Polyhydroxyurethanes (PHUs) Derived from Diphenolic Acid and

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Polyhydroxyurethanes (PHUs) derived from Diphenolic Acid and Carbon Dioxide and Their Application in Solvent- and Water-Borne PHU Coatings Zhongzhu Ma, Cheng Li, Hong Fan, Jintao Wan, Yingwu Luo, and Bo-Geng Li Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b04029 • Publication Date (Web): 07 Nov 2017 Downloaded from http://pubs.acs.org on November 12, 2017

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Industrial & Engineering Chemistry Research

Polyhydroxyurethanes (PHUs) derived from Diphenolic Acid and Carbon Dioxide and Their Application in Solvent- and Water-Borne PHU Coatings Zhongzhu Ma1, Cheng Li1, Hong Fan*a,1, Jintao Wan*b,2, Yingwu Luo1 and Bo-Geng Li1 1. State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China. 2. School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119, China. *

a Corresponding author (E-mail: [email protected])

*

b Corresponding author (E-mail: [email protected])

To develop biobased polyurethanes (PUs) via a less hazardous, non-isocyanate route, herein we synthesize a series of biobased polyhydroxyurethanes (PHUs) by reacting a new biobased cyclocarbonate (derived from renewable diphenolic acid and carbon dioxide) with ethylenediamine (EDA), diethylenetriamine (DETA) and isophoronediamine (IPDA), corresponding to PHU-EDA, PHU-DETA and PHU-IPDA, respectively. Their molecular structures are identified from the 1H NMR and FTIR analyses. Gel permeation chromatography (GPC) analysis shows that the molecular weights of these PHUs grow to as high as 5 kDa in a short reaction time (4 h) at a relatively low reaction temperature (80 o

C). Subsequently, the solvent-borne (in acetone) coatings of these PHUs are successfully fabricated with

diglycidyl ether of bisphenol-A as the crosslinker. The cured PHU coatings on aluminium panels show the high pencil hardness (up to 4 H), adhesive force (up to Grade 1), and glass transition as high as 116 oC, and initial thermal degradation temperature up to 190 oC. Furthermore, we realize the good dispersion of these PHUs in water by introducing chemically bonded carboxylic anions into the molecular backbone to form a stable aqueous emulsion with well controlled particle sizes, and further demonstrate its application in a water-borne PHU coating with good mechanical and thermal properties. Overall, we develop a facile yet effective method to prepare sustainable, biobased PHUs based on diphenolic acid and carbon dioxide via a safer, greener non-isocyanate route, and furthermore demonstrated their use as solvent-borne coatings and greener waterborne coatings of reduced environmental impact.

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1. Introduction Polyurethanes (PUs) are characterized by many outstanding properties and are widely used in huge volumes in many industrial sectors and commodity products including adhesives, coatings, sealants, foams, etc.1, 2 PUs are traditionally synthesized from polycondensation of a di- or multi-isocyanate monomer and a di- or polyol monomer to form linear and crosslink macromolecules. However, due to the high toxicity arising from handling of isocyanate monomers, some health issues occur. Furthermore, phosgene, the key raw material of isocyanate monomer production, is highly hazardous and toxic, thus causing serious environmental issues. To be compatible with environmental sustainability, in recent years non-isocyanate polyurethane (NIPU) attracts rapid growing attention from both academic and industrial communities.3-5 Quite different from traditional polyurethanes, without using any isocyanate monomers, NIPUs are mainly synthesized via three methods: copolymerization between aziridines and carbon dioxide,6 transurethanization polycondensation of a bis-carbamate with a and ring-opening step-growth diol,7-9 polymerization between cyclocarbonates (especially five membered cyclocarbonates) and amines.10, 11 Among them, the third approach is the most promising and important, because cyclocarbonates can be synthesized from corresponding epoxide through the fixation of carbon dioxide. In particular, using of carbon dioxide to produce polymers is inexpensive and safe. And more interestingly, a great diversity of cyclocarbonates can be readily synthesized from their parent epoxides, thus providing highly versatile properties for different applications. In addition, the synthesis process is relatively safer without using highly toxic and dangerous materials,12, 13 and the produced cyclocarbonates are less sensitive to the moisture in air and less toxic in contrast to traditional isocyanate monomers for PU synthesis. According to the method mentioned

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above, obtained reaction products, polyhydroxyurethanes (PHUs), not only contains the urethane linkage as in traditional polyurethanes, but also bears an additional hydroxyl groups produced from the ringopening reaction of each cyclocarbonate,14 which provides the potential of further functionalization. In addition to making better utilization of carbon dioxide in polymer synthesis like PHUs, there is a strong preference to develop sustainable bio-based epoxy resin materials to replace their petroleum-based counterparts.10 More interestingly, a number of five-membered ring cyclocarbonates synthesized from flexible bio-based epoxy monomers such as epoxidized vegetable oils by fixing carbon dioxide, exhibiting some attractive attributes as high flexibility, high bio-based contents and low cost.15-18 Other more rigid renewable monomers as vanillin,19 fatty acid,20 alcohols,21-24 lignin,25, 26 and ricinoleic acid27 were also used for NIPU synthesis with better thermal and mechanical properties. In addition, six- and even sevenmembered cyclocarbonates which synthesized from diols with specific chemical structure were also reported. Although six- and sevenmember-ring cyclocarbonates exhibited much higher reactivity than five-membered cyclocarbonates, the limitation of diol sources made them less popular.28-31 On the basis of the analysis above, the research on non-isocyanate polyurethane has achieved great progress, but any cyclocarbonate and resulting NIPU based on diphenolic acid (DPA) hasn’t been reported yet. Noticeably, DPA is synthesized from levulinic acid and phenol. Levulinic acid is one of a few very important biomass platform compounds massively produced with a low cost. On the other hand, the recent research has demonstrated that phenol could be derived from transformation of biomass such as abundant lignin32, 33 and cellulose.34 Thus DPA can be ideally converted from totally renewable biomass feedstocks. Besides, with the similarity to highly molecular structure rigidity of bisphenol A, DPA is expected to bring about


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the high chain rigidity, thus causing the increased heat resistance and the mechanical properties of the resulting NIPUs. Furthermore, to date little attention is paid to NIPUs aqueous emulsion, when considering that waterborne polyurethane systems (e.g., coatings and adhesives) with greatly reduced environmental impacts and health issues play an increasingly important role in practical applications as automotive industry and furniture. With these situations in mind, herein we, for the first time, synthesize a novel DPA-based cyclocarbonate prepared from parent DPAbased epoxy monomer and carbon dioxide in a simple, low-cost, scalable and highly effective binary catalytic system (Zn–Co(III) DMCC)35, and then use it to react with different amine chain extenders to produce the corresponding NIPUs with tuned molecular structures and thus properties. We also demonstrate the successful application of the NIPUs in both a traditional solvent coating system and an environmentalfriendly waterborne coating system, as well.

