EUROPEAN

POLYMERJOURNAL

European Polymer Journal 41 (2005) 1798–1803

www.elsevier.com/locate/europolj

A novel approach to fluorinated polyurethane bymacromonomer copolymerization

Min Jiang a,b, Xiuli Zhao a,b, Xiaobin Ding a,*, Zhaohui Zheng a, Yuxing Peng a,*

a Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, PR Chinab Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China

Received 14 November 2004; received in revised form 7 February 2005; accepted 10 February 2005

Available online 14 March 2005

Abstract

For the first time, through macromonomer radical copolymerization, a novel fluorinated polyurethane (FPU) was

synthesized based on partly acrylate-endcapped polyurethane macromonomers with hexafluorobutyl acrylate (HFBA).

Partly acrylate-endcapped polyurethane (PU) macromonomers were synthesized using isophronediisocyanate (IPDI),

dimethylol propionic acid (DMPA), polyethylene adipate glycols (PEA) etc. The novel fluorinated polymer, which bore

PU side chains and fluorinated side chains, was confirmed by F19 NMR spectroscopy, X-ray photoelectron spectro-

scopy (XPS), elemental analysis, scanning electron spectroscopy (SEM) etc. Copolymerization of polyurethane

macromonomers with hexafluorobutyl acrylate (HFBA) was briefly investigated. The surface tension of FPU solution

was measured and showed sharply decrease compared to that of pure polyurethane. Results from SEM showed a uni-

form size distribution of phase micro-domains on the fracture surface of FPU.

� 2005 Elsevier Ltd. All rights reserved.

Keywords: Macromonomers; Acrylate-endcapped; Copolymerization; Fluorinated polyurethane; Radical polymerization

1. Introduction

Fluorinated polymers possess a whole range of very

interesting bulk and surface properties, such as excellent

environmental stability, water and oil repellency, low

coefficient of friction, biocompatibility, excellent ther-

mal stability and chemical resistance and low interfacial

free energy [1–7].

Polyurethane is one material that could benefit from

characteristic properties of fluorinated polymers, as

mentioned above. Fluorinated polyurethane is new class

of new material. Recently, extensive work has been done

0014-3057/$ - see front matter � 2005 Elsevier Ltd. All rights reserv

doi:10.1016/j.eurpolymj.2005.02.013

* Corresponding authors. Tel./fax: +86 28 8523 3426.

E-mail address: xbding@cioc.ac.cn (X. Ding).

the synthesis and characterization of the fluorinated

polyurethane. Fluorocarbon chains have been incorpo-

rated into polyurethane via fluoro-containing diisocya-

nates [8], soft segments [9–11], hard segments [12–14]

or chain extenders [15–19], always by step polymeriza-

tion. For instance, polyurethane that contained perflu-

oropolyether as a soft segment was studied by Tonelli

et al. [9,10]. Kuo-yu Chen et al. [15] synthesized fluori-

nated polyurethane by using various fluoro chain

extenders and studied their properties. However, there

are several problems with both the synthesis and the sur-

face properties of polyurethane with fluorocarbon

extenders. For instance, semi fluorinated polyether itself

does not have a strong hydrophobic surface property be-

cause it is composed of a fluorinated segment, a hydro-

carbon segment, and hydrophilic linkage of oxygen.

ed.

M. Jiang et al. / European Polymer Journal 41 (2005) 1798–1803 1799

Therefore, the hydrophobic surface property of coating

films is not enhanced desirably, and the surface of the

coating film is still easily contaminated by wetting soils.

It is difficult to synthesise fluorinated polyurethane by

one step [20].

Fortunately, the present work showed that fluori-

nated polyurethane can be invariably obtained from

double bond-end capped polyurethane macromonomers

with fluorine-containing acrylate by radical copolymeri-

zation. As an alternative to the step polymerization, free

radical copolymerization has emerged as an attractive,

simple and seemingly general method for producing

fluorinated polyurethane. In this paper, we were inter-

ested in focusing on the synthesis of novel fluorinated

polyurethane based on partly acrylate-endcapped poly-

urethane macromonomer with hexafluorobutyl acry-

late (CH2@CH–COO–CH2–CF2–CHF–CF3, HFBA)

through radical solution copolymerization. The unique

partly acrylate-endcapped polyurethane macromono-

mers was prepared using step polymerization method.

