were obtained new biodegradable and biocompatible copolymer from PHB and PBA homopolymer.• The structures of these copolymers is random or microblock depending the on the experimental condition used.• The facile and flexible route described here to synthesize P(HB-co-BA) copolyesters, or potentially higher for lesser reaction times and DR, could allow to obtain new biodegradable materials based on microbial PHB at relatively lower cost than those obtainable from fermentation processes where engineered bacteria are used.• Their weight-average molecular weights range from 5,000 to 17,000 Da with a structure varying from partially crystalline to totally amorphous and with a single Tg, making them much easily processable than PHB, and suggesting their potential use as matrices for drug delivery systems.

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