Symmetric star poly(substituted glycolide) homopolymers and their surface properties

Abstract

Symmetric Star Poly(Substituted Glycolide) Homopolymers and Their Surface Properties The invention include the synthesis, thin film formation, surface properties, and comprehensive analysis of star-shaped well-defined symmetric poly(substituted glycolide) (s-PSG) homopolymers, which are alternatives to polylactides and polyglycolides. Four-armed symmetric poly(L-diisopropyl glycolide) (4s-PLDIPG) and poly(L-diisobutyl glycolide) (4s-PLDIBG) prepared by ring opening polymerization (ROP) under melt conditions with tin (II) 2- ethylhexanoate catalyst and pentaerythritol initiator exhibited high conversions (92-98%) and desirable PDI values (1.23-1.49). The NMR data of all s-PSGs showed that the methylene peaks of pentaerythritol were shifted, proving that polymerization took place in all arms. The molecular weights (Mn NMR, Mw GPC, Mn GPC) of s-PSGs determined by NMR and GPC data were consistent with the theoretical values. By increasing the side chain length of s-PSG homopolymers, there was a consistent increase in the water contact angles and surface roughness values of the thin films, whereas the surface free energy diminished.

Description

[0001] DESCRIPTION

[0002] Symmetric Star Poly(Substituted Glycolide) Homopolymers and Their Surface Properties

[0003] Technical Field

[0004] The invention relates to the synthesis of a series of star poly(substituted glycolide) (s-PSG) homopolymers and their surfaces characteristics.

[0005] Prior Art

[0006] Polylactides have benign toxicity, biocompatibility, renewability, and tunable mechanical properties, etc.1 2PSGs, which are structural analogs to polylactides, having the side groups such as diisopropyl, diisobutyl, isopropyl methyl, and butyl methyl offer the possibility to modify the physical properties of polylactides (glass transition temperature, crystallinity, hydrophobicity / philicity, degradability, etc.).31 4Improving the physical properties of PSG polymers for their potential use as biomaterials allow their desirable use in medical applications.5Diisobutyl glycolide (DIBG) and diisopropyl glycolide (DIPG) monomers were easily synthesized from cheap amino acids such as L-leucine and L-valine due to their advantages such as short reaction time, high yield and less solvent consumption.61 7DIBG monomer was polymerized with ROP in the presence of benzyl alcohol and Sn(Oct)2, and PDIBG exhibited a high conversion of 97.9% and a moderately narrow molar mass distribution of 1.47. Addition of silica nanoparticles as hydrophilic component to PDIBGs possessing hydrophobic parts resulted in the formation of amphiphilic underwater superoleophobic surfaces.8The nanocarriers in the range of 180-255 nm were prepared from linear PDIBG-mPEG diblock and PDIBG-PEG-PDIBG triblock copolymers with the conversions as high as 99.2% and polydispersity as low as 1.11 for the controlled release of paclitaxel.6On the other hand, linear PDIPG-PEG copolymers exhibited gel character at 35-37℃ and sol behavior at 42-45℃, suitable for i njection, for the potential treatment of solid tumors.7

[0007] Star polymers arising from a single core with at least three arms exhibit a large surface area, increased concentration of functional end groups and a spherical compact structure compared to linear polymers of similar molecular weights.9Reduced hydrodynamic radius of star polymers compared to their linear analogs facilitates nanoparticle passage through membranes resulting in efficient drug transportation in drug delivery systems (DDS).10-13Star PLAs synthesized by ROP in the presence of tin (II) 2-ethylhexanoate (Sn(Oct)2) and polyols (e.g. pentaerythritol) are of great interest for potential fields such as tissue engineering and DDS due to their geometric structure.14-18The contribution of hydrophobicchain units and hydrophilic end groups determines the hydrophilic / hydrophobic balance for star polymers. This also affects the microstructure, morphology and topography of its surface, which is of great importance for the in vitro and in vivo performance of a biomaterial characterized by surface techniques such as water contact angle, atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).19-23

[0008] Aims of the Invention

[0009] The aim of the invention is to synthesize four-armed symmetric star s(PSG) hompolymers and to study their surface properties.

[0010] Detailed Description of the Invention

[0011] The results obtained for the purposes of the invention are shown in the attached figures. These Figures are;

[0012] Figure 1: A view of1H NMR (A and B),13C NMR (C and D), and ATR-FTIR (E and F) spectra of compounds 3 and 8, respectively.

[0013] Figure 2: A view of1H NMR (A and B),13C NMR (C and D), and ATR-FTIR (E and F) full spectra of compounds 3 and 9, respectively.

[0014] Figure 3: A view of1H NMR (A and B),13C NMR (C and D), and ATR-FTIR (E and F) full spectra of compounds 3 and 10, respectively.