We have demonstrated the novel fluorinated polyure-

thane having polyurethane side chains and fluorinated

side chains. The structure of the novel fluorinated poly-

urethane was confirmed by F19 NMR and XPS. Surface

tension of fluorinated polyurethane solution with differ-

ent fluorine content was examined by JZHY-180 inter-

face tension instrument and bulk morphology of

fluorinated polyurethane was observed by scanning elec-

tron spectroscopy (SEM).

2. Experimental section

2.1. Materials

Isophronediisocyanate (IPDI) was purchased from

the Huls Co. Dimethylol propionic acid (DMPA), stan-

nous caprylate (SC) and polyethylene adipate glycols

(PEG) with molecular weight of 1179 g/mol were used

as received. Hydroxyethyl methacrylate (HEMA) was

purchased from TOKYO KASEI KOGYO., LTD.

Hexafluorobutyl acrylate(HFBA) was purchased from

XEOGIA Fluorine-silicon Chemical Co., Ltd. N-

methyl-2-pyrrolidone (NMP,CP grade) and methanol

(CP grade) were used. Triethylamine (TEA, CP grade)

was used as neutralization agent. 2,2 0 azobisisobutyro-

nitrile (AIBN, CP grade) was purified with heated

ethanol.

2.2. Synthesis of waterborne anionic partly acrylate-

endcapped polyurethane

Waterborne anionic partly acrylate-endcapped poly-

urethane macromonomers in this study were prepared

based on IPDI, DMPA, HEMA, TEM and methanol

and PEG. First, IPDI, DMPA, PEG and NMP were

added in turn and the mixture was heated to 110 �Cfor 3 h. Second, after cooling the prepolymer to 40 �C,HEMA, methanol and TEA were added and reacted

for 6 h. Last, the polyurethane macromonomers was al-

lowed to disperse into demonized water with vigorous

stirring.

2.3. Synthesis of fluorinated polyurethane

The mixture of polyurethane macromonomers,

HFBA and AIBN were dissolved in NMP as desired

content in a four-necked flask under nitrogen at 80 �Cfor 12 h, according to the schematic diagram showed

in Fig. 1. The final polymers were purified by precipitat-

ing in diethyl ether for three times to remove homopoly-

mer, and dried in vacuum oven at 60 �C for 24 h.

2.4. Characterization and sample preparation

F19 NMR data was obtained with BRUCK AC-P

(300 MHz), which deuterodimethyl sulfoxide was used

as deuterated solvent.

XPS was carried out on an XSAM-800 electron. The

spectrometer was equipped with a MgKa achromatic

X-ray source (20 kV, 10 mA) and take-off angle of 30�was used with X-ray source. The sample for XPS was

prepared by casting the polymer onto a clean glass disk

from 10% (w/w) mixed solution of ethyl acetate and eth-

anol. The disk was put into an oven at 60 �C for 12 h

and 60 �C for12 h under vacuum.

Elemental analysis was performed by chemical meth-

od to determine the amount of fluorine atom. A sample

was combusted with sodium peroxide in an oxygen rich

atmosphere using a Schoniger oxygen flask with distilled

water as the absorbing medium. An aliquot of the result-

ing solution (after filtration) was titrated with thorium

nitrate using alizarin red S as an indicator. The volume

of required titrant was the used to determine the per-

centage of fluorine in the sample.

Surface tensions were measured with JZHY-180

interface tension instrument. Samples for surface tension

measurement were the polymer solutions (0.06 g/ml in

NMP) with different fluorine content. These reported

values are an average of six measurements.