2. Experimental 2.1 Materials Diphenolic acid (>98%,) and propylene glycol methyl ether acetate (PGMAC, 99%,) were purchased from Aladdin Reagent. Isopropanol, epichlorohydrin, sulfuric acid, sodium hydroxide, sodium bicarbonate, magnesium sulfate anhydrous, ethylenediamine (EDA), diethylenetriamine (DETA), isophoronediam (IPDA), ethyl acetate, dichloromethane, tetrahydrofuran (THF), N-methyl pyrrolidone (NMP), ethyl ether, succinic anhydride, 2butanone, all analytical grade, were purchased from Sinopharm Chemical Reagent Co., Ltd. The used binary catalysts in study consisted of inexpensive and easy-access cetyltrimethylammonium bromide (CTAB) and zinc-cobalt cyanide complex (Zn–Co(III) DMCC)35 kindly supplied from Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University. All the chemicals were used as received.

2.2 Instrumentation and Characterization 1 H NMR spectra were carried out on a Brucker 400 MHz nuclear magnetic resonance spectrometer at 25 oC with CDCl 3 or d 6 acetone or d 6 -DMSO as solvent. FT-IR spectra were performed on a Nicolet 560 spectrometer using KBr pellet as substrate. The molecular weights and molecular weight distribution were analyzed by using a Waters 1525/2414 gel permeation chromatography (GPC) with tetrahydrofuran as the solvent. The particle size and its distribution of the polyhydroxyurethane emulsions were determined on a Zetasizer 3000 HSA nanometer particle size analyzer. The emulsion was dispersed in deionized water in low concertration. Every sample was scanned for 3 times (10 measurements for each time). The size of the polyhydroxyurethane emulsion particles were also investigated by using a transmission electron microscope (TEM) model Hitachi HT7700 operating at 120 KV. The diluted emulsion particles were scattered on a copper network and dried before TEM test. A TA Instruments Q200 was used for differential scanning calorimetry (DSC) measurements. To measure the glass transition temperature (T g ), a heat/cool/heat procedure was conducted under nitrogen protection. Both heating and cooling rates were 10 oC/min. The glass transition temperature (T g ) was determined by the midpoint of the heat capacity change. Thermogravimetric analysis (TGA) of the samples was performed on a TA Q500 thermogravimeter from room temperature to 850 oC at a heating rate of 10 oC/ min under constant N 2 flow. Thermal degradation temperatures (T d ) corresponded to the temperature at which 5% of weight loss occurred. The hydrophilic properties of the coatings were evaluated by surface contact angle analysis conducted on a Dataphysics OCA20 video-based contact angle measuring device. Using sessile drop method to get the static contact angle and every picture was taken when inter-surface was stable (15 seconds after



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contacting). A Nanoscope IIIA atomic force microscope (AFM) was used to observe the surface morphology of the coatings. All the PHU coated aluminium samples were cut into 10 mm × 10 mm × 1 mm. The mechanical properties, such as surface hardness and crosshatch adhesion properties were measured according to standards of GB/T 6739-2006 and GB/T 9286-1998, respectively.2.3 Synthesis of monomers and prepolymers Synthesis of isopropyl diphenolate (IP-DP) To a 1000 mL round flask equipped with a reflux condenser, a mixture of diphenolic acid (50 g), isopropanol (400 mL), and concentrated sulfuric acid (1 mL) were charged and heated to reflux with stirring for 24 h. After removal of by-product and excessive isopropanol under reduced pressure, the remaining product was dissolved in ethyl acetate (250 mL) and washed with 10% sodium bicarbonate (250 mL) and then deionized water several times until pH = 7. The collected organic phase was dried over anhydrous magnesium sulfate. After removal of solvent, the remaining product was further dried (60 oC, 1 mm Hg, 4h) to yield light yellow solid (yield: 87%). 1H NMR (400 MHz, CDCl3, δ ppm): 7.00 (d, 4H, -Ph), 6.75 (d, 4H, -Ph), 4.99 (m, 1H, (CH3)2-CH-O-), 2.40 (t, 2H, -CH2-CH2-), 2.10 (t, 2H, -CH2-CH2-), 1.55 (s, 3H, CH3-), 1.20(d, 6H, (CH3)2-CH-). Synthesis of diglycidyl ether of isopropyl diphenolate (DGE-IP-DP) To a three-neck, round-bottom flask (1000 mL) equipped with a reflux condenser and a magnetic stirrer, diphenolate ester (25.0 g), epichlorohydrin (15 eqiuv.), and isopropanol (115 mL) were mixed together and heated to reflux (~ 110 oC). After adding a 20% solution of aqueous sodium hydroxide containing 2.1 equiv. (relative to epoxy groups) of sodium hydroxide dropwise, the reaction was kept in reflux for 30 minutes. Then the flask was cooled down to room temperature and formed sodium chloride was removed by filtration. After concentration by removing most of solvent, the crude product was mixed with 50 mL of dichloromethane, and washed with 100

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mL of distilled water several times until pH = 7. The solvent was removed by rotary evaporation and the product was further dried (80 oC, 1 mmHg, 4h) to result in a viscous yellow liquid (yield: 82%). 1H NMR (400 MHz, CDCl 3 ,δ ppm): 7.00 (d, 4H, -Ph), 6.75 (d, 4H, -Ph), 4.75 (m, 1H, (CH 3 ) 2 -CH-O-), 3.65-4.20 (m, 4H, -O-CH 2 -CH-), 3.15 (m, 2H, CH of epoxide group), 2.55-2.70 (m, 4H, -CH 2 of epoxide group), 2.25 (m, 2H, -CH 2 -CH 2 -), 1.90 (m, 2H, -CH 2 -CH 2 -), 1.45 (s, 3H, CH 3 -), 1.20(d, 6H, (CH 3 ) 2 -CH-). Synthesis of diphenolic acid-based bis(cyclocarbonates) (DPA-BisCC) A 20 mL autoclave equipped with a magnetic stirrer was dried under vacuum for 4 h before using. A mixture of DGE-IP-DP (10 g), tetrahydrofuran (10 mL, used as solvent), catalyst (DMCC/CTAB, 20 mg/150 mg) was added to the autoclave. Then carbon dioxide was charged to the pressure of ~5 MPa followed by heating to 120 oC with stirring (500 rpm). After the reaction, the autoclave was cooled in an ice-water bath and the pressure was slowly vented. The crude product was dissolved in 50 mL of tetrahydrofuran and further purified by filtration. The solvent was removed by rotary evaporation. Then the final product was obtained under vacuum (100 oC,1 mmHg, 4h) in a yield of ~72% (DPA-BisCC). 1 H NMR (400 MHz, CDCl 3 ,δ ppm): 7.10 (d, 4H, -Ph), 6.80 (d, 4H, -Ph), 5.00 (m, 1H, (CH 3 ) 2 -CH-O-), 4.95 (m, 2H, -CH of cyclocarbonate group), 4.50-4.65 (m, 4H, -CH 2 of cyclocarbonate group), 4.10-4.25 (m, 4H, O-CH 2 -CH-), 2.25 (m, 2H, -CH 2 -CH 2 -), 1.90 (m, 2H, -CH 2 -CH 2 -), 1.45 (s, 3H, CH 3 -), 1.20(d, 6H, (CH 3 ) 2 -CH-). General procedures of synthesis of polyhydroxyurethanes (PHUs) The reaction was performed in a 20 mL roundbottom flask equipped with a water condenser and a magnetic stirrer. The flask was charged with 5 mmol DPA-BisCC, 5 mmol polyamine (ethylenediamine or diethylenetriamine or isophoronediamine) and 2 mL of the solvent


