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Synthesis and Properties of Block and Graft Waterborne Polyurethane Modified With [alpha],[omega]-Bis(3-(1-methoxy-2-hydroxypropoxy)propyl) polydimethylsiloxane and [alpha]-N, N-Dihydroxyethylaminopropyl-[omega]-butylpolydimethylsiloxane.

In this study, [alpha],[omega]-bis(3-(1-methoxy-2-hydroxypropoxy}-propyl)polydimethylsiloxane and [alpha]-N,N-dihydroxyethyla-minopropyl-[omega]-butylpolydimethylsiloxane were used to prepare block and graft waterborne polyureathane-polysiloxane copolymer dispersions. [alpha],[omega]-bis(3-(1-methoxy-2-hydroxypropoxy)propyl)polydimethylsiloxane and [alpha]-N,N-dihydroxyethyla-minopropyl-[omega]-butylpolydimethylsiloxane were used to prepare block and graft waterborne polyureathane-polysiloxane copolymer dispersions. [alpha],[omega]-bis(3-1-methoxy-2-hydroxypropoxy)propyl)polydimethylsiloxane was synthesized by hydrosilylatlon, methoxylation and equilibrium reactions; [alpha]-N,N-dihydroxyethylaminopropyl-[omega]-butylpolydimethylsiloxane was synthesized via hydroxyl protection, alkylation, anionic ring-opening polymerization, hydrosilylatlon. and deprotection. Block and graft waterborne polyurethane-polysiloxane copolymer dispersions were prepared by the reaction of polypropylene glycol) (PPG), toluene cliisocyanate (TDI). 2,2-dimethylol propionic acid (DMPA), 1,4-butanediol (BDO), [alpha],[omega]-bis(3-(1-methoxy-2-hydroxypropoxy)propyl)polydime-thylsiloxane, and [alpha]-N,N-dihydroxy-ethylaminopropyl-[omega]-butylpolydimethylsiloxane. The water absorption of block and graft waterborne polyurethane-polysiloxane copolymer films decreased from 163.9 to 40.2% and 17.3%, respectively, when percent of polysiloxane (w/w) increased from 0 to 5%, and the tensile strength of the block waterborne polyurethane-polysiloxane copolymer films decreased while the tensile strength of graft waterborne polyurethane-polysiloxane copolymer films increased with increase of percent of polysiloxane. For graft waterborne polyurethane-polysiloxane films, the Published online in Wiley Online Library (wileyonlinelihrury.com). O20I3 Society of Plastics Engineers tensile strength would decrease when percent of polysiloxane was more than 3%. POLYM. ENG. SCI., 54:805-811. 2014. [c]2013 Society of Plastics Engineers

INTRODUCTION

Polyurethane is a kind of polymer which is used widely in many fields (1-3). Polyurethane materials possess outstanding performance such as toughness, abrasion resistance, mechanical flexibility, and chemical resistance. However, with more severe regulations of volatile organic compounds (VOC) release, increased attention in water-home polyureihanes (WPU) materials have been received because of their applications in a variety of as foams, coatings and adhesives (4-8). During the synthesis of water-borne polyurethane. water as a dispersanl replaced the organic solvent, largely reducing the release of VOC. But due to the introduction of hydrophilic groups in the polyurethane chains, ihe water-resistance of waterborne polyureihanes is usually inferior to solvent-based polyureihanes and their applications were greatl\ restricted. One of the most used strategies to modify the WPU water-resistance perfonnances is lo prepare polyurethane-polysiloxane block or graft copolymers. It is well known that polysilox-anes possess superior water-resistance and low surface energy, and so on 19-11). Copolymerization of polysilox-anes and polyureihanes can endow polyurethanes with ihe excellent water-resistance properties of polysiloxanes so lhal new pol>urelhane materials can be obtained (12 14).

Generally, block and graft waterborne polyurethane-polysiloxane dispersions can be obtained via reaction between polysiloxane with a diol group and isocyanale; and. the chemical siruciure of ihe polysiloxanes used lo prepare block and grail waterborne polyurethane-polysiloxane dispersions were depicted as Scheme I.