The SEM measurements were performed on AM-

RAY-100. Polymer films for SEM were prepared by

casting the FPU (20% w/w in NMP) solution onto glass

plate, drying at 60 �C in a vacuum oven for 48 h, and

then stored in a desiccators at room temperature. Poly-

mer films were split by liquefied nitrogen.

3. Results and discussion

Copolymerization of polyurethane macromonomers

with hexafluorobutyl acrylate (HFBA) was briefly

CNO

CNO

HOCH2CH2O C

O

CH24C

O

OCH2CH2O Hn

+ +

CH3

OHHO

COOH

ONC NHC

O

OCH2CH2O C

OH2C C

4

O

OCH2CH2 O

n

C

O

NHCHN

O

O O

CH3

COOHC

O

NH HN C

O

O O

CH3

COOHC

O

NH

NH

NHCO

OCH2CH2O C

OH2C C

4

O

OCH2CH2 OnC

O

NHCHN

O

2HC C

CH3CO

OCH2CH2 O CO

O O

CH3

COO-

C

O

NH NHC

O

O O

CH3

COO-

C

O

NH

HEMA methanol TEA

H2O

CH3

PUCH2C

CH2HC CH2

H2C

CF3

C

FHC

PUC O

CH3

m s

F2C

HFBA

AIBN

NH+NH+

CNO

HN C

O

OCH3

Fig. 1. Schematic diagram for the synthesis of FPU.

1800 M. Jiang et al. / European Polymer Journal 41 (2005) 1798–1803

investigated in this work, the results showed that the

conversion of FPU in NMP (solid content = 20 wt%,

HFBA/PU = 50/50 g/g) could reach 90% after 4.5 h at

72 �C, showed in Fig. 2. In the time ranging from 15

to 270 min, the percent conversion increases rapidly,

due to the auto-accelerating affection.

To confirm the structure of outcome copolymer, sev-

eral measurements were used in our investigation. Sev-

eral samples were used for comparing characterization

in our investigation: Polymer A represents the outcome

and polymer B represents the hybrid of polyurethane

macromonomers and poly (HFBA). Contrastively, F19

NMR (Fig. 3) for the purified polymer A shows three

different peaks remarkably [�73.30 ppm (–CF2–);

�73.70 ppm (–CF3); �214.55 ppm (–CHF–)]. But F19

NMR for the polymer B purified based on the same

way with polymer A shows no peak. Also, XPS was used

to verify the result. The present of a strong signal attrib-

utable to fluorine atoms (F 1S: 683 eV) is clearly evident

in XPS survey spectra of the sample made by purified

polymer A (see Fig. 4).

The fluorine elementary analysis of FPU15 and

FPU11 is shown in Table 1. It is noted that the measure-

ment value of fluorine contents for the FPU15 and

0 50 100 150 200 250 3000

10

20

30

40

50

60

70

80

90

100

Time (min)

Perc

ent c

onve

rsio

n %

Fig. 2. The relationship between percent conversions of FPU

and time (20 wt% solid content in NMP, PU/HFBA = 50/50

g/g, T = 72 �C).

Fig. 4. XPS for the fluorinated polyurethane (PU/

HFBA = 50:50 g/g).

Table 1

Atomic percentages of fluorine in the fluorinated polyurethane

Content PU FPU15 FPU11

Theoretical valuea (F%) 0 8 24

Measurement value (F%) 0 2.63 4.96

a The data was obtained by stoichiometric ratio of reactants

inlet.

Table 2

Surface tension results of fluorinated polyurethane solution

(concentration = 0.06 g/ml)

Sample Surface tension10 �C (mN/m)