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. B

. A epichlorohydrin

isopropanol HO

HO

OH

OH

O

O

O

CH2 O

O

O

O

O O CH2

CH2

O

CH2

O CH2

O

O

O

CO2, 5 MPa

O

120 oC

O

O

o

R1 CH2

80 C 4h

NH2

H2N

O

O O CH2

O

O

HO O

O

O

O O

110 C

reflux, 24 h HO

O

o

O

O

O

O

CH2

O

O

H N R1

O

HO O

H N

O

n . C

-

+ O Na

-

+ O Na

O

O

o

O

O

60 C 24 h

O O

R2 HO

O

O O

H N

O

H N

O O

O

H N

H N

O

O O

-

+ O Na

O O

OH

o 60 C, 2h 120 oC, 2h 160 oC, 2h

R1 O

O

R1 O

O

HO

OH

N

N

O

R2

R1 O

. NaHCO3 aq

O

R2

n

O

HO O HO

OH

R2

O

O O

N

N

O

O O

O

O

O

O

O

O O

O

O

OH

O

OH

R2 O

H N R1

O

O

n

H N

O

O CH2

O

O

R1

O

CH2

n

O OH

CH2CH2

R1=

CH2NHCH2

R2=

= O

CH2

O

O

CH2

O O

O

Figure 1. (A) Synthesis of diphenolate acid-based Bis-cyclocarbonates (DPA-BisCC). (B) Synthesis of polyurethanes from bis(cyclocarbonates) and different amines. (C) Preparation of crosslinked polyhydroxyurethanes.

(NMP or PGMAC). Then, then reaction flask was heated to 80 oC with stirring for several hours. After the reaction, the mixture was transferred to 50 mL of ethyl ether to get the precipitate. Then the product was obtained by filtration and further purified under vacuum (60 o C, 1 mmHg, 24 h). PHUs synthesized from ethylenediamine (EDA). 1H NMR (400 MHz, CDCl3,δ ppm): 7.10 (d, 4H, -Ph), 6.80 (d, 4H, -Ph), 5.00 (m, 0.5H, -CH2-OH), 4.95 (m, 1H, (CH3)2-CH-O), 4.20 (m, 4H, Ph-O-CH2-CH-), 4.00 (m, 4H, -

CH-CH2-O-C=O), 3.40-2.80 (m, 4H, -CH2CH2-), 2.25 (m, 2H, -CH2-CH2-), 1.90 (m, 2H, -CH2-CH2-), 1.55 (s, 3H, CH3-), 1.01(d, 6H, (CH3)2-CH-). PHUs synthesized from diethylenetriamine(DETA). 1H NMR (400 MHz, CDCl3,δ ppm): 7.10 (d, 4H, -Ph), 6.80 (d, 4H, -Ph), 5.00 (m, 0.5H, -CH2-OH), 4.95 (m, 1H, (CH3)2-CH-O-), 4.20 (m, 4H, Ph-OCH2-CH-), 4.00 (m, 4H, -CH-CH2-O-C=O), 3.40-2.80 (m, 4H, -NH-CH2-CH2-), 2.25 (m,



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2H, -CH2-CH2-), 1.90 (m, 2H, -CH2-CH2-), 1.55 (s, 3H, CH3-), 1.01(d, 6H, (CH3)2-CH-). PHUs synthesized from isophoronediamine(IPDA). 1H NMR (400 MHz, CDCl3,δ ppm): 7.10 (d, 4H, -Ph), 6.80 (d, 4H, -Ph), 5.00 (m, 0.5H, -CH2-OH), 4.95 (m, 1H, (CH3)2-CH-O-), 4.20 (m, 4H, Ph-OCH2-CH-), 4.00 (m, 4H, -CH-CH2-O-C=O), 3.00 (s, 2H, -NH-CH2-), 2.70 (m, 1H, -NHCH-), 2.25 (m, 2H, -CH2-CH2-), 1.90 (m, 2H, CH2-CH2-), 1.55 (s, 3H, CH3-), 1.01(d, 6H, (CH3)2-CH-), 1.20-0.80 (m, 13H, C6 ring)。 Synthesis of carboxyl polyhydroxyurethane (PHU-EDA-Suc) The reaction was performed in a 20 mL roundbottom flask equipped with a water condenser and a magnetic stirring. A mixture of 0.8 mmol obtained PHU (PHU-IP-EDA), 0.8 mmol succinic anhydrides, and 2-butanone (15 mL, used as solvent) was added to the flask following by heating to 60 oC for 24 h. After the solvent was removed, the resulting solids were dissolved in 20 mL of ethyl acetate and washed with 10 mL deionized water several times. After drying under reduced pressure, Polyurethane-Suc was obtained as light yellow solid. (yield: 52%) 1H NMR (400 MHz, CDCl3,δ ppm): 7.10 (d, 4H, -Ph), 6.80 (d, 4H, Ph), 5.00 (m, 0.5H, -CH2-OH), 4.95 (m, 1H, (CH3)2-CH-O-), 4.20 (m, 4H, Ph-O-CH2-CH), 4.00 (m, 4H, -CH-CH2-O-C=O), 3.40-2.80 (m, 4H, -NH2-NH2-), 2.60 (m, 4H, -CH2-CH2of succinate group), 2.25 (m, 2H, -CH2-CH2-), 1.90 (m, 2H, -CH2-CH2-), 1.55 (s, 3H, CH3-), 1.01(d, 6H, (CH3)2-CH-). 2.4 Preparation of crosslinked PHU coating systems 2.4.1 The preparation of solvent-borne PHU coatings The solvent-borne PHU coatings were prepared by curing PHUs with commercial BPA-based epoxy resin (epoxy value: 0.51, the stoichiometric ratio between epoxy groups and secondary amino groups was 1:1) in acetone. The mixture was applied on the aluminum

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panels (20 mm × 30 mm × 1 mm, wiped with alcohol before use) by brushing following by the curing process (60 oC/2 h, 120 oC/2 h; 160 o C/2 h, 1 mmHg). After that, the thermal, mechanical and morphological properties of the cured coatings were characterized. 2.4.2 The preparation of water-borne PHU coatings The obtained PHU-EDA-Suc were dispersed in deionized water with different amount of sodium bicarbonate (the mass ratio of NaHCO 3 to PHU = 1:1, 1:5, 1:7, or 1:10) under ultrasonic assist. Then the water-borne PHU coatings were prepared by curing PHU emulsion with commercial BPA-based epoxy resin emulsion (solid epoxy value 0.325, 70% wt. in water) via an ultrasonic treatment for 5 minutes. The mixture was applied on aluminum panels (25 mm × 50 mm × 1 mm, wiped with alcohol before use) by brushing following with curing process (60 oC/2 h, 120 oC/2 h; 160 o C/2h, 1 mmHg). The particle size of PHU emulsions and thermal, mechanical and morphological properties of waterborne PHU coatings were characterized, respectively.