Nowadays, there have been some researches 1'ocused on polysiloxane block copolymcri/aiioti modification. Graft copolymeri/ations ol polysiloxane and polyurethane have been rare because of some difficulties in synthesizing polysiloxane with a diol end gmup (15, 66). In our previous research, we synthesized polysiloxane with a diol end group having two primary hvdroxyl groups. a-iV,W-dihydrox-yethyl-aminopropyl-w-butylpolydimethylsiloxane 117. 18). The study about block and graft waterborne polyurethane dispersions modified by polysiloxane wilh a diol group have been rare. So in this study, on ihe one hand, we synthesized a.w-bis(3-( 1 -melhoxy-2-hydroxypmrx>xy (propyl Ipolydime-thylsiloxane by hydrosilylalion. melhoxylation and equilibrium reactions 119) and o-A'A-dihydroxyethylaminopropyl-(D-butylpoly-dimcthylsiloxane via hydroxy I protection, alkylation. anionic ring-opening polymerization 120), hydrosilylalion, and deprotection, respectively. On the other hand, the block and graft waterborne polyurethane-polysiloxane dispersions were prepared via ihe reaction of poly(propylene glycol) (PPG), toluene diisocyanate (TDD, 2,2-dimelhylol propionic acid (DMPA). 1,4-butanediol (BDO), a,("-bis (3-( l-inelhoxy -2-hydroxypropoxy (propyl) polydimethylsi-loxane and a-A'JV-dihydroxy-elhylamino-pmpyl-oj-bulylpo-lydimeihylsiloxane which were shown in Scheme 2. From the schematic presentation for block and graft waterborne polyurethane-polysiloxane dispersion, il could be seen thai polydimethysiloxane moieties could be either blocked along Ihe polymer backbone or grafted from the polymer backbone as side-chains; and. the different way of introducing the polydimethysiloxane moieties would bring different influence on the properties of the block and graft polyurethane-polysiloxane copolymer dispersions and films. Therefore, in this study, the effect of polysiloxane on the viscosity, mechanical properties, water absorption of the block and graft waterborne polyurelhane-polysiloxane copolymer dispersions and films were mainly investigated. The influence of polysiloxane on the particle size. particle morphology, micropahse separation and surface properties of copolymer films will be discussed in the next study.

EXPERIMENTAL SECTION

Materials

Toluene diisocyanate (TDI, [greater than or equal to] 98%) purchased from Gansu Yinguang Chemical Industry Group was vacuum distilled before use. Poly(propylene glycol) (PPG; 2000 g/mol, 56 mgKOH/g) was dried and degassed al 80[degrees]C under vacuum for 5 h. 2.2-dimelhylol propionic acid (DMPA, [greater than or equal to] 98%) purchased from Chemical Technology Academy of Shandong Province was dried at 100[degrees]C under vacuum for 2 h. 1,4-butanediol (BDO, 99%). trie-ihylamine (TEA. 98%) and dielhylenetriamine (DETA. [greater than or equal to] 96%), all A.R, are products of Sinopec Beijing Yanshan Company. Sinophami Group and Nanjing Golden Chemical. All these chemicals were dried over 4 A molecular sieve before use.

Synthesis of [alpha],[omega]-Bis(3-(I-methoxy-2-hydroxypropoxy)propyl)polydiniethylsiloxane

[alpha],[omega]-Bis(3-(1-melhoxy-2-hydroxypropoxy)propyl)poly-dimethylsiloxane. was synthesized depicted in Scheme 3 according to the literatures (19).

Synthesis of [alpha]-N,N-Dihvtlroxyetliylaniinopropyl-[omega]-butylpolydimethylsiloxane

Polysiloxane with a diol end group. [alpha]-N-N-dihydroxye-thylaminopropyl-[omega]-bulyl-polydimelhylsiloxane. was synthesized depicted in Scheme 4 according lo our previous literatures (17, 18).

Synthesis of Waterborne Polyurethane Dispersion

Poly(propylene glycol) ([M.sub.n] = 2000 g/mol) and toluene diisocyanate (TDI) were mixed in the four-neck flask equipped wilh mechanical stirrer, thcnnomeler. and nitrogen inlet. The reaction system was kept for 1 h under stirring condition al 70[degrees]C; and. then dimclhylolpropionie acid (DMPA) and 1,4-butanediol (BDO) dissolved in N,N-dimethylformamide (DMF) were added into the mixture for another 1 h. After reaction, the percent of COOH and ihe value of NCO/OH were remained at about 2.3% and 1.28, respectively. Then irielhylamine (TEA) was injected into the system to neutralize ihe COOH group for 20 min to gel the polyurethane prepolymer. At last, ihe prepolymer was emulsified al vigorous slirring condition to keep solid content of about 25%. The waterborne polyurethane dispersion was denoted as WPU.