[0015] Figure 4: A view of1H NMR (A and B),13C NMR (C and D), and ATR-FTIR (E and F) spectra of compounds 6 and 11, respectively.

[0016] Figure 5: A view of1H NMR (A and B),13C NMR (C and D), and ATR-FTIR (E and F) full spectra of compounds 6 and 12, respectively.

[0017] Figure 6: A view of1H NMR (A and B),13C NMR (C and D), and ATR-FTIR (E and F) full spectra of compounds 6 and 13, respectively.

[0018] Figure 7: A view of1H NMR (A),13C NMR (B), GPC (C) and ATR-FTIR (D) full spectra of compound 14, respectively.

[0019] Figure 8: A view of1H NMR (A),13C NMR (B), GPC (C) and ATR-FTIR (D) full spectra of compound 15, respectively.

[0020] Figure 9: A view of1H NMR (A),13C NMR (B), GPC (C) and ATR-FTIR (D) full spectra of compound 16, respectively.Figure 10: A view of 1 H NMR (A),13C NMR (B), GPC (C) and ATR-FTIR (D) full spectra of compound 17, respectively.

[0021] Figure 11: A view of 1H NMR (A),13C NMR (B), GPC (C) and ATR-FTIR (D) full spectra of compound 18, respectively.

[0022] Figure 12: A view of 1 H NMR (A),13C NMR (B), GPC (C) and ATR-FTIR (D) full spectra of compound 19, respectively.

[0023] Figure 13: A view of GPC spectra for polymers 8-10 and 11-13.

[0024] Figure 14: A view of1HNMR spectrum of pentaerythritol.

[0025] Figure 15: A view of DSC spectrum (cooling run) of compound 8, 10 and 17.

[0026] Figure 16: A view of DSC spectra (2ndheating run) of compounds 8, 10, 17 (A) and 11, 13, 18 (B); TGA spectrum of compounds 8, 10, 17, 11, 13, 18 (C); and WAXD spectrum of compounds 8, 10, 17 (D).

[0027] Figure 17: A view of WAXD integral area for compounds 8, 10 and 17.

[0028] Figure 18: A view of correlation between contact angle variation and RMS values alteration of PSGs.

[0029] Figure 19: The SEM and AFM images of PLLA derivates (The circle emphasized the length of the side chain in the repeating unit)

[0030] Figure 20: The SEM and AFM images of PLDIPG derivates. (The circle emphasized the length of the side chain in the repeating unit)

[0031] Figure 21: The SEM and AFM images of PLDIBG derivates (The circle emphasized the length of the side chain in the repeating unit)

[0032] L-DIPG (3) and L-DIBG (6) monomers were synthesized and characterized according to our previous studies (Scheme 1).6 7

[0033] Four Arm Symmetric Poly(substituted glycolide)s. Four arm poly(L-diisopropyl glycolide)s (4s-PLDIPG 8-10) and poly(L-diisobutyl glycolide)s (4s-PLDIBG 11-13) polymers were obtained using a Sn(Oct)2catalyst via ROP of L-DIPG 3 and L-DIBG 6 monomers in presence of pentaerythritol core (Scheme 1). A polymerization tube with a screw cap was filled with Sn(Oct)2(16 mg, 0.0375 mmol), pentaerythritol (5.3 mg, 0.0375 mmol), and L-DIPG 3 (300 mg, 1.5 mmol) for the four-armed 4s-PLDIPG 8 star polymer, respectively. The reaction was carried out in an oil bath at 190 ℃ for one hour after argon gas was introduced to provide an inert atmosphere. Then, the polymer was dissolved withDCM and precipitated with MeOH (1:5 v / v) and kept at -22℃ overnight. Next, it was centrifuged for five minutes at 20,000 rpm and -20°C. 4s-PLDIPG 9, 10 and 4s-PLDIBG 11-13 were synthesized using the same ratios and purification method (Scheme 1). Table 1 presents the experimental parameters for each star homopolymer synthesis. For control and comparison, four-armed poly(L-lactide) star polymers 14-16 were produced in the same ratios.

[0034] 1HNMR (CDCl3, 400 MHz) for single arm of 4s-PLDIPG 8-10 δ: 4.85-5.20 (CHd, 1H, d), 4.1-4.22 (CHd' / CH2f, 3H, m), 2.55-2.7 (OHg, 1H, s), 2.25-2.45 (CHc, 1H, m), 2.1-2.25 (CHc', 1H, m), 0.97-1.15 (CH3 a / b, 6H, t), 0.90-0.97 (CH3 a' / b', 6H, m).13CNMR (CDCl3, 100 MHz) 6:

[0035] 168.7, 76.9, 30.2, 18.6, 16.9. ATR-FTIR (vmaxcm-1): 2970, 2883 (C-H); 1749 (C=O); 1462, 1374 (C-H); 1110, 1018 (C-O); 969 (C-H or -CO-O); 849, 782, 682 (C-C or -C=O).