3. Results and Discussion 3.1 Synthesis and characterization of monomers In the recent publications,36-38 diphenolic acidbased epoxy monomers showed some interesting properties such as high T g , high reactivity and tuned viscosity, but any diphenolic acid-based PHU has still not been reported so far. The rigid bisphenol ring structure of diphenolic acid was expected to confer high heat resistance and other properties to the corresponding PHUs. More preferentially, it is of high interest to synthesis diphenolic acid-based PHUs via a greener nonisocyanate route. Herein, a diphenolic acidbased epoxy monomer was synthesized firstly, followed by its cyclocarbonation reaction in the presence of carbon dioxide with a suitable catalyst, as seen in Figure 1B.


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A

a b c HO

CDCl3

d e HO O

bc

b c

CDCl3

CDCl3

CDCl3

f

g

6

f

h,i H2 O C

IP-DPEDGE

O j

k' f,j HO

j'

a b c

CH O O k' 2 O

d

e O O

g

4

k' f,j a b c

j'

CH O O k' 2

b c

2

1

7

m

r O NH O CH2 h,i j k O o OH

d e OO

O

g

PHU-DETA m DMSO g l n e d

h,i,k,j' n

e d a

m n e

g f

k' f j 6

PHU-EDA acetone a d g

H H m OH N O N O CH2 N n h,i j k O l H

g

DPA-BisCC

3

δ (ppm)

h,i,k,j'

f

HO

H2 j O O O C O h,i k,l

H n H2 OH O N O C N h ,i j k O m H

f

bc

j k l e d a

il f jh k 5

g

k ,l

h i

f

a b c d e O O

g

b c

d e O O

O

b c

e d a

b c

d e O O

H2 C O

bc 7

a

a

IP-DPE

f

f

g

O O

e O O

H2 C O

bc O

8

d

g

O

b c OH

j' H2 C O O k'

HO

B

e d a

a HO

DPA

OH

5

s qH N

PHU-IPDA r a DMSO

p

h,i,k,j' s m q 4

δ (ppm)

a

3

e d 2

g p o,n 1

Figure 2. 1H NMR spectra of the synthesis of monomers and polymers. (A) Diphenolic acid (DPA), isopropyl diphenolate (IP-DP), diglycidyl ether of isopropyl diphenolate (DGE-IPDPE), diphenolic acid-based bis(cyclocarbonates) (DPA-BisCC). (B) Different polyhydroxyurethanes (PHUs) synthesized by reacting DPA-BisCC with ethylenediamine (PHU-EDA), diethylenetriamine (PHU-DETA), and isophoronediamine (PHU-IPDA), respectively. In Figure 1B, the esterification reaction took place between diphenolic acid and isopropanol to result in isopropyl diphenolate bearing two reactive phenolic hydroxyl groups. The 1H NMR characterization (Figure 2(A))

Biscc 3442 (-COOR-)

1796 (C=O)

1719 1247 (C=O) (C-O)

PU-IPDA 1708 3308 (-CONH-) 3308 (-CONH-)

3307 (-CONH-) 3500

3000

1247 (C-O)

(C=O)

PU-EDA 1703

PU-DETA 2500

1175 (C-O)

(C=O)

1243 (C-O)

1703 (C=O)

1244 (C-O)

2000

1500

1000

500

Wavenumber (cm-1)

Figure 3. FTIR spectra of the cyclocarbonate (DPA-BisCC) and polyhydroxyurethanes (PHU-EDA, PHU-DETA, and PHU-IPDA).

confirmed the presence of substituted isopropyl group (H f , δ=5.0) and substitution reaction was complete. Additionally, a new and strong 1H NMR signal (H g ) due to the methyl group of the attached isopropyl appeared at δ=1.2 ppm. The ratio of integral area for substituted isopropyl groups, methyl groups and phenyl groups was measured approximately to be 1: 6: 8, which was well consistent with its expected chemical structure. Besides, the locations of the other signals were essentially unchanged and there was no other signal caused by impurity. Noted that the synthesized isopropyl diphenolate is expected to express a much lower hydrolysis rate than the corresponding methanol and ethanol esters does, due to the increased steric hindrance of the bulky isopropanol groups, which can slow down the breakage of this ester bond during subsequent transformation under basic condition. To be short, the carboxyl group of diphenolic acid has been successfully transformed to the isopropyl ester groups, while the two remaining phenolic hydroxyl groups would undergo a glycidylation reaction to yield a new bifunctional diphenolic acid-based epoxy monomer.



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Herein, the O-glycidylation reaction of the IP-DP was carried out in the presence of epichlorohydrin under catalysis of NaOH. After purification, the corresponding epoxy monomer (DGE-IP-DPE) was obtained. From 1H NMR analysis (Figure 2(A)), the ester bond’s resonance remained, and the signals assigned to the protons of the epoxy groups and the related phenyl groups were detected at δ= 2.55, 2.68, 3.15 and 6.70 – 7.10, respectively. The ratio of integral intensity for the above signals of resonances was found to be 1: 1: 0.93: 4.34 slightly deviating from theoretical value of 1: 1: 1: 4, which is likely due to the oligomerization of a small fraction of DGE-IP-DPE to form dipolymer or even higher molecular weight products. After that, IP-DP was catalytically reacted with CO 2 , and the resultant DPABisCC showed the new NMR peaks at δ= 4-5, whereas the peaks at δ= 2.55, 2.68 and 3.15 ppm no longer appeared, which suggested that the successful formation of cyclocarbonates. 3.2 Synthesis and characterization of NIPHUs Here three representative amines (EDA, DETA and IPDA) are chosen as the chain extenders to react with the synthesized cyclocarbonate (DPA-BisCC), and accordingly the resulting PHUs are named as PHU-EDA, PHU-DETA and PHU-IPDA, respectively. In the 1H NMR spectra (Figure 2(B)), after reacting with three amines the several marked peaks of cyclocarbonate at δ= 4.0 - 5.0 disappeared, whereas new peaks at δ= 2.5 - 4.0 were observed which were assigned to methylene groups in polyamines indicating the ringopening reaction of bis-(cyclocarbonates). For PHU-IPDA, it was clearer to see several peaks arising around δ= 1.0 which were attributed to the cycloalkyl group of IPDA. What’s more, due to the asymmetry structure of cyclocarbonate group and the random chainbreaking site of ring-opening reaction, urethanes with two different structures of hydroxyl groups are obtained (Figure 2B), resulting complex 1H NMR signals. Evidence from FT-IR analysis (Figure 3) illustrates that there are two characteristic absorption series of DPA-BisCC. Peaks at 1796