Synthesis of Block Waterborne Polyttrethane-Polysiloxane Dispersions

[alpha],[omega]-Bis(3-(1-inelhoxy-2-hydroxypropoxy)propyl)polydimethylsiloxane, poly(propylene glycol) ([M.sub.n] = 2000 g/mol), and toluene diisocyanate (TDI) were mixed in the four-neck flask equipped wilh mechanical stirrer, thermometer, and nitrogen inlet. The reaction mixture was stirred for 1 h at 70[degrees]C; and then, ditnethylolpropionic acid (DMPA) and 1,4-butanediol (BDO) dissolved in N,N-dimethylformamide (DMF) were added into the mixture and reacted for another 1 h. After reaction, the percent of COOH and the value of NCO/OH were remained al about 2.3% and 1.28, respectively. Then, trielhylamine (TEA) was fed into the reactor and mixed thoroughly for 20 min to neutralize the COOH group lo get Ihe polyurethane prepolymer. At last, the prepolymer was emulsified al vigorous siirring to kepi solid content of aboul 25%. By adding different amount of [alpha],[omega]-bis(3-(1-methoxy-2-hydroxypro-poxy)propyl)-polydimelhylsiloxane. the block waterborne polyurelhane-polysiloxane dispersions were obtained. The overall reaction scheme was summarized in Scheme 2a. The block waterborne polyurelhane-polysiloxane dispersions wilh different percent of polysiloxane (% w/w) were denoted as BPU-i. (i = 1, 2, 3).

Synthcsix of Graft Waterborne Polynrethane-Polysiloxane Dispersions

[alpha]-N,N-dihydroxyc(hylaminopropyl-[omega]-hulylp(ilydimelhyl-siloxane. poly(propylene glycol) ([M.sub.n] 2000 g/mol), and toluene diisocyanate (TDI) were mixed in the four-neck flask equipped with mechanical stirrer, thermometer and nitrogen inlet. The reaction mixlure was slirred for 1 h at 70[degrees]C; and then, dimelhylolpropionic acid (DMPA) and 1,4-butanediol (BDO) dissolved in N,N-dimethylforma-mide (DMF) were added into the mixture and reacted for another I h. After reaction, the percent of COOH and the value of NCO/OH were remained at about 2.3% and 1.28, respectively. Then, triethylamine (TEA) was fed into the reactor and mixed thoroughly for 20 min lo neutralize the COOH group to get ihe polyurethane prepolymer. At last, the prepolymer was emulsified at vigorous stirring lo kept solid content of about 25%. By adding different amount of [alpha]-N,N-dihydroxyethylaminopropyl-[omega]-butyl-polydimethylsiloxane, the waterborne polyurethane polysiloxane graft copolymer dispersions were obtained. The overall reaction scheme was summarized in Scheme 2b. The graft waterborne polyurelhane-polysiloxane dispersions with different percent of polysiloxane (% w/w) were denoted as GPU-i, (i = 1. 2. 3).

Chtiriiiwrizations

Sample Preparation. For the properties of block and graft waterborne polyurelhane-polysiloxane copolymer films measurements, the films were prepared by casting a copolymer solution in water (10 wt%). The solvent was evaporated over 4 days at room temperature; and then, all the films were dried to constant weight in a vacuum oven at 100[degrees]C for 24 h.

Viscosity Measurement. All the block and graft polyurethane-polysiloxane copolymer dispersions were diluted to the same solid content (23.4%). The viscosities of the copolymer dispersions were determined by Brook Held rotary viscosimeler (RV DV-II).

TABLE 1. Propentes of blink aiul (irait waterborne
polyurethane-polysiloxane dispersions and films.
               WPU    BPU-I  GPU-I  BPU-2  GPU-2  BPU-3  GPU-3
Percent of     0      1      1      1      3      5      5
polysiloxane
(% w/w)(a)
Appearance(b)  T      T      T      T      T      T      sub-T
Solid content  25.9   23.4   25.3   23.9   24.6   25.5   25.5
(%)
Viscosity(mPu  59.6   45.2   44.0   40.0   47.2   33.2   54.4
s)(c)
Shore          92.3   90.7   88.3   86.8   91.2   82.3   92.0
hardness
Tensile        14.0   19.4   18.7   13.2   26.3   5.6    23.5
strength)
(MPa)
Elongation at  344.2  401.3  404.5  411.7  427.8  429.7  430.4
break (%)
Water          163.9  102.6  73.1   58.5   45.9   40.2   17.3
ahsorption(%)


Shore A Hardness Measurements. The Shore A hardness measurements were measured by LX-A Shore Rubber Hardness and the test method is GB 2411-80. Each hardness measurement was repeated five limes.