[0036] 1HNMR (CDCI3, 400 MHz) for single arm of 4s-PLDIBG 11-136: 4.95-5.25 (CHe, 1 H, dd), 4.2-4,35 (CHe', 1H, dd), 4.0-4.2 (CH2 g, 2H, dd), 2.6-2.7 (OHh, 1H, s), 1.70-2.0 (CH2 c / CHd, 3H, m), 1.55-1.70 (CH2 C’ / CHd’, 3H, m), 0.85-1.0 (CH3 a / b, 6H, dd), 0.75-0.85 (CH3 a- / b-, 6H, dd).13CNMR (CDCI3, 100 MHz) 6: 169.9, 71.5, 39.4, 24.6, 23.2, 21.5. ATR-FTIR (vmaxcm-1): 2958, 2873 (C-H); 1752 (C=O); 1333 (C-H); 988 (C-H or -CO-O); 650 (C-C or -C=O).1HNMR (CDCI3, 400 MHz) for single arm of 4s-PLLA 14-16 6: 5.0-5.3 (CHb, 1H, q), 4.33-4.41 (CHb’, 1H, q), 4.08-4.25 (CH2 d, 2H, dd), 2.6-2.8 (OHe, 1 H, s), 1.55-1.70 (CH3 a, 3H, d), 1.45-1.55 (CH3 a>, 3H, d).13CNMR (CDCI3, 100 MHz) 6: 169.7, 69.1, 16.7. ATR-FTIR (vmaxcm-1): 2996, 2946 (C-H); 1748 (C=O).

[0037] Linear Poly(Substituted Glycolide)s. Poly(L-diisopropyl glycolide) PLDIPG 17, poly(L-diisobutyl glycolide) PLDIBG 18, and poly(L-lactide) PLLA 19 linear polymers were synthesized for comparison. The ROP of L-DIPG, L-DIBG, and L-LA was carried out in presence of BnOH initiator and Sn(Oct)2catalyst to obtain PLDIPG 17, PIDIBG 18, and PLLA 19 linear polymers. For PLDIPG 17 polymer, Sn(Oct)2(16 mg, 0.0375 mmol), BnOH (4 pl, 0.0375 mmol) and L-DIPG 3 (300 mg, 1.5 mmol) were placed in a screw-capped polymerization tube, respectively. The reaction was conducted in an oil bath at 190 ℃ for one hour after argon gas was introduced to provide an inert atmosphere. The polymer was dissolved with DCM and precipitated with MeOH (1:5 v / v) and kept at -22‘C overnight. Next, it was centrifuged for five minutes at 20,000 rpm and -200. The product was vacuum-dried until its weight remained constant. The remaining linear polymers 18 and 19 were synthesized using the same ratios and purification method. Table 1 displays the reaction conditions for each linear homopolymer.

[0038] 1HNMR (CDCI3, 400 MHz) for PLDIPG 176: 7.32-7.40 (CHg, 5H, m), 4.9-5.25 (CH2fZCHd, 2H / H, d), 4.12-4.17 (CHd>, 1H, d), 2.25-2.45 (CHc, 1 H, m), 2.10-2.25 (CHc>, 1 H, m), 1.0-1.20(CH3a / b, 6H, t), 0.9-1.0 (CHsa’ / b’, 6H, m).13CNMR (CDCI3, 100 MHz) 6: 168.7, 128.6, 76.9, 30.2, 18.6, 16.9. ATR-FTIR (vmaxcm’1): 2968, 2883 (C-H); 1750 (C=O).

[0039] 1HNMR (CDCl3, 400 MHz) for PLDIBG 18 δ: 7.32-7.40 (CHh, 5H, m), 5.00-5.30 (CH2g / CHe, 2H / H, dd), 4.2-4.3 (CHe', 1H, dd), 1.73-1.95 (CH2d / CHc, 3H, m), 1.6-1.73 (CH2d' / CHc', 3H, m), 0.85-1.05 (CH3 a / b, 6H, dd), 0.75-0.85 (CH3 a' / b', 6H, dd).13CNMR (CDCl3, 100 MHz) 6: 168.9, 128.6, 71.4, 39.3, 24.5, 23.0, 21.4. ATR-FTIR (v^cm’1): 2955, 2874 (C-H); 1754 (0=0).

[0040] 1HNMR (CDCl3, 400 MHz) for PLLA 19 δ: 7.32-7.40 (CHe, 5H, m), 5.10-5.30 (CH2 d / CHb, 2H / H, q), 4.34-4.42 (CHb>, 1H, q), 1.58-1.65 (CH3a, 3H, d), 1.50-1.58 (CH3a-, 3H, m).