Page 8 of 43

and 1175 cm-1 were assigned to the C=O and CO bonds on its cyclocarbonate rings and another pair of peaks (1719 and 1247 cm-1) were attributed to C=O and C-O bonds of isopropyl ester groups. After the reaction with the amines, the peaks at 1796 and 1175 cm-1 vanished in the spectra of PHU-EDA, PHUIPDA and PHU-DETA, while the new peaks at 3308 and 3307 cm-1 appeared due to the formation of hydroxyl groups. These changes confirmed the ring opening of BisCC after attack of the amines. On the other hand, the absorption of isopropyl ester groups (1719 and 1247 cm-1) was still observed after this transformation, so that the ammonolysis of the ester bond can be safely neglected. 3.3 Molecular Weight Characterization M n (number average molecular weight) of the PHU affects its ultimate properties greatly, and herein variables were set to clarity their influence on M n of the synthesized PHUs. The results in Table 1 reveal the correlation between the M n and various conditions such as amines, reaction time and solvents. For solvents, Ochiai39 compared propylene glycol methyl ether acetate (PGMAC) with NMP in silicone backbone PHUs synthesis. It was found that a higher M n (7000) of PHU was obtained in PGMAC with better monomer conversion and yield than in NMP (M n , 3000). And further when polymerizations were carried out in bulk, M n up to 30000 Da could be reached.40, 41 Considering that the high viscosity of bulk PHUs would raise the processing difficulties, here PGMAC was used as solvent. As the Table 1 showed (No. 3-6), the M n of PHU prepared in PGMAC were much higher than in NMP, and this trend agreed well with Ochiai’s finding.39 However, our experimental results revealed that DPA-BisCC exhibited much lower solubility in PGMAC than in NMP. Blain42 found that hydrogen bonds between polymer chains would prevent obtaining PHUs with high molar masses. Although carbonyl groups of NMP and PGMAC could both avoid the entanglement of PHU chains, the polymerization conducted in PGMAC was more likely to bulk-like reaction than in NMP due to phase separation during the


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Table 1. Polycondensation of BisCC and Polyamines in Various Conditionsa

a

Solvent

Amine

Time (h)

Mn(Da)

Polydispersity (PDI)

1

NMP

EDA

4

2020

1.8

2

NMP

EDA

8

2130

1.6

3

PGMAC

EDA

4

4360

2.0

4

PGMAC

EDA

8

4540

1.8

5

PGMAC

DETA

4

4820

2.0

6

PGMAC

IPDA

4

4610

2.2

Reaction conditions: biscyclocarbonate 5 mmol, diamine 5 mmol, solvent 2 mL, 80 °C.

reaction process. It was probably the main reason of the high M n PHU obtained. Besides, prolonging the reaction time only slightly affected the value of M n (Table 1, No. 1-4), which means, within a short time (4 h), the thoroughly conversion of bis(cyclocarbonate) and chain propagation have accomplished. At this point, the polymerization was constrained by molecular diffusion and potential sidereaction. Also, according to the literatures, the reactivity of polymerization was closely related with the chemical structure of the bis(cyclocarbonate). It was reported that a terephthalic acid derived bis(cyclocarbonate) could react with alkyl amines to obtain NIPU at room temperature.43 However, the reaction of 2,5-furandicarboxylic acid-based bis(cyclocarbonate) with alkyl diamines could only be conducted under high temperature (150 - 160 oC).44 However, when the reaction was carried out at 80 oC, the polymerization could hardly occurr. Hence, the high reactivity our diphenolic acid-based bis(cyclocarbonate) to amines might make it suitable to many important applications as coatings and adhesive with relatively low energy consumption. 3.4 Solvent-borne PHU coatings Since the M n of the obtained linear polyhydroxyurethane is still relatively low, the commercial BPA-based epoxy resin is used as curing agent to improve ultimate performances

for coating applications. Crosslinking network of the coating was generated by the reaction between epoxy groups and side hydroxyl groups or –NH of the urethane under high temperature. Besides, the polyhydroxyurethane prepolymer and curing agent are easily soluble in acetone, which was regarded as a lowtoxicity and inexpensive solvent, thus enhancing processing and handling safety and lowering the cost. 3.4.1 Glass relaxation temperature The glass transition temperatures of the prepared cured PHU coatings were determined on dynamic DSC analysis. All the PHU coatings displayed a single glass-rubber transition process as indicated by a dramatic change of specific heat in the DSC curves (Figure 4(A)), which implicated there was no apparent phase separation occurred in the PHU materials. PHU-DETA showed a higher Tg than PHU-EDA did (82 oC vs. 54 oC), because DETA could provide additional secondary amino hydrogen which was easy to react with epoxy resins to form a highly crosslinked network, thus further restricting the chain relaxation. Without introduction of any secondary amino hydrogen from the amine chain extender, PHU-IPDA (116 oC) showed a much higher T g than PHU-EDA did. This finding was analogue to the IPDA-cured DGEBA45 and IPDA-cured trifunctional epoxy



PHU-EDA PHU-IPDA PHU-DETA

116 82

100

B PHU-EDA PHU-IPDA PHU-DETA

80

Weight (%)

A

Heat Flow (W/g) (Exo Down)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 43

60

40

54

20

0 50

100 Temperature (oC)

200

400

Temperature (oC)

600

Figure 4. DSC thermograms (A, 10 oC/min) and TGA curves (B, 10 oC/min under nitrogen) of the PHU coatings prepared in acetone. resin46 featuring a very high T g , owing to the high rigid C 6 ring structure of IPDA. This finding suggested that thermal resistance of our synthesized PHU can be effectively tuned by using different amine chain extender from near room temperature to higher temperature. 3.4.2 Thermal stability The thermal degradation behaviors of the PHU coatings were examined from TG analysis in nitrogen, as shown in Figure 4(B). The data illustrated all the samples were quite stable up to ~190 oC. PHU-EDA firstly began degrading following PHU-DETA and PHU-IPDA. The T d ’s of three samples were measured to be 242 o C, 258 oC and 287 oC, respectively. However, PHU-IPDA degraded rapidly as the temperature

further increasing. The decomposition process accelerated and a minimum amount of residues was obtained. It was possibly owing to the thermal-instability of naphthenic group at high temperature. In addition, the slope of weight loss curves changed manifestly during three temperature ranges, indicating that the degradation process of PHU coatings was divided into three stages. The first decomposition took place in the temperature range 200-240 oC and it was attributed to the cleavage of side-chain ester groups (isopropyl ester).47 And the second step (240-300 oC) of weight loss mainly corresponded to the decomposition of the urethane bonds. Usually the urethane bonds began to decompose at approximately 200 oC.48 But this period

Figure 5. AFM images of the PHU coatings; (A) PHU-EDA, (B) PHU-DETA, (C) PHU-IPDA


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A

B

C

Figure 6. Water contact angles of PHU films. (A: PHU-EDA, 82.0o; B: PHU-DETA, 96.1o; C: PHUIPDA, 108.5o) delayed about 40 oC due to the existence of ester bonds. Then the weight of samples significantly decreased (300-420 oC) due to the complete decomposition of the crosslinking network. On the other hand, the charred residues at higher temperature (e.g. >500 oC) of the PHU coatings varied greatly, following the order of PHU-IPDA < PHU-DETA < PHU-EDA. The char yield was likely positively correlated to the amine’s nitrogen content (IPDA 16.5%, DETA 40.7%, and EDA 46.6%). This phenomenon indicated the increased nitrogen content of amine would benefit the high temperature carbonization ability of the polymer matrix under inert atmosphere, which is likely indicated lowered flammability.