Mechanical Properties Measurements. The mechanical properties tests were carried oui on a Zwick/Roell Z020 universal material tester (The lest method is GB16421-1996) at room temperature with a speed of 50 mm/min. The testing samples were cut from the solution cast films and all the measurements have an average of four runs. The dumbbell type specimen was 30-mm length at two ends. 0.2-mm thickness, and 4-mm wide at the neck. Each measurement was repealed at least four times.

Water Absorption Measurement. The water-resistance properties were determined as follows. The films by casting the emulsion on a leveled PTFE plate were dried lo constant weight in a vacuum oven at 100' C for 24 h. The weighed film ([W.sub.0]) was immersed into distilled water at room lemperaiure for 24 h. followed by wiping off the water on the surface with a piece of filler paper to determined the weight ([W.sub.1]). The absorbed water ratio ([W.sub.A]) of the film was calculated by the formula.

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

RESULTS AND DISCUSSION

Properties of Blin k and Graft Waterborne Polyarethane-Polysiloxane Dispersions

The appearance and viscosities of block and graft waterborne polyurethane-polysiloxane dispersions with different percent of polysiloxane (BPU-/ and GPU-/) were listed in Table I and Fig. 1. It is needed to denote that all the block and graft waterborne polyurethane-polysiloxane dispersions have the same solid conlenl (23.4%) to determine the viscosities of all the samples.

It could be seen from the Table I and Fig. I. for all the block waterborne polyurelhane-polysiloxane copolymer dispersions, the dispersion kepi transparent from 0 lo 5%of polysiloxane. Because of poor compatibility between polyurethane segments and polysiloxane segments, microphase separation would appear in the block and graft waterborne polyurelhane-polysiloxane copolymers. However, on one hand, from the copolymerization process of block waterborne polyurethane-polysiloxane copolymer (Scheme 2al, the polysiloxane segments were blocked to the copolymer backbone, and the urethane bond formed from the reaction of the OH and NCO groups restricted the polysiloxane lo migrate, stopping the occurrence of phase separalion. On ihe other hand. Ihe percent of polysiloxane added in Ihe copolymer system was less than 5%and phase separalion would nol be serious. Therefore, block waicrbome polyurethane-polysiloxane copolymer dispersions would keep transparent from 0 lo 5% of polysiloxane. Because of ihe superior water-resistance of polysiloxane, the polysiloxane segments reduced the interactions belween segments and the viscosity of block waterborne polyurethane-polysiloxane copolymer dispersions decreased with increase of percent of polysiloxane.

Although lor the graft waierborne polyurethane-polysiloxane copolymer dispersions, with increasing polysiloxane. graft waterborne polyurethane-polysiloxane dispersions became from transparent to sublransparcnl. and the viscosities of polyurethane-polysiloxane graft copolymer dispersions increased. Because in ihe process of graft copolymerization of NCO terminated polyurethane prepolymer and a-A/A-dihydroxyethylaniino-propyl-rj)-buiyl-polydimetlu Isilosane. hydrophobic polysiloxane chains would suspend from ihe polyurethane backbone and sierically hindered effect would appear. With increase of polysiloxane chains, hydrophobic polysiloxane chains increased and sterically hindered effect became more and more obvious, leading to the increase of viscosity and subiranspareni of graft waicrbome polyurelhane-polysiloxane dispersions.

Properties of Block and Graft Waterborne Polvurcthane-Polyxilo.xanc Films

Polysiloxanes possess superior water resistance and this properly can he introduced inlo ihe polyureihanes via blocking and grafting polysiloxane chain to the polyurethane chains. Figure 2 revealed the effecl of different percenl of polysiloxane on the water absorption of block and graft waterborne polyurethane-polysiloxane copoh tner films. From the relationship between percent of polysiloxane and water absorption, il could be seen lhal polysiloxane could improve ihe waler resistance properly effectively regardless of the way of introducing the polysiloxane segment. For instance, the waler absorption of graft waterborne polvureihane-polysiloxane copolymer films decreased from 163.9 lo 17.3% and block water-home polvureihane-polysiloxane copolymer films decreased from 163.9 to 40.2%. From the relationship between percent of polysiloxane and water absorption, the water absorption of the graft waterborne polyurethane-polysiloxane film was lower than lhal of block water-borne polyurethane-polysiloxane films. This was due lo lower surface-energy ol polysiloxane segments, polvsilox-ane segments would migrate on the surface of polyurethane-polysiloxane copolymers to prevent hydrophilic group from contacting water. From the block and grail copolymerization mechanism of NCO-lerminaled polyurethane prepolymer and polysiloxane with a diol group, polysiloxane moieties grafted from the copolymer backbone were easier to migrate to the copolymer surface lhan those blocked to the copolymer backbone; and. the polysiloxane moieties suspended from Ihe copolymer backbone would encapsulate the hydrophilic group and prevent them from contacting water. Therefore, for graft copolymer films, more polysiloxane chains migrated on ihe copolymer surface than block copolymer films wilh the same percenl of polysiloxane. and eventual!) polysiloxane chains grafted to the polyureihanes improved the water-resistance of waterborne polyurethane more effectively. From the water absorption of block and graft waierbome polyurethane films, the conclusion was con-finned by the fact ihat the water absorption of the graft waterborne polyurelhane-polysiloxane film was lower lhan that of block waterborne polyurelhane-polysiloxane films with the same percent of polysiloxane.