[0041] 13CNMR (CDCh, 100 MHz) 5: 169.6, 128.6, 69.0, 16.7. ATR-FTIR (vmaxcm’1): 2994, 2947(C-H); 1749 (C=O).

[0042] Surface Characterization of s-PSGs Thin Films. The thin films of s-PSG homopolymers were produced using the dip coating technique, in which the polymer was dissolved in THF at a concentration of 10 mg / mL. To measure the air-water contact angle, the images of droplets were taken with the Imaging Source DFK 27AUP006 camera. Then, the contact angle values of the droplets were determined using Imaged, a free image processing program. The contact angle measurement apparatus, which was specially designed, had a 1° precision.24The apparent contact angles of the film surfaces were measured at three distinct locations for both the interface of the air-test liquids (0app) with a maximum deviation of ± 2”. Air contact angles were measured by dropping five milliliters (pL) of ethylene glycol (EG), diiodomethane (DM), formamide (FA), a bromonaphthalene (BN), and water (W) onto the coated cover glasses. Additionally, the surface tension of the test liquids was evaluated using the pendant drop method.25The van OSS-Good-Chaudhary (vOGC) technique was used to determine the values of surface free energy using the apparent contact angle, in a manner comparable to published research.26'27The Oxford Instrument X-Max detector-equipped JEOL JSM-7100F (JEOL, Tokyo, Japan) was used to conduct SEM investigations on the film surfaces. Using a non-contact mode on the WITEC ALPHA 300 RS AFM system, RMS values were obtained over a 100x100 m scanning region.Scheme 1: Chemical structure

[0043] 1 2 3

[0044] 4 5 S

[0045]

[0046] 4 > a( i*i3>Table 1. Synthesis conditions and characterization results of four-armed star symmetric poly(substituted glycolide) polymers and their linear analogues.

[0047] Polymer ID [Mo] / [lo] / [Co] Time Temp. MwaMnaMnbMncMw / MnaConv. Yield Nb(OH) RU of polymer (hour) (CC) (g / mol) (g / mol) (g / mol) (g / mol) (%b) (%) exp.aexp.btheo 4S-PLDIPG 8 40 / 1 / 1 1 190 10850 8830 7950 7430 1.23 91 85 3.9 44 39 36

[0048] 9 80 / 1 / 1 3 190 22300 15140 14160 14880 1.47 92 90 3.9 75 70 74 10 120 / 1 / 1 4.5 190 30245 21105 18770 22250 1.43 92 90 3.9 105 93 110 4S-PLDIBG 11 40 / 1 / 1 1 175 15200 12300 9270 8810 1.24 95 85 3.9 53 40 38

[0049] 12 80 / 1 / 1 4.5 175 23915 16100 17260 18030 1.49 98 90 3.9 70 75 78 13 120 / 1 / 1 6.5 175 36560 25700 23650 26980 1.42 98 95 3.9 112 103 118 4S-PLLA 14 40 / 1 / 1 1 150 11315 9000 5610 5840 1.28 99 87 3.9 62 38 40

[0050] 15 80 / 1 / 1 3 150 21620 15040 7780 11210 1.44 96 90 3.8 104 53 77 16 120 / 1 / 1 3 160 29070 20260 12250 16570 1.43 95 87 3.9 140 84 114 PLDIPG 17 40 / 1 / 1 1 190 10800 6685 7320 7480 1.62 92 90 - 33 36 37 PLDIBG 18 40 / 1 / 1 1 175 13780 8775 8330 8510 1.57 92 85 - 38 36 37 PLLA 19 40 / 1 / 1 1 150 10125 7350 5010 5470 1.70 93 92 - 51 34 37

[0051]

[0052] Mo] / [lo] / [Co]: Monomer (L-DIPG, L-DIBG or L-LA) / Initiator (Pentaerythritol or Benzyl alcohol) / Catalyst (Sn(Oct)2), RU: repeating unit. Weight averag molecular weight (Mwa), number average molecular weight (Mna) and polydispersity index (PDI: Mw / Mn) values were determined by GPC. The numbe average molecular weight (Mnb) was found by equation Mnb:

[0053]

[0054] x4 + MWinitiatorusing NMR data. Here the field of methine protons the main chain is expressed as 6(Hd)=4.85-5.20 and the field of methine protons in the terminal group is expressed as 5(Hd’)=4.1-4.2 for4s-PLDIPG 8 (Figure 1B).15’17’28-30The number of initiating groups of pentaerythritol Nb(OH) was found for 4s-PLDIPG 8 using the equation NbOH'):-^—^ x (Figure 1B and Figure 14).31’32The theoretical average molecular weight (Mnc) of the polymers was found by the followinM

[0055]