surface roughness of the PHU coatings did not vary markedly with the chemical structure of the amine used, indicating its good spreading and self-levelling property on aluminium panels upon heating to suitable temperature. Besides, the static water contact angles of the surface of PHU coatings were measured to characterize the surface hydrophilic property. As shown in Figure 6, the water contact angles of PHU coatings varied with the amines used. For PHU-EDA and PHU-DETA, the amine chian extender affected the contact angles. And for PHU-IPDA, the existance of the substituted carbon-rich cyclohexyl ring futher improved the hydrophobicity of the resulting PHU coating. These finding likely suggested that the hydrophobicity of the DPA-based PHU coating can be adjusted moderately by reacting the 3.4.3 Surface morphology and water contact same DPA-derived bis(cyclocarbonates) with angle the different amines of the different The morphology of the PHU coatings was hydrophobicity and amino functionalities. further characterized by AFM. The results in Figure 5 showed that the three types of coatings 3.4.4 Mechanical properties exhibited remarkable smooth morphology, The mechanical properties of PHU coatings which was similar to silicone-modified coatings were shown in Table 2. The pencil hardness of with low surface energy.49, 50 Furthermore, the PHUs coatings ranged from 4H to 5H,

Table 2. Mechanical Properties of Various PHU Coatings PHU-EDA PHU-DETA

PHU-IPDA

Pencil hardnessa

4H

5H

5H

Adhesion gradeb

1

1

3

a

Ranging from 6B (soft) to 6H (hard). Ranging from grade 0 (best) to grade 5 (worst).

b



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

depending on the chemical structures of the amine chain extender used. These NIPUs showed superb performance in the surface hardness, and the amine slightly affect it. This was probably due to the inherent rigidity of the massive diphenolic acid-based BisCC. However, in terms of crosshatch adhesion, PHU-EDA and PHU-DETA both performed well (Grade 1) while the abscission part of PHU-IPDA was much more than others. The reason may be that the naphthenic group in IPDA wasn’t so compatible with the hydroxyl on the surface of aluminium panels, reducing the adhesion strength between PHU coating and the aluminium substrate. 3.5 Waterborne PHU coatings The PHU coatings prepared in acetone exhibited excellent properties, showing the possible potentials in coating industry. On the other hand, since in the recent years, environmental-friendly water-borne coatings attract a lot of research interest, here we also attempted to chemically modify PHU to develop environmental friendly coatings. Considering that the reaction between acid anhydride and side hydroxyl group in each repeated urethane bond is readily carried out, thus carboxyl group can be easily introduced by this reaction. Through further transformation from carboxyl groups to sodium salt, a stable PHU aqueous emulsion was formed and further used to prepare water-borne coatings. Herein the waterborne PHU was prepared by reacting succinic anhydride with the secondary hydroxyl groups of PHU-EDA, which was the most hydrophilic one among the PHUs. As Figure 7 shown, the 1H spectra of PHU-EDA-Suc was almost identical to PHUEDA, except for several NMR signals aroundδ=2.6 (Hp,o). These peaks were assigned to the methylene group in succinic anhydride, indicating that the reaction was carried out successfully. 3.5.1 Particle size and morphology analysis of PHU emulsion In this work, the obtained water-borne PHU was dispersed in deionized water with different addition of sodium bicarbonate, and the results

Page 12 of 43

were shown in Table 3. With the decreased amount of NaHCO 3 , the particle size of the emulsion systematically increased and the emulsion became muddier. Further evidence was obtained from TEM photographs of PHU emulsion particles (Figure 9). In the photograph (a), the emulsion particles were surrounded by the crystals of sodium bicarbonate. And in the photographs (b) and (c), the size of the emulsion particles increased when the addition of the NaHCO 3 dropped. Furthermore, a wider particle size distribution showed up when the mass ratio of NaHCO 3 was 7.1% (PHU4), which agreed with the previous data well (Fig. 8). By varying the amount of NaHCO3 used, the size of PHU particles could be precisely controlled. The samples of PHU coatings with different addition of sodium bicarbonates were subjected to differential scanning calorimetry (DSC). It was seen that all the PHU coatings displayed single glass transitions (Figure 10(A)) and the glass transition temperatures varied with the content of sodium bicarbonates. For PHU1, the glass transition temperature was measured to be 35 oC. And the T g surprisingly increased about 25 oC when the mass ratio of NaHCO 3 cut down into 16.7%. For polymer materials, high crosslinking density led to high glass transition

PHU-EDA j' HO H 2 C O O k' O

a b c d e O O

g

H 2 OH O O C h,i j k O

Acetone

f

b c

h,i,k

j,k' f O a b c

g

b c

6

d e O O

j' m n

e

OH p o

j' HO H2 C O O k' O

7

H n N m N H

d g

a

PHU-EDA-Suc

O

H n H2 O O N O C N h,i j k O m H

Acetone

f

j,k' f

h,i,k

5

4 δ (ppm)

j'm

n 3

p,o e

d g

2

a

1

Figure 7. 1H spectra of PHU-EDA and PHUEDA-Suc


Page 13 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 3. Properties of PHU emulsions with different amount of NaHCO3

a

Item

PHU1

PHU2

PHU3

PHU4

NaHCO3 in solute (w.t.%)

50

16.7

12.5

9.1

Appearancea

transparent

transparent

transparent

opaque

Particle size(nm)

78

120

187

321

After dissolved in deionized water

temperature. The excessive NaHCO 3 in PHU1 would phase out during the curing process and lower the crosslink density, which resulti ng in a low glass transition temperature. The highest T g showed up at PHU4 and it reached to 64 oC. The addition of NaHCO 3 provided the PHU particles with significantly increased hydrophilicity. In the meantime, these NaHCO 3 would exist as an impurity among the PHU crosslinking network. By setting a series of samples, the optimum addition of NaHCO 3 was obtained (PHU4, 9.1%). Besides, the Tg of PHU4 was 9 oC higher than PHU-EDA after curing process, indicating the increased thermal resistance after introducing the acid anhydride and ion bond into the polymer chains. Figure 8. Particle size and particle size distribution of various PHUs 3.5.3 Thermal stability The thermal degradation behaviors of the PHU coatings were examined according to thermogravimetric analysis (TGA) and the results were shown in Figure 10(B). The weight loss curves illustrated that all the samples were quite stable before 180 oC. And PHU1 began to degrade at a temperature of 190 oC and the T d was measured to be 240 oC. Other three samples displayed a higher initial degradation temperature at about 230 oC and the T d ’s were varied from 292 oC to 306 oC, indicating a better thermal stability than the PHU1. It was presumably due to the excessive amount of NaHCO 3 that reduced the crosslinking density resulting in thermal instability. The overall weight loss of PHU coatings was in the order of PHU1 > PHU2 > PHU3 > PHU4, indicating the relationship between the NaHCO 3 addition and the thermal stability, which agreed well with Figure 9. TEM photographs of PHU water dispersions; (a) PHU1, (b) PHU2, (c) PHU3, (d) the DSC results above. PHU4



A

PHU1 PHU2 PHU3 PHU4

Heat Flow (W/g) (Exo Down)