PU 61.4

FPU15 42.0

FPU11 38.9

M. Jiang et al. / European Polymer Journal 41 (2005) 1798–1803 1801

FPU11 are significantly lower than the theoretical value,

based on the stoichiometric ratio of reactants inlet. The

explanation for the lower measurement value of fluorine

content, we deem, is the different reactive ratios of the

partly acrylate-endcapped polyurethane macromono-

mers and hexafluorobutyl acrylate (HFBA). The rela-

tively high electro negativity of the CH2(CF2)5CF3

group may increase the reactivity, although its elec-

tron-withdrawing influence is decreased by the insulat-

ing capacity of the OCH2 spacer [21]. There are some

evidences in the literature [22,23] to support that the

reactivity ratio of fluorinated (methyl) acrylate is larger

than hydrogenated (methyl) acrylate. Owing to the rea-

son above and the long polymer chain of the partly acry-

late-endcapped polyurethane macromonomers, it can be

hypothesized that the relative lower contents of fluorine

in FPU15 and FPU11 than feed ratio were due to the

higher reactivity of HFBA than partly acrylate-end-

capped polyurethane in radical copolymerization. The

relative ratio of HFBA and partly acrylate-endcapped

polyurethane will be systemically investigated in our

future paper.

The surface tension of polymer solution (concentra-

tion = 0.06 g/ml) with different fluorine content was

measured; the results are showed in Table 2. The pure

polyurethane macromonomers solution exhibits a high

Fig. 3. F19 NMR for the fluorinated pol

surface tension of 61.4 mN/m, due to the present of ole-

ophilic properties. The fluorinated polyurethane solu-

tions have critical surface tension, which rFPU15 =

42.0 mN/m and rFPU11 = 38.9 mN/m. It is clear that

the low surface tension comes mainly from the chemical

structure of HFBA, which has strong oil repellencies,

and –CF2CHFCF3 groups have significantly declined

the surface tension of polymer solution.

yurethane (PU/HFBA = 50:50 g/g).

Fig. 5. The SEM of fluorinated polyurethane: (A) FPU (11) {F% bulk = 2.63%, magnification = 1000·}; (B) FPU (15) {F%

bulk = 4.96%, magnification = 2000·}.

1802 M. Jiang et al. / European Polymer Journal 41 (2005) 1798–1803

Hong Tan [18] found that phase separation on the

surface of fluorinated poly (carbonate urethanes) in-

creased with increasing containing fluorine attached on

hard block based on Atomic force microscopy (AFM).

In this study, differently, SEM was used to understand

the bulk morphology of fluorinated polyurethane. Fig.

5(A) is the SEM micrograph of fracture surface of the

FPU (11) based on the novel method. It shows an equa-

bly size distribution of phase micro-domains, with so

many small balls standing out, always of about 4 lmsize. The same morphology is observed for FPU (15)

[Fig. 5(B)]. It shows very different size of small ball from

FPU (11), about 1 lm diameter. The macrostructure of

FPU (11) and FPU (15) are all regular, which suggest

the being of micro-phase separation. All this is due to

a higher incompatibility between fluorinated side chains

soft segment, other soft segment and hard segment be-

cause of large differences in chemical structure. We deem

that the dimension of the balls attributes to the different

fluorine content in the FPU films. With the increasing

fluorine content, the size of balls tends to increase. Sim-

ilarly, the bulk structure of the fluorinated polyurethane

has intensively been investigated [10,24–27]. Tonelli

et al. [27] in the study of the fluorinated polyurethanes

composed of 4,4 0-methylenebis (phenylisocyanate)

(MDI), 1,4-butanediol (BDO) and perfluoropolyether

(PFPE), observed that the due to the incompatibility

of the fluorinated soft and the hard segments, and that

synthesis methods affected the morphology and

microstructure.

4. Conclusion

Macromonomer radical copolymerization is a new,

straightforward and simple approach to synthesize fluo-

rinated polyurethane. We have successfully prepared the

novel fluorinated polyurethane based on it. The surface

tension of FPU solution (concentration = 0.06 g/ml) de-

creased sharply with increasing fluorine content. Inter-

estingly, there was an equably size distribution of

phase micro-domains in the fracture surface of FPU

film, with so many small balls standing out. It was evi-

denced by SEM that there was micro-phase separation

in the bulk of the novel fluorinated polyurethane.

Acknowledgment

This project was supported by Science and Technol-

ogy Foundation for Youth Researcher of Sichuan Prov-

ince (2005).

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