[0056] "C;Hx^monomerx %inversion + MWbMlatm. equation.28The synthesis of monomers 3 and 6 was carried out in two steps (Scheme 1). Amino acids 1 and 4 were converted to hydroxy acids 2 and 5 in 50% and 80% yields, respectively, by diazotization reaction in the presence of NaNO2. Then, LDIPG 3 and LDIBG 6 monomers were successfully obtained in 40% yield by dimerization reaction of hydroxy acids 2 and 5 in the presence of PTSA catalyst.6'7| 33 13CNMR spectra of both monomers show that single signal for each carbon atom without splitting or formation of minor peaks (Figure 1C and 4C). No diastereomeric mixture was observed in the NMR analysis of monomers 3 and 6, proving that racemization did not occur.6 7

[0057] Table 1 offers detailed data on four-armed poly(substituted glycolide) star polymers at various monomer feed ratios at suitable temperatures and periods. For comparison, the Table 1 also includes four-armed star PLA 14-16, linear PLDIPG 17, PLDIBG 18, and PLLA 19. The high melting points of monomers 3 and 6 (about 160 ℃7, 33and 170 ℃6, 33, respectively) are the reason for choosing 190 and 175 ℃ as the polymerization temperatures, respectively. In the literature, there are studies reporting that the Mnvalues obtained by GPC for star polymers are lower than the theoretical Mnvalues due to the hydrodynamic volume difference between linear polystyrene standards used in GPC analysis and star polymers.34 35However, there are several studies reporting that the Mnvalues of GPC are higher than the theoretical values for star homopolymers.14'28'31As seen in Table 1, the number-average molecular weights (Mn) determined by GPC and NMR for 4s-PLDIPG 8-10 and 4s-PLDIBG 11-13 are extremely close to their theoretical values. The Mnvalues of GPC for 4s-PLDIPG and 4s-PLDIBG are slightly lower (three out of six data) and slightly higher (three out of six data) than the theoretical values. Somehow, Mnin GPC is higher than the theoretical value in all three data in the case of 4s-PLI_A. Although it is difficult to state a definite conclusion, the hydrodynamic radius will be influenced by the size and geometry of the side groups of the polymer chains as well as the star geometry of the polymer itself. Although the experiments were carried out under the same conditions, differences such as viscosity and high temperature may have been effective. As the monomer feed ratio increased, the monomodal curves moved to earlier elution periods, as would be expected given the increase in hydrodynamic volume caused by longer arms (Figure 13). From the linear growth of the molecular weights of the polymers as a function of [Mo]:[lo], PDI values as low as 1.23, conversion ratios as high as 98% and the absence of any oligomeric species, it is clear that the controlled polymerization of star-PSGs has been achieved. The high melting points of monomers and the need to keep the mediummolten during polymerization cause polymerizations to be carried out at high temperatures. Long exposure to high temperatures may have caused the PDI to increase further.

[0058] The methine (CH) groups of the isopropyl substituent on the main backbone and terminal end groups of 4s-PLDIPG 8 correspond to multiplet peaks at 2.25-2.45 ppm (c) and 2.10-2.25 ppm (o') in1H NMR, respectively. The other CH protons in the main skeleton appear as a doublet at 4.85-5.20 ppm (d), which differs significantly from the chemical shift of LDIPG 3 (4.71-4.76 ppm, Figure 1A), indicating the ring opening of 4s-PLDIPG 8-star homopolymer. The methyl protons of isopropyl groups on the main backbone and terminal ends of 4s-PLDIPG 8 are associated with signals in the range 0.97-1.15 ppm (a / b, triplet) and 0.90-0.97 ppm (a7b’, multiplet), respectively (Figure 1B). Each hydroxyl end group of pentaerythritol reacts with the monomer 3 or 6 during polymerizations in the presence of Sn(Oct)2catalyst, evidenced by the almost complete disappearance of -CH2- protons in pentaerythritol at 3.35-3.40 ppm (Figures 1 and 14, Table 1).10’14’16’17Furthermore, for each synthesis, the 2:1 ratio between -CH2- peaks (f) of pentaerythritol and the terminal -CH-peaks (d1) of 4s-PLDIPG 8 was preserved (Figure IB).17 28-31In addition, the ratio of peak integrations of -CH- protons in the main chain (d) to peak integrations of terminal -CH-protons (d1) or the -CH2- peaks of pentaerythritol (f), respectively, was used to calculate the average arm lengths for 4s-PLDI PG 8-10 (Figure 1B).