63

100

59 55

B

100

98

80 Weight (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 43

96

60

40

200

PHU1 PHU2 PHU3 PHU4

35

20 0

50 Temperature (oC)

100

200

400 Temperature (oC)

600

Figure 10. DSC thermograms (A) and TGA curves (B) of the waterborne PHUs coatings with different NaHCO3 addition. 3.5.4 Surface morphology and contact angle Figure 11 illustrated AFM images of the waterborne PHU coatings. For PHU1, we found that the regular crystal generated on the surface, and the roughness was in a high grade (-131.1 nm to 163.6 nm). And PHU2 and PHU3 exhibited an incredible maximum roughness of less than 2.5 nm. This result indicated that the polyurethane coatings spread easily over the aluminium surface. With the deduction amount of NaHCO 3 , the coating surface turned to be rougher. For PHU4, the polyhydroxyurethane and epoxy particles grew into a larger extent owing to the inadequate emulsification, thus a higher degree surface roughness was observed. And these hydrophobic “peaks” could prevent the surface from contacting the water. It was of interest to investigate the surface

wettability of PHU coatings after electrovalent bond was introduced into the molecular structure. In this work, the static water contact angles on the surface of polyurethane coatings were measured to characterized hydrophilic property. As shown in Figure 12, the water contact angles of polyurethane coatings were corresponded with the addition of NaHCO 3 . For PHU2, PHU3 and PHU4, the water contact angles were 62.8o, 65.0 o and 68.4 o, respectively. And for polyurethane with too much NaHCO 3 (PHU1, 50% wt), water contact angles decreased rapidly to 35.6 o. All the surfaces of polyurethane coatings were hydrophilic, which may find potential in biomedical materials to avoid the adverse effect arising from some hydrophobic polymeric body-contact materials.

Figure 11. AFM images of the polyurethane coatings; (a) PHU1, (b) PHU2, (c) PHU3, (d) PHU4


Page 15 of 43

3.5.5 Mechanical properties The pencil hardness and adhesion properties of coatings were shown in Table 4. For PHU1, the performance of worst hardness and crosshatch adhesion were accounted for the excessive NaHCO 3 . And with the reductive amounts of NaHCO 3 , the hardness of coating increased from 2H to 3H. So, there existed a minimum amount for NaHCO 3 addition. For adhesion test, these PHU coatings exhibited the same trend as hardness did. Compared with other bio-based coatings51, 52 (pencil hardness: 2B~3H, crosshatch adhesion grade: 1~2), the

68.4±1.5

65.0±4.9

62.8±2.7

80

Contact angle (degree)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60 35.6±5.9

40

20

PHU1

PHU2

PHU3

PHU4

PHU Film

Figure 12. Water contact angles of PHU films

Table 4. Mechanical Properties of Various PHU Coatings Item PHU1a PHU2 PHU3 PHU4 Pencil hardnessb Adhesion gradec aNaHCO

3B

2H

3H

3H

4

2

1

1

3 precipitated on the surface of the coating. bRanging from 6B (soft) to 6H (hard). cRanging from grade 0 (best) to grade 5 (worst).

bio-based polyurethane coatings in this work proved to be better. Furthermore, all these PHU-EDA derived waterborne polyhydroxyurethane coatings performed worse than original PHU-EDA coating. Future research may focus on the dual-enhance of hydrophilicity and mechanical properties.

4. Conclusions We have successfully synthesized a new biobased cyclocarbonate monomer (DPA-BisCC) derived from isopropyl diphenolate ester and carbon dioxide under catalysis of zinc-cobalt double metal cyanide complex (Zn–Co(III) DMCC). Then, DPA-BisCC was used to react ethylenediamine (EDA), with diethylenetriamine (DETA) or isophoronediamine (IPDA) under mild reaction conditions (80 oC, 4 h) to yield new biobased polyhydroxyurethanes (PHU-EDA, PHUDETA or PHU-IPDA). GPC analysis demonstrated that the molecular weights of the PHUs grow to as high as 5 kDa with a relatively low polydispersity. On the basis of these PHU prepolymers, the solvent-borne polyhydroxyurethane coating was prepared with acetone as the solvent and a bisphenol A epoxy resin as cross-linker. Results illustrated that the thermal properties depended greatly on the amine type of the chain extender used, for instance, tuned T g ’s achieved (PHU-EDA 54 oC, PHU-DETA 82 oC, PHU-IPDA 116 oC). And the solvent-borne coating also performed well in mechanical properties, such as hardness (up to 4H) and crosshatch adhesion(up to Grade 1). Atomic force microscope (AFM) photographs showed that the incredible smoothness (roughness less than 5 nm) of all the coating surfaces while the value of water contact angles varied with the amine used (from 82o to 108o). Also, the waterborne PHUs were successfully prepared by bonding the negatively charged carboxyl groups from succinic anhydride to the PHU main chain. By adjusting the degree of ionization of the carboxyl group through the salification between the attached carboxyl group and sodium



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

bicarbonate (NaHCO 3 ), we achieved the precise control of the PHU emulsion particles size (from 100 nm to 1 μm). Then an environmental friendly polyhydroxyurethane coating was produced after curing the PHU emulsion with water-borne bisphenol A epoxy resin. The T g and T d of PHU coating increased about 30 oC and 60 oC respectively when the mass ratio of the NaHCO 3 decreased from 50% (PHU1) to 7.1% (PHU4). And the thermal properties of several samples performed even better than PHU-EDA (before modification). The pencil hardness of these PHU coatings varies from 3B to 3H while adhesion grade is between grade 4 and grade 1; however, the excessive NaHCO 3 used deteriorated the coating properties. AFM images demonstrated the surface morphology of the waterborne PHU coatings, indicating that there was an optimal range (16.7% ~ 12.5%) of NaHCO 3 addition to reach the smoothness as solvent-borne PHU coating did. Waterborne PHU coatings showed higher hydrophilicity than solvent-borne counterpart due to introduction of the negatively charged carboxyl moieties to PHU backbone. In summary, our study provides a new solution to sustainable, greener PHUs based on DPA and carbon dioxide, and demonstrated its good promise for the applications not only in traditional solvent-borne but also in environmental friendly waterborne coatings with a number of interesting properties. In the future, more sophisticated functionalization of polyhydroxyurethanes and optimization of their final property will be worth of further studying to extend their potentials for applications.

Acknowledgements This research has received funding from national natural science foundation of China (NSFC) under grant agreement of No. 21636008. We would like to express our special thanks to the reviewers for commenting on our work. We also thank Professor Xinghong Zhang (from Key Laboratory of Macromolecular Synthesis and

Page 16 of 43

Functionalization, Department of Polymer Science and Engineering, Zhejiang University) for providing the catalyst and experimental facilities for cyclocarbonate synthesis.