Influence of ihe percenl of polysiloxane on the mechanical properties of the block and graft waterborne polvureihane-polysiloxane film was shown in Figs. 3 and 4. In the process of block and graft copolymerization of NCO-lerminaled polyurethane prepolymer. polysiloxane moieties as soft segment were introduced into the polymer wilh different ways. For block copolymerization, the polsiloxane moieties were blocked into the copolymer backbone, leading Lo increasing percent of soft segment and decreasing hardness. Although for the graft copolymerization. the polysiloxane moieties were suspended from the copolymer backbone, the percent of soft segment decreased relatively, resulting in increasing hardness. From the mechanical properties of the block waterborne polyurethane-polysiloxane copolymer films, ii could be seen that the lensile sirength decreased from 19.4 to 5.6 MPa with increase of ihe percenl of a.u>-bis(3-( l-melhoxy-2-hydroxypropoxy)propyll-polvdimethyl-siloxane while Ihe elongation at break increased. From analyses above, polysiloxane moielies were blocked from the poly urelhane backbone and soft segment increased and hardness of the films decreased so thai tensile strength decreased and elongation al break increased with increase of polysiloxane.

But for graft waterborne polyurelhane-polysiloxane copolymer films, polysiloxane moielies were grafted from the polymer backbone and the hard segment content increased relatively and the tensile sirength increased accordingly. From the experimental results illustraied in Fig. 4, the tensile strength of ihe copolymer films increased generally from 14.0 to 26.3 MPa while percent of polysiloxane increased from 0 lo 3%. The hard segment increased with increase of the percenl of a-A/A-dihydroxyelhylaminopropyl-u)-bulylpolydimethylsiloxanc so that hardness of the films increased and the tensile strength increased. However, the lensile strength would decrease when percent of polysiloxane was more lhan 3%. The excessive polysiloxane was disadvantageous to tensile strength improvement.

CONCLUSIONS

Block and graft waterborne polyurethane-polysiloxane copolymer dispersions which were modified with u.iu-bis(3-( l-methoxy-2-hydroxypropoxy)propyhpoly-dimethy-Isiloxane and a-A/.A/-dihydroxyeihylaminopropyl-u>buiylpolydimethyl-siloxane were prepared. The experimental results showed that tlie water absorption of block and graft waterborne polyurelhane-polysiloxane copolymer dispersions and films were improved obviously by blocking and grafting polysiloxane chain to polyureihanes. Ihe water absorption of block and graft copolymer films decreased from 163.9 to 40.2% and 17.3% w ith increase of percent of polysiloxane from 0 to 5% respeclively. The tensile strength of block waterborne polyurelhane-polysiloxane copolymer films decreased while ihe tensile strength of graft waierborne polyurelhane-polysiloxane copolymer films increased with increase of polysiloxane. The influence of polysiloxane on the panicle size, panicle morphology, micropahsc separation, and surface properties of copolymer films are in progress.

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Correspondence to: Yitao Yu: e-mail: yuyt@sdas.org Contract grant sponsor: Shandong Provincial Natural Science Foundation; contract grant number: ZR2013EMQ009; contract grant sponsor: Youth Science Funds of Shandong Academy of Sciences; contract grant number: 2013QN023. DOI 10.1002/pen.23623

Yitao Yu, (1) Jing Wang (2)

(1) Key Laboratory for Adhesion Ampersand Sealing Materials of Shandong Province, New Material Institute of Shandong Academy of Sciences, Jinan, 250014, Shandong, China

(2) Department of Art and Design, Shandong Yingcai University, Jinan 250104, Shandong, China
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Date:Apr 1, 2014
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