[0059] Methyl carbon (-CH3) (a), other methyl carbon (-CH3) (b), methine carbon (-CH) (c), α-methine carbon (-CH) (d), and carbonyl (-C=O) carbon (e) corresponded to 16.9, 18.6, 30.2, 76.9, and 168.7 ppm on the13C NMR spectrum of 4s-PLDIPG 8, respectively (Figure 1D). The successful polymerization of 4s-PLDIPG 8 was supported by the significant shift of the carbonyl carbon and a-methylene carbon of LDIPG 3 from 166.6 ppm to 168.7 ppm and from 79.8 ppm to 76.9 ppm, respectively (Fig. 1C, D).7’17’29The carbon peaks of the pentaerythritol core and the terminal carbon groups of homopolymer 8 could not be seen due to their low intensity relative to the arm length of the main chain. The ROP of the LDIBG 6 monomer causes distinct and significant shifts in the 4s-PLDIBG 11 star homopolymer, as well. 4s-PLDIBG 11 can be also interpreted similarly to the above (Figure 4A-D).

[0060] In the FTIR spectrum of 4s-PLDIPG 8, the peaks of monomer 3 at 1459 and 1355 cm-1, which correspond to the asymmetric and symmetric bending vibration of C-H of CH3, move to 1462 and 1374 cm-1, respectively.36-42The bands corresponding to the C-O stretchingfrequencies of monomer 3 at 1118 and 1032 cm-1shift to at 1110 and 1018 cm-1in 4s-PLDIPG 8, respectively.37-42Likewise, the C-C stretching411 42or -C=O bending361 43frequencies of LDIPG 3 at 844, 799 and 636 cm-1also shifts to 849, 782 and 682 cm-1in 4s-PLDIPG 8, respectively. The absence of the characteristic peak at 969 cm-1, belonging to -CH bond361 44or -CO-O (breathing mode)391 45of monomer 3 in 4s-PLDIPG 8, and the dramatic changes of the fingerprint region from monomer 3 to 4s-PLDIPG 8 are a clear evidence for the synthesis of star 4s-PLDIPG 8 (Figure 1 E, F). The differences in the signal of the LDIBG 6 monomer and 4s-PLDIBG 11 (Figure 4E, F) make the above discussion of ATR-FTIR analysis also valid for the PLDIBG 11 star.

[0061] Because of its short arm length and the star structure's tendency to limit crystal formation, 4s-PLDIPG 10 crystallizes at a lower temperature than PLDIPG 17 during the cooling run (Tc: 126.7 ℃ for 4s-PLDIPG 10 vs. 140.1 ℃ for PLDIPG 17, Table 2)., 4s-PLDIPG 8 has no Tcvalue probably due to its shorter chain length than 4s-PLDIPG 10 (Figure 15). The 4s-PLDIPG 8 star polymer displays a substantially lower Tmthan PLDIPG 17, and it has lower values of Tgand Tmthan 4s-PLDIPG 10, which has limited segmental mobility due to increased monomer feed ratio (Figure 16A and Table 2). Only 4s-PLDIPG 8 displayed an exothermic Tccvalue during the second heating run following cooling. The cold crystallization exotherm of 4s-PLDIPG 8 at 100.2 ℃ showed that the chains had time to crystallize because of their short arm length in comparison to 4s-PLDIPG 10 and that there were strong interactions between the short arm lengths and comparatively more hydroxyl end groups of 4s-PLDIPG 8.141 151 171 46Probably due to the presence of defective crystals and their different size and morphology, 4s-PLDIPG 8 and 10 have bimodal Tmvalues, whereas the linear PLDIPG 17 homopolymer displays a monomodal Tmvalue.151 171 181 304s-PLDIBG 11 shows a higher Tgvalue than its linear analogue PLDIBG 18 (Figure 16B, Table 2). This is because 4s-PLDIBG 11 has a higher Mnthan its linear counterpart 18, despite having the same monomer feed ratios. (Table 1). 4s-PLDIBG 13, whose segmental mobility is restricted as the monomer feed ratio increases, has a higher Tgvalue than 4s-PLDIBG 11. PLDIBG 18 and 4s-PLDIBG 11 and 13 polymers lack Tccand Tmvalues due to their amorphous state. 4s-PLDIBG 11 has additional -CH2than 4s-PLDIPG 8, which increases free volume and thus provides the structural flexibility, resulting in a lower Tg(Table 2).

[0062] Semi-crystalline polymers 8, 10 and 17 have greater decomposition onset (T5%) values than the amorphous polymers 11, 13 and 18, respectively (i.e., 257 ℃ for 4s-PLDIPG 10 vs 251 ℃ for 4s-PLDIBG 13, Table 2). Additionally, compared to 4s-PLDIPG 8 or4s-PLDIBG 11,T5% and the maximum weight loss rate (Tmax) of 4s-PLDIPG 10 or 4s-PLDIBG 13 increased considerably with growing chain lengths due to an increased monomer feed ratio (j.e., Tmax313 ℃ for 4s-PLDIPG 10 vs 291 ℃ for 4s-PLDIPG 8, Table 2).18>47As anticipated, all homopolymers showed one stage of thermal decomposition (Figure 16C). The values of 21.09° 19.44° 17.8° 16.65° 13.67° 12.86° and 9.87°are the crystalline diffractions of 4s- PLDIPG 8, and the values of 21.42° 19.56° 17.92° 16.78° 13.88° 13.03° and 10.00°are the crystalline diffractions of 4s-PLDIPG 10 (Figure 16D). Crystal diffractions for linear PLDIPG 17 were observed at 21.21° 19.4° 17.67° 1 6.61° 13.79° 12.9° and 9.83°.