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31. Tomita, H.; Sanda, F.; Endo, T., Polyaddition behavior of bis(fiveand six-membered cyclic carbonate)s with diamine. Journal of Polymer Science Part a-Polymer Chemistry 2001, 39, (6), 860-867. 32. Kim, Y. M.; Jae, J.; Myung, S.; Sung, B. H.; Dong, J. I.; Park, Y. K., Investigation into the lignin decomposition mechanism by analysis of the pyrolysis product of Pinus radiata. Bioresource Technology 2016, 219, 371-377. 33. Hu, L. B.; Luo, Y. P.; Cai, B.; Li, J. M.; Tong, D. M.; Hu, C. W., The degradation of the lignin in Phyllostachys heterocycla cv. pubescens in an ethanol solvothermal system. Green Chemistry 2014, 16, (6), 3107-3116. 34. Gibson, J. M.; Thomas, P. S.; Thomas, J. D.; Barker, J. L.; Chandran, S. S.; Harrup, M. K.; Draths, K. M.; Frost, J. W., Benzenefree synthesis of phenol. Angewandte Chemie-International Edition 2001, 40, (10), 1945-1948. 35. Zhang, X. H.; Wei, R. J.; Zhang, Y. Y.; Du, B. Y.; Fan, Z. Q., Carbon Dioxide/Epoxide Copolymerization via a Nanosized Zinc-Cobalt(III) Double Metal Cyanide Complex: Substituent Effects of Epoxides on Polycarbonate Selectivity, Regioselectivity and Glass Transition Temperatures. Macromolecules 2015, 48, (3), 536-544. 36. Maiorana, A.; Spinella, S.; Gross, R. A., Bio-Based Alternative to the Diglycidyl Ether of Bisphenol A with Controlled Materials Properties. Biomacromolecules 2015, 16, (3), 1021-1031. 37. Patel, A.; Maiorana, A.; Yue, L.; Gross, R. A.; Manas-Zloczower, I., Curing Kinetics of Biobased Epoxies for Tailored Applications. Macromolecules 2016, 49, (15), 5315-5324. 38. Varghai, D.; Maiorana, A.; Meng, Q. K.; Gross, R. A.; ManasZloczower, I., Sustainable, electrically-conductive bioepoxy nanocomposites. Polymer 2016, 107, 292-301. 39. Ochiai, B.; Kojima, H.; Endo, T., Synthesis and Properties of Polyhydroxyurethane Bearing Silicone Backbone. Journal of Polymer Science Part a-Polymer Chemistry 2014, 52, (8), 1113-1118. 40. Maisonneuve, L.; More, A. S.; Foltran, S.; Alfos, C.; Robert, F.; Landais, Y.; Tassaing, T.; Grau, E.; Cramail, H., Novel green fatty acid-based bis-cyclic carbonates for the synthesis of isocyanate-free poly(hydroxyurethane amide)s. Rsc Advances 2014, 4, (49), 2579525803. 41. Sheng, X. F.; Ren, G. J.; Qin, Y. S.; Chen, X. S.; Wang, X. H.; Wang, F. S., Quantitative synthesis of bis(cyclic carbonate) s by iron catalyst for non-isocyanate polyurethane synthesis. Green Chemistry 2015, 17, (1), 373-379. 42. Blain, M.; Cornille, A.; Boutevin, B.; Auvergne, E.; Benazet, D.; Andrioletti, B.; Caillol, S., Hydrogen bonds prevent obtaining high molar mass PHUs. Journal of Applied Polymer Science 2017, 134, (45). 43. Steblyanko, A.; Choi, W. M.; Sanda, F.; Endo, T., Addition of fivemembered cyclic carbonate with amine and its application to polymer synthesis. Journal of Polymer Science Part a-Polymer Chemistry 2000, 38, (13), 2375-2380. 44. Zhang, L.; Luo, X. L.; Qin, Y. S.; Li, Y. B., A novel 2,5furandicarboxylic acid-based bis(cyclic carbonate) for the synthesis of biobased non-isocyanate polyurethanes. Rsc Advances 2017, 7, (1), 37-46. 45. Chrysanthos, M.; Galy, J.; Pascault, J. P., Influence of the BioBased Epoxy Prepolymer Structure on Network Properties. Macromolecular Materials and Engineering 2013, 298, (11), 12091219. 46. Aouf, C.; Nouailhas, H.; Fache, M.; Caillol, S.; Boutevin, B.; Fulcrand, H., Multi-functionalization of gallic acid. Synthesis of a novel bio-based epoxy resin. European Polymer Journal 2013, 49, (6), 1185-1195.



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Figure 1. (A) Synthesis of diphenolate acid-based Bis-cyclocarbonates (DPA-BisCC). (B) Synthesis of polyurethanes from bis(cyclocarbonates) and different amines. (C) Preparation of crosslinked polyhydroxyurethanes. 176x148mm (300 x 300 DPI)


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Figure 2. 1H NMR spectra of the synthesis of monomers and polymers. (A) Diphenolic acid (DPA), isopropyl diphenolate (IP-DP), diglycidyl ether of isopropyl diphenolate (DGE-IP-DPE), diphenolic acid-based bis(cyclocarbonates) (DPA-BisCC). (B) Different polyhydroxyurethanes (PHUs) synthesized by reacting DPABisCC with ethylenediamine (PHU-EDA), diethylenetriamine (PHU-DETA), and isophoronediamine (PHUIPDA), respectively. 297x251mm (300 x 300 DPI)



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Figure 3. FTIR spectra of the cyclocarbonate (DPA-BisCC) and polyhydroxyurethanes (PHU-EDA, PHU-DETA, and PHU-IPDA). 297x250mm (300 x 300 DPI)


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Figure 2. 1H NMR spectra of the synthesis of monomers and polymers. (A) Diphenolic acid (DPA), isopropyl diphenolate (IP-DP), diglycidyl ether of isopropyl diphenolate (DGE-IP-DPE), diphenolic acid-based bis(cyclocarbonates) (DPA-BisCC). (B) Different polyhydroxyurethanes (PHUs) synthesized by reacting DPABisCC with ethylenediamine (PHU-EDA), diethylenetriamine (PHU-DETA), and isophoronediamine (PHUIPDA), respectively. 297x254mm (300 x 300 DPI)



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Figure 4. DSC thermograms (A, 10 oC/min) and TGA curves (B, 10 oC/min under nitrogen) of the PHU coatings prepared in acetone. 297x234mm (300 x 300 DPI)


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Figure 4. DSC thermograms (A, 10 oC/min) and TGA curves (B, 10 oC/min under nitrogen) of the PHU coatings prepared in acetone. 297x225mm (300 x 300 DPI)



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Figure 5. AFM images of the PHU coatings; (A) PHU-EDA, (B) PHU-DETA, (C) PHU-IPDA 96x91mm (160 x 160 DPI)


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Figure 6. Water contact angles of PHU films. (A: PHU-EDA, 82.0o; B: PHU-DETA, 96.1o; C: PHU-IPDA, 108.5o) 297x221mm (300 x 300 DPI)



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Figure 7. 1H spectra of PHU-EDA and PHU-EDA-Suc 297x255mm (300 x 300 DPI)


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Figure 8. Particle size and particle size distribution of various PHUs 297x236mm (300 x 300 DPI)



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Figure 9. TEM photographs of PHU water dispersions; (a) PHU1, (b) PHU2, (c) PHU3, (d) PHU4 161x161mm (80 x 80 DPI)


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Figure 10. DSC thermograms (A) and TGA curves (B) of the waterborne PHUs coatings with different NaHCO3 addition 297x217mm (300 x 300 DPI)


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Figure 11. AFM images of the polyurethane coatings; (a) PHU1, (b) PHU2, (c) PHU3, (d) PHU4 96x91mm (160 x 160 DPI)



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Figure 12. Water contact angles of PHU films 297x226mm (300 x 300 DPI)


Polyhydroxyurethanes (PHUs) Derived from Diphenolic Acid and

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