[0063] Compared to linear polymers, star polymers may show a lower crystallization percentage due to their structure (Figure 16D and 17). For instance, the four arms in 4s-PLDIPG 8 have shorter arm lengths than the single arm linear PLDIPG 17 at the same monomer feeding ratio, leading to difficulties in folding and orderly packing of the each arms due to mutual their competition in the crystallization (16.7% for 4s-PLDIPG 826.7% for PLDIPG 17, Table 2).30’48Crystallinity increased as the chains moved away from the core as a result of increasing monomer feed ratio (19.1% for4s-PLDIPG 10 vs 16.7 % for4s-PLDIPG 8, Table 2).Table 2. Thermal characterization of four-armed star symmetric poly(substituted glycolide) homopolymers and their linear analogues.

[0064] DSC TGA WAXD

[0065] Polymer ID Tg(℃) Tcc(℃) Tm(℃) Tc(℃) ΔHcc(J / g) ΔHm(J / g) ΔHcT5%(℃) Tmax.(℃) Yc Xc CC) (J / g) % % 4s-PLDIPG 8 33.7 100.2 129,2 - 9.2 -5.6 - 247 291 2.8 16.7

[0066] 143.9

[0067] 10 35.9 - 171,2 126.7 - -20.7 117.2 257 313 2.4 19.1

[0068] 183.4

[0069] PLDIPG 17 - - 190.6 140.1 - -27.6 145.9 252 290 3.1 26.7 4S-PLDIBG 11 20.2 - - - - - - 245 291 3.8 - 13 22.6 - - - - - - 251 300 3.5 - PLDIBG 18 16.8 - - - - - - 241 292 4.8 -

[0070]

[0071] Tg: Glass transition temperature, Tcc: Crystallization during heating, Tm: Melting temperature, Tc: Crystallization during cooling, AHCC: Enthalpy during heating, AHm: Melting enthalpy, AHC: Enthalpy during cooling measured by DSC. T5%: Onset decomposition temperature, Tmax: The temperature at which maximum weight loss, and Yc: Char yields measured by TGA. Xc: Crystallinity degree was calculated by WAXD.Table 3 displays the RMS (nm) of tested liquids and apparent contact angle values for both linear and star-shaped PSGs. Water contact angle values increased with rising RMS values depending on the substituent nature and lengths of the polymer chains in three different PSGs. Interestingly, there was no discernible change in the RMS values when the linear PLLA 19, PLDIPG 17 and PLDIBG 18 polymers were compared with each other. However, as the side chain substituent expanded, the water contact angle increased from 40° to 77°. Both RMS (16: 89.5 vs 10: 117.0 vs 13: 180.0; 14: 66.8 vs 8: 72.0 vs 11: 96.8) and water contact values (14: 55 vs 8: 70 vs 11: 81; 16: 63 vs 10: 85 vs 13: 87) increased as the side chain substituent was extended when 4s-PLLA 16, 4s-PLDIPG 10, and 4s-PLDIBG 13 (or 4s-PLLA 14, 4s-PLDIPG 8, and 4s-PLDIBG 11) were compared within themselves (Table 3).

[0072] Table 3. The apparent contact angle values of linear and star shape PSGs.

[0073] Polymer ID RMS (nm) D IV a £) FA

[0074] vapp vapp DM A BN

[0075] vapp vapp A vapp EG

[0076] PLLA 19 26.0 40 37 12 55 52

[0077] 4S-PLLA 14 66.8 55 34 8 37 50

[0078] 16 89.5 63 33 9 47 51

[0079] PLDIPG 17 24.7 46 34 12 55 50

[0080] 4S-PLDIPG 8 72.0 70 32 10 55 53

[0081] 10 117.0 85 37 8 62 53

[0082] PLDIBG 18 22.7 77 39 9 58 60

[0083] 4S-PLDIBG 11 96.8 81 33 11 39 56

[0084] 13 180.0 87 40 8 62 55

[0085]

[0086] W: Water, DM: diiodomethane, FA: formamide, BN: a-Bromonaphthalene, and EG: Ethylene glycol.

[0087] θappwof the PLLA, which comprises -CH3groups in the repeating units, varied from 40° to 63° degrees depending on RMS values of both linear and star structures (Table 3 and Figure 18). When comparing the RMS values of the 4-arm star PLLA 14 and PLLA 16, it was found that the RMS value grew as the number of repeating units increased. Among the polymers 14, 16 and 19, linear PLLA 19 had the lowest RMS value. The AFM and SEM images of these PLLA derivatives were given in Figure 19.

[0088] A spherical nanoparticle morphology was seen in the SEM images of 4s-PLLA 14, and the linear PLLA 19 surfaces showed a similar morphology. However, samples of 4s-PLLA 16exhibited a crack-like morphology when the n unit was 120. The aggregation of the longer side chains could be the cause of this alteration.

[0089] θappwvalue of PLDIPG derivatives increased from 46° to 85° depending on the RMS value, similar to PLLA derivatives (Figure 18). According to the AFM and SEM images of PLDIPG derivatives given in Figure 20, all PLDIPG derivatives form particle morphology having crack moieties.

[0090] Due to the extended side chains, the highest RMS values were acquired in s-PDIBG. Additionally, as the RMS increased, the θappwof all PDIBG derivatives changed from 77° to 87° (Figure 18). The AFM and SEM images of PLDIBG derivatives in Figure 21 show that linear PLDIBG 18, displaying the lowest RMS values, has a flat surface morphology, while 4s-PLDIBG 11 with the repeating units of 40 exhibits a particle-like morphology. Furthermore, when the number of repeating units reached from 40 to 120 for 4s-PLDIBG 13, crack and particle morphology were obtained.

[0091] It was observed that the surface free energy (SFE) values determined by the vOGC method increased from 41.2 mJ / m2to 55.7 depending on decreasing number of repeating units and side chain length in all series PSGs (Table 4). More particular, SFE values increased as the side chain substituent decreased when 4s-PLDIBG 11, 4s-PLDIPG 8, and 4s-PLLA 14 (or 4s-PLDIBG 13, 4s-PLDIPG 10, and 4s-PLLA 16) were compared among themselves (11: 42.7 vs 8: 44.8 vs 14: 48.2; 13: 41.2 vs 10: 42.0 vs 16: 45.9).

[0092] Table 4. Values of the Lifshitz-van der Waals, acidic and basic components (mJ / m2) of PSGs calculated by van Oss-Chaudhury-Good method.

[0093] Polymer ID rsLWr* / s’ / s'4*3 / s™

[0094] PLLA 19 41.1 0.89 60.1 14.6 55.7

[0095] 4S-PLLA 14 42.0 0.28 34.6 6.21 48.2

[0096] 16 42.2 0.14 23.6 3.68 45.9

[0097] PLDIPG 17 41.8 0.54 48.7 10.3 52.0

[0098] 4S-PLDIPG 8 42.3 0.09 15.7 2.41 44.8

[0099] 10 41.3 0.05 2.80 0.74 42.0

[0100] PLDIBG 18 40.8 0.19 11.4 3.00 43.8

[0101]

[0102] 4S-PLDIBG 11 42.1 0.02 6.13 0.67 42.7

[0103] 13 40.6 0.04 2.23 0.61 41.2

[0104]

[0105] Overall, increases in the number of repeating units and side chain length led to an increase in the values of water contact angle and a decrease in the SFE values based on rising RMS values, as determined by AFM, SEM, and wettability behavior tests.

[0106] Acknowledgements

[0107] This study was financed by Kocaeli University Scientific Research Projects fund with 2018 / 157. We thank the Council of Higher Education (100 / 2000) and the Scientific and Technological Research Council of Turkiye (2211-C) for PhD scholarships for Y. Ç.References:

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Claims

CLAIMS1. The invention relates to the synthesis and characterization of a series of star-shaped poly(substituted glycolides) (s-PSGs) homopolymers with well-tuned parameters such as monomer feed ratio, temperature and time,- The following product, PSG homopolymer, (Formula I) was obtained from the ring opening polymerization (ROP) of L-diisopropyl glycolide under bulk conditions using pentaerythritol as an initiator and tin(ll) 2-ethylhexanoate as a catalyst,Four armed symmetric star poly(L-diisopropyl substituted glycolide) (4s-PLDIPG) homopolymers as shown in Formula I,The following product, PSG homopolymer, (Formula II) was obtained via ROP of L- diisobutyl glycolide under bulk conditions using pentaerythritol as an initiator and tin(ll) 2-ethylhexanoate as a catalyst,Four armed symmetric symmetric star poly(L-diisobutyl substituted glycolide) (4s- PLDIBG) homopolymers as shown in Formula II(II)2. s-PSGs such as 4s-PLDIPG and 4s-PLDIBG homopolymers according to Claim 1 were characterized using spectroscopic (ATR-FTIR, NMR), chromatographic (GPC), thermal (DSC, TGA) and morphological (WAXD) methods.

3. According to Claims I and II, the surface properties of s-PSGs homopolymer thin films formed were characterized by air-water contact angle measurement, SEM and AFM techniques.

Images